Organic Carbon Isotope Ratios Research Articles

Relationship between shelf sedimentation and climate changes in the upper Pliocene Dainenji Formation in Fukushima, northeastern Japan

Pliocene Dainenji Formation is distributed in the Pacific Ocean side of the Fukushima Prefecture. The depositional age is from 4.18 to 2.6 Ma. We carried out facies analysis and geochemical analysis, such as total organic carbon (TOC), total sulfur (TS), and stable carbon isotope ratio of organic matter (δ13Corg). Our results are as follows : (1) Abundant land-derived organic matter was transported to the shelf and was preserved in the sediment in warm period (3.75-3.5 Ma), (2) Productivity of marine organism increased in the early cooling period (3.5-3.35 Ma), (3) The considerable variations in TS, TOC and δ13Corg are seen in cooling stage after 3 Ma, which succeeded to the Quaternary ice age. Theses considerable variation are shown in δ18O curve of the same age.

Evaluating sedimentary geochemical lake-level tracers in Walker Lake, Nevada, over the last 200 years

Walker Lake, a hydrologically closed, saline, alkaline lake located along the western margin of the Great Basin of western United States, has experienced a 77% reduction in volume and commitment drop in lake level as a result of anthropogenic perturbations and climatic fluctuations over the last century. The history of lake-level change in Walker Lake has been recorded instrumentally since 1860. A high-resolution multi-proxy sediment core record from Walker Lake has been generated through analysis of total inorganic carbon (TIC), total organic carbon (TOC), and oxygen and carbon isotope ratios (δ18O and δ13 C) of both downcore bulk TIC and ostracods over the last 200 yr. This allows us to examine how these sediment indices respond to actual changes in this lake’s hydrologic balance at interannual to decadal timescales. In Walker Lake sediments, changes in %TIC, %TOC, and δ13C and δ18O of TIC and ostracods are all associated to varying degrees with changes in the lake’s hydrologic balance, with δ18O of the TIC fraction (δ18OTIC) being the most highly correlated and the most effective hydrologic indicator in this closed-basin lake. The δ18OTIC record from Walker Lake nearly parallels the instrumental lake-level record back to 1860. However, comparison with sporadic lake-water δ18O and dissolved inorganic carbon δ13C (δ13CDIC) results spanning the last several decades suggests that the isotopic values of downcore carbonate sediments may not be readily translated into absolute or even relative values of corresponding lake-water δ18O and δ13CDIC. Changes in the lake’s hydrologic balance usually lead to changes in isotopic composition of lake waters and downcore sediments, but not all the variations in downcore isotopic composition are necessarily caused by hydrologic changes.

Early evolution of atmospheric oxygen from multiple-sulfur and carbon isotope records of the 2.9 Ga Mozaan Group of the Pongola Supergroup, Southern Africa

Sulfur isotope mass-independent fractionation (S-MIF) is a unique geologic record of Archean atmospheric chemistry that provides important constraints on the evolution of the early Earth’s atmosphere and its impact on early life. In this contribution, we report multiple-sulfur (33S/32S, 34S/32S, and 36S/32S) isotope ratios of sulfide minerals and carbon (13C/12C) isotope ratios of organic carbon for shale in the ~2.96 to ~2.84 Ga Mozaan Group of the Pongola Supergroup, Southern Africa. The δ13C of organic carbon shows two populations: one with δ13C of ~ −26 ‰ and another with δ13C of −32 ‰. The Δ33S values from nine samples ranges from −0.49 to +0.36 ‰, which is considerably smaller than what was measured for the sulfide and sulfate minerals from other Archean intervals but outside the range of Δ33S values measured for post-2.0 Ga sulfide and sulfate minerals. Moreover, some samples from the Mozaan Group yield Δ36S/Δ33S ratios that are different from Phanerozoic sulfides, suggesting sulfide sulfur from the Mozaan Group carries mass-independent isotope fractionation originated from atmospheric photochemistry. The relatively small Δ33S values for the Mozaan Group may suggest that the atmosphere became slightly oxidized at ~2.9 Ga with oxygen level above 10−5 but below 10−2 times present atmospheric level. This intermediate oxygen level would allow production of S-MIF in atmospheric chemistry but prohibit preservation of large S-MIF signatures in surface deposits. Our hypothesis implies the evolution of oxygenic photosynthesis as early as ~2.9 Ga. Such an ephemeral oxidation event could have triggered the Mozaan-Witwatersrand glaciation by destabilizing an existing methane-rich Archean atmosphere.

