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

Observed 80-Years of Climate Change in Baffin Bay: Facts, Fiction, and the NAO. Melissa Zweng and Andreas Münchow College of Marine Studies University of Delaware. Surface Properties along 25-day USCGC Healy Ship Track. in 2003. Temperature. Latitude. Salinity. Nares Strait. Baffin Bay.

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

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  1. Observed 80-Years ofClimate Change in Baffin Bay: Facts, Fiction, and the NAO Melissa Zweng and Andreas Münchow College of Marine Studies University of Delaware

  2. Surface Properties along 25-day USCGC Healy Ship Track in 2003 Temperature Latitude Salinity Nares Strait Baffin Bay Labrador Sea

  3. Salinity maximum (below 100-m): • Uniform 34.48 over slope and basin • Fresher towards north and on shelves Temperature on salinity maximum: • Warm over Greenland slope • Largest gradients in Davis Strait • Cooling towards the north West Greenland “Current” BIO data 1916-1999

  4. 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

  5. 100-m 500-m Trends are significant not significant 95% confidence 900-m 1500-m 2100-m Labrador Sea salinity 1920 1960 2000

  6. Northern Labrador Sea (62N-66N): Depth (km) Significant freshening above 1500-m Depth (km) • Lazier (1995), • Dickson et al. (2002), • Curry et al. (2003), • Lozier (yesterday)

  7. 100-m 500-m Trends are significant not significant 95% confidence 900-m 1500-m 2100-m Baffin Bay temperature 1920 1960 2000

  8. Baffin Bay (67N-80N): Depth (km) Significant warming below 700-m Depth (km) Significant freshening above 300-m

  9. 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) 95% confidence that r0 for r95<r

  10. Winter Time North-Atlantic Oscillation Index (NAO, explains <30% of variance) 1965-2000 (blue) period may not tell the whole story Non-dimensional number Lanczos low-pass filtered NAO in red Year

  11. 2.5 2.5 1.5 1.5 0.5 0.5 isobath (km) isobath (km) Properties averaged along isobaths east and west of the “talweg” NAO > +0.5 NAO < -0.5 67-76N density salinity Depth (m) temperature Baffin Greenland Baffin Greenland

  12. -0.5 -1.5 2.5 1.5 0.5 Baffin Greenland isobath (km) Properties averaged along isobaths for NAO+ (red) and NAO- (blue) (“meridional” averaging as isobath trend north-south) Density: lighter off Baffin, heavier off Greenland during NAO+ relative to NAO- Salinity: fresher off Baffin, saltier off Greenland during NAO+ relative to NAO- Temperature: similar off Baffin, warmer off Greenland during NAO+ relative to NAO-

  13. Conclusions: • Temperature fluctuations correlate with NAO in [600-1200] m depth range where warming occurs; Significant warming in Baffin Bay below Davis Strait sill depth; • West Greenland Current most likely source of warming • Baroclinic surface circulation more intense during NAO+

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