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!