Interannual Changes in Arctic Ice-edge Blooms Graham Quartly 1 & Mahé Perrette 2 1 – National Oceanography Centre (NOC), UK 2 – Potsdam Institute for Climate Impact Research (PIK), Germany
Arctic Ocean: Region of change [from Wassmann et al. (2011) C oncern about effect of reduced ice coverage ?? Impact on vitality of ecosystem ?? Effect on fish stock ?? Importance for CO 2 drawdown
Arctic: A mix of different ecosystems Three distinct marine environments: Open water year round Permanent ice cover Seasonal ice cover Seasonal ice cover in 2007 Chukchi Sea Baffin Bay Barents Sea
Outline of talk Development of ice-edge blooms Productivity models Interannual variations
Schematic of bloom development [From Sakshaug and Skjoldal (1989) ] Algae underneath the ice Ice conc. too high Ice-edge bloom Bloom fini-shed Stratification may develop, and then open-water bloom
Example from Baffin Bay Ice data from NSIDC or OSISAF (uses SSM/I) Chl data from NASA Goddard (SeaWiFS)
Bloom characteristics 50% Time (year day) Longitude (65°W – 54°W) 10% 20 days Westward 3 km / day 60 km 300 km 3 months mg m -3 Hovmöller diagram : transect perpendicular to the ice edge
Marginal Ice Zone MIZ period = any time up to 20 days after ice < 10%
Primary Productivity PP = f ( Chl, SST, day length, PAR ) [from Perrette et al. (2011)} ] VGPM Carr Marra et al.
Ice vs. Spring Intensity, longevity, total contribution
Ratio VGPM Carr Marra et al
Bloom occurrence & timing (2007) March May July > 20 < 0 0 - 20 < 15 > 30
Most observations in June – August
90% of adequately observed pixels experience chl > 0.5 mg.m -3 , and 70% > 1 mg.m -3
Blooms take place later as the season advances (and as the MIZ moves futher North)
overall 50 % of blooms > 0.5 mg.m -3 are over within 30 days
Apr. June Aug. Peak Termination Observations
Interannual variability I Year day chlorophyll (mg.m -3 ) First ice-free day Bloom peak Baffin Bay: Late melt => Weak peak (also 2004, 2008) 2005 2006 2007 Mar. April May June July Aug.
Interannual Variability II Early melt mismatch ? Year day chlorophyll (mg.m -3 ) Sep. First ice-free day Bloom peak Barents Sea: Early melt => Weak peak 1998 2001 2006 Mar. April May June July Aug.
Changes in timing Histogram of first ice-free day Histogram of peak lag after ice-retreat Late blooms Early ice retreat MIZ period Open water Barents Sea Mar. May July Sep.
Large changes in melt date affects intensity of ice-edge bloom
Ecosystem may lose dual-bloom nature
Highly variable effects on other trophic levels
?? Effects on total productivity and CO 2 drawdown
Ice-edge bloom is an important ecological niche (bloom within 20 days of ice-melt occurs in ~90% of seasonal ice zone)
Growth and productivty dependent upon timing (likely different response for different regions)
Early ice-melt may affect other trophic levels
Perrette, M. et al. (2011), Near-ubiquity of ice-edge blooms in the Arctic, Biogeosciences , 8, 515–524.
Changes in ice melt
Data consistency SSM/I Combining SeaWiFS, MERIS, MODIS, need to allow for: chlorophyll calibration data flagging swath width sampling time 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 Pixel SEAWIFS 9 km MERGED 9 km MODIS 9 km NSIDC 25 km OSISAF 10 km