Multiple controls on carbon dioxide sequestration in the beagle channel (Southern Patagonia) in early fall

12 pages, 8 figures, 1 table.-- Data availability: Data will be made available on request
Subpolar coastal waters are key hotspots in the global carbon cycle. However, the small-scale distribution of partial pressure of carbon dioxide (pCO2) in these environments and the physical and biological controls underlying this variability are still poorly understood. Here, we examine simultaneous high-resolution spatial measurements of wind speed and pCO2, temperature, salinity, and in-vivo chlorophyll-a fluorescence (chl-a fluo, a proxy of phytoplankton biomass) in surface waters that were obtained during an oceanographic survey in the Argentinian Beagle Channel (subantarctic Atlantic Patagonian) in early fall 2017. The 240 km study transect (centered at 55°S - 67°W) was divided into two zones: (A1) The Beagle Channel innermost portion, semi-enclosed and subject to strong continental influence and (A2) its eastern outlet towards the open Southwest Atlantic. Discrete seawater samples were also collected for apparent oxygen utilization (AOU), nutrients and pH measurements. High-resolution spatial measurements revealed the persistence of pCO2 below atmospheric equilibrium, increasing in median (interquartile range 25–75%) from 314 μatm in the inner Beagle Channel (A1) to 348 μatm towards the adjacent open sea (A2). A decrease in atmospheric CO2 sequestration was associated with an increase in water temperature from 9.5 °C to 10.7 °C, salinity from 30.8 to 32.5, and chl-a fluo from 2.24 to 2.91 mg m−3 along the coastal-offshore gradient. Low AOU and nutrient levels were found in regions inside the channel. Indeed, the relationships between CO2 and temperature or salinity were significantly different from those expected from the theoretical solubility effect, indicating a dominance of metabolic over physicochemical controls on this gas. Moreover, physical factors such as vertical stratification contributed to the variable surface pCO2 values. These findings reveal the existence of short-scale spatial variability of CO2 in the Beagle Channel, improving our understanding of the multiple controls on atmospheric carbon sequestration in extensive subpolar continental shelves
We acknowledge support from the Spanish Government through grants CTM2014-56987-P (VA-DE-RETRO Project) and RTI2018-100844-B-C33 (SAGA project) and also recognize the institutional support of the Spanish Government through the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S). This study was funded by grants from the Council for Research and Scientific Development of Brazil (CNPq, 203366/2019-0, 314995/2020-0) and the Research Support Foundation of the State of Rio de Janeiro (E-26/211.329/2021 and E-26/201.118/2022). H.M. and L.C.C. were awarded by CNPq Research Productivity and FAPERJ Scientist of Our State fellowships. L.C.C. was awarded by UERJ/PROCIENCIA fellowship