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 1

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

Outline 1.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 3

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

Method of projecting Climate Change in the Ocean Eddy-Resolving Model 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 Chamberlain et al

Change in Boundary Currents – e.g. EAC Sun et al 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 6

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

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

Observed SST trends (°C / century 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 9

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

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

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

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

Change in Annual Mean Phytoplankton (mmol N/m 3 ) Matear et al. 2013, JGR OEMGCM PP increases by 10% in the Tasman Sea (30- 50S and 145 – 170E 14

Change in Phytoplankton (mmol N/m 3 ) Matear et al. 2013, JGR 15 STZ 40S ESAZ 50S E

Conclusions 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 16

Thank you

Phytoplankton– model vs observed chlorophyll OEMObserved

Phytoplankton– model vs observed chlorophyll OEMObserved

Change in Pacific phytoplankton concentrations 10 ICSHMO. Climate Change Science to Adaption Model BGC shows region of subsurface phytoplankton in western Pacific. Shoaling of thermocline with climate change makes relative subsurface response greater than surface. mmol(NO3)/m 3 mmol(NO3)/m s 2060s-1990s

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

Method of projecting Climate Change in the Ocean Eddy-Resolving Model 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. 10 ICSHMO. Climate Change Science to Adaption GCM Mk3.5 GCM Mk3.5 OEM OFAM OEM OFAM 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) Chamberlain et al

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

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 ° S. Increased EAC extension flow south of 36S 10 ICSHMO. Climate Change Science to Adaption Sun et al Black – 1990s Red – 2060s