Tracing Carbon Dynamics in the Southern Ocean and Great Barrier Reef Using Strontium and Calcium
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| Publicado en: | PQDT - Global (2025) |
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ProQuest Dissertations & Theses
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| Acceso en línea: | Citation/Abstract Full Text - PDF |
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| Resumen: | This study examines carbon cycling in the Southern Ocean and the Great Barrier Reef using strontium (Sr) and calcium (Ca) tracers. Traditionally, major cations like Ca and Sr were considered to have constant concentrations due to their long residence times. However, recent studies reveal that when normalised to salinity, their distribution is heterogeneous, suggesting a significant influence of biological processes. Sr and Ca are closely linked to the carbon cycle, which regulates air-sea CO2exchange and deep-ocean carbon storage. Calcifying organisms, such as corals and pelagic plankton, reply on CaCO3formation for their skeletons, but climate change threatens this process, potentially disrupting the carbon cycle. By analysing Sr and Ca, this research aims to improve understanding of how biological processes influence the carbon cycle and CO2regulation, which is essential for predicting the impacts of ocean acidification on global carbon cycles. The thesis covers Sr and Ca cycling in both the open ocean and coral reefs, followed by a description of the high-precision Ca and Sr analysis method. The main chapters explore three objectives: examining Ca and Sr cycling in the Southern Ocean (Chapters 3 and 4) and the Great Barrier Reef (Chapter 5).Chapter 3 investigates the CaCO3cycling in the Southern Ocean using total alkalinity (TA) and Ca tracers. The CaCO3cycling is an important component of the marine carbon cycle and modifies the seawater carbonate chemistry. The Southern Ocean is a key area for carbon sequestration and climate change regulation. Prior research revealed discrepancies between TA and Ca-derived CaCO3variations with depth in major ocean basins. These discrepancies were attributed to nutrient variations affecting TA or hydrothermal inputs of Ca, which are unrelated to calcification/dissolution. This study finds agreement between nutrient-corrected, salinitynormalised TA (potentially alkalinity, PA) and Ca. This suggests that PA and Ca are predominantly controlled by calcification/dissolution in the Southern Ocean. As a result, both can be used as reliable tracers for CaCO3cycling. The assessment of particulate inorganic carbon (PIC) export using dissolved Ca concentration reveals substantial contributions in the Southern Ocean, especially in the Subantarctic Zone. This suggests that dissolved Ca can serve as a valuable tool to estimate PIC export fluxes, helping to enhance our understanding of theChapter 4 focuses on the role of Acantharia in Sr cycling in the Southern Ocean and their potential impact on particulate organic carbon (POC) export. Acantharia are unicellular eukaryotes that belong to Radiolaria. They are characterised by their star-shaped skeletons, composed of strontium sulphate, or celestite. Celestite is the densest biogenic mineral in the ocean at 3.96 g/cm3, twice as dense as CaCO3. This unique feature makes Acantharia potential ballast material for POC, helping it to sink to the deep ocean. Initially, Acantharia were overlooked in POC export studies, as it was assumed that they would readily dissolve upon death in SrSO4-undersaturated seawater. However, emerging evidence suggests that Acantharia descend to the base of mesopelagic and even bathypelagic zones in high-latitude regions, contributing significantly to POC export. This chapter investigates Acantharia’s contribution to Sr and carbon cycling in the Southern Ocean. This study analyses both dissolved and particulate Sr concentrations, alongside sediment trap data collected at 1000 m depth. Key findings reveal that Acantharia play a key role in dissolved Sr distribution through their precipitation of SrSO4 and subsequent export to depth. Additionally, seasonal variations in particulate Sr fluxes show peaks during the summer, contributing up to 7% to POC export. These results address the importance of Acantharia in deep-water organic carbon export. They also highlight the need for further research to integrate Acantharia’s contribution into more accurate carbon budget models, particularly over seasonal cycles CaCO3cycle and refine the carbon budget. |
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| ISBN: | 9798311948777 |
| Fuente: | ProQuest Dissertations & Theses Global |