Processes of supply and removal of dissolved silicon in the oceans

A critical assessment has been made of the processes of supply and removal of dissolved silicon in the ocean. The only sources of importance appear to be continental drainage (supplying 4.3 × 10¹⁴ g SiO₂/yr), Antarctic weathering and migration from sediment pore waters. The magnitudes of the last two processes are uncertain but there is evidence that they may add significantly to the river input. The total input appears to lie uncertainly within the range of 5.12 × 10₁₄ g SiO₂/yr.Estimates of removal in estuarine mixing processes (less than 1 × 10₁₄ g SiO₂/yr) and in pelagic siliceous oozes (less than 2 × 10₁₄ g SiO₂/yr) suggest that deposition by these processes may not balance the input. Other removal processes could include biological deposition in coastal waters, but the hypothesis that some removal in the sea occurs by inorganic processes, such as reverse weathering reactions, cannot be discounted.     

Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations

The isotopic composition of Nd in the water column from several western North Atlantic sites and formational areas for North Atlantic Deep Water shows extensive vertical structure at all locations. In regions where a thermocline is well-developed, large isotopic shifts (2 to 3 ϵ units) are observed across the base of the thermocline. Regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth. In general, the data reveal an excellent correlation between the Nd isotopic distribution in the western North Atlantic water column and the distribution of water masses identified from temperature and salinity characteristics. NADW, as identified from T-S properties, is also characterized by a well-defined isotopic composition having ϵ_Nd(0) = −13.5 ± 0.5. This signature is associated with waters identified as NADW from high latitudes near formational areas in the Labrador Sea down to the equatorial region. The isotopic signature of NADW would appear to be formed by a blend of more negative waters originating in the Labrador Sea (ϵ_Nd(0) < −18) and more positive waters originating in the overflows from the Norwegian and Greenland Seas (ϵ_Nd(0) ≈ −8 to −10) and is consistent with classical theories on the formation of NADW. The isotopic signature of NADW is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic Nd associated with northward-spreading Antarctic Intermediate and Bottom Waters. The preservation of the isotopic signature of NADW over these large distances indicate that the REE undergo extensive lateral transport. The isotopic composition of Nd is largely conservative over the time scales of mixing within the Atlantic in spite of the intrinsic nonconservative behavior of neodymium. Nd concentration gradients generally show surface waters to be depleted in Nd relative to deep waters, which must require vertical transport processes. However, isotopic differences in the water column preclude the local downward transport of REE from the surface into underlying deep waters as a simple explanation of the concentration gradient. The apparent decoupling of REE in NADW from overlying (local) surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved.     

Major change in Atlantic Deep and bottom waters 700,000 yr ago: Benthonic foraminiferal evidence from the South Atlantic

In the modern South Atlantic the transition between deep water and bottom water is marked by a clear change in the associated benthonic foraminiferal fauna. uvigerina and Globocassidulina characterize oxygen-poor Circumpolar Deep Water which has long been isolated from the surface. Planulina and miliolids are found associated with the more newly formed, oxygen-rich North Atlantic Deep Water. Antarctic Bottom Water is characterized by “Epistominella” umbonifera. Analysis of the benthonic foraminiferal faunas in two sediment cores recovered from the Vema and Hunter Channels in the western South Atlantic shows that the level of the transition between deep and bottom waters shallowed sharply about 700,000 yr ago. This rise indicates a sharp, sustained increase in the volume of bottom water flowing through the South Atlantic after this time. Prior to about 700,000 yr ago, the amount of Antarctic Bottom Water entering the western South Atlantic was greatly reduced and Circumpolar Deep Water apparently accounted for the bulk of northward flow. Production of southward-flowing North Atlantic Deep Water seems not to have been affected. The timing of this change in circulation regime suggests a possible causal link to similar changes in records of terrestrial and sea-surface climate.     

The Southern Ocean silica cycle

The Southern Ocean is a major opal sink and plays a key role in the silica cycle of the world ocean. So far however, a complete cycle of silicon in the Southern Ocean has not been published. On one hand, Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica, DSi) from the rest of the world ocean through the upwelling of the Circumpolar Deep Water, fed by contributions of deep waters of the Atlantic, Indian, and Pacific Oceans. On the other hand, the Southern Ocean exports a considerable flux of the silicic acid that is not used by diatoms in surface waters through the northward pathways of the Sub-Antarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water. Thus the Southern Ocean is a source of DSi for the rest of the world ocean. Here we show that the Southern Ocean is a net importer of DSi: because there is no significant external input of DSi, the flux of DSi imported through the Circumpolar Deep Water pathway compensates the sink flux of biogenic silica in sediments.     

