The biological carbon pump (BCP) is principally mediated by the sinking of particulate organic carbon (POC) from the upper ocean to depth and varies strongly across regions and time. Here we present results from the most comprehensive study to quantify the BCP efficiency in the Labrador Sea to date. The Labrador Sea is a globally significant region for deep-water formation, playing a critical role in biogeochemical cycles. Field work was conducted in the Eastern Labrador Sea during a Phaeocystis bloom for a 15-day period in May-June 2022 capturing the bloom to senescence period of production. POC export fluxes are quantified using high vertical and spatial resolution measurements of Th-234 in the upper 500 m of the water column (15 depths, 15 stations), combined with the collection of particles obtained using large volume filtration pumps and marine snow catchers. POC flux estimates are used along with net primary production (NPP) rates to quantify the magnitude of POC export at the base of the euphotic zone relative to NPP (export efficiency), and the efficiency by which POC fluxes are transferred throughout the upper twilight zone (transfer efficiency). These assessments allow us to quantify the efficiency of the BCP in the Labrador Sea, put it into context of other oceanic regions, and better understand the impact of Phaeocystis blooms on POC export. This study will enhance our understanding of the BCP in the Labrador Sea and, in turn, improve future predictions of carbon cycling in the Northwest Atlantic and beyond. 

Primary Presenter: Montserrat Roca-Martí, Universitat Autònoma de Barcelona (montserrat.roca.marti@uab.cat)

Authors:

Montserrat Roca-Martí, Universitat Autònoma de Barcelona  (Montserrat.Roca.Marti@uab.cat)

Madeline Healey, Dalhousie University  (mhealey@dal.ca)

Rachel Sipler, Bigelow Laboratory for Ocean Sciences  (rsipler@bigelow.org)

Colleen McBride, Memorial University  (cemcbride@mun.ca)

Elisa Romanelli, University of California Santa Barbara  (elisa_romanelli@ucsb.edu)

Carolina Cisternas-Novoa, Memorial University  (acisternasno@mun.ca)

Maria Armstrong, Dalhousie University  (maria.armstrong@dal.ca)

Ken Buesseler, Woods Hole Oceanographic Institution  (kbuesseler@whoi.edu)

Stephanie Kienast, Dalhousie University  (stephanie.kienast@dal.ca)