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At least 397 records · Page 22Linked to original sources
USGS2019

Streamflow gains and losses in New Fork and Green Rivers, upstream from Fontenelle Reservoir, Wyoming, October 2015

The Wyoming Landscape Conservation Initiative is a program created to implement a long-term, science-based program of assessing natural resources while facilitating responsible energy and other development and does studies in much of southwestern Wyoming, including all or parts of Lincoln, Sublette, Fremont, Sweetwater, and Carbon Counties. A synoptic study was completed by the U.S. Geological Survey as part of ongoing contributions to the Wyoming Landscape Conservation Initiative to better understand the streamflow dynamics in the New Fork and Green Rivers in an area with historical, current, and future energy development. Streamflow measurements were collected October 19–22, 2015, at 19 sites on the New Fork and Green Rivers in Wyoming to determine changes in streamflow and, where applicable, describe the inflow and outflow of groundwater. Streamflow in the New Fork River generally increased from 50 cubic feet per second (ft 3 /s) at the most upstream site near Pinedale, Wyoming, to 350 ft 3 /s at the mouth of the river. Streamflow in the Green River generally increased downstream from 250 ft 3 /s at the most upstream site at Warren Bridge to around 800 ft 3 /s at the most downstream site near La Barge, Wyo., upstream from Fontenelle Reservoir. Estimated streamflow gains and losses were calculated for five reaches on the New Fork River. Four of the five reaches on the New Fork River had a change greater than the associated measurement error and were gaining reaches; the reach with the largest gain was the most upstream reach. One reach, the most downstream reach, had a calculated change in streamflow less than the associated measurement error. Estimated streamflow gains and losses were calculated for four reaches on the Green River. One reach was determined to be a gaining reach, one was a losing reach, and two reaches had changes less than the associated measurement error. Comparing the annual streamflow hydrographs for three long-term streamgages likely showed the effects of applying irrigation water to the upstream areas of land draining to the Green and New Fork Rivers. Streamflows in the New Fork River near Big Piney and the Green River near La Barge, Wyo., are sustained later in the season compared to the upstream site of Green River at Warren Bridge, which has few diversions and minimal irrigation.

Wyoming↗
USGS2017

Earth Stewardship: An initiative by the Ecological Society of America to foster engagement to sustain Planet Earth

The Ecological Society of America (ESA) has responded to the growing commitment among ecologists to make their science relevant to society through a series of concerted efforts, including the Sustainable Biosphere Initiative (1991), scientific assessment of ecosystem management (1996), ESA’s vision for the future (2003), Rapid Response Teams that respond to environmental crises (2005), and the Earth Stewardship Initiative (2009). During the past 25 years, ESA launched five new journals, largely reflecting the expansion of scholarship linking ecology with broader societal issues. The goal of the Earth Stewardship Initiative is to raise awareness and to explore ways for ecologists and other scientists to contribute more effectively to the sustainability of our planet. This has occurred through four approaches: (1) articulation of the stewardship concept in ESA publications and Website, (2) selection of meeting themes and symposia, (3) engagement of ESA sections in implementing the initiative, and (4) outreach beyond ecology through collaborations and demonstration projects. Collaborations include societies and groups of Earth and social scientists, practitioners and policy makers, religious and business leaders, federal agencies, and artists and writers. The Earth Stewardship Initiative is a work in progress, so next steps likely include continued nurturing of these emerging collaborations, advancing the development of sustainability and stewardship theory, improving communication of stewardship science, and identifying opportunities for scientists and civil society to take actions that move the Earth toward a more sustainable trajectory.

