Cambio Climático

GEOLOGICAL SURVEY OF CANADA BULLrnN 534

HOLOCENE CLIMATE AND ENVIRONMENTAL CHANGE IN THE PALLISER TRIANGLE:

A GEOSCIENTIFIC CONTEXT FOR EVALUATING THE IMPACTS OF CLIMATE CHANGE ON

THE SOUTHERN CANADIAN PRAIRIES

Edited by D.S. Lemmen and R.E. Vanee

kimloveGeoPub white

GEOLOGICAL SURVEY OF CANADA BULLETIN 534

HOLOCENE CLIMATE AND ENVIRONMENTAL CHANGE IN THE PALLISER TRIANGLE:

A GEOSCIENTIFIC CONTEXT FOR EVALUATING THE IMPACTS OF CLIMATE CHANGE ON THE

SOUTHERN CANADIAN PRAIRIES

Edited by D.S. Lemrnen and R.E. Vance

OHer Majesty the Queen in Right of Canada, 1999 Catalogue No. M42-534E ISBN 0-660-17887-7

Available in Canada from Geological Survey of Canada offices:

601 Booth Street Ottawa, Ontario KIA OE8

3303-33rd Street N.W. Calgary, Alberta T2L 2A7

101-605 Robson Street Vancouver, B.C. V6B 553

A deposit copy of this publication is also available for reference in selected public libraries across Canada

Price subject to change without notice

Cover illustration

The Red Deer River valley about 10 krn downstream from Drumheller, Alberta. The river channel and terraces occupy a glacial meltwater channel cut into Upper Cretaceous bedrock, with tributary streams having incised deeply during the late Holocene. Agriculture is the dominant landuse, and the potential impact of future climate changes on water and soil resources is an issue of regional concern. Photograph by D.J. Sauchyn. GSC 1999-049

Editors' addresses

D.S. Lemmen Geological Survey of Canada 3303-33rd Street NW Calgcity, Alberta T2L 2A7

R.E. Vance Natural Resources Canada 580 Booth Street Ottawa, Ontario K I A 0E4

Original nzanuscript submitted: 1998-08 Final version approved for publication: 1999-07

CONTENTS

Introduction D.S. Lemmen and R.E. Vance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

An overview of the Palliser Triangle Global Change Project D.S. Lemmen and R.E. Vance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Geolimnology of the Great Plains of western Canada W.M. Last . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Groundwater in the Palliser Triangle: an overview of its vulnerability and potential to archive climate information V.H. Remenda and S.J. Birks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Diatom-based salinity reconstructions from Palliser Triangle lakes: a summary of two Saskatchewan case studies S.E. Wilson and J.P. Smol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Groundwater inputs to a closed-basin saline lake, Chappice Lake, Alberta S.J. Birks and V.H. Remenda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1

Mineralogy, lithostratigraphy, and inferred geochemical history of North Ingebrigt lake, Saskatchewan

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Y.Shangand W.M.Last 95

Late Holocene paleolimnology of Killarney Lake, Manitoba K.-A. Richmond and L.G. Goldsborough . . . . . . . . . . . . . . . . . . . . . . . . . 11 1

Multiproxy record of prairie lake response to climatic change and human activity, Clearwater Lake, Saskatchewan P.R. Leavitt, R.D. Vinebrooke, R.I. Hall, S.E. Wilson, J.P. Smol, R.E. Vance, and W.M. Last. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

A postglacial plant macrofossil record of vegetation and climate change in southern Saskatchewan C.H. Yansa and J.F. Basinger . . . . . . . . . . . . . . . . . . . . . . . . . .

The lithostratigraphic record of late Pleistocene-Holocene environmental change at the Andrews site near Moose Jaw, Saskatchewan A.E. Aitken, W.M. Last, and A.K. Burt . . . . . . . . . . . . . . . . . . . . . . . . . . 173

Sand dunes of the northern Great Plains of Canada and the United States D.R.MuhsandS.A.Wolfe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Monitoring of dune activity in the Great Sand Hills region, Saskatchewan S.A. Wolfe and D.S. Lemmen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

Using optical dating to determine when a sediment was last exposed to sunlight D.J. Huntley and O.B. Lian. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

Activity cycle of parabolic dunes based on morphology and chronology from Seward sand hills, Saskatchewan P.P. David, S.A. Wolfe, D.J. Huntley, and D.S. Lemmen . . . . . . . . . . . . . . . . . 223

Geomorphology of the western Cypress Hills: climate, process, stratigraphy, and theory D.J. Sauchyn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

Groundwater influence on valley-head geomorphology, upper Battle Creek basin, Alberta and Saskatchewan

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.D. Spence and D.J. Sauchyn

Origin and erosion of the Police Point landslide, Cypress Hills, Alberta D.J. Sauchyn and H.L. Nelson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

Geomorphic surfaces and postglacial landscape evolution of the Maple Creek basin, Saskatchewan W.J. Vreeken. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

Author index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

Introduction

Donald S. em men land Robert E. vance2

Lernrnen, D.S. and Vance, R.E., 1999: Introduction; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lernrnen and R.E. Vance; Geological Survey of Canada, Bulletin 534, p. 1-6.

The Palliser Triangle is the driest portion of the Canadian Prairies, and one of the most climatically sensitive regions in Canada. Extending from the southwestern corner of Manitoba across all of southern Saskatchewan to south-central Alberta, these lands were deemed by Captain John Palliser to have marginal agricultural potential following his 1857-1860 expedition. Despite Palliser's assessment, extensive Eurocanadian settlement occurred during the late nineteenth and early twentieth centuries, and it has since proven to be one of the world's most important agricultural areas. Nonetheless, the social, economic, and environmental impacts of severe drought in the 1920s, 1930s, and 1980s highlighted the region's sensitivity to climatic variability.

As we enter the twenty-first century, concerns of drought and associated impacts in the Prairie region largely centre around the issue of global climate change. Human activities are altering the composition of the atmosphere, which in turn will likely affect climate. Gen- eral Circulation Models predict that future global warming will be most pronounced in northern regions and continental interiors, including the Great Plains of North America. While uncertainties remain in these projections, particularly with respect to precipitation, there is general agreement that the Palliser Triangle is likely to become more arid, and that drought frequency may increase. Evidence of warming is already present in the regional climate record.

Le Triangle de Palliser, qui est la partie la plus skche des Prairies canadiennes, est une des regions du Canada dont le climat est le plus sensible. S'Ctendant du coin sud-ouest du Manitoba jusqu'au centre-sud de 17Alberta, en traversant tout le sud de la Saskatchewan, ces terres Etaient consider6es par le capitaine John Palliser, B I'issue de son expedition de 1857-1860, comme &ant dotbes d'un potentiel agricole negligeable. En depit de l'bvaluation de Palliser, une colonisation eurocanadienne inten- sive y a eu lieu au 19e et au dkbut du 20e sibcles et elles se sont rCv616es depuis lors comme une des rkgions agricoles les plus importantes du monde. Toutefois, les incidences sociales, Bconorniques et environnementales des graves secheresses des annkes 1920, 1930 et 1980 ont mis en lumikre la sensibilitk de cette region h la variabilitk climatique.

A l'aube du 21e sibcle, les prkoccupations relatives aux secheresses et 21 leurs incidences dans la rkgion des Prairies s'articulent pour l'essentiel autour du problbme des changements climatiques globaux. En effet, les activites humaines modifient la composition de l'atrnosphkre, laquelle se repercute 21 son tour selon toute vraisemblance sur le climat. Les modbles de circulation gCnCrale predisent que le futur rechauffement global sera le plus marque dans les regions septentrionales et h I'intkrieur des continents, notamment la region des grandes plaines d'AmCrique du Nord. Bien qu'il subsiste des incertitudes dans ces prkdictions, en particulier eu dgard aux precipitations, on s'accorde gCnCralement pour admettre que le Triangle de Palliser deviendra probablement plus aride et que la frkquence des ~Ccheresses y augmentera. Les donnees climatiques rkgionales prksentent dbjh des indices de rechauffement.

Change inevitably results in adaptation: natural sys- Le changement engendre inkvitablement I'adaptation. Les tems will respond to climate change autonomously. How- systkmes naturels repondent aux changements climatiques de ever, human response has potential to be both strategic and manikre autonome, mais les reactions humaines pourront faire anticipatory if we can determine what the impacts of cli- preuve de strattgie et d'anticipation si nous sommes en mesure mate change are likely to be. Hence, to improve our de determiner les incidences probables des changements

' Terrain Sciences Division, Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta T2L 2A7 Natural Resources Canada, 580 Booth Street, Ottawa, Ontario KIA OE4

GSC Bulletin 534

understanding of the role of climate, attention must be focused on the dynamics of natural, social, and economic systems. The study of analogues is a powerful tool for understanding system dynamics: if we document the impacts that resulted from past climate change and variability, we will have a much stronger basis for assessing the impacts of future climate change. With respect to biophysical systems, the geological record contains unique information on the impacts of a wide range of past climate changes. It is this paleoenvironmental record, and the context it provides for assessing the impacts of future climate change, that has been the focus of the Palliser Triangle Global Change Project.

