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Results for “Climate Change Responses”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 379 records · Page 21Linked to original sources
USGS1997

Responses of sediment geochemistry to climate change in Owens Lake sediment: An 800-k.y. record of saline/fresh cycles in core OL-92

Geochemical parameters of sediments from drill hole OL-92 indicate that Owens Lake was saline, alkaline, and highly productive during interglacial periods, and was hydrologically open and relatively unproductive during glacial periods. Abundance of CaCO 3 , organic carbon, and cation-exchange capacity of the clay fraction show cyclic variation down the core. Six minima in these components during the past 500 k.y. are interpreted as caused by intensive overflow that occurred during Sierran glacial advances. Maxima in these components indicate closed-lake conditions, reflecting warmer and more arid interglacial climates. The pattern of CaCO 3 abundance suggests that closed lake conditions predominated over the past 500 k.y. The absence of gaylussite and gypsum in the sediments, however, indicates lake salinity never exceeded about 15 wt %, a limit which requires flushing of accumulated salts every 10 k.y. Oscillations of CaCO 3 generally indicate a 100-k.y. dominant cycle, a characteristic of the marine δ 18 O record. Four of the last five marine isotope terminations are clearly shown in the Owens Lake record. The last interglacial at Owens Lake appears to have occurred between 120 ka and 50 ka. The roughly 10-k.y. offset between this interval and marine oxygen-isotope stage 5 reflects either error in the age-depth model, or alternatively, a time lag between changes in Northern Hemisphere ice volumes and the manifestation of local climate change in lake geochemistry and sedimentology.

California↗
USGS2008

Late pleistocene aggradation and degradation of the lower colorado river: Perspectives from the Cottonwood area and other reconnaissance below Boulder Canyon

Where the lower Colorado River traverses the Basin and Range Province below the Grand Canyon, significant late Pleistocene aggradation and subsequent degrada tion of the river are indicated by luminescence, paleomagnetic, and U-series data and stratigraphy. Aggradational, finely bedded reddish mud, clay, and silt are underlain and overlain by cross-bedded to plane-bedded fine sand and silt. That sequence is commonly disconformably overlain by up to 15 m of coarse sand, rounded exotic gravel, and angular, locally derived gravel. Luminescence dates on the fine sediments range from ca. 40 ka to 70 ka, considering collective uncertainties. A section of fine grained sediments over a vertical range of 15 m shows normal polarity magnetization and little apparent secular variation beyond dispersion that can be explained by com paction. Aggradation on large local tributaries such as Las Vegas Wash appears to have been coeval with that of the Colorado River. The upper limits of erosional rem nants of the sequence define a steeper grade above the historical river, and these late Pleistocene deposits are greater than 100 m above the modern river north of 35??N. Ter race gravels inset below the upper limit of the aggradational sequence yield 230Th dates that range from ca. 32 ka to 60 ka and indicate that degradation of the river system in this area closely followed aggradation. The thick sequence of rhythmically bedded mud and silt possibly indicates set tings that were ponded laterally between valley slopes and levees of the aggrading river. Potential driving mechanisms for such aggradation and degradation include sediment-yield response to climate change, drought, fire, vegetation-ecosystem dynam ics, glaciation, paleofloods, groundwater discharge, and building and destruction of natural dams produced by volcanism and landslides. ?? 2008 The Geological Society of America.

Conference Paper↗
USGS2017

Luminescence dating of paleolake deltas and glacial deposits in Garwood Valley, Antarctica: Implications for climate, Ross ice sheet dynamics, and paleolake duration

The formation of perched deltas and other lacustrine deposits in the McMurdo Dry Valleys of Antarctica is widely considered to be evidence of valley-filling lakes dammed by the grounded Ross Sea ice sheet during the local Last Glacial Maximum, with lake drainage interpreted as a record of grounding line retreat. We used luminescence dating to determine the age of paleolake deltas and glacial tills in Garwood Valley, a coastal dry valley that opens to the Ross Sea. Luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years. Results suggest that late Holocene delta deposition into paleolake Howard in Garwood Valley persisted until ca. 3.5 ka. This is significantly younger than the date when grounded ice is thought to have retreated from the Ross Sea. Our evidence suggests that the local, stranded ice-cored till topography in Garwood Valley, rather than regional ice-sheet dynamics, may have controlled lake levels for some McMurdo Dry Valleys paleolakes. Age control from the supraglacial Ross Sea drift suggests grounding and up-valley advance of the Ross Sea ice sheet into Garwood valley during marine oxygen isotope stage (MIS) 4 (71–78 ka) and the local Last Glacial Maximum (9–10 ka). This work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation, glacial position, and stream discharge in response to climate change.

