Search

Microfossils offer a wealth of paleoenvironmental information, but their extraction from consolidated material, especially ancient rocks, is time-consuming and often lacks systematic methodological development. This study examined the efficacy of repeated freeze-thaw processing paired with different surfactants (anionic, cationic, and detergent) on the extraction of fossils from the order Dacryoconarida, conically shaped calcareous microfossils that occur in diverse marine facies of the Devonian Period. A stepwise technique was developed involving saturation of rocks in either 18 Ω water or 25% NaCl, followed by freezing and then boiling in surfactant (Pinequat, Decon 90, or Calgon in Na 2 CO 3 solution). In comparison with saturation in NaCl solution, saturation in water generally had higher yields of disaggregated material and more intact fossils. All surfactants performed better at extraction compared to boiling in pure water. Across all lithologies examined, Na 2 CO 3 -buffered Calgon (sodium hexametaphosphate) disaggregated rock most efficiently, but Na 2 CO 3 solution alone generally had the highest yield of total and intact fossil specimens. Pinequat, a cationic surfactant, yielded more disaggregate for siliclastic samples compared to calcareous samples, but had lower fossil yield. Decon 90, an anionic surfactant, performed better at disaggregating limestones and had higher fossil extraction efficiency than Pinequat across all lithologies. Freeze-thaw processing pairing water saturation and 5% Na 2 CO 3 simmering is an effective treatment for the disaggregation of rocks to extract analytically viable amounts of dacryoconarids from fossiliferous samples. This pairing had greater fossil extraction potential than surfactants at the concentrations tested in this study and is recommended if the elemental composition of the target rocks is unconstrained. • For limestones, alkaline solutions and anionic surfactants extracted the most intact fossils. • Black shale was resistant to surfactants. Repeated water-based freeze-thaw processing was most effective for extraction. • For lithologies with high clay content Calgon and Na 2 CO 3 were most efficient at disaggregation. •.Calgon and Na 2 CO 3 have high disaggregating potential, but Calgon is more fragmentary to fossils than Na 2 CO Calgon and Na 2 CO 3 have high disaggregating potential, but Calgon is more fragmentary to fossils than Na 2 CO 3. • For arenaceous rocks, cationic surfactants may have a slightly higher disaggregation potential than anionic surfactants. [ABSTRACT FROM AUTHOR]

The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today's, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene–Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene–Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic–anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals. [ABSTRACT FROM AUTHOR]

Public and regulatory agencies are concerned over the potential for drinking water contamination related to high-volume hydraulic fracturing (hydrofracking) of the Marcellus shale in Pennsylvania and in New York State (NYS), where exploitation of Marcellus gas has not yet begun. Unique natural tracers are helpful for distinguishing the influence of formation water and/or flow-back water. Here we use halogen concentrations, particularly bromine and iodine, to characterize natural variability of baseline water chemistry in the southern tier of NYS. Majority of streams and drinking water wells have Br and I concentrations below 1 and 0.1 μM, respectively, a range typical for relatively pristine surface water and shallow groundwater. Wells that have higher Br and I concentrations are likely affected by formation waters. Br/I ratios indicate two different sources of formation waters in these wells, possibly controlled by geologic settings. Our results suggest that iodine, combined with other halogens, may be a novel and sensitive tool for fingerprinting trace levels of formation water signal in drinking water sources. [ABSTRACT FROM AUTHOR]

Abstract: Calcium carbonate can crystallize in a hydrated form as ikaite at low temperatures. The hydration water in ikaite grown in laboratory experiments records the δ18O of ambient water, a feature potentially useful for reconstructing δ18O of local seawater. We report the first downcore δ18O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula (AP), a region sensitive to climate fluctuations. We are able to establish the zone of ikaite formation within shallow sediments, based on porewater chemical and isotopic data. Having constrained the depth of ikaite formation and δ18O of ikaite crystals and hydration waters, we are able to infer local changes in fjord δ18O versus time during the late Holocene. This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula. [Copyright &y& Elsevier]

