Earth and Environmental Sciences

Ratios of strontium to calcium have been analyzed by laserablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) in a skeletal section of the sclerosponge Ceratoporella nicholsoni. The growth period, representative of 3 yr, was stained in the skeleton with a fluorochrome (calcein). Temperatures were recorded at 2 h intervals within the shallow, cryptic reef enclosure that the sclerosponge inhabited on the northern coast of Jamaica, allowing the formulation of a direct empirical relationship between Sr/Ca and temperature. To verify this calibration, Sr/Ca ratios of two sclerosponges of the same species from depths of 67 m and 136 m in Exuma Sound, Bahamas, were analyzed by LA-ICP-MS and compared to the temperatures from these depths over a decade prior to collection. The result is an independently verified, highresolution empirical calibration for the temperature sensitivity of Sr/Ca ratios in the aragonite skeletons of sclerosponges from Jamaica and the Bahamas. The calibration is a first for C. nicholsoni and indicates that sclerosponges are more sensitive temperature recorders than zooxanthellate corals. It represents an important step in establishing skeletal geochemistry of sclerosponges as a proxy of temperature in the upper 250 m of the ocean.

This paper presents data to support the presence of (i) intra-annual signals in the chemical composition (δ 18 O and Sr/Ca) of the skeletons of sclerosponges from the Bahamas, and (ii) variable rates of skeletal accretion. These conclusions are based on data obtained by using a microsampling method for the stable oxygen and carbon isotopes in which material was

The trace and minor element composition have been investigated in the accretionary skeletons of two specimens of the Caribbean sclerosponge species, Ceratoporella nicholsoni; one from Tongue of the Ocean, Bahamas (TOTO), and the other from Pear Tree Bottom, Jamaica (PTB). Both sclerosponges were analyzed at high resolution using laser ablation ICP-MS (LA-ICP-MS) and verified using wet chemical methods (ICP-OES). The shallow PTB sclerosponge (25 m) was analyzed for a short, temperature-calibrated record of trace and minor elements while the TOTO sclerosponge (146 m) was analyzed for a century long record from subsurface waters. The resulting Ba/Ca, Mg/Ca, Pb/Ca, and U/Ca ratios were compared with Sr/Ca ratios, which have been shown to reliably record seasonal-scale temperature change in sclerosponges, close to equilibrium precipitation of inorganic aragonite. Sclerosponge aragonite incorporates minor and trace elements according to general mineralogic constraints with less “vital” effects than other calcium carbonate secreting organisms. This is perhaps most obvious in the behavior of Mg/Ca ratios which show an inverse correlation to temperature unlike any other calcite or aragonite organism, despite having Mg concentrations (∼ 1 mmol/mol) within published estimates of equilibrium aragonite. Ratios of Mg/Ca and Ba/Ca show a strong positive correlation despite large differences in ionic radii and U/Ca values (∼ 3.15 μmol/mol) are 2.5× higher in sclerosponge aragonite than in aragonite from corals, supporting earlier work. Ratios of U/Ca show an insignificant correlation with temperature-dependent Sr/Ca ratios (r2 = 0.05), supporting existing theories that temperature signals recorded by U/Ca ratios can be convolved with pH, [CO3− 2], and phosphate signals. Differences between sclerosponge aragonite and other calcium carbonate arising from siliceous spicule contamination are unlikely because of the small mole percent of silicon in the aragonite. Small differences between the two sclerosponges were noticed in Pb/Ca and Sr/Ca because of the average ages of the sampled material and average temperatures of the ambient environment, respectively. Anomalies between LA-ICP-MS and ICP-OES were noticed in measurements of Ba/Ca and Pb/Ca due to standardization differences for LA-ICP-MS (Ba/Ca) and measurements close to the instrument detection limits of Pb (ICP-OES).

A gas-accepting microwave-plasma ion source is being developed for continuous-flow Accelerator Mass Spectrometry (AMS). Characteristics of the ion source will be presented. Schemes for connecting a gas or liquid chromatograph to the ion source will also be discussed.