GSA Bulletin↗
USGS2017

Climate change refugia and habitat connectivity promote species persistence

Background Climate change refugia, areas buffered from climate change relative to their surroundings, are of increasing interest as natural resource managers seek to prioritize climate adaptation actions. However, evidence that refugia buffer the effects of anthropogenic climate change is largely missing. Methods Focusing on the climate-sensitive Belding’s ground squirrel ( Urocitellus beldingi ), we predicted that highly connected Sierra Nevada meadows that had warmed less or shown less precipitation change over the last century would have greater population persistence, as measured by short-term occupancy, fewer extirpations over the twentieth century, and long-term persistence measured through genetic diversity. Results Across California, U. beldingi were more likely to persist over the last century in meadows with high connectivity that were defined as refugial based on a suite of temperature and precipitation factors. In Yosemite National Park, highly connected refugial meadows were more likely to be occupied by U. beldingi . More broadly, populations inhabiting Sierra Nevada meadows with colder mean winter temperatures had higher values of allelic richness at microsatellite loci, consistent with higher population persistence in temperature-buffered sites. Furthermore, both allelic richness and gene flow were higher in meadows that had higher landscape connectivity, indicating the importance of metapopulation processes. Conversely, anthropogenic refugia, sites where populations appeared to persist due to food or water supplementation, had lower connectivity, genetic diversity, and gene flow, and thus might act as ecological traps. This study provides evidence that validates the climate change refugia concept in a contemporary context and illustrates how to integrate field observations and genetic analyses to test the effectiveness of climate change refugia and connectivity. Conclusions Climate change refugia will be important for conserving populations as well as genetic diversity and evolutionary potential. Our study shows that in-depth modeling paired with rigorous fieldwork can identify functioning climate change refugia for conservation.

California↗
USGS2012

A plant distribution shift: temperature, drought or past disturbance?

Simple models of plant response to warming climates predict vegetation moving to cooler and/or wetter locations: in mountainous regions shifting upslope. However, species-specific responses to climate change are likely to be much more complex. We re-examined a recently reported vegetation shift in the Santa Rosa Mountains, California, to better understand the mechanisms behind the reported shift of a plant distribution upslope. We focused on five elevational zones near the center of the gradient that captured many of the reported shifts and which are dominated by fire-prone chaparral. Using growth rings, we determined that a major assumption of the previous work was wrong: past fire histories differed among elevations. To examine the potential effect that this difference might have on the reported upward shift, we focused on one species, Ceanothus greggii : a shrub that only recruits post-fire from a soil stored seedbank. For five elevations used in the prior study, we calculated time series of past per-capita mortality rates by counting growth rings on live and dead individuals. We tested three alternative hypotheses explaining the past patterns of mortality: 1) mortality increased over time consistent with climate warming, 2) mortality was correlated with drought indices, and 3) mortality peaked 40–50 years post fire at each site, consistent with self-thinning. We found that the sites were different ages since the last fire, and that the reported increase in the mean elevation of C. greggii was due to higher recent mortality at the lower elevations, which were younger sites. The time-series pattern of mortality was best explained by the self-thinning hypothesis and poorly explained by gradual warming or drought. At least for this species, the reported distribution shift appears to be an artifact of disturbance history and is not evidence of a climate warming effect.