Abstract: The Akita and Niigata Basins are part of the Green Tuff region of Honshu, Japan, which hosts major occurrences of oil and gas and of hydrothermal sulfide-sulfate Kuroko Deposits. The Green Tuff formation is associated with the opening of the Japan Sea, which occurred in the Early Miocene and was accompanied by large-scale volcanic activities. We measured halogen concentrations and 129I/I ratios in oil and gas field brines and hot springs in order to determine the origin of iodine and, indirectly, of hydrocarbons in this area and their association with geological processes during the formation of the Japanese Island Arc. Based on the concentration of iodine, these samples fall into three categories: Type A (I>190 μM), Type B (150 μM>I>90 μM), and Type C (I<50 μM). Samples in Types A and B come predominantly from oil/gas fields and have 129I/I ratios below 300×10−15, corresponding to ages essentially in the Eocene epoch. In contrast, samples in Type C are generally from hot springs and have 129I/I ratios above 400×10−15, corresponding to Oligocene to Miocene ages. Source formations for Type C were accumulated during the active opening of the Japan Sea, however, those for Types A and B probably are organic-rich Eocene sediments or older basement rocks which predate the volcanic formations associated with the backarc spreading of the Japanese Island. The observation that oil and gas is predominantly found in reservoir formations of middle to late Miocene age suggests mobilization of these brines in association with the tectonic and volcanic/hydrothermal activities during the opening of the Japan Sea which also led to the formation of the Kuroko Deposits in the same area. The hot spring samples of Type C reflect these processes most directly. Because of the close association of iodine with methane and other hydrocarbons, oil and gas in the Green Tuff area probably is also derived from sources considerably older than the current reservoir formations. [Copyright &y& Elsevier]

Abstract: Hydrate Ridge off the coast of Oregon, USA, is a prime example for gas hydrate occurrences in active margin settings. It is part of the Cascadia Margin and was the focus of Ocean Drilling Program (ODP) Leg 204, which successfully recovered fluids from nine sites from the southern part of the ridge. Iodide concentrations in pore fluids associated with gas hydrates are strongly enhanced, by factors up to 5000 compared to seawater, which allows the use of this biophilic element as tracer for organic source regions. We applied the cosmogenic isotope 129I (T 1/2 =15.7 Ma) system to determine the age of the organic source formation responsible for the iodide enrichment. In all sites at ODP Leg 204, 129I/I ratios were found to decrease with depth to values around 250×10−15, corresponding to minimum ages of 40 Ma, but in several sites, maxima in the 129I/I ratios point to the local addition of young iodide. The results indicate that a large amount of iodide was derived from deep accreted sediments of Eocene age, and that additional source regions provide iodide of Late Miocene age. The presence of old iodide in the pore waters suggests that fluid pathways are open to allow transport over large distances into the gas hydrate fields. The strong correlation between iodide and methane in hydrate fields coupled with the similarity in transport parameters in aqueous solutions suggests that a large fraction of methane in gas hydrates also has old sources and is transported into the present locations from source regions of Eocene age. [Copyright &y& Elsevier]

Abstract: A gas hydrate field with highly active venting of methane was recently found near Sado Island in the eastern Japan Sea. Piston cores were collected from active venting sites and nearby locations in the Umitaka Spur–Joetsu Knoll area during two cruises in 2004 (UT04) and 2005 (KY05-08). We report here halogen concentrations and 129I/I ratios in pore waters associated with gas hydrates from these expeditions. The strongly biophilic behavior of I and, to a lesser degree, of Br together with the presence of the long-lived iodine radioisotope (129I) allow evaluation of potential source materials for methane in gas hydrate systems. Depth profiles of all three halogens, particularly the very rapid downward increases of Br and I concentrations, strongly suggest input of deep fluids enriched in Br and I, but the profiles also display the effects of gas hydrate formation and dissociation. Although the 129I/I ratios are modified by 129I from seawater and sediments at shallow depth, likely ratios of the deep fluids are estimated to be between 400×10−15 and 600×10−15, equivalent to a Late Oligocene to Early Miocene age. Ages in the active methane venting sites typically are closer to the old end of this range than those in the reference sites. This age range suggests that the methane associated with venting and gas hydrate formation in this area is derived from organic materials accumulated during the initial opening of the Japan Sea. The Umitaka Spur–Joetsu Knoll gas hydrate field demonstrates the movement of deep fluids associated with the release of significant amounts of methane from the seafloor, processes which might be important components of mass transfer and carbon cycle in the shallow geosphere. [Copyright &y& Elsevier]

