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At least 487 records · Page 27Linked to original sources

USGS2012

High-resolution digital elevation dataset for Crater Lake National Park and vicinity, Oregon, based on LiDAR survey of August-September 2010 and bathymetric survey of July 2000

Crater Lake partially fills the caldera that formed approximately 7,700 years ago during the eruption of a 12,000-foot volcano known as Mount Mazama. The caldera-forming or climactic eruption of Mount Mazama devastated the surrounding landscape, left a thick deposit of pumice and ash in adjacent valleys, and spread a blanket of volcanic ash as far away as southern Canada. Because the Crater Lake region is potentially volcanically active, knowledge of past events is important to understanding hazards from future eruptions. Similarly, because the area is seismically active, documenting and evaluating geologic faults is critical to assessing hazards from earthquakes. As part of the American Recovery and Reinvestment Act (ARRA) of 2009, the U.S. Geological Survey was awarded funding for high-precision airborne LiDAR ( Li ght D etection A nd R anging) data collection at several volcanoes in the Cascade Range through the Oregon LiDAR Consortium, administered by the Oregon Department of Geology and Mineral Industries (DOGAMI). The Oregon LiDAR Consortium contracted with Watershed Sciences, Inc., to conduct the data collection surveys. Collaborating agencies participating with the Oregon LiDAR Consortium for data collection in the Crater Lake region include Crater Lake National Park (National Park Service) and the Federal Highway Administration. In the immediate vicinity of Crater Lake National Park, 798 square kilometers of LiDAR data were collected, providing a digital elevation dataset of the ground surface beneath forest cover with an average resolution of 1.6 laser returns/m 2 and both vertical and horizontal accuracies of ±5 cm. The LiDAR data were mosaicked in this report with bathymetry of the lake floor of Crater Lake, collected in 2000 using high-resolution multibeam sonar in a collaborative effort between the U.S. Geological Survey, Crater Lake National Park, and the Center for Coastal and Ocean Mapping at the University of New Hampshire. The bathymetric survey collected 16 million soundings with a spatial resolution of 2 meters using an EM1002 system owned and operated by C&C Technologies, Inc. The combined LiDAR and bathymetric dataset has a cell size of 1 meter and will contribute to understanding past volcanic events and their deposits, recognizing of faults and volcanic landforms, and quantifying landscape modification during and after the next volcanic eruption at Crater Lake.

Oregon↗

USGS2014

Geologic implications of gas hydrates in the offshore of India: results of the National Gas Hydrate Program Expedition 01

The Indian National Gas Hydrate Program Expedition 01 (NGHP-01) is designed to study the occurrence of gas hydrate along the passive continental margin of the Indian Peninsula and in the Andaman convergent margin, with special emphasis on understanding the geologic and geochemical controls on the occurrence of gas hydrate in these two diverse settings. The NGHP-01 expedition established the presence of gas hydrates in the Krishna-Godavari and Mahanadi Basins, and the Andaman Sea. The expedition discovered in the Krishna-Godavari Basin one of the thickest gas hydrate accumulations ever documented, in the Andaman Sea one of the thickest and deepest gas hydrate stability zones in the world, and established the existence of a fully developed gas hydrate petroleum system in all three basins. The primary goal of NGHP-01 was to conduct scientific ocean drilling/coring, logging, and analytical activities to assess the geologic occurrence, regional context, and characteristics of gas hydrate deposits along the continental margins of India. This was done in order to meet the long-term goal of exploiting gas hydrate as a potential energy resource in a cost effective and safe manner. During its 113.5-day voyage, the D/V JOIDES Resolution cored and/or drilled 39 holes at 21 sites (1 site in Kerala-Konkan, 15 sites in Krishna-Godavari, 4 sites in Mahanadi, and 1 site in the Andaman deep offshore area), penetrated more than 9250 m of sedimentary section, and recovered nearly 2850 m of core. Twelve holes were logged with logging-while-drilling (LWD) tools and an additional 13 holes were wireline logged. The science team utilized extensive on-board laboratory facilities to examine and prepare preliminary reports on the physical properties, geochemistry, and sedimentology of all the data collected prior to the end of the expedition. Samples were also analyzed in additional post-expedition shore-based studies conducted in leading laboratories around the world. One of the specific objectives of this expedition was to test gas hydrate formation models and constrain model parameters, especially those that account for the formation of concentrated gas hydrate accumulations. The necessary data for characterizing the occurrence of in situ gas hydrate, such as interstitial water chlorinities, core-derived gas chemistry, physical and sedimentological properties, thermal images of the recovered cores, and downhole measured logging data (LWD and/or conventional wireline log data), were obtained from most of the drill sites established during NGHP-01. Almost all of the drill sites yielded evidence for the occurrence of gas hydrate; however, the inferred in situ concentration of gas hydrate varied substantially from site to site. For the most part, the interpretation of downhole logging data, core thermal images, interstitial water analyses, and pressure core images from the sites drilled during NGHP-01 indicate that the occurrence of concentrated gas hydrate is mostly associated with the presence of fractures in the sediments, and in some limited cases, by coarser grained (mostly sand-rich) sediments.

