The overlooked contribution of the seasonal mixed layer pump to carbon export in low-latitude oceans.
The seasonal mixed layer pump (MLP) is an important pathway transporting organic carbon from the upper ocean to the ocean interior. While the MLP's export role has been well-studied in high latitudes, its contribution in low latitudes remains uncertain. Here, we quantify the seasonal MLP-driven carbon export (EMLP) in low-latitude oceans using data from 26 biogeochemical profiling floats. Our analysis reveals that EMLP ranges from -0.9 to 7.6 g C m-2 yr-1, contributing up to 53% of carbon export in certain areas. We find the relative positions of the mixed layer depth, euphotic depth, and nitracline depth regulate EMLP strength in low-latitude oceans. Global extrapolation of these observations across low-latitude oceans yields a total EMLP of 0.07 ± 0.02 Pg C yr-1, 75% higher than previous estimates, underscoring the previously underestimated role of the seasonal MLP in low-latitude oceans. These results reveal the controlling mechanisms of low-latitude seasonal MLP and highlight its disproportionately important role in regional ecosystems, particularly in oligotrophic oceans where carbon export pathways are limited.