Contents of Fe, Mn and other elements in four ferromanganese crusts recovered from the central North Pacific are analyzed at high depth-resolution by electron microprobe for reconstructing factors controlling their deposition. Manganese (IV) in hydrogenetic ferromanganese crusts is mainly supplied as colloidal precipitates from the Oxygen Minimum Zone (OMZ), which concentrates high amounts of dissolved Mn (II). The iron is derived from carbonate dissolution and silicate particles of eolian dust. An increase in paleoproductivity during cooler climate would potentially lead to a decrease in Mn deposition due to enlargement of the OMZ which has a "temporary storage" effect for Mn. On the other hand, not affected by the OMZ, the iron entering the Fe-Mn crust would likely increase with the eolian dust input and surface productivity at glacial stages. As a result, the increasing Fe/Mn ratio should indicate a cooling climate. This is supported by the following observations. In the profile of the past 1 Ma, the variations of Fe/Mn ratio coincide with benthic oxygen isotope fluctuation in glacial- interglacial cycles. Three episodes with high Fe/ Mn ratios, approximately at 2.6, 1.8 and 0.8 Ma, are detected within the past 3 Ma and coincide with major climate transitions and cooling events. The secular evolution pattern of Fe/Mn ratio in the Cenozoic is similar to the Pb isotope evolution which is mainly controlled by eolian dust and related to climate. The Fe/Mn evolution pattern is also broadly consistent with the global deep-sea oxygen isotope records. Therefore, Fe/Mn ratio recorded in the ferromanganese crusts may be a new proxy for climate change. [ABSTRACT FROM AUTHOR]

Numerous closed-basin prairie wetlands throughout the Prairie Pothole Region (PPR) of North America maintain moderate surface pond salinities (total dissolved solids [TDS] from 1 to 10 g L − 1 ) under semiarid climate by accumulation of gypsum and saline lenses of sulfate-rich porewater (TDS > 10 g L − 1 ) in wetland sediments during droughts. In order to understand the hydrogeochemical origin and composition of these saline porewaters, we made a detailed geochemical survey of Cl − , SO 4 2 − , Br, and I in the porewater, pondwater, and upland groundwater of a typical closed-basin prairie wetland (P1 in the Cottonwood Lake study area, North Dakota). Concentrations of Cl − ranged up to 5.9 mM in the saline porewaters, and was strongly correlated with SO 4 2 − and Br (Pearson's r > 0.7, p < 0.05; concentrations ranging up to 131 mM and 39 μM, respectively) due to the conservative effects of surface water evaporation. In contrast, total dissolved I was not significantly correlated with Cl − (Pearson's r = 0.18, p = 0.273) and was concentrated in porewaters located above the saline lenses with a peak concentration of 4.1 μM beneath the center of the wetland— the highest value for dissolved I ever measured in a terrestrial aquatic system and an order of magnitude above that of seawater. We hypothesize that chromatographic separation between more mobile anions (Cl − , SO 4 2 − , Br − ) and I occurs during droughts when wetland ponds dry and sedimentary iodide (I − ) oxidizes to its less-mobile form, iodate (IO 3 − ). Understanding the origin and geochemical composition of porewater salinity that develops beneath prairie wetlands during drought can help to fingerprint sources of salinity to wetland ponds during wet climate and elucidate halogen systematics in saline and organic-rich subsurface environments associated with hydrocarbon generation. [ABSTRACT FROM AUTHOR]

Unsaturated zone pore water has the potential to record history of recharge, palaeoenvironment, pollution movement and water-rock interaction as it percolates through and moves towards the water table. In this study, two 6-m cores from the Badain Jaran desert (NW China) were collected to explore this potential using directly extracted moisture. Pore waters in these unsaturated zone sediments (1–5% moisture by wet weight) were directly extracted using immiscible liquid displacement and then analysed for major anions, cations and trace elements. Results show enrichment in pore water chemistry in the top 1–2 m where strong temperature and moisture fluxes occur. The enrichment in cations relative to chloride is primarily due to silicate mineral dissolution during infiltration. High nitrate and low iron concentrations indicate the overall oxidizing environment, which allows the mobility of oxyanions, such as uranium, arsenic and chromium. The trace elements show enrichment in the upper zone of fluctuation where chemical gradients are strong, but with lesser reaction lower in the profile. The calculated groundwater recharge rates using the chloride mass balance are negligible in this arid region between 1.5 and 3.0 mm/year. The modern rainfall infiltration signature contrasts with that of the underlying groundwater body, which has a distant, regional recharge signature. This reconnaissance study demonstrates the potential for a new geochemical approach to studying geochemical processes in the unsaturated sediments in semi-arid environments due to both natural and human influences. The use of directly extracted water, rather than extraction by dilution (elutriation), facilitates an improved understanding of hydrological and geochemical processes in the unsaturated zone and into the capillary fringe at the water table, because it avoids potential chemical changes induced during elutriation. [ABSTRACT FROM AUTHOR]

Otolith chemistry is often useful for tracking provenance of fishes, as well as examining migration histories. Whereas elements such as strontium and barium correlate well with salinity and temperature, experiments that examine manganese uptake as a function of these parameters have found no such correlation. Instead, dissolved manganese is available as a redox product, and as such, is indicative of low-oxygen conditions. Here we present evidence for that mechanism in a range of habitats from marine to freshwater, across species, and also present ancillary proxies that support the mechanism as well. For example, iodine is redox-sensitive and varies inversely with Mn; and sulfur stable isotope ratios provide evidence of anoxic sulfate reduction in some circumstances. Further, S may be incorporated trophically whereas other elements appear to be taken up directly from water. This research suggests a potential means to identify individual fish exposure to hypoxia, over entire lifetimes. With further testing and understanding, in the future fish may be able to be used as “mobile monitors” of hypoxic conditions. [ABSTRACT FROM AUTHOR]