松島湾における溶存有機物質と鉄の空間分布及び季節変化

In this study, we investigated the spatial and seasonal distributions of dissolved organic matter (DOM) and iron in Matsushima Bay, Japan from November 2003 to October 2004. The chemical characteristics of DOM, such as concentrations of dissolved organic carbon (DOC) and XAD resin absorbed organic carbon (XOC), UV absorbance, molecular weight and carbon stable isotope ratio, were also studied in the bay and the Takagi River. In the bay, DOC concentration increased particularly in summer. The XOC concentration and molecular weight of DOM decreased along the river to the bay. The carbon isotope ratio of DOM indicated that a significant amount of humic substance was produced in the bay. Dissolved iron concentration rapidly decreased with the increase in salinity from the river to the bay and was extremely low in seawater of high salinity. It was considered that this decrease in dissolved iron concentration was attributable to the precipitation of dissociated iron from organic compounds caused by the increase in the concentration of metal cations as river water meets seawater.

Major factors controlling Holocene δ13Corg changes in a seasonal sea‐ice environment, Adélie Land, East Antarctica

In an effort to investigate the controlling factors behind Holocene δ13Corg changes in East Antarctica we report high‐resolution down‐core records of bulk organic matter carbon isotopic ratios (δ13Corg), diatom census counts, total organic carbon, and biogenic silica content taken from one core recovered in the Adélie Trough. A good correspondence between the δ13Corg record and records of small/large and pennate/centric ratios in many of the core segments indicates that diatom species composition affected Holocene δ13Corg variations, possibly via diatom shape and size effects. Variations in the surface water CO2 concentration and in the isotopic composition of the source during the Holocene cannot be ruled out although they cannot explain rapid and large‐amplitude δ13Corg changes. Within the limit of our investigation, our results argue against active carbon acquisition through a carbon concentration mechanism as evidenced in low‐latitude upwelling systems. The bulk organic matter thus represents a mixing of diatom taxa having different fractionation affinity to aqueous CO2. Our results confirm previous evidence which demonstrates that δ13Corg down‐core records should be used with great caution to reconstruct past CO2 content in surface waters.

The East Siberian Sea as a transition zone between Pacific‐derived waters and Arctic shelf waters

In the present study we report hydrological (T and S) and hydrochemical data obtained during a Russian Trans‐Arctic cruise in 2000 onboard the Hydrographic Vessel (HV) Nikolay Kolomeytsev, and describe the top layer of the sediment (a typical sample was taken from the upper 0–5 cm layer of bottom sediment) and the distribution of the organic carbon (δ13Corg) and nitrogen (δ15Norg) isotope ratios. Using both historical water data and data from our cruise, we divide the ESS into two specific areas: the Western area, influenced strongly by Lena River input, and the Eastern area, under direct influence of Pacific‐derived water. We also used the stable δ13Corg and δ15Norg isotopes to detect the sediment geochemical boundary (or “geochemical FZ”) between Pacific “marine‐derived sediments” and “terrestrial derived sediments” which can be considered to reflect the long‐term (on a scale of 102 years) position of the most westward extension of Pacific water. These are among the first reliable hydrological and geochemical data reported for the ESS from the Dmitry Laptev Strait to the Long Strait, and they reveal novel insights about interaction between Pacific water and local shelf water.

A 200-year record of natural and anthropogenic changes in water quality from coastal lagoon sediments of Lake Shinji, Japan

We analyzed organic carbon, total nitrogen, and total phosphorus concentrations together with the stable isotope ratios of organic carbon and total nitrogen from three cores of sediments collected at Lake Shinji, an oligohaline lagoon situated in southwest Japan, to trace both natural and anthropogenic effects on the water quality of the coastal lagoon for the past 200 years. The increase of carbon and nitrogen concentrations in the core sediments collected near the mouth of the freshwater river suggested that the anthropogenic eutrophication first started in the 1940s due to the increase of loads caused by the increased population in the drainage area. δ 15N of the sediments also implied that the eutrophication continues to date even after the end of population growth, due presumably to the use of chemical fertilizer. Organic carbon and total nitrogen concentrations showed higher values during the early 19th century than the present in the core sediments collected at the east end of the lake where polyhaline water occasionally flows back. These higher concentrations were attributed to more frequent backflow of polyhaline water.

