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

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

3. 3 4012020016080 Hot spots of primary production (g C m -2 yr -1 ) Antarctic polynyas

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

5. Hot spots of primary production (g C m -2 yr -1 ) Can support high densities of marine mammals and birds Ann Annual production (mg C m -2 yr -1 ) Weddell seal pups weaned Seal Pups vs. Polynya Productivity R 2 = 0.63 5 Arrigo and Rotella (submitted) Antarctic polynyas

6. Hot spots of primary production (g C m -2 yr -1 ) Can support high densities of marine mammals and birds Large sinks for anthropogenic CO 2 Anthropogenic CO 2 flux (g C m -2 yr -1 ) 6 Arrigo et al. (2008) Ross Sea

7. Question: What controls phytoplankton abundance in Antarctic coastal polynyas? 7 Photo: John Weller Phaeocystis antarctica

8. Approach 8 SeaWiFS AVHRR SSM/I For 1998-2012: Used satellite data to identify polynyas, track changes in sea ice, measure chlorophyll a concentration, and calculate primary production (Arrigo et al. 2008)

9. Pacific Ocean Indian Ocean Atlantic Ocean ANTARCTICA 9

10. Polynya number Chlorophyll a (mg m -3 ) Pacific IndianAtlantic Annual mean phytoplankton abundance in 46 coastal polynyas 10

11. Polynya number Pacific IndianAtlantic Annual mean phytoplankton abundance in 46 coastal polynyas Not controlled by light or temperature (p > 0.05) 11 Chlorophyll a (mg m -3 )

12. Polynya number Pacific IndianAtlantic Shelf width (km) Annual mean phytoplankton abundance in 46 coastal polynyas Related to width of local continental shelf 12 Chlorophyll a (mg m -3 )

13. Polynya number Pacific IndianAtlantic Shelf width (km) Annual mean phytoplankton abundance in 46 coastal polynyas Related to width of local continental shelf R 2 = 0.40 p < 0.01 Chlorophyll a (mg m -3 ) Shelf width (km) 13 Chlorophyll a (mg m -3 )

14. Blue = Low iron concentration Orange = High iron concentration visibleearth.nasa.gov 14 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

15. Polynya number Pacific IndianAtlantic 15 What other factors control phytoplankton abundance in coastal polynyas? Chlorophyll a (mg m -3 )

16. Polynya number Pacific IndianAtlantic 16 What other factors control phytoplankton abundance in coastal polynyas? 39 of 46 coastal polynyas are adjacent to melting ice shelves Chlorophyll a (mg m -3 )

17. Polynya number Pacific IndianAtlantic Basal melt rate (Gt yr -1 ) What other factors control phytoplankton abundance in coastal polynyas? 39 of 46 coastal polynyas are adjacent to melting ice shelves Basal melt rates are now available (Rignot et al. 2013) 17 Chlorophyll a (mg m -3 )

18. Basal melt rate (Gt yr -1 ) Polynya number Pacific IndianAtlantic R 2 = 0.59 p < 0.01 What other factors control phytoplankton abundance in coastal polynyas? Chlorophyll a (mg m -3 ) Basal melt rate (Gt yr -1 ) 18 Chlorophyll a (mg m -3 )

19. Basal melt rate (Gt yr -1 ) Polynya number Pacific IndianAtlantic Polynyas w/o ice shelf = 0.40±0.13 mg m -3 What about coastal polynyas not near ice shelves? 19 Chlorophyll a (mg m -3 )

20. Basal melt rate (Gt yr -1 ) Polynya number Pacific IndianAtlantic y-intercept = 0.40 mg m -3 Chlorophyll a (mg m -3 ) Basal melt rate (Gt yr -1 ) What about coastal polynyas not near ice shelves? Polynyas w/o ice shelf = 0.40±0.13 mg m -3 20 Chlorophyll a (mg m -3 )

21. Basal melt rate (Gt yr -1 ) Polynya number Pacific IndianAtlantic y-intercept = 0.40 mg m -3 Chlorophyll a (mg m -3 ) Basal melt rate (Gt yr -1 ) What about coastal polynyas not near ice shelves? Very productive polynyas receive input of glacial meltwater Polynyas w/o ice shelf = 0.40±0.13 mg m -3 21 Chlorophyll a (mg m -3 )

22. (CDW) Phytoplankton bloom 22 Why the relationship between phytoplankton abundance and basal melt rate of nearby ice shelves? Particulate and dissolved iron is released into seawater From ground up bedrock and Fe accumulated in ice Facilitated by upwelling of warm CDW

23. Why the relationship between phytoplankton abundance and basal melt rate of nearby ice shelves? Particulate and dissolved iron is released into seawater From ground up bedrock and Fe accumulated in ice Facilitated by upwelling of warm CDW Iron taken up by growing phytoplankton 23 Modified from Gerringa et al. (2012) 0 100 200 300 Depth (m) Dissolved iron (nM) 0.8 0.6 0.4 0.2 0 200250150100500 Distance from Pine Island Glacier (km) Chlorophyll > 5 mg m -3 Chlorophyll > 10 mg m -3 DynaLiFe Cruise

24. 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 (R 2 =0.19) Antarctic polynyas are a 0.2 Pg C yr -1 sink for anthropogenic CO 2 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 24 CONCLUSIONS

25. 25 THANK YOU! Ocean Biology and Biogeochemistry Cryosphere Science Program