The late Cambrian Steptoean positive carbon isotope excursion (SPICE) is a distinct chemostratigraphic feature of the Paleozoic, marked by a 4–5‰ shift in carbonate δ13C that has been recognized across the globe during the Paibian Stage. The SPICE may be related to enhanced burial of organic matter and pyrite during the expansion of marine euxinia, which as a source of O 2 also results in a pulse of atmospheric oxygen. However, geochemical proxies have not clearly illustrated how the ocean redox evolved with atmospheric oxygen changes during the SPICE. This study presents new carbonate I/Ca data, a redox proxy for the upper ocean, from three basins. I/Ca values are low at Great Basin and South China from early into the peak of SPICE, indicating generally anoxic conditions in shallow waters. The overall increasing trend in I/Ca through the peak and recovery phase of the SPICE roughly correlates with the previously modeled rise in atmospheric oxygen. Spatially, the Georgina Basin (Mt. Whelan) might have recorded a relatively more oxic upper ocean compared to the Great Basin and South China. Earth system model simulations also demonstrate the importance of paleogeographic and oceanographic settings on local redox conditions, highlighting the redox heterogeneity during the SPICE. • I/Ca proxy was used for reconstructing redox condition during SPICE. • An oxygenation event in the upper ocean was found during the peak and recovery phase of SPICE. • The ocean redox changes varied in different paleogeographic settings. [ABSTRACT FROM AUTHOR]

Abstract: Iodine and its radioisotope 129I have been successfully used to trace the origin of pore waters in submarine fluid escape structures because of their close association with organic material in deeply buried sediments. We report here halogen concentrations and 129I/I ratios for fluids of five mud volcanoes sampled along an E–W transect across the Gulf of Cadiz in the NE Atlantic Ocean. Concentrations of iodide and bromide increase consistently seaward accompanied by a decrease in 129I/I ratios from 6490×10−15 to 663×10−15. The exceptionally high 129I/I ratios at the near-shore locations reflect the presence of fissiogenic 129I, produced in situ by spontaneous fission of 238U within terrigenous sediments and released into pore water during clay mineral diagenetic processes. The observed 129I/I and halogen trends, together with similar changes in 87Sr/86Sr ratios, indicate a progressive seaward transition from inorganic-terrigenous to organic-marine fluid sources. Comparison of our results with literature data for varying geological settings reveals a general relationship between fissiogenic 129I, radiogenic 87Sr and the lithology or provenance of rocks and sediments, respectively. While 129I/I ratios in continental rock-hosted aquifers and terrigenous sedimentary systems are dominated by in situ production of fissiogenic 129I, iodine isotopes in oceanic settings or volcanogenic marine sediments reflect the release of ‘old’ iodine from deeply buried organic matter. The Gulf of Cadiz represents the full transition between these continental and oceanic 129I/I and 87Sr/86Sr end members. This is the first systematic investigation of fissiogenic 129I production in marine sedimentary environments. [Copyright &y& Elsevier]

Abstract: The authors report here halogen concentrations in pore waters and sediments collected from the Mallik 5L-38 gas hydrate production research well, a permafrost location in the Mackenzie Delta, Northwest Territories, Canada. Iodine and Br are commonly enriched in waters associated with CH4, reflecting the close association between these halogens and source organic materials. Pore waters collected from the Mallik well show I enrichment, by one order of magnitude above that of seawater, particularly in sandy layers below the gas hydrate stability zone (GHSZ). Although Cl and Br concentrations increase with depth similar to the I profile, they remain below seawater values. The increase in I concentrations observed below the GHSZ suggests that I-rich fluids responsible for the accumulation of CH4 in gas hydrates are preferentially transported through the sandy permeable layers below the GHSZ. The Br and I concentrations and I/Br ratios in Mallik are considerably lower than those in marine gas hydrate locations, demonstrating a terrestrial nature for the organic materials responsible for the CH4 at the Mallik site. Halogen systematics in Mallik suggest that they are the result of mixing between seawater, freshwater and an I-rich source fluid. The comparison between I/Br ratios in pore waters and sediments speaks against the origin of the source fluids within the host formations of gas hydrates, a finding compatible with the results from a limited set of 129I/I ratios determined in pore waters, which gives a minimum age of 29Ma for the source material, i.e. at the lower end of the age range of the host formations. The likely scenario for the gas hydrate formation in Mallik is the derivation of CH4 together with I from the terrestrial source materials in formations other than the host layers through sandy permeable layers into the present gas hydrate zones. [Copyright &y& Elsevier]