Marine and Petroleum Geology↗

USGS2002

Mercury in feathers from Chilean birds: Influence of location, feeding strategy, and taxonomic affiliation

This study reports baseline concentrations of mercury (Hg) in feathers from different species of birds sampled at various locations off the Chilean coast (Southeastern Pacific). Hg concentrations were evaluated in relation to geographic location, taxonomic affiliation, and feeding strategies. Between January and March of 1995, we collected mature contour feathers from 116 birds belonging to 22 species, mostly seabirds. Birds were collected from 10 different locations (26??09???S, 70??40???W to 54??56???S, 67??37???W). Feather Hg concentrations ranged from 0.11 to 13 ??gg-1 dry weight. We found differences in feather Hg concentrations across taxonomic groups, with highest concentrations in petrels, shearwaters, and albatrosses (Procellaridae), followed by boobies (Sulidae), gulls, terns, skuas (Laridae) and cormorants (Phalacrocoracidae). Ibises and oystercatchers (Threskiornithidae and Charadriidae) had intermediate values, whereas ducks and geese (Anatidae) contained the least amount of Hg. Oceanic species preying on mesopelagic fish (the Procellariformes albatrosses, petrels, and fulmars) had over twice as much Hg (overall average of 3.9 ??gg-1) when compared to the rest of the species sampled (overall average of 1.5 ??gg-1). We did not find higher Hg concentrations in birds inhabiting the more heavily industrialized and urbanized areas of the country (central and northern regions), but in birds inhabiting the remote Juan Ferna??ndez Archipelago. This is not surprising, since all the Procellariformes (the group with highest Hg values in this study) were collected from these islands. Except for Hg in Kermadec petrels (mean of 12 ??gg-1), the range of Hg values reported here (0.11-7.3 ??gg-1) fell below those known to cause adverse health and reproductive effects in birds. ?? 2002 Elsevier Science Ltd. All rights reserved.

Marine Pollution Bulletin↗

USGS2016

Observed decrease in atmospheric mercury explained by global decline in anthropogenic emissions

Observations of elemental mercury (Hg 0 ) at sites in North America and Europe show large decreases (&sim;1–2% y −1 ) from 1990 to present. Observations in background northern hemisphere air, including Mauna Loa Observatory (Hawaii) and CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) aircraft flights, show weaker decreases (<1% y −1 ). These decreases are inconsistent with current global emission inventories indicating flat or increasing emissions over that period. However, the inventories have three major flaws: ( i ) they do not account for the decline in atmospheric release of Hg from commercial products; ( ii ) they are biased in their estimate of artisanal and small-scale gold mining emissions; and ( iii ) they do not properly account for the change in Hg 0 /Hg II speciation of emissions from coal-fired utilities after implementation of emission controls targeted at SO 2 and NO x . We construct an improved global emission inventory for the period 1990 to 2010 accounting for the above factors and find a 20% decrease in total Hg emissions and a 30% decrease in anthropogenic Hg 0 emissions, with much larger decreases in North America and Europe offsetting the effect of increasing emissions in Asia. Implementation of our inventory in a global 3D atmospheric Hg simulation [GEOS-Chem (Goddard Earth Observing System-Chemistry)] coupled to land and ocean reservoirs reproduces the observed large-scale trends in atmospheric Hg 0 concentrations and in Hg II wet deposition. The large trends observed in North America and Europe reflect the phase-out of Hg from commercial products as well as the cobenefit from SO 2 and NO x emission controls on coal-fired utilities.