This Bulletin contains 18 papers related to two major objectives of the Palliser Triangle Project: 1) reconstmc- tion of Holocene climatic and hydrological changes; and 2) evaluation of the relationships between climate and landscape processes. Each paper was written to stand on its own as a conwibution to a specific geoscience discipline. However, we hope that by bringing this set of papers together in a regionally focused volume, we are able to highlight the need for interdisciplinary and multi- disciplinary studies when addressing global change issues. The papers in this volume alone do not form a comprehensive summary of project research. Many results, particularly related to the first objective above, have been previously published. Readers are directed to these additional publications through references provided in this volume.

The first paper, by Lemmen and Vance (1999), is an overview of the project and a broad synthesis of major results. The subsequent papers provide thematic reviews of environmental settings, systems, and methodologies critical to the understanding of past regional climate change, as well as results of detailed, site-specific studies supported by the project.

The nine papers that follow the project overview, which make up the first half of the volume, are devoted to records of past climate and hydrological change documented in paleolimnological and hydrogeological studies. Introductory papers familiarize the reader with the physical lake environments of the Canadian Prairies (Last, 1999) and the critical role that groundwater plays in main- taining these lakes (Remenda and Birks, 1999). These papers detail the diversity and complexity of hydrological systems, highlighting difficulties involved in determining a coherent paleoclimatic signal from lake sediments. They emphasize the need for a thorough understanding of the hydrological dynamics when formulating paleoenvironmental interpretations. An introduction to biological proxy data is provided by Wilson and Smol (1999), who summarize diatom studies from two lakes within the Palliser Triangle. The similarities and differences evident in these records underscore the importance of examining sites from a variety of topographic, climatic, and

climatiques. Aussi, pour amCliorer notre comprChension du r61e du climat, importe-t-il d'accorder une attention touteparticulibre 2 la dynamique des systbmes naturels, sociaux et Cconomiques. Les analogies sont un outil puissant pour la comprChension de la dynamique des systbmes; si nous recensons les incidences des changements et de la variabilitC du climat dans le passC, nous serons beaucoup mieux CquipCs pour Cvaluer les incidences des changements climatiques h l'avenir. Pour ce qui est des systkmes biophysiques, les donnCes gCologiques renferment des informations uniques sur les incidences d'un vaste Cventail de changements climatiques passCs. Ces donnCes palCoenvironne- mentales et le contexte qu'elles fournissent pour 1'Cvaluation des changements climatiques futurs constituent l'axe central du Projet sur le Triangle de Palliser et les changements climatiques globaux.

Ce bulletin contient 18 textes portant sur deux des principaux objectifs du Projet sur le Triangle de Palliser : (1) la reconstitution des changements climatiques et hydrologiques de 1'Holocbne et (2) 1'Cvaluation des rapports entre le climat et les processus fa~onnant le paysage. Chaque texte a Ct6 rCdigC de manibe 2 fournir une contribution autonome B une discipline gkoscientifique spkcifique. Nous espCrons qu'en rassemblant cet ensemble de textes en un volume B orientation regionale nous serons en mesure de mettre en relief la nCcessitC d'effectuer des Ctudes interdisciplinaires et multidisciplinaires pour aborder les problbmes relatifs aux changements climatiques globaux. 11 faut Cgalement noter que les textes de ce seul volume ne constituent pas un rCsumC complet des recherches menCes dans le cadre du projet. De nombreux rCsultats relatifs en particulier au premier objectif CnumCrC plus haut ont kt6 publies antkrieurement. Ces publications supplCmentaires sont signalCes au lecteur dans les rCfCrences incluses dans ce volume.

Le premier texte, de Lernrnen et Vance (1999), est un rCsumC du projet et une vaste synthkse des principaux rksultats. Les textes suivants prksentent des rCsumCs thCmatiques des cadres environnementaux et des systbmes et mCthodologies qui sont d'importance critique pour la comprChension des changements climatiques rCgionaux passCs, ainsi que les rCsultats d'6tudes dCtaillCes sur des sites spCcifiques soutenues par le projet.

Les neuf textes qui suivent le rCsumC de projet et qui constituent donc la premibre moitiC de ce volume sont consacrCs aux donnCes sur les changements climatiques et hydrologiques passks qui sont dCcrites dans les Ctudes palColimnologiques et hydrogCologiques. Des textes introductifs familiarisent le lecteur avec le milieu physique des lacs des prairies (Last, 1999) et avec le r81e critique que jouent les eaux souterraines pour la persistance de ces lacs (Remenda et Birks, 1999). Ces textes expliquent en dCtail la diversit6 et la complexitC des systbmes hydrologiques, tout en mettant en relief les difficult& que comporte la dktermination d'un signal palCoclimatique cohkrent h partir de sidirnents lacustres. 11s souligent la nkcessitC d'une profonde comprChension de la dynamique hydrologique lorsqu'il s'agit de formuler des interprCtations environnementales. Une introduction aux donnkes indirectes en biologie est fournie par Wilson et Smol (1999) qui rCsument des Ctudes sur les diatomees dans deux lacs du Triangle de Palliser. Les similitudes et diffkrences qui sont manifestes dans ces donnCes soulignent 2 quel point il est important d'examiner des sites dans des cadres topographiques, climatiques et hydrologiques

D.S. Lemmen and R.E. Vance

hydrological settings in order to differentiate variability related to regional factors, including climate, from local dynamics, such as groundwater discharge.

The next two papers present results of detailed hydrogeological and minerological studies. Despite the important role that groundwater plays in controlling lakes in this environment, only Chappice Lake has a groundwater monitoring study (Bisks and Remenda, 1999) to support a detailed paleoenvironmental record. While the duration and scope of this groundwater study precluded the development of a quantitative hydrogeological budget, the results emphasize the importance of such data for inter- preting paleohydrological conditions. Similar studies are required elsewhere on the northern Great Plains if a regional paleoclimatic signal is to be derived.

Groundwater is also a key factor influencing the stratigraphic record of North Ingebrigt lake (Shang and Last, 1999), one of many hypersaline lakes and playas found on the northern Great Plains (see overview paper by Last, 1999). Such basins have traditionally received limited attention in paleoenvironmental research, as the high salinity restricts or even precludes most organisms used as proxy climate indicators. However, this paper exemplifies how the salts, which comprise the majority of the sediment record, provide detailed paleolimnological and paleohydsological data (particularly related to brine composition), and valuable paleoclimatic insights (in this case reconstruction of relative humidity).

Biological proxy data are emphasized in the following two papers. The late Holocene sedimentary record in Killarnev Lake in southeastern Manitoba documents changes in diatoms and pigments that are correlative with sites to the west, suggesting that there is a recognizable regional climate signal (Richmond and Goldsborough, 1999). In addition, this paper provides a context for assessing the impact of recent human activities in the region, particularly in terms of water quality. The study of Clearwater Lake by Leavitt et al. (1999) is an example of the insights that can be gained through collaborative research using multiple proxy indicators. Through integration of diatom, pigment, plant macrofossil, and mineralogical data, the study provides more details of past changes than would be evident from any single indicator. They demonstrate that changes in land use over the past century dominate the cli- matesignal at this site. This highlights arecurrent theme of the Palliser Project: that a fundamental requirement of any rigorous paleoclimatic reconstruction must be an objective assessment of all factors in environmental change, rather than simply the role of climate.

The final two papers of the first set utilize data from an excavated prairie pothole to derive insights about environmental conditions during the latest Pleistocene-early Holocene. The extremely diverse plant macrofossil assemblages at this site (Yansa and Basinger, 1999)

diffkrents afin de pouvoir distinguer la variabilitC like des facteurs rCgionaux, y compris le climat, de la dynarnique locale, par exemple des Ccoulements d'eau souterraine.

Les deux textes suivants prCsentent les rksultats d'Ctudes hydrogtologiques et mintralogiques dCtaillCes. En dtpit du r6le important que jouent les eaux souterraines dans la regulation des lacs de ce milieu, seul le lac Chappice a fait l'objet d'une Ctude de contr6le des eaux souterraines (Birks et Remenda, 1999) permettant de recueillir des donnCes environnementales dCtaillCes. MEme si la dur6e et l'ampleur de cette Ctude sur les eaux souterraines ont emp$chC l'klaboration d'un budget hydrogCologique quantitatif, les rCsultats soulignent l'importance de telles donnCes pour l'interprktation des conditions paltohydrologiques. ~ e s - Ctudes semblables sont ntcessaires ailleurs dans les grandes plaines septentrionales si l'on veut dCtecter un signal palCoclimatique regional.

Les eaux souterraines constituent un facteur clC influenpnt Cgalement les donnCes stratigraphiques du lac North Ingebrigt (Shang et Last, 1999), un des nombreux lacs hypersalins/playas que l'on trouve dans les grandes plaines septentrionales (voir l'aperqu par Last, 1999). Dans le pass6, on a gCnCralement pr$tC peu d'attention h de tels bassins en recherche pal6oenvironne- mentale, car la salinitC ClevCe restreint, voire ernpeche la prCsence de la plupart des organismes utilisCs comme indicateurs indirects du climat. Ce texte explique toutefois pourquoi les sels, qui constituent la plus grande partie des dCp6ts ~Cdimentaires, fournissent des donnCes palColimnologiques et palCohydrologiques dttailltes (likes en particulier 9 la composition des saumures) et d'utiles aperps palCoclimatiques (dans ce cas, la reconstitution de l'humiditk relative).

