Carbonate system and elementary geochemistry: Paleoceanographic and paleoclimatic implications in the South China Sea along the Late Quaternary

• Ano de defesa: 2022
• Autor(a) principal: Gerotto, Amanda
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Aporte terrígeno; Carbonate preservation; Coccoliths; Cocólitos; Foraminíferos planctônicos; Mar Sul da China; Planktonic foraminifera; Preservação do carbonato; South China Sea; Terrigenous supply
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/21/21137/tde-19102022-143532/

Understanding past ocean carbonate chemistry changes is critical to elucidate the role of the oceans in the global carbon cycle and Earth\'s climate control according to its large carbon dioxide (CO2) storage capacity. The South China Sea (SCS) is a tropical basin of great interest for understanding the evolution of the carbonate system. This marginal basin is under the influence of the East Asian Monsoon (EAM) which has a profound impact on the interactions between the atmosphere, land, and oceans. In this context, the present work aims to evaluate changes in SCS carbon system considering the carbonate cycles that acted in the basin along with the Quaternary controlling dissolution and dilution processes. For this, we applied using a multiproxy approach in marine sedimentary samples from cores recovered in the eastern, northeast, and northern sub-basins of the SCS - Hole IODP U1431D (4240 m depth), Hole U1432C (3829 m), and ODP 1146 (2092 m) - and in surface sediments collected along the basin (R/V Sonne, SO-95) at depths between 629-3809 m. We evaluated (i) the abundance, fragmentation, and dissolution indexes of planktonic foraminifera and total organic carbon in the last 600 ka; (ii) terrigenous input by the determination of major and trace elements in sediments and variations in natural gamma radiation; and (iii) performed the calibration of morphological attributes of coccoliths in response to a laboratory dissolution experiment and oceanic environmental parameters, generating a new proxy that was applied in the reconstruction of dissolution patterns in the last 210 kyr. The results showed that the records located below the modern lysocline and carbonate compensation were under strong dissolution. A punctual increase in planktonic foraminifera abundance was related to primary productivity and EAM dynamics, with the occurrence of turbidites influencing CaCO3 preservation. Despite the low carbonate preservation inherent to the depth of these records, the dilution of biogenic sediments by the terrigenous input was recorded due to the more significant terrigenous contribution of sediments potentially sourced from Luzon in response to the strengthened summer EAM. The dissolution experiment and the evaluation of surface sediments showed that changes in coccolith morphology, obtained by the ks factor, are mainly controlled by changes in carbonate saturation, and can be used as a proxy to track changes in carbonate saturation limits. When applied as dissolution proxy the ks factor recorded changes possibly related to variations in lysocline depth over the last 210 kyr consistent with changes in deepwater circulation between the Pacific and the SCS. The results of this thesis demonstrate that post-burial dissolution has a major influence on the composition of micro and nannofossils assemblages and in the carbonate preservation at SCS sediments and that the coccolith ks factor is a reliable proxy for tracking changes in carbonate chemistry.