Document Type

Campus-Only Access for One (1) Year

Embargo Period

9-1-2019

Degree Program

Geosciences

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2018

Month Degree Awarded

September

Abstract

Ocean gateways facilitate water circulation between ocean basins, and therefore directly impact thermohaline circulation and global climate. In order to better predict the effects of future climate change, it is critical to constrain past changes in ocean gateway behavior, and corresponding changes in thermohaline circulation, particularly during analogue periods for modern climate change. The Indonesian Throughflow (ITF) is a primary ocean gateway and vital component of the global conveyor that transports water from the Pacific Ocean into the Indian Ocean, however due to a lack of long and continuous sedimentary records from locations under its influence, changes in ITF behavior remain poorly constrained. In this study organic geochemical biomarkers preserved in marine sediments are used to reconstruct both sea surface and continental air temperatures in Northwest (NW) Australia from sediments spanning the mid-Pliocene Warm Period (mPWP), a critical carbon dioxide (CO2) and temperature analogue period for modern climate change spanning 3.3-3.0 Ma. These sediments were collected during IODP Expedition 356 from Site U1463, located near the outlet of the ITF, and are therefore sensitive to changes in ITF behavior over time. Here, NW Australian air temperatures were reconstructed from 1.5-3.5 Ma using the MBT’5ME proxy (Weijers et al., 2007a; De Jonge et al., 2014a), and offshore sea surface temperatures (SSTs) were reconstructed using both the TEX86 proxy (Schouten et al., 2002; Tierney & Tingley, 2014) and the Long Chain Diol Index (LDI; Rampen et al., 2012). Global climate events, including Marine Isotope Stages (MIS) 55, 63, 64, 82, 84, 88, 92, G10, G18, G20, G22, and M2 (Lisiecki & Raymo, 2005) are apparent in all of our records. TEX86 SSTs suggest a stronger cooling signal during MIS Stages G18, G20 and G22 relative to cooling during MIS M2, however LDI SSTs do not yield the same result. Overall, all three proxies indicate higher temperatures across the Pliocene and a cooling trend from ~1.7-1.5 Ma. Cooling occurs during an arid interval identified by Christensen et al. (2017), from 2.4-1.0 Ma, which suggests that offshore cooling contributed to shifts in NW Australian continental hydrology. Cooling from 3.5-1.5 Ma at Site U1463 was likely a reflection of 1) constriction of the ITF from 5-2 Ma and a switch from warm South Pacific to cool North Pacific source waters, and 2) an increase in meridional SST gradients at 1.8 Ma; the particularly strong cooling signal identified in all three records at 1.7 Ma is likely a direct response to the latter. This study helps elucidate ITF variability and shifts in thermohaline circulation across the Plio-Pleistocene and the mPWP, which will help modelers better predict the effects of future climate change.

First Advisor

Isla S. Castañeda

Available for download on Sunday, September 01, 2019

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