Geology topics

A. Paytan

Publications and source records attributed to A. Paytan.

12 recordsLinked to original sources

USGS2017

Reconstructing the evolution of the submarine Monterey Canyon System from Os, Nd, and Pb isotopes in hydrogenetic Fe-Mn crusts

The sources of terrestrial material delivered to the California margin over the past 7 Myr were assessed using 187 Os/ 188 Os, Nd, and Pb isotopes in hydrogenetic ferromanganese crusts from three seamounts along the central and southern California margin. From 6.8 to 4.5 (± 0.5) Ma, all three isotope systems show more radiogenic values at Davidson Seamount, located near the base of the Monterey Canyon System, than in Fe-Mn crusts from the more remote Taney and Hoss seamounts. At the Taney seamounts, approximately 225 km farther offshore from Davidson Seamount, 187 Os/ 188 Os values, but not Pb and Nd isotope ratios, also deviate from the Cenozoic seawater curve towards more radiogenic values from 6.8 to 4.5 (± 0.5) Ma. However, none of the isotope systems in Fe-Mn crusts deviate from seawater at Hoss Seamount located approximately 450 km to the south. The regional gradients in isotope ratios indicate that substantial input of dissolved and particulate terrestrial material into the Monterey Canyon System is responsible for the local deviations in the seawater Nd, Pb, and Os isotope compositions from 6.8 to 4.5 (± 0.5) Ma. The isotope ratios recorded in Fe-Mn crusts are consistent with a southern Sierra Nevada or western Basin and Range provenance of the terrestrial material which was delivered by rivers to the canyon. The exhumation of the modern Monterey Canyon must have begun between 10 and 6.8 ± 0.5 Ma, as indicated by our data, the age of incised strata, and paleo-location of the Monterey Canyon relative to the paleo-coastline.

California↗

USGS2010

Phosphorus dynamics in soils irrigated with reclaimed waste water or fresh water - A study using oxygen isotopic composition of phosphate

Transformations of phosphate (Pi) in different soil fractions were tracked using the stable isotopic composition of oxygen in phosphate ( δ 18 O p ) and Pi concentrations. Clay soil from Israel was treated with either reclaimed waste water (secondary, low grade) or with fresh water amended with a chemical fertilizer of a known isotopic signature. Changes of δ 18 O p and Pi within different soil fractions, during a month of incubation, elucidate biogeochemical processes in the soil, revealing the biological and the chemical transformation impacting the various P pools. P in the soil solution is affected primarily by enzymatic activity that yields isotopic equilibrium with the water molecules in the soil solution. The dissolved P interacts rapidly with the loosely bound P (extracted by bicarbonate). The oxides and mineral P fractions (extracted by NaOH and HCl, respectively), which are considered as relatively stable pools of P, also exhibited isotopic alterations in the first two weeks after P application, likely related to the activity of microbial populations associated with soil surfaces. Specifically, isotopic depletion which could result from organic P mineralization was followed by isotopic enrichment which could result from preferential biological uptake of depleted P from the mineralized pool. Similar transformations were observed in both soils although transformations related to biological activity were more pronounced in the soil treated with reclaimed waste water compared to the fertilizer treated soil.

Geoderma↗

USGS2009

Characterizing the oxygen isotopic composition of phosphate sources to aquatic ecosystems

The oxygen isotopic composition of dissolved inorganic phosphate (δ 18 O p ) in many aquatic ecosystems is not in isotopic equilibrium with ambient water and, therefore, may reflect the source δ 18 O p . Identification of phosphate sources to water bodies is critical for designing best management practices for phosphate load reduction to control eutrophication. In order for δ 18 O p to be a useful tool for source tracking, the δ 18 O p of phosphate sources must be distinguishable from one another; however, the δ 18 O p of potential sources has not been well characterized. We measured the δ 18 O p of a variety of known phosphate sources, including fertilizers, semiprocessed phosphorite ore, particulate aerosols, detergents, leachates of vegetation, soil, animal feces, and wastewater treatment plant effluent. We found a considerable range of δ 18 O p values (from +8.4 to +24.9‰) for the various sources, and statistically significant differences were found between several of the source types. δ 18 O p measured in three different fresh water systems was generally not in equilibrium with ambient water. Although there is overlap in δ 18 O p values among the groups of samples, our results indicate that some sources are isotopically distinct and δ 18 O p can be used for identifying phosphate sources to aquatic systems.