Book chapter↗
USGS2012

A science plan for a comprehensive assessment of water supply in the region underlain by fractured rock in Maryland

The fractured rock region of Maryland, which includes land areas north and west of the Interstate 95 corridor, is the source of water supply for approximately 4.4 million Marylanders, or approximately 76 percent of the State's population. Whereas hundreds of thousands of residents rely on wells (both domestic and community), millions rely on surface-water sources. In this region, land use, geology, topography, water withdrawals, impoundments, and other factors affect water-flow characteristics. The unconfined groundwater systems are closely interconnected with rivers and streams, and are affected by seasonal and climatic variations. During droughts, groundwater levels drop, thereby decreasing well yields, and in some cases, wells have gone dry. Low ground-water levels contribute to reduced streamflows, which in turn, can lead to reduced habitat for aquatic life. Increased demand, over-allocation, population growth, and climate change can affect the future sustainability of water supplies in the region of Maryland underlain by fractured rock. In response to recommendations of the 2008 Advisory Committee on the Management and Protection of the State's Water Resources report, the Maryland Department of the Environment's Water Supply Program, the Maryland Geological Survey, the Maryland Department of Natural Resources, Monitoring and Non-Tidal Assessment (MANTA) Division, and the U.S. Geological Survey have developed a science plan for a comprehensive assessment that will provide new scientific information, new data analysis, and new tools for the State to better manage water resources in the fractured rock region of Maryland. The science plan lays out five goals for the comprehensive assessment: (1) develop tools for the improved management and investigation of groundwater and surface-water resources; (2) characterize factors affecting reliable yields of individual groundwater and surface-water supplies; (3) investigate impacts on nearby water withdrawal users caused by groundwater and surface-water withdrawals; (4) assess the role of streamflow and water withdrawals on the ecological integrity of streams; and (5) improve understanding of the distribution of water-quality conditions in fractured rock aquifers. To accomplish these goals, accurate data collection, review, and analysis are needed, including the study of "Research Watersheds" that can provide detailed information about the potential effects that climate change and water withdrawals may have on groundwater, streamflow, and aquatic life. The assessment planning started in 2009 and is being conducted with close interagency coordination. A Fractured Rock Aquifer Information System is currently (2012) undergoing initial development. Other major tasks that will be performed include the development of work plans for each science goal, the estimation of daily streamflow at ungaged streams, and the design and implementation of Research Watersheds. Finally, scenarios will be modeled to evaluate current water allocation permitting methodologies, investigate effects on nearby water withdrawal users caused by groundwater and surface-water withdrawals, and assess the potential impacts of climate change on water resources. Desktop and Web-based tools will be developed in order to meet the diverse research needs of the assessment. These tools, including the Fractured Rock Aquifer Information System will be continuously improved during the assessment to store relevant groundwater and surface-water data in spatially referenced databases, estimate streamflows, locate higher-yielding wells, estimate the impacts of withdrawals on nearby users, and assess the cumulative impacts of withdrawals on the aquatic resource. Tools will be developed to serve the needs of many audiences, including water resource managers, water suppliers, planners, policymakers, and other scientific investigators.

Maryl↗
USGS2010

U.S. Geological Survey Rewarding Environment Culture Study, 2002

In its 2001 review of the U.S. Geological Survey (USGS), the National Research Council (NRC, p. 126) cautioned that ?high-quality personnel are essential for developing high-quality science information? and urged the USGS to ?devote substantial efforts to recruiting and retaining excellent staff.? Recognizing the importance of the NRC recommendation, the USGS has committed time and resources to create a rewarding work environment with the goal of achieving the following valued outcomes: ? USGS science vitality ? Customer satisfaction with USGS products and services ? Employee perceptions of the USGS as a rewarding place to work ? Heightened employee morale and commitment ? The ability to recruit and retain employees with critical skills To determine whether this investment of time and resources was proving to be successful, the USGS Human Resources Office conducted a Rewarding Environment Culture Study to answer the following four questions. ? Question 1: Does a rewarding work environment lead to the valued outcomes (identified above) that the USGS is seeking? ? Question 2: Which management, supervisory, and leadership behaviors contribute most to creating a rewarding work environment and to achieving the valued outcomes that the USGS is seeking? ? Question 3: Do USGS employees perceive that the USGS is a rewarding place to work? ? Question 4: What actions can and should be taken to enhance the USGS work environment? To begin the study, a conceptual model of a rewarding USGS environment was developed to test assumptions about a rewarding work environment. The Rewarding Environment model identifies the key components that are thought to contribute to a rewarding work environment and the valued outcomes that are thought to result from having a rewarding work environment. The 2002 Organizational Assessment Survey (OAS) was used as the primary data source for the study because it provided the most readily available data. Additional survey data were included as they became available The dividends of creating a rewarding work environment can be great. As the results of the USGS Rewarding Environment Culture Study of 2002 indicate, creating a rewarding work environment is an investment that can have an important impact on the outcomes that the USGS values?the vitality of our science, the satisfaction of our customers, and the morale, commitment, and performance of our employees.