Proceedings of the National Academy of Sciences↗

USGS2020

Cryptic lives of conspicuous animals: Otolith chemistry chronicles life histories of coastal lagoon fishes

Bar-built coastal lagoons are dynamic ecosystems at the land-sea interface that are important habitats for a variety of species. This study examined the habitat ecology of two lagoon species, the endangered Tidewater Goby ( Eucyclogobius newberryi ) and the Prickly Sculpin ( Cottus asper ) by reconstructing individual life histories from patterns in the concentration of the element Sr (as ratioed to Ca; Sr:Ca) in otoliths. Specific objectives were to (1) elucidate any movements of individual fishes among three primary habitat components of typical bar-built lagoon systems: coastal ocean, brackish lagoon, and freshwater watershed streams, and (2) determine if either species exhibited a consistent life history as defined by a stereotypical otolith Sr:Ca chronology, which could be indicative of a consistent range of salinity or temperature occupied through ontogeny. Results suggested that Tidewater Goby was a lagoon resident and that Prickly Sculpin exhibited migrations between lagoon and watershed stream habitats. There was no strong evidence in either species of ocean occupancy or of a stereotypical Sr:Ca chronology, the latter suggesting the full range of available lagoon habitat in terms of salinity and temperature was likely utilized at all life stages. These findings add to the body of evidence that bar-built lagoons are not isolated habitats, and holistic management of these habitats with adjoining watershed and marine environments could increase habitat connectivity across the landscape, with potential benefits to fishes.

California↗

USGS2020

Data-driven, multi-model workflow suggests strong influence from hurricanes on the generation of turbidity currents in the Gulf of Mexico

Turbidity currents deliver sediment rapidly from the continental shelf to the slope and beyond; and can be triggered by processes such as shelf resuspension during oceanic storms; mass failure of slope deposits due to sediment- and wave-pressure loadings; and localized events that grow into sustained currents via self-amplifying ignition. Because these operate over multiple spatial and temporal scales, ranging from the eddy-scale to continental-scale; coupled numerical models that represent the full transport pathway have proved elusive though individual models have been developed to describe each of these processes. Toward a more holistic tool, a numerical workflow was developed to address pathways for sediment routing from terrestrial and coastal sources, across the continental shelf and ultimately down continental slope canyons of the northern Gulf of Mexico, where offshore infrastructure is susceptible to damage by turbidity currents. Workflow components included: 1) a calibrated simulator for fluvial discharge (Water Balance Model - Sediment; WBMsed ); 2) domain grids for seabed sediment textures ( dbSEABED ); bathymetry, and channelization; 3) a simulator for ocean dynamics and resuspension (the Regional Ocean Modeling System; ROMS ); 4) A simulator ( HurriSlip ) of seafloor failure and flow ignition; and 5) A Reynolds-averaged Navier–Stokes ( RANS ) turbidity current model ( TURBINS ). Model simulations explored physical oceanic conditions that might generate turbidity currents, and allowed the workflow to be tested for a year that included two hurricanes. Results showed that extreme storms were especially effective at delivering sediment from coastal source areas to the deep sea, at timescales that ranged from individual wave events (~hours), to the settling lag of fine sediment (~days).

