Observations of carbon export by small sinking particles in the upper mesopelagic

Durkin, Colleen A.; Estapa, Margaret L.; Buesseler, Ken O.

doi:10.1016/j.marchem.2015.02.011

Cited by 106 publications

(143 citation statements)

References 40 publications

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“…On the global scale, the relative contribution of small POC rises from almost 0 in the noRC experiment to about 20 % in the RC experiment. This significant contribution of small, slowly sinking particles to the export of carbon in the interior of the ocean is supported by recent observations (Durkin et al, 2015). The export at 2000 m, about 0.8 PgC year −1 , is overestimated relative to recent estimates by Henson et al (2012b) and Guidi et al (2015) of, respectively, 0.45 and 0.33 PgC year −1 .…”

Section: Concentrations Of Pocsupporting

confidence: 67%

Variable reactivity of particulate organic matter in a global ocean biogeochemical model

et al. 2017

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Abstract. The marine biological carbon pump is dominated by the vertical transfer of particulate organic carbon (POC) from the surface ocean to its interior. The efficiency of this transfer plays an important role in controlling the amount of atmospheric carbon that is sequestered in the ocean. Furthermore, the abundance and composition of POC is critical for the removal of numerous trace elements by scavenging, a number of which, such as iron, are essential for the growth of marine organisms, including phytoplankton. Observations and laboratory experiments have shown that POC is composed of numerous organic compounds that can have very different reactivities. However, this variable reactivity of POC has never been extensively considered, especially in modelling studies. Here, we introduced in the global ocean biogeochemical model NEMO-PISCES a description of the variable composition of POC based on the theoretical reactivity continuum model proposed by Boudreau and Ruddick (1991). Our model experiments show that accounting for a variable lability of POC increases POC concentrations in the ocean's interior by 1 to 2 orders of magnitude. This increase is mainly the consequence of a better preservation of small particles that sink slowly from the surface. Comparison with observations is significantly improved both in abundance and in size distribution. Furthermore, the amount of carbon that reaches the sediments is increased by more than a factor of 2, which is in better agreement with global estimates of the sediment oxygen demand. The impact on the major macronutrients (nitrate and phosphate) remains modest. However, iron (Fe) distribution is strongly altered, especially in the upper mesopelagic zone as a result of more intense scavenging: vertical gradients in Fe are milder in the upper ocean, which appears to be closer to observations. Thus, our study shows that the variable lability of POC can play a critical role in the marine biogeochemical cycles which advocates for more dedicated in situ and laboratory experiments.

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Section: Concentrations Of Pocsupporting

confidence: 67%

Variable reactivity of particulate organic matter in a global ocean biogeochemical model

et al. 2017

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“…While we do not yet know if a summer export pulse was recorded during our study period, our data indicate that either extremely high export ratios would be required to fuel the observed magnitude of summer export pulses or the abundance and activity of large diazotrophs would need to be significantly greater than observed in this study. Further study of diazotroph abundances in conjunction with cell-specific rate measurements and imaging based records of cell export (e.g., Durkin et al, 2015) in this region is necessary to elucidate the linkages between growth and community structure of diazotrophs in the surface ocean and their relative contributions to particle export.…”

Section: Discussionmentioning

confidence: 99%

Temporal Variability of Trichodesmium spp. and Diatom-Diazotroph Assemblages in the North Pacific Subtropical Gyre