Open-File Report↗
USGS2003

Natural and anthropogenic factors affecting the structure of the benthic macroinvertebrate community in an effluent-dominated reach of the Santa Cruz River, AZ

This study provides an assessment of the ecological conditions of a 46-km effluent-dominated stream section of the Santa Cruz River in the vicinity of the International Waste Water Treatment Plant, Nogales, AZ. We associated changes in the structure of the macroinvertebrate community to natural and anthropogenic chemical and physical variables using multivariate analysis. The analysis shows that biological criteria for effluent-dominated streams can be established using macroinvertebrate community attributes only with an understanding of the contribution of three classes of variables on the community structure: (1) low flow hydrological discharge as affected by groundwater withdrawals, treatment plant discharge, and subsurface geomorphology; (2) chemical composition of the treatment plant discharge and natural dilution; and (3) naturally produced floods resulting from seasonality of precipitation. ?? 2003 Elsevier Science Ltd. All rights reserved.

Ecological Indicators↗
USGS2025

Foundational science in flight—USGS bird programs support conservation, culture, and a thriving U.S. economy

Birds are vital to our economy, ecosystems, and cultural heritage. Investing in bird conservation benefits communities, businesses, and working lands while reinforcing our nation’s legacy of stewardship and biodiversity. By valuing birds, we ensure a richer, healthier, and more vibrant future for all Americans. The USGS leads two national bird monitoring programs Thriving bird populations contribute over $ 100 billion in related purchases to the U.S. economy annually, helping to support 1.4 million jobs and $ 90 billion in labor-related income. Across our nation, Federal and State wildlife agencies, Flyway Councils, non-governmental organizations, and more consider data from the U.S. Geological Survey’s (USGS) Bird Banding Laboratory (BBL) and Breeding Bird Survey (BBS) to be critical to meeting their mandates to set healthy harvest levels and in identifying species of conservation need. However, without stable and sufficient resources for the BBL and BBS, the capacity to monitor and address the rapidly evolving needs of migratory bird populations is at risk, jeopardizing the foundation of collaborative conservation efforts across North America.

Fact Sheet↗
USGS2021

SSA task force on diversity, equity, and inclusion: Toward a changing, inclusive future in earthquake science

In the United States, a wide variety of studies show that the geoscience community does not reflect the broader societal makeup (e.g., Velasco and Jaurrieta de Velasco, 2010; Dutt, 2020; Howley, 2020). In fact, only about 10% of all Science, Technology, Engineering, and Mathematics (STEM) Ph.D. degrees are awarded to people of color, although they represent more than a third of the population (Dutt, 2020). These numbers have changed little over the past 40 yr (e.g., Bernard and Cooperdock, 2018; Dutt, 2020). Recent events in the United States have again raised awareness of this discrepancy in many fields; similar divergences may be present throughout the world. This discrepancy represents a tremendous loss of talent and contributes to ongoing bias and racism. As the premier international seismological professional society, Seismological Society of America (SSA) is committed, as stated in its ethics policy, to “freedom and transparency in research and education, which should be conducted in a supportive, inclusive, and respectful environment, free from any discrimination, harassment or bullying.” SSA convened the SSA Diversity, Equity, and Inclusion (DEI) Task Force to identify specific and actionable recommendations that the Society can take to start to address the significant issues surrounding the systematic underrepresentation in seismology and related geosciences by marginalized groups on both short- and long- term time horizons. This report, written by the Task Force, outlines actionable items that SSA can undertake as well as a framework by which progress can be measured to help guide the Society and its members forward as a community to make earthquake science more just, equitable, diverse, and inclusive. We recognize that this document cannot address the multiple individual, cultural, and historical barriers that some members may face (e.g., Núñez et al., 2020), nor can it reflect all possibilities or all recommended practices (e.g., Ali et al., 2021). What this document does represent, however, is the beginning of what we hope to be a significant cultural change in how we conduct earthquake science as an organization, not the end of this process as the Task Force fulfills its charter. As a note, some of the recommendations that the Task Force has outlined here have already been implemented within SSA or are actively being considered. For completeness, we still include them here because this highlights the commitment to change that SSA leadership has embraced.