The Devonian Period witnessed the expansion of vascular land plants and an atmospheric oxygenation event associated with enhanced organic mass burial. The deposition of organic-rich shales (e.g. black shales of the Marcellus subgroup) and several biotic crises in the marine realm have been linked to Devonian ocean anoxia. However, it is not clear how redox conditions evolved in different parts of the water column in such a context of dynamic changes in the atmosphere-ocean system. To address this problem, we use the bulk carbonate I/Ca proxy on core samples from Yates County, NY, in order to reconstruct the water column redox history through the Onondaga Limestone into the lower Marcellus shale. On the secular scale, the range of I/Ca values support the notion of a Devonian rise in atmospheric oxygen, relative to time intervals earlier in the Paleozoic. In terms of Eifelian Stage stratigraphic trends, I/Ca ratios are generally stable and high in the Onondaga Formation but show large fluctuations in lower Marcellus strata. Low I/Ca ratios are found near the onset of organic-rich shale deposition indicating relatively reducing subsurface waters. The pattern of redox changes resembles that of contemporaneous sea-level changes. Finally, the reconstructed oxygenation changes are correlated to three biotic transitions in Devonian marine systems. [ABSTRACT FROM AUTHOR]

Profound changes in upper ocean oxygenation have taken place in recent decades and are expected to continue in the future, but the complexity of the processes driving these changes has yet to be fully unraveled. Planktic foraminiferal I/Ca is a promising tool to reconstruct the extent of past upper ocean oxygenation, but a thorough assessment is necessary to evaluate both its potential and its limitations. We used foraminifers from Holocene core-tops (Southeast Atlantic Ocean) to document planktic I/Ca across a range of oceanographic conditions. Subsurface O 2 concentrations may be the dominant control on planktic foraminiferal I/Ca and planktic I/Ca decreases rapidly at low O 2 conditions (O 2 < ∼70–100 µmol/kg). We thus document that low planktic I/Ca can be used empirically to indicate hypoxia in the upper water column, but questions remain as to the mechanistic understanding of the relation between seawater iodine speciation change, its O 2 threshold and foraminiferal I/Ca. Planktic I/Ca records from core GeoB1720-2 (Benguela Upwelling System, SE Atlantic) suggest that hypoxic waters were present near the site persistently during the last 240 ka, without clear glacial-interglacial variability. [ABSTRACT FROM AUTHOR]

Profound changes in environmental conditions, particularly atmospheric oxygen levels, are thought to be important drivers of several major biotic events (e.g. mass extinctions and diversifications). The early Paleozoic represents a key interval in the oxygenation of the ocean–atmosphere system and evolution of the biosphere. Global proxies (e.g. carbon ( δ 13 C) and sulfur ( δ 34 S) isotopes) are used to diagnose potential changes in oxygenation and infer causes of environmental change and biotic turnover. The Cambrian–Ordovician contains several trilobite extinctions (some are apparently local, but others are globally correlative) that are attributed to anoxia based on coeval positive δ 13 C and δ 34 S excursions. These extinction and excursion events have yet to be coupled with more recently developed proxies thought to be more reflective of local redox conditions in the water column (e.g. I/Ca) to confirm whether these extinctions were associated with oxygen crises over a regional or global scale. Here we examine an Early Ordovician (Tremadocian Stage) extinction event previously interpreted to reflect a continuation of recurrent early Paleozoic anoxic events that expanded into nearshore environments. δ 13 C, δ 34 S, and I/Ca trends were measured from three sections in the Great Basin region to test whether I/Ca trends support the notion that anoxia was locally present in the water column along the Laurentian margin. Evidence for anoxia is based on coincident, but not always synchronous, positive δ 13 C and δ 34 S excursions (mainly from carbonate-associated sulfate and less so from pyrite data), a 30% extinction of standing generic diversity, and near-zero I/Ca values. Although evidence for local water column anoxia from the I/Ca proxy broadly agrees with intervals of global anoxia inferred from δ 13 C and δ 34 S trends, a more complex picture is evident where spatially and temporally variable local trends are superimposed on time-averaged global trends. Stratigraphic sections from the distal and deeper part of the basin (Shingle Pass and Meiklejohn Peak) preserve synchronous global ( δ 13 C and δ 34 S) and water column (I/Ca) evidence for anoxia, but not at the more proximal section (Ibex, UT). Although geochemical and paleontological evidence point toward anoxia as the driver of this Early Ordovician extinction event, differences between I/Ca and δ 13 C– δ 34 S signals suggest regional variation in the timing, extent, and persistence of anoxia. [ABSTRACT FROM AUTHOR]

