Fossil corals as an archive of secular variations in seawater chemistry since the Mesozoic

Gothmann, Anne M.; Stolarski, Jarosław; Adkins, Jess F.; Schoene, Blair; Dennis, Kate J.; Schrag, Daniel P.; Mazur, Maciej; Bender, Michael L.

doi:10.1016/j.gca.2015.03.018

Cited by 98 publications

(93 citation statements)

References 113 publications

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“…Therefore, these regions better preserved their original structures in fossil corals ( 19 ). We considered the TDs in the fossil coral skeletons to be well preserved only when meeting all of the following criteria ( 19 , 20 ): (i) arrangement of crystals and crystal habits identical to those in modern Scleractinia, (ii) absence of Mn-induced luminescence, and (iii) purely aragonitic mineralogy. In addition, areas of well-preserved TDs in a skeleton were required to be large enough to be comfortably sampled with a microdrill (drill bit diameter, 350 μm).…”

Section: Resultsmentioning

confidence: 99%

Photosymbiosis and the expansion of shallow-water corals

et al. 2016

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Section: Resultsmentioning

confidence: 99%

Photosymbiosis and the expansion of shallow-water corals

et al. 2016

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“…One coral specimen (452K1) was analysed geochemically using LA-ICP-MS (Böcker, 2014) with regard to concentrations of environmentally sensitive elements (e.g. Sr / Ca, U / Ca, B / Ca) and following recommendations for evaluating the diagenetic status of corals from strongly lithified and altered limestone (Anagnostou et al, 2011;Gothmann et al, 2015). LA-ICP-MS analyses were performed at the Max Planck Institut für Chemie (Mainz, Germany) using a NewWave UP 213 laser ablation system coupled to a ThermoFisher Element 2 ICP-MS.…”

Section: Methodsmentioning

confidence: 99%

“…According to our conviction, all these data provide no critical evidence for the alteration of the original skeleton. Because of this line of reasoning and low overall calcite content evident from XRD analysis (calcite below detection limits), we refrained from measuring element ratios sensitive to the redox conditions of calcite precipitating freshwaters or burial fluids (Fe / Ca, Mn / Ca) and other more sophisticated geochemical methods as potential measures of alteration (Anagnostou et al, 2011;Gothmann et al, 2015).…”

Section: Preservationmentioning

confidence: 99%

“…While the petrographic aspect of the calcite documents the type of freshwater or burial alteration environment, cathodoluminescence analysis and geochemical data may provide further information as to the redox character of the diagenetic fluids (Flügel, 2004). Alteration of aragonite is commonly a rapid process, but in the rare event of low porewater circulation rates, corals do escape diagenetic alteration (Anagnostou et al, 2011;Brachert et al, 2006aBrachert et al, , 2016Denniston et al, 2008a;Gothmann et al, 2015;Griffiths et al, 2013;Mertz-Kraus et al, 2008).…”

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Low Florida coral calcification rates in the Plio-Pleistocene

et al. 2016

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Abstract. In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO 3 ) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands often allow for reconstructions of annual extension (= growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. This report presents the bulk density, extension rates and calcification rates of fossil reef corals which underwent minor diagenetic alteration only. The corals derive from unlithified shallow water carbonates of the Florida platform (south-eastern USA), which formed during four interglacial sea level highstands dated approximately 3.2, 2.9, 1.8, and 1.2 Ma in the mid-Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, voids are commonly present along centres of calcification which lack secondary cements. Mean extension rates were 0.44 ± 0.19 cm yr −1 (range 0.16 to 0.86 cm yr −1 ), mean bulk density was 0.96 ± 0.36 g cm −3 (range 0.55 to 1.83 g cm −3 ) and calcification rates ranged from 0.18 to 0.82 g cm −2 yr −1 (mean 0.38 ± 0.16 g cm −2 yr −1 ), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification rates with those of modern zooxanthellate corals (z corals) from the Western Atlantic (WA) and Indo-Pacific calibrated against sea surface temperature (SST). In the fossil data, we found a widely analogous relationship with SST in z corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger temperature window during the Plio-Pleistocene. With regard to the environment of coral growth, stable isotope proxy data from the fossil corals and the overall structure of the ancient shallow marine communities are consistent with a well-mixed, open marine environment similar to the present-day Florida Reef Tract, but variably affected by intermittent upwelling. Upwelling along the platform may explain low rates of reef coral calcification and inorganic cementation, but is too localised to account also for low extension rates of Pliocene z corals throughout the tropical WA region. Low aragonite saturation on a more global scale in response to rapid glacialinterglacial CO 2 cyclicity is also a potential factor, but PlioPleistocene atmospheric pCO 2 is generally believed to have been broadly similar to the present day. Heat stress related to globally high interglacial SST only episodically moderated by intermittent upwelling affecting the Florida platform seems to be another likely reason for low calcification rates. From these observatio...

