High-resolution spatial and temporal measurements of particulate organic carbon flux using thorium-234 in the northeast Pacific Ocean during the export processes in the ocean from remote sensing field campaign
Buesseler, Ken (Woods Hole Oceanographic Institution. Department of Marine Chemistry & Geochemistry)
Benitez-Nelson, Claudia (University of South Carolina)
Roca Martí, Montserrat (Woods Hole Oceanographic Institution. Department of Marine Chemistry & Geochemistry)
Wyatt, Abigale M. (Princeton University. Department of Geosciences)
Resplandy, Laure (Princeton University. Department of Geosciences)
Clevenger, Samantha J. (Woods Hole Oceanographic Institution. Department of Marine Chemistry & Geochemistry)
Drysdale, Jessica A. (Woods Hole Oceanographic Institution. Department of Marine Chemistry & Geochemistry)
Estapa, Margaret L. (Skidmore College. Geosciences Department)
Pike, Steven (Woods Hole Oceanographic Institution. Department of Marine Chemistry & Geochemistry)
Umhau, Blaire P. (University of South Carolina)

Data:	2020
Resum:	The EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) program of National Aeronautics and Space Administration focuses on linking remotely sensed properties from satellites to the mechanisms that control the transfer of carbon from surface waters to depth. Here, the naturally occurring radionuclide thorium-234 was used as a tracer of sinking particle flux. More than 950 234Th measurements were made during August-September 2018 at Ocean Station Papa in the northeast Pacific Ocean. High-resolution vertical sampling enabled observations of the spatial and temporal evolution of particle flux in Lagrangian fashion. Thorium-234 profiles were remarkably consistent, with steady-state (SS) 234Th fluxes reaching 1,450 + 300 dpm m-2 d-1 at 100 m. Nonetheless, 234Th increased by 6%-10% in the upper 60 m during the cruise, leading to consideration of a non-steady-state (NSS) model and/or horizontal transport, with NSS having the largest impact by decreasing SS 234Th fluxes by 30%. Below 100 m, NSS and SS models overlapped. Particulate organic carbon (POC)/234Th ratios decreased with depth in small (1-5 mm) and mid-sized (5-51 mm) particles, while large particle (>51 mm) ratios remained relatively constant, likely influenced by swimmer contamination. Using an average SS and NSS 234Th flux and the POC/234Th ratio of mid-sized particles, we determined a best estimate of POC flux. Maximum POC flux was 5. 5 + 1. 7 mmol C m-2 d-1 at 50 m, decreasing by 70% at the base of the primary production zone (117 m). These results support earlier studies that this site is characterized by a modest biological carbon pump, with an export efficiency of 13% + 5% (POC flux/net primary production at 120 m) and 39% flux attenuation in the subsequent 100 m (POC flux 220 m/POC flux 120m). This work sets the foundation for understanding controls on the biological carbon pump during this EXPORTS campaign.
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Biological carbon pump ; EXPORTS ; Ocean Station Papa ; Particulate organic carbon flux ; Thorium-234
Publicat a:	Elementa (Washington DC), Vol. 8, Issue 1 (December 2020) , art. 030, ISSN 2325-1026

DOI: 10.1525/elementa.2020.030

19 p, 1.2 MB

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