California↗
USGS2016

Ungulate reproductive parameters track satellite observations of plant phenology across latitude and climatological regimes

The effect of climatically-driven plant phenology on mammalian reproduction is one key to predicting species-specific demographic responses to climate change. Large ungulates face their greatest energetic demands from the later stages of pregnancy through weaning, and so in seasonal environments parturition dates should match periods of high primary productivity. Interannual variation in weather influences the quality and timing of forage availability, which can influence neonatal survival. Here, we evaluated macro-scale patterns in reproductive performance of a widely distributed ungulate (mule deer, Odocoileus hemionus ) across contrasting climatological regimes using satellite-derived indices of primary productivity and plant phenology over eight degrees of latitude (890 km) in the American Southwest. The dataset comprised > 180,000 animal observations taken from 54 populations over eight years (2004–2011). Regionally, both the start and peak of growing season (“Start” and “Peak”, respectively) are negatively and significantly correlated with latitude, an unusual pattern stemming from a change in the dominance of spring snowmelt in the north to the influence of the North American Monsoon in the south. Corresponding to the timing and variation in both the Start and Peak, mule deer reproduction was latest, lowest, and most variable at lower latitudes where plant phenology is timed to the onset of monsoonal moisture. Parturition dates closely tracked the growing season across space, lagging behind the Start and preceding the Peak by 27 and 23 days, respectively. Mean juvenile production increased, and variation decreased, with increasing latitude. Temporally, juvenile production was best predicted by primary productivity during summer, which encompassed late pregnancy, parturition, and early lactation. Our findings offer a parsimonious explanation of two key reproductive parameters in ungulate demography, timing of parturition and mean annual production, across latitude and changing climatological regimes. Practically, this demonstrates the potential for broad-scale modeling of couplings between climate, plant phenology, and animal populations using space-borne observations.

Arizona, Colorado, Utah↗
USGS2019

Climate vulnerability assessment for Pacific salmon and steelhead in the California Current Large Marine Ecosystem

Major ecological realignments are already occurring in response to climate change. To be successful, conservation strategies now need to account for geographical patterns in traits sensitive to climate change, as well as climate threats to species-level diversity. As part of an effort to provide such information, we conducted a climate vulnerability assessment that included all Pacific salmon and steelhead (Oncorhynchus spp.) listed under the U.S. Endangered Species Act. Using an expert-based scoring system, we ranked 20 attributes for the 28 listed units, and 5 additional units. Attributes captured biological sensitivity, or the strength of linkages between each listing unit and the present climate; climate exposure, or the magnitude of projected change in local environmental conditions; and adaptive capacity, or the ability to modify phenotypes to cope with new climatic conditions. Each listing unit was then assigned one of four vulnerability categories.

California↗
USGS2015

Improved arrival-date estimates of Arctic-breeding Dunlin ( Calidris alpina arcticola )

The use of stable isotopes in animal ecology depends on accurate descriptions of isotope dynamics within individuals. The prevailing assumption that laboratory-derived isotopic parameters apply to free-living animals is largely untested. We used stable carbon isotopes (δ 13 C) in whole blood from migratory Dunlin ( Calidris alpina arcticola ) to estimate an in situ turnover rate and individual diet-switch dates. Our in situ results indicated that turnover rates were higher in free-living birds, in comparison to the results of an experimental study on captive Dunlin and estimates derived from a theoretical allometric model. Diet-switch dates from all 3 methods were then used to estimate arrival dates to the Arctic; arrival dates calculated with the in situ turnover rate were later than those with the other turnover-rate estimates, substantially so in some cases. These later arrival dates matched dates when local snow conditions would have allowed Dunlin to settle, and agreed with anticipated arrival dates of Dunlin tracked with light-level geolocators. Our study presents a novel method for accurately estimating arrival dates for individuals of migratory species in which return dates are difficult to document. This may be particularly appropriate for species in which extrinsic tracking devices cannot easily be employed because of cost, body size, or behavioral constraints, and in habitats that do not allow individuals to be detected easily upon first arrival. Thus, this isotopic method offers an exciting alternative approach to better understand how species may be altering their arrival dates in response to changing climatic conditions.

