Extensive and rapid changes in seawater chemistry during the Phanerozoic: evidence from Br contents in basal halite

Abstract

Variation of seawater chemical composition during the Phanerozoic is still a contentious subject. Br concentration in primary marine basal halites was used to indicate variations in seawater composition during the past 550 Ma. Evaporation experiments and thermodynamic modelling suggests that the partition coefficient of Br in halite depends on the composition of the seawater. A combination of this correlation with the time‐dependent models for ocean chemistry of Hardie leads to a prediction of Br in basal halite during the Phanerozoic. This prediction is in good agreement with data from different ancient evaporite basins. The Br data give evidence for rapid and massive changes in seawater chemistry during the Phanerozoic and are thus a first independent test for the Hardie model.

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

“…1) using the echinoid plate Mg fractionation algorithm (calibrated for crinoid ossicles when applicable; Table 2; Ries, 2004) Dickson's (2002) supplementary data] from paleogeographic and paleotemperature maps (Golonka et al, 1994). The resulting Mg/Ca ratios are consistent with other estimates and models of paleoceanic Mg/Ca over Phanerozoic time (Hardie, 1996;Lowenstein et al, 2001;Horita et al, 2002;Siemann, 2003;Demicco et al, 2005).…”

“…The observed correlation between rates of calcification ( Fig. 15) and rates of population growth is consistent with the hypothesis that calcification enhances photosynthesis within some species of coccolithophores via the liberation of CO 2 (Paasche, 1968;Sikes et al, 1980). However, this appears not to be the case for all species of coccolithophores, as other experiments have revealed that photosynthesis within Emiliania huxleyi is not diminished when the coccolithophore's calcification is reduced under low-[Ca 2+ ] conditions (Leonardos et al, 2009).…”

“…It has been proposed that photosynthesis in some calcareous bryopsidalean algae and coccolithophores is enhanced by CO 2 liberated by calcification (Paasche, 1968;Borowitzka and Larkum, 1976b;Borowitzka, 1977;Sikes et al, 1980;Reiskind et al, 1988Reiskind et al, , 1989Ries, 2005aRies, , 2006aRies, , 2009Stanley et al, 2005Stanley et al, , 2010. The equilibrium reactions that govern the aqueous carbonate system can be summarized as follows:…”

“…White bars are 1 µm; black bars are 100 nm. From Stanley et al (2005). suggests that calcification enhances photosynthesis via the liberation of CO 2 for some -but not all -species of coccolithophores (Paasche, 1968;Sikes et al, 1980;Leonardos et al, 2009). 4.…”

“…Hardie's oceanic Mg/Ca model is further supported by synchronized transitions between MgSO 4 and KCl evaporites (Hardie, 1996), fluid inclusion data (Lowenstein et al, J. B. Ries: Effects of secular variation in seawater Mg/Ca on marine biocalcification 2837 , 2005Brennan and Lowenstein, 2002;Brennan, 2002;Horita et al, 2002;Brennan et al, 2004;Timofeeff et al, 2006), secular variation in the skeletal Mg/Ca ratio of rugose corals (Webb and Sorauf, 2002), echinoderms (Dickson, 2002(Dickson, , 2004Hasiuk and Lohmann, 2008), and abiogenic carbonates (Hasiuk and Lohmann, 2008); secular variation in the ratio of aragonite-to-calcite within bi-mineralic calcareous serpulid worm tubes (Railsback, 1993); secular variation in the Sr/Mg ratio of abiogenic marine carbonates (Cicero and Lohmann, 2001); the occurrence of higher seawater Sr/Ca ratios during predicted calcite sea intervals than during predicted aragonite sea intervals (Sr would be depleted in seawater during aragonite sea intervals because Sr is more readily incorporated in aragonite than in calcite; Steuber and Veizer, 2002); and secular variation in the Br concentration of marine halite (Siemann, 2003).…”