Sedimentary CaCO3 constraints on the Equatorial and South Pacific deep circulation during the Holocene and LGM

Abstract

Deep ocean circulation governs marine carbon cycles over centennial to millennial time scales. Deep-sea carbonate saturation state is linked to ocean circulation which affects respiration and accumulation of organic carbon in the ocean interior. Previous studies suggested that depth-profiles of surface sedimentary calcium carbonate contents (wt%CaCO₃) from the North Pacific can be used to infer local deep water carbonate saturation states. Here, we apply a simple CaCO₃ accumulation model and, for the first time, show that the modern deep water-mass distribution controls the vertical profiles of surface sedimentary wt%CaCO₃ in the South Pacific. We further analyze wt%CaCO₃ profiles during the Last Glacial Maximum (LGM), which reveals an improved preservation of CaCO₃ in the deep Eastern Equatorial Pacific. In contrast, no enhanced LGM CaCO₃ preservation is found in the Central Pacific. In line with other proxy interpretations, changes of the LGM CaCO₃ preservation can be attributed to alterations of deep water-mass distribution in the east-versus-west equatorial Pacific regions during the LGM with more Lower Circumpolar Deep Water (LCDW) in the glacial Eastern Equatorial Pacific compared to today. Our study demonstrates the value of using wt%CaCO₃ to constrain past ocean circulation and carbon cycle changes, particularly for regions with scarce traditional proxy data.