This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1016/j.pocean.2023.103170. This is version 1 of this Preprint.
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This manuscript presents an overview of NASA’s EXport Processes in the Ocean from Remote Sensing 2021 Field Campaign in the North Atlantic (EXPORTS NA) and provides quantitative and dynamical descriptions of the physical processes modulating water transformations during the study. A major programmatic goal was to conduct the sampling in a Lagrangian mode so that ocean ecological and biogeochemical changes can be observed independent from physical advective processes. To accomplish this goal, EXPORTS NA conducted a multi-ship, multi-asset field sampling program within a retentive, anticyclonic mode water eddy. Beneath depths of ~100 m, Lagrangian sampling assets remained within the eddy core waters (ECWs) throughout the experiment, demonstrating that the ECWs within the mode water eddy were retentive. However, strong westerly winds from four storm events deepened the mixed layer (ML) of the surface core waters (SCWs) above the eddy’s mode water core by 25-40 m and exchanged some of the SCWs with surface waters outside of the eddy via Ekman transport. Estimates of flushing times ranged from 5-8 days, with surface exchange fractions ranging from 20-75% and were consistent with particle tracking advected by combined geostrophic and Ekman velocities. The relative contributions of horizontal and vertical advection on changes in SCW tracers depend on the horizontal and vertical gradients of that tracer. For example, in the surface waters, horizontal advection played a large role in salinity fluxes, yet vertical entrainment played a larger role in the fluxes of nutrients into the ML. Each storm injected nutrients and low oxygen waters into the ML, after which the surface ocean ecosystem responded by reducing nutrient concentrations and increasing %O2 saturation levels. Overall, SCW values of chlorophyll and POC were the largest at the onset of the field program and decreased throughout the campaign. The analysis presented provides a physical oceanographic context for the many measurements made during the EXPORTS NA field campaign. Illustrated are the many challenges of conducting a production-flux experiment even in a Lagrangian frame and the inherent uncertainties of interpreting biological carbon pump observations that were collected in a Eulerian frame of reference.
Biogeochemistry, Oceanography and Atmospheric Sciences and Meteorology
Carbon Export, North Atlantic Bloom, Phytoplanton bloom, Ocean Physics, Eddy Dynamics
Published: 2023-06-07 04:15
Conflict of interest statement:
Data Availability (Reason not available):
All NASA funded EXPORTS data is being archived at NASA’s SeaWiFS Bio-optical Archive and Storage System (SeaBASS) under the EXPORTS Experiment (DOI: 10.5067/SeaBASS/EXPORTS/DATA001). All CTD and nutrient data can be found under Principal Investigator (PI) Norman Nelson, Lagrangian Float data under PI Eric D’Asaro, Glider data under PI Craig Lee. A curated dataset with all the data used for this manuscript was submitted to PANGEA and is being processed. BGC Argo floats data is publicly available at https://biogeochemical-argo.org/data-access.ph.