Effects of Deep Circulation on CaCO₃ Dissolution and Accumulation in the Southwestern Atlantic Ocean

Abstract

Deep oceanic circulation regulates seafloor calcium carbonate (CaCO3) accumulation by transporting atmospheric carbon dioxide (CO2) to depth and then transferring it, with respired CO2, along the global ocean conveyor belt. This creates the shallowing trend of CaCO3 preservation from the Atlantic to the Pacific Oceans. The thermohaline flow can be, however, complex on a basin‐wide scale; here, we use a state‐of‐the‐art data compilation and a carbonate accumulation/dissolution model to explain the CaCO3 distribution within the basins of the Southwestern Atlantic Ocean. Our results demonstrate that different currents foster systematically dissimilar CaCO3 preservation within these connected ocean basins. The more undersaturated, faster moving, northward‐flowing Antarctic bottom water readily dissolves more CaCO3 than the southward‐flowing North Atlantic deep water. We are able to predict quantitatively these observations, based on benthic carbonate chemistry and mass‐transfer rates. Our model and CaCO3 records in such basins have the potential to provide new understanding about deep‐ocean circulation of the past.

Influence of terrigenous supply from the African continent on sedimentary CaCO3 distribution in the Southeast Atlantic Ocean

“…It has been established that [CO 3 2− ] of deep waters predominantly determines the large‐scale interbasinal sedimentary wt% CaCO 3 distribution (Li et al 2021; Liu et al 2022), and shoaling of the CSD from the Guinea Basin to the Cape Basin coincides with the decrease of [CO 3 2− ] along the flow path of the North Atlantic Deep Water. Besides, effective CaCO 3 dissolution rate constants ( k* ) for sediment in the Guinea and Cape Basins are greater than those in the Angola Basin, in accordance with the latitudinal variations of deep current velocity in the Southeast Atlantic Ocean (Arhan et al 2003).…”

“…For example, enhanced carbonate dissolution in the pelagic‐marginal transitional region compared to the pelagic region of Argentina Basin (Fig. 5a), which corresponds to the higher k * value (7.5 vs. 3.7 m yr −1 ), is possibly resulted from the rapid deep western boundary current (Liu et al 2022). Moreover, the complex bottom topography in marginal seas exerts an extra effect on the regional carbonate dissolution.…”

“…Once locations of CSD and CCD in the study area are determined, the effective rate constant for CaCO 3 dissolution at the sediment–water interface ( k *; m yr −1 ), which is related to the velocity of deep ocean currents (Sulpis et al 2018), can be calculated and used to generate a CaCO 3 depth profile, with known [CO 3 2− ] in the deep ocean, PIC rain ( F B ), and noncarbonate flux ( F M ) (Li et al 2021; Liu et al 2022). Noncarbonate flux can be derived from the relatively constant sedimentary wt% CaCO 3 immediately above Z sat and constrained by measured or model‐simulated dust deposition (Liu et al 2022).…”

Deep Ocean Circulation Governs Sedimentary CaCO3 Accumulation in the Northeast Pacific Ocean

“…The CCD is determined by identifying the depth below which there is no accumulation of CaCO 3 from the observed depth-distribution pattern of sedimentary CaCO 3 . Observed CCD by finding the mean depth at which sedimentary wt CaCO 3 % equal to zero allows for calculating the dissolution rate of CaCO 3 (k*; Table 1) with known particulate inorganic carbon (PIC) flux (F B ), and deep-sea [ 𝐴𝐴 CO 2− 3 ] values (Li et al, 2022;Liu et al, 2022):…”

“…Accumulation and dissolution of CaCO 3 in sediments in the North Pacific Ocean highlights not only the buffering capacity to take up atmospheric CO 2 (Ridgwell & Zeebe, 2005) but also changes in the largest marine carbon reservoir (Archer et al., 1998) and deep ocean circulation (Adkins, 2013). Additionally, spatial distribution of basin‐scale sedimentary CaCO 3 has recently been found to correlate with different thermohaline currents that overlay sediments in adjacent ocean basins (Liu et al., 2022).…”