Biomineral Formation in the Subtropical South Pacific: Insights From Major Ions and Carbonate Chemistry Along GEOTRACES Section GP21

Abstract

The South Pacific Ocean (SPO) hosts diverse biogeographical environments including the productive Peru‐Chile upwelling region and ultra‐oligotrophic subtropical gyre; however, vast areas are understudied regarding the cycling of dissolved calcium (Ca) and strontium (Sr), and distribution of major biomineral‐forming pelagic marine organisms. This study presents a high‐resolution basin‐scale analysis of dissolved Ca and Sr along the GEOTRACES GP21 transect to trace the production of calcium carbonate (CaCO ₃ ) and celestine (SrSO ₄ ). We used Optimum Multiparameter Analysis (OMPA) to correct for conservative water mass mixing, and quantify cumulative non‐conservative behavior of Ca and Sr along isopycnals to infer basin‐wide biomineral export production rates of CaCO ₃ and SrSO ₄ . Our findings revealed distinct, yet spatially variable rates of change in Ca and Sr associated with different balances between biomineral production and export driven by regional productivity gradients. In the upwelling region, biomineral export associated with high primary production was largely offset by strong biological recycling through higher grazing and shallow biomineral dissolution, reducing export efficiency. In contrast, lower grazing rates in the oligotrophic gyre led to a higher export rate. We highlighted the potential contribution of Acantharia to particulate organic carbon export production in the nutrient‐poor SPO oligotrophic gyre and underscored the need for their inclusion in global biogeochemical models. This work advances our understanding of pelagic CaCO ₃ and SrSO ₄ cycling and its implications for carbon production and sequestration in the sparsely sampled SPO.