Glacially-controlled variations in the biological pump of the Ross Sea in the Mid-to-Late Pliocene

• Main Author: Nirenberg, Jared
• Other Authors: Ash, Jeanine, Masiello, Carrie
• Format: Thesis
• Language: English
• Published: Rice University 2020
• Subjects: Ross Sea; Pliocene; West Antarctic Ice Sheet; biogeochemistry; sedimentology; Antarctic; Southern Ocean; Antarc*; Ice Sheet; Sea ice
• Online Access: https://hdl.handle.net/1911/109255

An undergraduate thesis submitted in partial application for the Honors degree in Earth Sciences. The mid-to-late Pliocene (~3.3 – 2.5 Ma) is an intriguing period for investigating Earth’s past climate dynamics as a potential analogue for future warmth due to anthropogenic climate change. In the Southern Ocean, the Ross Sea and the adjacent West Antarctic Ice Sheet exert significant influence on global climate through their roles in carbon cycle processes, deep ocean circulation, and eustatic sea level. Previous ocean drilling records have shown that the marine-based West Antarctic Ice Sheet exhibited highly dynamic behavior in the Pliocene and responded to cyclical variations in Earth’s orbital geometry. However, fundamental questions remain regarding the biogeochemical response of Southern Ocean marine productivity to changes in ice sheet dynamics and sea ice cover. The International Ocean Discovery Program’s Expedition 374 to the Ross Sea (2018) recovered multiple sediment cores, including those from Site U1524 on the continental rise. I present a 900,000 year record of the carbon and nitrogen content in bulk sediment in the Pliocene-aged cores from Hole U1524A. This record shows the response of carbon export from the Ross Sea continental shelf to orbital and longer-term forcings of the West Antarctic Ice Sheet and global climate. From 3.3 to 3.0 million years ago, I observe a gradual, non-monotonic increase in organic carbon to nitrogen ratios, followed by a decrease from 3.0 to 2.8 million years ago. Sediment color reflectance measurements, implying changes in surface water productivity, are tightly anti-correlated with organic carbon to nitrogen ratios between 3.3 and 3.0 million years ago, but are positively correlated between 3.0 and 2.8 million years ago. I discuss these trends in the context of concurrent sedimentology, physical oceanography, and ice-sheet dynamics. Finally, I note that potential diagenetic effects limit interpretation of this record, and I suggest that bulk carbon and nitrogen ...