Alabama, Florida, Louisiana, Mississippi, Texas↗

USGS2024

The early Earth as an analogue for exoplanetary biogeochemistry

Planet Earth has evolved over the past 4.5 billion years from an entirely anoxic planet with possibly a different tectonic regime to the oxygenated world with horizontal plate tectonics that we know today. For most of this time, Earth has been inhabited by a purely microbial biosphere albeit with seemingly increasing complexity over time. A rich record of this geobiological evolution over most of Earth’s history thus provides insights into the remote detectability of microbial life under a variety of planetary conditions. Here we leverage Earth’s geobiological record with the aim of (a) illustrating the current state of knowledge and key knowledge gaps about the early Earth as a reference point in exoplanet science research; (b) compiling biotic and abiotic mechanisms that controlled the evolution of the atmosphere over time; and (c) reviewing current constraints on the detectability of Earth’s early biosphere with state-of-the-art telescope technology. We highlight that life may have originated on a planet with a different (stagnant lid) tectonic regime and strong hydrothermal activity, and under these conditions, biogenic CH 4 gas was perhaps the most detectable atmospheric biosignature. Oxygenic photosynthesis, which is responsible for essentially all O 2 gas in the modern atmosphere, appears to have emerged concurrently with the establishment of modern plate tectonics and the emergence of continental crust, but O 2 accumulation to modern levels only occurred late in Earth’s history, perhaps tied to the rise of land plants. Nutrient limitation in anoxic oceans, promoted by hydrothermal Fe fluxes, may have limited biological productivity and O 2 production. N 2 O is an alternative biosignature that was perhaps significant on the redox-stratified Proterozoic Earth. We conclude that the detectability of atmospheric biosignatures on Earth was not only dependent on biological evolution but also strongly controlled by the evolving tectonic context.

Reviews in Mineralogy and Geochemistry↗

USGS2005

Nutrient contributions to the Santa Barbara Channel, California, from the ephemeral Santa Clara River

The Santa Clara River delivers nutrient rich runoff to the eastern Santa Barbara Channel during brief (???1-3 day) episodic events. Using both river and oceanographic measurements, we evaluate river loading and dispersal of dissolved macronutrients (silicate, inorganic N and P) and comment on the biological implications of these nutrient contributions. Both river and ocean observations suggest that river nutrient concentrations are inversely related to river flow rates. Land use is suggested to influence these concentrations, since runoff from a subwatershed with substantial agriculture and urban areas had much higher nitrate than runoff from a wooded subwatershed. During runoff events, river nutrients were observed to conservatively mix into the buoyant, surface plume immediately seaward of the Santa Clara River mouth. Dispersal of these river nutrients extended 10s of km into the channel. Growth of phytoplankton and nutrient uptake was low during our observations (1-3 days following runoff), presumably due to the very low light levels resulting from high turbidity. However, nutrient quality of runoff (Si:N:P = 16:5:1) was found to be significantly different than upwelling inputs (13:10:1), which may influence different algal responses once sediments settle. Evaluation of total river nitrate loads suggests that most of the annual river nutrient fluxes to the ocean occur during the brief winter flooding events. Wet winters (such as El Nin??o) contribute nutrients at rates approximately an order-of-magnitude greater than "average" winters. Although total river nitrate delivery is considerably less than that supplied by upwelling, the timing and location of these types of events are very different, with river discharge (upwelling) occurring predominantly in the winter (summer) and in the eastern (western) channel. ?? 2004 Elsevier Ltd. All rights reserved.

Estuarine, Coastal and Shelf Science↗

USGS2005

Elemental content of lichens of the Point Reyes Peninsula, northern California

The Point Reyes peninsula in northern California is about 45 km northwest of San Francisco and occasionally receives air masses from the city contributing to haze and lowered visibility. Although gaseous pollutants are not a problem, fine particulates containing carbon and other elements are measurable at the park. In this study, five lichen species were sampled along a 40-km linear transect from southeast to northwest from the town of Bolinas at the southern end of the peninsula. Elevated levels of Na and S and the Na/S ratio at localities nearer the ocean confirmed there is a definite marine aerosol influence on lichen elemental content. Elevated potassium and mercury concentrations were also found at high elevation sites that intercept fog. However, arsenic and lead were found to decrease with distance from Bolinas along the transect, suggesting these two elements originate in the fine particulate haze that enters the park from San Francisco. Concentrations of elements were not at enriched levels for other lichen species. A possible local influence of roads on element content needs further study.

