Investigating Particle Size-Flux Relationships and the Biological Pump Across a Range of Plankton Ecosystem States From Coastal to Oligotrophic Christian Fender, Thomas Kelly, Lionel Guidi, Mark Ohman, Matthew Smith, Michael Stukel To cite this version: Christian Fender, Thomas Kelly, Lionel Guidi, Mark Ohman, Matthew Smith, et al.. Investigat- ing Particle Size-Flux Relationships and the Biological Pump Across a Range of Plankton Ecosys- tem States From Coastal to Oligotrophic. Frontiers in Marine Science, Frontiers Media, 2019, 6, 10.3389/fmars.2019.00603. hal-02386832 HAL Id: hal-02386832 https://hal.archives-ouvertes.fr/hal-02386832 Submitted on 8 Jan 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution - NonCommercial| 4.0 International License fmars-06-00603 September 30, 2019 Time: 12:9 # 1 ORIGINAL RESEARCH published: 01 October 2019 doi: 10.3389/fmars.2019.00603 Investigating Particle Size-Flux Relationships and the Biological Pump Across a Range of Plankton Ecosystem States From Coastal to Oligotrophic Christian K. Fender1*, Thomas B. Kelly1,2, Lionel Guidi3, Mark D. Ohman4, Matthew C. Smith1 and Michael R. Stukel1,2 1 Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL, United States, 2 Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL, United States, 3 Observatoire Océanologique, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, Villefranche-sur-Mer, France, Edited by: 4 Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA, United States Andrew M. P. McDonnell, University of Alaska Fairbanks, United States Sinking particles transport organic carbon produced in the surface ocean to the ocean Reviewed by: interior, leading to net storage of atmospheric CO2 in the deep ocean. The rapid growth Morten Hvitfeldt Iversen, of in situ imaging technology has the potential to revolutionize our understanding of Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research particle flux attenuation in the ocean; however, estimating particle flux from particle size (AWI), Germany and abundance (measured directly by in situ cameras) is challenging. Sinking rates are Colleen Andrea Durkin, dependent on several factors, including particle excess density and porosity, which vary Moss Landing Marine Laboratories, United States based on particle origin and type. Additionally, particle characteristics are transformed *Correspondence: while sinking. We compare optically measured particle size spectra profiles (Underwater Christian K. Fender Vision Profiler 5, UVP) with contemporaneous measurements of particle flux made [email protected] using sediment traps and 234Th:238U disequilibrium on six process cruises from the Specialty section: California Current Ecosystem (CCE) LTER Program. These measurements allow us to This article was submitted to assess the efficacy of size-flux relationships for estimating fluxes from optical particle Marine Biogeochemistry, a section of the journal size measurements. We find that previously published parameterizations that estimate Frontiers in Marine Science carbon flux from UVP profiles are a poor fit to direct flux measurements in the CCE. Received: 29 March 2019 This discrepancy is found to result primarily from the important role of fecal pellets in Accepted: 11 September 2019 particle flux. These pellets are primarily in a size range (i.e., 100–400 mm) that is not Published: 01 October 2019 well-resolved as images by the UVP due to the resolution of the sensor. We develop Citation: Fender CK, Kelly TB, Guidi L, new, CCE-optimized parameters for use in an algorithm estimating carbon flux from UVP x Ohman MD, Smith MC and P B Stukel MR (2019) Investigating data in the southern California Current (Flux = niAdi 1di), with A = 15.4, B = 1.05, D Particle Size-Flux Relationships i 1 −2 −1 and the Biological Pump Across d = particle diameter (mm) and Flux in units of mg C m d . We caution, however, that a Range of Plankton Ecosystem increased accuracy in flux estimates derived from optical instruments will require devices States From Coastal to Oligotrophic. Front. Mar. Sci. 6:603. with greater resolution, the ability to differentiate fecal pellets from low porosity marine doi: 10.3389/fmars.2019.00603 snow aggregates, and improved sampling of rapidly sinking fecal pellets. We also find Frontiers in Marine Science| www.frontiersin.org 1 October 2019| Volume 6| Article 603 fmars-06-00603 September 30, 2019 Time: 12:9 # 2 Fender et al. Investigating Particle