Carbonate-associated iodine (I/Ca) has been used as a proxy of local, upper-ocean redox conditions, and has successfully demonstrated highly dynamic spatial and temporal patterns across different time scales of Earth history. To further explore the utility of iodine as a paleo-environmental proxy, we present here a new method of extracting organically bound iodine (I org ) from shale using volumes of samples on the order of tens of milligrams, thus offering the potential for high-resolution work across thin shale beds. The ratio of I org to total organic carbon (I/TOC) in modern surface and subsurface sediments decreases with decreasing bottom-water oxygen, which may be used to reconstruct paleo-redox changes. As a proof of concept, we evaluate the I/TOC proxy in Holocene sediments from the Baltic Sea, Landsort Deep (IODP 347) and discuss those data within a framework of additional independent redox proxies, e.g., iron speciation and [Mo]. The results imply that I/TOC may be sensitive to hypoxic–suboxic conditions, complementary to proxies sensitive to more reducing, anoxic–euxinic conditions. Then, we test the usage of I/TOC in sediments deposited during Late Cretaceous, Cenomanian–Turonian Oceanic Anoxic Event (OAE) 2 from ~ 94 million years ago (Ma). We generated I/TOC and I org records from six OAE 2 sections: Tarfaya (Morocco), Furlo (central Italy), Demerara Rise (western equatorial Atlantic), Cape Verde Basin (eastern equatorial Atlantic), South Ferriby (UK), and Kerguelen Plateau (southern Indian Ocean), which provide a broad spatial coverage. Generally, I/TOC decreases over the interval recorded by the positive carbon-isotope excursion, the global signature of OAE 2, suggesting an expansion of more reducing bottom-water conditions and consistent with independent constraints from iron speciation and redox-sensitive trace-metals (e.g., Mo). Relatively higher I/TOC values (thus more oxic conditions) are recorded at two high latitude sites for OAE 2, supporting previous model simulations (cGENIE) that indicated higher bottom water oxygen concentrations in these regions. Our results also indicate that organic-rich and oxygenated seafloors are likely a major sink of iodine and correspondingly influence its global seawater inventory. [ABSTRACT FROM AUTHOR]

Road salt used as a deicing agent in winter months has become an emerging contaminant to streams and groundwater. In central New York, road salts are applied heavily during winter months. Recognizing potential sources of salinity to a river may reveal processes controlling the salinization of freshwater systems, with implications for future management practices. The Tioughnioga River, located in central New York, is a headwater of the Susquehanna River, which flows into the Chesapeake Bay. Salinity of the Tioughnioga River water has been increasing since the late 1930s. In this study, water samples were collected weekly at the East and West Branches of the Tioughnioga River from 2012 to 2014. We characterize natural and anthropogenic sources of salinity in the Tioughnioga River, using two independent approaches: (1) chloride to bromide ratios (Cl/Br) and (2) linear discriminant analysis. Ratios of Cl/Br suggest that road salt runoff influence is notable in both branches, but is more significant in the West Branch, consistent with a greater area of urban land. Linear discriminant analysis confirms the results of Cl/Br in the West Branch and further indicates presence of Appalachian Basin Brines in the East Branch, although their contribution may be volumetrically small. Longitudinal stream Cl concentration profiles indicate that sources of pollution are particularly concentrated around urban areas. Residence time of Cl in the watershed is estimated to be approximately 20 to 30 years using a mixing model, suggesting that stream Cl concentrations likely will continue to rise for several decades. [ABSTRACT FROM AUTHOR]