Les donnCes biologiques indirectes sont mises en relief dans les deux textes suivantsl Le lac Killarney, dans le sud-est du Manitoba, qui renferme des dCp6ts de 1'Holocbne supkrieur, ttmoigne de changements relatifs aux diatomties et aux pigments qui sont en corrClation avec des sites 9 l'ouest, ce qui laisse penser qu'il existe un signal climatique rkgional reconnaissable (Richmond et Goldsborough, 1999). Cet article fournit en outre un contexte permettant d'Cvaluer les incidences des activitCs humaines rCc&tes dans la rCgion, en particulier relativement la qualit6 de l'eau. L'Ctude de Leavitt et al. (1999) sur le lac Clearwater fournit un exemple des aperps qu'offrent les recherches concertCes utilisant des indicateurs indirects multiples. Gr2ce 9 1'intCgration de donntes sur les diatomCes, les pigments et les macrofossiles vCgCtaux et de donnCes min6a- logiques, cette Ctude fournit plus de dCtails sur les changements passCs que ne le rkvtlerait un indicateur unique. Leavitt et al. (1999) montrent que les changements dans l'utilisation du sol depuis un sikcle dominent le signal climatique de ce site. Cela illustre une thCmatique rCcurrente du projet sur le Triangle de Palliser, B savoir que 1'Cvaluation objective de tous les facteurs de changement environnemental, par opposition 9 la seule prise en consid6ration du r61e du climat, doit constituer une exigence fondamentale de toute reconstitution palCoclimatique ngoureuse.

Les deux derniers textes de cette sCrie utilisent des donntes provenant d'une cuvette des Prairies excavCe afin de trouver des indices sur les conditions environnementales pendant le PlCistochne sommital et 1'Holocbne inftirieur. L'extreme diversit6 des assemblages de macrofossiles vCgCtaux de ce site

GSC Bulletin 534

document, among other things, the postglacial migration of white spruce through southwestern Saskatchewan. The roles of climate, hydrology, and landscape instability are all considered in the reconstruction of local conditions extending from deglaciation to about 6000 years ago. The lithostratigraphy of the same site, as interpreted by Aitken et al. (1999), provides an interesting contrast. While strong similarities between the studies exist, mineralogical data suggest somewhat different interpretations of climate dynamics than those derived from the plant macrofossil data. Again, these results emphasize the importance of integrating multiple proxy indicators to achieve realistic paleoenvironmental interpretations.

The papers in the second half of the volume focus on geomorphic processes in the Palliser Triangle, and how these respond to climate forcing. An overview of regional eolian, fluvial, and mass-wasting systems, as well as soil redistribution, was presented by Lemmen et al. (1998), based on literature predating the Palliser Project. That review concluded that eolian landscapes are the most sensitive to climatic variability, and that much of the region lies near a threshold of extensive eolian activity.

The first four papers in this set focus on eolian environments. Muhs and Wolfe (1999) place sand dunes of the Palliser Triangle within the broader context of the northern Great Plains. They review the major controls on dune formation and activity, evidence of past dune activity from geological, pedological, and historical sources, and finally the value of dune areas in developing paleoenvironmental reconstructions. Among many important conclusions is that most dune fields on the northern Great Plains are not simply relics of Late Pleistocene deglaciation, but have been active during the late Holocene and are only margin- ally stable at present. A second overview paper with a strong eolian theme concerns optical dating (Huntley and Lian, 1999). This comparatively new dating technique has provided a breakthrough in our understanding of sand dune activity (see paper by David et al., 1999). By providing an age of the last time sediment was exposed to sunlight, the technique is able to directly document periods of past eolian activity, in contrast to other techniques, such as radiocarbon dating of paleosols, which document periods of minimal eolian activity.

The other two papers on eolian environments summarize recent field studies in the Palliser Triangle. The present level of sand dune activity in the central Palliser Triangle lends itself well to monitoring studies (Wolfe and Lemmen, 1999), providing baseline data that is critical to evaluating both paleoenvironmental interpretations and the controls on modern eolian activity. Despite the limited duration of the data set, insights are provided into the sea- sonality of dune activity, as well as rates of blowout erosion and slipface advance. Morphological and geochronological (optical dating) data are used by David et al. (1999) to develop the concept of an 'activity cycle'

(Yansa et Basinger, 1999) permet notamment de reconstituer la migration postglaciaire de 1'Cpinette blanche dans le sud-ouest de la Saskatchewan. On a tenu compte des r6les respectifs du climat, de l'hydrologie et de l'instabilit6 des paysages pour reconstituer les conditions locales 8 partir de la dCglaciation jusqu78 il y a environ 6 000 ans. La lithostratigraphie du meme site, telle qu'interpretke par Aitken et al. (1999), fournit un contraste inttressant. Bien qu'il existe de fortes similitudes entre les deux Ctudes, les donnCes minCralogiques suggbrent des interprktations quelque peu differentes de la dynamique climatique que celles suggCrCes par les donnCes macrofossiles vCgCtales. La encore, ces rCsultats soulignent l'importance de I'intCgration de multiples indicateurs indirects pour parvenir 2 des interprktations palCoenvironnementales rtalistes.

Les textes de la seconde moiti6 de ce volume s'articulent autour des processus gComorphologiques dans le Triangle de Palliser et de la manihe dont ces processus repondent au for~age climatique. Une vue d'ensemble des systbmes Coliens, fluviaux et de mouvements de masse rCgionaux ainsi que de la rtpartition des sols a CtC pr6sentCe par Lemmen et al. (1998), sur la base d'une documentation antkrieure au projet sur le Triangle de Palliser. Les auteurs concluent que les paysages Coliens sont les plus sensibles h la variabilitk climatique et qu'une bonne partie de la region est proche du seuil d'une activitC Colienne intense.

Quatre textes de ce bulletin sont axes sur les milieux Coliens. Muhs et Wolfe (1999) replacent les dunes de sable du Triangle de Palliser dans le contexte plus vaste des grandes plaines septentrionales. 11s examinent les contr6les principaux sur la formation et I7activitC des dunes, les indices d'activitt des dunes dans le pass6 h partir de sources g6010giques, pCdologiques et historiques et, enfin, l'utilitt des rCgions de dunes pour les reconstitutions palCoenvironnementales. Une des nombreuses conclusions importantes qu'ils tirent est que la plupart des champs de dunes des grandes plaines septentrionales ne sont pas simplement des vestiges de la deglaciation du PlCistocbne supCrieur, mais ont CtC actifs pendant 1'Holocbne supCrieur et sont h peine stables aujourd'hui. Un deuxibme texte servant de tour d'horizon et B forte thematique Colienne concerne la datation optique (Huntley et Lian, 1999). Cette technique de datation relativement rCcente a fourni une percCe dans notre comprChension de I'activitC des dunes de sable (voir David et al., 1999). En permettant de dater la dernibre exposition d'un sediment h la lumibre solaire, cette technique peut renseigner directement sur les pCriodes d'activit6 6olienne du passC, ce qui contraste avec d'autres techniques telles que la datation au radiocarbone des palCosols, qui fournissent des renseignements sur des pCriodes d'activit6 Colienne minimale.

Les deux textes ultCrieurs sur les milieux Coliens rCsument des Ctudes de terrain rkcentes dans le Triangle de Palliser. Le niveau actuel d'activitk des dunes de sable dans la partie centrale du Triangle de Palliser se prete bien aux Ctudes de contr6le (Wolfe et Lemmen, 1999), car il permet d'obtenir des donnCes de base qui sont d'importance critique pour 1'Cvaluation des interprktations palCoenvironnementales et des contr6les de I'activitC Colienne contemporaine. En dCpit du caractkre limit6 dans le temps de l'ensemble de donnees, les auteurs fournissent des aperys sur la saisonnalitC de l'activitk des dunes ainsi que sur les taux d'Crosion des cuvettes de deflation et d'avande des talus croulants. Des donnees morphologiques et


for parabolic dunes. Moisture availability, reflected by fluctuations in the groundwater table, is considered the ultimate control on dune activity. The conceptual model presented in this paper incorporates fundamental geomorphic principals such as threshold response and responselrelaxation times that are required for assessing the potential response of dune systems to future climate change.

The next three papers focus on geomorphic data from the Cypress Hills. The first of these (Sauchyn, 1999) places previous observations within a broader framework of theoretical geomorphology. In discussing the importance of scale (both spatial and temporal) and the bias of the stratigraphic record to low-frequency, high-magnitude (e.g. extreme) events, this paper highlights the challenge facing the geomorphologist when attempting to address the impacts of climate on landscape processes. The subsequent two papers underscore Sauchyn's views while examining controls on fluvial and mass-wasting processes in the Cypress Hills. Spence and Sauchyn (1999) integrate field monitoring with geographic information system (GIs) analysis to derive insights concerning the role of groundwater discharge on local geomorphic processes. Ongoing monitoring studies are the focus of Sauchyn and Nelson's (1999) paper on Police Point landslide, the largest historic landslide in the Cypress Hills. This work documents significant 'downstream' impacts of the slide more than tw; decades after the initial failure occurred. exem- plifying the significant response times o f many geomorphic systems. This fundamental point must be considered when addressing future adaptation needs.