Seismological Research Letters↗
USGS2020

Estimating burn severity and carbon emissions from a megafire in boreal forests of China

Wildfires, especially those of large size, worsen air quality and alter the carbon cycle through combustion of large quantities of biomass and release of carbon into the atmosphere. The Black Dragon fire, which occurred in 1987 in the boreal forests of China is among the top five of such megafires ever recorded in the world. With over 30 years of accumulation of data and availability of new greenhouse gas emission accounting methods, carbon emissions from this megafire can now be estimated with improved precision and greater spatial resolution. To do this, we combined field and remote sensing data to map four burn severity classes and calculated combustion efficiency in terms of the biomass immediately consumed in the fire. Results of the study showed that 1.30 million hectares burned and 52% of that area burned with high severity. The emitted carbon dioxide equivalents (CO2e), accounted for approximately 10% of total fossil fuel emissions from China in 1987, along with CO (2%–3% of annual anthropogenic CO emissions from China) and non-methane hydrocarbons (NMHC) contributing to the atmospheric pollutants. Our study provides an important basis for carbon emission estimation and understanding the impacts of megafires.

Science of the Total Environment↗
USGS2022

Air, land, and water variables associated with the first appearance and current spatial distribution of toxic Prymnesium parvum blooms in reservoirs of the Southern Great Plains, USA

This study examined the association of air, land, and water variables with the first historical occurrence and current distribution of toxic Prymnesium parvum blooms in reservoirs of the Brazos River and Colorado River, Texas (USA). One impacted and one reference reservoir were selected per basin. Land cover and use variables were estimated for the whole watershed (WW) and a 0.5-km zone on either side of streams (near field, NF). Variables were expressed in annual values. Principal component and trend analyses were used to determine (1) differences in environmental conditions before and after the 2001 onset of toxic blooms in impacted reservoirs (study period, 1992–2017), and (2) traits that uniquely discriminate impacted from reference reservoirs (2001–2017). Of thirty-three variables examined, two positively aligned with the reoccurring appearance of blooms in impacted reservoirs (air CO 2 and herbicide Glyphosate) and another two negatively aligned (insecticides Terbufos and Malathion). Glyphosate use was observed throughout the study period but a turning point for an upward trend occurred near the year of first bloom occurrence. While the relevance of the decreased use of insecticides is uncertain, prior experimental studies reported that increasing concentrations of air CO 2 and water Glyphosate can enhance P. parvum growth. Consistent with prior findings, impacted reservoirs were of higher salinity than reference reservoirs. In addition, their watersheds had far lower wetland cover at NF and WW scales. The value of wetlands in reducing harmful algal bloom incidence by reducing nutrient inputs has been previously recognized, but wetlands can also capture pesticides. Therefore, a diminished wetland cover could magnify Glyphosate loads flowing into impacted reservoirs. These observations are consistent with a scenario where rising levels of air CO 2 and Glyphosate use contributed to the establishment of P. parvum blooms in reservoirs of relatively high salinity and minimal wetland cover over their watersheds.

