DEEP SEA BEDFORMS AND ECOSYSTEM RESPONSE TO …€¦ · 1. OPEN SLOPE PATHWAY On the open slope,...
1
Geo-marine Research on the Mediterranean and European-Atlantic Margins International Conference and TTR-17th Post-Cruise Meeting of the Training-through-Research Programme Granada, February 2nd to 5th, 2009 Consiglio Nazionale delle Ricerche ISMAR - Istituto di Scienze Marine Sede di Bologna Via Gobei, 101 – 40129 Bologna, Italy DEEP SEA BEDFORMS AND ECOSYSTEM RESPONSE TO CASCADING SHELF WATERS IN THE SOUTH ADRIATIC Trincardi F. (1), Taviani M. (1), Verdicchio G. (2), Asioli A. (3), Campiani E. (1), Dalla Valle G. (1), Foglini F. (1), Gamberi F. (1), Piva A. (1), Remia A. (1), Angeletti L. (1) (1) Istituto di Scienze Marine ISMAR - CNR - Bologna, (2) Edison S.p.A. - Milano, (3) Istituto di Geoscienze e Georisorse IGG- CNR - Padova depth (m) -200 -400 -600 -800 -1000 Gondola slide slope area more impacted by bottom currents NAdDW LIW 10000 m 1000 m N NAdDW LIW Turchetto et al.,2007 8 km N Sediment samples Location of mooring stations (current-metre and sediment trap) NAdDW production area NAdDW LIW -126 m depth -1186 Cascading North Adriatic Dense Water (NAdDW) impact energetically the seafloor of the SW Adriatic margin, eroding and depositing large amounts of fine-grained sediment below a markedly erosional upper slope. This cascading NAdDW is generated in the broad and shallow North Adriatic shelf through intense winter cooling and evaporation. The NAdDW flows, southward along the Italian coast, reaches the shelf break, typically over a prolonged interval (several weeks) at the end of the winter season, and sinks across the slope 2. BARI CANYON PATHWAY A branch of the cascading NAdDW is confi- ned and accelerated through the Bari Canyon where it produces a strong current capable of reaching down-slope velocities greater than 60cm/sec, eroding the canyon thalweg and entraining large amounts of fine-grained sediment. At the exit of the canyon, in water depth greater than 900m, the current becomes less con- fined, spreads laterally and generates an 80-km 2 -wide field of mud waves; these bedforms migrate up current and show amplitudes up to 50m and wavelengths of about 1km. 1. OPEN SLOPE PATHWAY On the open slope, patchy fields of mud waves show up-current migration. All these fields are located down-slope of large erosio- nal areas but occupy distinctive slope sectors characterised by dissimilar morphologies. Furrows and comet marks are spatially and genetically associated with the mud waves, particularly on their downslope (and down- flow) limbs, where current flows reach their maximum strength. Data regarding the distri- bution, morphology, orientation and stratigra- phy of these patchy fields of mud waves are interpreted to record the long-term (millennial-scale) average of the seasonally variable direction and intensity of the NAdDW cascading currents, evidencing their prefer- red pathways across the slope. The main erosional, transitional and depositional features observed on the sea floor define the time averaged current path of the NAdDW OCEANOGRAPHIC SETTING The Mediterranean circulation describes an open thermohaline cell leading to the transformation of the Atlantic Water, which enters from the Gibraltar Strait, in the Levantine Intermediate Water (LIW) that flows typically between 200 and 600 m water depth and is the main contributor to the Mediterranean outflow. The LIW form in the Levantine Basin through summer evaporation and winter coo- ling. This salty water mass (T ~ 14°C, S ~ 38.7 and σ t ~ 29.1) enters the south Adriatic through the Otranto Strait and flows southward along the SAM. The NAdDW (T ~ 11°C, S ~ 38.5, σ t ~ 29.5-29.6) represents the densest water of the whole Mediterranean and forms in January-February through strong surfa- ce cooling on the broad and shallow north Adriatic shelf impacted by Bora ca- thabatic winds. The NAdDW spreads toward the South along the Italian coast reaching the south Adriatic slope circa 2 months later (end of March - beginning of April), and ca- scading across the SAM slope. Year-round current-metre moorings on the open slope and in Bari canyon reveal bottom current speeds greater than 60cm