988 / 2024-09-19 23:58:31

Upper water column structure and heat content reconstructions in the Coral Sea over the last 1500 years

EAC,Thermocline depth,Mixed layer depth,ocean heat content,late Holocene

Session 8 - Modern and past processes of ocean-atmosphere-climate interactions in the low-latitude Pacific and Indian Ocean

The East Australian Current (EAC)，the western boundary current of the South Pacific，plays a crucial role in redistributing heat and moisture between the tropics and mid-latitudes，thereby modulating the climate of the southwest Pacific region. However，previous reconstructions of past EAC transport and temperature changes are limited and contradictory，hindering a comprehensive understanding of its pre-industrial variability，which hampers reliable projections of future tropical and subtropical climate change. This study reconstructed EAC variations over the past 1500 years using planktic foraminiferal Mg/Ca ratios and stable isotopes from two sediment cores in the Coral Sea. Mg/Ca ratios of the thermocline-dwelling planktic foraminifera species Neogloboquadrina dutertrei were used to derive thermocline water temperatures (TWT)，which are combined with previously published planktic foraminifera Globigerinoides ruber sea surface temperatures (SST)estimates to calculate the ocean heat content (OHC)as a proxy for EAC heat transport，and TWT-SST differences (ΔT)as a proxy for thermocline depth changes. The results reveal that the ΔT gradually increased after ~1400 CE，indicating a shoaling of the thermocline concurrent with an increasing OHC trend，collectively reflecting an intensification of EAC heat transport after ~1400 CE. The intensification of the EAC is accompanied by changes in planktic foraminiferal δ¹³C values at both sites，most likely related to enhanced water mass mixing and/or upwelling driven by the strengthened EAC flow. The EAC intensification is most likely attributed to a shift of Southern Annular Mode (SAM)towards its positive mode and more frequent El Niño-like conditions after ~1400 CE. This study underscores the importance of resolving multi-centennial EAC variability and its drivers for improving projections of future southwest Pacific climate under anthropogenic global warming.