The Auk↗
USGS2010

Testing alternative models of climate-mediated extirpations

Biotic responses to climate change will vary among taxa and across latitudes, elevational gradients, and degrees of insularity. However, due to factors such as phenotypic plasticity, ecotypic variation, and evolved tolerance to thermal stress, it remains poorly understood whether losses should be greatest in populations experiencing the greatest climatic change or living in places where the prevailing climate is closest to the edge of the species' bioclimatic envelope (e.g., at the hottest, driest sites). Research on American pikas (Ochotona princeps) in montane areas of the Great Basin during 1994-1999 suggested that 20th-century population extirpations were predicted by a combination of biogeographic, anthropogenic, and especially climatic factors. Surveys during 2005-2007 documented additional extirpations and within-site shifts of pika distributions at remaining sites. To evaluate the evidence in support of alternative hypotheses involving effects of thermal stress on pikas, we placed temperature sensors at 156 locations within pika habitats in the vicinity of 25 sites with historical records of pikas in the Basin. We related these time series of sensor data to data on ambient temperature from weather stations within the Historical Climate Network. We then used these highly correlated relationships, combined with long-term data from the same weather stations, to hindcast temperatures within pika habitats from 1945 through 2006. To explain patterns of loss, we posited three alternative classes of direct thermal stress: (1) acute cold stress (number of days below a threshold temperature); (2) acute heat stress (number of days above a threshold, temperature); and. (3) chronic heat stress (average summer temperature). Climate change was defined as change in our thermal metrics between two 31-y.r periods: 1945-1975 and 1976-2006. We found that patterns of persistence were well predicted by metrics of climate. Our best models suggest some effects of climate change; however, recent and long-term metrics of chronic heat stress and acute cold stress, neither previously recognized as sources of stress for pikas, were some of the best predictors of pika persistence. Results illustrate that extremely rapid distributional shifts can be explained by climatic influences and have implications for conservation topics such as reintroductions and early-warning indicators. ?? 2010 by the Ecological society of America.

Ecological Applications↗
USGS2010

National ecosystem assessments supported by scientific and local knowledge

An understanding of the extent of land degradation and recovery is necessary to guide land-use policy and management, yet currently available land-quality assessments are widely known to be inadequate. Here, we present the results of the first statistically based application of a new approach to national assessments that integrates scientific and local knowledge. Qualitative observations completed at over 10 000 plots in the United States showed that while soil degradation remains an issue, loss of biotic integrity is more widespread. Quantitative soil and vegetation data collected at the same locations support the assessments and serve as a baseline for monitoring the effectiveness of policy and management initiatives, including responses to climate change. These results provide the information necessary to support strategic decisions by land managers and policy makers. ?? The Ecological Society of America.

Frontiers in Ecology and the Environment↗
USGS2013

Relaxing the closure assumption in single-season occupancy models: staggered arrival and departure times

Occupancy statistical models that account for imperfect detection have proved very useful in several areas of ecology, including species distribution and spatial dynamics, disease ecology, and ecological responses to climate change. These models are based on the collection of multiple samples at each of a number of sites within a given season, during which it is assumed the species is either absent or present and available for detection while each sample is taken. However, for some species, individuals are only present or available for detection seasonally. We present a statistical model that relaxes the closure assumption within a season by permitting staggered entry and exit times for the species of interest at each site. Based on simulation, our open model eliminates bias in occupancy estimators and in some cases increases precision. The power to detect the violation of closure is high if detection probability is reasonably high. In addition to providing more robust estimation of occupancy, this model permits comparison of phenology across sites, species, or years, by modeling variation in arrival or departure probabilities. In a comparison of four species of amphibians in Maryland we found that two toad species arrived at breeding sites later in the season than a salamander and frog species, and departed from sites earlier.

Ecology↗
USGS2014

Freshwater availability and coastal wetland foundation species: ecological transitions along a rainfall gradient

Climate gradient-focused ecological research can provide a foundation for better understanding critical ecological transition points and nonlinear climate-ecological relationships, which is information that can be used to better understand, predict, and manage ecological responses to climate change. In this study, we examined the influence of freshwater availability upon the coverage of foundation plant species in coastal wetlands along a northwestern Gulf of Mexico rainfall gradient. Our research addresses the following three questions: (1) what are the region-scale relationships between measures of freshwater availability (e.g., rainfall, aridity, freshwater inflow, salinity) and the relative abundance of foundation plant species in tidal wetlands; (2) How vulnerable are foundation plant species in tidal wetlands to future changes in freshwater availability; and (3) What is the potential future relative abundance of tidal wetland foundation plant species under alternative climate change scenarios? We developed simple freshwater availability-based models to predict the relative abundance (i.e., coverage) of tidal wetland foundation plant species using climate data (1970-2000), estuarine freshwater inflow-focused data, and coastal wetland habitat data. Our results identify regional ecological thresholds and nonlinear relationships between measures of freshwater availability and the relative abundance of foundation plant species in tidal wetlands. In drier coastal zones, relatively small changes in rainfall could produce comparatively large landscape-scale changes in foundation plant species abundance which would affect some ecosystem good and services. Whereas a drier future would result in a decrease in the coverage of foundation plant species, a wetter future would result in an increase in foundation plant species coverage. In many ways, the freshwater-dependent coastal wetland ecological transitions we observed are analogous to those present in dryland terrestrial ecosystems.