sec -1 during the flow of the NAdDW across the margin. Crossing the SAM slope, the NAdDW entrains the surrounding LIW before sinking toward the bottom of the basin and contributing to the Adriatic outflow. By cascading across the slope, the dense NAdDW impinges the seafloor and interacts with the complex margin mor- phology, generating: patchy fields of large-scale mud waves; a variety of erosional bed forms, such as moats, furrows and comet marks; an area of widwspread sea floor ero- sion. All these bed forms are active during the modern interglacial as well as during the last interglacial, when climatic forcing also allowed the formation of the NAdDW on the shallow north Adriatic shelf. Bari Canyon System (BCS) is a major sediment conduit on the SW Adriatic margin. After the last glacial low stand, processes typical of active submarine canyons, such as turbidity currents and mass-transport events, were replaced or overshadowed by intense cascading currents impacting seasonally the area and accelerating through the canyon. When cap- tured by the BCS, the off-shelf cascading current becomes confined eroding, transporting and depositing fine-grained sediment mimicing a dilute turbidity current. 1. BCS is characterised by a marked morphological asymmetry with a high-relief and a steep erosional southern flank. 2. Channel-levee complex B was particularly active during the last glacial lowstand, deve- loping a pronounced levee asymmetry, and becoming abandoned afterwards. 4. Today, cold and dense bottom water enters the BCS with a reduced load but is capable to hug the seafloor and entrain sediment. 5. This dense water can reach velocities greater than 60 cm sec-1 and, during modern hi- ghstand conditions, down cut the upper portion of channel B. In deeper waters, instead, the most actively eroded element is canyon C, to the south. 6. Cascading water flush the upper trunk of B, overspill towards the right, accelerate through canyon C and expand generating a field of mud waves (MW). Artegiani A., Bregant D., Paschini E., Pinardi N., Raicich F., A. Russo (1997) - The Adriatic Sea General Circula- tion. Part II: Baroclinic circulation structure. J. Phys. Oceanogr. 27, 1515-1532. Bignami F., Salusti E., Schiarini S. (1990) - Observations on a bottom vein of dense water in the Southern Adriati- cand Ionian Seas. J. Geophys. Res., 95, 7249-7259. Canals M., Danovaro R., Heussner S., Lykousis V., Puig P., Trincardi F., Calafat A. M., Durrieu De Madron X. and Palanques A. (2009) - Cascades in Mediterranean Submarine Grand Canyons. Oceanography, 22, pp: 32-49, in press. Cushman-Roisin B., Gacic M., Poulain P.M., Artegiani A. (Eds.) (2001) - Physical oceanography of the Adriatic Sea Past, present and future. 304 pp., Kluwer Academic Publisher, London. Freiwald A., Beuk L., Rüggeberg A., Taviani M., Hebbeln D. and R/V METEOR M70-1 Participants (2009) - The white coral community in the Central Mediterranean Sea revealed by ROV surveys. Oceanography, 22, in press. Gačić M., Civitarese G., Miserocchi S., Cardin V., Crise A., Mauri E. (2002) - The open ocean convection in the Southern Adriatic: a controlling mechanism of the phytoplankton bloom. Cont. Shelf Res., 22, 1897-1908. Malanotte-Rizzoli P., Manca B., Ribera d’Alcala M., Theocharis A., Bergamasco A., Bregant D., Budillon G., Civitarese G., Georgopoulos D., Michelato A., Sansone E., Scarazzato P., E. Souvermezoglou (1997) - A synthesis of the Ionian Sea hydrography, circulation and water mass pathways during POEM Phase I. Prog. Ocean. 39, 153-204. Manca B. B, Kovacevic V., Gacic M., Viezzoli D. (2002) - Dense water formation in the southern Adriatic Sea ans spreading in the Ionian Sea in the period 1997-1999. J. Mar. Syst., 33/34,133-154. Ridente D., Foglini F., Minisini D., Trincardi F., Verdicchio G. (2007) - Shelf-edge erosion, sediment failure and inception of Bari Canyon on the South-Western Adriatic Margin (Central Mediterranean). Marine Geology, Vol. 246: pp. 193-207. Tesi T., Langone L., Goñi M. A., Turchetto M., Miserocchi S., Boldrin A. - Source and composition of organic matter in the Bari canyon (Italy): dense water cascading vs particulate export from the upper ocean. Deep Sea Res., in