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 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 - CO 2 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) Sutton & Hodson, based on SSTs in North Atlantic -thought to be linked to the strength of the MOC

Johannessen et al Tellus Early-1900s Warming Sea Surface Temperature Change ( vs )

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

Dickson et al. 1988; Schmidt, 1996 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 Hatun, 2008

Cold on the Scotian Shelf, High NAO Warm on the Scotian Shelf, Low NAO Transport Effects on Scotian Shelf Transport of Labrador Water influences Scotian Shelf

Role of Climate on the Food Web

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

Under certain conditions cod 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 Connection 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

Atlantic Herring Norwegian Sea 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, (lighter solid line), the average weight in the longline fishery, (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 YearTemperature

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 Annual mean temperatures (°C)Primary production (gC 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 Warm temperate slope species Beaugrand et al Science 296, Subarctic Species Subtropic Species There is a limit to northward movement however due to light limitations.

Changes in Phenology SST (deg C)Phenology C. helgolandicus (month) 1980s 1990s 2000s Beaugrand, 2009

Changes in Mean Size of Calanoids North Sea

Tropical Fish Moving Northward along Continental Shelf Edge

General Northward Movement in Response to Warming Shifts in Fish Distribution

Herring Kola Temperatures Herring SSB (10 6 tons)Temperature (°C) Atlantic Herring Toresen and Østvedt, 2000 Changes in Fish Abundance 1

Invasive Species Snake Pipefish

Seabirds

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

? 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) Temperature 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!