Award: OCE-1851224

This project aimed to combine continuous underwater autonomous glider observations and monthly ship-based water sampling to 1) generate high resolution records of changes in the biological processes that contribute to carbon export fluxes from the surface waters of the Sargasso Sea to deeper waters and sediments, and 2) understand the chemical and physical processes that regulate these changes. This project has been conducted in close association with the multi-decadal BATS (Bermuda Atlantic Time-series Study), and also leveraged resources tied to the BIOS-SCOPE program privately supported campaign, in conjunction with BIOS (Bermuda Institute of Ocean Sciences), to better understand the role of microbes and zooplankton in the biological carbon pump (i.e. the removal of biological processes in sequestering carbon from the surface waters to deeper waters and sediments) in our study region. Our results to date, have provided a detailed account of net oxygen production and nitrate supply over annual cycles, including the contributions from various physical processes (e.g. entrainment, diffusion, and air-sea exchanges). Annual net community production (ANCP), estimated from changes in oxygen and converted to carbon equivalents, amounts to net primary production in the Sargasso Sea of 30 g C m-2; this was calculated based on an estimate of 105 g C m-2in the euphotic zone (the sunlit layer of the ocean where photosynthesis occurs) minus 75 g C m-2(carbon respired and remineralized) in the aphotic zone down to the base of the winter mixed layer. One very exciting outcome of this project was the observation that spring-time Salp (a group of zooplankton) blooms were a cause of biologically-induced turbulent mixing, resulting nutrients being mixed into the euphotic zone where photosynthesis occurs. This phenomenon was observed in two separate years (2021 and 2023), and appears to be an important source of net primary production during the stratified period when nutrients would not normally be actively mixed into the euphotic zone. The implications of these observations is quite profound, because it provides an additional mechanism for delivering nutrients from deeper depths to the euphotic zone where these new nutrients can fuel primary production. This boost to primary production can then lead to increased carbon sequestration to deeper waters and sediments. Based on the results from this project, the PIs have five manuscripts in various stages of preparation: Curry, R., M. Lomas, D. Grundle, J. Chapman and M. Sullivan. Annual net community production the Sargasso Sea from autonomous underwater glider observations. Targeted forBiogeochemical Cycles. Curry, R., J. Chapman, R. Lueck, L. Blanco-Bercial, H. Gossner, M. Lomas. D. Grundle. Turbulent mixing by salps affects the Sargasso Sea water column and biological carbon pump. Targeted forNature. Vertical diffusivity profiles in the central Sargasso Sea: glider-based observation vs. parameterized values. Note: Complete author list and targeted journal to be determined. Glider chlorophyll and backscatter relationships to phytoplankton biomass measured by flow cytometry. Note: Complete author list and targeted journal to be determined. Grundle, D., R. Hamme, O. Tognotti, R. Bakker, M. Lomas, R. Curry. Quantifying net community production and subsurface variability at the Bermuda Atlantic Time-series Study using oxygen/argon approaches. Note: A sub-set of the results for this manuscript will be presented at the 2024 Ocean Sciences Meeting. Last Modified: 12/11/2023 Submitted by: DamianSGrundle