Effects of lower surface ocean pH upon the stability of shallow water carbonate sediments

Tynan, Sarah; Opdyke, Bradley N.

doi:10.1016/j.scitotenv.2010.12.007

Cited by 31 publications

(15 citation statements)

References 19 publications

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“…The presence of relatively high Mg concentrations may explain, in addition to their microcristalline structure, the low preservation potential of holococcoliths, which have very sporadic fossil records (Bown et al 2004). Differences in the Mg and Ca content of holo-and heteroccolithophores could also have consequences in relation to the increasing acidification of the world oceans (Orr et al 2005) because high-Mg calcite dissolves faster than low-Mg calcite after a drop in pH (Tynan and Opdyke 2011).…”

Section: Discussionmentioning

confidence: 99%

Elemental composition of coccoliths: Mg/Ca relationships

Cros¹,

Fortuño²,

Estrada³

2013

Sci. Mar.

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SUMMARY: Coccolithophores produce calcium carbonate platelets, the coccoliths, and play a significant role in the C and Ca cycles. Coccoliths are important components of marine biogenic carbonate sediments and their chemical analysis can provide tools for paleoceanographic investigation. In particular, the Mg/Ca ratio of coccoliths has been proposed as a paleotemperature proxy. The present study uses X-ray microanalysis to evaluate the Ca and Mg composition of heterococcoliths and holococcoliths of different coccolithophore species. Our measurements indicate that the Mg values in heterococcoliths do not exceed a low threshold and do not show any consistent relationship with the Ca content, while the Mg content of holococcoliths spans a wider range, can reach much higher values and shows a linear relationship with the Ca content. Several heterococcolithophore species tend to form separate clusters according to their Mg and Ca values. Within each cluster, there were no consistent differences in the Mg/Ca ratios of specimens sampled at different temperatures or seasons, suggesting that using the Mg/Ca ratio as a paleothermometer may be problematic. Our findings could have implications for the interpretation of the fossil record because Mg-rich calcite dissolves more easily.Keywords: coccolithophores, X-ray microanalysis, calcium, magnesium, holococcoliths, heterococcoliths. RESUMEN: ComposiCión elemental de CoColitos. RelaCiones mg/Ca. -Los cocolitóforos producen unas plaquitas de carbonato de calcio denominadas cocolitos, y juegan un papel significativo en los ciclos biogeoquímicos del C y el Ca. Los cocolitos constituyen un componente importante del registro sedimentario y su análisis químico puede proporcionar herramientas para la investigación paleoceanográfica. En particular, se ha sugerido que la relación Mg/Ca podría ser usada como un indicador de paleotemperatura. En este trabajo presentamos un estudio, realizado mediante la técnica de microanálisis por rayos X, de la composición elemental de holo-y heterococolitos pertenecientes a diferentes especies de cocolitóforos. Se ha observado que el contenido de Mg en los heterococolitos no supera un umbral muy bajo y no presenta relación con el de Ca, mientras que en los holococolitos el contenido de Mg es en general más elevado, abarca un rango más amplio y guarda una relación lineal con el de Ca. Diversas especies de heterococolitóforos tendían a formar grupos separados en función de su contenido en Ca y Mg. Dentro de cada especie, no se detectaban diferencias consistentes en la relación Mg/Ca de especímenes de muestras de agua de distintas temperaturas o tomadas en diferentes estaciones del año, lo que indica que el uso de la relación Mg/Ca como paleotermómetro puede ser problemático. Nuestras observaciones pueden tener implicaciones para la interpretación del registro sedimentario, ya que la calcita rica en Mg se disuelve más rápidamente.

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Section: Discussionmentioning

confidence: 99%

Elemental composition of coccoliths: Mg/Ca relationships

Cros¹,

Fortuño²,

Estrada³

2013

Sci. Mar.

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“…The same may be true for dissolution arising as a result of bioerosion . In support of these predictions, experiments investigating the response of CaCO 3 sediments or substrates have shown convincing evidence of dissolution or increasing rates of dissolution as a result of increasing seawater CO 2 and acidity (Keir, 1980;Walter and Morse, 1985;Tribble and Mackenzie, 1998;Halley and Yates, 2000;Barnes and Cuff, 2000;Morse et al ., 2006;Andersson et al ., 2007;Tynan and Opdyke, 2011) . Similarly, coral blocks infested with communities of euendolithic and epilithic bioeroding organisms and exposed to seawater pCO 2 levels similar to those anticipated in the atmosphere by the end of the century (750 matm) dissolved at rates 48% higher than under control conditions (400 matm; Tribollet et al ., 2009) .…”

Section: Caco 3 Dissolution and Bioerosion On Coral Reefsmentioning

confidence: 99%

The Marine Carbon System and Ocean Acidification during Phanerozoic Time

Mackenzie¹,

Andersson²

2013

geochempersp

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“…Later, Andersson and colleagues (Andersson et al, , 2005(Andersson et al, , 2007Morse et al, 2006) showed in a number of papers based on a numerical modeling approach that the global coastal ocean, as well as most shallow water environments in general, will not be significantly buffered by dissolution of carbonate minerals on time-scales of decades to hundreds of years. However, these authors have failed to convince skeptics as the issue is continuously being raised or mentioned in a number of forums and settings based on, for example, incorrect thermodynamic calculations (e.g., Loáiciga, 2006; see technical comment by Caldeira et al, 2007) (e.g., Tribollet et al, 2009;Hauck et al, 2011;Tynan and Opdyke, 2011). The first condition that requires recognition is that evidence of dissolution of CaCO 3 does not automatically mean that a significant buffer effect can be achieved.…”

Section: A J Andersson and F T Mackenzie: Revisiting Four Scientimentioning

confidence: 99%

Revisiting four scientific debates in ocean acidification research

2012

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Abstract. In recent years, ocean acidification has gained continuously increasing attention from scientists and a number of stakeholders and has raised serious concerns about its effects on marine organisms and ecosystems. With the increase in interest, funding resources, and the number of scientific investigations focusing on this environmental problem, increasing amounts of data and results have been produced, and a progressively growing and more rigorous understanding of this problem has begun to develop. Nevertheless, there are still a number of scientific debates, and in some cases misconceptions, that keep reoccurring at a number of forums in various contexts. In this article, we revisit four of these topics that we think require further thoughtful consideration including: (1) surface seawater CO 2 chemistry in shallow water coastal areas, (2) experimental manipulation of marine systems using CO 2 gas or by acid addition, (3) net versus gross calcification and dissolution, and (4) CaCO 3 mineral dissolution and seawater buffering. As a summation of these topics, we emphasize that: (1) many coastal environments experience seawater pCO 2 that is significantly higher than expected from equilibrium with the atmosphere and is strongly linked to biological processes; (2) addition of acid, base or CO 2 gas to seawater can all be useful techniques to manipulate seawater chemistry in ocean acidification experiments; (3) estimates of calcification or CaCO 3 dissolution based on present techniques are measuring the net of gross calcification and dissolution; and (4) dissolution of metastable carbonate mineral phases will not produce sufficient alkalinity to buffer the pH and carbonate saturation state of shallow water environments on timescales of decades to hundreds of years to the extent that any potential negative effects on marine calcifiers will be avoided.

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Effects of lower surface ocean pH upon the stability of shallow water carbonate sediments

Cited by 31 publications

References 19 publications

Elemental composition of coccoliths: Mg/Ca relationships

Elemental composition of coccoliths: Mg/Ca relationships

The Marine Carbon System and Ocean Acidification during Phanerozoic Time

Revisiting four scientific debates in ocean acidification research

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