Assessment of oceanographic conditions during the North Atlantic EXport processes in the ocean from RemoTe sensing (EXPORTS) field campaign

Creators: Johnson, Leah¹; Siegel, David A.²; Thompson, Andrew F.³; Fields, Erik²; Erickson, Zachary K.⁴; Cetinic, Ivona^{5, 6}; Lee, Craig M.¹; D'Asaro, Eric A.¹; Nelson, Norman B.²; Omand, Melissa M.⁷; Sten, Michaela²; Traylor, Shawnee^{8, 9}; Nicholson, David P.⁹; Graff, Jason R.¹⁰; Steinberg, Deborah K.¹¹; Sosik, Heidi M.⁸; Buesseler, Ken O.⁸; Brzezinski, Mark A.²; Ramos, Inia Soto^{6, 7}; Carvalho, Filipa¹²; Henson, Stephanie A.¹²

1. University of Washington
2. University of California, Santa Barbara
3. California Institute of Technology
4. Pacific Marine Environmental Laboratory
5. Goddard Space Flight Center
6. Morgan State University
7. University of Rhode Island
8. Massachusetts Institute of Technology
9. Woods Hole Oceanographic Institution
10. Oregon State University
11. William & Mary
12. National Oceanography Centre

Abstract

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 to 8 days, with surface exchange fractions ranging from 20 to 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 ECW tracers depended on the horizontal and vertical gradients of that tracer. For example, horizontal advection played a large role in ECW salinity fluxes, while vertical entrainment played a larger role in the fluxes of nutrients into SCW 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, ECW 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 while illustrating 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.

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Acknowledgement

The EXPORTS Science Team would like to acknowledge support from the NASA Ocean Biology and Biogeochemistry program and the National Science Foundation Biological and Chemical Oceanography programs. We greatly acknowledge the cooperation, skill and commitment of the Captains, Crews, Research Technicians and Administrative Staffs of the RRS James Cook (JC214), RRS Discovery (DY130 & DY131) and the R/V Sarmiento de Gamboa for making the EXPORTSNA field deployment a reality. Special thanks to Laura Lorenzoni (NASA HQ), Mike Sieracki (formally NSF BIO-OCE), Paula Bontempi (formally NASA HQ), and Quincy Allison and his team (ESPO - NASA AMES) for their vision and support throughout the development and implementation of the EXPORTS NA field campaign. Seaglider piloting, asset tracking and data communication essential for real time sampling strategies were made possible by the work of Geoff Schilling. Technical assistance with Slocum deployment was provided by Marine Autonomous Robotic Systems (NOC). We are grateful for the support of our collaborators from the Natural Environment Research Council (NERC, Porcupine Abyssal Plain – Sustained Observatory).

Funding

The EXPORTS program is funded by the NASA Ocean Biology and Biogeochemistry program with contributions from the U.S. National Science Foundation. In particular, LJ, CML, EAD, AFT, DN, and ST were funded through NASA Grant 80NSSC17K0663. DAS, EF, NBN and MS were funded through NASA Grant 80NSSC17K0692. MO was funded through NASA Grants 80NSSC17K0663 and 80NSSC21K0015. NSF grants OCE1756642 to M.A.B. This is PMEL contribution number 5523.

The NOC glider mission was partially supported by a European Research Council Consolidator grant (GOCART, agreement number 724416) to SH, which also supported the contributions of FC and SH, and IFADO (Innovation in the Framework of the Atlantic Deep Ocean) EAPA_165/2016. All three gliders were deployed during the DY130 cruise, funded by the Natural Environment Research Council (NERC, Porcupine Abyssal Plain – Sustained Observatory) through the Climate Linked Atlantic Sector Science (CLASS) project supported by NERC National Capability funding (NE/R015953/1).

Data Availability

All NASA funded EXPORTS data is being archived at NASA’s SeaWiFS Bio-optical Archive and Storage System (SeaBASS) under the EXPORTS Experiment (10.5067/SeaBASS/EXPORTS/DATA001). Data collected during the EXPORTSNA field expedition onboard the Sarmiento the Gamboa was archived under the OTZ_WHOI experiment (10.5067/SeaBASS/OTZ_WHOI/DATA001) and cruise name SG2105. All CTD and nutrient data can be found under Principal Investigator (PI) Norman Nelson, Lagrangian Float data under PI Eric D’Asaro, and Glider data under PI Craig Lee. A curated dataset with all the data used for this manuscript was archived under the main author’s (SeaBASS investigator) Leah Johnson and experiments (DOI's) EXPORTS and OTZ_WHOI. To access the data in SeaBASS, search for investigator Leah Johnson and download the files and associated documents for each DOI. BGC Argo floats data is publicly available at https://biogeochemical-argo.org/data-access.ph.

Data has been submitted to SeaBass.

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Resource type: Journal Article
Publisher: Elsevier
Published in: Progress in Oceanography, 220, 103170, ISSN: 0079-6611.
Languages: English