1] We report a detailed programmed-temperature pyrolysis/combustion methodology for radiocarbon ( 14 C) dating of Antarctic sub-ice shelf sediments. The method targets the autochthonous organic component in sediments that contain a distribution of acid-insoluble organic components from several sources of different ages. The approach has improved sediment chronology in organic-rich sediments proximal to Antarctic ice shelves by yielding maximum age constraints significantly younger than bulk radiocarbon dates from the same sediment horizons. The method proves adequate in determining isotope ratios of the pre-aged carbon end-member; however, the isotopic compositions of the low-temperature measurements indicate that no samples completely avoided mixing with some proportion of pre-aged organic material. Dating the unresolved but desired young end-member must rely on indirect methods, but a simple mixing model cannot be developed without knowledge of the sedimentation rate or comparable constraints. A mathematical approach allowing for multiple mixing components yields a maximum G 3

A revised calibration is presented relating the oxygen isotope composition of the aragonite-secreting sclerosponge Ceratoporella nicholsoni, oxygen isotope composition of seawater, and ambient water temperature. This new relationship has been obtained using high-resolution d 18 O data measured in sclerosponges from the Bahamas and Jamaica compared to ambient temperature measurements and d 18 O values of seawater from the two locations, both measured and published. New data improve an existing calibration which was determined using measurements of salinity rather than directly measured d 18 O values of the seawater and was composed of measurements from different species of sclerosponge and other aragonite-secreting organisms. The updated calibration (n = 12, r 2 = 0.95) is:

1] New d 13 C data are presented from 10 coral skeletons collected from Florida and elsewhere in the Caribbean (Dominica, Dominican Republic, Puerto Rico, and Belize). These corals range from 96 to 200 years in age and were collected between 1976 and 2002. The change in the d 13 C of the skeletons from these corals between 1900 and 1990 has been compared with 27 other published coral records from the Atlantic, Pacific, and Indian Oceans. The new data presented here make possible, for the first time, a global comparison of rates of change in the d 13 C value of coral skeletons. Of these records, 64% show a statistically significant (p < 0.05) decrease in d 13 C towards the modern day (23 out of 37). This decrease is attributable to the addition of anthropogenically derived CO 2 ( 13 C Suess effect) to the atmosphere. Between 1900 and 1990, the average rate of change of the d 13 C in all the coral skeletons living under open oceanic conditions is approximately −0.01‰ yr −1 . In the Atlantic Ocean the magnitude of the decrease since 1960,−0.019 yr −1 ±0.015‰, is essentially the same as the decrease in the d 13 C of atmospheric CO 2 and the d 13 C of the oceanic dissolved inorganic carbon (−0.023 to −0.029‰ yr −1 ), while in the Pacific and Indian Oceans the rate is more variable and significantly reduced (−0.007‰ yr −1 ±0.013). These data strongly support the notion that (i) the d 13 C of the atmosphere controls ambient d 13 C of the dissolved inorganic carbon which in turn is reflected in the coral skeletons, (ii) the rate of decline in the coral skeletons is higher in oceans with a greater anthropogenic CO 2 inventory in the surface oceans, (iii) the rate of d 13 C decline is accelerating. Superimposed on these secular variations are controls on the d 13 C in the skeleton governed by growth rate, insolation, and local water masses. Citation: Swart, The 13 C Suess effect in scleractinian corals mirror changes in the anthropogenic CO 2 inventory of the surface oceans, Geophys.

The 230 Th content of subsurface Bahamas seawater has been estimated from incrementally deposited aragonite skeletons of sclerosponges using U-series age models which imply syndepositional incorporation of 230 Th. First order age models, assuming constant growth rate and zero initial 230 Th activity, display an average surface age of 63 ± 18 y despite the fact that the surfaces of the organisms were known to be alive at the time collection in the 1990s. A knowledge of the initial 230 Th activity is necessary to incorporate the surface age constraint into an age model. In the Bahamas, this approach estimates an initial 230 Th/ 232 Th activity ratio of 4.3 ± 1.1 when applied to several individuals of the Caribbean sclerosponge Ceratoporella nicholsoni. These results differ from the same approach applied to previous work on Jamaican sclerosponges accreting aragonite in an environment closer to crustal sources and with less carbonate substrate. We report new measurements of Jamaican sclerosponge suggesting initial activity ratios of 230 Th/ 232 Th of $1, albeit with a high amount of uncertainty, indicating a regional difference in initial thorium activities. The estimates of initial 230 Th/ 232 Th activity ratios in the Bahamas are similar to the dissolved ratio rather than the particulate ratio and can be explained by mixing of open ocean water and bank-top surface water, however no information regarding temporal changes in the amount of initial 230 Th/ 232 Th activity available for incorporation into biogenic aragonite can be constrained using this approach. Growth rates do not change after correction for initial thorium and they display an inverse relationship with depth. Although this paper deals uniquely with sclerosponge aragonite, it is likely that the approach can be used on any incrementally deposited biogenic aragonite, provided information is known a priori about the first order growth model and there is evidence that initial thorium incorporation is representative of ambient environment rather than individual physiology.