Gulf Of Mexico↗
USGS1983

Present and former equilibrium-line altitudes near Mount Everest, Nepal and Tibet

New information on equilibrium-line altitudes (ELAs) of present and former glaciers in the Mount Everest area of eastern Nepal and southern Tibet has been derived from field mapping and interpretation of topographic maps and Landsat imagery. Present ELAs rise from south to north across the Himalayan Range from 5200 to 5800 m, as indicated by the altitudes of lowest cirque glaciers and highest lateral and medial moraines on valley glaciers. In contrast, ELAs during maximum late Pleistocene glaciation rose in altitude from 4300 to 5500 m across the range, as indicated by altitudes of lowest cirque floors and maximum extent of glacial deposits. Highest ELAs occurred on previously unrecognized ice caps that formerly covered extensive highland areas in Tibet north of the range crest. During four distinct Holocene glacial advances of subequal magnitude, ELAs were depressed about 30% as much as the late Pleistocene maximum depression. Depression of ELAs during the late Pleistocene glaciation was about twice as great south of the range crest (950 m) as north of it (400 m). Although the present northward decrease in precipitation causes ELAs to rise northward for 85 km at 7.1 m km -1 , the gradient during maximum late Pleistocene glaciation was 11 m km -1 . Such a great contrast in glacier response to climate change over a short distance is remarkable and probably reflects increased aridity on the Tibetan Plateau and increased climatic contrast across the Himalayan Range during glacial ages.

Mount Everest↗
USGS2012

Strategic directions for U.S. Geological Survey water science, 2012-2022 - Observing, understanding, predicting, and delivering water science to the Nation

Executive Summary This report expands the Water Science Strategy that was begun in the USGS Science Strategy, “Facing Tomorrow’s Challenges—U.S. Geological Survey Science in the Decade 2007–2017” (U.S. Geological Survey, 2007). The report looks at the relevant issues facing society and develops a strategy built around observing, understanding, predicting, and delivering water science for the next 5 to 10 years by building new capabilities, tools, and delivery systems to meet the Nation’s water-resource needs. This report begins by presenting the vision of water science for the USGS and the societal issues that are influenced by, and in turn influence, the water resources of our Nation. The essence of the Water Strategic Science Plan is built on the concept of “water availability,” defined as spatial and temporal distribution of water quantity and quality, as related to human and ecosystem needs, as affected by human and natural influences . The report also describes the core capabilities of the USGS in water science—the strengths, partnerships, and science integrity that the USGS has built over its 130-year history. Nine priority actions are presented in the report, which combine and elevate the numerous specific strategic actions listed throughout the report. Priority actions were developed as a means of providing the audience of this report with a list for focused attention, even if resources and time limit the ability of managers to address all of the strategic actions in the report. Priority actions focus on the following: Improve integrated science planning for water. Expand and enhance water-resource monitoring networks. Characterize the water cycle through development of state-of-the-art 3-D/4-D hydrogeologic framework models at multiple scales. Clarify the linkage between human water use (engineered hydrology) and the water cycle (natural hydrology). Advance ecological flow science. Provide flood-inundation science and information. Develop rapid deployment teams for water-related emergencies. Conduct integrated watershed assessment, research, and modeling. Deliver water data and analyses to the Nation. The body of the report is presented as a hierarchal set of 5 goals, 14 objectives, and 27 strategic actions that the USGS should undertake to advance water science through year 2022. The goals deal with: Providing society the information it needs regarding the amount and quality of water in all components of the water cycle at high temporal and spatial resolution, nationwide; Advancing our understanding of processes that determine water availability; Predicting changes in the quantity and quality of water resources in response to changing climate, population, land use, and management scenarios; Anticipating and responding to water-related emergencies and conflicts; and Delivering timely hydrologic data, analyses, and decision-support tools seamlessly across the Nation to support water-resource decisions. Scientific information produced on water resources would be without value if it were not communicated to society in a fashion that can inform decisions and actions. Therefore, the chapter following the goals describes how the USGS should inform, involve, and educate society about the science it produces. This includes discussions on local outreach and the use of social media for effective communication. This report concludes with a chapter devoted to the crosscutting science issues of the Water Mission Area with the other USGS Mission Areas: Climate and Land Use Change, Core Science Systems, Ecosystems, Energy and Minerals, Environmental Health Science, and Natural Hazards. Not one of these Mission Areas stands alone—all must work together and integrate their actions to fulfill the USGS science mission for the future. This final chapter identifies the important linkages that must be realized and maintained for this integration to occur.