press. Trincardi F., Verdicchio G., Miserocchi S. (2007) - Sea-floor evidence for the interaction between Cascading and along-slope bottom-water masses. Journal of Geophysical Research (Earth Surface). Vol. 112, F03011, doi:10.1029/2006JF000620. Trincardi F., Foglini F., Verdicchio G., Asioli A., Correggiari A., Minisini D., Piva A., Remia A., Ridente D., Taviani M. (2007) - The impact of cascading currents on the Bari Canyon System, SW-Adriatic Margin (Central Mediterranean). Marine Geology, Vol. 246: pp. 208-230. Turchetto M., Boldrin A., Langone L., Miserocchi S., Tesi T., Foglini F. (2007) - Water dynamics and sediment transport associated with the Bari canyon in the southern Adriatic Sea. Marine Geology, Vol. 246: pp. 231-247. Verdicchio G. & Trincardi F. (2006) - Short-distance variability in slope bed-forms along the Southwestern Adriatic Margin (Central Mediterranean). Marine Geology (Weaver P., Canals M., e Trincardi F. Eds.), Vol. 234, pp. 271–292. Verdicchio G., Trincardi F., Asioli A. (2007) - Mediterranean bottom current deposits: an example from the South- western Adriatic Margin. Geological Society of London, Special Publication, Vol. 276: pp. 199–224. Vilibic I. (2003) - An analysis of dense water production in the North Adriatic Shelf. Estuar. Coas. Shelf Sci., 56, 697-707. Zoccolotti L. & Salusti E. (1987) - Observation of a vein of very dense marine water in the southern Adriatic Sea. Cont. Shelf Res. 7, 535-551. Zore-Armanda M. (1963) - Les masses d’eau de la mer Adriatique. Acta Adriatica 10, 5–88. 3. ECOSYSTEM RESPONSE Chandelier-shaped live coral colonies (Madrepora oculata) on the southern wall of Bari Canyon. © QUEST-ROV MARUM Universität Bremen. Pioneer organism (juvenile byssate specimen of Karnekampia bruei) co- lonizing hardground surface under the periodical impact of cascading currents (distal part of Gondola slide). Slumped block from Gon- dola slide with live corals (Lophelia pertusa) and sponges (~ -700 m). © QUEST-ROV MARUM Universität Bremen 5 mm
Transcript of DEEP SEA BEDFORMS AND ECOSYSTEM RESPONSE TO …€¦ · 1. OPEN SLOPE PATHWAY On the open slope,...
Geo-marine Research on the Mediterranean and European-Atlantic MarginsInternational Conference and
TTR-17th Post-Cruise Meeting of the Training-through-Research ProgrammeGranada, February 2nd to 5th, 2009
Consiglio Nazionale delle RicercheISMAR - Istituto di Scienze Marine
Sede di BolognaVia Gobetti, 101 – 40129 Bologna, Italy
DEEP SEA BEDFORMS AND ECOSYSTEM RESPONSE TO CASCADING SHELF WATERS IN THE SOUTH ADRIATIC
Trincardi F. (1), Taviani M. (1), Verdicchio G. (2), Asioli A. (3), Campiani E. (1), Dalla Valle G. (1), Foglini F. (1), Gamberi F. (1), Piva A. (1), Remia A. (1), Angeletti L. (1)(1) Istituto di Scienze Marine ISMAR - CNR - Bologna, (2) Edison S.p.A. - Milano, (3) Istituto di Geoscienze e Georisorse IGG- CNR - Padova
depth (m)
-200
-400
-600
-800
-1000
Gondola slideslope area more impacted by bottom currents
NAdDW
LIW
10000 m
1000 m
N
NAdDW
LIW
Turc
hett
o et
al.,
2007
8 km
N
Sediment samples
Location of mooring stations(current-metre and sediment trap)
NAdDWproduction
area
NAdDWLIW
-126 m depth
-1186
Cascading North Adriatic Dense Water (NAdDW) impact energetically the seafloor of the SW Adriatic margin, eroding and depositing large amounts of fine-grained sediment below a markedly erosional upper slope.
This cascading NAdDW is generated in the broad and shallow North Adriatic shelf through intense winter cooling and evaporation.
The NAdDW flows, southward along the Italian coast, reaches the shelf break, typically over a prolonged interval (several weeks) at the end of the winter season, and sinks across the slope
2. BARI CANYON PATHWAYA branch of the cascading NAdDW is confi-ned and accelerated through the Bari Canyon where it produces a strong current capable of reaching down-slope velocities greater than 60cm/sec, eroding the canyon thalweg and entraining large amounts of fine-grained sediment. At the exit of the canyon, in water depth greater than 900m, the current becomes less con-fined, spreads laterally and generates an 80-km2-wide field of mud waves; these bedforms migrate up current and show amplitudes up to 50m and wavelengths of about 1km.