Previously unpublished AMS radiocarbon measurements of a sclerosponge from tongue of the ocean (TOTO), Bahamas, as well as preliminary data from an investigation of the radiocarbon records of sclerosponges living at different depths in the adjacent Bahamas basin, Exuma Sound, are interpreted in terms of U-series age models. The data are compared to an existing Caribbean sclerosponge radiocarbon bomb curve measured using standard gas proportional beta counting and used to interpret a 210 Pb age model. The D 14 C records from the sclerosponges illustrate a potential for use of radiocarbon both as a tracer of subsurface water masses or as an additional age constraint on recently sampled sclerosponges. By using an independent age model, this study lays the framework for utilizing sclerosponges from different locations in the tropics and subtropics and different depths within their wide depth range (0-250 m) to constrain changes in production of subtropical underwater in the Atlantic Ocean. This framework is significant because the proxy approach is necessary to supplement the short and coarse time series being used to constrain variability in the formation of Caribbean subtropical underwater, the return flow of a shallow circulation cell responsible for nearly 10% of the heat transported poleward in the N. Atlantic.

Determination of 14 C in aragonite (CaCO3) decomposed thermally to CO2 using an yttrium-aluminum-garnet doped neodymium laser is reported. Laser decomposition accelerator mass spectrometer (LD-AMS) measurements reproduce AMS determinations of 14 C from conventional reaction of aragonite with concentrated phosphoric acid. The lack of significant differences between these sets of measurements indicate that LD-AMS radiocarbon dating can overcome the significant fractionation that has been observed during stable isotope (C and O) laser decomposition analysis of different carbonate minerals. The laser regularly converted nearly 30% of material removed to CO2 despite being optimized for ablation, where laser energy breaks material apart rather than chemically altering it. These results illustrate promise for using laser decomposition on the front-end of AMS systems that directly measure CO2 gas. The feasibility of such measurements depends on 1. the improvement of material removal and/or CO2 generation efficiency of the laser decomposition system and 2. the ionization efficiency of AMS systems measuring continuously flowing CO2.

A reef monitoring program off Roatan, Bay Islands, Honduras has produced base line data for platform bathymetry, major macrofauna distribution, and sediment attributes. Because erosion accompanying accelerated island development will be increasing in the near future, measurements of total suspended solids and sedimentation rate were made. Results show TSS range from 8 to 70 mg/l in the summer and 30 to 222mgll in the winter. Sedimentation rates in the fore reef, where finer-grained terrigenous material would potentially accumulate, are 0.14mglcm 2/day to 7.07mglcm 2/day in the summer and 41 to 7lmglcm 2/day in the winter. The summer values are well within the ranges of published results from other Caribbean carbonate platforms, however winter values are up to ten times that of other localities.

Atmospheric teleconnections between the tropical Atlantic and the African continent, extending to the Indian Ocean basin, modulate the interannual variability of precipitation in highly vulnerable and densely populated regions like the Sahel and the Indian peninsula. Additionally, increasing evidence supports the notion

