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Discerning Local and Long-Range Causes of Deoxygenation and Their Impact on the Accumulation of Trace, Reduced Compounds.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Discerning Local and Long-Range Causes of Deoxygenation and Their Impact on the Accumulation of Trace, Reduced Compounds./
作者:	Evans, Natalya.
面頁冊數:	1 online resource (178 pages)
附註:	Source: Dissertations Abstracts International, Volume: 84-06, Section: B.
Contained By:	Dissertations Abstracts International84-06B.
標題:	Chemical oceanography. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30241860click for full text (PQDT)
ISBN:	9798358489271

Discerning Local and Long-Range Causes of Deoxygenation and Their Impact on the Accumulation of Trace, Reduced Compounds.
Evans, Natalya.

Discerning Local and Long-Range Causes of Deoxygenation and Their Impact on the Accumulation of Trace, Reduced Compounds. - 1 online resource (178 pages)

Source: Dissertations Abstracts International, Volume: 84-06, Section: B.

Thesis (Ph.D.)--University of Southern California, 2022.

Includes bibliographical references

Climate change is driving deoxygenation across the world's oceans. This deoxygenation restructures ecosystem energy transfer, foraging habitats, and the abundance of both critical and toxic compounds in the water column. In the absence of oxygen, microbes respire using terminal electron acceptors such as iodate, nitrate, ferric (oxy)hydroxides, and sulfate. These metabolisms produce reduced compounds such as iodide, nitrite, Fe(II), and sulfide, which have different properties and distributions in the water column. The research in this dissertation analyzes the causes and interconnections in the distribution of these reduced compounds.Nitrite, an intermediate in dissimilatory nitrate reduction, indicates that this metabolism is occurring in marine Oxygen Deficient Zones (ODZs). Spatial heterogeneity in nitrite distributions observed during multiple sampling campaigns in the Eastern Tropical North Pacific (ETNP) ODZ could not be explained using oxygen or nutrient concentrations. By deconvoluting the source waters sampled on these cruises, I determined that mesoscale features transporting the 13 ºC Water mass westward led to nitrite accumulation in the ETNP ODZ. With this source water mass framework, I identified the basin-wide stoichiometry of anaerobic respiration in the ETNP ODZ. These results reveal that 50%-70% of the nitrite produced is re-oxidized to nitrate in subsurface waters, and I developed a method that can estimate nitrite re-oxidation using only nutrient and carbon measurements. I also applied this source water mass framework to seven cruises spanning a 50-year time series on the 110 ºW line. With these data, I reveal that the ETNP ODZ became 30% stronger in 2019 than 1994. More importantly, I also calculated the first confidence interval for the strength of the ETNP ODZ and concluded that anthropogenic climate change has not yet influenced the strength of the ETNP ODZ, but likely will soon.Previous research in the Moffett lab has investigated the flux of Fe, specifically Fe(II), as well as iodide from ODZs. In these regions, mesoscale features transport Fe(II) from waters that intersect the continental margin. This phenomenon transports extremely high iodide concentrations and iodide has a significantly higher residence time in the subsurface ocean than Fe(II). These findings suggest that iodide could be used to trace sources of Fe(II) in low oxygen waters. To examine the processes that control the distributions and couplings of these compounds, I studied seasonally hypoxic waters on the Oregon continental margin. The presence of low oxygen water in this region prevents water column denitrification like in the ETNP ODZ, but sediment denitrification still occurs. I explored the factors that control Fe(II) accumulation and transport on the Oregon continental shelf, where Fe(II) concentrations exceed 50 nM. Surprisingly, we observed minimal iodide accumulation in this region, unlike in ODZs. With this comparison and a re-analysis of iodate in the ETNP ODZ, I contrast the nitrogen, Fe, and sulfur cycles in these two reducing margins. These findings suggest that sulfide accumulation likely drives iodate depletion in these low oxygen waters. The findings within this dissertation highlight the physical processes that influence reduced compounds and the interconnections of these elemental cycles.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798358489271Subjects--Topical Terms:

516760
Chemical oceanography.
Subjects--Index Terms:

Astern boundary upwelling systemsIndex Terms--Genre/Form:

542853
Electronic books.

Discerning Local and Long-Range Causes of Deoxygenation and Their Impact on the Accumulation of Trace, Reduced Compounds.
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520 $a Climate change is driving deoxygenation across the world's oceans. This deoxygenation restructures ecosystem energy transfer, foraging habitats, and the abundance of both critical and toxic compounds in the water column. In the absence of oxygen, microbes respire using terminal electron acceptors such as iodate, nitrate, ferric (oxy)hydroxides, and sulfate. These metabolisms produce reduced compounds such as iodide, nitrite, Fe(II), and sulfide, which have different properties and distributions in the water column. The research in this dissertation analyzes the causes and interconnections in the distribution of these reduced compounds.Nitrite, an intermediate in dissimilatory nitrate reduction, indicates that this metabolism is occurring in marine Oxygen Deficient Zones (ODZs). Spatial heterogeneity in nitrite distributions observed during multiple sampling campaigns in the Eastern Tropical North Pacific (ETNP) ODZ could not be explained using oxygen or nutrient concentrations. By deconvoluting the source waters sampled on these cruises, I determined that mesoscale features transporting the 13 ºC Water mass westward led to nitrite accumulation in the ETNP ODZ. With this source water mass framework, I identified the basin-wide stoichiometry of anaerobic respiration in the ETNP ODZ. These results reveal that 50%-70% of the nitrite produced is re-oxidized to nitrate in subsurface waters, and I developed a method that can estimate nitrite re-oxidation using only nutrient and carbon measurements. I also applied this source water mass framework to seven cruises spanning a 50-year time series on the 110 ºW line. With these data, I reveal that the ETNP ODZ became 30% stronger in 2019 than 1994. More importantly, I also calculated the first confidence interval for the strength of the ETNP ODZ and concluded that anthropogenic climate change has not yet influenced the strength of the ETNP ODZ, but likely will soon.Previous research in the Moffett lab has investigated the flux of Fe, specifically Fe(II), as well as iodide from ODZs. In these regions, mesoscale features transport Fe(II) from waters that intersect the continental margin. This phenomenon transports extremely high iodide concentrations and iodide has a significantly higher residence time in the subsurface ocean than Fe(II). These findings suggest that iodide could be used to trace sources of Fe(II) in low oxygen waters. To examine the processes that control the distributions and couplings of these compounds, I studied seasonally hypoxic waters on the Oregon continental margin. The presence of low oxygen water in this region prevents water column denitrification like in the ETNP ODZ, but sediment denitrification still occurs. I explored the factors that control Fe(II) accumulation and transport on the Oregon continental shelf, where Fe(II) concentrations exceed 50 nM. Surprisingly, we observed minimal iodide accumulation in this region, unlike in ODZs. With this comparison and a re-analysis of iodate in the ETNP ODZ, I contrast the nitrogen, Fe, and sulfur cycles in these two reducing margins. These findings suggest that sulfide accumulation likely drives iodate depletion in these low oxygen waters. The findings within this dissertation highlight the physical processes that influence reduced compounds and the interconnections of these elemental cycles.
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