Total dissolved cobalt and labile dissolved cobalt distributions measured by shipboard voltammetry in the Amundsen Sea, Ross Sea, and Terra Nova Bay during the CICLOPS expedition on RVIB Nathaniel B. Palmer (NBP1801) from Dec 2017 to Feb 2018

Cobalt (Co) is often a scarce but essential micronutrient for marine plankton in the Southern Ocean and coastal Antarctic seas where dissolved cobalt (dCo) concentrations can be extremely low. This dataset presents total dCo and labile dCo distributions measured via shipboard voltammetry in the Amundsen Sea, Ross Sea, and Terra Nova Bay during the CICLOPS (Cobalamin and Iron Co-Limitation of Phytoplankton Species) expedition on RVIB Nathaniel B. Palmer (NBP1801). The resulting profiles indicate that a significantly smaller dCo inventory was observed during the 2017/2018 CICLOPS expedition compared to the 2005/2006 CORSAC expeditions to the Ross Sea over a decade earlier. The dCo inventory loss (~10–20 pM) was present in both the surface and deep ocean and can be attributed to the loss of labile dCo, resulting in the near-100% strong ligand-bound complexation of dCo in the photic zone. This perturbation of the Southern Ocean cobalt biogeochemical cycle could signal changes in the nutrient limitation regimes, phytoplankton bloom composition, and carbon sequestration sink of the Southern Ocean.