Climatic change in Central Asia during MIS 3/2: a case study using biological responses from Lake Baikal

A Marine Isotope Stage (MIS) 3/early MIS 2 section from a structural high along the east coast of the North Basin of Lake Baikal was analysed for diatoms, C/N ratios, and organic carbon isotope ratios. Diatoms were present throughout MIS 3 and early MIS 2, with high concentrations of the planktonic taxa Cyclotella sp. c.f. gracilis between 54 and 51.5 kyr BP indicating relatively warm, interstadial, conditions. Following a %TOC inferred climatic cooling between 43.2 and 39.1 kyr BP, evidence of a more muted δ 13C (organic) and %TOC inferred climatic warming from c. 39.1–34.7 kyr BP coincides with a period of very high diatom concentrations, indicating high aquatic productivity, at the Buguldeika Saddle in the South Basin of Lake Baikal. No evidence exists for a ‘Kuzmin’ catchment erosional event in the North Basin during MIS 3. This, however, may reflect the location of the coring site away from major riverine inputs. Abrupt climatic cooling at the culmination of both warm phases in the North Basin are associated, on the basis of the palaeomagnetic age-model and correlations to existing sites in Lake Baikal, with the initiation of Heinrich events 5 (c. 50 kyr BP) and 4 (c. 35 kyr BP), respectively, in the North Atlantic. The amount of organic material declines across the MIS 3/MIS 2 transition while constant C/N ratios suggest organic material to be predominantly derived from phytoplankton. An increase in δ 13C (organic) at the MIS 3/MIS 2 transition may therefore indicate changes in aquatic productivity, pCO 2 or the inorganic carbon pool.

Stable carbon isotope ratios in lake and swamp sediments as a proxy for prehistoric forest clearance and crop cultivation in the Neotropics

Close correspondence between stable carbon isotope ratios (δ 13 C), pollen, and charcoal profiles in sediment cores from Laguna Zoncho and Machita swamp, Costa Rica, shows that prehistoric forest clearance and crop cultivation can be detected in the stable carbon isotope ratios of total organic carbon (δ 13C TOC ). Analyses of I´ 13C TOC complement evidence from pollen, charcoal, and phytoliths and provide a proxy that is sensitive to the intensity and/or proximity to core sites of prehistoric forest clearance and agriculture in watersheds. Stable carbon isotope analyses are particularly useful in situations in which other evidence of forest clearance and agriculture is limited.

Climate as the dominant control on C3 and C4 plant abundance in the Loess Plateau: Organic carbon isotope evidence from the last glacial-interglacial loess-soil sequences

Abundance of C3 and C4 photosynthesis plants can be inferred relatively from stable carbon isotopic composition of organic matter in soils. The samples from five sequences of the last glacialinterglacial loesssoil in the Chinese Loess Plateau have been measured for organic carbon isotopic ratios (δ13 Corg). The organic carbon isotope data show that relative abundance (or biomass) of C4 plants was increased ca. 40% for each sampling site from the last glacial maximum (LGM) to Holocene optimum, and increased southeastward on the Loess Plateau during both periods of LGM and Holocene. Statistic analyses on the steady maximum δ13 Corg values of Holocene soils and modern climatic data from the Loess Plateau and Inner Mongolia indicate that the C4 plant abundance increases with increasing temperature and decreasing precipitation. The C4 plant abundance is related much closer with mean April temperature and precipitation than annual. These results lead us to deduce following conclusions. First, temperature is the major factor for control on variations in C4 plant abundance in the Loess Plateau from the last glacial to interglacial. In the absence of favorable temperature condition, both of low moisture and low atmospheric CO2 concentration are insufficient to drive an expansion of the C4 plants in the plateau. Second, δ13 Corg in the loess-paleosol sequences, as a proxy of the relative abundance of C4 plants in the Loess Plateau, could not be used as an indicator of changes in the summer monsoon intensity unless the temperature had changed without great amplitude. Since all C4 plants are grasses, finally, the increase of the C4 plants supports that forest has not been dominant in the ecosystem on the Loess Plateau during Holocene although precipitation and atmospheric CO2 were largely increased relative to those during LGM.