Environmental Science & Technology↗

USGS2008

Characterization of calcium isotopes in natural and synthetic barite

The mineral barite (BaSO4) accommodates calcium in its crystal lattice, providing an archive of Ca-isotopes in the highly stable sulfate mineral. Holocene marine (pelagic) barite samples from the major ocean basins are isotopically indistinguishable from each other (??44/40Ca = -2.01 ?? 0.15???) but are different from hydrothermal and cold seep barite samples (??44/40Ca = -4.13 to -2.72???). Laboratory precipitated (synthetic) barite samples are more depleted in the heavy Ca-isotopes than pelagic marine barite and span a range of Ca-isotope compositions, ??44/40Ca = -3.42 to -2.40???. Temperature, saturation state, a Ba2 + / a SO42 -, and aCa2+/aBa2+ each influence the fractionation of Ca-isotopes in synthetic barite; however, the fractionation in marine barite samples is not strongly related to any measured environmental parameter. First-principles lattice dynamical modeling predicts that at equilibrium Ca-substituted barite will have much lower 44Ca/40Ca than calcite, by -9??? at 0 ??C and -8??? at 25 ??C. Based on this model, none of the measured barite samples appear to be in isotopic equilibrium with their parent solutions, although as predicted they do record lower ??44/40Ca values than seawater and calcite. Kinetic fractionation processes therefore most likely control the extent of isotopic fractionation exhibited in barite. Potential fractionation mechanisms include factors influencing Ca2+ substitution for Ba2+ in barite (e.g. ionic strength and trace element concentration of the solution, competing complexation reactions, precipitation or growth rate, temperature, pressure, and saturation state) as well as nucleation and crystal growth rates. These factors should be considered when investigating controls on isotopic fractionation of Ca2+ and other elements in inorganic and biogenic minerals. ?? 2008 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗

USGS2008

The release of dissolved actinium to the ocean: A global comparison of different end-members

The measurement of short-lived 223Ra often involves a second measurement for supported activities, which represents 227Ac in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of 227Ac, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles 227Ac data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine end-members. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of 227Ac near its potential sources. The average 227Ac activities of nearshore marine end-members range from 0.4??dpm m- 3 at the Gulf of Mexico to 3.0??dpm m- 3 in the coastal waters of the Korean Strait. In analogy to 228Ra, we find the extension of adjacent shelf regions to play a substantial role for 227Ac activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean 227Ac inventory of 1.35 * 1018??dpm 227Acex in the ocean, which corresponds to 37??moles, or 8.4??kg. This implies a flux of 127??dpm m-2 y- 1 from the deep-sea floor. For the shelf regions, we obtain a global inventory of 227Ac of 4.5 * 1015??dpm, which cannot be converted directly into a flux value, as the regional loss term of 227Ac to the open ocean would have to be included. Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to 231Paex. Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released [Moore, W.S., Ussler, W. and Paull, C.K., 2008-this issue. Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge. Marine Chemistry]. Another potential mechanism of producing deviations in 227Ac/228Ra and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including 227Ac in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution. ?? 2007 Elsevier B.V. All rights reserved.

Marine Chemistry↗

USGS2008

Submarine groundwater discharge and nutrient addition to the coastal zone and coral reefs of leeward Hawai'i

Multiple tracers of groundwater input (salinity, Si, 223Ra, 224Ra, and 226Ra) were used together to determine the magnitude, character (meteoric versus seawater), and nutrient contribution associated with submarine groundwater discharge across the leeward shores of the Hawai'ian Islands Maui, Moloka'i, and Hawai'i. Tracer abundances were elevated in the unconfined coastal aquifer and the nearshore zone, decreasing to low levels offshore, indicative of groundwater discharge (near-fresh, brackish, or saline) at all locations. At several sites, we detected evidence of fresh and saline SGD occurring simultaneously. Conservative estimates of SGD fluxes ranged widely, from 0.02-0.65??m3??m- 2 d- 1at the various sites. Groundwater nutrient fluxes of 0.04-40??mmol N m- 2 d- 1 and 0.01-1.6??mmol P m- 2 d- 1 represent a major source of new nutrients to coastal ecosystems along these coasts. Nutrient additions were typically greatest at locations with a substantial meteoric component in groundwater, but the recirculation of seawater through the aquifer may provide a means of transferring terrestrially-derived nutrients to the coastal zone at several sites. ?? 2007 Elsevier B.V. All rights reserved.

