Atlantic sediments reveal interacting environmental and physiological controls on coccolithophore calcite production.

Coccolithophores contribute 20-80% of the open ocean's total calcite production, playing a pivotal role in the marine carbon cycle. Links between environment, coccolithophore physiology and calcite production remain unclear due to challenges in extrapolating culture experiments to sedimentary nannofossil records. Here, we develop a framework to reconstruct physiology and calcite production of dominant coccolithophore species from sedimentary records. Using well-preserved Atlantic surface sediments, this study establishes factors controlling coccolithophore calcite production via measurements of species composition, primary production, growth (μ), and calcification rates. Contrasting μ-calcification relationships of major groups indicate differing carbon requirements. Optimal μ is the primary control on group-specific maximum calcite production, defining a meridional bimodal structure with a boundary at ~40°N, aligned with oceanic physicochemical gradients. Group-specific cellular carbon demand relative to supply show that this boundary separates reaction-limited cells to the north from mass-transport-limited cells to the south, and likely migrates latitudinally with changing ocean carbon.