The final paper of the volume (Vreeken, 1999) is a comprehensive evaluation of processes and events controlling Holocene landscape evolution in a closed drainage basin. Focused primarily on fluvial systems, this study demonstrates that, for this basin, geological and geomorphic controls dominate climate at a temporal scale of centuries to millennia. It also shows that simple temporal correlation between climatic and geomorphic events does not demonstrate a causal relationship. With respect to impacts of future climate change, the paper emphasizes that only through knowledge of all factors controlling the system of interest can the specific role of climate be assessed.

As a final note, readers should be aware that review manuscripts for some contributions were submitted as early as March 1997. Hence some aspects of the work presented here may have been expanded upon or superceded by additional research prior to release of this volume. Readers are asked to contact individual contributors concerning possible follow-up to material presented herein.

gCochronologiques (datation optique) sont utilisCes par David et al. (1999) pour Claborer le concept de

GSC Bulletin 534

Aitken, A.E., Last, W.M., and Burt, A.K. 1999: The lithostratigraphic record of late Pleistocene-Holocene environ-

mental change at the Andrews site near Moose Jaw, southern Saskatchewan; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Le~nmen and R.E. Vance; Geological Survey of Canada, Bul- letin 534.

irks, S.J. and Remenda, V.H. B 1999: Groundwater inputs to a closed-basin saline lake, Chappice Lake,

Alberta; in Holocene Climate and Environmental Change in the Palliser Triande: A Geoscientific Context for Evaluating the Impacts of ~ l imatc Change on the Southern Canadian ~rairiesr(ed.) D.S. Lemmen and R.E. Vance; Geological Survev of Canada, Bul-

-

letin 534. David, P.P., Wolfe, S.A., Huntley, D.J., and Lemmen, D.S. 1999: Activity cycle of parabolic dunes based on morphology and chro-

nology~of-Seward sand hills, Saskatchewan; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Huntley, D.J. and Lian, O.B. 1999: Determining when a sediment was last exposed to sunlight using

optical dating; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Changeon the Southern Canadian Prairies, (ed.) D.S. Lemrnen and R.E. Vance; Geological Survey of Canada, Bul- letin 534.

Last, W.M. 1999: Geolirnnology of the Great Plains of western Canada; in Holocene

Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Leavitt, P.R., Vinebrooke, R.D., Hall, R.I., Wilson, S.E., Smol, J.P., Vance, R.E., and Last, W.M. 1999: Multiproxy record of prairie lake response to climate change and

human activity, Clearwater Lake, Saskatchewan; in Holocene Cli- mate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemrnen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Lemmen, D.S. and Vance, R.E. 1999: An overview of the Palliser Triangle Global Change Project; in

Holocene Climate and Environmental Change in the Palliser Trian- gle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Lemmen, D.S., Vance, R.E., Campbell, I.A., David, P.P., Pennock, D.J., Sauchyn, D.J., and Wolfe, S.A. 1998: Geomorphic systems of the Palliser Triangle, southern Canadian

Prairies: description and response to changing climate; Geological Survey of Canada, Bulletin 521,72 p.

Muhs, D.R. and Wolfe, S.A. 1999: Sand dunes of the northern Great Plains of Canada and the United

States; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bul- letin 534.

Reinenda, V.H. and Birks, S.J. 1999: Groundwater in the Palliser Triangle: an overview of its vulnerabil-

ity and potential to archive climate information; in Holocene CLi- mate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Richmond, K.-A. and Goldsborough, L.G. 1999: Late Holocene paleolimnology of Killarney Lake, Manitoba; in

Holocene Climate and Environmental Change in tlie Palliser Trian- gle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lem~nen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Sauchyn, D.J. 1999: Geomorphology of the western Cypress Hills: climate, process,

stratigraphy and theory; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evalu- ating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lem~nen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Sauchyn, D.J. and Nelson, H.L. 1999: Origin and erosion of the Police Point landslide, Cypress Hills,

southeastern Alberta; in Holocene Climate and E~ivironme~ital Change in the Palliser Triangle: A Geoscientific Context for Evalu- ating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Shang, Y. and Last, W.M. 1999: Mineralogy, lithostratigraphy, and inferred geochemical history of

North Ingebrigt lake, Saskatchewan; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemrnen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Spence, C.D. and Sauchyn, D.J. 1999: Groundwater influence on valley-head geomorphology, upper Bat-

tle Creek basin, Alberta and Saskatchewan; in Holocene Climate and Environmental Change in thepalliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Le~nmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Vreeken, W.J. 1999: Geomorphic surfaces and postglacial landscape evolution of the

Maple Creek basin, Saskatchewan; in Holocene Climate and Envi- ronmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prair~es, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Wilson, S.E. and Smol, J.P. 1999: Diatom-based salinity reconstructions from Palliser Triangle lakes:

a summary of two Saskatchewan case studies; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Wolfe, S.A. and Lemmen, D.S. 1999: Monitoring of sand dune activity in the Great Sand Hills region,

southwestern Saskatchewan; in Holocene Climate and Environ- mental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

Yansa, C.H. and Basinger, J.F. 1999: A postglacial plant macrofossil record of vegetation and climate

change in southern Saskatchewan; in Holocene Climate and Envi- ronmental Change in the Palliser Triangle: A Geoscientific Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemmen and R.E. Vance; Geological Survey of Canada, Bulletin 534.

A11 overview of the Palliser Triangle Global Change Project

Donald S. em men' and Robert E. vance2

Lemmen, D.S. and Vance, R.E., 1999: An overview of the Palliser Triangle Global Change Project; in Holocene Climate and Environmental Change in the Palliser Triangle: A Geoscientijic Context for Evaluating the Impacts of Climate Change on the Southern Canadian Prairies, (ed.) D.S. Lemrnen and R.E. Vance; Geological Survey of Canada, Bulletin 534, p. 7-22.

Abstract: The Palliser Triangle is the driest portion of the Canadian Prairies, and one of the most climatically sensitive regions in Canada. The potential biophysical impacts of future climate changes are addressed in the Palliser Triangle Global Change Project through an improved understanding of Holocene climate and hydrological changes, and associated landscape response.

Water availability, particularly in relation to groundwater fluctuations, is the single most important factor controlling regional environmental change. Three major intervals are defined for the Holocene, reflecting climate, hydrological, and human factors, and geomorphic activity during those intervals is assessed. Projections of future geological impacts must be based on a thorough understanding of hydrological and geomorphic system dynamics, including the importance of thresholds and antecedent conditions. Systems that are still responding to past major disturbances are unlikely to show a predictable response to climate change. Significant response and relaxation times in many systems indicate that some climate impacts will not be immediately apparent, but may have considerable long-term consequences.

RCsumC : Le Triangle de Palliser constitue la partie la plus skche des Prairies canadiennes et une des r6gions canadiennes dont le climat est le plus sensible. L'Ctude des incidences biophysiques potentielles des futurs changements climatiques est abordCe par le Projet sur le Triangle de Palliser et les changements climatiques globaux, qui vise i amtliorer notre comprehension du climat et des changements hydrologiques au cours de 1'Holockne et des rtactions associees du paysage.

La disponibilitC de l'eau en gCnCra1, et les fluctuations des eaux soutei-raines en particulier, constituent le facteur de contr8le des changements environnementaux rkgionaux le plus important. Trois intervalles principaux, refletant les facteurs climatologiques, hydrologiques et humains, ont Ctt dtfinis dans 17Holocbne; l'activitk gComorphologique au cours de ces intervalles a Cgalement t t t CtudiCe. Les projections des incidences gCologiques futures doivent &tre fondtes sur une comprehension approfondie de la dynamique des systkmes hydrologiques et gComorphologiques, notamment de l'importance des seuils et des conditions anterieures. U est peu probable que les systkmes qui rkagissent encore aux perturbations majeures du pass6 manifestent une reaction prkvisible aux changements climatiques. La longueur des temps de reaction et des pCriodes de relaxation de nombreux systkmes indique que certaines incidences climatiques ne seront pas immediatement manifestes, bien qu'elles puissent avoir des consCquences i long terme considkrables.

' Terrain Sciences Division, Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta T2L 2A7 Natural Resources Canada, 580 Booth Street, Ottawa, Ontario KIA 0E4

GSC Bulletin 534

INTRODUCTION

Extending from southwestern Manitoba to south-central Alberta, the Palliser Triangle is the driest part of the Canadian Prairies (Fig. 1). The following assessment of the region was provided by Captain John Palliser following his land survey of 1 857-1 860 (Spry, 1968):

. . .in the central part of the continent there is a region, desert, or semi-desert in character, which can never be expected to become occupied by settlers .... Although there are fertile spots throughout its extent i t can never be of much advantage to us as a possession.

For the most part, the twentieth century has proven Palliser to have been overly pessimistic, as the region that bears his name forms much of the highly productive Canadian wheat belt. Nonetheless, the social, economic, and environmental impacts of historical drought, exemplified by the 1920s, 1930s, and 1980s, highlight the region's sensitivity to climatic variability (Wheaton et al., 1992).

Concerns over the impacts of climate variability on human activities are amplified when placed in the context of projected future climate change. There is general agreement among General Circulation Model (GCM) simulations that enhanced atmospheric concentrations of greenhouse gases will be associated with increased temperatures and decreased summertime precipitation across much of the North American Great Plains (e.g. Karl et al., 1991). This, in turn, could cause increased frequency and magnitude of drought, by far the greatest climatic hazard to economic sustainability

on the Canadian Prairies (Herrington et al., 1997; Nemanishen, 1998). While major advances have been made in climate modelling over the last decade, confidence in some projections, particularly those of precipitation and soil moisture, remains comparatively low. Furthermore, regional climate models (RCMs), which can provide data at the spatial scale necessary to address the regional impacts of climate change, remain in the early stages of development (Laprise et al., 1997).