High‐ and low‐latitude climate control on the position of the southern Peru‐Chile Current during the Holocene

We reconstructed changes of temperature, salinity, and productivity within the southern Peru‐Chile Current during the last 8000 years from a high‐resolution sediment core recovered at 41°S using alkenones, isotope ratios of planktic foraminifera, biogenic opal, and organic carbon. Paleotemperatures and paleosalinities reached maximum values at ∼5500 years ago and thereafter declined to modern values, whereas paleoproductivity continuously increased throughout the last 8000 years. We ascribe these long‐term Holocene trends primarily to latitudinal shifts of the Antarctic Circumpolar Current (ACC). The concurrence with shifts in the position of the Southern Westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern Chile. Millennial‐ to centennial‐scale fluctuations of paleotemperatures and paleosalinities, on the other hand, lag displacements in the position of the Southern Westerlies but reveal a significant correlation to short‐term temperature changes in Antarctica, indicating a high‐latitude control of the ACC at these timescales.

Source dependent behaviour of lead and organic matter in the Glomma estuary, SE Norway: evidence from isotope ratios

Abstract Concentrations and isotope ratios of lead, organic carbon and nitrogen suggest that the Hvaler basin, SE Norway is more strongly influenced by inputs of atmospheric lead to the coastal current than by discharges from the river Glomma, while the Glomma estuary is affected by lead from the river Glomma. This difference was more pronounced in the early 1900s than in the 1970s. Simultaneously, the shallow Glomma estuary has experienced an increased marine influence in the sedimentary organic matter, interpreted to reflect an increased primary production caused by elevated nutrient input to the estuary. The inner part of the Glomma estuary is over the year dominated by terrestrial organic matter with low δ 13 C ratio while during spring snow melt the river bottom is resuspended and locally derived lead, atmospheric lead and organic matter deposited over the winter months are washed out into the estuary. Later the river plume withdraws to the inner estuary and atmospheric lead and marine organic matter becomes dominant in the outer part of the estuary. Anthropogenic lead enters the estuary as ‘dissolved’, and it is concluded that this lead is carried through the estuary associated to small particles, which settles in the outer estuary. Marine organic matter seems to be superior to terrestrial organic matter in this process of trapping river borne anthropogenic lead by coagulation and aggregation.

Carbon and nitrogen isotope disturbances and an end-Norian (Late Triassic) extinction event

Major perturbations of organic carbon and nitrogen isotope ratios from a Norian-Rhaetian (Late Triassic) boundary section in British Columbia coincide with an extinction of the dominant, deep-water invertebrate fauna of the Late Triassic (monotids and most ammonoids). The carbon isotope excursion is attributed to the development of widespread oceanic stagnation that favored organic-rich shale deposition. The coincident nitrogen isotope excursion suggests that progressively more nitrate-limited productivity forced a change to nitrogen-fixing cyanobacteria populations as ocean stagnation created nutrient-starved conditions. The biotic crisis and geochemical events of the Norian-Rhaetian boundary predate the latest Rhaetian (end-Triassic) mass extinction. Thus, the Late Triassic interval was marked by more than one extinction event.

Geochemical characteristics across the oxic/anoxic interface ( Rote Fäule front) within the Kupferschiefer of the Lubin-Sieroszowice mining district (SW Poland)