California↗

USGS2020

Spatial and temporal variations in SO2 and PM2.5 levels around Kīlauea volcano, Hawai'i during 2007–2018

Among the hazards posed by volcanoes are the emissions of gases and particles that can affect air quality and damage agriculture and infrastructure. A recent intense episode of volcanic degassing associated with severe impacts on air quality accompanied the 2018 lower East Rift Zone (LERZ) eruption of Kīlauea volcano, Hawai'i. This resulted in a major increase in gas emission rates with respect to usual emission values for this volcano, along with a shift in the source of the dominant plume to a populated area on the lower flank of the volcano. This led to reduced air quality in downwind communities. We analyse open-access data from the permanent air quality monitoring networks operated by the Hawai'i Department of Health (HDOH) and National Park Service (NPS), and report on measurements of atmospheric sulfur dioxide (SO 2 ) between 2007 and 2018 and PM 2.5 (aerosol particulate matter with diameter <2.5 μm) between 2010 and 2018. Additional air quality data were collected through a community-operated network of low-cost PM 2.5 sensors during the 2018 LERZ eruption. From 2007 to 2018 the two most significant escalations in Kīlauea's volcanic emissions were: the summit eruption that began in 2008 (Kīlauea emissions averaged 5–6 kt/day SO 2 from 2008 until summit activity decreased in May 2018) and the LERZ eruption in 2018 when SO 2 emission rates reached a monthly average of 200 kt/day during June. In this paper we focus on characterizing the airborne pollutants arising from the 2018 LERZ eruption and the spatial distribution and severity of volcanic air pollution events across the Island of Hawai'i. The LERZ eruption caused the most frequent and severe exceedances of the Environmental Protection Agency (EPA) PM 2.5 air quality threshold (35 μg/m 3 as a daily average) in Hawai'i in the period 2010–2018. In Kona, for example, the maximum 24-h-mean mass concentration of PM 2.5 was recorded as 59 μg/m 3 on the twenty-ninth of May 2018, which was one of eight recorded exceedances of the EPA air quality threshold during the 2018 LERZ eruption, where there had been no exceedances in the previous 8 years as measured by the HDOH and NPS networks. SO 2 air pollution during the LERZ eruption was most severe in communities in the south and west of the island, as measured by selected HDOH and NPS stations in this study, with a maximum 24-h-mean mass concentration of 728 μg/m 3 recorded in Ocean View (100 km west of the LERZ emission source) in May 2018. Data from the low-cost sensor network correlated well with data from the HDOH PM 2.5 instruments, confirming that these low-cost sensors provide a robust means to augment reference-grade instrument networks.

Hawaii↗

USGS2013

How old is the Isthmus of Panama?

The Standard Model of the formation of the Isthmus of Panama proposes that final closure occurred at 4–3 Ma. The model is based on evidence from studies of marine stratigraphy, fossil sequences, divergent molecular phylogenies, the timing of the Great American Biological Interchange (GABI), and proxies for marine paleosalinity, paleobathymetry, productivity, and paleotemperatures. The new model uses cooling of magmas in the Cretaceous to Early Miocene Central American Volcanic arc to propose Eocene emergence of the discrete structural blocks of the arc and then U/Pb dating, paleomagnetic pole rotations, and atlantic sea-floor anomalies to reconfigure the blocks for different time slices back to 25 Ma. Closure is proposed at 15 Ma, because by this time the alignment of the blocks leaves no space for trans-isthmian marine passages. We propose that the Indonesian Australian Archipelago (IAA) provides a model for the Central American arc between 15 and 3 Ma because it accounts for the extensive marine interchange between the Pacific and Indian oceans through few and narrow passages while maintaining a complete separation of the terrestrial faunas (Wallace and Lydekker lines) of the two continental platforms of Sunda and Sahul. Using the Indonesian Volcanic arc as a model, we can now accommodate the general tectonic configuration and much of the emergence of the new model, while accounting for the marine fossil record, the molecular evidence of rapid recent speciation, and the delayed Great American Biotic Interchange that the New Model fails to explain.

Bulletin of Marine Science↗

USGS2014

An 8700 year paleoclimate reconstruction from the southern Maya lowlands

Analysis of a sediment core from Lago Puerto Arturo, a closed basin lake in northern Peten, Guatemala, has provided an &sim;8700 cal year record of climate change and human activity in the southern Maya lowlands. Stable isotope, magnetic susceptibility, and pollen analyses were used to reconstruct environmental change in the region. Results indicate a relatively wet early to middle Holocene followed by a drier late Holocene, which we interpret as reflecting long-term changes in insolation (precession). Higher frequency variability is more likely attributable to changes in ocean/atmosphere circulation in both the North Atlantic and the Pacific Oceans. Pollen and isotope data show that most of the period of prehispanic agricultural settlement, i.e. &sim;5000–1000 cal yr BP, was characterized by drier conditions than previous or subsequent periods. The presence of Zea (corn) pollen through peak aridity during the Terminal Classic period (&sim;1250–1130 cal yr BP) suggests that drought may not have had as negative an impact as previously proposed. A dramatic negative shift in isotope values indicates an increase in precipitation after &sim;950 cal yr BP (hereafter BP).