1. OPEN SLOPE PATHWAYOn the open slope, patchy fields of mud waves show up-current migration. All these fields are located down-slope of large erosio-nal areas but occupy distinctive slope sectors characterised by dissimilar morphologies. Furrows and comet marks are spatially and genetically associated with the mud waves, particularly on their downslope (and down-flow) limbs, where current flows reach their maximum strength. Data regarding the distri-bution, morphology, orientation and stratigra-phy of these patchy fields of mud waves are interpreted to record the long-term (millennial-scale) average of the seasonally variable direction and intensity of the NAdDW cascading currents, evidencing their prefer-red pathways across the slope.
The main erosional, transitional and depositional features observed on the sea floor define the time averaged current path of the NAdDW
OCEANOGRAPHIC SETTINGThe Mediterranean circulation describes an open thermohaline cell leading to the
transformation of the Atlantic Water, which enters from the Gibraltar Strait, in the Levantine Intermediate Water (LIW) that flows typically between 200 and 600 m water depth and is the main contributor to the Mediterranean outflow.
The LIW form in the Levantine Basin through summer evaporation and winter coo-ling. This salty water mass (T ~ 14°C, S ~ 38.7 and σt~ 29.1) enters the south Adriatic through the Otranto Strait and flows southward along the SAM.
The NAdDW (T ~ 11°C, S ~ 38.5, σt~ 29.5-29.6) represents the densest water of the whole Mediterranean and forms in January-February through strong surfa-ce cooling on the broad and shallow north Adriatic shelf impacted by Bora ca-thabatic winds.
The NAdDW spreads toward the South along the Italian coast reaching the south Adriatic slope circa 2 months later (end of March - beginning of April), and ca-scading across the SAM slope.
Year-round current-metre moorings on the open slope and in Bari canyon reveal bottom current speeds greater than 60cm sec-1 during the flow of the NAdDW across the margin.
Crossing the SAM slope, the NAdDW entrains the surrounding LIW before sinking toward the bottom of the basin and contributing to the Adriatic outflow.
By cascading across the slope, the dense NAdDW impinges the seafloor and interacts with the complex margin mor-phology, generating:
patchy fields of large-scale mud waves;a variety of erosional bed forms, such as moats, furrows and comet marks;an area of widwspread sea floor ero-sion.
All these bed forms are active during the modern interglacial as well as during the last interglacial, when climatic forcing also allowed the formation of the NAdDW on the shallow north Adriatic shelf.
Bari Canyon System (BCS) is a major sediment conduit on the SW Adriatic margin.After the last glacial low stand, processes typical of active submarine canyons, such as turbidity currents and mass-transport events, were replaced or overshadowed by intense cascading currents impacting seasonally the area and accelerating through the canyon. When cap-tured by the BCS, the off-shelf cascading current becomes confined eroding, transporting and depositing fine-grained sediment mimicing a dilute turbidity current.
1. BCS is characterised by a marked morphological asymmetry with a high-relief and a steep erosional southern flank.2. Channel-levee complex B was particularly active during the last glacial lowstand, deve-loping a pronounced levee asymmetry, and becoming abandoned afterwards.4. Today, cold and dense bottom water enters the BCS with a reduced load but is capable to hug the seafloor and entrain sediment.5. This dense water can reach velocities greater than 60 cm sec-1 and, during modern hi-ghstand conditions, down cut the upper portion of channel B. In deeper waters, instead, the most actively eroded element is canyon C, to the south.6. Cascading water flush the upper trunk of B, overspill towards the right, accelerate through canyon C and expand generating a field of mud waves (MW).
Artegiani A., Bregant D., Paschini E., Pinardi N., Raicich F., A. Russo (1997) - The Adriatic Sea General Circula-tion. Part II: Baroclinic circulation structure. J. Phys. Oceanogr. 27, 1515-1532.
Bignami F., Salusti E., Schiarini S. (1990) - Observations on a bottom vein of dense water in the Southern Adriati-cand Ionian Seas. J. Geophys. Res., 95, 7249-7259.