Samples of profiles from Lower Zechstein in the Lubin-Sieroszowice mining district (SW Poland) were collected within and at different distance to the oxidized facies (Rote Fäule), developed within the Zechstein strata around the Zary Pericline. The samples include Kupferschiefer, underlying Weissliegendes sandstone and overlying Zechstein Limestone from Rote Fäule zones, adjacent Cu-mineralized strata, and drill cores from the Pb/Zn-mineralized zone more distant to the Rote Fäule front. The Kupferschiefer samples show differences in ore paragenesis and composition of organic matter, which are accompanied by variations in base metal and trace element contents, and isotope ratios of organic carbon and carbonates. The results from Rock-Eval analyses provide evidence for an oxidative alteration of organic matter in Kupferschiefer samples within and adjacent to the Rote Fäule zones related to base metal mineralization. The extent of this alteration is reflected by differences in the temperature of maximum pyrolysis yield ( T max), hydrogen and oxygen indices (HI, OI). In contrast to Kupferschiefer from Pb/Zn-mineralized areas, organic matter is characterized by lower hydrogen equivalents, and by higher T max values. The changes in the isotopic composition of organic carbon and carbonates reflect the alteration of organic matter. Kerogen within, or close to, Rote Fäule zones is enriched in 13C caused by the preferential release of isotopically light organic compounds through progressive degradation of organic matter. The opposite tendency towards lower δ 13C values of calcite provides evidence for organic matter remineralization. Isotopic exchange reactions of carbonate with the isotopically distinct oxidizing brines at temperatures between 100 and 120 °C caused decreasing δ 18O values of calcite. The regional zonation in the Kupferschiefer with respect to sulfide paragenesis and base metal composition in the mines is explained by metal precipitation from oxidizing brines through decreasing Eh conditions during the infiltration of the brines into the reduced Kupferschiefer. Relationships between selected trace elements, organic carbon and sulfur contents, and HI values are consistent with that model of ore formation.

Tracking nutrient and productivity variations over the Last Deglaciation in the Arctic Ocean

We have reconstructed the surface water environment of the Arctic Ocean over the last ∼ 50,000 years using measurements of the organic nitrogen and carbon isotope ratios, carbonate and total organic carbon concentrations (TOC), and terrestrial biomarkers (lignin and long‐chain n‐alkanes) in four multicores. Variations in nitrogen isotope ratios that are concordant with TOC and carbonate concentrations (representing foraminifera and excluding ice‐rafted‐debris) reflect differences in relative nutrient utilization of phytoplankton in the surface waters. However, δ15N variations also appear to be dependent on the stratification of the water column and therefore potentially track the exchange of nutrients between deep and surface waters. Low Last Glacial Maximum (LGM) δ15N values and higher Holocene values are opposite to those recorded in the Southern Ocean. The Arctic Ocean with higher nutrient utilization today compared to the LGM therefore acts as a counterpart to the Southern Ocean, although the global impact on carbon dioxide variations compared to the Southern Ocean is probably low.

Comparative Study of the C3/CAM Intermediate Species Clusia parviflora Saldanha et Engi. and the Obligate CAM Species Clusia hilariana Schlecht. Growing Sympatrically Exposed and Shaded in the Coastal Restinga of Brazil

Abstract: The C3/CAM intermediate species, C/usia parviflora Saldanha et EngI., and the obligate CAM species Clusia hilariana Schlecht., occur sympatrically in the coastal sand dune vegetation of the Restinga of Brazil. Their photosynthetic activity at an exposed and at a shaded site was compared by measuring gas exchange (porometry), chlorophyll a fluorescence parameters, organic acid levels (malic and citric) and carbon isotope ratios. At the shaded site, low photosynthetic photon flux densities (PPFD) strongly restricted photosynthetic activity. However, C parviflora could readily make use of light flecks. At the exposed site, C. parviflora was much less affected by photoinhibition than C. hilariana. The CAM species showed higher apparent rates of linear photosynthetic electron transport (ETR) and higher effective quantum yield of PSII (ΔF/F'm) than did C. parviflora during high insolation in the middle of the day, i.e., the time of Phase Ill of CAM. Nevertheless, it suffered much more severe acute photoinhibition that was not reversible after 20 min of darkening during this time, and even some chronic photoinhibition not reversible overnight. Comparative studies of sympatric physiotypes with different modes of photosynthesis of a given leaf morphotype, as available in the genus Cksia, challenge some CAM dogmas, e.g., CAM may not always be superior at exposed sites and may not always provide better photoprotection at high PPFD. However, the idea that C3/CAM plasticity allows occupation of a wider range of habitats is supported.

Evaluation of bottom sediment data from the Winyah Bay estuarine system

In order to investigate the carbon cycle of a partially mixed Coastal Plain estuary (Winyah Bay, South Carolina), several characteristics have to be observed and checked for temporal and spatial stability and sediment grain size distribution. In this study bulk organic carbon content and carbon isotope ratios in bottom sediment samples in Winyah Bay and two of its principal tributaries, the Pee Dee and Sampit Rivers, were analyzed for modeling purposes. Testing these two variables as functions of fraction size, sampling site and sampling season showed a good separation between fine and coarse sediment fractions. Additionally, the Winyah Bay sampling stations had more positive carbon isotope ratios compared to Pee Dee and Sampit River stations and were lower in bulk organic carbon content. No seasonal effects on the isotopic ratios and organic carbon content were observed.

