Reconstructing Surface Water Carbonate Ion Concentration Changes in the Eastern Equatorial Pacific Across Glacial Transitions

<p>Today, the eastern equatorial Pacific (EEP) plays a critical role in the global CO₂ budget as a major source of CO₂ to the atmosphere, but recent studies suggest the region may shift to a sink for atmospheric CO₂ under different climate states. Here, I focus on two transitional periods, the last deglaciation (25 kyr to present) and last glaciation (the Marine Isotope Stage (MIS) 5a-4 transition, 96 to 60 kyr), to investigate how the carbon system in the EEP responds to major climate changes. I measured B/Ca ratios in the planktic foraminifera Globigerina bulloides from core MV1014-17JC (00º10.83’S, 85º52.00’W; 2846 m water depth) as a proxy for changes in surface water carbonate ion concentration ([CO₃^2-]) in the EEP across both climate transitions. Because calcification rate (controlled by [CO₃^2-]) drives the uptake of boron in foraminiferal tests, [CO₃^2-] can be calculated from B/Ca ratios. In addition to the B/Ca proxy, the relationship between δ¹³C values in the planktic foraminifera <em>Globigerinoides ruber</em> and <em>Trilobatus sacculifer</em> to surface water [CO32-] differ in response to changes in seawater [CO₃^2-]. Therefore, I also measured δ¹³C in these two species as another proxy for surface water Δ[CO₃^2-] change. Because surface water [CO₃^2-] is linked to surface water CO₂ concentrations and thus atmospheric <em>p</em>CO₂, I use reconstructed [CO₃^2-] to indicate if the EEP was more or less of a source of CO₂ to the atmosphere in the past. Results indicate that across both the deglaciation and glaciation, the EEP remained as much or more of a source of CO₂ than today. Enhanced upwelling across these glacial transitions coupled with an expansion of the oxygen minimum zone (OMZ) likely delivered CO_2- and nutrient-rich water to the surface. However, this increase in nutrient concentrations coupled with dust fertilization across cold Heinrich events failed to stimulate biological productivity to the point where the region switched to being a sink for atmospheric CO₂. Sustained lower-than-modern surface water [CO₃^2-] across both climate transitions indicate that the EEP may remain a source of CO₂ to the atmosphere across anthropogenic climate changes in the future.</p>

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Ocean & Earth Sciences

Year dc:date.available

2021

Author dc:creator

• Ward, Lenzie Gail

Contributors dc:contributor

• Matthew W. Schmidt
• Alexander Bochdansky
• Margaret Mulholland

• Carbon cycling
• Carbonate ion
• Eastern Equatorial Pacific
• Foraminifera
• Paleoceanography
• Paleoclimatology
• Climate
• Geochemistry
• Geology
• Paleontology

Statement dc:rights

• <p>In Copyright. URI: <a href="http://rightsstatements.org/vocab/InC/1.0/">http://rightsstatements.org/vocab/InC/1.0/</a> This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).</p>

Identifier

9798515245863

OAI identifier oai:identifier

oai:digitalcommons.odu.edu:oeas_etds-1177