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  • 1
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    Global database of surface ocean particulate organic carbon export fluxes diagnosed from the 234Th technique (2013)
    PANGAEA
    In:  Supplement to: Le Moigne, Frédéric A C; Henson, Stephanie A; Sanders, Richard J; Madsen, Esben (2013): Global database of surface ocean particulate organic carbon export fluxes diagnosed from the 234Th technique. Earth System Science Data, 5, 295-304, https://doi.org/10.5194/essd-5-295-2013
    Details
    Publication Date: 2024-04-27
    Description: Through the processes of the biological pump, carbon is exported to the deep ocean in the form of dissolved and particulate organic matter. There are several ways by which downward export fluxes can be estimated. The great attraction of the 234Th technique is that its fundamental operation allows a downward flux rate to be determined from a single water column profile of thorium coupled to an estimate of POC/234Th ratio in sinking matter. We present a database of 723 estimates of organic carbon export from the surface ocean derived from the 234Th technique. Data were collected from tables in papers published between 1985 and 2013 only. We also present sampling dates, publication dates and sampling areas. Most of the open ocean Longhurst provinces are represented by several measurements. However, the Western Pacific, the Atlantic Arctic, South Pacific and the South Indian Ocean are not well represented. There is a variety of integration depths ranging from surface to 220m. Globally the fluxes ranged from -22 to 125 mmol of C/m**2/d. We believe that this database is important for providing new global estimate of the magnitude of the biological carbon pump.
    Keywords: -; Carbon, organic, flux; Comment; DATE/TIME; Date/time end; Day of the year; DEPTH, water; Identification; LATITUDE; LONGITUDE; Primary production of carbon per area, daily; Reference/source; Thorium-234, flux
    Type: Dataset
    Format: text/tab-separated-values, 4621 data points
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    DATA PANGAEA
  • 2
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    On the proportion of ballast versus non-ballast associated carbon export in the surface ocean (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L15610, doi:10.1029/2012GL052980.
    Description: The role of biominerals in driving carbon export from the surface ocean is unclear. We compiled surface particulate organic carbon (POC), and mineral ballast export fluxes from 55 different locations in the Atlantic and Southern Oceans. Substantial surface POC export accompanied by negligible mineral export was recorded implying that association with mineral phases is not a precondition for organic export to occur. The proportion of non-mineral associated sinking POC ranged from 0 to 80% and was highest in areas previously shown to be dominated by diatoms. This is consistent with previous estimates showing that transfer efficiency in such regions is low. However we propose that, rather than the low transfer efficiency arising from diatom blooms being inherently characterized by poorly packaged aggregates which are efficiently exported but which disintegrate readily in mid water, it is due to such environments having very high levels of unballasted organic C export.
    Description: This work is part of the lead author’s doctoral research and was supported by the CalMarO program, (E.U, grant agreement 215157) and by the U.K. Ocean 2025 program.
    Description: 2013-03-11
    Keywords: 234Th ; POC ; Ballast ; Particles export
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
    Format: text/plain
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    PAPER (OA)
  • 3
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    A reduced estimate of the strength of the ocean's biological carbon pump (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L04606, doi:10.1029/2011GL046735.
    Description: A major term in the global carbon cycle is the ocean's biological carbon pump which is dominated by sinking of small organic particles from the surface ocean to its interior. Several different approaches to estimating the magnitude of the pump have been used, yielding a large range of estimates. Here, we use an alternative methodology, a thorium isotope tracer, that provides direct estimates of particulate organic carbon export. A large database of thorium-derived export measurements was compiled and extrapolated to the global scale by correlation with satellite sea surface temperature fields. Our estimates of export efficiency are significantly lower than those derived from the f-ratio, and we estimate global integrated carbon export as ∼5 GtC yr−1, lower than most current estimates. The lack of consensus amongst different methodologies on the strength of the biological carbon pump emphasises that our knowledge of a major planetary carbon flux remains incomplete.
    Keywords: Carbon export ; Thorium-234 ; Satellite data
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: text/plain
    Format: application/pdf
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    PAPER (OA)
  • 4
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    Observations and modeling of slow-sinking particles in the twilight zone (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 28 (11). pp. 1327-1342.
