1. Review of ocean temperature, salinity and oxygen changes in the Pacific and subtropical southern hemisphere Red = In IPCC AR4 Green = after IPCC AR4 Climate Change Copenhagen 2009 Session 3: Changes in Ocean Circulation Related to Regional Climate Lynne D. Talley Scripps Institution of Oceanography, UCSD, La Jolla, CA, USA

2. IPCC AR4Towards IPCC AR5 Ocean Observations: schematics of climate change Sea level, heating, P-E, ice sheets, sea ice, ocean T, salinity, CaCO3, pH Zonally-averaged Focus on meridional redistributions Focus on Atlantic view Almost no circulation changes incorporated Sea level, heating, P-E, ice sheets, sea ice, ocean T, salinity, CaCO3, pH Zonally-averaged Focus on meridional redistributions Focus on Atlantic view Almost no circulation changes incorporated Global view Including zonal redistributions Ocean circulation changes Ocean oxygen changes Changes in natural climate modes Global view Including zonal redistributions Ocean circulation changes Ocean oxygen changes Changes in natural climate modes ? Thermal expansion 1995-2003 (Ishii et al., 2006, IPCC AR4)

3. Salinity

4. Salinity balances and changes: example of importance of zonal redistribution pathways in addition to meridional Saltier Atlantic and Indian Fresher Pacific 1. Freshwater convergences required to maintain mean salinity distribution 1500 m surface 2. Meridional FW transports from evaporative tropics/subtropics to high latitudes 3. Zonal FW transports from Atlantic/Indian to Pacific (Talley, PiO 2008)

5. Climate change and precipitation/evaporation: IPCC AR4 A warmer world pumps more water vapor into the atmosphere (with the ocean an enormous holding tank for the water): increased hydrological cycle Impacts of change are recorded in ocean salinity Potential for (indirect) feedbacks on climate through changed ocean stratification Predicted precipitation change Dry areas become drier Wet areas become wetter

6. Salinity trends and relation to changes in freshwater forcing Salty oceans becoming saltier Fresher oceans becoming fresher Atlantic saltier Pacific fresher Indian saltier Global: neutral Boyer et al. (2005) Linear trend 1955-1998, zonally-averaged salinity

7. Salinity variation: new data set to observe global pattern Example of what will be possible with many years of Argo. Just one year, but the pattern much cleaner than historical trend because sampling is so much better. Saltier N. AtlanticFresher N. Pacific Hosoda et al., 2008 Surface salinity 2005 (Argo) minus WOA01 climatology

8. Salinity variations: northern North Atlantic salinification Hughes et al., 2008 (ICES Report 291) Surface salinity increasing since about 1996, following fresh period commencing with the Great Salinity Anomaly in the 1970s. Surface temperatures also increasing, so salinity change is somewhat compensating in density. Water mass salinities are a different matter – see other talks in session. 2007 salinity anomalies 19502000 2007 temp. anomalies

9. IPCC AR4Towards IPCC AR5 Salinity changes from quasi-synoptic data: trends or variability? Freshening of AAIW, LSW, NADW,NPIW Salinification of subtropics Atlantic (Curry et al., 2003) Pacific (after Wong et al., 2001) Pacific (2006 minus 1991) Atlantic (2003 minus 1989) 1990s minus 1950s-1960s2000s minus 1990s Freshening of SAMW Saltier northern N. Atlantic Mixed results in subtropics Indian (2007 minus 1995)

10. Salinity changes in the last decade? Southern hemisphere subtropical gyre pycnoclines 1500 Talley et al. (in prep) Atlantic 2003 minus 1992 Indian: 2002 minus 1987Pacific: 2003 minus 1991 Fresher South Pacific, saltier Indian and eastern Atlantic Salinity changes are within the subducted thermocline, SAMW, shallower than the AAIW Consistent with stronger ST gyre circulation

11. Salinity trends and relation to changes in freshwater forcing: global patterns (zonally averaged) Bindoff et al. (2009) Salinity trend 1970-2005 Top: shallow salinity maximum Bottom: NPIW-SAMW-AAIW Bottom: zonally-averaged salinity change Middle: implied change in P-E Top: IPCC model results Shallower (lower latitude outcropping) isopycnals are saltier Slightly deeper (higher lat. outcropping) isopycnals are fresher Consistent with higher precipitation at higher latitudes, higher evaporation in the subtropics

