Yehoshua Kolodny

Fractionation of oxygen isotopes between mammalian bone-phosphate and environmental drinking water

The δ18O of mammalian bone-phosphate varies linearly with δ18O of environmental water, but is not in isotopic equilibrium with that water. This situation is explained by a model of δ18O in body water in which the important fluxes of exchangeable oxygen through the body are taken into account. Fractionation of oxygen isotopes between body and environmental drinking water is dependent on the rates of drinking and respiration. Isotopic fractionation can be estimated from physiological data and the estimates correlate very well with observed fractionation. Species whose water consumption is large relatively to its energy expenditure is sensitive to isotopic ratio changes in environmental water.

Oxygen isotope variations in phosphate of biogenic apatites, I. Fish bone apatite—rechecking the rules of the game

Abstract The major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone (and teeth) building organisms are alive, and the record is nearly perfectly preserved after death. Fish from seven water bodies of different temperatures (3–23°C) and different δ 18 O (values −16 to +3) of the water were analysed. The δ 18 O values of the analysed PO 4 vary from 6 to 25. The system passed the following tests: (a) the temperatures deduced from isotopic analyses of the sequence of fish from Lake Baikal are in good agreement with the temperatures measured in the thermally stratified lake; (b) the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish, but only by temperature and water composition. Isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates.

Oxygen isotope variations in phosphate of biogenic apatites, IV. Mammal teeth and bones

Groups of rats grown from birth to death in identical conditions, but with different δ18O of drinking water (δw), were studied for variations of δ18O of their body water (δBW) and bone phosphate (δp). There is a high linear correlation (r = 0.99) between δBW and between δp and δw. The regression lines have similar slope coefficients (0.53 and 0.49). Values of δp of different teeth and bones are the same, within the precision of the method (±0.5‰). The isotopic fractionation coefficient between phosphate and body water is 1.0178 and close to the estimated value of 1.0173 derived from the phosphate paleotemperature equation. Deviations from constant fractionation between bone phosphate and environmental drinking water depend primarily on rates of drinking and metabolism. Environment conditions have relatively little effect on oxygen isotope fractionation between water sources and bone phosphate.

Oxygen isotope variations in phosphate of biogenic apatites, II. Phosphorite rocks

Abstract Phosphorites from sedimentary sequences ranging in age from Archaean to Recent were analysed for δ 18 O in both the PO 4 (δ 18 O p ) and CO 3 (δ 18 O c ) in the apatite lattice. The oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts. The use of the Longinelli and Nuti [8] temperature equation yields temperatures for Recent phosphorites that are in good agreement with those measured in the field. The δ 18 O p values of ancient phosphorites decrease with increasing age. These changes with time are not likely to be due to post-depositional exchange. Changes in δ 18 O values of seawater and variations of temperature with time can account for the δ 18 O p time trend, but the latter explanation is preferred. In Ancient phosphorites δ 18 O c in structurally bound carbonate in apatite is not a reliable geochemical indicator.

Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates

Abstract The abundances and isotopic composition of boron in modern, biogenic calcareous skeletons from the Gulf of Elat, Israel, the Great Barrier Reef, Australia, and in deep-sea sediments have been examined by negative thermal-ionization mass spectrometry. The selected species (Foraminifera, Pteropoda, corals, Gastropoda, and Pelecypoda) yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals. The boron content of the biogenic skeletons is independent of mineralogical composition and is probably related to biological (vital) effects. The δ 11 B values of the carbonates range from 14.2 to 32.2%. (relative to NBS SRM 951) and overlap with the δ 11 B values of modern deep-sea carbonate sediments ( δ 11 B = 8.9 to 26.2%.). The variations of δ 11 B may be controlled by isotopic exchange of boron species in which 10 B is preferentially partitioned into the tetrahedral species, and coprecipitation of different proportions of trigonal and tetrahedral species in the calcium carbonates. Carbonates with low δ 11 B values (~ 15%.) may indicate preferential incorporation of tetrahedral species, whereas the higher δ 11 B values (~30%.) may indicate 1. (1) uptake of both boron species assuming equilibrium with seawater 2. (2) preferential incorporation of B(OH) 4 − from in situ high-pH internal fluids of organisms that are isolated from seawater. The B content and δ 11 B values of deep-sea sediments, Foraminifera tests, and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition. As a result of enrichment of B in corals, a substantially higher biogenic sink of 6.4 ± 0.9 × 10 10 g/yr is calculated for carbonates. This is only slightly lower than the sink for desorbable B in marine sediments (10 × 10 10 g/yr) and approximately half that of altered oceanic crust (14 × 10 10 g/yr). Thus, carbonates are an important sink for B in the oceans being ~20% of the total sinks. The preferential incorporation of 10 B into calcium carbonate results in oceanic 11 B-enrichment, estimated as 1.2 ± 0.3 × 10 12 per mil · g/yr. The boron-isotope composition of authigenic, well-preserved carbonate skeletons may provide a useful tool to record secular boron-isotope variations in seawater at various times in the geological record. The potential use of boron-isotope geochemistry in skeletons as a tracer for palaeoenvironments is demonstrated in Ostracoda and Foraminifera from the Gulf of Carpentaria, Australia. The δ 11 B values of glacial-age, buried skeletons (4.0 and 4.9%., respectively) are lower than that of their modern equivalents (17.6 and 13.3%., respectively). This may reflect a “terrestrial” boron-isotope signature of the water in the gulf during the Late Quaternary when it was isolated from the ocean.

