Bibliography - K. Matsumoto

1. Matsumoto, K., and Jorge Sarmiento, 2008: A corollary to the silicic acid leakage hypothesis. Paleoceanography, 23(PA001515), doi:10.1029/2007PA001515
   [ Abstract ]

   The silicic acid leakage hypothesis (SALH) attempts to explain part of the large and regular atmospheric CO₂ changes over the last glacial-interglacial cycles. It calls for a reduction in the carbonate pump through a growth in diatoms at the expense of coccolithophorids in low-latitude surface waters, driven by a ‘‘leakage’’ of high-Si:N waters from the Southern Ocean. Recent studies that present low opal accumulation rates from the glacial eastern equatorial Pacific have challenged SALH. In a corollary to SALH, we argue that the key to SALH is the dominance of diatoms over coccolithophorids, and this does not depend on the magnitude of diatom production per se. In support of our claim, we show in a numerical model that atmospheric CO₂ can be lowered with even a reduced absolute flux of silicic acid leakage, provided that Si:N in the leakage is elevated and that the excess Si can be used by diatoms to shift the floral composition in their favor.

2. Matsumoto, K., Jorge Sarmiento, R. M. Key, O. Aumont, J. L. Bullister, K. Caldeira, J.-M. Campin, S. C. Doney, H. Drange, J. C. Dutay, Y. Gao, A. Gnanadesikan, and N. Gruber, et al., 2004: Evaluation of ocean carbon cycle models with data-based metrics. Geophysical Research Letters, 31(L07303), doi:10.1029/2003GL018970
   [ Abstract ]

   New radiocarbon and chlorofluorocarbon-11 data from the World Ocean Circulation Experiment are used to assess a suite of 19 ocean carbon cycle models. We use the distributions and inventories of these tracers as quantitative metrics of model skill and find that only about a quarter of the suite is consistent with the new databased metrics. This should serve as a warning bell to the larger community that not all is well with current generation of ocean carbon cycle models. At the same time, this highlights the danger in simply using the available models to represent the state-of-the-art modeling without considering the credibility of each model.

3. Brezeinski, M. A., C. J. Pride, V. M. Franck, Daniel Sigman, Jorge Sarmiento, K. Matsumoto, and N. Gruber, 2002: A switch from Si(OH)₄ to NO₃ depletion in the glacial Southern Ocean. Geophysical Research Letters, 29(12), doi:10.1029/2001GL014349 1564
   [ Abstract ]

   Phytoplankton in the Antarctic deplete silicic acid (Si(OH)₄) to a far greater extent than they do nitrate (NO₃). This pattern can be reversed by the addition of iron which dramatically lowers diatom Si(OH)₄: NO₃ uptake ratios. Higher iron supply during glacial times would thus drive the Antarctic towards NO₃ depletion with excess Si(OH)₄ remaining in surface waters. New δ³⁰SI and δ ¹⁵N records from Antarctic sediments confirm diminished Si(OH)₄ use and enhanced NO₃ depletion during the last three glaciations. The present low-Si(OH)₄ water is transported northward to at least the subtropics. We postulate that the glacial high-Si(OH)₄ water similarly may have been transported to the subtropics and beyond. This input of Si(OH)₄ may have caused diatoms to displace coccolithophores at low latitudes, weakening the carbonate pump and increasing the depth of organic matter remineralization. These effects may have lowered glacial atmospheric pCO₂ by as much as 60 ppm.

4. Matsumoto, K., Jorge Sarmiento, and M. A. Brezeinski, 2002: Silicic acid leakage from the Southern Ocean: A possible explanation for glacial atmospheric pCO₂. Global Biogeochemical Cycles, 16(3), doi:10.1029/2001GB001442
   [ Abstract ]

   Using a simple box model, we investigate the effects of a reduced Si:N uptake ratio by Antarctic phytoplankton on the marine silica cycle and atmospheric pCO₂. Recent incubation experiments demonstrate such a phenomenon in diatoms when iron is added [Hutchins and Bruland, 1998; Takeda, 1998; Franck et al., 2000]. The Southern Ocean may have supported diatoms with reduced Si:N uptake ratios compared to today during the dustier glacial times [Petit et al., 1999]. A similar reduction in the uptake ratio may be realized with an increased production of nondiatom phytoplankton such as Phaeocystis. Our model shows that reduced Si:N export ratios in the Southern Ocean create excess silicic acid, which may then be leaked out to lower latitudes. Any significant consumption of the excess silicic acid by diatoms that leads to an enhancement in their growth at the expense of coccolithophorids diminishes CaCO₃production and therefore diminishes the carbonate pump. In our box model the combination of a reduced carbonate pump and an open system carbonate compensation draw down steady state atmospheric CO₂ from the interglacial 277 to 230–242 ppm, depending on where the excess silicic acid is consumed. By comparison, the atmospheric pCO₂ sensitivity of general circulation models to carbonate pump forcing is •3.5–fold greater, which, combined with carbonate compensation, can account for peak glacial atmospheric pCO₂. We discuss the importance of the initial rain ratio of CaCO₃ to organic carbon on atmospheric pCO₂ and relevant sedimentary records that support and constrain this ‘‘silicic acid leakage’’ scenario.

5. Sarmiento, Jorge, J. P. Dunne, A. Gnanadesikan, R. M. Key, K. Matsumoto, and R. D. Slater, 2002: A new estimate of the CaCO₃ to organic carbon export ratio. Global Biogeochemical Cycles, 16(4), doi:10.1029/2002GB001919
   [ Abstract ]

   We use an ocean biogeochemical-transport box model of the top 100 m of the water column to estimate the CaCO₃ to organic carbon export ratio from observations of the vertical gradients of potential alkalinity and nitrate. We find a global average molar export ratio of 0.06 ± 0.03. This is substantially smaller than earlier estimates of 0.25 on which a majority of ocean biogeochemical models had based their parameterization of CaCO₃ production. Contrary to the pattern of coccolithophore blooms determined from satellite observations, which show high latitude predominance, we find maximum export ratios in the equatorial region and generally smaller ratios in the subtropical and subpolar gyres. Our results suggest a dominant contribution to global calcification by low-latitude nonbloom forming coccolithophores or other organisms such as foraminifera and pteropods.

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