Open-File Report↗
USGS2013

Design of Cycle 3 of the National Water-Quality Assessment Program, 2013-23: Part 2: Science plan for improved water-quality information and management

This report presents a science strategy for the third decade of the National Water-Quality Assessment (NAWQA) Program, which since 1991, has been responsible for providing nationally consistent information on the quality of the Nation's streams and groundwater; how water quality is changing over time; and the major natural and human factors that affect current water quality conditions and trends. The strategy is based on an extensive evaluation of the accomplishments of NAWQA over its first two decades, the current status of water-quality monitoring activities by USGS and its partners, and an updated analysis of stakeholder priorities. The plan is designed to address priority issues and national needs identified by NAWQA stakeholders and the National Research Council (2012) irrespective of budget constraints. This plan describes four major goals for the third decade (Cycle 3), the approaches for monitoring, modeling, and scientific studies, key partnerships required to achieve these goals, and products and outcomes that will result from planned assessment activities. The science plan for 2013–2023 is a comprehensive approach to meet stakeholder priorities for: (1) rebuilding NAWQA monitoring networks for streams, rivers, and groundwater, and (2) upgrading models used to extrapolate and forecast changes in water-quality and stream ecosystem condition in response to changing climate and land use. The Cycle 3 plan continues approaches that have been central to the Program’s long-term success, but adjusts monitoring intensities and study designs to address critical information needs and identified data gaps. Restoration of diminished monitoring networks and new directions in modeling and interpretative studies address growing and evolving public and stakeholder needs for water-quality information and improved management, particularly in the face of increasing challenges related to population growth, increasing demands for water, and changing land use and climate. However, a combination of funding growth and extensive collaboration with other USGS programs and other Federal, State, and local agencies, public interest groups, professional and trade associations, academia, and private industry will be needed to fully realize the monitoring and modeling goals laid out in this plan (USGS Fact Sheet 2013-3008).

Open-File Report↗
USGS2014

Identifying resource manager information needs for the North Pacific Landscape Conservation Cooperative

Landscape Conservation Cooperatives (LCCs) are a network of 22 public-private partnerships, defined by ecoregion, that share and provide science to ensure the sustainability of land, water, wildlife and cultural resources in North America. LLCs were established by the U.S. Department of Interior (DOI) in recognition that response to climate change must be coordinated on a landscape-level basis because important resources, ecosystem processes and resource management challenges extend beyond national wildlife refuges, Bureau of Land Management lands, national parks, and even international boundaries. Therefore, DOI agencies must work with other Federal, State, Tribal (U.S. indigenous peoples), First Nation (Canadian indigenous peoples), and local governments, as well as private landowners, to develop landscape-level strategies for understanding and responding to climate change.

Alaska;British Columbia;California;Oregon;Washingt↗
USGS1979

Subsurface stratigraphy and geochemistry of late Quaternary evaporites, Searles Lake, California, with a section on radiocarbon ages of stratigraphic units

