Distributions and sources of bulk organic matter from surface sediments along the Southwestern Atlantic Margin

In this study, published and unpublished data on bulk organic matter from surficial sediments along the Southwestern Atlantic Margin (SAM) were gathered to identify sources and understand carbon transport over this large and complex area under the regime of strongly coupled climatic-hydrological-oceanographic interactions. To achieve this goal, total organic carbon (TOC), total nitrogen (TN), stable carbon (δ13C), and nitrogen (δ15N) isotopes, as well as calcium carbonate data from 242 sedimentary samples over the SAM were analyzed. Cluster analysis defined three geochemically distinct groups, closely related to sedimentary and hydrodynamic controls. Our results show that the latitude of 28°S marks a transition region in terms of the sedimentary bulk organic matter. To the south, organic material is strongly influenced by the continental contribution from the La Plata River and by the action of the Brazilian Coastal Current, whereas to the north, the contribution of La Plata River gradually decreases. Oceanographic fronts, currents, and river supply are the main mechanisms that drive organic matter distribution over the SAM. •Sedimentary organic matter is associated with mud content and areas of intense primary productivity.•Sedimentary organic matter exhibits distinct characteristics both south and north of Cape Santa Marta, as well on the continental shelf compared to the slope.•Sedimentary δ15N provides insights into the nitrogen sources absorbed during primary production, revealing nuances in nutrient availability and algal utilization in different SAM regions.•Despite the La Plata River's role as a significant terrigenous source, marine organic matter signals dominate the SAM, potentially overshadowing terrigenous contributions.