Texas↗
USGS2023

Bifenthrin, a ubiquitous contaminant, impairs the development and behavior of the threatened Longfin Smelt during early life stages

The Longfin Smelt ( Spirinchus thaleichthys ) population in the San Franscisco Bay/Sacramento-San Joaquin Delta (Bay-Delta) has declined to ∼1% of its pre-1980s abundance and, as a result, is listed as threatened under the California Endangered Species Act. The reasons for this decline are multiple and complex, including the impacts of contaminants. Because the spawning and rearing seasons of Longfin Smelt coincide with the rainy season, during which concentrations of contaminants increase due to runoff, we hypothesized that early life stages may be particularly affected by those contaminants. Bifenthrin, a pyrethroid insecticide commonly used in agricultural and urban sectors, is of concern. Concentrations measured in the Bay-Delta have been shown to disrupt the behavior, development, and endocrine system of other fish species. The objective of the present work was to assess the impact of bifenthrin on the early developmental stages of Longfin Smelt. For this, embryos were exposed to 2, 10, 100, and 500 ng/L bifenthrin from fertilization to hatch, and larvae were exposed to 2, 10, and 100 ng/L bifenthrin from one day before to 3 days post-hatch. We assessed effects on size at hatch, yolk sac volume, locomotory behavior, and upper thermal susceptibility (via cardiac endpoints). Exposure to these environmentally relevant concentrations of bifenthrin did not significantly affect the cardiac function of larval Longfin Smelt; however, exposures altered their behavior and resulted in smaller hatchlings with reduced yolk sac volumes. This study shows that bifenthrin affects the fitness-determinant traits of Longfin Smelt early life stages and could contribute to the observed population decline.

Environmental Science and Technology↗
USGS2007

Persistent chlordane concentrations in long island sound sediment: Implications from chlordane, 210 Pb, and 137 Cs profiles

Concentrations of chlordane, a banned termiticide and pesticide, were examined in recently collected surficial sediment (10 sites) and sediment cores (4 sites) in Long Island Sound (LIS).The highest chlordane concentrations were observed in western LIS, near highly urbanized areas. Chlordane concentrations did not decrease significantly in the past decade when compared to the data collected in 1996, consistent with the observation of near-constant chlordane levels in blue mussel tissues collected during the same time period. Chlordane concentrations in many of the sites exceeded levels above which harmful effects on sediment-dwelling organisms are expected to frequently occur. Chlordane concentrations in two of the four sediment cores showed a peak below the sediment surface, suggesting reduced chlordane inputs in recent years. The lack of a chlordane concentration maximum below the sediment surface in the other two cores, coupled with the lack of a well-defined 137 Cs peak, indicated significant sediment mixing. Simulations of 137 Cs and 210 Pb profiles in sediment cores with a simple sediment-mixing model were used to constrain both the deposition rate and the bioturbation rate of the sediment. Simulations of the chlordane profiles indicated continued chlordane input to LIS long after chlordane was phased out in the U.S. Continued chlordane input and significant sediment mixing may have contributed to the persistent chlordane concentrations in surficial sediment, which poses long-term threats to benthic organisms in LIS.

New York↗
USGS2006

Monitoring super-volcanoes: Geophysical and geochemical signals at Yellowstone and other large caldera systems

Earth's largest calderas form as the ground collapses during immense volcanic eruptions, when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the Earth's crust over a period of days to weeks. Continuing long after such great eruptions, the resulting calderas often exhibit pronounced unrest, with frequent earthquakes, alternating uplift and subsidence of the ground, and considerable heat and mass flux. Because many active and extinct calderas show evidence for repetition of large eruptions, such systems demand detailed scientific study and monitoring. Two calderas in North America, Yellowstone (Wyoming) and Long Valley (California), are in areas of youthful tectonic complexity. Scientists strive to understand the signals generated when tectonic, volcanic and hydrothermal (hot ground water) processes intersect. One obstacle to accurate forecasting of large volcanic events is humanity's lack of familiarity with the signals leading up to the largest class of volcanic eruptions. Accordingly, it may be difficult to recognize the difference between smaller and larger eruptions. To prepare ourselves and society, scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption. ?? 2006 The Royal Society.