Environmental evolution and southwest monsoon changes in mid-Holocene recorded by lake sediments in Erhai Lake

IN recent years, much progress has been made in the research of the temporal and spatial changes of East Asian monsoon[1s ' I . To research the environmental evolution and monsoon variations in Holocene in the region of Southwest China, a 310-cm continuous lake sediments core in Erhai Lake, Yunnan Province was sampled with Livingston sampler on July 6, 1996. The lake sediments were separated at 2-cm intervals and the core samples were analyzed with chronology, stable isotope ratios of organic carbon and diatoms determination. Three 14C ages are ( 4 473 + 40) a B. P. (98-102 cm) , (5 825 + 85) a B. P. (144-148 cm) and (7 754 + 45) a B. P . (198-202 cm) . By 137Cs dating, the sedimentation rate is about 0 . 3 mm/a and this result is close to the 14c dating results. The average sedimentation rates indicate that the core samples of 0-210 cm stand for the past 8 . 1 ka sedimentation. Here we first present the environmental evolution and southwest monsoon changes recorded by lake sediments from Erhai Lake, Yunnan Province in mid-Holocene (8.1-3.0 ka B. P. ) . This period coincided with the Holocene Megatherma1 period in East Asian monsoon. The stable isotope ratios ( 6 13c) of organic carbon are related to the source of organic carbon in lake

Early Holocene climatic instability in Japan: organic geochemical evidence in sediment cores from Lake Biwa, Lake Kizaki and the Japan Sea

Sediment cores from Lake Biwa (Shiga Prefecture) and Lake Kizaki (Nagano Prefecture) provide evidence of variations in the climate of Japan subsequent to the end of the last glacial period. Concentrations of organic carbon increase in sediments deposited after the Pleistocene–Holocene boundary, as wetter climates washed in more soil nutrients and aquatic productivity increased. Organic matter C/N ratios simultaneously decrease, indicating smaller proportions of land-derived plant matter. Lake Biwa C/N ratios and organic carbon isotope ratios fluctuate markedly between 10 and 4 Kya, suggesting that both delivery of land-derived organic matter and production of lake-derived organic matter were variable during this period of time. Similar variability in biotic paleoceanographic indicators has been reported in sediments from the Oki Ridge in the Japan Sea and has been interpreted to record early Holocene fluctuations in the intensity of the Tsushima Current. Such fluctuations in this warm-water current are likely to have caused concordant fluctuations in climate on Honshu, a relationship that explains the variability in rainfall evident in the organic matter of the lake sediments.

Role of organic matter and sulphate-reducing bacteria for metal sulphide precipitation in the Bahloul Formation at the Bou Grine Zn/Pb deposit (Tunisia)

The origin of the Bou Grine Zn/Pb deposit of Tunisia was investigated during a geochemical study of the Cretaceous Bahloul Formation. The inorganic and organic chemical compositions of the bituminous marls and limestones, as well as the light stable isotope ratios of organic carbon and carbonates were measured. Closely spaced samples were collected along two profiles, at different distances from the enrichments in Zn and Pb, which are best developed near the Bou Grine diapir. The organic geochemical data suggest sulphide precipitation at the Bou Grine deposit by sulphate-reducing bacteria (SRB). SRB utilized hydrocarbons derived both from the Bahloul sediments and from external source rocks. Production of S(-II) by the bacteria was most probably limited by the availability of sulphate, although, sulphate was available to the bacteria in high concentrations in close proximity to the Triassic salt dome. Ground waters evolved to hypersaline basinal brines by dissolution of salt and anhydrite at the contact of the diapir. These brines would have been capable of leaching metals from the sedimentary sequences adjacent to the salt dome. The Triassic series has often been advocated as the source of the metals, and the Cretaceous sediments themselves are carriers of metallic elements. Ore deposition apparently resulted when metal-bearing solutions that migrated upward into the roof zone of the diapir, mixed with S(-II)-bearing solutions. Those formed when SRB oxidized the high amounts of hydrocarbons within the Bahloul sediments and in the brines, using SO 4 2− from sulphate-rich waters in the anhydrite caprock as an oxidant.