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  • 1
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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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  • 2
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    Does a ballast effect occur in the surface ocean? (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2010. 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 37 (2010): L08602, doi:10.1029/2010GL042574.
    Description: The oceanic biological carbon pump (BCP), a large (10 GT C yr−1) component of the global carbon cycle, is dominated by the sinking (export) of particulate organic carbon (POC) from surface waters. In the deep ocean, strong correlations between downward fluxes of biominerals and POC (the so-called ‘ballast effect’) suggest a potential causal relationship, the nature of which remains uncertain. We show that similar correlations occur in the upper ocean with high rates of export only occurring when biominerals are also exported. Exported particles are generally biomineral rich relative to the upper ocean standing stock, due either to: (1) exported material being formed from the aggregation of a biomineral rich subset of upper ocean particles; or (2) the unfractionated aggregation of the upper ocean particulate pool with respiration then selectively removing POC relative to biominerals until particles are dense enough to sink.
    Description: This research was supported by the UK Natural Environment Research Council.
    Keywords: Biological carbon pump ; Ballast ; Calcite ; Opal ; Upper ocean
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
    Format: text/plain
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  • 3
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    A carbon budget for a naturally iron fertilized bloom in the Southern Ocean (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    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 Global Biogeochemical Cycles 25 (2011): GB3004, doi:10.1029/2010GB003780.
    Description: Subantarctic islands in the high-nutrient, low-chlorophyll (HNLC) Southern Ocean are natural sources of iron and stimulate blooms in their proximity, such as the one observed close to the Crozet Islands (52°E, 46°S). During 2004/2005, particulate organic carbon (POC) export was measured using the 234Th technique in the Crozet bloom and compared with an HNLC control region. Initial results showed that iron release had no effect on daily POC export rates, thus any iron-driven enhancement in POC export was due to a longer export phase in the bloom region when compared to the control region. The duration of the export event was empirically estimated by closing the silicon budget, thus allowing seasonal POC export to be calculated by applying the export duration to the daily rates of POC export. This yields a seasonal estimate of POC export that is 3.6 times larger (range 1.9–7.1) in the iron-fertilized region than in the HNLC control region. These estimates of POC export were then compared to independent estimates of organic matter storage in the upper ocean, which are significant in both the HNLC and control regions. Overall, integrated POC export was significantly (approximately 50%) lower than estimated seasonal new production, the fraction of production that is supported by inputs of new nutrients. Finally, the sequestration efficiency, the numerical relationship between the supply of the limiting nutrient, iron, and the key ecosystem function of POC export at 100 m, is estimated to be 16,790 mol:mol.
    Description: Funding for CROZEX came from the NERC core strategic program BICEP.
    Keywords: Silicon budget ; CROZEX ; POC ; HNLC ; Carbon export
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/msword
    Format: text/plain
    Format: application/pdf
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  • 4
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    Intercalibration studies of short-lived thorium-234 in the water column and marine particles (2014)
    Association for the Sciences of Limnology and Oceanography
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography: Methods 10 (2012): 631-644, doi:10.4319/lom.2012.10.631.
    Description: Intercomparision of 234Th measurements in both water and particulate samples was carried out between 15 laboratories worldwide, as a part of GEOTRACES inter-calibration program. Particulate samples from four different stations namely BATS (both shallow and deep) and shelf station (shallow) in Atlantic and SAFE (both shallow and deep) and Santa Barbara station (shallow) in Pacific were used in the effort. Particulate intercalibration results indicate good agreement between all the participating labs with data from all labs falling within the 95% confidence interval around the mean for most instances. Filter type experiments indicate no significant differences in 234Th activities between filter types and pore sizes (0.2-0.8 μm). The only exception are the quartz filters, which are associated with 10% to 20% higher 234Th activities attributed to sorption of dissolved 234Th. Flow rate experiments showed a trend of decreasing 234Th activities with increasing flow rates (2-9 L min-1) for 〉 51 μm size particles, indicating particle loss during the pumping process. No change in 234Th activities on small particles was observed with increasing flow-rates. 234Th intercalibration results from deep water samples at SAFe station indicate a variability of 〈 3% amongst labs while dissolved 234Th data from surface water at Santa Barbara Station show a less robust agreement, possibly due to the loss of 234Th from decay and large in-growth corrections as a result of long gap between sample collection and processing.
    Description: This research is funded by NSF Chemical Oceanography program. LM will like to thank Fisheries and Oceans Canada for support. PM is supported through ICREA Academia funded by Generalitat de Catalunya. The International Atomic Energy Agency is grateful to the Government of the Principality of Monaco for the support provided to its Environment Laboratories.
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 5
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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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  • 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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    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
  • 8
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    Does a ballast effect occur in the ocean? (2010)
    In:  [Poster] In: 14. Biennial Challenger Society Conference for Marine Science 2010, 06-09.09.2010, Southampton, UK .
    Details
    Publication Date: 2015-01-07
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 9
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    Measurements of 234Th-derived POC and biomineral export in the surface ocean to investigate a potential ballast effect (2010)
    In:  [Talk] In: Coccos workshop 2010, 23.-26.06.2010, Bergen, Norway .
    Details
    Publication Date: 2015-01-07
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 10
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    Does a ballast effect occur in the ocean? (2012)
    In:  [Poster] In: EGU General Assembly 2012, 22.-27.04.2012, Vienna, Austria .
    Details
    Publication Date: 2015-01-07
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
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