Boron isotope variations during fractional evaporation of sea water: New constraints on the marine vs. nonmarine debate

Examination of boron isotopes, elemental B, Br, and Li in brines, and coprecipitated salts during fractional evaporation of sea water shows that Br, Li, and B in the evaporated sea water have lower concentrations than expected, as determined from mass-balance calculations. The deficiency is found beyond a degree of evaporation of ∼30 and is associated with a gradual increase in the δ11B values of the evaporated sea water, from 39‰ to 54.7‰ (relative to standard NBS 951). The high δ11B values of the brines and the relatively lower δ11B values of the coexisting precipitates (MgSO4 and K-MgSO4 salts; δ11B = 11.4‰ to 36.0‰) suggest selective uptake of 10B by the salts. Applying Rayleigh distillation equations, the empirical fractionation factors for the depletion of the salts in 11B are estimated as 30‰ (α = 0.969) for the early stages of precipitation (gypsum and halite range) and 20‰ (α = 0.981) for the late stages (K-MgSO4 minerals). Coprecipitation of B(OH)4- species with the salts, and/or precipitation of Mg-borate minerals with a coordination number of 4 are the proposed mechanisms for boron isotope fractionation during fractional evaporation of sea water. The boron isotope composition of sea water (δ11B = 39‰) is significantly higher than that of continental water (δ11B = -3‰ ±5‰). Our study shows that salt deposits may be depleted in 11B by 20‰ to 30‰ relative to their parent brines. These variations suggest that boron isotopes can be used to determine the origin (marine vs. nonmarine) of brines and ancient evaporitic environments.

Variations in oxygen isotopic compositions of human teeth and urinary stones

Abstract A previously reported, experimentally determined, relationship between the oxygen isotopic composition of bone and teeth phosphate (δ p ) and drinking water (δ w ), which has application to paleoclimatic interpretations, is shown to require modifications when applied to present day human populations. The oxygen isotopic compositions of 40 well documented human teeth and 11 urinary stones have shown that in both cases δ p is well correlated with δ w . The slope of the linear regression ffit of this relationship is, however, lower than expected. This is explained by a mixing of intake waters from high and low latitudes in a diet of a modern human. Urinary stones are enriched in 18 O by about 2% which we explain by: (a) different physiological (metabolic) rates of humans when teeth are formed (below the age of 20) compared to those rates when urinary stones form (generally in middle age); or (b) variations in the relative proportions of the different water intakes and outputs between healthy individuals and those forming urinary stones.

Boron isotope geochemistry of Australian salt lakes

Boron isotope geochemistry has been investigated in brines, groundwaters, and sediments from the modern Australian salt lakes of Victoria, South Australia, and Western Australia by applying negative thermal-ionization mass spectrometry techniques. The geochemical history of the brines has been reconstructed by using δ11B, BCl, and NaCl ratios. The Victorian volcanic-crater lakes of southeastern Australia have water salinities of up to 60 g/L, molar NaCl ratios (0.87) similar to the marine ratio, molar BCl ratios of 2.9 × 10−4 to 4.9 × 10−4, and δ11B values of 54%. to 59%. (relative to NBS 951). The depletion of total B and the high positive δ11B values relative to seawater (BClratio = 7.9 × 10−4; δ11B = 39%.) are attributed to a marine (cyclic) salt origin together with adsorption processes in closed systems with low water/sediment (WR) ratios. In contrast, salt lakes from South Australia and Western Australia which are large shallow playas associated with halite, gypsum, and detrital clay minerals have interstitial and surface brines characterized by salinities of 80 to 280 g/L, molar NaCl ratios of 0.85 to 1, molar BCl ratios of 4 × 10−6 to 4 × 10−4, and δ11 values of 25%. to 48%.. The δ11 values of these brines are different from those of groundwaters from the Great Artesian Basin (δ11 = −15.9%. to 2.2%.; with high molar BCl ratios of 1 × 10−3 to 3.8 × 10−2), country rocks (δ11B = −8.7%. to 6.8%.), and modern detrital sediments present in these salt lakes (δ11B = −3.2%. to 12.3%.). The δ11B values of these salt lakes overlap with those of surface and brackish waters (δ11B = 28%. to 35%.) and with the B isotopic composition of seawater (δ11B = 39%.). Both low molar NaCl ratios ( 39%) of some brines indicate interaction of the brines with detrital sediments within the salt lake systems, δ11 values < 39% suggest mixing of brines of marine origin from which B was partly removed by adsorption, with waters of terrestrial origin with low δ11 values. NaCl ratios are used as indicators of the origin of the salts as well as of halite dissolution-precipitation. The δ11 values and BCl ratios are sensitive to a marine or non-marine origin, adsorption of boron onto clays, and the effective water/sediment ratio. At low WR ratios, the preferential removal of 10B from the solution affects the bulk solution, whereas at high WR ratios, the δ11 value of a solution is not affected by adsorption. Although the δ11 value of borate minerals may be a discriminant of marine or non-marine origin, boron isotopes are less distinctive in evaporative environments where boron is not an abundant component and where water/sediment interaction occurs.

