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  • 1
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Roca-Marti, M., Benitez-Nelson, C. R., Umhau, B. P., Wyatt, A. M., Clevenger, S. J., Pike, S., Horner, T. J., Estapa, M. L., Resplandy, L., & Buesseler, K. O. Concentrations, ratios, and sinking fluxes of major bioelements at Ocean Station Papa. Elementa: Science of the Anthropocene, 9(1), (2021): 00166, https://doi.org/10.1525/elementa.2020.00166.
    Description: Fluxes of major bioelements associated with sinking particles were quantified in late summer 2018 as part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign near Ocean Station Papa in the subarctic northeast Pacific. The thorium-234 method was used in conjunction with size-fractionated (1–5, 5–51, and 〉51 μm) concentrations of particulate nitrogen (PN), total particulate phosphorus (TPP), biogenic silica (bSi), and particulate inorganic carbon (PIC) collected using large volume filtration via in situ pumps. We build upon recent work quantifying POC fluxes during EXPORTS. Similar remineralization length scales were observed for both POC and PN across all particle size classes from depths of 50–500 m. Unlike bSi and PIC, the soft tissue–associated POC, PN, and TPP fluxes strongly attenuated from 50 m to the base of the euphotic zone (approximately 120 m). Cruise-average thorium-234-derived fluxes (mmol m–2 d–1) at 120 m were 1.7 ± 0.6 for POC, 0.22 ± 0.07 for PN, 0.019 ± 0.007 for TPP, 0.69 ± 0.26 for bSi, and 0.055 ± 0.022 for PIC. These bioelement fluxes were similar to previous observations at this site, with the exception of PIC, which was 1 to 2 orders of magnitude lower. Transfer efficiencies within the upper twilight zone (flux 220 m/flux 120 m) were highest for PIC (84%) and bSi (79%), followed by POC (61%), PN (58%), and TPP (49%). These differences indicate preferential remineralization of TPP relative to POC or PN and larger losses of soft tissue relative to biominerals in sinking particles below the euphotic zone. Comprehensive characterization of the particulate bioelement fluxes obtained here will support future efforts linking phytoplankton community composition and food-web dynamics to the composition, magnitude, and attenuation of material that sinks to deeper waters.
    Description: The authors would like to acknowledge support from the National Aeronautics and Space Administration as part of the EXport Processes in the Ocean from RemoTe Sensing program awards 80NSSC17K0555 and 80NSSC17K0662. They also acknowledge the funding from the Woods Hole Oceanographic Institution’s Ocean Twilight Zone study for MRM and KOB, the National Science Foundation Graduate Research Fellowship Program for AMW, and the Ocean Frontier Institute for MRM.
    Keywords: Biological pump ; Bioelements ; Particulate fluxes ; Transfer efficiency ; Size-fractionated particles ; EXPORTS
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Siegel, D. A., Cetinic, I., Graff, J. R., Lee, C. M., Nelson, N., Perry, M. J., Ramos, I. S., Steinberg, D. K., Buesseler, K., Hamme, R., Fassbender, A. J., Nicholson, D., Omand, M. M., Robert, M., Thompson, A., Amaral, V., Behrenfeld, M., Benitez-Nelson, C., Bisson, K., Boss, E., Boyd, P. W., Brzezinski, M., Buck, K., Burd, A., Burns, S., Caprara, S., Carlson, C., Cassar, N., Close, H. H., D’Asaro, E., Durkin, C., Erickson, Z., Estapa, M. L., Fields, E., Fox, J., Freeman, S., Gifford, S., Gong, W., Gray, D., Guidi, L., Haëntjens, N., Halsey, K., Huot, Y., Hansell, D., Jenkins, B., Karp-Boss, L., Kramer, S., Lam, P., Lee, J-M., Maas, A., Marchal, O., Marchetti, A., McDonnell, A., McNair, H., Menden-Deuer, S., Morison, F., Niebergall, A. K., Passow, U., Popp, B., Potvin, G., Resplandy, L., Roca-Martí, M., Roesler, C., Rynearson, T., Traylor, S., Santoro, A., Seraphin, K. D., Sosik, H. M., Stamieszkin, K., Stephens, B., Tang, W., Van Mooy, B., Xiong, Y., Zhang, X. An operational overview of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) Northeast Pacific field deployment. Elementa: Science of the Anthropocene, 9(1), (2021): 1, https://doi.org/10.1525/elementa.2020.00107.
    Description: The goal of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign is to develop a predictive understanding of the export, fate, and carbon cycle impacts of global ocean net primary production. To accomplish this goal, observations of export flux pathways, plankton community composition, food web processes, and optical, physical, and biogeochemical (BGC) properties are needed over a range of ecosystem states. Here we introduce the first EXPORTS field deployment to Ocean Station Papa in the Northeast Pacific Ocean during summer of 2018, providing context for other papers in this special collection. The experiment was conducted with two ships: a Process Ship, focused on ecological rates, BGC fluxes, temporal changes in food web, and BGC and optical properties, that followed an instrumented Lagrangian float; and a Survey Ship that sampled BGC and optical properties in spatial patterns around the Process Ship. An array of autonomous underwater assets provided measurements over a range of spatial and temporal scales, and partnering programs and remote sensing observations provided additional observational context. The oceanographic setting was typical of late-summer conditions at Ocean Station Papa: a shallow mixed layer, strong vertical and weak horizontal gradients in hydrographic properties, sluggish sub-inertial currents, elevated macronutrient concentrations and low phytoplankton abundances. Although nutrient concentrations were consistent with previous observations, mixed layer chlorophyll was lower than typically observed, resulting in a deeper euphotic zone. Analyses of surface layer temperature and salinity found three distinct surface water types, allowing for diagnosis of whether observed changes were spatial or temporal. The 2018 EXPORTS field deployment is among the most comprehensive biological pump studies ever conducted. A second deployment to the North Atlantic Ocean occurred in spring 2021, which will be followed by focused work on data synthesis and modeling using the entire EXPORTS data set.