Aluminium in the northwest Atlantic

A series of profiles between Woods Hole and Bermuda has been measured on board ship for Al. The extrema in the upper waters can be explained by the accumulation of aeolian inputs in the thin summer mixed layer, the depletion of the underlying “Winter Water” by scavenging during the Spring bloom and the enrichment of the Subtropical Mode (18°C) Water by aeolian accumulation during winter and local convection before the Spring bloom. The pronounced minimum at mid-depth is associated with the Antarctic Intermediate Water and the underlying Labrador Sea-Med Water complex. Presumably, the AAIW and the Med Water are depleted by the ageing effect on this short residence time element during their transit to the area. The LSW is formed from surface waters containing a large component of Arctic waters, extremely depleted in Al, advected south in the East Greenland Current. The linear increase to the bottom is caused by mixing of enriched lower North Atlantic Deep Water with the depleted Bottom Water and LSW cores. The enrichment in the Deep Water appears to be produced by the entrainment of high-Al waters from the North European Shelf by the gyre in the Norwegian-Greenland Sea and its injection into the Denmark Straits overflow waters in a manner recently described for the radiocaesium releases from the Windscale reprocessing plant on the Irish Sea. An additional contribution probably comes from the shelf north of Iceland.     

Deglacial radiocarbon history of tropical Atlantic thermocline waters: absence of CO2 reservoir purging signal

A current scenario to explain much of the atmospheric CO₂ increase during the Glacial to Holocene climate transition requires the outgassing of a deep, old oceanic CO₂ reservoir thought to be located in the Southern Ocean. In this scenario, CO₂-rich and ¹⁴C-depleted subsurface Antarctic-sourced water, ventilates the thermocline where it is purged to the atmosphere in the equatorial regions, a view that has been met with conflicting results. Using a novel approach (paired surface and deep-dwelling planktonic foraminifer radiocarbon analyses), we document that the equatorial Atlantic thermocline did not see old, ¹⁴C-depleted water, which would be characteristic of the proposed isolated deep ocean CO₂ reservoir. Data from several studies concur that, during the deglaciation, Antarctic intermediate waters were contributing to Atlantic thermocline waters even more than today, therefore, our observations challenge the current purging hypothesis. Together with other studies, these results suggest that the mechanism responsible for the deglacial CO₂ rise cannot invoke contemporary circulation modes and/or thermocline ventilation pathways.     

The chemical control of soluble phosphorus in the Amazon estuary

The factors which control concentrations of soluble inorganic phosphorus in the Amazon estuary are described and the efflux of phosphorus through the estuary is estimated using estuarine data collected on three field excursions (two in December, 1982 and one in May, 1983), and various laboratory mixing experiments. There is evidence to suggest that suspended sediments release significant quantities of inorganic phosphate to the estuarine waters. Bottom sediments collected from the estuary released soluble inorganic phosphorus at rates of approximately 0.2 μM day⁻¹, when suspended in mixtures of seawater and deionized water. Release rates depended on salinity but were independent of sediment concentrations. Inputs of phosphate persisted for approximately 3 days in suspensions with sediment concentrations of 0.5 g l⁻¹, but the duration of release increased to greater than 8 days at concentrations greater than 10 gl⁻¹. A one-dimensional dispersion model was developed incorporating input rates derived from the laboratory mixing experiments. The model predicts phosphate concentrations which are consistent with field observations, and it provides quantitative estimates for total fluxes of soluble inorganic phosphorus to the high salinity fringes of the estuary (~25 ppt) of approximately 15 × 10⁶molesday⁻¹ and 27 × 10⁶molesday⁻¹ during December, 1982 and May, 1983 respectively. The data indicate a significant phosphate loss from estuarine waters at salinities from 0–4 ppt, possibly associated with iron and humate removal. More than 50% of the predicted flux could be contributed by phosphate released from suspended sediments within the turbid part of the estuary.     