    Details
    Publication Date: 2019-08-06
    Description: The biological carbon pump (BCP) transfers carbon from the surface ocean into the oceans' interior, mainly in the form of sinking particles with an organic component, and thereby keeps atmospheric CO2 at significantly lower levels than if the oceans were abiotic. The depth at which these sinking particles are remineralized is a key control over atmospheric CO2. Particle sinking speed is likely to be a critical parameter over remineralization depth. Carbon export is usually controlled by large, rapidly sinking particles (〉150 m·d−1); however, under some circumstances sinking velocity distributions are strongly bimodal with a significant fraction of total flux being carried by slowly (〈10 m·d−1) sinking particles. Therefore, there is an interest in determining sinking particle velocities and their variations with depth, as well as in understanding the interplay between sinking velocity distributions and carbon export. Here, we use profiles of total and particulate concentrations of the naturally occurring radionuclide pair 210Po-210Pb from the Porcupine Abyssal Plain (PAP) site (48°N, 16.5°W) to estimate depth variation in particle sinking speed using a one-box model and inverse techniques. Average sinking speeds increase from 60 ± 30 m·d−1 at 50 m, to 75 ± 25 m·d−1 and 90 ± 20 m·d−1 at 150 and 500 m. Furthermore, a sensitivity analysis suggests that at the PAP site the measured 210Po profiles are inconsistent with the usually assumed sinking velocities of 200 m·d−1. We hypothesize that a trend of increasing velocity with depth might be caused by a gradual loss of slow-sinking material with depth, a factor with significant implications for regional carbon budgets.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2014GB004981
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Export of organic carbon and biominerals derived from 234Th and 210Po at the Porcupine Abyssal Plain (2013)
    Elsevier
    In:  Deep-Sea Research Part I-Oceanographic Research Papers, 72 . pp. 88-101.
    Details
    Publication Date: 2014-12-08
    Description: The simultaneous estimation of particulate organic carbon (POC), particulate inorganic carbon (PIC) and biogenic silica (BSi) export fluxes is key to the study of carbon export due to the hypothesized role of biominerals in the sinking of organic particles. This paper presents of the first attempts to measure downward fluxes of POC, PIC and BSi from the surface ocean using both the 234Th-238U and the 210Po-210Pb disequilibria and drifting sediments trap synchronously at the Porcupine Abyssal Plain in summer 2009. The combined use of the three techniques allowed us to analyze their suitability not only for POC flux estimates, but also as tracers of PIC and BSi fluxes. POC and biomineral/radionuclide ratios were measured in two size fractions to better understand differences between 234Th derived export and 210Po derived export. 210Po derived POC and biomineral fluxes were unexpectedly closer to POC and biomineral fluxes recorded by sediment traps than 234Th derived POC and biomineral fluxes which were higher than obtained from the other two approaches. We suggest that 210Po, because of its biogeochemical behavior, is a better proxy for POC and mineral fluxes than is 234Th in post bloom conditions. The contribution of smaller (1–53 μm) particles to flux is also considered in order to explain the differences in derived fluxes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.dsr.2012.10.010
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    On the proportion of ballast versus non-ballast associated carbon export in the surface ocean (2012)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 39 (15). n/a-n/a.
    Details
    Publication Date: 2014-12-08
    Description: The role of biominerals in driving carbon export from the surface ocean is unclear. We compiled surface particulate organic carbon (POC), and mineral ballast export fluxes from 55 different locations in the Atlantic and Southern Oceans. Substantial surface POC export accompanied by negligible mineral export was recorded implying that association with mineral phases is not a precondition for organic export to occur. The proportion of non-mineral associated sinking POC ranged from 0 to 80% and was highest in areas previously shown to be dominated by diatoms. This is consistent with previous estimates showing that transfer efficiency in such regions is low. However we propose that, rather than the low transfer efficiency arising from diatom blooms being inherently characterized by poorly packaged aggregates which are efficiently exported but which disintegrate readily in mid water, it is due to such environments having very high levels of unballasted organic C export.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2012GL052980
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    How does dynamical spatial variability impact 234Th-derived estimates of organic export? (2012)
    Elsevier
    In:  Deep-Sea Research Part I-Oceanographic Research Papers, 68 . pp. 24-45.
    Details
    Publication Date: 2014-12-08
    Description: In this study we first evaluate the small-scale spatial variability of particulate export, using a set of synoptic thorium-234 activity observations sampled within a one-degree radius. These data show significant variability of surface thorium activity on scales of the order of 100 km (∼270–550 dpm m−3). This patchiness of export potentially affects the robustness of point observations and our interpretation of them. Motivated by these observations we subsequently couple an explicit model of thorium-234 dynamics to a coupled physical–biogeochemical basin model capable of resolving these small-scales. The model supports the observations in displaying marked thorium variability on spatial scales of the order of 100 km and smaller, with highest values in the regions of large eddy kinetic energy and large primary productivity. The model is also used to quantify the impact of small-scale variability on export estimates. Our model shows that the primary source of error associated with the presence of small-scale spatial variability is related to the standard assumptions of steady state and non-steady state (〉40% during bloom condition). The non-steady state method can misinterpret variations due to patchiness in thorium activity as temporal changes and lead to errors larger than those introduced by the simpler steady state approach. We show that the non-steady state approach could improve the flux estimates in some cases if the sampling was conducted in a Lagrangian framework. Undersampling the spatial variability results in further bias (〉20%) that can be reduced when the sampling density is increased. Finally, errors due to the dynamical transport of thorium associated with small-scale structures are relatively low (〈20%) except in regions of high eddy kinetic energy.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.dsr.2012.05.015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Nitrogen uptake by phytoplankton in the Atlantic sector of the Southern Ocean during late austral summer (2011)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 8 (10). pp. 2947-2959.
