Global Warming Trend

1. 1 Climate Change Projections of the Tasman Sea from an Ocean Eddy-resolving Model – the importance of eddies Richard Matear, Matt Chamberlain, Chaojiao Sun, Ming Feng CSIRO Marine and Atmospheric Research Sun et al 2012, Chamberlain et al 2012, Matear et al., 2013 in press JGR

2. Global Warming Trend • Maximum warming in the Western Boundary Current regions due shifts and intensification of the WBC Wu et al., NCC 2012.

3. Outline 3 • Why use Ocean Eddy-resolving Model? • To resolve important processes like Boundary Currents and Eddies 2. How do we project climate change with an Ocean Eddy-resolving model • Use climate anomalies from a global climate model projection to drive high-resolution model. 3. Consequence of resolving boundary currents and eddies • Sea surface temperature • Phytoplankton

4. Oceans around Australia – climate and high-resolution models 4 • Climate model captures large-scale ocean circulation, but misses the boundary currents (e.g. Leeuwin and East Australia Currents) and eddies Sun et al. 2012.

5. Method of projecting Climate Change in the Ocean Eddy-Resolving Model 5 Chamberlain et al. 2012 Models used: • Global Climate Model (GCM) – CSIRO Mk3.5 • 1°x 2° horizontal resolution ocean model • Used output from the SRES A1b, “integrated world, balanced energy sources” emission scenario, IPCC’s AR4 • calculated climate change anomalies from the GCM and used them to force the ocean eddy resolving model (minimise the effect of model bias in eddy-resolution projection). – Anomalies include change in Ocean State (T,S, N, Phytoplankton, Zooplankton) and changes in forcing (Heat, Freshwater and winds) • Simulations presented for the decade of 2060s • Ocean Eddy-resolving Model (OEM) – BlueLINK’s Ocean Forecasting Australia Model (OFAM1.0). • Global domain with 10-km resolution around Australia. • Present-day state simulated with observed forcings • Future state adds anomalies to present day

6. Change in Boundary Currents – e.g. EAC 6 GCM OEM Multi-year averages • GCM missing fine structure shown in the OEM. • GCM has increased in the EAC extension flow along the coast of Australia • OEM the increased flow in the EAC extension is due to eddies Sun et al. 2012.

7. Change in upper ocean Temperature: OEM – observation comparison 7 • Model Observed multiyear averages Matear et al. 2013, JGR

8. Change in upper ocean Temperature: 2060s – 1990s 8 • OEM GCM multiyear averages Matear et al. 2013, JGR

9. Observed SST trends (°C / century 9 Observed warming in Tasman in last 30 years closely resembles the projected warming Correlation with projected change GCM – 0.65 OEM – 0.74 Matear et al., 2013 JGR

10. Mixed Layer Depth Maximum (m): model verus observations 10 • OEM Observed multiyear averages Matear et al. 2013, JGR

11. Change in Mixed Layer Depth (m): Maximum and January 11 • Seasonal Maximum Jan. Matear et al. 2013, JGR

12. Change in Mixed Layer Depth (m): 2060s – 1990s from OEM 12 • STZ 40S 145-170E SAZ 50S 145-170E Matear et al. 2013, JGR

13. Eddy Kinetic Energy: 1990s and change 13 • OEM Observed Matear et al. 2013, JGR

14. Change in Annual Mean Phytoplankton (mmol N/m3) 14 • OEM GCM PP increases by 10% in the Tasman Sea (30-50S and 145 – 170E Matear et al. 2013, JGR

15. Change in Phytoplankton (mmol N/m3) 15 • STZ 40S 145-170E SAZ 50S 145-170E Matear et al. 2013, JGR

16. Conclusions 16 Ocean Eddy-resolving Model alters the climate projection from the coarse resolution GCM by • Changing the upper ocean warming (less warming along Tasmania) • Changing the East Australian Current (EAC) response – increased EAC and increased EAC extension (more eddies) • Increasing the phytoplankton concentrations north of the Sub-Tropical Front due to increased nutrient supply from eddy-pumping. • Primary Production in the oligotrophic Tasman Sea increases by 10% with climate change rather than declining as projected by the GCM

17. Thank you

18. Phytoplankton– model vs observed chlorophyll • OEM Observed

19. Phytoplankton– model vs observed chlorophyll • OEM Observed

20. Change in Pacific phytoplankton concentrations 2060s Model BGC shows region of subsurface phytoplankton in western Pacific. Shoaling of thermocline with climate change makes relative subsurface response greater than surface. 2060s-1990s mmol(NO3)/m3 mmol(NO3)/m2 10 ICSHMO. Climate Change Science to Adaption

21. Oceans around Australia - schematic Website imos.org.au 10 ICSHMO. Climate Change Science to Adaption

22. Method of projecting Climate Change in the Ocean Eddy-Resolving Model 22 • Use change in ocean state (2060s – 1990s) of temperature, salinity and biogeochemistry to define OEM projection initial condition. • Use change in surface fluxes (heat, freshwater, wind stress) to modify OEM fluxes. GCM Mk3.5 • Spinup experiment • Use ‘observed’ fluxes. • Diagnose correction fluxes by restoring to observed surface temperature + salinity. • Projection (2060s) • Modified initial condition. • Observed fluxes + correction + climate anomalies (+ feedback) OEM OFAM Chamberlain et al. 2012 10 ICSHMO. Climate Change Science to Adaption

23. EAC current GCM OEM Multi-year averages • GCM missing fine structure shown in the OEM. Sun et al. 2012. 10 ICSHMO. Climate Change Science to Adaption

24. Change in Boundary Currents – southward transport of EAC • Both GCM (dashed) and OEM (solid) show increase in EAC transport, but differ in the details. • GCM – increased EAC only south of 32S – increase in the southward extension of the EAC • OEM - increased EAC north of 32°S with most of the increased flowing east between 32 - 34° S. Increased EAC extension flow south of 36S Black – 1990s Red – 2060s Sun et al. 2012. 10 ICSHMO. Climate Change Science to Adaption