Brad E. Rosenheim

The 13C Suess effect in scleractinian corals mirror changes in the anthropogenic CO2 inventory of the surface oceans

[1] New δ 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 δ 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 δ 13 C value of coral skeletons. Of these records, 64% show a statistically significant (p < 0.05) decrease in δ 13 C towards the modem 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 δ 13 C in all the coral skeletons living under open oceanic conditions is approximately - 0.01%o 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 δ 13 C of atmospheric CO 2 and the δ 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 δ 13 C of the atmosphere controls ambient δ 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 δ 13 C decline is accelerating. Superimposed on these secular variations are controls on the δ 13 C in the skeleton governed by growth rate, insolation, and local water masses.

High-resolution Sr/Ca records in sclerosponges calibrated to temperature in situ

Ratios of strontium to calcium have been analyzed by laser- ablation inductively coupled plasma-mass spectrometry (LA-ICP- MS) in a skeletal section of the sclerosponge Ceratoporella nichol- soni. The growth period, representative of 3 yr, was stained in the skeleton with a fluorochrome (calcein). Temperatures were record- ed at 2 h intervals within the shallow, cryptic reef enclosure that the sclerosponge inhabited on the northern coast of Jamaica, al- lowing 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, high- resolution empirical calibration for the temperature sensitivity of Sr/Ca ratios in the aragonite skeletons of sclerosponges from Ja- maica 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.

Perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in West Bengal, India

excess of 4600 m gk g −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 Ha ndd 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. W. Neal, T. J. Mohajerin, T. Ocheltree, B. E. Rosenheim, C. D. White, and K. H. Johannesson (2011), Perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in West Bengal, India, Geophys. Res. Lett., 38, L20404, doi:10.1029/2011GL049301.

Evidence for permafrost thaw and transport from an Alaskan North Slope watershed

Burial of organic carbon (OC) in marine sediments is one of the most important linkages between the short-term biologic carbon cycle and the long-term geologic carbon cycle. Yet much is still unknown about the fate of terrigenous OC in marine coastal margins. Here the delivery of particulate OC (POC) to the Colville River deltaic region in the Alaskan Beaufort Sea by particulates of varying densities is studied through the use of ramped temperature pyrolysis and radiocarbon analyses. The Colville River is the largest river in North America whose watershed is underlain completely by high Arctic permafrost tundra. A variety of sources of POC are considered, including terrestrial soils, Pleistocene-aged yedoma-like sediments, coastal peat erosion, and marine POC. We provide the first evidence that riverine POC from the Colville River contains old (Pleistocene-sourced) OC, suggesting ongoing thaw and mobilization of yedoma-like permafrost OC from this northern Alaskan watershed. Additionally, much of this OC appears to be fairly labile and therefore could be readily oxidized and returned to the atmosphere.

A High-Performance 14C Accelerator Mass Spectrometry System

A new and unique radiocarbon accelerator mass spectrometry (AMS) facility has been constructed at the Woods Hole Oceanographic Institution. The defining characteristic of the new system is its large-gap optical elements that provide a larger-than-standard beam acceptance. Such a system is ideally suited for high-throughput, high-precision measurements of 14C. Details and performance of the new system are presented.

Blank Corrections for Ramped Pyrolysis Radiocarbon Dating of Sedimentary and Soil Organic Carbon

Ramped pyrolysis (RP) targets distinct components of soil and sedimentary organic carbon based on their thermochemical stabilities and allows the determination of the full spectrum of radiocarbon ((14)C) ages present in a soil or sediment sample. Extending the method into realms where more precise ages are needed or where smaller samples need to be measured involves better understanding of the blank contamination associated with the method. Here, we use a compiled data set of RP measurements of samples of known age to evaluate the mass of the carbon blank and its associated (14)C signature, and to assess the performance of the RP system. We estimate blank contamination during RP using two methods, the modern-dead and the isotope dilution method. Our results indicate that during one complete RP run samples are contaminated by 8.8 ± 4.4 μg (time-dependent) of modern carbon (MC, fM ∼ 1) and 4.1 ± 5.5 μg (time-independent) of dead carbon (DC, fM ∼ 0). We find that the modern-dead method provides more accurate estimates of uncertainties in blank contamination; therefore, the isotope dilution method should be used with caution when the variability of the blank is high. Additionally, we show that RP can routinely produce accurate (14)C dates with precisions ∼100 (14)C years for materials deposited in the last 10,000 years and ∼300 (14)C years for carbon with (14)C ages of up to 20,000 years.

Varying relative degradation rates of oil in different forms and environments revealed by ramped pyrolysis.

