Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the  Florida platform (USA)

Brachert, Thomas C.; Reuter, Markus; Krüger, Stefan; Kirkerowicz, Julia; Klaus, James S.

doi:10.5194/bg-13-1469-2016

Cited by 5 publications

(22 citation statements)

References 65 publications

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“…We discuss whether the patterns of z coral calcification found in the fossils from the Florida Platform is a local or global signature corresponding with temperature stress or low supersaturation of the sea water with respect to aragonite ( aragonite ) during the PlioPleistocene interglacials. This study complements two previous papers using sclerochronology of bivalves and z corals for reconstructions of the paleoenvironments and long-term changes of seasonality in southern Florida (Brachert et al, , 2016 and provides a discussion of the quantitative data in the context of recent global z coral calcification patterns.…”

supporting

confidence: 50%

“…In contrast, seasonal SST variability (∼ 7 • C) inferred from cyclic δ 18 O variations of the fossils is more independent of assumptions of δ 18 O water . Reconstructed seasonality is not only remarkably constant within specimens and over the last 3.2 Ma, but also fits modern surface seasonality along the reef tract (Brachert et al, , 2016. Large seasonality as prevailing off North Carolina (Macintyre and Pilkey, 1969) or in inner coastal waters of Florida Bay (FB; Swart et al, 1996) has not been encountered in the data from the reef corals and has also been taken for inferring a normal shallow-marine environment without unusual stress from cool waters or evaporation and freshwater influxes .…”

Section: The Florida Platform During the Plio-pleistocene Interglacialsmentioning

confidence: 89%

“…In this approach, the CoralXDS software compares the gray values recorded in X-radiographs from corals with those from aluminum plates having the same thickness as a background picture and an aluminum wedge for density calculations. Measurements were done along transects parallel to the corallites and parallel to the sampling transects for stable isotope analyses (Brachert et al, 2016). Bulk skeletal density was calculated as the mean of all individual measurements taken along a given transect.…”

Section: Methodsmentioning

confidence: 99%

“…Combined oxygen and carbon stable isotope data (δ 18 O, δ 13 C) of diagenetically pristine mollusks and z corals from the platform sediments reflect the complexity of the depositional setting including brackish to hypersaline and well-mixed, open marine environments Lloyd, 1969;Tao and Grossman, 2010). The reasons for high benthic carbonate productivity by mollusks during the Plio-Pleistocene is controversial, and has been suggested to be due to high nutrient concentrations resulting from freshwater input (Tao and Grossman, 2010) or upwelling (Allmon, 2001;Allmon et al, 1995;Brachert et al, 2016;Emslie and Morgan, 1994;Jones and Allmon, 1995 (Brachert et al, 2016). In contrast, seasonal SST variability (∼ 7 • C) inferred from cyclic δ 18 O variations of the fossils is more independent of assumptions of δ 18 O water .…”

Section: The Florida Platform During the Plio-pleistocene Interglacialsmentioning

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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supporting

confidence: 50%

Section: The Florida Platform During the Plio-pleistocene Interglacialsmentioning

confidence: 89%

Section: Methodsmentioning

confidence: 99%

Section: The Florida Platform During the Plio-pleistocene Interglacialsmentioning

confidence: 99%

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confidence: 99%

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Low Florida coral calcification rates in the Plio-Pleistocene

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Geochemical and Crystallographic Study ofTurbo Torquatus(Mollusca: Gastropoda) From Southwestern Australia

Roger

George

Shaw

et al. 2018

Geochem Geophys Geosyst

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Shells of the marine gastropod Turbo torquatus were sampled from three different locations along the Western Australian coastline, namely Marmion Lagoon (31°S), Rottnest Island (32°S), and Hamelin Bay (34°S). Marmion Lagoon and Rottnest Island have similar sea surface temperature ranges that are ∼1°C warmer than Hamelin Bay, with all sites influenced by the warm southward flowing Leeuwin Current. The shells were characterized using crystallographic, spectroscopic, and geochemical analyses. Shell mineral composition varies between the three sites suggesting the influence of sea surface temperature, oxygen consumption, and/or bedrock composition on shell mineralogy and preferential incorporation and/or elemental discrimination of Mg, P, and S. Furthermore, T. torquatus was found to exert control over the incorporation of most, if not all, the elements measured here, suggesting strong biological regulation. At all levels of testing, the concentrations of Li varied significantly, which indicates that this trace element may not be a suitable environmental proxy. Variation in Sr concentration between sites and between specimens reflects combined environmental and biological controls suggesting that Sr/Ca ratios in T. torquatus cannot be used to estimate sea surface temperature without experimentally accounting for metabolic and growth effects. The mineral composition and microstructure of T. torquatus shells may help identify sea surface temperature variations on geological time scales. These findings support the previously hypothesized involvement of an active selective pathway across the calcifying mantle of T. torquatus for most, if not all, the elements measured here.

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