Stable oxygen isotope variability in seawater: Insights into past and present ocean circulation and hydroclimate

Murray, Nicole Kathleen

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https://hdl.handle.net/2142/125581 Copy

Description

Title

Stable oxygen isotope variability in seawater: Insights into past and present ocean circulation and hydroclimate

Author(s)

Murray, Nicole Kathleen

Issue Date

2024-07-09

Director of Research (if dissertation) or Advisor (if thesis)

Conroy, Jessica L

Doctoral Committee Chair(s)

Conroy, Jessica L

Committee Member(s)

• Anders, Alison
• Johnson, Thomas
• Proistosescu, Cristian

Department of Study

Geology

Discipline

Geology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

stable oxygen isotopes, seawater, salinity, hydroclimate

Abstract

The stable oxygen isotope partitioning that occurs during meteoric water movement through the climate system can provide information on moisture balance, moisture recycling, and moisture pathways, and the temporal variability in these processes. In the ocean, the stable oxygen isotopic composition of seawater (δ18Osw) can track these hydrologic changes through the imprint of precipitation stable oxygen isotope values on δ18Osw values. However, ocean circulation also influences δ18Osw, to the extent that δ18Osw values are considered a key water mass tracer in the ocean. The potential for δ18Osw to serve as both an ocean circulation and atmospheric hydrology indicator has led to stable oxygen isotopes becoming a key proxy used in many different paleoclimate archives to reconstruct past climate and oceanographic changes. In this work I assess δ18Osw in modern observations as well as past and modern climate model simulations in order to understand the spatio-temporal variability in δ18Osw and its relationship to hydrologic and ocean circulation variables. First, using machine learning techniques and an up-to-date global observational dataset of salinity and δ18Osw values, I define regions with distinct δ18Osw – salinity relationships that can be used for regional paleoclimate reconstruction. I find that the slopes and intercept of δ18Osw – salinity regressions are highly variable, and strongly forced by the atmosphere. Building on this work, I investigate temporal changes in δ18Osw, salinity and the δ18Osw – salinity relationship from 850-2006 CE using isotope-enabled transient simulations from iCESM, an isotope-enabled global climate model. I find that δ18Osw in the tropics records a strong atmospheric signal and that δ18Osw – salinity relationships are highly dependent on temporal scale, which has significant implications for paleoclimate reconstructions based on modern δ18Osw – salinity. Global δ18Osw datasets and simulations are critical to ocean and atmospheric science as they can resolve the influences of large-scale hydroclimate variability and ocean circulation on δ18Osw. However, long-term observational δ18Osw time series from single locales are of great value, as they are extremely rare and can offer improved understanding of the temporal variability in δ18Osw and the ocean and atmosphere influences on δ18Osw through time. In my final chapter I present a 9-year record of δ18Osw and precipitation stable oxygen isotope values (δ18Op) from Palau, located in the Western Pacific Warm Pool. I use this data to understand the role of hydroclimate processes and ocean circulation in controlling δ18Osw. Results show δ18Osw values strongly covary with Palau δ18Op, as well as precipitation rates and outgoing longwave radiation across the tropical Pacific, related to the El Niño-Southern Oscillation (ENSO). I also find a strong relationship between ocean current velocities in the location of the Mindanao Current and Palau δ18Op, with high δ18Osw values occurring in months when the Mindanao current is stronger. Both of these atmospheric and the oceanic drivers of δ18Osw are strongly modulated by ENSO in a constructive manner, making Palau δ18Osw a strong and consistent proxy for ENSO.

Graduation Semester

2024-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/125581

Copyright and License Information

Copyright 2024 Nicole Murray

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