Marine Chemistry↗

USGS2008

A dynamic marine calcium cycle during the past 28 million years

Multiple lines of evidence have shown that the isotopic composition and concentration of calcium in seawater have changed over the past 28 million years. A high-resolution, continuous seawater calcium isotope ratio curve from marine (pelagic) barite reveals distinct features in the evolution of the seawater calcium isotopic ratio suggesting changes in seawater calcium concentrations. The most pronounced increase in the ??44/40Ca value of seawater (of 0.3 per mil) occurred over roughly 4 million years following a period of low values around 13 million years ago. The major change in marine calcium corresponds to a climatic transition and global change in the carbon cycle and suggests a reorganization of the global biogeochemical system.

Science↗

USGS2007

Identifying sources of nitrogen to Hanalei Bay, Kauai, utilizing the nitrogen isotope signature of macroalgae

Sewage effluent, storm runoff, discharge from polluted rivers, and inputs of groundwater have all been suggested as potential sources of land derived nutrients into Hanalei Bay, Kauai. We determined the nitrogen isotopic signatures (δ 15 N) of different nitrate sources to Hanalei Bay along with the isotopic signature recorded by 11 species of macroalgal collected in the Bay. The macroalgae integrate the isotopic signatures of the nitrate sources over time, thus these data along with the nitrate to dissolved inorganic phosphate molar ratios (N:P) of the macroalgae were used to determine the major nitrate source to the bay ecosystem and which of the macro-nutrients is limiting algae growth, respectively. Relatively low δ 15 N values (average −0.5‰) were observed in all algae collected throughout the Bay; implicating fertilizer, rather than domestic sewage, as an important external source of nitrogen to the coastal water around Hanalei. The N:P ratio in the algae compared to the ratio in the Bay waters imply that the Hanalei Bay coastal ecosystem is nitrogen limited and thus, increased nitrogen input may potentially impact this coastal ecosystem and specifically the coral reefs in the Bay. Identifying the major source of nutrient loading to the Bay is important for risk assessment and potential remediation plans.

Hawaii↗

USGS2007

New isotopic evidence for the origin of groundwater from the Nubian Sandstone Aquifer in the Negev, Israel

The geochemistry and isotopic composition (H, O, S, O sulfate , C, Sr) of groundwater from the Nubian Sandstone (Kurnub Group) aquifer in the Negev, Israel, were investigated in an attempt to reconstruct the origin of the water and solutes, evaluate modes of water–rock interactions, and determine mean residence times of the water. The results indicate multiple recharge events into the Nubian sandstone aquifer characterized by distinctive isotope signatures and deuterium excess values. In the northeastern Negev, groundwater was identified with deuterium excess values of ∼16‰, which suggests local recharge via unconfined areas of the aquifer in the Negev anticline systems. The δ 18 O H2O and δ 2 H values (−6.5‰ and −35.4‰) of this groundwater are higher than those of groundwater in the Sinai Peninsula and southern Arava valley (−7.5‰ and −48.3‰) that likewise have lower deuterium excess values of ∼10‰. Based on the geochemical differences between groundwater in the unconfined and confined zones of the aquifer, a conceptual geochemical model for the evolution of the groundwater in the Nubian sandstone aquifer has been reconstructed. The isotopic composition of shallow groundwater from the unconfined zone indicates that during recharge oxidation of pyrite to SO 4 ( δ 34 S SO4 ∼−13‰; δ 18 O SO4 ∼+7.7‰) and dissolution of CaCO 3 ( 87 Sr/ 86 Sr ∼0.70787; δ 13 C DIC = −3.7‰) occur. In the confined zone of the aquifer, bacterial SO 4 reduction removes a significant part of dissolved SO 4 2 - "> SO42- , thereby modifying its isotopic composition ( δ 34 S SO4 ∼−2‰; δ 18 O SO4 ∼+8.5‰) and liberating dissolved inorganic C that contains little or no radiocarbon ( 14 C-free) with low δ 13 C DIC values (<−12‰). In addition to local recharge, the Sr and S isotopic data revealed contribution of external groundwater sources to the Nubian Sandstone aquifer, resulting in further modifications of the groundwater chemical and isotopic signatures. In the northeastern Negev, it is shown that SO 4 -rich groundwater from the underlying Jurassic aquifer contributes significantly to the salt budget of the Nubian Sandstone aquifer. The unique chemical and isotopic composition of the Jurassic groundwater ( δ 34 S SO4 ∼ +14‰; δ 18 O SO4 ∼ 14‰; 87 Sr/ 86 Sr ∼0.70764) is interpreted as reflecting dissolution of Late Triassic marine gypsum deposits. In the southern Arava Valley the authors postulate that SO 4 -rich groundwater with distinctively high Br/Cl (3 × 10 −3 ) low 87 Sr/ 86 Sr (0.70734), and high δ 34 S SO4 values (+15‰) is derived from mixing with underlying brines from the Paleozoic units. The radiocarbon measurements reveal low 14 C activities (0.2–5.8 pmc) in both the northeastern Negev and southern Arava Valley. Taking into account dissolution of carbonate rocks and bacterial SO 4 reduction in the unconfined area, estimated mean residence times of groundwater in the confined zone in the northeastern Negev are on the order of 21–38 ka, which suggests recharge predominantly during the last glacial period. The 14 C signal in groundwater from the southern Arava Valley is equally low but due to evidence for mixing with external water sources the residence time estimates are questionable.

