Sanders
Richard J.
Sanders
Richard J.
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ArticleDoes a ballast effect occur in the surface ocean?(American Geophysical Union, 2010-04-29) Sanders, Richard J. ; Morris, Paul J. ; Poulton, Alex J. ; Stinchcombe, Mark C. ; Charalampopoulou, Anastasia ; Lucas, Mike I. ; Thomalla, Sandy J.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.
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ArticleA reduced estimate of the strength of the ocean's biological carbon pump(American Geophysical Union, 2011-02-18) Henson, Stephanie A. ; Sanders, Richard J. ; Madsen, Esben ; Morris, Paul J. ; Le Moigne, Frederic A. C. ; Quartly, Graham D.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.
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ArticleOn the proportion of ballast versus non-ballast associated carbon export in the surface ocean(American Geophysical Union, 2012-08-11) Le Moigne, Frederic A. C. ; Sanders, Richard J. ; Villa-Alfageme, Maria ; Martin, Adrian P. ; Pabortsava, Katsiaryna ; Planquette, Helene ; Morris, Paul J. ; Thomalla, Sandy J.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.
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ArticleA carbon budget for a naturally iron fertilized bloom in the Southern Ocean(American Geophysical Union, 2011-07-08) Morris, Paul J. ; Sanders, Richard J.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.