NW Atlantic Ocean Climate Change Workshop Bedford Institute, Dartmouth, Canada February 16, 2010. Physical and related biological variability in the large-scale North Atlantic, with implications for the NW Atlantic. Ken Drinkwater
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NW Atlantic Ocean Climate Change Workshop Bedford Institute, Dartmouth, Canada February 16, 2010 Physical and related biological variability in the large-scale North Atlantic, with implications for the NW Atlantic Ken Drinkwater Institute of Marine Research and Bjerknes Center for Climate Research, Bergen, Norway
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)
NAO Hurrell 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) -based on SSTs in North Atlantic -thought to be linked to the strength of the MOC Sutton & Hodson, 2005
Early-1900s Warming Johannessen et al. 2004. Tellus 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 Effects of Warm Currents on West Greenland during recent warming. Melting of Glaciers in Greenland fjords Holland et al., 2008
Also affects of Arctic outflow. Recent lower salinities along east coast of Canada thought to be due to increased Arctic outflow Greene & Pershing 2005
Great Salinity Anomalies Dickson et al. 1988; Schmidt, 1996
The decadal climate signal is mainly linked to the interaction between atmospheric and oceanic circulation Increased inflow of Atlantic Water Hatun, 2008 Increased outflow of cold Arctic water Sundby and Drinkwater (2007)
Transport Effects on Scotian Shelf Transport of Labrador Water influences Scotian Shelf Cold on the Scotian Shelf, High NAO Warm on the Scotian Shelf, Low NAO
Biological Variability • NAO
Changes in Growth Rates Growth 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).
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
West Greenland Iceland Connection In the 1920s these conditions were right for the drift of larvae from Iceland to West Greenland and there was good survival once there. Under certain conditions cod larvae drift from Iceland to West Greenland This continued through to the 1960s with increased abundances and the development of a cod fishery that dominated the Greenland economy.
Atlantic cod moved northward by 1500 km in response to warming. Hansen 1940
Norwegian Sea Atlantic Herring The population of Norwegian spring spawning herring rose dramatically in parallel with the temperatures as recorded in the Kola Section. Vilhjalmsson, 1997 Toresen and Østvedt, 2000
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. 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
Climate Responses of the Barents Cod Spawning In warm periods: - northward displacement- increase in spawning-stock biomass In cold periods: - southward displacement - decrease in spawning-stock biomass Temperature Year Sundby and Nakken (2008)
Benthos 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. Benthic Species Arctic Atlantic Blacker, 1957
Biological Variability • Recent Changes
Phytoplankton in Arctic and boreal marine ecosystems Temperature influence primary production at high latitudes Gulf of Maine / 500 Georges Bank (P < 0.001) Gulf of Alaska 400 (n.s.) Bering Sea (P = 0.039) Primary production (gC m-2) 300 200 Norwegian Sea (n.s.) Barents Sea (P = 0.093) 2 4 6 8 10 Mueteret al. (2009) Norway-USComparisons (MENU) Annual mean temperatures (°C)
Shifts in Zooplankton Distribution There is a limit to northward movement however due to light limitations. Subtropic Species Beaugrand et al. 2003. Science 296, 1692-1694 Warm temperate slope species Subarctic Species
Changes in Phenology SST (deg C) Phenology C. helgolandicus (month) 1980s 1990s Beaugrand, 2009 2000s
Changes in Mean Size of Calanoids North Sea Beaugrand, 2009
Shifts in FishDistribution General Northward Movement in Response to Warming
Changes in FishAbundance 1 Atlantic Herring Herring SSB (106 tons) Temperature (°C) Herring Kola Temperatures Toresen and Østvedt, 2000
InvasiveSpecies 2003 2004 Snake Pipefish 2005 2006
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.
Fishing increases sensitive to climate variability 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
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 ? Temperature Year Sundby (2008)
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)