"During photosynthesis, organic carbon matter is formed from both HCO − 3 and CO 2 (aq) (Tortell et al., 1997) using both active and indirect transportation mechanisms (Sültemeyer et al., 1993) and C 3 and C 4 photosynthetic pathways (Reinfelder et al., 2000). Marine studies including those from the Bering Sea and North Pacific Ocean have demonstrated that the majority of diatom carbon originates from HCO − 3 via direct transportation (Tortell and Morel, 2002; Cassar et al., 2004; Martin and Tortell, 2006; Tortell et al., 2006, 2008). "
[Show abstract][Hide abstract] ABSTRACT: In comparison to other sectors of the marine system, the palaeoceanography of the subarctic North Pacific Ocean is poorly constrained. New diatom isotope records of δ13C, δ18O, δ30Si (δ13Cdiatom, δ18Odiatom, δ30Sidiatom), are presented alongside existing geochemical and isotope records to document changes in photic zone conditions, including nutrient supply and the efficiency of the soft-tissue biological pump, between Marine Isotope Stage (MIS) 4 and MIS 5e. Peaks in opal productivity in MIS 5b/c and MIS 5e are both associated with the breakdown of the regional halocline stratification and increased nutrient supply to the photic zone. Whereas the MIS 5e peak is associated with low rates of nutrient utilisation, the MIS 5b/c peak is associated with significantly higher rates of nutrient utilisation. Both peaks, together with other smaller increases in productivity in MIS 4 and 5a culminate with a~significant increase in freshwater input which strengthens/re-establishes the halocline and limits further upwelling of sub-surface waters to the photic zone. Whilst δ30Sidiatom and previously published records of diatom δ15N (δ15Ndiatom) (Brunelle et al., 2007, 2010) show similar trends until the latter half of MIS 5a, the records become anti-correlated after this juncture and into MIS 4, suggesting a possible change in photic zone state such as may occur with a shift to iron or silicon limitation.
Climate of the Past 01/2015; 11(1):15-25. DOI:10.5194/cp-11-15-2015 · 3.38 Impact Factor
"In addition, we do not consider this mechanism very likely, as most diatoms have been found to be able to Mar Ecol Prog Ser 273: 1–15, 2004 utilise HCO 3 – as carbon source in one way or another (e.g. Nimer et al. 1997, Tortell et al. 1997, Hobson et al. 2001). A third potential explanation for the effect of pH on DA production could be that pH-mediated changes in speciation of metals affect the production of DA due to increased toxicity or reduced bioavailability of the metal. "
[Show abstract][Hide abstract] ABSTRACT: The effect of elevated pH on growth and on production of the neurotoxin domoic acid was studied in selected diatoms belonging to the genera Pseudo-nitzschia and Nitzschia. Growth of most of the 11 species studied stopped at pH values of 8.7 to 9.1. However, for P. delicatissima and N. navis-varingica the pH limit for growth was higher, 9.3 and 9.7 to 9.8, respectively. A compilation of all available data on the pH limits for growth of marine planktonic diatoms suggests that species from ponds and rock pools all have higher limits than coastal and oceanic species. Taking only coastal and oceanic species into account, the data suggest that smaller species have a higher upper pH limit for growth than larger species. Elevated pH induced production of domoic acid in P, multiseries in amounts comparable to those detected previously under silicate and phosphate limitation. As Pseudo-nitzschia species are found in high concentrations in nutrient- enriched areas, high pH and hence induction of the production of domoic acid would be expected during blooms. These results may help to understand when and why Pseudo-nitzschia species produce domoic acid in the field.
[Show abstract][Hide abstract] ABSTRACT: The carbon isotopic fractionation of phytoplankton photosynthesis (epsilon(P)) has been interpreted by previous authors as inconsistent with active bicarbonate uptake. This interpretation contradicts the results of numerous physiological studies demonstrating significant active bicarbonate uptake in phytoplankton. Using a simple model of cellular regulation of carbon acquisition we show that an upward curvature of epsilon(p) as a function of the ratio of growth rate to carbon dioxide concentration does not exclude active bicarbonate uptake. Our model describes adequately published carbon isotope data for cyanobacteria, diatoms, and coccolithophores consistent with active bicarbonate uptake.
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