Quantifying organic carbon fluxes and the efficiency of the biological carbon pump in the Labrador Sea, Northwest Atlantic

The sinking flux of particulate organic carbon, i.e., the downward limb of the biological carbon pump, is estimated to supply 8-10 petagrams of carbon to the ocean interior every year. The sinking of carbon co-regulates atmospheric CO₂ concentrations and provides energy for mesopelagic and deep ecosystems, including lucrative commercial fisheries. In this context, the Labrador Sea in the Northwest Atlantic plays a critical role as this region supports enormous phytoplankton spring blooms, important fisheries, and coastal communities that rely on marine resources. While there is concern that changes in ocean conditions due to climate warming will negatively impact both productivity and the biological carbon pump in the Northwest Atlantic, mechanistic understanding of the biological carbon pump remains poor, which is reflected in the lack of skill and predictive power of state-of-the-art numerical models.

Here, we present new data collected in the framework of the collaborative Biological Export in the Labrador Sea (BELAS) project, one of the most comprehensive examinations of the carbon pump in the Labrador Sea to date. Building on field campaigns during the spring of 2022, 2024, and 2025, we will discuss (a) fluxes of sinking organic carbon and opal based on the ²³⁴Th/²³⁸U disequilibrium method, (b) particle data from underwater vision profilers (UVP), and (c) net primary productivity estimates. These data sets enable us to compare sinking carbon and opal fluxes between years and between different phytoplankton communities (Phaeocystis versus diatoms) and provide observational constraints on the efficiency of the biological carbon pump in this region.