Climate Impacts on the Southern Ocean Ecosystem(s)

1. Climate Impacts on the Southern Ocean Ecosystem(s) Eileen Hofmann, John Klinck, Mike Dinniman Walker O. Smith Eugene Murphy, Nadine Johnston, Rachel Cavanaugh (BAS) SO GLOBEC Investigators

2. Presentation Outline • Background on Southern Ocean GLOBEC program • Southern Ocean food webs • Consider potential climate change effects on mesopelagic-shelf coupling • Summarize possible effects of climate change on physical habitat and consequences for biological production and food webs

3. UK Germany Korea Australia US, Germany SO GLOBEC Field Study Sites

5. Target Species

6. Southern Ocean Food Webs Circumpolar System Not similar food web throughout Considerable heterogeneity in forcing and habitat structure Regional differences in responses

7. Southern Ocean is Undergoing Major Environmental Changes Parkinson (2002) 30% decline in Antarctic krill in South Atlantic in last 30 years Upper ocean temperatures have increased by 1ºC in the last 50 years -WAP most rapidly warming region on planet

8. What happened in the past? Harvesting has generated massive perturbations over more than 2 centuries Fur-seals From 1778; economic extinction within 35 years Whales 1906 to 1966, residual thereafter Fin-fish, krill From late 1960s, continuing Top-down effects => Krill surplus?

9. Challenges for Southern Ocean • Climate Impacts • Harvesting effects • Biogeochemistry • Food Webs Can we develop experimental and modeling programs to address these effects and interactions at a circumpolar scale?

10. What is a Southern Ocean Food Web?

11. Is This the Only Food Web? Classical Food Web Western Antarctic Peninsula Ross Sea

12. Why the Differences? Seasonal length Sub Antarctic Differences due to Circulation Sea-ice Biogeochemistry Production Seasonality High Antarctic Low Production High Production

13. Mesopelagic Environment • Region between about 200 m and 700 m • For much of the Antarctic this is the depth of the continental shelf • Shelf region is flooded with oceanic water, Circumpolar Deep Water (CDW), between 200-700 m - various forms of CDW • Provides a direct connection between epipelagic and mesopelagic regions • Focus on western Antarctic Peninsula

14. WAP Circulation Shelf depth ~400 m ACC flows along shelf edge Deep trenches that provide connections between shelf and oceanic environments

15. Fall 2001 Warm and salty water mass Extends across shelf at specific sites Floods shelf below 200 m (Klinck et al., 2004) Southern Ocean Sentinel Workshop Hobart, Tasmania, 20-24 April 2009

17. CDW Effects Inputs of heat and salt Surface water above freezing in winter Salt excess Klinck et al. (2004)

18. Phytoplankton assemblage dominated by diatoms CDW - regions of high primary production Prezelin et al. (2002)

19. Biological Hot Spots (Costa et al., 2007) Not all parts of the shelf are biologically similar

20. Climate Change Effects on CDW • Effects of increased and decreased wind strength and increased transport of Antarctic Circumpolar Current on CDW intrusions onto the WAP shelf • Modified wind scenarios represent regional effects - positive Southern Annular Mode gives stronger westerlies • Change in ACC transport represents large-scale circulation effects - global thermohaline circulation

21. Circulation Model Characteristics ROMS: 4 km horizontal resolution, 24 levels Ice shelves (mechanical and thermodynamic) Dynamic sea ice Bathymetry: ETOPO2v2 + WHOI SOGLOBEC region + Padman grid+ BEDMAP + Maslanyj Open boundaries: T + S set to SODA, barotropic V relaxed to SODA, baroclinic V pure radiation Daily wind forcing from a blend of QSCAT data and NCEP reanalyses Other atmospheric parameters from several sources, including Antarctic Mesoscale Prediction system (AMPS)

22. Simulation Configuration Track dye concentration as proxy for CDW Dye concentration off the shelf set to 100 below 200 m and at temperatures > 0ºC Allow 4-year spin up of circulation model Simulations begin in January and run for 2 years that correspond to 2000-2002 Set up a reference case using current conditions to provide comparisons

23. Model Domain Includes ice shelves

24. Focus on Marguerite Bay and Crystal Sound regions of WAP

25. Dye distribution for current conditions - February Level of CDW (210-420 m)

26. 50% increase in wind speed 20% decrease in wind speed

27. 20% increase in wind speed 20% increase in wind speed and increase in ACC transport

28. Vertical dye distribution Current conditions 50% increase in wind speed

29. Vertical temperature distribution Current conditions 50% increase in wind speed

30. Summer sea ice distribution 50% increase in wind speed Current conditions

31. Winter sea ice distribution 50% increase in wind speed Current conditions Summer sea ice

32. Dye concentration for Crystal Sound Inner portion of WAP shelf Stronger winds and ACC provide more CDW to region Is this beneficial? Will region persist as a biological hot spot?

33. Summary • Strong coupling between mesopelaic and epipelagic environments • Intrusions of CDW are controlling habitat structure and biological production • Modified by winds and circulation changes • Biological hot spots are coincident with intrusions of CDW • What are the consequences of changes in CDW intrusions? • Is this specific to WAP region?

34. Biological continuum that is driven by subsurface intrusions of CDW Prezelin et al. (2004) Shift to a diatom-dominated system?

35. Alternative Food Web Pathways High krill Low krill Alternative pathways buffer change - reflect/support long-term change? Need better quantification of alternative pathways

36. Krill Penguins Salps Zooplankton Krill 20% Killer Whales 60% 20% Benthos Zooplankton Salps P Zooplankton Salps Salps Benthos Detritus Penguins Killer Whales Zooplankton Krill Ballerini et al. (in prep) Change in production Salps Zooplankton Krill 60% 20% 20% P Salps Zooplankton Krill 20% 20% 60% P

37. Change in production Fish Cephalopods 14% 3% Z K 83% P Cephalopods Fish 80% 20% Z K Ballerini et al. (in prep) 0% P

38. Large-scale distribution of ACC fronts

39. Potential Consequences • Reduction in winter sea ice- current food web components disappear? • Time history of seasonal heating/cooling of surface layers changed - implications for air-sea exchanges and sea ice formation? • Timing of productivity changed - same annual production but different time distribution?

40. Potential Consequences Larger areas of shelf influenced by warm CDW - change in habitat structure and food web linkages? Open/close more habitat - more regions where Antarctic krill can reproduce, reduced regions for Adélie penguins? More emphasis on benthic system - warmer bottom temperatures Mixing processes of CDW still a matter of research and debate - basic physical understanding still needs to be developed

41. Relevance to Global Ecosystems Global carbon budget models lack biological detail Current models do not capture what is known about SO ecosystems

42. Joint program under IMBER and GLOBEC - 10 year effort • Circumpolar, interdisciplinary program focused on climate interactions and feedbacks to ecosystem function and biogeochemical cycles • Extend and further develop circulation, ecosystem, and biogeochemical models • Focus on end-to-end food web models • Combine food web and biogeochemical communities

43. Thank you! Photos by D. Costa