High-resolution records of seawater temperature and salinity , based on geochemical proxies in the skeletons of scleractinian corals 1-8 , are currently limited to near-surface waters and to the last 200-300 years. Because of their greater depth range (0-250m) and longer lifespan (500-1000y) than corals, sclerosponges can potentially extend pre-instrumental ocean temperature and salinity records beyond the last millennium and below the thermocline in tropical and sub-tropical waters 9-11 . Here we establish an empirical calibration for the temperature sensitivity of Sr/Ca ratios in the aragonite skeletons of sclerosponges from Jamaica and the Bahamas. Sr/Ca(mmol·mol -1 ) = 12.49 (±1.23) -0.102 (±0.034) T(°C) eq. (1) We then apply this calibration to a century long record of Sr/Ca and δ 18 O from a sclerosponge collected at 146m in the Bahamas 12 . Our data suggest that significant changes to water mass transport have occurred over the last 100y in the western subtropical Atlantic Ocean as a result of wind driven down-mixing, isopycnal advection, or a combination of both. These data highlight the importance of high resolution pre-instrumental temperature and salinity records constraining the thermocline in subtropical and tropical oceans. The oxygen isotopic ( 18 O/ 16 O) and minor element (Sr, Mg, U) content of the skeletons of scleractinian corals provide valuable information on surface salinity and temperature in tropical and subtropical oceans over the past several centuries. However, these records are generally limited to 200-300y and are restricted to the photic zone. Additional proxies are needed to extend oceanographic records below the tropical thermocline and to increase the length of high-resolution temperature and salinity records predating instrumental records. One primary candidate is the sclerosponge, Ceratoporella nicholsoni, which lives in cryptic environments at depths up to 250m throughout the Caribbean Sea. This species secretes a dense aragonite skeleton at rates of approximately 200µm/y in the Caribbean 11,13-15 , therefore specimens of only 20cm in diameter can possess ages in excess of 1000 years. Several workers have established that the δ 18 O values of sclerosponge skeletons are close to equilibrium with seawater 16

Upper Permian and Lower Triassic palaeosols from northeastern Tethyan localities exposed within the Bogda Mountains, NW China, provide a wealth of information regarding long-term palaeoclimatic and palaeoenvironmental variations. Wuchiapingian palaeosols are characterized by intense redoximorphy, accumulation of vascular plant matter, accumulation of clay minerals and Fe-oxides, slickensides, and clastic dikes, suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget. Changsinghian to early Induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter, indicative of sub-humid to sub-arid soil moisture and variable soil moisture regimes. Induan to Olenekian palaeosols contain pedogenic CaCO3 accumulations and gypsum pseudomorphs, indicating a drier environment characterized by net soil moisture deficiency. Elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus Potassium (CIA-K) proxy. Estimates from various Wuchiapingian strata indicate relatively stable palaeoprecipitation. During the late Changsinghian and early Induan, palaeoprecipitation appears to have decreased from 1100 to 230 (± 180) mm/year over less than 100 m of vertical stratigraphic section. In the Induan and Olenekian, palaeoprecipitation appears much less stable than in Wuchiapingian, with values vacillating from 290 to 1014 mm/year. The transition to a relatively unstable precipitation state coincides generally with the Permian–Triassic boundary, and may reflect climatic disturbances associated with the end-Permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics, moisture availability, and expansion of the subtropical high pressure belt.

1] Arsenic (As) concentrations and stable hydrogen (d 2 H) and oxygen (d 18 O) isotope ratios of surface and groundwaters from a representative site in West Bengal, India, are reported. Shallow groundwaters (≤35 m) from the study site have among the highest As concentrations measured in the entire Bengal Basin, reaching values in excess of 4600 mg kg −1 . Stable isotope ratios of waters from constructed, perennial ponds indicate the ponds are chiefly recharged during the summer monsoon, and subsequently undergo extensive evaporation during the dry (winter) season. In contrast, groundwaters with high As concentrations plot along the local meteoric water line (LMWL) near where the annual, volume-weighted mean precipitation values for d 2 H and d 18 O would plot. The stable isotope data demonstrate that groundwaters are directly recharged by local precipitation without significant evaporation, and thus are not recharged by, nor mixed with, the pond waters. Furthermore, reactive transport modeling indicates that dissolved organic matter (DOM) derived from pond waters does not fuel microbial respiration and As mobilization at depth in the underlying aquifer because travel times for pond-derived DOM exceed groundwater ages by thousands of years. Instead, organic matter within the aquifer sediments must drive dissimilatory iron reduction and As release to groundwaters. Citation: Datta, S., A.

