Observed 80-Years of Climate Change in Baffin Bay: Facts, Fiction, and the NAO
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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+