Post on 29-Jan-2016
Physical and related biological variability in the large-scale North Atlantic, with
implications for the NW Atlantic
Ken DrinkwaterInstitute of Marine Research and Bjerknes Center for Climate
Research, Bergen, Norway
NW Atlantic Ocean Climate Change Workshop
Bedford Institute, Dartmouth, Canada
February 16, 2010
Outline
•Climate Forcing
•Climate Variability in the N. Atlantic over the Past Century
•Large-scale forcing (NAO, AMO)
•Impacts of Climate Variability on Foodwebs
Climate Forcing• Natural Variability
-Solar variations, internal atmospheric dynamics, volcanoes, etc.
• Anthropogenic climate change-CO2 and other greenhouse gases
Time Scales-Hour to weeks (weather)-Months (seasonal)-Years (interannual) -Decadal (NAO/AO)-Multidecadal (AMO)-Centenial+ (Climate change)
NAOHurrell Index
NAO
Sea Ice Indices from Labrador Shelf and Barents Sea –Out of Phase
Since 1995 they have been more in phase, both less ice, warmer conditions
Atlantic Multidecadal Oscillation (AMO)
Sutton & Hodson, 2005
-based on SSTs in North Atlantic-thought to be linked to the strength of the MOC
Joh
an
ness
en
et
al.
20
04
. Tellu
s
Early-1900s Warming
Sea Surface Temperature Change (1930-60 vs 1961-90)
Recent Warming
Warming conditions in the North Atlantic during 1990s and into 2000s.
ICES IROC
Holliday et al. 2008
In early 20th century warming, not only increased atmospheric heat but increased transport of warm water into the Barents Sea, north along Svalbard, along northern Iceland and into the Labrador Sea. Also seeing this in present warming.
Implications for NW Atlantic
Holland et al., 2008
Effects of Warm Currents on West Greenland during recent warming.
Melting of Glaciers in Greenland fjords
Also affects of Arctic outflow.
Recent lower salinities along east coast of Canada thought to be due to increased Arctic outflow
Greene & Pershing 2005
Dic
kson
et a
l. 19
88;
Sch
mid
t, 19
96
Great Salinity Anomalies
Increased outflow of cold Arctic water
Increased inflow of Atlantic Water
Sundby and Drinkwater (2007)
The decadal climate signal is mainly linked to the interaction between atmospheric and oceanic
circulation
Hat
un, 2
008
Cold on the Scotian Shelf, High NAO
Warm on the Scotian Shelf, Low NAO
Transport Effects on Scotian ShelfTransport of Labrador Water influences Scotian Shelf
Role of Climate on the Food Web
Biological Variability
• NAO
Changes in Growth RatesGrowth rates (blue line), as measured by weight change between ages 3-5 declined drastically through the 1970s and 1980s.
This paralleled the changes in the NAO index (red line).
400
800
1200
1600
1974 1976 1978 1980 1982 1984 1986 1988 1990 1992
We
igh
t C
ha
ng
e A
ge
s 3
-5 (
gm
)
5
10
15
20
25
30
35
NA
O In
de
x
Changes in Recruitment
• Cod Recruitment in Barents Sea (Ottersen et al., 2003)
• Cod Recruitment in many areas of North Atlantic (Brander and Mohn, 2004; Stige et al., 2006)
Biological Variability
• AMO
1925 1935 1945 1955 1965 1975 1985
100
300
500
0
100
200
0
First
Intermittent
Frequent
665
Under certain conditionscod larvae drift from Iceland to West Greenland
In the 1920s these conditions were right for the drift of larvae from Iceland to West Greenland and there was good survival once there.
Iceland ConnectionIceland Connection
West West GreenlandGreenland
This continued through to the 1960s with increased abundances and the development of a cod fishery that dominated the Greenland economy.
60oW 50oW 40oW
60oN
65oN
70oN
60oW 50oW 40oW
60oN
65oN
70oN
60oW 50oW 40oW
60oN
65oN
70oN
60oW 50oW 40oW
60oN
65oN
70oN
60oW 50oW 40oW
60oN
65oN
70oN
60oW 50oW 40oW
60oN
65oN
70oN
60oW 50oW 40oW
60oN
65oN
70oN
Greenland
1922
Greenland
1919
Greenland
1900
Greenland
1917-18
Greenland
1927-30
Greenland Greenland
Late 1930s1931-36
Atlantic cod moved northward by Atlantic cod moved northward by 1500 km in response to warming.1500 km in response to warming.
