TEMPERATURE VARIABILITY IN CONTINENTAL NORTHWEST AUSTRALIA DURING THE PLIO-PLEISTOCENE (3.5 TO 1.5 MA): THE BRGDGT RECORD FROM IODP SITE U1463

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced in soils, peats, rivers and lakes by bacteria, possibly Acidobacteria. These compounds can reach marine environments via wind or river runoff or may be produced in-situ in some marine settings. Notably, brGDGT distributions correlate to mean annual air (soil) temperatures (MAAT) of the environment in which the source organism(s) lived. This allows for continental MAAT reconstruction via the methylation index of branched tetraethers (MBT’_5ME). Here we examine continental MAAT in Northwest Australia from 3.5-1.5 Ma by applying the MBT’_5ME proxy to marine sediments from IODP Site U1463, located on the Northwest Australian shelf and close to the outlet of the Indonesian Gateway. At this Site, which is far removed from any river inputs, brGDGTs are delivered primarily by wind via the Northwest Dust Pathway, and thus the MBT’_5Me record reflects continental MAAT. We compare our MAAT record to both hydroclimate and sea surface temperature (SST) records from the same site to investigate the influence of offshore SST on Australian continental climate. Additionally, we use these Site U1463 records to constrain the dynamics of the Indonesian Gateway, the corresponding Indonesian Throughflow, and the associated Leeuwin Current, since the Pliocene. Altogether, our results indicate that SST exerted a main control on Australian continental hydroclimate and MAAT since the Pliocene. Cooling occurs in both the MAAT and SST records after ~1.7 Ma, which we hypothesize indicates a net constriction of the Indonesian Gateway, resulting in a slowing and cooling of the Indonesian Throughflow and Leeuwin Current passing over Site U1463. Our new brGDGT record offers one of the first continuous records of Australian continental climate.