Early marine diagenesis of biogenic aragonite and Mg-calcite: new constraints from high-resolution STEM and AEM analyses of modern platform carbonates

Hover, Victoria C.; Walter, Lynn M.; Peacor, Donald R.

doi:10.1016/s0009-2541(00)00326-0

Cited by 77 publications

(64 citation statements)

References 39 publications

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“…The second reason is that within a given set of solubility constants in any one study, the solubility of Mg calcite is also a function of the Mg content of the material. Thus in the absence of more detailed information on the mineralogy, composition (e.g., Mg content), and properties of the carbonate minerals undergoing dissolution in LSI sediments (e.g., as in the recent study of Hover et al 2001) it is difficult to examine this problem in further detail. However, the interpretation of these pore water results, as well as the calcium data discussed below, is that they are consistent with the occurrence of preferential dissolution of high-Mg calcite in LSI sediments (also see similar discussions in Morse et al 1985).…”

Section: Resultsmentioning

confidence: 99%

Impact of sea grass density on carbonate dissolution in Bahamian sediments

Burdige

Zimmerman

2002

Limnology & Oceanography

131

112

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Carbonate dissolution has been widely observed in shallow water tropical sediments. However, sediment budgets have generally not been closed with respect to the amount of acid required to produce the observed carbonate dissolution. Recently it has been suggested that enhanced oxygen transport into sediments through the roots and rhizomes of sea grasses might play a role in resolving this mass balance problem. We conducted studies of sea grass-carbonate sediment interactions around Lee Stocking Island, Exuma Islands, Bahamas to further examine this problem. Our studies showed that alkalinity, total dissolved inorganic carbon (⌺CO 2 ) and Ca 2ϩ increased with depth in the pore waters, while pH and calculated carbonate ion concentration decreased with depth. These observations are consistent with the occurrence of carbonate dissolution in these sediments. The magnitude of pore water alkalinity, ⌺CO 2 , and Ca 2ϩ changes was also related to sea grass density, with the largest gradients seen in the sediments of dense sea grass beds. Calculations suggested that less than ϳ50% of the O 2 needed to drive aerobic respiration (and ultimately carbonate dissolution via CO 2 production) could be supplied by transport processes such as diffusion, bioturbation, and physical pore water advection. Furthermore, the O 2 needed to balance the carbonate dissolution budget could be provided by the transport of Ͻ15% of the photosynthetically derived O 2 to the sediments through sea grass roots and rhizomes without enhancing the removal of carbonate dissolution end products. Thus sea grasses play an important role in controlling the rates of carbonate dissolution in shallow water tropical marine sediments.

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Section: Resultsmentioning

confidence: 99%

Impact of sea grass density on carbonate dissolution in Bahamian sediments

Burdige

Zimmerman

2002

Limnology & Oceanography

131

112

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“…Especially for Mn/Ca, high values are commonly associated with Mn oxyhydroxides and Mn carbonates, which form on the test of buried foraminifera (Boyle, 1983;Barker et al, 2003). Use of the CellTracker Green method aimed to minimize the impact of diagenetic coatings on the Mn/Ca values in this study, even though diagenesis cannot be completely excluded (Hover et al, 2001). …”

Section: Hydrographymentioning

confidence: 98%

Mg/Ca and Mn/Ca ratios in benthic foraminifera: the potential to reconstruct past variations in temperature and hypoxia in shelf regions

Groeneveld

Filipsson

2013

Biogeosciences

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Abstract. Shelf and coastal regions are exceptionally important for many countries as they provide the main habitat for many economically important fish and shellfish species. With ongoing climate change and human-induced eutrophication the shelf regions are especially affected, resulting in increased temperatures and stratification as well as oxygen depletion of the bottom waters. In order to be able to predict the magnitude of these changes in the future, it is necessary to study how they varied in the past. Commonly used foraminiferal climate and environmental proxies, e.g., stable isotopes and trace metal/Ca ratios, that are applied in open-ocean settings are not necessarily applicable in shelf regions, either as faunas are significantly different or as conditions can change much faster compared to the open ocean. In this study we explore the use of Mg/Ca as paleothermometer and Mn/Ca as a potential proxy for changing dissolved oxygen conditions in bottom water on the benthic foraminifera Bulimina marginata and Globobulimina turgida. Living specimens were collected from the Skagerrak and the Gullmar Fjord (SW Sweden); the latter is hypoxic for several months a year. As the specimens were alive when collected, we assume it unlikely that any diagenetic coatings have already significantly affected the trace metal/Ca ratios. The Mg/Ca ratios are similar to previously published values but display much larger variation than would be expected from the annual temperature change of less than 2 °C. An additional impact of the difference in the calcite saturation state between the Skagerrak and the Gullmar Fjord could explain the results. Mn/Ca ratios from G. turgida can potentially be related to variations in dissolved oxygen of the habitat where the foraminifera calcify. Samples from the Skagerrak display increased Mn/Ca in specimens that lived deeper in the sediment than those that lived near the surface. G. turgida samples from the low-oxygen Gullmar Fjord showed significantly increased Mn/Ca, being highest when bottom water dissolved oxygen was at a minimum. Our study suggests that trace metal/Ca ratios in benthic foraminifera from shelf regions have the potential to record past variations in bottom water temperature and dissolved oxygen concentrations, but an additional impact of the inorganic carbonate chemistry cannot be excluded.

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“…High-Mg calcite can rapidly lose Mg during even the early stages of diagenesis (Mü ller et al, 1972;Mackenzie et al, 1983;Morse, 1983;Hover et al, 2001). Therefore, one of the greatest challenges in using fossil Mg/Ca to deduce oceanic Mg/Ca is the identification of carbonate material that has retained evidence of its original Mg content.…”

Section: Effects Of Diagenesismentioning

confidence: 99%

Mg fractionation in crustose coralline algae: Geochemical, biological, and sedimentological implications of secular variation in the Mg/Ca ratio of seawater

Ries

2006

Geochimica et Cosmochimica Acta

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Early marine diagenesis of biogenic aragonite and Mg-calcite: new constraints from high-resolution STEM and AEM analyses of modern platform carbonates

Cited by 77 publications

References 39 publications

Impact of sea grass density on carbonate dissolution in Bahamian sediments

Impact of sea grass density on carbonate dissolution in Bahamian sediments

Mg/Ca and Mn/Ca ratios in benthic foraminifera: the potential to reconstruct past variations in temperature and hypoxia in shelf regions

Mg fractionation in crustose coralline algae: Geochemical, biological, and sedimentological implications of secular variation in the Mg/Ca ratio of seawater

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