Canals M., Danovaro R., Heussner S., Lykousis V., Puig P., Trincardi F., Calafat A. M., Durrieu De Madron X. and Palanques A. (2009) - Cascades in Mediterranean Submarine Grand Canyons. Oceanography, 22, pp: 32-49, in press.
Cushman-Roisin B., Gacic M., Poulain P.M., Artegiani A. (Eds.) (2001) - Physical oceanography of the Adriatic Sea Past, present and future. 304 pp., Kluwer Academic Publisher, London.
Freiwald A., Beuk L., Rüggeberg A., Taviani M., Hebbeln D. and R/V METEOR M70-1 Participants (2009) - The white coral community in the Central Mediterranean Sea revealed by ROV surveys. Oceanography, 22, in press.
Gačić M., Civitarese G., Miserocchi S., Cardin V., Crise A., Mauri E. (2002) - The open ocean convection in the Southern Adriatic: a controlling mechanism of the phytoplankton bloom. Cont. Shelf Res., 22, 1897-1908.
Malanotte-Rizzoli P., Manca B., Ribera d’Alcala M., Theocharis A., Bergamasco A., Bregant D., Budillon G., Civitarese G., Georgopoulos D., Michelato A., Sansone E., Scarazzato P., E. Souvermezoglou (1997) - A synthesis of the Ionian
Sea hydrography, circulation and water mass pathways during POEM Phase I. Prog. Ocean. 39, 153-204.
Manca B. B, Kovacevic V., Gacic M., Viezzoli D. (2002) - Dense water formation in the southern Adriatic Sea ans
spreading in the Ionian Sea in the period 1997-1999. J. Mar. Syst., 33/34,133-154.
Ridente D., Foglini F., Minisini D., Trincardi F., Verdicchio G. (2007) - Shelf-edge erosion, sediment failure and inception of Bari Canyon on the South-Western Adriatic Margin (Central Mediterranean). Marine Geology, Vol. 246: pp. 193-207.
Tesi T., Langone L., Goñi M. A., Turchetto M., Miserocchi S., Boldrin A. - Source and composition of organic matter in the Bari canyon (Italy): dense water cascading vs particulate export from the upper ocean. Deep Sea Res., in press.
Trincardi F., Verdicchio G., Miserocchi S. (2007) - Sea-floor evidence for the interaction between Cascading and along-slope bottom-water masses. Journal of Geophysical Research (Earth Surface). Vol. 112, F03011, doi:10.1029/2006JF000620.
Trincardi F., Foglini F., Verdicchio G., Asioli A., Correggiari A., Minisini D., Piva A., Remia A., Ridente D., Taviani M. (2007) - The impact of cascading currents on the Bari Canyon System, SW-Adriatic Margin (Central Mediterranean). Marine Geology, Vol. 246: pp. 208-230.
Turchetto M., Boldrin A., Langone L., Miserocchi S., Tesi T., Foglini F. (2007) - Water dynamics and sediment transport associated with the Bari canyon in the southern Adriatic Sea. Marine Geology, Vol. 246: pp. 231-247.
Verdicchio G. & Trincardi F. (2006) - Short-distance variability in slope bed-forms along the Southwestern Adriatic Margin (Central Mediterranean). Marine Geology (Weaver P., Canals M., e Trincardi F. Eds.), Vol. 234, pp. 271–292.
Verdicchio G., Trincardi F., Asioli A. (2007) - Mediterranean bottom current deposits: an example from the South-western Adriatic Margin. Geological Society of London, Special Publication, Vol. 276: pp. 199–224.
Vilibic I. (2003) - An analysis of dense water production in the North Adriatic Shelf. Estuar. Coas. Shelf Sci., 56, 697-707.
Zoccolotti L. & Salusti E. (1987) - Observation of a vein of very dense marine water in the southern Adriatic Sea. Cont. Shelf Res. 7, 535-551.
Zore-Armanda M. (1963) - Les masses d’eau de la mer Adriatique. Acta Adriatica 10, 5–88.
3. ECOSYSTEM RESPONSE
Chandelier-shaped live coral colonies (Madrepora oculata) on the southern wall of Bari Canyon.© QUEST-ROV MARUM Universität Bremen.
Pioneer organism (juvenile byssate specimen of Karnekampia bruei) co-lonizing hardground surface under the periodical impact of cascading currents (distal part of Gondola slide).
Slumped block from Gon-dola slide with live corals (Lophelia pertusa) and sponges (~ -700 m).© QUEST-ROV MARUM Universität Bremen
5 mm