12. Oxygen

13. Oxygen changes/variability: N. Pacific subpolar and subtropical decline Similar result for 30°N thermocline - oxygen decrease: Mecking et al. (2006, 2008) N. Pacific oxygen decreases at base of pycnocline Reduced ventilation at these densities (warmer or slower) Deutsch et al., 2005

14. Oxygen changes/variability: N. Atlantic subpolar and subtropical decline Johnson and Gruber, 2005 Data from I. Yashayaev Labrador Sea (1999 minus 1990) Eastern central (2003 minus 1988) SPMW layer (27.1-27.6) (O 2 decrease) Oxygen decline pronounced at base of pycnocline (mode water) NADW layer (28.0) (O 2 increase) LSW/NADW layer (27.9) (O 2 decrease) Decline in LSW Increase in shallower part of NADW

15. Oxygen decline in the tropical O 2 minima: a global pattern Stramma et al (2008) Oxygen minimum zones expanding, oxygen content decreasing Consistent with climate change response (Bopp et al., 2002). Time series 1960-present Oxygen in the oxygen minima

16. Southern hemisphere subtropical gyre (30°S) oxygen increase in thermocline Indian Ocean ST gyre O2 increase. Consistent with gyre spinup of 10-20%. McDonagh et al. (2005) Pacific ST O2 increase, also consistent with gyre spinup (Talley, in prep) Atlantic ST O2 increase, also consistent with gyre spinup (Talley, in prep)

17. Global oxygen changes: overall decline Bindoff et al. (2009) Decline in oxygen throughout the upper ocean, stronger at higher latitudes (poleward of 40°). Net decrease in oxygen inventory, reduction in water mass formation Oxygen trend 1970-2005 Top: change on density surfaces Bottom: change due to heaving of density surfaces O2, pressure and pot. Temp. changes as a function of density

18. What are the implications of ocean O 2 decline? 400 ppm decline in atmospheric oxygen, not as much as expected given the observed CO 2 increase. Is the ocean a part of the decreasin budget? 19902007 O 2 /N 2 ratio (per meg) Atmospheric oxygen decline (R. Keeling and group) Calculating anthropogenic carbon contributions to DIC increase (Sabine et al., 2008) : O 2 decline helps quantify ocean ventilation change, so that natural changes in ocean carbon budget can be removed from observed DIC change due to circulation change Anthropogenic DIC change Pacific 150W (central meridian)

19. Circulation

20. Southern ocean circulation: intensification and shift of ACC Circumpolar warming at mid-depth Consistent with slight southward shift of ACC system Consistent with southward shift and strengthening of westerlies, which would also strengthen the SH subtropical gyres Gille (2002) Cai (2006) Temperature trend at 900 m from 1930s to 2000

21. Southern ocean circulation: intensification of Indian ST gyre Indian Ocean subtropical oxygen increase Helium/tritium and oxygen OUR used to date water. Conclusion: 15-20% increased circulation, hence increased subduction advecting near-surface waters northward faster Presumed due to increased wind forcing McDonagh et al. (2005)

22. Southern ocean circulation: intensification of S. Pacific ST gyre Increase in Southern Annular Mode Strengthening of SH westerlies in the 1990s 20% intensification of S. Pacific ST gyre, based on SSH, subsurface floats Change in SLP and Ekman pumping Southern Annular Mode 5-year running mean (CPC) Dyn.ht. changes Argo-WOCE 1000/1800 200/1800 Change in SST II Roemmich et al. (2007)

23. Large-scale decadal climate patterns that strongly affect the Pacific and S.O. What is the projection of climate change on these and other natural modes? El Nino Southern Oscillation (Southern Oscillation Index) Pacific Decadal Oscillation (could also show the PNA) Southern Annular Mode

24. Moving towards the IPCC AR5 Equal attention should be given to global-reaching changes originating in the Antarctic/Southern Ocean (e.g. deep heat content increases – Johnson et al., Kawano et al.) Analysis in terms of global redistributions, not just meridional changes Apparent trends based on decadal differences must be treated with caution; changes in integrating properties such as salinity, temperature, oxygen can be better interpreted in terms of trends than can synoptic changes in circulation Can ocean heat, chemistry and circulation changes be partially understood in terms of the natural modes of variability?

25. IPCC AR4Towards IPCC AR5 Ocean Observations: schematics of climate change Global view Ocean circulation changes Ocean oxygen changes Changes in natural climate modes Global view Ocean circulation changes Ocean oxygen changes Changes in natural climate modes ?