Search USGSSearch

SEARCH · Search USGS

Results for “Arctic Science”

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

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources

Opening the arctic: The drilling of Umiat #1

One of the greatest excitements for a petroleum geologist is to venture into the frontier, to explore and drill "where no man has gone before." Over 50 years ago Bill Rex, a Kansas oilman, was tapped to lead the first oil drilling expedition into the Alaskan Arctic. He successfully assembled and outfitted a Naval Seabee expedition whose mission was to drill the first well north of the Arctic Circle, Umiat #1. The story of Umiat #1 is one of anecdotes and personal accounts. This paper relates the successes and tribulations of that Seabee exploration venture, as told to the writer by some of the participants.

Northeastern Geology and Environmental Sciences

Offshore-onshore correlation of upper Pleistocene strata, New Jersey Coastal Plain to continental shelf and slope

High-resolution seismic reflection profiles (~ 1-5 m resolution), including Geopulse(TM), Uniboom(TM), minisparker, small air gun, and water gun sources, are used to trace the ?? 18O stage 5 portion of the outcropping Cape May Formation across the shelf to the continental slope. The ?? 18O stage 5/6 boundary identified at Ocean Drilling Project (ODP) Site 903 on the continental slope anchors the onshore-offshore seismic correlations. Above the ?? 18O stage 5 sequence, there are distinguishable lowstand systems tracts (LST), transgressive systems tracts (TST) and highstand systems tracts (HST) that correlate with ?? 18O stages 4 through 1. Atlantic Margin Coring Project (AMCOR) holes 6009, 6010, 6011, 6020, and 6021C provide age and paleoenvironmental indicators that agree with these correlations. The sub-arctic paleoenvironmental indicators in sequences of ?? 18O stage 3 agree with the cooler temperatures and lower sea-level highstands of that time. Thicker ?? 18O stage 3 and 4 sequences are preserved in the Paleo-Hudson River incised valley across the shelf. The expanded ice sheets during stage ?? 18O 3 compared to ?? 18O stages 1 and 5 probably increased sediment discharge in the Hudson River drainage system. (C) 2000 Elsevier Science B.V. All rights reserved.

Conference Paper

Historical and contemporary imagery to assess ecosystem change on the Arctic coastal plain of northern Alaska

The Arctic Coastal Plain of northern Alaska is a complex landscape of lakes, streams, and wetlands scattered across low-relief tundra that is underlain by permafrost. This region of the Arctic has experienced a warming trend over the past three decades leading to thawing of on-shore permafrost and the disappearance of sea ice at unprecedented rates. The U.S. Geological Survey’s (USGS) Changing Arctic Ecosystems (CAE) research initiative was developed to investigate and forecast these rapid changes in the physical environment of the Arctic, and the associated changes to wildlife populations, in order to inform key management decisions by the U.S. Department of the Interior and other agencies. Forecasting future wildlife responses to changes in the Arctic can benefit greatly from historical records that inform what changes have already occurred. Several Arctic wildlife and plant species have already responded to climatic and physical changes to the Arctic Coastal Plain of northern Alaska. Thus, we located historical aerial imagery to improve our understanding of recent habitat changes and the associated response to such changes by wildlife populations. In this report, we describe and make available a set of 61 georectified aerial images of the Arctic Coastal Plain (taken from 1948 to 2010) that were obtained by the USGS to inform research objectives of the USGS CAE Initiative. Here, we describe the origins, metadata, and public availability of these images that were obtained within four main study areas on the Arctic Coastal Plain: Teshekpuk Lake Special Area, Chipp River, the Colville River Delta, and locations along the Dalton Highway Corridor between the Brooks Range and Deadhorse. We also provide general descriptions of observable changes to the geomorphology of landscapes that are apparent by comparing historical and contemporary images. These landscape changes include altered river corridors, lake drying, coastal erosion, and new vegetation communities. All original and georectified images and metadata are available through the USGS Alaska Science Center Portal (search under ‘Project Name’ using title of this report) or by contacting ascweb@usgs.gov .

Alaska

Complex vulnerabilities of the water and aquatic carbon cycles to permafrost thaw

The spatial distribution and depth of permafrost are changing in response to warming and landscape disturbance across northern Arctic and boreal regions. This alters the infiltration, flow, surface and subsurface distribution, and hydrologic connectivity of inland waters. Such changes in the water cycle consequently alter the source, transport, and biogeochemical cycling of aquatic carbon (C), its role in the production and emission of greenhouse gases, and C delivery to inland waters and the Arctic Ocean. Responses to permafrost thaw across heterogeneous boreal landscapes will be neither spatially uniform nor synchronous, thus giving rise to expressions of low to medium confidence in predicting hydrologic and aquatic C response despite very high confidence in projections of widespread near-surface permafrost disappearance as described in the 2019 Intergovernmental Panel on Climate Change Special Report on the Ocean and Cryosphere in a Changing Climate: Polar Regions. Here, we describe the state of the science regarding mechanisms and factors that influence aquatic C and hydrologic responses to permafrost thaw. Through synthesis of recent topical field and modeling studies and evaluation of influential landscape characteristics, we present a framework for assessing vulnerabilities of northern permafrost landscapes to specific modes of thaw affecting local to regional hydrology and aquatic C biogeochemistry and transport. Lastly, we discuss scaling challenges relevant to model prediction of these impacts in heterogeneous permafrost landscapes.

