Makassar Transport Variability Over the Past Century - A Synthesis of Observations, Coral d18O and High-Resolution Ocean Models

Abstract:

Recent mooring campaigns in the Indonesian Seas such as the INSTANT and MITF programs have provided velocity data within the Makassar Strait, the primary pathway of the Indonesian Throughflow (ITF), since 2004 allowing for a characterization of intra-seasonal, seasonal and interannual features. However, the short extent of observations from these programs limit examination of decadal to multi-decadal variability. An extended time series would allow for a more robust analysis at seasonal and interannual scales, an exploration of decadal changes, and thus a better understanding of the impacts of climate change on the ITF. We approach this problem by synthesizing the observed Makassar transport, coral d¹⁸O records, and simulated ocean variability (salinity, temperature, ocean heat content) from state-of-the-art 1/4º to nested 1/20º ocean model hindcasts to explore drivers of seasonal to multi-decadal ITF variability. We first compare observed Makassar transport to coral d¹⁸O from three sites along main ITF pathways, including the southern Makassar Strait (87 years), and both the northern and southern Lombok Strait (110 and 183 years, respectively). The coral d¹⁸O proxy at these sites records upper ocean salinity, which plays a key role in Makassar transport. Preliminary results suggest coral d¹⁸O is in good agreement with Makassar volume transport at seasonal time scales, particularly within the southern Lombok Strait. Relationships between the overlapping coral records and Makassar transport timeseries should allow for coral-based reconstructions of Makassar transport, extending this timeseries back roughly 150 years. Synthesizing these records with the high-resolution ocean model simulations should thus provide a better understanding of the drivers of ITF variability over the 19^th and 20^th centuries.