Presentation Information
[U11-P20]Glacial–interglacial CO2 dynamics over the last 800 kyr revealed by multi-proxy geochemical analyses of planktic foraminifera from the South China Sea
*Yi-Ning Chen1, Kuo-Fang Huang1 (1.Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan)
Keywords:
Glacial-interglacial cycles,CO2 dynamics,Ocean carbonate system,Boron isotopes,Foraminiferal shell chemistryForaminiferal shell chemistry,South China Sea
Carbon dioxide (CO2), the dominant long-lived greenhouse gas, varies systematically over glacial-interglacial cycles. These cycles are driven by Milankovitch orbital forcing, which modulates incoming solar radiation and induces changes in temperature and sea level that are closely linked to CO2 variability. In addition to orbital forcing, glacial-interglacial fluctuations in atmospheric CO2 partial pressure reflect feedbacks involving deep-ocean carbon storage and sea-level-controlled nutrient dynamics in marginal seas, which regulate the efficiency of CO2 exchange between the upper ocean and the atmosphere. Together, these coupled physical and biological processes underscore the need for a comprehensive understanding of ocean carbonate chemistry in marginal seas.
The South China Sea (SCS), a marginal sea in the western Pacific, is a climatically sensitive region characterized by pronounced monsoon variability, dynamic ocean circulation, and substantial sea-level changes. It is therefore regarded as a key region for investigating the interactions between regional and global carbon cycles. The objective of this research is to establish robust relationships between foraminiferal shell chemistry and the carbonate system. Specifically, we aim to reconstruct past CO2 variability over the last 800 kyr and to identify the dominant controls on CO2 changes across different timescales: (i) millennial-scale CO2 variability during the last deglaciation, potentially influenced by monsoon dynamics and changes in ocean circulation; and (ii) long-term CO2 variations across multiple glacial-interglacial cycles, likely governed by orbital forcing and associated changes in ocean carbonate chemistry. To address these objectives, this study focuses on three key components : (1) reconstruction of seawater pCO2 concentrations using boron isotopes (δ11B) in mixed-layer-dwelling planktic foraminifera; (2) estimation of past ocean temperatures based on foraminiferal Mg/Ca ratios; and (3) evaluation of changes in upwelling intensity and primary productivity using published foraminifera-bound δ15N and, newly introduced in this study, Ba/Ca ratios.
The South China Sea (SCS), a marginal sea in the western Pacific, is a climatically sensitive region characterized by pronounced monsoon variability, dynamic ocean circulation, and substantial sea-level changes. It is therefore regarded as a key region for investigating the interactions between regional and global carbon cycles. The objective of this research is to establish robust relationships between foraminiferal shell chemistry and the carbonate system. Specifically, we aim to reconstruct past CO2 variability over the last 800 kyr and to identify the dominant controls on CO2 changes across different timescales: (i) millennial-scale CO2 variability during the last deglaciation, potentially influenced by monsoon dynamics and changes in ocean circulation; and (ii) long-term CO2 variations across multiple glacial-interglacial cycles, likely governed by orbital forcing and associated changes in ocean carbonate chemistry. To address these objectives, this study focuses on three key components : (1) reconstruction of seawater pCO2 concentrations using boron isotopes (δ11B) in mixed-layer-dwelling planktic foraminifera; (2) estimation of past ocean temperatures based on foraminiferal Mg/Ca ratios; and (3) evaluation of changes in upwelling intensity and primary productivity using published foraminifera-bound δ15N and, newly introduced in this study, Ba/Ca ratios.