    Description: DAS, NN, KB, EF, SK, AB, AM, UP: NASA 80NSSC17K0692. MJB, EB, JG, LG, KH, LKB, JF, NH: NASA 80NSSC17K0568. KB, CBN, LR, MRM: NASA 80NSSC17K0555. CC, DH, BS: NASA 80NSSC18K0437. HC: NSF 1830016. BP, KDS: NSF 1829425. ME, KB, CD, MO: NASA 80NSSC17K0662. AF: NSF 1756932. BJ, KB, MB, SB, SC: NSF 1756442. PH, OM, JML: NSF 1829614. CL, ED, DN, MO, MJP, AT, ZN, ST: NASA 80NSSC17K0663. AM, NC, SG, WT, AN, WG: NASA 80NSSC17K0552. SMD, TR, HM, FM: NASA 80NSSC17K0716. CR, HS: NASA 80NSSC17K0700. AS, PB: NASA 80NSSC18K1431. DS, AM, KS NASA 80NSSC17K0654. BVM: NSF 1756254. XZ, DG, LG, YH: NASA 80NSSC17K0656 and 80NSSC20K0350.
    Keywords: Biological pump ; NASA field campaign ; NPP fates ; Carbon cycle ; Organic carbon export ; Export pathways
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Estapa, M., Buesseler, K., Durkin, C. A., Omand, M., Benitez-Nelson, C. R., Roca-Marti, M., Breves, E., Kelly, R. P., & Pike, S. Biogenic sinking particle fluxes and sediment trap collection efficiency at Ocean Station Papa. Elementa: Science of the Anthropocene, 9(1), (2021): 00122, https://doi.org/10.1525/elementa.2020.00122.
    Description: Comprehensive field observations characterizing the biological carbon pump (BCP) provide the foundation needed to constrain mechanistic models of downward particulate organic carbon (POC) flux in the ocean. Sediment traps were deployed three times during the EXport Processes in the Ocean from RemoTe Sensing campaign at Ocean Station Papa in August–September 2018. We propose a new method to correct sediment trap sample contamination by zooplankton “swimmers.” We consider the advantages of polyacrylamide gel collectors to constrain swimmer influence and estimate the magnitude of possible trap biases. Measured sediment trap fluxes of thorium-234 are compared to water column measurements to assess trap performance and estimate the possible magnitude of fluxes by vertically migrating zooplankton that bypassed traps. We found generally low fluxes of sinking POC (1.38 ± 0.77 mmol C m–2 d–1 at 100 m, n = 9) that included high and variable contributions by rare, large particles. Sinking particle sizes generally decreased between 100 and 335 m. Measured 234Th fluxes were smaller than water column 234Th fluxes by a factor of approximately 3. Much of this difference was consistent with trap undersampling of both small (〈32 μm) and rare, large particles (〉1 mm) and with zooplankton active migrant fluxes. The fraction of net primary production exported below the euphotic zone (0.1% light level; Ez-ratio = 0.10 ± 0.06; ratio uncertainties are propagated from measurements with n = 7–9) was consistent with prior, late summer studies at Station P, as was the fraction of material exported to 100 m below the base of the euphotic zone (T100, 0.55 ± 0.35). While both the Ez-ratio and T100 parameters varied weekly, their product, which we interpret as overall BCP efficiency, was remarkably stable (0.055 ± 0.010), suggesting a tight coupling between production and recycling at Station P.
    Description: The authors would like to acknowledge funding support from the NASA EXPORTS program (Award 80NSSC17K0662) for all sediment trap data presented here. Net primary production data collection was supported by EXPORTS (Award 80NSSC17K568) to Oregon State University. Thorium data collection was supported by EXPORTS (Award 80NSSC17K0555) to KB, CRBN, and L. Resplandy.
    Keywords: Biological carbon pump ; Ocean Station Papa ; Sediment traps ; Carbon flux ; Particle size distribution ; Swimmers
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Buesseler, K. O., Benitez-Nelson, C. R., Roca-Marti, M., Wyatt, A. M., Resplandy, L., Clevenger, S. J., Drysdale, J. A., Estapa, M. L., Pike, S., & Umhau, B. P. 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. Elementa: Science of the Anthropocene, 8(1), (2020): 030, https://doi.org/10.1525/elementa.030.
    Description: 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 μm) and mid-sized (5–51 μm) particles, while large particle (〉51 μm) 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.
    Description: The authors would like to acknowledge support from the National Aeronautics and Space Administration (NASA) as part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) program awards 80NSSC17K0555 and 80NSSC17K0662; the Woods Hole Oceanographic Institution’s Ocean Twilight Zone study for KOB and MRM, and the National Science Foundation Graduate Research Fellowship Program (NSF-GRFP) for funding and support of AW.
    Keywords: Thorium-234 ; Ocean Station Papa ; Particulate organic carbon flux ; EXPORTS ; Biological carbon pump
    Repository Name: Woods Hole Open Access Server
    Type: Article
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