A complementary approach to the modelling of future climates and associated impacts is the study of past environmental change. Paleoenvironmental research provides numerous unique contributions to our understanding of climate change. In the case of climate dynamics, a paleoenvironmental perspective spanning several millennia is required to define the full range of climate variability, and hence provide context for recent climate trends (e.g. Lemrnen et al., 1997). Further- more, paleoclimatic data is critical for differentiating between anthropogenic and other (natural) drivers of climate change (Mann et al., 1998), as well as providing a basis for validation of GCMs through hindcasting (Gajeweski et al., in press).

In addition to providing proxy climate data, paleoenvironmental research provides information about the response of biophysical systems to climate forcing. In documenting system response (autonomous adaptation (Smit et al., in press)) to a range of past climatic changes, these studies provide a basis for assessing climatic sensitivity. Given that the paleoenvironmental record encompasses a greater range of climatic variability than documented in the historic

A A ~ * * Mtn.

,"d *a.

Figure 1. The Palliser Triangle (bold dashed line) as defined by John Palliserduring the 1857-1860 British North American Exploring Expedition (from Spry, 1968). Isolines denote ratio of average annual precipitation to potential transpiration, based on 30-year means (climate data from Environment Canada, 1993). Lower values indicate greater aridity; values have been interpolated for the Cypress Hills. Shaded area is the Brown Chernozemic Soil Zone; bold dotted line is the continental drainage divide.


(instrumental) climate record, it potentially contains analogues of projected future climates. The great advantage of such information, compared to model-based analyses, is that it is based upon what has actually happened, as opposed to projections of what may happen. Furthermore, the paleoenvironmental record will reflect the integrated response of a complex, dynamic system that may not be ade- quately represented in static models. An improved understanding of past climate changes and associated environmental response therefore provides critical context for any assessment of the impacts of future climate change.

THE PROJECT

The Palliser Triangle Integrated Research and Monitoring Area (IRMA) was established in recognition of the climatic sensitivity of the Prairies, projections of significant future climate change in that region, and the role that paleoenvironmental research can play in addressing the impacts of climate change. The broad objective of the project, one of three regionally focused global change research initia- tives co-ordinated by the Geological Survey of Canada, was to enhance understanding of past environmental changes in order to prepare for the potential biophysical impacts of future climate change (Lemmen et al., 1993). It included three primary research foci: 1) records of past climate and hydrological changes, 2) understanding relationships between climate and landscape processes, and 3) analysis of landscape sensitivity. This volume presents the results of work related to the first two of these.

The project's success resulted from the collaborative approach taken by all participants. Basic funding for graduate student research was provided through a competitive project grant program, and supplemented by other sources of univer- sity funding. Project workshops were held in 1991 (Calgary), 1992 (Regina), and 1996 (Saskatoon). In total, the project involved 35 researchers (including graduate students) from Canada and the United States, contributing to 8 M.Sc. theses, 3 Ph.D. theses, and more than 50 journal publications.

While project research was restricted to geological records and processes, it must be emphasized that the long human history of the southern Prairies is another extremely record of Holocene environmental change. As this important subject is not represented in this volume, interested readers are directed to Vickers (1986), Walker (1992), and Beaudoin (1999).

STUDY AREA

Climate While Captain Palliser's descriptions allow the Triangle to be delineated on a map (Fig. I), the region is implicitly defined on the basis of climate rather than geography. The most dis- tinguishing characteristics are a strong annual moisture defi- cit and variable climate at all time scales. According to the United Nations Environmental Programme (1992) climatic

classification, the area is dry subhumid to subhumid. Average annual potential evapotranspiration exceeds average total precipitation by 20 to more than 40%, with the driest portion lying within southeastern Alberta and southwestern Saskatchewan (Fig. 1). Recurrent drought is capable of pro- ducing true semiarid conditions over large areas (Wolfe, 1997). Drought has occurred in at least some portion of the southern Prairies in virtually every decade of the twentieth century (Chakravarti, 1976), with major regional droughts occurring in the 1920s, the 1930s, 1961, and the 1980s. Con- secutive drought years, such as 1936-1937 and 1987-1988, brought about the most severe economic and environmental impacts (Wheaton and Arthur, 1989).

The extreme climatic variability of the region is mainly a function of its continental location in the lee of the Rocky Mountains, and the interaction between Pacific and Arctic air masses (Lemmen et al., 1998). The annual temperature range of more than 80C is the largest in Canada (Hare and Thomas, 1979). The Canadian record-high air temperature of 45C was recorded at Midale and Yellowgrass in southern Saskatchewan on July 5, 1937. Winter record lows approach -50C across most of the region (Wheaton, 1998). June is the wettest month, typically accounting for about 25% of total annual precipitation. Annual snowfall is relatively low (70-180 cm), accounting for only about 30% of total annual precipitation (Environment Canada, 1993).

The longest instrumental climate records from the Palliser Triangle extend back slightly more than 100 years. Analysis of long-term temperature trends reveals a statistically significant warming of 0.9"C during the period 1895-1991, within which three distinct phases can be defined: a warming trend from the late 1890s to the 1940s, a cooling trend from the 1940s to the 1970s, and a warming trend from the 1970s through the 1990s (Fig. 2A; Gullett and Skinner, 1992). Pre- cipitation does not show any statistically significant trend over the century of instrumental record (Fig. 2B; Environ- ment Canada, 1995), although Wolfe et al. (1998) noted a cumulative drying trend since 1948, consistent with other data suggesting increasing aridity (e.g. Judiesch and Cutforth, 1996).

Biophysical environment The Palliser Triangle is the northernmost extension of the North American Great Plains, the vast grassland of the continental interior. It is a landscape of considerable topographic, geological, and ecological diversity, all of which influence land use (Fig. 3). The summary presented here is based on the more detailed description of the geology, physiography, soils, and vegetation of the central Palliser Triangle by Lernmen et al. (1998).

Total relief in the Palliser Triangle exceeds 950 m. Rising from 300 to 600 m above the adjacent plains, the Cypress Hills (Fig. 1) include the highest point in southern Canada between the Rocky and Torngat mountains (1465 m; see Sauchyn, 1999). A number of uplands, including the Hand Hills, Wood Mountain, Moose Mountain, and Turtle Moun- tain, dot the landscape (Fig. 1). Like most large-scale physiographic features on the southern Prairies, these uplands are

GSC Bulletin 534

$' 100 5 P $ 0 E .-

g-100 4 " I ' '

- Best-fit linear trend

,- E I - Five-year running mean n. -200

E - -4.0-

I I I I I I I I I I I I

1900 1920 1940 1960 1980 2000 Year

1 1 1 1 I I I I I I 1

Figure 2. Instrumental climate records for the prairie region, 1895-1991, expressed as departures fronz 1951-1 980 mean: A) tenzperature (adapted from Gullet and Skinner, 1992), with solid line indicating best-fit linear trend (significantly different from 0C a t the 95% confidence level) and dashed lines indicating apparent shorter term trends; B) precipitation (Environment Canada, 1995), with solid line indicating five-year running mean.

1900 1920 1940 1960 1980 2000

largely bedrock controlled and most represent remnant surfaces of Late Tertiary fluvial erosion (Alden, 1932; Klassen, 1989). The Missouri Coteau, another major physiographic feature of the Palliser Triangle, crosses the region as a north- west-trending escarpment rising from 50 to more than 250 m above the plains to the east (Fig. 1).

Superimposed on bedrock-controlled physiographic ele- ments are smaller scale landforms related to Pleistocene glaciation. With the exception of the highest parts of the Cypress Hills and Wood Mountain upland, all of the region has been glaciated (Klassen, 1989). Till is the dominant surficial material, and there are extensive belts of ice-thrust features and hummocky moraine, particularly along The Missouri Coteau, the margins of the Cypress Hills, and the summits of other uplands. Glaciolacustrine sediments, remnants of extensive proglacial lakes, form the flat to rolling plains that underlie the most productive agricultural soils of the region. Glaciofluvial deposits, although limited in extent, are extremely important surficial and shallow groundwater aquifers. Reworking of coarse glaciolacustrine deposits and glaciofluvial sands by wind has produced significant areas of sand dunes (see Muhs and Wolfe, 1999). One of these, the

Great Sand Hills of southwestern Saskatchewan (Fig. l), is the largest contiguous dune area in southern Canada (David, 1977).

Modern drainages strongly reflect the influence of glaciation. Glacial diversion of pre-existing drainages, plus large tracts of hummocky terrain and a relatively dry climate, com- bine to produce large, internally drained basins covering more than 25% of the region (Fisheries and Environment Canada, 1978). Most through-flowing drainages have developed from a network of deglacial meltwater channels, many of which are steep walled and incised up to 100 m. These features often form the most significant relief over large areas (Kehew and Teller, 1994). The Palliser Triangle includes part of the modern continental drainage divide (Fig. I), with run- off from parts of southernmost Alberta and Saskatchewan flowing to the Gulf of Mexico via the Missouri, while the remainder drains northeast to Hudson Bay.