Summary: Understanding streamflow generation using natural tracers in semi-arid, seasonally snow-covered mountain streams is essential for water resources management, water quality study and evaluation of impacts from climate change. This study reports temporal variations in stable isotopic ratios and concentrations of major dissolved ions of streamwater and precipitation between October, 2005 and May, 2007 in Red Canyon Creek and its tributary, Cherry Creek, draining carbonate-rich catchments on the southeastern flank of Wind River Range (Wyoming, USA). Although the isotopic ratios of oxygen and hydrogen in precipitation increased from approximately −33‰ to −13‰ and −260‰ to −110‰, respectively, during winters of 2006 and 2007, the oxygen and hydrogen isotopic compositions of streamwater at all sites remained unchanged throughout the year at −18.6±0.3‰ (n =88) and −142±1.6‰ (n =40) for δ18O and δ2H, respectively. The isotopic values for the streamwater were identical to that found in groundwater, which had the values of −18.6±0.2‰ (n =26) and −142±1.1‰ (n =26) for δ18O and δ2H, respectively. On the other hand, the temporal pattern of streamwater chemistry differed in space. In upper Red Canyon Creek, major dissolved ion concentrations in water varied little throughout the year. Nearly constant isotopic and chemical composition of streamwater at upper Red Canyon Creek indicated the dominance of the groundwater contribution throughout the year. In contrast, Cherry Creek had clear dilution of base metal and sulfate concentrations during increasing discharge at snowmelt, which is a clear indication of “new” water coming from fresh snowmelt. The contrasting behavior of stable isotopes and dissolved solutes during snowmelt at Cherry Creek suggests the isotopic tracers traditionally used in hydrograph separation failed to indicate different water sources at Cherry Creek. Combining isotopes and geochemical tracers indicates that streamwater at Cherry Creek during snowmelt is primarily a mixture of snowmelt and groundwater which have similar isotopic compositions but different chemical concentrations. The snowmelt is well mixed during temporary storage in a headwater wetland before reaching the sampling site. Such mixing plays an important role in reducing temporal variability of stable isotope values of fresh snowmelt water. We suggest that development of direct tracer experiments might help address the hydrodynamics of these kinds of watersheds in future research. [Copyright &y& Elsevier]

Benthic foraminiferal surface porosity (the mean percentage of surface area covered by pores; higher porosity: lower oxygenation) and iodine to calcium ratio (I/Ca, higher I/Ca: higher oxygenation) are both promising paleoceanographic proxies that will advance through testing in down-core studies. Here we report the first down-core comparison (~45 kyr) of these proxies for a core from the southern Brazilian margin (26°40.22′ S, 46°26.46′ W, 475 m water depth). Both proxies are most sensitive to low-O 2 conditions (<50 μmol/kg), and not well-constrained at higher O 2 concentrations. Porosity values are generally low (<15%) and I/Ca ranges between ~4 and ~ 6 μmol/mol throughout the core. The two proxies are overall consistent, suggesting that bottom-water oxygen concentrations at the site remained above 50 μmol/kg during the last 45 kyr. Several non-O 2 factors (e.g., iodate reduction rates, water mass mixing, temperature, foraminiferal shell robustness) could influence the proxies and require further investigation. • Benthic foraminiferal surface porosity and I/Ca are generally consistent. • Both proxies are most sensitive when O 2 <50 μmol/kg. • At the studied site, BWO likely remained >50 μmol/kg over the last 45 kyr. [ABSTRACT FROM AUTHOR]

Abstract: Fluid migration in subduction zones is one of the key phenomena to understand the global mass transfer system. While active volcanoes provide the most recognizable conduits for fluid flow in active margins, the existence of a large number of active fluid seepages demonstrates that other forms of fluid release are also important in subduction zone settings. The authors collected fluid samples from springs and wells across the forearc area in Kyushu, a southwestern island of Japan, covering hot spring activities associated with active volcanism and the Median Tectonic Line (MTL), a major fault system present in the southwestern part of Japan. In order to determine sources of these fluids, halogen concentrations as well as 129I/I and 36Cl/Cl ratios were measured in samples from several locations. While Cl concentrations of the forearc fluids in Kyushu range between seawater and meteoric water value, I concentrations are considerably higher than seawater value. Fluids in the Miyazaki area are much higher in I, and somewhat higher in Br, than waters in the Oita area, which is closely associated with the MTL. The differences between those two areas are also pronounced in 129I/I ratios, which range between 800 and 900×10−15 in the Oita area and between 100 and 360×10−15 in the Miyazaki area. The 129I/I ratios obtained from the Oita area are compatible with an I derivation from subducting marine sediments, similar to findings from an earlier investigation of fluids collected from Satsuma-Iwojima, an active volcano south of Kyushu Island. In the Miyazaki area, on the other hand, I ages are too old to be derived from currently subducting marine sediments and point to a derivation from old organic-rich materials in the upper plate of the forearc region. The results demonstrate the presence of very different fluid systems in the forearc area of Kyushu: old CH4-rich fluids dominate in the seaward side of the forearc, while fluids close to the MTL and the Quaternary Volcanic Front demonstrate derivations from subducting marine sediments. The latter fluids in the MTL area probably are transported through the fractures associated with the fault activities, suggesting that this fault system reaches the transition zone between upper and lower plates in this region. [Copyright &y& Elsevier]