2018

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In oligotrophic ocean regions such as the North Pacific Subtropical Gyre (NPSG), N 2 fixation (i.e., diazotrophy) by a diverse consortium of microorganisms has been shown to contribute significantly to new production and particle export. In 2015 and 2016, we measured near-monthly abundances of the large cell-sized (> 10 µm) diazotrophic genera Trichodesmium and diatom-associated Richelia and Calothrix spp. in the NPSG via microscopy and quantitative PCR of nifH genes. Of these genera, we find Trichodesmium to be the more abundant over our study period, with cell concentrations in the upper water column (0-45 m) ranging from 1 to 5,988 cells L −1 , while the sum of Richelia and Calothrix spp. abundances ranged from 4 to 157 heterocysts L −1 . Significant discrepancies between absolute abundances were noted between cell and gene-based approaches to biomass determination (nifH copies L −1 were up to 10 2 -10 3 higher than cell concentrations). Potential explanations for these striking discrepancies are discussed. Using the maximum N fixation rates per cell found in the existing literature for these genera, we estimate potential N 2 fixation rates via these large diazotroph communities to be between 0.01 and 1.5 nmol N L −1 d −1 . When comparing these rates to available 15 N 2 tracer measurements, we conclude that large diazotrophs were generally minor (<10%) contributors to bulk N 2 fixation in the surface ocean during our study period. Conversely, high concentrations of Trichodesmium observed in fall-winter of 2015 and 2016 were estimated to drive >50% of measured N 2 fixation rates. While these large cell-sized and heterogeneously distributed organisms may still disproportionately contribute to export, cell-abundance based rate estimates suggests that other diazotrophs are largely responsible for N 2 fixation rates measured in bottle-based incubations.

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“…Recent sediment trap work has suggested that smaller, slow sinking particles could contribute to the overall flux in oligotrophic regions (Durkin et al, 2015;Hung et al, 2012;Puigcorbé et al, 2015). A previous study in the northwestern Pacific also showed elevated Mn in subsurface traps that could have resulted from small, slow sinking…”

Section: On the Use Of Large Versus Small Particle E: 234 Thmentioning

confidence: 95%

An investigation of basin-scale controls on upper ocean export and remineralization

Black¹

2018

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The biological carbon pump (BCP) helps to moderate atmospheric carbon dioxide levels by bringing carbon to the deep ocean, where it can be sequestered on timescales of centuries to millennia. Climate change is predicted to decrease the efficiency of the global BCP, however, the magnitude and timescale of this shift is largely uncertain and will likely impact some areas of the global ocean more significantly than others. Therefore, it is imperative that we (1) accurately quantify surface export and remineralization of particulate organic carbon (POC) via the BCP over large regions of the global ocean, (2) examine the factors controlling these POC fluxes and their variability, which includes the cycling of biologically-relevant trace metals, and (3) establish if and how the BCP is changing over time.This thesis focuses on addressing various aspects of these objectives using the 234 Th-238 U method across basin-scale GEOTRACES transects. First, the export and remineralization of POC were examined across large gradients in productivity, upwelling, community structure, and dissolved oxygen in the southeastern tropical Pacific Ocean. Although low oxygen zones are traditionally thought to have decreased POC flux attenuation relative to other regions of the global ocean and the low oxygen Pacific locations followed this pattern, regions that were functionally anoxic had enhanced attenuation in the upper 400 m. Second, trace metal export and remineralization were quantified across the Pacific transect. Because many trace metals are necessary for the metabolic functions of marine organisms and can co-limit marine productivity, the controls on the cycling of trace metals in the upper ocean were examined. Lastly, POC export was determined across two transects in the Western Arctic Ocean, where light and nutrient availability drive the biological pump. Upper ocean export estimates in the central basin did not reflect a substantial change in the biological pump compared to studies from the last three decades, however, an extensive maximum in 234 Th relative to 238 U deeper in the water column indicated that rapid vertical transport had occurred, which could suggest a more efficient biological pump in the Arctic Ocean.

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Observations of carbon export by small sinking particles in the upper mesopelagic

Cited by 106 publications

References 40 publications

Variable reactivity of particulate organic matter in a global ocean biogeochemical model

Variable reactivity of particulate organic matter in a global ocean biogeochemical model

Temporal Variability of Trichodesmium spp. and Diatom-Diazotroph Assemblages in the North Pacific Subtropical Gyre

An investigation of basin-scale controls on upper ocean export and remineralization

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