The native vegetation cover of the Palliser Triangle is referred to as 'northern mixed-grass prairie' (Risser et al., 1981), or simply 'mixed prairie' (Coupland, 1950, 1961). Considerable compositional variability results primarily from the effects of relief and aspect on moisture availability. Coupland (1950, 1961) utilized variation in seven major species to define all mixed prairie communities. Drought adapta- tions include apredominance of perennial, cool season forms that begin growth in early spring and are dormant by July (Risser et al., 1981). Since the onset of extensive Eurocanadian settlement in the late nineteenth century, most of this native grass cover has either been supplanted by cereal crops or modified by grazing and the introduction of non-native species. Of the ecological changes associated with Eurocanadian settlement, Coupland (1961) deemed the elim- ination of fire as the single most significant event.

Uplands in the Palliser Triangle support forest cover, particularly along north-facing slopes and seepage areas. The Cypress Hills support white spruce (Picea glauca), lodgepole pine (Pinus contorta), trembling aspen (Populus tremuloides), and balsam poplar (P, balsamifera), with orographic precipitation providing critical moisture. The Moose Mountain upland is distinguished by an extensive paper birch (Betula papyrifera) population. Woody vegetation is also found in coulees, interdune areas, and deeply incised river valleys where groves of cottonwood (Populus acuminata, P. angustifolin, and P. deltoides) colonize allu- vial flats.

The soils of the Palliser Triangle strongly reflect the subhumid climate and grassland vegetation of the region. Soils of the Chernozemic Order dominate (Canada Soil Inventory, 1987a, b), and are by far the most important in terms of agricultural productivity. The region encompasses all of the Brown Chernozemic Soil Zone (Fig. I), which was used by Lemmen et al. (1998) as a working definition of the Palliser Triangle. Dark Brown Chernozemic soils occur on the higher elevations of plateaus and along the margin of the Brown Soil Zone, while Chernozemic Black soils are found on the highest portions of the Cypress Hills. The differing colour of the A-horizon of these soils reflects differences in organic matter content (Rostad et al., 1993), which is in turn a reflection of


Figure 3. Geomorphic and land-use diversity in the Palliser Triangle: A) west block of the Cypress Hills, Alberta, rising to 600 rn above the adjacent plains and supporting coniferous forest on north-facing slopes; photograph courtesy of the Prairie Farm Rehabilitation Administration; B) partially active sand d~irzes in the Great Sand Hills, Saskatchewan, the largest contiguous dune occurrence in southern Canada; photograph by S.A. Wove; GSC 1999-042A; C) badlands in Dinosaur Provincal Park, Alberta; small areas of badlands contribute large volumes of suspended sediment to rivers; photograph courtesy of1.A. Campbell; D) and E) agriculture is the lifeblood of the southern Prairies; lake plains gerzerally contain the most productive soils; grazing dominates on sandy soils and in the driest portions of the Palliser Triangle, with dugouts providing critical water for cattle; photographs courtesy of the Prairie Farm Rehabilitation Adnzinistration; F ) recreation in Grasslands National Park, Saskatchewan; photograph by D.J. Sauchyn; GSC 1999-042B.

GSC Bulletin 534

moisture availability. Significant areas of Solonetzic and Regosolic soils also occur in the Palliser Triangle. Solonetzic soils reflect a local or regional concentration of sodium in the soil profile, and are commonly associated with areas of saline soils. Regosols lack significant soil development, and are regionally associated with three distinct environments: unsta- ble sandy soils (including sand dunes), valley slopes of major river systems, and areas of exposed bedrock.

RESULTS

Past climate and hydrological changes An understanding of regional climatic variability, as well as the timing and nature of past climatic changes, is essential to any assessment of future climate-change impacts, and was therefore the first major objective of the Palliser Triangle project. Although grasslands are potentially one of the more sus- ceptible environments to climate change, they are also one of the most difficult settings in which to obtain paleoenvironmental data (Barnosky et al., 1989). As a result, prior to the initiation of this project, there was at best only a very rudi- mentary understanding of past climate dynamics in the Palliser Triangle (Vance et al., 1992).

Tree-ling records are generally the most reliable, widely distributed source of annual-resolution proxy climate data. However, within the Palliser Triangle there is only one such record available, a 3 12-year dendroclimatic reconstruction of precipitation from the Cypress Hills (Sauchyn and Beaudoin,

1998). This record indicates that some droughts of the eighteenth and nineteenth centuries were more severe than those recorded in the historic (instrumental) climate record, and that the most severe drought event occurred in the late 1700s. Case and MacDonald (1995) arrived at similar conclusions based on a 500-year dendroclimatic reconstruction of precipitation in the foothills of southern Alberta.

Despite the high resolution of the tree-ring data, the brief duration of these records and the limited potential for additional sites are serious shortcomings in developing an understanding of regional paleoclimatic change. In an effort to bridge this gap, Palliser Triangle project research focused on millennium-scale reconstruct ions derived from paleolimnological data (Vance, 1997). Such data provide not only a proxy of past climate, but also a direct record of past changes in surface-water quantity (water levels) and quality (water chemistry). These paleohydrological reconstructions are particularly important in the Palliser Triangle, where water is considered to be the single most critical resource issue with respect to impacts of future climate change (Herrington et al., 1997).

Lakes are widespread throughout the Palliser Triangle, and exhibit tremendous diversity in terms of hydrology, morphology, chemistry, and sedimentary processes (see detailed review by Last (1999)). As well, many appear to respond pre- dictably to environmental change, as shown by aerial photographs documenting recent water-level changes (Fig. 4). Unfortunately, most lakes in the region are saline and ephem- eral, and therefore contain not only a limited range of

Figure 4. Vertical aerial photographs showing dramatic drop in water level in Antelope Lake, Saskatchewan (site 4, Fig. 5), between A) 1961 (NAPL A17302-26) and B) 1991 (NAPL A27728-73).


biological proxy climate indicators but also discontinuous sedimentary records. Hence, most Palliser Triangle lakes are less than ideal candidates for paleoenvironmental studies. However, lakes fed by shallow groundwater with significant aquifer capacity are comparatively immune to frequent desic- cation. and lakes situated on local uolands also tend to contain continuous sedimentary records. Considerable effort was therefore directed toward identification of appropriate groundwater discharge and groundwater recharge sample sites that formed transects across environmental gradients (Vance and Last, 1994). General methods of core collection, sampling, and analysis were described by Vance (1997). ~ d d i t i o n a l details can be found in publications of site-specific studies (e.g. Vanceet al., 1997; Last et al., 1998).

Nine lakes were chosen for detailed paleolirnnological study using multiple proxy indicators (Fig. 5 , Table 1 ; Vance, 1997). In addition, North Ingebrigt lake (Fig. 5) was the subject of detailed sedimentological and mineralogical studies (Shang and Last, 1999), and plant macrofossil and ~edimentolo~ical analyses of a prairie pothole on The Mis- souri Coteau (Andrews site, Fig. 5 ) provided a unique record of late Pleistocene-early Holocene environments (Yansa, 1998; Yansa and Basinger, 1999; Aitken et al., 1999). Of the nine principal study sites (Table l), four lie either on or along the flanks of regional uplands (Elkwater, Harris, Kenosee, and Max), two on The Missouri Coteau (Clearwater and Oro), and three on the plains (Chappice, Antelope, and Killarney). They reflect a range (Table 1) of water depth (9 m) and salinity (freshwater (0.17 g - ~ - l ) to hypersaline (165 g .~ - l ) ) . Although several lakes contain laminated sedimentary sequences (Last and Vance, 1997), varves are not demon- strably present at any site. Geochronology was dependent upon AMS radiocarbon dating of shoreline and terrestrial plant macrofossils and 2 1 0 ~ b dating (Vance, 1997). Sedimen- tary records of at least three of these study sites contain significant unconformities (Table 1).

A primary goal in the study of these sites was to integrate multiple, independent proxies of environmental change in order to develop a comprehensive evaluation of the role of climate versus other limnological controls (Table 1). At

times, contradictions between various proxies are apparent, as documented in a series of papers on Harris Lake (Sauchyn and Sauchyn, 1991; Last and Sauchyn, 1993; Wilson et al., 1997; Porter et al., 1999). Integrative approaches to resolving these apparent contradictions were outlined in investigations at Kenosee Lake (Vance et al., 1997) and Clearwater Lake (Last et al., 1998; Leavitt et al., 1999). These approaches resulted in reconstructions that include events and drivers (principally hydrogeological and anthropogenic) that likely could not be derived using any single indicator.

Detailed results from some sites remain unpublished, and there has as yet been no opportunity to integrate individual sites into a regional synthesis. Nonetheless, a preliminary integration of results from these nine sites has allowed the identification of three major hydroclimatic intervals within the Holocene (Fig. 6; Vance et al., 1998).

Early Holocene (ca. 10 000-7000 BP) Basal sediments in Harris, Clearwater, Oro, and Killarney lakes all predate 9000 BP. These records indicate that the early Holocene was an interval characterized by generally high lake levels and freshwater conditions, although short-term, low-water, more saline intervals are evident at all sites. Rapidly changing conditions that do not appear syn- chronous between sites are interpreted to reflect a groundwater-dominated hydrology. Surficial and shallow aquifers, fully charged following deglaciation, may have buffered lakes from climate-driven changes in the early Holocene. Since this groundwater effect appears to have been most pronounced on The Missouri Coteau (Clearwater Lake (Last et al., 1998) and Oro Lake (Vance and Last, 1996)), an area of extensive hummocky terrain, it may relate to the melting of stagnant glacier ice thousands of years after retreat of the active ice margin.