Philosophical Transactions of the Royal Society A:↗
USGS1991

Rapid formation of Ontong Java Plateau by Aptian mantle plume volcanism

The timing of flood basalt volcanism associated with formation of the Ontong Java Plateau (OJP) is estimated from paleomagnetic and paleontologic data. Much of OJP formed rapidly in less than 3 million years during the early Aptian, at the beginning of the Cretaceous Normal Polarity Superchron. Crustal emplacement rates are inferred to have been several times those of the Deccan Traps. These estimates are consistent with an origin of the OJP by impingement at the base of the oceanic lithosphere by the head of a large mantle plume. Formation of the OJP may have led to a rise in sea level that induced global oceanic anoxia. Carbon dioxide emissions likely contributed to the mid-Cretaceous greenhouse climate but did not provoke major biologic extinctions.

Science↗
USGS2000

Revelations from a single strong-motion record retreived during the 27 June 1998 Adana (Turkey) earthquake

During the 27 June 1998 Adana (Turkey) earthquake, only one strong-motion record was retrieved in the region where the most damage occurred. This single record from the station in Ceyhan, approximately 15 km from the epicenter of that earthquake, exhibits characteristics that are related to the dominant frequencies of the ground and structures. The purpose of this paper is to explain the causes of the damage as inferred from both field observations and the characteristics of a single strong-motion record retrieved from the immediate epicentral area. In the town of Ceyhan there was considerable but selective damage to a significant number of mid-rise (7-12 stories high) buildings. The strong-motion record exhibits dominant frequencies that are typically similar for the mid-rise building structures. This is further supported by spectral ratios derived using Nakamura's method [QR of RTRI, 30 (1989) 25] that facilitates computation of a spectral ratio from a single tri-axial record as the ratio of amplitude spectrum of horizontal component to that of the vertical component [R = H(f)/V(f)]. The correlation between the damage and the characteristics exhibited from the single strong-motion record is remarkable. Although deficient construction practices played a significant role in the extent of damage to the mid-rise buildings, it is clear that site resonance also contributed to the detrimental fate of most of the mid-rise buildings. Therefore, even a single record can be useful to explain the effect of site resonance on building response and performance. Such information can be very useful for developing zonation criteria in similar alluvial valleys. Published by Elsevier Science Ltd.

Soil Dynamics and Earthquake Engineering↗
USGS2010

Analogues to features and processes of a high-level radioactive waste repository proposed for Yucca Mountain, Nevada

Natural analogues are defined for this report as naturally occurring or anthropogenic systems in which processes similar to those expected to occur in a nuclear waste repository are thought to have taken place over time periods of decades to millennia and on spatial scales as much as tens of kilometers. Analogues provide an important temporal and spatial dimension that cannot be tested by laboratory or field-scale experiments. Analogues provide one of the multiple lines of evidence intended to increase confidence in the safe geologic disposal of high-level radioactive waste. Although the work in this report was completed specifically for Yucca Mountain, Nevada, as the proposed geologic repository for high-level radioactive waste under the U.S. Nuclear Waste Policy Act, the applicability of the science, analyses, and interpretations is not limited to a specific site. Natural and anthropogenic analogues have provided and can continue to provide value in understanding features and processes of importance across a wide variety of topics in addressing the challenges of geologic isolation of radioactive waste and also as a contribution to scientific investigations unrelated to waste disposal. Isolation of radioactive waste at a mined geologic repository would be through a combination of natural features and engineered barriers. In this report we examine analogues to many of the various components of the Yucca Mountain system, including the preservation of materials in unsaturated environments, flow of water through unsaturated volcanic tuff, seepage into repository drifts, repository drift stability, stability and alteration of waste forms and components of the engineered barrier system, and transport of radionuclides through unsaturated and saturated rock zones.

