Radiolarian artificial neural network based paleo sea surface water temperature and salinity changes during the last glacial cycle in the Timor Sea, Indian Ocean

Abstract:

The western Pacific water enters into the Timor Sea (tropical Indian Ocean) by the thermohaline conveyor belt, and this region is under the influence of the SW monsoon. The higher precipitation during the monsoon rains lower the surface salinity in the north-eastern Indian Ocean towards the Bay of Bengal; whereas, the Arabian Sea remains highly saline due to higher evaporation in the region surrounding Arabian deserts. The salinity contrast in the northern Indian Ocean is very unique, and the radiolarian micro-zooplanktons living in the surface water serve a very good proxy for the monsoonal changes in the surface sea-water temperature (SST) and salinity in the geological past. We studied radiolarian faunal variation in the core MD01-2378, located at ~13^oS and ~121^oE (1783 m water depth), at the inlet of the thermohaline circulation into the Timor Sea. We applied the modern radiolarian based artificial neural networks (ANNs) (Gupta and Malmgren, 2009) to derive the SST and salinity during August-October for the last 140 ka (the full last glacial cycle). Based on the mean estimates of the 10 ANNs, the root mean square error in prediction (RMSEP) for SST is ~1.4^oC with correlation between observed and estimated values r=0.98 (Gupta and Malmgren, 2009). Similarly, the RMSEP is 0.3 psu (r=0.94) for the salinity estimates. We derived paleo-SSTs and salinity values using modern radiolarian ANNs and the fossil radiolarian data generated from the core for the last 140-ka (Fig.1). The age model of the core is based on δ¹⁸O benthic oxygen isotope stratigraphy and 21 AMS ¹⁴C ages up to ~30-ka (Holbourn et al., 2005). Paleo SST-summer varied between 22-28.5^oC, and it is in very good agreement with the δ¹⁸O benthic record of Holbourn et al. (2005) defining the Last Glacial Maximum (~24 ka) and the Eemian (~125 ka) stages. The salinity fluctuated between 34-35 psu, and compared well with oxygen isotope record representing the LGM and Eemian periods. We gratefully acknowledge Prof. Ann Holbourn (Keil Univ. Germany) for providing the core samples, AMS ¹⁴C dates and oxygen isotope data of the core.