Quaternary Science Reviews↗

USGS2013

The significance of ultra-refracted surface gravity waves on sheltered coasts, with application to San Francisco Bay

Ocean surface gravity waves propagating over shallow bathymetry undergo spatial modification of propagation direction and energy density, commonly due to refraction and shoaling. If the bathymetric variations are significant the waves can undergo changes in their direction of propagation (relative to deepwater) greater than 90° over relatively short spatial scales. We refer to this phenomenon as ultra-refraction. Ultra-refracted swell waves can have a powerful influence on coastal areas that otherwise appear to be sheltered from ocean waves. Through a numerical modeling investigation it is shown that San Francisco Bay, one of the earth's largest and most protected natural harbors, is vulnerable to ultra-refracted ocean waves, particularly southwest incident swell. The flux of wave energy into San Francisco Bay results from wave transformation due to the bathymetry and orientation of the large ebb tidal delta, and deep, narrow channel through the Golden Gate. For example, ultra-refracted swell waves play a critical role in the intermittent closure of the entrance to Crissy Field Marsh, a small restored tidal wetland located on the sheltered north-facing coast approximately 1.5 km east of the Golden Gate Bridge.

California↗

USGS2011

Review of flow rate estimates of the Deepwater Horizon oil spill

The unprecedented nature of the Deepwater Horizon oil spill required the application of research methods to estimate the rate at which oil was escaping from the well in the deep sea, its disposition after it entered the ocean, and total reservoir depletion. Here, we review what advances were made in scientific understanding of quantification of flow rates during deep sea oil well blowouts. We assess the degree to which a consensus was reached on the flow rate of the well by comparing in situ observations of the leaking well with a time-dependent flow rate model derived from pressure readings taken after the Macondo well was shut in for the well integrity test. Model simulations also proved valuable for predicting the effect of partial deployment of the blowout preventer rams on flow rate. Taken together, the scientific analyses support flow rates in the range of ~50,000–70,000 barrels/d, perhaps modestly decreasing over the duration of the oil spill, for a total release of ~5.0 million barrels of oil, not accounting for BP's collection effort. By quantifying the amount of oil at different locations (wellhead, ocean surface, and atmosphere), we conclude that just over 2 million barrels of oil (after accounting for containment) and all of the released methane remained in the deep sea. By better understanding the fate of the hydrocarbons, the total discharge can be partitioned into separate components that pose threats to deep sea vs. coastal ecosystems, allowing responders in future events to scale their actions accordingly.

Alabama;Florida;Louisiana;Mississippi;Texas↗

USGS2008

Coherent changes in relative C4 plant productivity and climate during the late Quaternary in the North American Great Plains

Evolution of the mixed and shortgrass prairie of the North American Great Plains is poorly understood because of limited proxies available for environmental interpretations. Buried soils in the Great Plains provide a solution to the problem because they are widespread both spatially and temporally with their organic reservoirs serving as a link to the plants than once grew on them. Through stable carbon isotopic analysis of soil organic carbon (??13C), the percent carbon from C4 plants (%C4) can be ascertained. Because C4 plants are primarily warm season grasses responding positively to summer temperature, their representation has the added advantage of serving as a climate indicator. To better understand grassland and climate dynamics in the Great Plains during the last 12 ka (ka=1000 radiocarbon years) we developed an isotopic standardization technique by: determining the difference in buried soil ??13C and modern soil ??13C expected for that latitude (????13C), and transferring the ????13C to ??%C4 (% C4) using mass balance calculations. Our analysis reveals two isotopic stages in the mixed and shortgrass prairie of the Great Plains based on trends in ??%C4. In response to orbital forcing mechanisms, ??%C4 was persistently below modern in the Great Plains between 12 and 6.7 ka (isotopic stage II) evidently because of the cooling effect of the Laurentide ice sheet and proglacial lakes in northern latitudes, and glacial meltwater pulses cooling the Gulf of Mexico and North Atlantic Ocean. The ??%C4 after 6.7 ka (isotopic stage I) increased to modern levels as conditioned by the outflow of warm, moist air from the Gulf of Mexico and dry incursions from the west that produced periodic drought. At the millennial-scale, time series analysis demonstrates that ??%C4 oscillated with 0.6 and 1.8 ka periodicities, possibly governed by variations in solar irradiance. Our buried soil isotopic record correlates well with other environmental proxy from the Great Plains and surrounding regions. ?? 2008 Elsevier Ltd.