Professional Paper↗
USGS2012

Expansion of urban area and wastewater irrigated rice area in Hyderabad, India

The goal of this study was to investigate land use changes in urban and peri-urban Hyderabad and their influence on wastewater irrigated rice using Landsat ETM + data and spectral matching techniques. The main source of irrigation water is the Musi River, which collects a large volume of wastewater and stormwater while running through the city. From 1989 to 2002, the wastewater irrigated area along the Musi River increased from 5,213 to 8,939 ha with concurrent expansion of the city boundaries from 22,690 to 42,813 ha and also decreased barren lands and range lands from 86,899 to 66,616 ha. Opportunistic shifts in land use, especially related to wastewater irrigated agriculture, were seen as a response to the demand for fresh vegetables and easy access to markets, exploited mainly by migrant populations. While wastewater irrigated agriculture contributes to income security of marginal groups, it also supplements the food basket of many city dwellers. Landsat ETM + data and advanced methods such as spectral matching techniques are ideal for quantifying urban expansion and associated land use changes, and are useful for urban planners and decision makers alike. ?? 2011 Springer Science+Business Media B.V.

Irrigation and Drainage Systems↗
USGS2004

Tracing the history of submarine hydrothermal inputs and the significance of hydrothermal hafnium for the seawater budget - A combined Pb-Hf-Nd isotope approach

Secular variations in the Pb isotopic composition of a mixed hydrogenous-hydrothermal ferromanganese crust from the Bauer Basin in the eastern Equatorial Pacific provide clear evidence for changes in hydrothermal contributions during the past 7 Myr. The nearby Galapagos Rise spreading center provided a strong hydrothermal flux prior to 6.5 Ma. After 6.5 Ma, the Pb became stepwise more radiogenic and more similar to Equatorial Pacific seawater, reflecting the westward shift of spreading to the presently active East Pacific Rise (EPR). A second, previously unrecognized enhanced hydrothermal period occurred between 4.4 and 2.9 Ma, which reflects either off-axis hydrothermal activity in the Bauer Basin or a late-stage pulse of hydrothermal Pb from the then active, but waning Galapagos Rise spreading center. Hafnium isotope time-series of the same mixed hydrogenous-hydrothermal crust show invariant values over the past 7 Myr. Hafnium isotope ratios, as well as Nd isotope ratios obtained for this crust, are identical to that of hydrogenous Equatorial Pacific deep water crusts and clearly indicate that hydrothermal Hf, similar to Nd, does not travel far from submarine vents. Therefore, we suggest that hydrothermal Hf fluxes do not contribute significantly to the global marine Hf budget. ?? 2004 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗
USGS2016

Final Laurentide ice-sheet deglaciation and Holocene climate-sea level change

Despite elevated summer insolation forcing during the early Holocene, global ice sheets retained nearly half of their volume from the Last Glacial Maximum, as indicated by deglacial records of global mean sea level (GMSL). Partitioning the GMSL rise among potential sources requires accurate dating of ice-sheet extent to estimate ice-sheet volume. Here, we date the final retreat of the Laurentide Ice Sheet with 10 Be surface exposure ages for the Labrador Dome, the largest of the remnant Laurentide ice domes during the Holocene. We show that the Labrador Dome deposited moraines during North Atlantic cold events at ∼10.3 ka, 9.3 ka and 8.2 ka, suggesting that these regional climate events helped stabilize the retreating Labrador Dome in the early Holocene. After Hudson Bay became seasonally ice free at ∼8.2 ka, the majority of Laurentide ice-sheet melted abruptly within a few centuries. We demonstrate through high-resolution regional climate model simulations that the thermal properties of a seasonally ice-free Hudson Bay would have increased Laurentide ice-sheet ablation and thus contributed to the subsequent rapid Labrador Dome retreat. Finally, our new 10 Be chronology indicates full Laurentide ice-sheet had completely deglaciated by 6.7 ± 0.4 ka, which re quires that Antarctic ice sheets contributed 3.6–6.5 m to GMSL rise since 6.3–7.1 ka.

Quaternary Science Reviews↗