Particulate manganese dynamics in Gulf Stream warm-core rings and surrounding waters of the N.W. Atlantic

Manganese has been measured in size-fractionated paniculate matter profiles obtained by large volume in situ filtration of the upper 1000 m of the N.W. Atlantic as part of the Warm Core Rings Experiment (WCRE) in 1982. Environments sampled included Warm Core Rings (WCR) 82B and 82H, the entrainment zone at the edge of these rings, the Slope Water surrounding rings, and the Gulf Stream (GS) and Sargasso Sea (SS) from which the rings formed.Manganese concentrations ranged from 10 pmol kg⁻¹ to 10,000 pmol kg⁻¹ with the extreme values observed in the quasi-isolated core waters of WCR 82B and in a tongue of shelf water at the periphery of WCR 82B, respectively. The majority of the Mn was in the 1–53 μm particle size fraction and most Mn was probably close to 1 μm in size. Mn showed no correlation with major biogenic phases indicating that formation by local biological processes was not an important source. Instead, most paniculate Mn present in the waters sampled originated in reducing sediments at the continental margin.A manganese budget for the quasi-isolated core waters of WCR 82B between February and June 1982 showed that most Mn removal was by the aggregation of the small Mn-oxyhydroxide particles into fecal material, followed by sedimentation.Calculations show that WCRs cause offshore particulate Mn transports from the continental margin between 66°W and Cape Hatteras of 8.5 × 10⁴ to 14 × 10⁴ mol d⁻¹ with most derived from the continental shelf. Only 4% of the shelf derived Mn becomes entrained into WCRs and the rest is left to disperse in the Slope Water or enter the circulation of the Gulf Stream. The WCR-induced offshore Mn transports may account for a large fraction of the Mn flux to sediments on the continental slope and upper continental rise.     

Palaeoproductivity evolution in the centre of the western Pacific warm pool during the last 250 ka

To reconstruct the palaeoproductivity evolution history of the centre of the western Pacific warm pool (WPWP) over the last 250 ka, multi‐proxies were analysed in sediment core WP7 recovered from the Ontong–Java Plateau. Palaeoproductivity evolution at the centre of the WPWP during the last 250 ka is closely related to glacial–interglacial cycles and the insolation controlled by precession. The glacial higher primary productivity relative to the interglacial conditions could have resulted from both thermocline shoaling associated with persistent El Niňo‐like conditions and the increased influx of dust resulting from intensified winter monsoon together with important changes in the thermocline. The minimum primary productivity values during the last three terminations could be resulted from deglacial thermocline deepening and intensified stratification associated with persistent La Niña‐like conditions, and the concurrent Neogloboquadrina dutertrei δ¹³C minimum events probably reflect the chemical signatures of Subantarctic Mode Water and Antarctic Intermediate Water. In addition, primary productivity values are also controlled by the thermocline variations resulting from El Niño/La Niña‐Southern Oscillation processes responding to precession forcing, and lead the δ¹⁸O by about 4 ka. The 33.1 ka, 19 ka and “half‐precession” periods are prominent in the palaeoproductivity records. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatial Distribution and Longitudinal Variation of Clay Minerals in the Central Indian Basin

Grain size and clay mineral distribution up to 45 cm depth in the silty clay sediments from 26 box cores from 10°to 16°S along four longitudes(73.5°-76.5°E)were studied for understanding spatial variability in the Central Indian Basin(CIB).It was observed that the average sand content in the basin is 3.8%,which decreases systematically and longitudinally to 0.3%towards south.The average illite and chlorite major clay mineral abundance also decrease southwards along the four longitudes from 10°S,and show ...     

The supply and accumulation of silica in the marine environment

Rivers and submarine hydrothermal emanations supply 6.1 × 10¹⁴g SiO₂/yr to the marine environment. Approximately two-thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep-sea deposits. Siliceous deep-sea sediments located beneath the Antarctic Polar Front (Convergence) account for over a fourth (1.6 × 10¹⁴g SiO₂/yr) of the silica supplied to the oceans. Deep-sea sediment accumulation rates beneath the Polar Front are highest in the South Atlantic with values as large as 53cm/kyr during the last 18.000 yr. Siliceous sediments in the Bering Sea, Sea of Okhotsk, and Subarctic North Pacific accumulate 0.6 × 10¹⁴g SiO₂/yr or 10% of the dissolved silica input to the oceans. The accumulation of biogenic silica in estuarine deposits removes a maximum of 0.8 × 10¹⁴g SiO₂/yr. Although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters, the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters. Siliceous sediments from continental margin upwelling areas (e.g. Gulf of California, Walvis Bay, or Peru-Chile coast) have the highest biogenic silica accumulation rates in the marine environment (69 g SiO₂ cm²/kyr). Despite the rapid accumulation of biogenic silica, upwelling areas account for less than 5% of the silica supplied to the marine environment because they are confined laterally to such small areas.     

