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The paleoenvironment conditions that existed in the Late Pleistocene at the archaeological-paleontological site of El Arenoso, Sonora, NW Mexico, were inferred using the carbon and oxygen stable isotopes from one bison, one mammoth, and thirteen horses as well as the pedological characteristics and the carbon isotopes of calcium carbonates from paleosoil. The values d13C of the bison (-1.4%), the horses (-2.8%), and the mammoth (-4.3%) show that these animals fed mainly on C4 plants and carbon isotopic values from profile horizons of locality 4Bgk (-3.4%), 3Ck (-3.4%), and 2Bgk2 (-5.7%) indicated the presence of C3/C4 vegetation mixed in El Arenoso. The oxygen isotopic ratios of the bison (-4.3%), the horses (-2.6%), and the mammoth (-5.1%) show that these animals inhabited an arid environment, consistent with the results from the analyses of paleosols. [ABSTRACT FROM AUTHOR]

Abstract: Shallow water carbonates from Florida Bay, the Florida Reef Tract, and a Mexican Caribbean fringing reef at Punta Maroma were studied to determine the range of Ca-isotope variation among a cohort of modern carbonate producers and to look for local-scale Ca-cycling effects. The total range of Ca-isotope fractionation is 0.4‰ at Punta Maroma, yielding an allochem-weighted average δ44/40Ca value of −1.12‰ consistent with bulk sediment from the lagoon with a value of −1.09‰. These values are virtually identical to bulk carbonate sediments from the Florida Reef Tract (−1.11‰) and from one location in Florida Bay (−1.09‰) near a tidal inlet in the Florida Keys. No evidence was found for the ∼0.6‰ fractionation between calcite and aragonite which has been observed in laboratory precipitation experiments. Combining these results with carbonate production modes and δ44/40Ca values for pelagic carbonates taken from the literature, we calculate a weighted average value of −1.12±0.11‰ (2σ) for the global-scale Ca-output flux into carbonate sediments. The δ44/40Ca value of the input Ca-flux from rivers and hydrothermal fluids is –1.01±0.04‰ (2σ mean), calculated from literature data that have been corrected for inter-laboratory bias. Assuming that the ocean Ca cycle is in steady state, we calculate a δ44/40Ca value of −1.23±0.23‰ (2σ) for submarine groundwater discharge (SGD) on a global scale. The SGD Ca-flux rivals river flows and mid-ocean ridge hydrothermal vent inputs as a source of Ca to the oceans. It has the potential to differ significantly in its isotopic value from these traditional Ca-inputs in the geological past, and to cause small changes in the δ44/40Ca value of oceans through time. In the innermost water circulation restricted region of northeastern Florida Bay, sediments and waters exhibit a 0.7‰ gradient in δ44/40Ca values decreasing towards the Florida Everglades. This lowering of δ44/40Ca is predominantly caused by local-scale Ca-inputs from SGD, which has a high Ca concentration (450mg/L) and low δ44/40Ca value (−0.96‰). Mixing calculations show that Ca inputs from SGD and surface water runoff from the Florida Everglades contribute between 8% and 60% of the dissolved Ca to the studied waters with salinities between 30 and 14, respectively. Similar degrees of circulation restriction between epeiric seas and oceans in the geological past may have also led to overprinting of sedimentary carbonate δ44/40Ca values in nearshore regions of epeiric seas due to local-scale cycling of seawater through coastal carbonate aquifers. Local Ca-cycling effects may explain some of the scatter in δ44/40Ca values present in the Ca-isotope evolution curve of Phanerozoic oceans. [Copyright &y& Elsevier]

Corn tortillas are the staple food of Mexico. During their preparation, calcium is added to the tortillas; therefore, tortillas are the main source of calcium for a large proportion of the population. The bioavailability of calcium from lime-treated tortillas in humans is not known. The objectives of the present study were to determine calcium absorption from corn tortilla, to determine the effect of lime treatment on calcium absorption from corn tortilla, and to compare calcium absorption from tortilla prepared with a commercial corn flour and tortillas prepared with the traditional lime treatment at home. Nonpregnant, nonlactating women (n = 9) were administered 3 different treatments: 1) 180 g of corn tortilla prepared from corn flour with no lime treatment (CF), 2) 180 g of corn tortilla prepared from lime-treated commercial corn flour (LTCCF), or 3) 180 g of corn tortillas prepared from lime-treated home-prepared corn flour (LTHCF). Calcium absorption was measured using an established dual-tracer stable isotope technique. Calcium absorption of CF, LTCCF, and LTHCF was (mean +/- SD): 44 +/- 3.2, 32 +/- 4.4, and 30 +/- 2.4%, respectively; the fractional calcium absorption from CF differed from that of either LTCCF or LTHCF (P < 0.01). The total amount of calcium absorbed per treatment was higher in LTHCF (98.10 mg +/- 21.7) than in LTCCF (59.9 mg +/- 23.7, P < 0.001) and CF (3.78 mg +/- 0.9, P < 0.0.001). In conclusion, calcium absorption from corn tortillas is high and dependent on calcium concentration. The addition of calcium during lime treatment increases calcium concentration and total calcium absorption.