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Silverman, J, Schneider K, Kline DI, Rivlin T, Rivlin A, Hamylton S, Lazar B, Erez J, Caldeira K.  2014.  Community calcification in Lizard Island, Great Barrier Reef: A 33 year perspective. Geochimica Et Cosmochimica Acta. 144:72-81.   10.1016/j.gca.2014.09.011   AbstractWebsite

Measurements of community calcification (G(net)) were made during September 2008 and October 2009 on a reef flat in Lizard Island, Great Barrier Reef, Australia, 33 years after the first measurements were made there by the LIMER expedition in 1975. In 2008 and 2009 we measured G(net) = 61 +/- 12 and 54 +/- 13 mmol CaCO3 m(-2).day(-1), respectively. These rates are 27-49% lower than those measured during the same season in 1975-76. These rates agree well with those estimated from the measured temperature and degree of aragonite saturation using a reef calcification rate equation developed from observations in a Red Sea coral reef. Community structure surveys across the Lizard Island reef flat during our study using the same methods employed in 1978 showed that live coral coverage had not changed significantly (similar to 8%). However, it should be noted that the uncertainty in the live coral coverage estimates in this study and in 1978 were fairly large and inherent to this methodology. Using the reef calcification rate equation while assuming that seawater above the reef was at equilibrium with atmospheric PCO2 and given that live coral cover had not changed G(net) should have declined by 30 +/- 8% since the LIMER study as indeed observed. We note, however, that the error in estimated G(net) decrease relative to the 1970's could be much larger due to the uncertainties in the coral coverage measurements. Nonetheless, the similarity between the predicted and the measured decrease in G(net) suggests that ocean acidification may be the primary cause for the lower CaCO3 precipitation rate on the Lizard Island reef flat. (C) 2014 Elsevier Ltd. All rights reserved.

Nash, MC, Troitzsch U, Opdyke BN, Trafford JM, Russell BD, Kline DI.  2011.  First discovery of dolomite and magnesite in living coralline algae and its geobiological implications. Biogeosciences. 8:3331-3340.   10.5194/bg-8-3331-2011   AbstractWebsite

Dolomite is a magnesium-rich carbonate mineral abundant in fossil carbonate reef platforms but surprisingly rare in modern sedimentary environments, a conundrum known as the "Dolomite Problem". Marine sedimentary dolomite has been interpreted to form by an unconfirmed, post-depositional diagenetic process, despite minimal experimental success at replicating this. Here we show that dolomite, accompanied by magnesite, forms within living crustose coralline alga, Hydrolithon onkodes, a prolific global tropical reef species. Chemical micro-analysis of the coralline skeleton reveals that not only are the cell walls calcitised, but that cell spaces are typically filled with magnesite, rimmed by dolomite, or both. Mineralogy was confirmed by X-ray Diffraction. Thus there are at least three mineral phases present (magnesium calcite, dolomite and magnesite) rather than one or two (magnesium calcite and brucite) as previously thought. Our results are consistent with dolomite occurrences in coralline algae rich environments in fossil reefs of the last 60 million years. We reveal that the standard method of removing organic material prior to Xray Diffraction analysis can result in a decrease in the most obvious dolomite and magnesite diffraction patterns and this may explain why the abundant protodolomite and magnesite discovered in this study has not previously been recognized. This discovery of dolomite in living coralline algae extends the range of palaeo-environments for which biologically initiated dolomite can be considered a possible source of primary dolomite.