Groundwater samples were collected along flow paths within the Carrizo Sand aquifer (southeastern Texas) and the Aquia aquifer (coastal Maryland) for analysis of dissolved tungsten (W) concentrations, along with the major solutes, pH, and measures of in situ redox conditions [e.g., dissolved Fe(II), Fe(III), and S(-II) concentrations]. In addition, sediment samples were collected from both aquifers to evaluate the solid-phase speciation of W. Tungsten concentrations in the Carrizo Sand aquifer range from 3.64 to 1297 pmol kg −1 (mean ± SD = 248 ± 440 pmol kg −1 ), with the lowest concentrations reported from the recharge area. Tungsten concentrations progressively increase down gradient along the flow path within Carrizo Sand aquifer groundwaters, reaching the highest levels in sulfidic groundwater roughly 50-60 km from the recharge zone. Tungsten is strongly correlated with pH and dissolved sulfide [i.e., S(-II)] concentrations in Carrizo groundwaters (r = 0.78 and 0.95, respectively). In Aquia aquifer groundwaters W concentrations range between 14.3 and 184.4 pmol kg −1 (mean ± SD = 63.9 ± 59 pmol kg −1 ), and exhibit no, or at best, weak relationships with other geochemical parameters measured along the flow path (e.g., r = 0.4 and 0.08 for W vs. pH and S(-II), respectively). The data suggest that the increase in W concentrations in Carrizo groundwaters reflects, in part, pH-related adsorption/desorption, which has been shown to be substantial for groundwaters and lake waters with pH > 8. Owing to the similar chemical properties of W and Mo, which form thiomolybdates in sulfidic waters, the formation of thiotungstate complexes may also be important in the sulfidic waters of the Carrizo aquifer. The substantially lower W concentrations in Aquia aquifer groundwaters reflect the fact that the maximum groundwater pH never exceeds 8.4 (mean ± SD pH = 7.97 ± 0.23), dissolved low S(-II) concentrations remain low (mean ± SD S(-II) =0.29 ± 0.16 μmol kg −1 ), and that Aquia aquifer sediments have substantially higher Fe(III) oxide/oxyhydroxide contents compared to the Carrizo Sand aquifer. Our data indicate that pH-related adsorption/desorption reactions and the Fe(III) oxide/oxyhydroxide content of aquifer sediments are key controls affecting W concentrations in oxic, suboxic, and anoxic groundwaters, and, further, that the formation of thiotungstate species may also be important in some anoxic (i.e., sulfidic) waters.

Sediments from the Aquia aquifer in coastal Maryland were collected as part of a larger study of As in the Aquia groundwater flow system where As concentration are reported to reach levels as high as 1072 nmol kg À1 , (i.e., $80 lg/L). To test whether As release is microbially mediated by reductive dissolution of Fe(III) oxides/oxyhydroxides within the aquifer sediments, the Aquia aquifer sediment samples were employed in a series of microcosm experiments. The microcosm experiments consisted of sterilized serum bottles prepared with aquifer sediments and sterilized (i.e., autoclaved), artificial groundwater using four experimental conditions and one control condition. The four experimental conditions included the following scenarios: (1) aerobic; (2) anaerobic; (3) anaerobic + acetate; and (4) anaerobic + acetate + AQDS (anthraquinone-2,6-disulfonic acid). AQDS acts as an electron shuttle. The control condition contained sterilized aquifer sediments kept under anaerobic conditions with an addition of AQDS. Over the course of the 27 day microcosm experiments, dissolved As in the unamended (aerobic and anaerobic) microcosms remained constant at around $28 nmol kg À1 (2 lg/L). With the addition of acetate, the amount of As released to the solution approximately doubled reaching $51 nmol kg À1 (3.8 lg/L). For microcosm experiments amended with acetate and AQDS, the dissolved As concentrations exceeded 75 nmol kg À1 (5.6 lg/L). The As concentrations in the acetate and acetate + AQDS amended microcosms are of similar orders of magnitude to As concentrations in groundwaters from the aquifer sediment sampling site (127-170 nmol kg À1 ). Arsenic concentrations in the sterilized control experiments were generally less than 15 nmol kg À1 (1.1 lg/L), which is interpreted to be the amount of As released from Aquia aquifer sediments owing to abiotic, surface exchange processes. Iron concentrations released to solution in each of the microcosm experiments were higher and more variable than the As concentrations, but generally exhibited similar trends to the As concentrations. Specifically, the acetate and acetate + AQDS amended microcosm typically exhibited the highest Fe concentrations (up to 1725 and 6566 nmol kg À1 , respectively). The increase in both As and Fe in the artificial groundwater solutions in these amended microcosm experiments strongly suggests that microbes within the Aquia aquifer sediments mobilize As from the sediment substrate to the groundwaters via Fe(III) reduction.