Searles Lake is a dry salt pan, about 100 km 2 in area, that lies on the floor of Searles Valley, in the desert of southeast California. Several salt bodies of late Quaternary age lie beneath the surface, mostly composed of sodium and potassium carbonate, sulfate, chloride, and borate minerals. Mud layers separate the salt bodies, which contain interstitial brine that is the source of large quantities of industrial chemicals. The value of annual production from the deposit exceeds $30 million; total production to date exceeds $1 billion. The salts and muds were deposited during Pleistocene and Holocene times by a series of large lakes (200 m maximum depth, 1,000 km 2 maximum area) that fluctuated in size in response to climatic change. Salts were deposited during major dry (interpluvial) episodes, muds during wet (pluvial) episodes that correlate with glacial advances in other parts of North America and the world. Data based on cores from the deposit are used in this paper to establish the stratigraphy of the deposit, the chemical and mineral compositions of successive units, and the total quantities of components contained by them. These parameters are then used to determine the geochemical evolution of the sedimentary layers. The results provide a refined basis for reconstructing the limnology of Searles Lake and the regional climate during late Quaternary time. Six main stratigraphic units were distinguished and informally named earlier on the basis of their dominant composition: Unit Typical thickness 14C age, uncorrected (in meters) (years B.P.) Overburden Mud 7 0 to >3,500 Upper Salt 15 >3,500 to 10,500 Parting Mud 4 10,500 to 24,000 Lower Salt 12 24,000 to 32,500 Bottom Mud 30 32,500 to 130,000 Mixed Layer 200+ > 130,000 (The age of 130,000 years for the Mixed Layer is based on extrapolated sedimentation rates.) The Lower Salt is subdivided into seven salt units (S-l to S-7) and six mud units (M-2 to M-7), the Mixed Layer into six units (A to F). For each salt unit, the areal extent, volume, shape, mineralogy, and chemical composition of the solids and brines have been determined; for each mud unit (which originally extended over much of the basin), the shape and volume within a standard area, and the mineralogy, have been determined. The bulk compositions (brines plus salts) of the combined Lower Salt units S-l to S-5 and units S-6 and S-7, and the Upper Salt, were determined so that the total quantities and ratios of ions in the initial brines could be reconstructed. The 74 published HC dates on Searles Lake core samples from all but the oldest unit are supplemented by 14 new dates (determined by Minze Stuiver) on the Lower Salt. Most of the age control comes from dates based on disseminated organic carbon; two dates are on wood; dates on carbonate minerals are less reliable. Although the probable disequilibrium between the carbon in the lake and atmosphere (because of contamination, slow equilibrium rates, and other factors) causes disseminated carbon dates to be an estimated 500-2,500 years 'too old,' the ages of the major and minor units are relatively well established. The list above indicates rounded and uncorrected ages for the contacts of major units. The age of the only salt bed in the Lower Salt which indicates desiccation (S-5) is about 28,000 years. The average uncorrected sedimentation rate in the Parting Mud is 4

Professional Paper↗
USGS2021

Temperature variation and host immunity regulate viral persistence in a salmonid host

Environmental variation has important effects on host–pathogen interactions, affecting large-scale ecological processes such as the severity and frequency of epidemics. However, less is known about how the environment interacts with host immunity to modulate virus fitness within hosts. Here, we studied the interaction between host immune responses and water temperature on the long-term persistence of a model vertebrate virus, infectious hematopoietic necrosis virus (IHNV) in steelhead trout ( Oncorhynchus mykiss ). We first used cell culture methods to factor out strong host immune responses, allowing us to test the effect of temperature on viral replication. We found that 15 ∘ "> ∘ C water temperature accelerated IHNV replication compared to the colder 10 and 8 ∘ "> ∘ C temperatures. We then conducted in vivo experiments to quantify the effect of 6, 10, and 15 ∘ "> ∘ C water temperatures on IHNV persistence over 8 months. Fish held at 15 and 10 ∘ "> ∘ C were found to have higher prevalence of neutralizing antibodies compared to fish held at 6 ∘ "> ∘ C. We found that IHNV persisted for a shorter time at warmer temperatures and resulted in an overall lower fish mortality compared to colder temperatures. These results support the hypothesis that temperature and host immune responses interact to modulate virus persistence within hosts. When immune responses were minimized (i.e., in vitro) virus replication was higher at warmer temperatures. However, with a full potential for host immune responses (i.e., in vivo experiments) longer virus persistence and higher long-term virulence was favored in colder temperatures. We also found that the viral RNA that persisted at later time points (179 and 270 days post-exposure) was mostly localized in the kidney and spleen tissues. These tissues are composed of hematopoietic cells that are favored targets of the virus. By partitioning the effect of temperature on host and pathogen responses, our results help to better understand environmental drivers of host–pathogen interactions within hosts, providing insights into potential host–pathogen responses to climate change.

Pathogens↗