Size-Flux Relationships that the particle size-flux relationships may be different within the euphotic zone than in the shallow twilight zone and hypothesize that the changing nature of sinking particles with depth must be considered when investigating the remineralization length scale of sinking particles in the ocean. Keywords: carbon export, optical imaging, biological carbon pump, California Current, export production, particulate organic carbon, fecal pellet, biogeochemistry INTRODUCTION require a substantial ship-time investment, because they typically require that a large research vessel remain in the vicinity of Each year, approximately 40–50 Pg of carbon dioxide (CO2) deployment for a period of days. This substantial cost has is fixed into organic matter in the ocean via photosynthesis limited such time-series to only a few oceanic regions (Church (Le Quéré et al., 2018). The majority of this fixed carbon fuels the et al., 2013; Lomas et al., 2013). Large, conical time-series surface ecosystem and is quickly respired back into CO2, which traps, by contrast, offer an affordable approach to quantifying then equilibrates with the atmosphere. A small fraction of the annual fluxes in the deep ocean (Honjo et al., 2008), but organic matter produced by primary productivity escapes the may exhibit extreme biases when deployed at shallow depths euphotic zone and is transported to depth, primarily as sinking (Buesseler et al., 2010). particles (Ducklow et al., 2001; Siegel et al., 2016). This process, Clearly additional approaches are necessary in order to known as the biological carbon pump (BCP), isolates carbon measure interannual variability in the global magnitude of from the atmosphere for decades to centuries (Volk and Hoffert, the BCP. Radionuclide disequilibrium techniques (especially 1985), and is estimated to transport between 5 and 13 Pg C from 238U-234Th) provide one approach that requires substantially less the euphotic zone each year (Henson et al., 2011; Laws et al., ship-time investment (Buesseler et al., 1995; Van der Loeff et al., 2011; Siegel et al., 2014). Since marine photosynthesis accounts 2006; Waples et al., 2006). These methods exploit differences for about half of global photosynthesis (Field et al., 1998), the in activity between a conservative parent radionuclide and a BCP is a key component in determining global and regional particle-reactive, shorter-lived daughter isotope (Cochran et al., carbon budgets, which in turn are important for understanding 2006; Waples et al., 2006). When the daughter particle is climate change and for predicting environmental changes in removed from the surface ocean through scavenging onto sinking future climate scenarios. Unfortunately, due to the numerous particles a disequilibrium between parent and daughter is created. and complex processes that contribute to and influence the Measurement of this disequilibrium provides an estimate of BCP, predicting its responses to climate change remains difficult radionuclide flux during a period of time related to the half- (Passow and Carlson, 2012; Boyd, 2015; Burd et al., 2016). life of the daughter particle (Savoye et al., 2006). Radionuclide The BCP is comprised of a suite of processes including approaches are a powerful tool, because they measure a property active transport by vertically migrating zooplankton and nekton (disequilibrium) that is directly created via particle flux and (Steinberg et al., 2000; Hannides et al., 2009; Stukel et al., measurements can typically be made from a single CTD-Niskin 2013; Davison et al., 2015; Kelly et al., 2019), subduction of rosette cast (Benitez-Nelson et al., 2001). However, substantial refractory dissolved organic carbon (Carlson et al., 1994; Hansell uncertainty can be introduced into carbon flux estimates et al., 1997), and subduction of particulate organic matter (Levy from radionuclide disequilibrium due to high variability in et al., 2013; Omand et al., 2015; Stukel and Ducklow, 2017; carbon:radionuclide ratios over even relatively small distances Llort et al., 2018), in addition to the flux of sinking particles (Buesseler et al., 2006; Hung and Gong, 2010; Stukel and Kelly, (Martin et al., 1987; Buesseler and Boyd, 2009). However, sinking 2019). Furthermore, radionuclide disequilibrium approaches are particles are typically assumed to dominate vertical flux relative to a moderately costly and time-intensive approach (at sea and these other pathways