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“…Most evidence from altered ophiolite assemblages and the fossil record indicate elevated [Sr] in seawater during times of elevated [Ca] (20)(21)(22), with fairly small overall changes to the seawater Sr/Ca ratio. However, lower than modern Sr/Ca ratios for the period between 30-180 Ma have also been proposed based on analyses of carbonate veins in altered oceanic crust (23).…”

Section: Paleoseawater Chemical Variationsmentioning

confidence: 99%

Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

Antonelli

Pester

Brown

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Variations in the Mg, Ca, Sr, and SO 4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges (MOR). We present a model for evaluating the nature and magnitude of these previously unappreciated effects, using available estimates of paleoseawater composition over Phanerozoic time as inputs and 87 Sr/ 86 Sr of ophiolite epidosites and epidote-quartz veins as constraints. The results suggest that modern hydrothermal fluids are not typical due to low Ca and Sr relative to Mg and SO 4 in modern seawater. At other times during the last 500 million years, particularly during the Cretaceous and Ordovician, hydrothermal fluids had more seawater-derived Sr and Ca, a prediction that is supported by Sr isotope data. The predicted 87 Sr/ 86 Sr of vent fluids varies cyclically in concert with ocean chemistry, with some values much higher than the modern value of ∼0.7037. The seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic Ca and Sr to seawater in hydrothermal systems, which varies by a factor of ∼1.6 over the Phanerozoic, with minima when seawater Mg and SO 4 are low. This effect provides a modest negative feedback on seawater composition and 87 Sr/ 86 Sr changes. For the mid-Cretaceous, the low 87 Sr/ 86 Sr of seawater requires either exceptionally large amounts of lowtemperature exchange with oceanic crust or that the weathering flux of continentally derived Sr was especially small. The model also has implications for MOR hydrothermal systems in the Precambrian, when low-seawater SO 4 could help explain low seawater 87 Sr/ 86 Sr.paleoseawater | Sr isotopes | hydrothermal systems | midocean ridges M idocean ridge (MOR) hydrothermal circulation, fueled by persistent heat from shallow magma reservoirs, is a key component in the long-term regulation of global climate and ocean chemistry (1). Hydrothermal fluids that emerge from these systems, at temperatures up to ∼400°C, are chemically distinct from seawater due to reactions with newly forming oceanic crust. Relative to seawater, fluids emanating from modern MOR hydrothermal systems are enriched in Ca and transition metals, have lower pH and Eh, and have little to no Mg and SO 4 (2-5).Hydrothermal circulation at MOR is dominated by two important chemical reactions: the removal of seawater SO 4 through mineral precipitation with seawater Ca, and the removal of seawater Mg through precipitation of hydroxy-silicate minerals (3, 6, 7). Seawater SO 4 is primarily lost through the formation of anhydrite (CaSO 4 ) early during hydrothermal circulation, as anhydrite precipitation occurs by simply heating seawater >130°C (8). There can also be minor losses of SO 4 through thermochemical sulfate reduction (9, 10) and bacterial processes.Seawater Mg is lost from hydrothermal fluids at both low and high temperatures, by exchange of seawater Mg for basaltic Ca through the transformation of primary igneous minerals to alteration phases such as montmorillonite ...

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Fossil corals as an archive of secular variations in seawater chemistry since the Mesozoic

Cited by 98 publications

References 113 publications

Photosymbiosis and the expansion of shallow-water corals

Photosymbiosis and the expansion of shallow-water corals

Low Florida coral calcification rates in the Plio-Pleistocene

Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

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