This strong groundwater influence makes definitive conclusions concerning early Holocene climate difficult. How- ever, sedimentological and mineralogical evidence of arid intervals do exist, such as 1) a saline to hypersaline phase

Figure 5. Principal study sites of the Palliser Triungle Global Change Project. Brown Chernozemic Soil Zone is shaded. Open circles denote paleolimnological study sites, with numbers corresponding to those in Table 1. Additional study sites are NI (North Ingebrigt lake) and AS (Anclrews site). Solid circles denote geomorphic study sites.

GSC Bulletin 534

Table 1. Primary paleolimnological study sites of the Palliser Triangle Global Change Project. Site numbers correspond to Figure 5. Analyses were conducted on multiple cores from each site.

Site Latitude, (references) longitude

Chappice

Birks and Remenda.

Elevation (m a.s.1)

730

~a r r l s ' (Sauchyn and Sauchyn, 1991; Last and Sauchyn, 1993; Wilson et al., 1997; Porter et ai., 1999; Wilson and Smol, 1999) Antelope (Last and Vance, 1996; Vance, 1997)

2

1850 * 70 (at 2.9 m)

Maximum deptha

(m) 0.32

No No

No?

1999) Elkwater (Vance and Last, 1994; Vance. 19971

S, M, G, I, MA S, M. G, MA, D,O, P

Surface T D S ~

( g . ~ ' ) 121-165

S, M, G, I, MA, A

4g039'N, 11018'W

Clearwater (Last et al., 1998; Leavitt et al., 1999; Wilson and Smol. 1999)

Core lengthC

( 4 8.7

680 9.4 0.87-1.21 3.2 3430 f 80 NO S, M. G, I, MA, A 1 1 / . i ' g 9 8 o * 7 o yes 1 s, M, G, 1, MA, D

1209

Or0 4g047'N, 6.4 17.5-40.2 8.1 9420f230 No? S,M,G,I,MA,D,O, (Vance and Last. 1996; ( 10520'W 1 700 ( 1 1 1 I I PM Vance. 19971

Basal dated

7325 * 70

Kenosee 1 4 4 9 N 1 735 4.3 1 2.07-3.63 1 2 4 0 9 0 1 1 1 0 1 No S,M.G.I.MA,O,A 1 IVance et al.. 19971 10218'W

8.3

1 49';5'N, 1 665 1 3.5 / 0.26-0.34 ( 3.8 1 3330 k 70 1 No S, M. G, MA. D 0 , A 1 1 %ce and Last. 1994: 100 09 W I

Uncon- formities

Yes

~ n a l y s e s ~

S, M, G, I, MA, P

0.25-0.30

I I Goldsborouah. 1999) 1 I I I I I I I I 9

a Maximum depth recorded during water chemistry sampling. Range of total dissolved solids observed in surveys conducted in August 1994, January 1995, and May 1995. Refers to core collected from the central basin of each lake. A nearshore core from Clearwater Lake is included because it is much longer and older than the core collected from the central basin. In radiocarbon years, determined by accelerator mass spectrometry (AMS) dating of shoreline and terrestrial plant macrofossils. In most cases, dated sample lies above base of core. Analyses: S, sedimentology (includes particle size, water content, and organic matter); M, mineralogy; G, geochemistry; I, stable isotopes; MA, macrofossils; D, diatoms; 0, ostracodes; A, algal pigments; P, pollen; PM, paleomagnetism. Includes analyses of 9.6 m long core collected prior to start of the Palliser Triangle project.

5.5

(salinities approx. 20-70 g . ~ - l ) between 9800 and 8600 BP at Clearwater Lake (Last et al., 1998); 2) an abrupt change from freshwater conditions to a hypersaline, meromictic lake at Oro Lake between ca. 9400 and 9000 BP (Vance and Last, 1996); and 3) a rapid transition from fresh to highly saline conditions at ca. 10 000 BP at the Andrews site (Aitken et al., 1999). It is possible that, at times, early Holocene climate (associated with the insolation maximum) was as arid as, or more arid than, during any subsequent interval. However, since the hydrological setting was predominantly driven by groundwater, high freshwater lake conditions dominated.

~ance, 1997) Killarney (Richmond and

Mid-Holocene (ca. 7000-5000 BP)

4940k 70

The mid-Holocene was characterized by widespread low lake levels in the Palliser Triangle. Only three of the study sites (Chappice, Harris, and Oro lakes) contain sedimentary

49"l I'N, 99"42W

records within the 7000-5000 BP interval. In each case, the lake was significantly more saline than at present. Chappice (Vance et al., 1992,1993) and Killarney (R.E. Vance, unpub. data, 1997) lakes dried completely during this interval, the only time this happened at either site during the Holocene. The absence of sediments dating to this interval in other basins indicates that they were also completely dry at this time (with the exception of Elkwater Lake, which was likely cre- ated by a landslide ca. 5000 BP). Present lake depths of 6 m (Killarney Lake) to 9.5 m (Clearwater Lake) provide a rough estimate of the magnitude of this mid-Holocene groundwater decline (Lernmen et a1.,1997). Even at the end of this interval, water levels in Kenosee Lake lay 5 m below present (Vance et al., 1997). Remenda and Birlts (1999) suggested that the actual mid-Holocene decline in regional water tables may have been on the order of 6-15 m, based on depth of oxidized sediments noted in hydrogeological studies.

No S, M, G, MA, 0

490 5.9 0.44-0.64 4.2 9180 f 80 Yes S, M, G, I, MA, D, A


Early Holocene (ca. 10 000 - 7000 BP)

C I

Mid-Holocene (ca. 7000 - 5000 BP)

1

Late Holocene (ca. 5000 BP to present) -

Water level Salinity

High Low 2 Dry

Figure 6. Regional paleohydrological summary based on nine principal paleolimnological study sites. Site numbers corresponcl with those in Table 1. Dashed line denotes eastern margin of Palliser Triangle; areas of internal drainage are shaded. See text for discussion.

GSC Bulletin 534

The mid-Holocene was evidently an interval of severe aridity across the southern Prairies. Based on the thickness of distinctive laminated sequences indicative of drought events in Chappice Lake, Vance et al. (1992) suggested that this interval was one in which drought conditions (as defined by historic climate) predominated for decades to perhaps centuries. Given the focus of the project - multiple proxy records - quantitative climatic transfer functions were not developed as part of this study. However, previous estimates derived from pollen records outside the Palliser Triangle in Alberta and Manitoba suggest summer temperatures at this time were about 2C warmer than present, and grow- ing-season precipitation was 15% less (Vance et al., 1995). These values are comparable to GCM projections for prairie climate under an enhanced greenhouse gas (2 x C02) scenario (Wheaton et al., 1992). Although the drivers of climatic warming in the mid-Holocene were different (insolation) than those used in future projections (greenhouse gases), these paleoenvironmental results highlight the vulnerability of prairie water resources to a warmer climate.

Late Holocene (ca. 5000 BP to present) All study sites preserve a sedimentary record of this most recent period of climatic and hydrological change. Rising groundwater tables resulted in regional infilling of lake basins beginning about 5000 BP, roughly coincident with the onset of Neoglaciation. Maximum water levels and freshwater conditions prevailed between about 3000 and 2000 BP. At many lakes, evidence of fluctuations in water level and water chemistry may correlate with well lcnown climatic events, such as the Medieval Warm Period (ca. AD 900-1200) and the Little Ice Age (ca. AD 1450-1850). Although limitations in chronological control render such correlations tentative, strong similarities in the records from several lakes suggest regional climatic controls (Richmond and Goldsborough, 1999). In contrast, lakes in the Cypress Hills (Harris and Elkwater lakes) remained fresh and relatively stable throughout this interval (Wilson and Smol, 1999). Another important aspect of the late Holocene record is the impact of Eurocanadian settlement and associated agricultural prac- tices (Leavitt et al., 1999; Richmond and Goldsborough, 1999). In some basins, these anthropogenic impacts appear to have overwhelmed any signal of recent climate fluctuations.

In general, the climate of the last 5000 years in the Palliser Triangle was significantly more humid than during the pre- ceding half of the Holocene. The relative importance of increased precipitation versus decreased temperatures in reducing regional aridity in the late Holocene remains unknown. Besides the high water levels and freshwater conditions pervasive across the region, one of the strongest indi- cations of cooler conditions was the proliferation of birch (Betula papyrifera) on Moose Mountain upland during the Little Ice Age (Vance et al., 1997). As important as the humid extremes, however, is the magnitude of climatic variability during the late Holocene. The thickness of laminated sediments at Chappice Lake suggests that droughts of the Medi- eval Warm Period lasted longer than those of the historic (instmmental) climate record. This is particularly significant since the major global controls on climate at this time were

essentially the same as at present, implying that such drought events could occur in future, even in the absence of anthropogenically induced climate change.

Synopsis Among the common findings of the paleolimnological studies conducted as part of the Palliser Triangle project is that the observed changes in fossil, mineralogical, and sedimentary records reflect an intregration of climatic, hydrological, and anthropogenic factors. Another commonality is the restric- tion imposed by limited chronological control (Vance, 1997). Together, these factors make establishment of high- resolution, long-term paleoclimatic records sensu strict0 difficult, and perhaps impossible, for this region. Nonetheless, through the integration of multiple proxy records, the data provide an important record of the paleohydrological changes.