Quaternary Science Reviews↗

USGS2012

Out of the tropics: the Pacific, Great Basin lakes, and late Pleistocene water cycle in the western United States

The water cycle in the western U.S. changed dramatically over glacial cycles. In the last 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation is hypothesized to result from a southward shift of Pacific winter storm tracks. We compared Pacific Ocean data to lake levels from the interior west and found that Great Basin lake high stands are older than coastal wet periods at the same latitude. Westerly storms were not the source of high precipitation. Instead, air masses from the tropical Pacific were transported northward, bringing more precipitation into the Great Basin when coastal California was still dry. The changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle.

Science↗

USGS2021

Enhanced susceptibility of methylmercury bioaccumulation into seston of the Laurentian Great Lakes

Mercury concentrations in the Laurentian Great Lakes waters are among the lowest reported in the literature, while game fish concentrations approach consumption advisory limits, particularly in Lakes Superior, Huron, and Michigan, indicating efficient methylmercury transfer from water to game fish. To determine if increased transfer efficiency is evident within the lower food web, we measured (2010–2018) mercury and dissolved organic carbon (DOC) in water, and in size-sieved seston, dietary tracers (carbon and nitrogen isotope ratios), phytoplankton methylmercury bioaccumulation, and methylmercury biomagnification between increasing seston size fractions. We observed consistently low filter-passing methylmercury (<0.010 ng L –1 ) and comparatively variable DOC (1.1 to 3.4 mg L –1 ) concentrations. Methylmercury biomagnification factors between size-sieved seston were similar between lakes. Bioaccumulation factors in phytoplankton were among the highest in the literature (log 5.5 to 6.1), exceeding those in oceans, smaller lakes, and streams, and was influenced by DOC. Higher bioaccumulation rates increase the susceptibility of methylmercury accumulation into the food web. Because mercury is dominantly delivered to the Great Lakes through the atmosphere and the biota therein is highly susceptible to methylmercury uptake, we propose that the Laurentian Great Lakes are excellent sentinels to trace the success of efforts to decrease global mercury emissions (e.g., Minamata Treaty) in the future.

Environmental Science and Technology↗

USGS1991

Neogene biostratigraphy and paleoenvironments of Enewetak Atoll, equatorial Pacific Ocean

Micropaleontologic analyses of Neogene sediments from Enewetak Atoll, Marshall Islands, provide data on the age of lagoonal deposits, stratigraphic disconformities and the paleoenvironmental and subsidence history of the atoll. Benthic foraminifers, planktic foraminifers, calcareous nannofossils and ostracodes were studied from six boreholes, the deepest penetrating 1605 feet below the lagoon floor into upper Oligocene strata. The Oligocene-Miocene boundary occurs at about 1200 ft below the lagoon floor. The early and middle Miocene is characterized by brief periods of deposition and numerous hiatuses. Ostracodes and benthic foraminifers indicate a shallow-marine reefal environment with occasional brackish water conditions. Upper Miocene and lower Pliocene deposits placed in calcareous nannofossil Zones NN9-15 and in planktic foraminifer Zones N16-19 contain species-rich benthic microfaunas which indicate alternating reefal and brackish water mangrove environments. The upper Pliocene contains at least two major depositional hiatuses that coincide with a major faunal turnover in benthic foraminiferal and ostracode assemblages. The Quaternary is characterized by benthic microfaunas similar to those of modern atoll lagoons and is punctuated by at least 11 disconformities which signify periods of low sea level. Atoll subsidence rates during the last 10 Ma averaged 30 to 40 m/m.y. ?? 1991 Elsevier Science Publishers B.V. All rights reserved.

Marine Micropaleontology↗