The expansion of unconventional oil and gas development (UOGD) by means of horizontal drilling and high-volume hydraulic fracturing has been accompanied by concerns regarding the potential impacts to water resources and public health. The ban on UOGD in New York State (NYS) allows the natural processes that control groundwater chemistry and dissolved methane to be evaluated without complications that could arise in regions impacted by prior unconventional shale gas development. We evaluated the controls on the occurrence and spatial variability of methane, chloride, bromine, and iodine, covering much of NYS and encompassing a range of underlying bedrock geologies. Groundwater samples were collected from 108 domestic and public supply wells. Methane concentrations in groundwater ranged from <0.001–84.6 mg/L. The variables most consistently associated with methane occurrence in groundwater included: 1) bedrock geology penetrated by wells, 2) groundwater chemical composition, and 3) confinement characterization of the well. The geochemical parameters iodine, chloride, and sodium/calcium suggested that elevated concentrations of methane were likely associated with deep brines. Elevated methane concentrations were frequently accompanied by both high bromine and iodine concentrations in this study, indicating that the potential of halogens as tracers for dissolved methane needs to be further investigated. • Groundwater quality surveyed (including methane and halogens) in New York State. • Halogens used to understand the occurrence of methane in shallow groundwater. • Shallow aquifers influenced by the natural migration of formation waters. [ABSTRACT FROM AUTHOR]

• Detailed I/(Ca + Mg) profiles from a shallow-to-deep transect of Doushantuo cap carbonates. • Low I/(Ca + Mg) in calcites with extremely low δ13C. • Spatial I/(Ca + Mg) patterns may support stronger fluid-buffered diagenesis in slopes. • Multiple events may have influenced I/(Ca + Mg) patterns on a temporal scale. Late Neoproterozoic cap carbonates formed following the Cryogenian glaciations may record information about the significant climate change and ocean chemistry evolution immediately after the Snowball Earth events. Large negative carbon isotope anomalies and enigmatic sedimentary structures have been identified from the post-Marinoan cap carbonates across the globe, but their formation mechanism remains debatable due to difficulties of distinguishing overlapped chemical signatures and diagenetic alterations. In this study, we present I/(Ca + Mg) profiles of four sections from a shallow-to-deep water transect of the basal Doushantuo cap carbonates, one of the most extensively studied Ediacaran units in South China. Most samples have I/(Ca + Mg) values lower than 1 μmol/mol with a few exceptions in the shelf sections up to ~2.5 μmol/mol. All calcite samples with extremely low δ13C have iodine signal below detection limit, suggesting carbonate precipitation from anoxic seawater or diagenetic fluids. Among the four sections, the slope section has the lowest I/(Ca + Mg) values, suggesting that it may have experienced more extensive fluid-buffered diagenesis and more severe loss of IO 3 –. In combination with available major, trace, rare earth element and isotope data, the temporal I/(Ca + Mg) variations support freshwater mixing and deep-water upwelling in proximal sites and transient oxidation during deposition of the Doushantuo cap carbonates. [ABSTRACT FROM AUTHOR]

The decline in dissolved oxygen in global oceans (ocean deoxygenation) is a potential consequence of global warming which may have important impacts on ocean biogeochemistry and marine ecosystems. Current climate models do not agree on the trajectory of future deoxygenation on different timescales, in part due to uncertainties in the complex, linked effects of changes in ocean circulation, productivity and organic matter respiration. More (semi-)quantitative reconstructions of oceanic oxygen levels over the Pleistocene glacial cycles may provide a critical test of our mechanistic understanding of the response of oceanic oxygenation to climate change. Even the most promising proxies for bottom water oxygen (BWO) have limitations, which calls for new proxy development and a multi-proxy compilation to evaluate glacial ocean oxygenation. We use Holocene benthic foraminifera to explore I/Ca in Cibicidoides spp. as a BWO proxy. We propose that low I/Ca (e.g., <3 μmol/mol) in conjunction with benthic foraminiferal carbon isotope gradients and/or the surface pore area percentages in foraminiferal tests (e.g., >15%) may provide semi-quantitative estimates of low BWO in past oceans (e.g., <∼50 μmol/kg). We present I/Ca records in five cores and a global compilation of multiproxy data, indicating that bottom waters were generally less-oxygenated during glacial periods, with low O 2 waters (<∼50 μmol/kg) occupying some parts of the Atlantic and Pacific Oceans. Water mass ventilation and circulation may have been important in deoxygenation of the glacial deep Pacific and South Atlantic, whereas enhanced remineralization of organic matter may have had a greater impact on reducing the oxygen content of the interior Atlantic Ocean. • Validation of I/Ca as a bottom water oxygen proxy in epifaunal benthic foraminifera. • Down-core I/Ca records of glacial oceans from multiple basins. • Large compilation of (semi-)quantitative proxy data in comparison with I/Ca. [ABSTRACT FROM AUTHOR]