Hansen 1940
Atlantic Atlantic HerringHerring
Norwegian SeaNorwegian Sea
Herring SSB (106 tons) Temperature (°C)
Toresen and Østvedt, 2000
The population of Norwegian spring spawning herring rose dramatically in parallel with the temperatures as recorded in the Kola Section.
Vilhjalmsson, 1997
Mean weights in the catches of spawning cod in the Lofoten region of Norway, 1883-1952 (lighter solid line), the average weight in the longline fishery,1932-98 (dashed-dotted line) and a low-frequency polynomial regression to entire data.
Godø 2003
NE Arctic Cod Stock
The highest total biomass and spawning stock biomass during the 20th century was during the warm period of the 1920s to 1960s. The increased production was due to high recruitment and increased mean weights.
Climate Responses of the Barents Cod Spawning
Sundby and Nakken (2008)
In cold periods:
- southward displacement
- decrease in spawning-stock biomass
In warm periods: - northward displacement
- increase in spawning-stock biomass
Year
Tem
pera
ture
Off West Svalbard, comparison of benthos prior to the 1930s with those of the 1950s indicated that Atlantic species spread northward by approximately 500 km.
Blacker, 1957
Arctic
Atlantic
Benthic Species
Benthos
Biological Variability
• Recent Changes
Temperature influence primary production at
high latitudes
2 4 6 8 10
200
300
400
500
Annual mean temperatures (°C)
Prim
ary
prod
uctio
n (g
C m
-2)
Barents Sea(P = 0.093)
Norwegian Sea(n.s.)
Bering Sea(P = 0.039)
Gulf of Maine /Georges Bank
(P < 0.001)
Gulf of Alaska(n.s.)
Mueter et al. (2009) Norway-US Comparisons (MENU))
Phytoplankton in Arctic and boreal marine ecosystems
Shifts in Zooplankton Distribution Shifts in Zooplankton Distribution
Warm temperate slope species
Be
aug
ran
d e
t al.
20
03.
Sci
enc
e 2
96, 1
69
2-1
69
4
Subarctic Species
Subtropic Species
There is a limit to northward movement however due to light limitations.
Changes in PhenologySST (deg C) Phenology C. helgolandicus (month)
1980s
1990s
2000s
Bea
ugra
nd, 2
009
Bea
ugra
nd, 2
009
Changes in Mean Size of Calanoids
North Sea
Tropical Fish Moving Northward along Continental Shelf Edge
GeneralNorthward Movement
in Response
to Warming
Shifts in Fish DistributionShifts in Fish Distribution
Herring
Kola Temperatures
Herring SSB (106 tons) Temperature (°C)
Atlantic Herring
Toresen and Østvedt, 2000
Changes in Fish Abundance 1Changes in Fish Abundance 1
2003
20062005
2004
Invasive Invasive SpeciesSpecies
Snake Pipefish
SeabirdsSeabirds
Climate vs Fishing Impacts
Climate vs Fishing Effects
It is often stated that we need to separate the effects of climate from fishing. However, for many stocks this can not be achieved as the two interact in a non-linear way.
This can lead to changes in the ecosystem structure and function. Different size individuals and different
species respond to climate in different ways.
Ottersen et al. (2006) noted the age structure of Barents Sea cod has changed due to fishing. Old spawners have been removed.
They also found correlations between temperature and recruitment increasing and interpreted this as a result of the changing age structure, i.e. An effect of fishing.
Running Correlation Coefficient
Fishing increases sensitive to climate variability
Future Projections
2,5
3,0
3,5
4,0
4,5
5,0
5,5
6,0
1900 1920 1940 1960 1980 2000 2020 2040 2060 2080
Temperatur
År ?
Atlantic water temperature in the Barents Sea during the 20th century (PINRO and IMR)
and Barents Sea temperature projections (Furevik et al. 2003) towards 2080
Sundby (2008)
Tem
per
atu
re
Year
Summary•Multiple Scales of Variability•Natural variability likely to continue to dominate over climate change in near future •Circulation changes are and will be important under climate change•Variability is reflected in the biology from biogeochemical cycling and through the food web to upper trophic levels•Changes affect productivity, distribution, phenology, etc.•Fishing affects ecosystem and often cannot separate from climate effects (i.e. non-linear interactions)
Thank you!