Other limitations of the paleolimnological record are also emerging. For example, the drought of the late eighteenth century, identified in the tree-ring record as the most severe of the last 500 years, is not evident in the paleolimnological record. This may relate to limited chronological control, but also to the importance of antecedent conditions in controlling the sensitivity of lake basins. The impact of drought will be far less evident if it occurs during a generally humid interval, owing to the buffer provided by fully charged shallow aquifers and the 'reservoir effect' of the lakes themselves. Lakes at a low level with depleted local aquifers are much more responsive to climatic change.

Beyond the basic framework of Holocene hydroclimatic changes, a few fundamental conclusions must be emphasized with respect to potential impacts of future climate change. First, the historic (instrumental) climate record does not cap- ture the full range of climate variability that can be expected with present climate-forcing factors. This is particularly true for aiTidity, since prior drought intervals appear to have been far more severe than those of the twentieth centuly. Similar conclusions have been reached by researchers studying the American Great Plains (Laird et al., 1996; Woodhouse and Overpeck, 1998). Second, because many lakes on the southern Prairies have experienced major changes in water levels and water quality in response to past global changes, it is rea- sonable to conclude that future climate changes (resulting from both anthropogenic forcing and climatic variability) will also affect the region. But, perhaps most significantly, in documenting the response of complex systems to past changes in multiple controlling factors, these studies provide the foundation for evaluating the potential impacts of future climate change on surface and shallow groundwater resources.

Landscape response to climate The second major objective of the Palliser Triangle project was to improve understanding of the relationships between climate and geomorphic processes, in order to assess potential landscape response to future climate change. This work builds upon the review of regional eolian, fluvial,


mass-wasting, and soil redistribution systems presented by Hence landscape adjustments observed in the recent strati- Lemmen et al. (1998). Although climate is an important con- graphic record largely reflect geomo~yhic response towards a trol in all of these geomorphic systems, they concluded that new dynamic equilibrium, upon which other factors, includ- eolian landscapes are the most sensitive to climate change. ing climate change, are superimposed. The relative immatu- Soil redistribution, however, has the greatest implication for rity of the landscape is an important distinction between the regional economic sustainability. While land-use decisions northernmost Great Plains and nonglaciated regions to the and land-management techniaues are the most critical factors south.

u

influencing erosion of agricultural soils, there is high potential for significant soil loss in all cultivated areas under a climate that is warmer and drier than at present (Lernmen et al., 1998).

Research on landscape response involved the following approaches: geomorphic, stratigraphic, and geochronological analysis to determine past landscape changes; and monitoring of present rates of geomorphic processes that can be related to instrumental climate data (Lemmen et al., 1993). While both approaches have limitations when attempting to

Variability in geomorphic activity throughout the Holocene is presented schematically in Figure 7. This dia- gram represents a subjective assessment of activity relative to the range observed for the Holocene as a whole, and is placed in the context of the major hydroclimatic intervals discussed previously. A more objective assessment of past geomorphic activity, based on distribution of relevant radiocarbon dates, has been developed for southeastern Alberta by Campbell and Campbell (1997). The value of this approach is acknowl- edged, although it is not adopted here for the following rea-

assess future landscape change over time scales ranging from sons: l ) the limited number of absolute dates clearly related to decades to centuries (Sauchyn, 1999), they provide a means specific geomorphic events in the Palliser Triangle; 2) the of evaluating the climatic sensitivity of geomorphic systems strong spatial clustering of what chronological data are avail- and a basis for estimating thresholds and response times able, with risk of local and event bias not representative of the likely to be associated with future climate changes. Study region; and 3) the bias of many stratigraphic records to either sites were clustered in the central, driest part of the Palliser recent or high-magnitude events (Sauchyn, 1999). In addi- Triangle (Brown Chernozernic Soil Zone, Fig. 5) , assuming tion, significant response and relaxation times suggest that that this is the most climatically sensitive area and therefore simple chronological correlation between climatic and most likely to show significant geomorphic response to cli- geomorphic events does not demonstrate a causal relation- mate change (Bull, 1991). ship (Vreeken, 1999). Therefore, it must be emphasized that

~ i g u r e 7 presents a conceptual framework only, to be tested In to assess the and modified when a more extensive chronological database

changes on the prairie landscape, it must be noted that Late is available, Pleistocene glaciation was by far the single most important event influencing recent regional landscape evolution In addition to documenting past geomorphic activity, (Lernmen, 1998; Vreelten, 1999). Glaciation disrupted previ- paleoenvironmental research makes it possible to assess the ously integrated drainages, significantly modified local top- relative importance of climate versus conditions internal to ography through deposition of moraines and incision of geomorphic systems, as controls on regional geomorphic meltwater channels, and altered regional base levels through activity (Table 2). Geomorphic systems that are near a glacio-isostatic adjustments (Klassen, 1989). Much of the dynamicequilibrium willshow themostpredictableresponse Palliser Triangle features a landscape still responding to to climate change. In such cases, climate is herein deemed the disequilibriums established more than 12 000 years ago. dominant factor controlling system response. However,

Time I Late Early Mid- Late Pleistocene Holocene Holocene Holocene Climate

Humid Dealacial Arid

System Activitv

Fluvial Extreme Fan formatlon

Extreme Mass-wasting rn

I---,

Extreme Eolian 7 ,,,D,U'?,aC?'?Y,, =z -m~r-- - I-

Loess deposition ; - - Negligible

Extreme Soil erosion High

Low I( Negligible

D a t e d e v e n t s ) 1 a 1 I a I a 1 I 1 I

Figure 7. Schematic summary of relative geomorphic activity thro~igh the Holocene. Slzading denotes intervals when activity was most regionally pervasive. See text for discussion. Note also com- pilation of Campbell and Campbell (1997), based ciporz distribution of radiocarbon dates in southern Alberta.

- - - Inferred 16 12 8 4 0 Time (x l o 3 BP)

D.S. Lemrnen and R.E. Vance

between climate and dune activity is not simple, with dune activation occurring as a threshold response controlled by antecedent moisture conditions (Wolfe et al., 1998). The fact that there has been a trend towards net dune stabilization throughout the twentieth century (David, 1993; Wolfe and Lernrnen, 1999), despite an overall warming trend and several severe droughts during this period, highlights the complexity of this system. Detailed chronological control through optical dating (Huntley et al., 1985; Huntley and Lian, 1999) suggests a response time of one to three decades for dune activation following extended severe drought (Table 2; David et al., 1999). Relaxation times associated with dune stabilization may be even longer. For example, Wolfe and Lemmen (1999) suggested that some of the present dune activity in the Palliser Triangle is relict, relating to the regional activity of the nineteenth century.

The predominance of agricultural lands in the Palliser Triangle necessitates inclusion of soil erosion in any exam- ination of regional landscape processes. Discussion of the processes and rates of soil redistribution has been presented by Pennock et al. (1995) and Lemmen et al. (1998). Rates of wind and water erosion on bare soil are estimated to be two to five orders of magnitude greater than those occurring on fully vegetated pasture or native grassland (Evans, 1980; Coote, 1984). Thus, from the perspective of Holocene landscape evolution, soil erosion was comparatively insignificant prior to breaking of the prairie grassland by Eurocanadian settlers (Fig. 7). In contrast, soil erosion today represents by far the most regionally important geomorphic process, in terms of both volume of sediment redistributed and associated economic costs.

While anthropogenic activity is clearly the predominant factor controlling soil redistribution (Table 2), wind and water erosion of agricultural soils are closely related to extreme climate events. Drought is a necessary precursor to widespread wind erosion (Jones, 1991). The droughts of the 1930s clearly demonstrated that inappropriate land-use prac- tices can lead to widespread destabilization of soils. In contrast, the droughts of the 1980s were climatically comparable, but improved soil management resulted in far less severe environmental impacts, despite severe economic impacts (Wheaton and Arthur, 1989).

Research presented herein highlights a number of key points with respect to assessing the potential geomorphic impacts of future climate change. Perhaps most fundamental is that climate is but one of several factors controlling geomorphic response (e.g. Vreeken, 1999). Systems that are still responding to past major disturbances are unlikely to show a predictable response to climate change. Projections of future impacts must be based on a thorough understanding of system dynamics, including the importance of antecedent conditions and threshold response (e.g. David et al., 1999). While paleoenvironmental research makes an important contribution to this understanding, monitoring studies are also important in providing direct measurement of processes inferred for past geomorphic response (e.g. Wolfe and Lemmen, 1999; Sauchyn and Nelson, 1999). Significant

response and relaxation times in many systems suggest that some climate impacts will not be immediately apparent, but may have considerable long-term consequences.

ACKNOWLEDGMENTS

The constructive comments of Steve Wolfe significantly improved this manuscript. The authors would also like to thank Trevor Robertson, Susan Ball, Murray Hay, Mark Birchard, Jo-yi Wei, and Sonia Utting for cartographic, field, and laboratory assistance while in the employ of the Geological Survey of Canada.

REFERENCES

Aitken, A.E., Last, W.M., and Burt, A.K. 1999: The lithostratigraphic record of late Pleistocene-Holocene environ-

Cambio Climático

Documents

Transcript of Cambio Climático