    Details
    Publication Date: 2014-12-08
    Description: As part of the Bonus-GoodHope (BGH) campaign, 15N-labelled nitrate, ammonium and urea uptake measurements were made along the BGH transect from Cape Town to ~60° S in late austral summer, 2008. Our results are categorised according to distinct hydrographic regions defined by oceanic fronts and open ocean zones. High regenerated nitrate uptake rate in the oligotrophic Subtropical Zone (STZ) resulted in low f-ratios (f = 0.2) with nitrogen uptake being dominated by ρurea, which contributed up to 70 % of total nitrogen uptake. Size fractionated chlorophyll data showed that the greatest contribution (〉50 %) of picophytoplankton (〈2 μm) were found in the STZ, consistent with a community based on regenerated production. The Subantarctic Zone (SAZ) showed the greatest total integrated nitrogen uptake (10.3 mmol m−2 d−1), mainly due to enhanced nutrient supply within an anticyclonic eddy observed in this region. A decrease in the contribution of smaller size classes to the phytoplankton community was observed with increasing latitude, concurrent with a decrease in the contribution of regenerated production. Higher f-ratios observed in the SAZ (f = 0.49), Polar Frontal Zone (f= 0.41) and Antarctic Zone (f = 0.45) relative to the STZ (f = 0.24), indicate a higher contribution of NO3−-uptake relative to total nitrogen and potentially higher export production. High ambient regenerated nutrient concentrations are indicative of active regeneration processes throughout the transect and ascribed to late summer season sampling. Higher depth integrated uptake rates also correspond with higher surface iron concentrations. No clear correlation was observed between carbon export estimates derived from new production and 234Th flux. In addition, export derived from 15N estimates were 2–20 times greater than those based on 234Th flux. Variability in the magnitude of export is likely due to intrinsically different methods, compounded by differences in integration time scales for the two proxies of carbon export.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-8-2947-2011
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    The relative contribution of fast and slow sinking particles to ocean carbon export (2012)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 26 (1). GB1026.
    Details
    Publication Date: 2014-12-08
    Description: Particulate organic carbon (POC) generated by primary production and exported to depth, is an important pathway for carbon transfer to the abyss, where it is stored over climatically significant timescales. These processes constitute the biological carbon pump. A spectrum of particulate sinking velocities exists throughout the water column, however numerical models often simplify this spectrum into suspended, fast and slow sinking particles. Observational studies suggest the spectrum of sinking speeds in the ocean is strongly bimodal with >85 POC flux contained within two pools with sinking speeds of 〈10 m day -1 and >350 m day -1. We deployed a Marine Snow Catcher (MSC) to estimate the magnitudes of the suspended, fast and slow sinking pools and their fluxes at the Porcupine Abyssal Plain site (48°N, 16.5°W) in summer 2009. The POC concentrations and fluxes determined were 0.2μ g C L -1 and 54 mg C m -2 day -1 for fast sinking particles, 5μ g C L -1 and 92μ mg C m -2 day -1 for slow sinking particles and 97 g C L -1 for suspended particles. Our flux estimates were comparable with radiochemical tracer methods and neutrally buoyant sediment traps. Our observations imply: (1) biomineralising protists, on occasion, act as nucleation points for aggregate formation and accelerate particle sinking; (2) fast sinking particles alone were sufficient to explain the abyssal POC flux; and (3) there is no evidence for ballasting of the slow sinking flux and the slow sinking particles were probably entirely remineralised in the twilight zone. Copyright 2012 by the American Geophysical Union.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011GB004085
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    A reduced estimate of the strength of the ocean's biological carbon pump (2011)
    American Geophysical Union (AGU)
    In:  Geophysical Research Letters, 38 (4). n/a-n/a.
    Details
    Publication Date: 2020-07-30
    Description: A major term in the global carbon cycle is the ocean's biological carbon pump which is dominated by sinking of small organic particles from the surface ocean to its interior. Several different approaches to estimating the magnitude of the pump have been used, yielding a large range of estimates. Here, we use an alternative methodology, a thorium isotope tracer, that provides direct estimates of particulate organic carbon export. A large database of thorium-derived export measurements was compiled and extrapolated to the global scale by correlation with satellite sea surface temperature fields. Our estimates of export efficiency are significantly lower than those derived from the f-ratio, and we estimate global integrated carbon export as ∼5 GtC yr−1, lower than most current estimates. The lack of consensus amongst different methodologies on the strength of the biological carbon pump emphasises that our knowledge of a major planetary carbon flux remains incomplete.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011GL046735
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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