13C Record of benthic foraminifera in the last interglacial ocean: Implications for the carbon cycle and the global deep water circulation

The ¹³C/¹²C ratios of Upper Holocene benthic foraminiferal tests (genera Cibicides and Uvigerina) of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide (TCO₂) measured during the GEOSECS program. The δ¹³C difference between benthic foraminifera and TCO₂ is 0.07 ± 0.04‰ for Cibicides and ?0.83 ± 0.07‰ for Uvigerina at the 95% confidence level. δ¹³C analyses of the benthic foraminifera that lived during the last interglaciation (isotopic substage 5e, about 120,000 yr ago) show that the bulk of the TCO₂ in the world ocean had a δ¹³C value 0.15 ± 0.12‰ lower than the modern one at the 95% confidence level, reflecting a depletion, compared to the present value, of the global organic carbon reservoir. Regional differences in δ¹³C between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one: the Antarctic Bottom Water production was higher than today during the last interglaciation, but the eastward transport in the Circumpolar Deep Water was lower.     

Adsorption kinetics and intraparticulate diffusivities of Hg, As and Pb ions on unmodified and thiolated coconut fiber

As, Hg and Pb are examples of heavy metals which are present in different types of industrial effluents responsible for environmental pollution. Their removal is traditionally made by chemical precipitation, ion-exchange and so on. However, this is expensive and not completely feasible to reduce their concentrations to the levels as low as required by the environmental legislation. Biosorption is a process in which solids of natural origin are employed for binding the heavy metal. It is a promising alternative method to treat industrial effluents, mainly because of its low cost and high metal binding capacity. The kinetics was studied for biosorption experiments using coconut fiber for As (III), Hg (II) and Pb (II) ions adsorption. The specific surface area and surface charge density of the coconut fiber are 1.186×10²⁵ (m²/g) and 5.39 ×10²⁴ (meq/m²), respectively. The maximum adsorption capacity was found to be the highest for Pb (II) followed by Hg (II) and As (III). The modification of the adsorbent by thiolation affected the adsorption capacity. Equilibrium sorption was reached for the metal ions at about 60 min. The equilibrium constant and free energy of the adsorption at 30 °C were calculated. The mechanism of sorption was found to obey the particle-diffusion model. The kinetic studies showed that the sorption rates could be described by both pseudo first-order and pseudo second-order models. The pseudo second-order model showed a better fit with a rate constant value of 1.16 × 10^?4/min. for all three metal ions. Therefore, the results of this study show that coconut fiber, both modified and unmodified, is an efficient adsorbent for the removal of toxic and valuable metals from industrial effluents.     

Biogeochemical cycling in an organic-rich coastal marine basin—I. Methane sediment-water exchange processes

Methane produced in anoxic organic-rich sediments of Cape Lookout Bight, North Carolina, enters the water column via two seasonally dependent mechanisms: diffusion and bubble ebullition. Diffusive transport measured in situ with benthic chambers averages 49 and 163 μmol · m ^?2 · hr ^?1 during November–May and June–October respectively. High summer sediment methane production causes saturation concentrations and formation of bubbles near the sediment-water interface. Subsequent bubble ebullition is triggered by low-tide hydrostatic pressure release. June–October sediment-water gas fluxes at the surface average 411 ml (377 ml STP: 16.8 mmol) · m^?2 per low tide. Bubbling maintains open bubble tubes which apparently enhance diffusive transport. When tubes are present, apparent sediment diffusivities are 1.2–3.1-fold higher than theoretical molecular values reaching a peak value of 5.2 × 10^?5 cm² · sec^?1. Dissolution of 15% of the rising bubble flux containing 86% methane supplies 170μmol · m^?2 · hr^?1 of methane to the bight water column during summer months; the remainder is lost to the troposphere. Bottom water methane concentration increases observed during bubbling can be predicted using a 5–15 μm stagnant boundary layer dissolution model. Advective transport to surrounding waters is the major dissolved methane sink: aerobic oxidation and diffusive atmospheric evasion losses are minor within the bight.     

