1. Melting glaciers help fuel productivity hotspots around Antarctica
Kevin R. Arrigo
Gert van Dijken
Stanford University 1

2. Antarctic polynyas Areas of open water surrounded by sea ice
Can be identified with SSM/I satellite data
Based on days of open water
Red = Max
Blue = Min
Polynyas are blue areas near coast 2

3. Antarctic polynyas Hot spots of primary production (g C m-2 yr-1) 4080
120
160
200
Hot spots of primary production (g C m-2 yr-1) 3

4. Antarctic polynyas Hot spots of primary production (g C m-2 yr-1)
Ann
Adelie Penguins vs. Polynya Productivity
Hot spots of primary production (g C m-2 yr-1)
Can support high densities of marine mammals and birds
Mean colony size (1000 pairs)
R2 = 0.63
Annual production (mg C m-2 yr-1)
Arrigo and Van Dijken (2003) 4

5. Anthropogenic CO2 flux (g C m-2 yr-1)
Antarctic polynyas
Anthropogenic CO2 flux (g C m-2 yr-1)
Hot spots of primary production (g C m-2 yr-1)
Can support high densities of marine mammals and birds
Large sinks for anthropogenic CO2
Ross Sea
Arrigo et al. (2008) 5

6. Question:
What controls phytoplankton abundance in Antarctic coastal polynyas?
Phaeocystis antarctica
Photo:
John Weller 6

7. Approach
SeaWiFS
For :
Used satellite data to identify polynyas, track changes in sea ice, measure chlorophyll a concentration, and calculate primary production (Arrigo et al. 2008)
SSM/I
AVHRR 7

8. Atlantic
Ocean
ANTARCTICA
Indian
Ocean
Pacific
Ocean 8

9. Annual mean phytoplankton abundance in 46 coastal polynyas
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
Polynya number 9

10. Annual mean phytoplankton abundance in 46 coastal polynyas
Not controlled by light or temperature (p > 0.05)
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
Polynya number 10

11. Annual mean phytoplankton abundance in 46 coastal polynyas
Related to width of local continental shelf
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
Shelf width (km)
Polynya number 11

12. Annual mean phytoplankton abundance in 46 coastal polynyas
Related to width of local continental shelf
R2 = 0.40
p < 0.01
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
Shelf width (km)
Chlorophyll a (mg m-3)
Shelf width (km)
Polynya number 12

13. Highest seawater iron concentrations are on the shelf
Why the relationship between phytoplankton abundance and continental shelf width?
Highest seawater iron concentrations are on the shelf
Wider shelves have larger iron inventory and permit greater entrainment of iron into surface waters (Bruland et al. 2005, Biller et al. 2013)
More iron = higher phytoplankton biomass
Blue = Low iron concentration
Orange = High iron concentration
visibleearth.nasa.gov 13

14. What other factors control phytoplankton abundance in coastal polynyas?
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
Polynya number 14

15. 37 of 46 coastal polynyas are adjacent to melting ice shelves
What other factors control phytoplankton abundance in coastal polynyas?
37 of 46 coastal polynyas are adjacent to melting ice shelves
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
Polynya number 15

16. 37 of 46 coastal polynyas are adjacent to melting ice shelves
What other factors control phytoplankton abundance in coastal polynyas?
37 of 46 coastal polynyas are adjacent to melting ice shelves
Basal melt rates are now available (Rignot et al. 2013)
Pacific
Atlantic
Indian
Pacific
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
Polynya number 16

17. Basal melt rate (Gt yr-1)
What other factors control phytoplankton abundance in coastal polynyas?
R2 = 0.59
p < 0.01
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
Basal melt rate (Gt yr-1)
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
Polynya number 17

18. What about coastal polynyas not near ice shelves?
Pacific
Atlantic
Indian
Pacific
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
Polynyas w/o ice shelf = 0.44±0.19 mg m-3
Polynya number 18

19. Basal melt rate (Gt yr-1)
What about coastal polynyas not near ice shelves?
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
y-intercept = 0.40 mg m-3
Basal melt rate (Gt yr-1)
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
Polynyas w/o ice shelf = 0.44±0.19 mg m-3
Polynya number 19

20. Basal melt rate (Gt yr-1)
What about coastal polynyas not near ice shelves?
Very productive polynyas require input of glacial meltwater
Pacific
Atlantic
Indian
Pacific
Chlorophyll a (mg m-3)
y-intercept = 0.40 mg m-3
Basal melt rate (Gt yr-1)
Basal melt rate (Gt yr-1)
Chlorophyll a (mg m-3)
Polynyas w/o ice shelf = 0.44±0.19 mg m-3
Polynya number 20

21. Ice sheets grind up bedrock as they flow to sea
Why the relationship between phytoplankton abundance and basal melt rate of nearby ice shelves?
Ice sheets grind up bedrock as they flow to sea
Particulate and dissolved iron is released into seawater
Facilitated by upwelling of warm CDW
Iron taken up by growing phytoplankton
Phytoplankton
bloom
(CDW) 21

22. Ice sheets grind up bedrock as they flow to sea
Why the relationship between phytoplankton abundance and basal melt rate of nearby ice shelves?
Ice sheets grind up bedrock as they flow to sea
Particulate and dissolved iron is released into seawater
Facilitated by upwelling of warm CDW
Iron taken up by growing phytoplankton
DynaLiFe Cruise
Dissolved iron (nM)
Chlorophyll > 10 mg m-3
0.8
Chlorophyll > 5 mg m-3
100
0.6
Depth (m)
0.4
200
0.2
300
250
200
150
100 50
Distance from Pine Island Glacier (km)
Modified from Gerringa et al. (2012) 22

23. CONCLUSIONS Even coastal Antarctic polynyas are iron limited
Together, basal melt rate and continental shelf width explain 70% of variance in phytoplankton abundance in coastal polynyas
Basal melt rate and shelf width are weakly correlated with each other (R2=0.19)
Antarctic polynyas are a 0.2 Pg C yr-1 sink for anthropogenic CO2
Larger than entire high latitude Southern Ocean
No interannual trends over 15 year time series
However, if the rate of ice sheet melting accelerates, polynyas could become even more productive in the future 23

24. THANK YOU! Ocean Biology and Biogeochemistry
Cryosphere Science Program