Degradation of oil contamination yields stabilized products by removing and transforming reactive and volatile compounds. In contaminated coastal environments, the processes of degradation are influenced by shoreline energy, which increases the surface area of the oil as well as exchange between oil, water, sediments, microbes, oxygen, and nutrients. Here, a ramped pyrolysis carbon isotope technique is employed to investigate thermochemical and isotopic changes in organic material from coastal environments contaminated with oil from the 2010 BP Deepwater Horizon oil spill. Oiled beach sediment, tar ball, and marsh samples were collected from a barrier island and a brackish marsh in southeast Louisiana over a period of 881 days. Stable carbon ((13)C) and radiocarbon ((14)C) isotopic data demonstrate a predominance of oil-derived carbon in the organic material. Ramped pyrolysis profiles indicate that the organic material was transformed into more stable forms. Our data indicate relative rates of stabilization in the following order, from fastest to slowest: high energy beach sediments > low energy beach sediments > marsh > tar balls. Oil was transformed most rapidly where shoreline energy and the rates of oil dispersion and exchange with water, sediments, microbes, oxygen, and nutrients were greatest. Still, isotope data reveal persistence of oil.

Linking ramped pyrolysis isotope data to oil content through PAH analysis

Ramped pyrolysis isotope (13C and 14C) analysis coupled with polycyclic aromatic hydrocarbon (PAH) analysis demonstrates the utility of ramped pyrolysis in screening for oil content in sediments. Here, sediments from Barataria Bay, Louisiana, USA that were contaminated by oil from the 2010 BP Deepwater Horizon spill display relationships between oil contamination, pyrolysis profiles, and isotopic composition. Sediment samples with low PAH concentrations are thermochemically stable until higher temperatures, while samples containing high concentrations of PAHs pyrolyze at low temperatures. High PAH samples are also depleted in radiocarbon (14C), especially in the fractions that pyrolyze at low temperatures. This lack of radiocarbon in low temperature pyrolyzates is indicative of thermochemically unstable, 14C-free oil content. This study presents a proof of concept that oil contamination can be identified by changes in thermochemical stability in organic material and corroborated by isotope analysis of individual pyrolyzates, thereby providing a basis for application of ramped pyrolysis isotope analysis to samples deposited in different environments for different lengths of time.

Rare Earth Elements in Stromatolites—1. Evidence that Modern Terrestrial Stromatolites Fractionate Rare Earth Elements During Incorporation from Ambient Waters

Ancient chemical sediments may provide critical information about early microbial life and ancient environmental conditions. For example, the rare earth element (REE) content and fractionation patterns of Archean and Proterozoic banded iron formations (BIF) and other chemical sediments are thought to preserve the REE patterns of ancient seawater, and as such have been employed to investigate secular trends in seawater chemistry through geologic time. Recently it was suggested that REEs could provide evidence for distinguishing between biotic and abiotically precipitated chemical sediments. However, it is important to underscore that very little is actually known about how stromatolites and other microbialites obtain their REE concentrations and fractionation patterns, including what biological processes, if any, the REEs may record. Here, we present REE concentration and fractionation patterns for modern, lacustrine stromatolites and the ambient waters within which they form. We show that the REE patterns of the stromatolites are highly fractionated compared to the ambient waters. Specifically, the stromatolites exhibit heavy REEs (HREE) enrichments relative to upper crustal proxies (i.e., shale composites), whereas the ambient waters are substantially depleted in the HREEs. We propose that surface complexation and subsequent preferential incorporation of HREEs by organic ligands associated with bacterial cell walls, microbialite biofilms, and/or exopolymeric substances may explain the HREE enrichments of the stromatolites.

Petroleum hydrocarbon persistence following the Deepwater Horizon oil spill as a function of shoreline energy.

An important aspect of oil spill science is understanding how the compounds within spilled oil, especially toxic components, change with weathering. In this study we follow the evolution of petroleum hydrocarbons, including n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs, on a Louisiana beach and salt marsh for three years following the Deepwater Horizon spill. Relative to source oil, we report overall depletion of low molecular weight n-alkanes and PAHs in all locations with time. The magnitude of depletion, however, depends on the sampling location, whereby sites with highest wave energy have highest compound depletion. Oiled sediment from an enclosed bay shows high enrichment of high molecular weight PAHs relative to 17α(H),21β(H)-hopane, suggesting the contribution from sources other than the Deepwater Horizon spill, such as fossil fuel burning. This insight into hydrocarbon persistence as a function of hydrography and hydrocarbon source can inform policy and response for future spills.