Hydrochemical and isotopic properties of Heybeli geothermal area (Afyon,Turkey)

The thermal waters at the Heybeli (K?z?lkirse) low-temperature geothermal field located in the Afyonkarahisar Province (western Turkey) are discharged from Paleozoic recrystallized limestone. The temperature, specific electrical conductivity, and pH values of the thermal waters are within the range of 28.9 to 54.7 °C, 587 to 3580 μS/cm, and 6.32 to 7.37, respectively. The Heybeli geothermal system is fed by meteoric waters. The waters are heated at depth by high geothermal gradient caused by the neotectonic activity in the deep and ascend to the surface through fractures and faults by convection. The thermal waters are of Na-Ca-HCO₃-SO₄ type and their chemical composition of the waters is mainly controlled by water-rock interaction and mixing processes. The δ¹⁸O, δ²H and tritium compositions show that the thermal waters are of meteoric origin and the residence time at the reservoir is longer than 50 years. Isotope data (δ³⁴S and δ¹³C) indicate recrystallized limestones as origin of CO₂ and structural substitution of sulfate into marine carbonates (CAS) as origin of sulfur. Chemical, \( {\updelta}^{18}{\mathrm{O}}_{\left({\mathrm{SO}}_4-{\mathrm{H}}_2\mathrm{O}\right)} \) isotope geothermometers and mineral equilibrium diagrams applied to thermal waters gave reservoir temperatures between 62 and 115 °C. Saturation index calculations show that the most expected minerals causing scaling at outflow conditions during the production and utilization of Heybeli geothermal waters are calcite, aragonite, dolomite, quartz, and chalcedony.     

Hydrochemical,isotopic, and reservoir characterization of the Pasinler (Erzurum) geothermal field,eastern Turkey

The reservoir temperature and conceptual model of the Pasinler geothermal area, which is one of the most important geothermal areas in Eastern Anatolia, are determined by considering its hydrogeochemical and isotope properties. The geothermal waters have a temperature of 51 °C in the geothermal wells and are of Na–Cl–HCO₃ type. The isotope contents of geothermal waters indicate that they are of meteoric origin and that they recharge on higher elevations than cold waters. The geothermal waters are of immature water class and their reservoir temperatures are calculated as 122–155 °C, and their cold water mixture rate is calculated as 32%. According to the δ¹³C_VPDB values, the carbon in the geothermal waters originated from the dissolved carbon in the groundwaters and mantle-based CO₂ gases. According to the δ³⁴S_CDT values, the sources of sulfur in the geothermal waters are volcanic sulfur, oil and coal, and limestones. The sources of the major ions (Na⁺, Ca²⁺, Mg²⁺, Cl^?, and HCO₃ ^?) in the geothermal waters are ion exchange and plagioclase and silicate weathering. It is determined that the volcanic rocks in the area have effects on the water chemistry and elements like Zn, Rb, Sr, and Ba originated from the rhyolite, rhyolitic tuff, and basalts. The rare earth element (REE) content of the geothermal waters is low, and according to the normalized REE diagrams, the light REE are getting depleted and heavy REE are getting enriched. The positive Eu and negative Ce anomalies of waters indicate oxygen-rich environments.     

Iron, manganese, and lead at Hawaii Ocean Time-series station ALOHA: Temporal variability and an intermediate water hydrothermal plume