Applied Geochemistry↗

USGS2006

Nitrogen sources and cycling in the San Francisco Bay estuary: A nitrate dual isotopic composition approach

We used the dual isotopic composition of nitrate (δ 15 N and δ 18 O) within the estuarine system of San Francisco (SF) Bay, California, to explore the utility of this approach for tracing sources and cycling of nitrate (NO 2 − ). Surface water samples from 49 sites within the estuary were sampled during July–August 2004. Spatial variability in the isotopic composition suggests that there are multiple sources of nitrate to the bay ecosystem including seawater, several rivers and creeks, and sewage effluent. The spatial distribution of nitrate from these sources is heavily modulated by the hydrodynamics of the estuary. Mixing along the estuarine salinity gradient is the main control on the spatial variations in isotopic composition of nitrate within the northern arm of SF Bay. However, the nitrate isotopic composition in the southern arm of SF Bay exhibited a combination of source mixing and phytoplankton drawdown due mostly to the long residence time during the summer study period. Very low δ 18 O NO3 values (as low as −5.0%) at the Sacramento–San Joaquin River delta region give rise to a wide range of δ 18 ONO3 values in the SF Bay system. The range in δ 18 O NO3 values is more than twice that of δ 15 N NO3 , suggesting that δ 18 O NO3 is an even more sensitive tool for tracing nitrate sources and cycling than δ 15 N NO3 .

Limnology and Oceanography↗

USGS2006

The importance of submarine groundwater discharge to the nearshore nutrient supply in the Gulf of Aqaba (Israel)

We used two short-lived radium isotopes (223Ra, 224Ra) and a mass balance approach applied to the radium activities to determine the nutrient contribution of saline submarine groundwater discharge to the coastal waters of the northern Gulf of Aqaba (Israel). Radium isotope activities were measured along transects during two seasons at a site that lacked any obvious surficial water input. An onshore well and an offshore end member were also sampled. For all samples, nutrients and salinity data were collected. Radium isotope activities generally decreased with distance offshore and exhibited significant tidal variability, which is consistent with a shore-derived tidally influenced source. Submarine groundwater contributes only 1-2% of the water along this coast, but this groundwater provides 8-46% of the nutrients. This saline groundwater is derived predominately from tidally pumped seawater percolating through the unconfined coastal aquifer and leaching radium and nutrients. This process represents a significant source of nutrients to the oligotrophic nearshore reef. ?? 2006, by the American Society of Limnology and Oceanography, Inc.

Limnology and Oceanography↗

USGS2004

A precise method for the analysis of δ18O of dissolved inorganic phosphate in seawater

A method for preparation and analysis of the oxygen isotope composition (δ 18 O) of dissolved inorganic phosphate (DIP) has been developed and preliminary results for water samples from various locations are reported. Phosphate is extracted from seawater samples by coprecipitation with magnesium hydroxide. Phosphate is further purified through a series of precipitations and resin separation and is ultimately converted to silver phosphate. Silver phosphate samples are pyrolitically decomposed to carbon monoxide and analyzed for δ 18 O. Silver phosphate samples weighing 0.7 mg (3.5 µmol oxygen) can be analyzed routinely with an average standard deviation of about 0.3‰. There is no isotope fractionation during extraction and blanks are negligible within analytical error. Reproducibility was determined for both laboratory standards and natural samples by multiple analyses. A comparison between filtered and unfiltered natural seawater samples was also conducted and no appreciable difference was observed for the samples tested. The δ 18 O values of DIP in seawater determined using this method range from 18.6‰ to 22.3‰, suggesting small but detectable natural variability in seawater. For the San Francisco Bay estuary DIP δ 18 O is more variable, ranging from 11.4‰ near the San Joaquin River to 20.1‰ near the Golden Gate Bridge, and was well correlated with salinity, phosphate concentration, and δ 18 O of water.

California↗