Salinity effects on the Mg/Ca and Sr/Ca in starfish skeletons and the echinoderm relevance for paleoenvironmental reconstructions

Abstract

Skeletal Mg/Ca ratios of well-preserved fossil echinoderms have been used to reconstruct past Mg/Ca ratio in seawater up to the Phanerozoic, taking into account the known temperature effect on this ratio. This study investigates the effects of salinity and growth rate on Mg/Ca and Sr/Ca ratios in starfi sh calcite skeletons grown in experimental conditions. Both ratios are not related to growth rate: on the contrary, both are positively related to salinity. This effect induces an error on the reconstructed Mg/Ca ratio in seawater that may reach 46%. An intriguing inverse relation between skeletal Sr/Ca ratio and temperature was recorded. The salinity effects are presumably due to physiological regulation processes.

Patterns of magnesium content in Arctic bryozoan skeletons along a depth gradient

“…In addition, our bryozoan data were gathered only from the Arctic, whereas the crinoid data of Kroh and Nebelsick (2010) came from all around the world and included tropical sites and fewer polar sites. Borremans et al (2009) among others have noted that patterns of ocean chemistry are spatially homogenous, and geographical factors can be ruled out as the cause of the observed differences. However, the crinoid data ranged down to Biol (2013) 36:193-200 197 depths of more than 2,000 m, an order of magnitude greater than our bryozoan data.…”

“…However, for the depth range covered by our bryozoan analysis, crinoids show a clear pattern of decreasing Mg, contrasting with the lack of correlation in the bryozoans. Salinity should also be considered as a potential factor explaining the difference between the crinoid and bryozoan patterns, due to the known influence of salinity on magnesium content in skeletons such as those of echinoids (e.g., Borremans et al 2009). In the case of the analyzed bryozoans, salinity is rather unimportant because our material came from a region where salinity showed little geographical variation (e.g., Karnovsky et al 2003;Walkusz et al 2009), while at the global scale of the crinoid data salinity is expected to vary more greatly.…”

Unshelled abalone and corrupted urchins: development of marine calcifiers in a changing ocean

“…For urchin, we consulted data for V ar and V ca because the Marine calcifiers in a changing ocean M. Byrne et al 2377 saturation state of echinoderm magnesium calcite is not known, although is likely to be closest to aragonite [44]. The saturation dynamics of the echinoderm skeleton depends on its Mg þþ content, and this is variable [28,45].…”

Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification

“…Other factors such as salinity (ionic strength;Muller et al, 1972;Folk, 1974;Hardie, 1976, 1980;Borremans et al, 2009) has also been shown to influence Mg incorporation in calcite. However, experiments conducted by Mucci and Morse (1983), Burton and Walter (1991), Hartley and Mucci (1996), De ChoudensSanchez and Gonzalez (2009), and Lee and Morse (2010) revealed that atmospheric pCO 2 and solution saturation state had no statistically significant effect on the Mg-content of calcite that precipitated from experimental seawater solutions.…”

“…However, the accuracy of the ancient seawater Mg/Ca calculations will be inherently limited for fossils whose Mg fractionation algorithms cannot be calibrated with extant representatives. The accuracy of the algorithms may also be limited by other factors that may have influenced biogenic Mg fractionation in the past, yet are not incorporated into the model (e.g., variations in growth rates, fluctuations of other ions in seawater, fluctuations in salinity, fluctuations in salinity; e.g., Borremans et al, 2009). Dickson's (2002Dickson's ( , 2004 paleo-seawater Mg/Ca ratios were recalculated (Fig.…”