Publication Date

2024

Document Type

Dissertation/Thesis

First Advisor

Dodd, Justin P.

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Earth, Atmosphere, and Environment

Abstract

Increased melting of the Antarctic Ice Sheet (AIS) in recent decades, has had a significant impact on many aspects of the global ocean. Models indicate that by the end of the 21st century atmospheric carbon dioxide (CO2) concentrations may exceed 500 ppm, and the average global temperature will likely warm by more than 2°C. However, data that provide model constraints on potential feedbacks in ice-ocean-atmosphere system are limited by short-timescales (e.g., decadal- to centennial-scale) and incomplete spatial coverage. In particular, little is known about the impacts of future warming and widespread melting of AIS on marine biological productivity, silicate weathering rates, nutrient dynamics, or global-scale ocean circulation and bottom water production. Past warmer-than-present intervals in Earth’s history provide valuable analogs for understanding how changes to the AIS and potential feedbacks in the ocean-ice system may significantly affect the rate and magnitude of future climate change. The Miocene Climatic Optimum (MCO) is often cited as potential analogue for a warmer and higher-atmospheric-CO2 world. During the MCO, the AIS was likely greatly reduced in extent, and much of the coastal and continental shelf regions of Antarctica were ice free for at least part of the year. This has led to the hypothesis that during past warm intervals, regions of high nutrient upwelling associated with the Antarctic Circumpolar Current (ACC) shifted south and resulted in increased marine productivity along the Antarctic continental margin. In the modern Southern Ocean (SO) diatoms are the most prolific primary producers (e.g., opal belt), and provide a critical link between the silicon and carbon cycles at a global scale. Understanding diatom productivity and nutrient dynamics in the coastal regions of Antarctica during past warm intervals will provide a critical link between variability in the AIS and marine productivity. These data can then be used to better refine our understanding of, and capacity to predict, the impact of future warming on marine productivity and carbon burial.

Here, I present a multiproxy record of diatom productivity in the Ross Sea during the MCO to test the hypothesis that changes in the AIS during these warm intervals drove significant changes in upwelling-driven nutrient dynamics and marine productivity. Specifically, changes in the source and concentration of dissolved silica (dSi) was highly variable during these intervals. dSi is a critical nutrient for biogenic silica (bSi) production by diatoms. I present a combined record of biogenic silica (bSi), silicon (δ30Siopal), carbon (δ13Corg), nitrogen (δ15Norg) isotopes that provide a geochemical record of changes in nutrient dynamics and diatom productivity during these warmer than present intervals. These data from marine sediment cores collected in the Ross Sea provide new constraints on how AIS variability and high-latitude processes may impact marine productivity and storage of organic carbon in marine sediments. This study contributes to a better understanding the role of the Antarctic continental margin and the Southern Ocean in the global climate system and the connections between changes of the AIS and the marine biogeochemical cycles.

Extent

112 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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