Trace metal clean techniques were used to sample Hawaii Ocean Time-series (HOT) station ALOHA on seven occasions between November 1998 and October 2002. On three occasions, full water-column profile samples were obtained; on the other four occasions, surface and near-surface euphotic zone profiles were obtained. Together with three other published samplings, this site may have been monitored for “dissolved” (≤0.4 or ≤0.2 μm) Fe more frequently than any other open ocean site in the world.Low Fe concentrations (<0.1 nmol kg⁻¹) are seen in the lower euphotic zone, and Fe concentrations increase to a maximum in intermediate waters. In the deepwaters (>2500 m), the concentrations we observe (0.4-0.5 nmol kg⁻¹) are significantly lower than some other deep North Pacific stations but are similar to values that have been reported for a station 350 miles to the northeast. We attribute these low deepwater values to transport of low-Fe Antarctic Bottom Water into the basin and a balance between Fe regeneration and scavenging in the deep water. Near-surface waters have higher Fe levels than observed in the lower euphotic zone. Significant temporal variability is seen in near-surface Fe concentrations (ranging from 0.2-0.7 nmol kg⁻¹); we attribute these surface Fe fluctuations to variable dust deposition, biological uptake, and changes in the mixed layer depth. This variability could occur only if the surface layer Fe residence time is less than a few years, and based on that constraint, it appears that a higher percentage of the total Fe must be released from North Pacific aerosols compared to North Atlantic aerosols. Surprisingly, significant temporal variability and high particulate Fe concentrations are observed for intermediate waters (1000-1500 m). These features are seen in the depth interval where high δ³He from the nearby Loihi Seamount hydrothermal fields has been observed; the total Fe/³He ratio implies that the hydrothermal vents are the source of the high and variable Fe.The vertical profile of Mn at ALOHA qualitatively resembles other North Pacific Mn profiles with surface and intermediate water maxima, but there are some significant quantitative differences from other reported profiles. The ≤0.4 μm Mn concentration is highest near the surface, decreases sharply in the upper 500 m, then shows an intermediate water maximum at 800 m and then decreases in the deepest waters; these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations. It appears that there is a significant Mn gradient (throughout the water column) from HOT towards the northeast.Compared to the first valid oceanic Pb data for samples collected in 1976, Pb at ALOHA in 1997-1999 shows decreases in surface waters and waters shallower than 200 m. Pb concentrations in central North Pacific surface waters have decreased by a factor of 2 during the past 25 yr (from ∼65 to ∼30 pmol kg⁻¹); surface water Pb concentrations in the central North Atlantic and central North Pacific are now comparable. We attribute the surface water Pb decrease to the elimination of leaded gasoline in Japan and to some extent by the U.S. and Canada. We attribute most of the remaining Pb in Pacific surface waters to Asian emissions, more likely due to high-temperature industrial activities such as coal burning rather than to leaded gasoline consumption. A 3-year mixed-layer time series from the nearby HALE-ALOHA mooring site (1997-1999) shows that there is an annual cycle in Pb with concentrations ∼20% higher in winter months; this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher Pb in the upper thermocline (Pb concentrations double between the surface and 200 m). From 200 m to the bottom, Pb concentrations decrease to levels of 5-9 pmol kg⁻¹ near the bottom; for most of the water column, thermocline and deepwater Pb concentrations do not appear to have changed significantly during the 23-yr interval.     

Neogene deep sea benthic foraminiferal diversity in the Indian Ocean: Paleoceanographic implications

The species diversity indices, as defined by the number of species,S; Shannon-Wiener index,H(S) and Buzas-Gibson index,É, of DSDP sites 219, 220, 237 and 238 were measured to determine the benthic foraminiferal diversity patterns in the Indian Ocean deep sea sequences during the Neogene. The Time-Stability hypothesis could satisfactorily explain the observed diversity patterns. The general patterns of diversity suggest environmental stability during the Neogene. However, few small fluctuations in diversity during the Middle Miocene (c.14·8 Ma), Late Miocene (c.6·0 Ma) and Late Pliocene (c.2·0 Ma) may possibly be the effects of Antarctic Bottom Water (AABW) activity in this region. The benthic foraminiferal diversity in the tropical Indian Ocean is more than the high latitudinal areas with comparable depths.     

Hydrogeochemical and hydrogeological investigations of thermal waters in the Usak Area (Turkey)

Thermal waters of the Usak area have temperatures ranging from 33 to 63°C and different chemical compositions. These waters hosted by the Menderes Metamorphic rocks emerge along fault lineaments from two geothermal reservoirs in the area. The first reservoir consists of gneiss, schists, and marbles of the Menderes Metamorphic rocks. The recorded reservoir is Pliocene lacustrine limestone. Hydrogeochemical studies indicate that thermal waters were mixed with surface waters before and/or after heating at depth. The results of mineral equilibrium modeling indicate that all the thermal waters are undersaturated at discharge temperatures for gypsum, anhydrite, and magnesite minerals. Calcite, dolomite, aragonite, quartz, and chalcedony minerals are oversaturated in all of the thermal waters. Water from the reservoir temperatures of the Usak area can reach upto120°C. According to δ¹⁸O and δ²H values, all thermal and cold groundwater are of meteoric origin.