Oxygen isotopes in phosphatic fish remains from Israel: paleothermometry of tropical Cretaceous and Tertiary shelf waters

The isotopic composition of oxygen in phosphate was measured on 24 fossil fishes from Israel and Jordan ranging in age from Cretaceous to Eocene. From these, the first paleotemperatures were calculated for shallow water Cretaceous Paleotropics. The results were compared to those of fish from other Mediterranean localities and to Late Cretaceous marine reptiles from Israel. δ18O in the fish average 18.0‰ in the Early Cretaceous, 17.8‰ in the Cenomanian, 18.3‰ in the Coniacian, 18.2‰ in the Santonian, 19.4‰ in the Campanian, 20.1‰ in the Maastrichtian and 18.4‰ in the Early Eocene. Such variations suggest a warm Cenomanian-Turonian, cooling towards the end of the Cretaceous, and warming up again in the Eocene. The deduced temperatures for the Cretaceous range between 20°C and 34°C, which is about 10° higher than Cretaceous water surface temperatures in Northern Europe. Apatite from marine reptile skeletons yields similar δ18O to coexisting fish. The good agreement between these and previously known paleotemperature data give further credence to the validity of paleotemperatures obtained by isotopic analysis of oxygen in phosphates. The relatively large thermal gradient between middle and low paleolatitudes favors Barrons (1983) “coolest” Cretaceous model.

Chemical and boron isotope compositions of non-marine brines from the Qaidam Basin, Qinghai, China

The general chemistry and boron isotope composition were investigated in fresh waters and hypersaline brines from the Qaidam Basin, northern Qinghai-Xizang (Tibet) Plateau, China. This basin is a large, tectonically active system, isolated from the ocean and composed of thick clastic and evaporite sediments. The modern playas are subject to intense evaporation and are characterized by hypersaline brines as well as potash and borate evaporites. The chemical composition of the dissolved solutes in the modern brines and waters reveals three main sources: (1) inflow of hot springs enriched in sodium, sulphate and boron. Evaporation of these waters leads to a high Na/Cl ratio (>1), a NaClSO4 brine and an evaporite mineral assemblage of halite-mirabilite-borate (Lakes Daqaidam and Xiaoqaidam); (2) inflow surface river waters which are modified by preferential dissolution of halite and potassium and magnesium salts characterized by a Na(Mg)Cl solute type with low Na/Cl (<1), BrCl,LiCl and BCl ratios; and (3) Ca-chloridic subsurface brines which are controlled by both salt dissolution and dolomitization processes. Evaporation and salt crystallization of mixtures of the latter two types leads to a “marine-like” brine (e.g., NaMgCl type, NaCl ratio ⪡ 1) and mineral assemblages similar to that predicted for progressive evaporation of seawater (e.g., Qarhan playa: halite-sylvite-carnallite-bischofite). The δ11 B-values of the input waters to the Qaidam Basin (range of −0.7 to + 10.9%. vs. NBS-951 and brines from salt lakes (+0.5 to + 15.0%.) are similar to those of associated granitic rocks (δ11B= −2.3 to +3.7%.; n=3) and hence indicate the non-marine origin of these fluids. The highest δ11B-values are associated with fluids with low BLi ratios, indicating selective removal of elemental boron and 10B by adsorption onto clay minerals. The magnitude of 11B enrichment due to adsorption is ∼15–20%., and thus non-marine brines are well distinguished from marine-derived brines (δ11B of +39 to +59%.) preserving the large isotopic difference (∼40%.) of their source waters. It is proposed to use this distinctive isotopic signature for tracing the origin of ancient evaporite environments.