AGU 12/10/2004 1/13 Observed 80-Years of Climate Change in Baffin Bay: Facts, Fiction, and the NAO Melissa Zweng and Andreas Münchow College of Marine.

AGU 12/10/2004

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Observed 80-Years ofClimate Change in Baffin Bay:

Facts, Fiction, and the NAOMelissa Zweng and Andreas Münchow

College of Marine StudiesUniversity of Delaware

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Baffin BayNares Strait

LabradorSea

Temperature

Latitude

Salinity

Surface Properties along 25-day USCGC Healy Ship Track

in 2003

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Salinity maximum (below 100-m):

Temperature on salinity maximum:

West Greenland “Current”

•Uniform 34.48 over slope and basin•Fresher towards north and on shelves

•Warm over Greenland slope•Largest gradients in Davis Strait•Cooling towards the north

BIO data 1916-1999

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Temporal Analysis method

• Separate data into 200-m vertical depth bins

• Average– each profile into 200-m vertical bins (weights CTD and bottle profiles

more evenly)– all profiles for each year for each vertical bin (minimizes bias by years

with many profiles over years with few profiles)

• Linear regression analysis on each bin – Use Fofonoff (1979) method to estimate error– All error bars shown are 95% confidence intervals– Degrees of freedom = number of years of data - 2

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Labrador Sea salinity100-m

500-m

900-m

1500-m

2100-m

1920 1960 2000

significant

not significant95% confidence

Trends are

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Northern Labrador Sea (62N-66N):

Significant fresheningabove 1500-m

Dep

th (

km)

Dep

th (

km)

Lazier (1995),

Dickson et al. (2002),

Curry et al. (2003),

Lozier (yesterday)

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Baffin Bay temperature

100-m

500-m

900-m

1500-m

2100-m

1920 1960 2000

significant

not significant95% confidence

Trends are

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Dep

th (

km)

Dep

th (

km)

Baffin Bay (67N-80N):

Significant warmingbelow 700-m

Significant fresheningabove 300-m

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95% confidencethat r0 forr95<r

Relation of warming to NAO

• Deep Baffin Bay basin, 1928-1999

• 200-m vertical bin average

• 1-year temporal bin average

• Correlation with NAO (1-year lead)

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Winter Time North-Atlantic Oscillation Index(NAO, explains <30% of variance)

Lanczos low-passfiltered NAO in red

Year

Non

-dim

ensi

onal

num

ber

1965-2000 (blue) periodmay not tell the whole story

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NAO > +0.5 NAO < -0.5

Dep

th (

m)

density

salinity

temperature

67-76N

Baffin Greenland Baffin Greenland

Properties averaged along isobaths east and west of the “talweg”

2.5 1.5 0.5isobath (km)

2.5 1.5 0.5isobath (km)

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2.5 1.5 0.5

isobath (km)

-0.5 -1.5GreenlandBaffin

lighter off Baffin, heavier off Greenlandduring NAO+ relative to NAO-

Properties averaged along isobaths for NAO+ (red) and NAO- (blue)(“meridional” averaging as isobath trend north-south)

fresher off Baffin, saltier off Greenlandduring NAO+ relative to NAO-

similar off Baffin, warmer off Greenlandduring NAO+ relative to NAO-

Density:

Salinity:

Temperature:

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Conclusions:

•Significant warming in Baffin Bay below Davis Strait sill depth;

•Temperature fluctuations correlate with NAO in [600-1200] m depth range where warming occurs;

•West Greenland Current most likely source of warming

•Baroclinic surface circulation more intense during NAO+