Arctic

Impacts of ocean-atmosphere teleconnection patterns on the south-central United States

Recent research has linked the climate variability associated with ocean-atmosphere teleconnections to impacts rippling throughout environmental, economic, and social systems. This research reviews recent literature through 2021 in which we identify linkages among the major modes of climate variability, in the form of ocean-atmosphere teleconnections, and the impacts to temperature and precipitation of the South-Central United States (SCUSA), consisting of Arkansas, Louisiana, New Mexico, Oklahoma, and Texas. The SCUSA is an important areal focus for this analysis because it straddles the ecotone between humid and arid climates in the United States and has a growing population, diverse ecosystems, robust agricultural and other economic sectors including the potential for substantial wind and solar energy generation. Whereas a need exists to understand atmospheric variability due to the cascading impacts through ecological and social systems, our understanding is complicated by the positioning of the SCUSA between subtropical and extratropical circulation features and the influence of the Pacific and Atlantic Oceans, and the adjacent Gulf of Mexico. The Southern Oscillation (SO), Pacific-North American (PNA) pattern, North Atlantic Oscillation (NAO) and the related Arctic Oscillation (AO), Atlantic Multidecadal Oscillation/Atlantic Multidecadal Variability (AMO/AMV), and Pacific Decadal Oscillation/Pacific Decadal Variability (PDO/PDV) have been shown to be important modulators of temperature and precipitation variables at the monthly, seasonal, and interannual scales, and the intraseasonal Madden-Julian Oscillation (MJO) in the SCUSA. By reviewing these teleconnection impacts in the region alongside updated seasonal correlation maps, this research provides more accessible and comparable results for interdisciplinary use on climate impacts beyond the atmospheric-environmental sciences.

Arkansas, Louisiana, New Mexico, Oklahoma, Texas

Arctic Alaska deepwater organic carbon burial and environmental changes during the late Albian–early Campanian (103–82 Ma)

The middle Cretaceous greenhouse period experienced profound environmental change including episodes of enhanced global burial of organic carbon marked by carbon isotopic excursions (CIEs). However, the role and response of polar regions like the newly formed, partially enclosed Arctic Ocean Basin during middle Cretaceous carbon burial remains enigmatic. We present the first Arctic deepwater CIE record that characterizes conditions offshore of the Alaska margin north of 75°N paleolatitude. Organic carbon isotopes (δ 13 C org ) and 103–82 Ma ash zircon U-Pb dates from the distal Hue Shale record multiple Albian–Campanian CIEs during slow ∼3–15 m/Myr sediment accumulation rates. Average total organic carbon (TOC) increased substantially during large 2–3 ‰ CIEs of the ∼101 Ma Albian-Cenomanian boundary event (from 7 to 18 % TOC) and ∼94 Ma Cenomanian-Turonian boundary event (5 to 10 % TOC). Turonian TOC remained elevated (8–13 %) during high global sea levels and temperatures of the Cretaceous Thermal Maximum, followed by an increase from 7 to 11 % TOC during the ∼90 Ma late Turonian event 1.5 ‰ CIE. Average TOC subsequently decreased in the Coniacian–Campanian, but relative maxima occurred during subtle 0.5–1 ‰ CIEs interpreted as the ∼87 Ma late Coniacian event (increase from 4 to 7 % TOC), ∼85 Ma Horseshoe Bay event (3.5 to 4.5 % TOC), and ∼84 Ma Santonian-Campanian boundary event (3.5 to 5 % TOC). Increases in hydrogen index and productivity proxies (P, Ba, Nd) that accompanied each CIE episode with enhanced TOC suggest a strong link between marine productivity and organic carbon burial at short-term CIE timescales. However, long-term (>5–8 Myr) changes in trace metal redox (Mo, Fe, V) and salinity (B/Ga) proxies suggest shifts in prevailing environmental conditions at timescales longer than the CIEs. Late Albian–middle Turonian marine salinity occurred during euxinic (103–98 Ma) and suboxic (98–90 Ma) conditions with deposition interpreted to have occurred within and beneath an oxygen minimum zone, respectively. In contrast, late Turonian–early Campanian (90–82 Ma) freshening and restricted euxinic basin conditions may signal the start of widespread restriction known to characterize the Paleogene Arctic. Overall, these results highlight that middle Cretaceous Arctic deepwater remained a productive marine carbon sink coupled to the global carbon cycle despite evolving Arctic greenhouse conditions.

Alaska

The central arctic caribou herd

From the mid-1970s through the mid-1980s, use of calving and summer habitats by Central Arctic herd caribou ( Rangifer tarandus granti ) declined near petroleum development infrastructure on Alaska's arctic coastal plain (Cameron et al. 1979; Cameron and Whitten 1980, Smith and Cameron 1983. Whitten and Cameron 1983a, 1985: Dau and Cameron 1986). With surface development continuing to expand westward from the Prudhoe Bay petroleum development area (Fig. 4.1), concerns arose that the resultant cumulative losses of habitat would eventually reduce productivity of the caribou herd. Specifically, reduced access of adult females to preferred foraging areas might adversely affect growth and fattening (Elison et al. 1986. Clough et al. 1987), in turn depressing calf production (Dauphiné 1976, Thomas 1982, Reimers 1983, White 1983, Eloranta and Nieminen 1986. Lenvik et al. 1988, Thomas and Kiliaan 1991) and survival (Haukioja and Salovaara 1978, Rognmo et al. 1983, Skogland 1984, Eloranta and Nieminen 1986, Adamczewski et al. 1987). Those concerns, though justified in theory, lacked empirical support. With industrial development in arctic Alaska virtually unprecedented, there was little basis for predicting the extent and duration of habitat loss, much less the secondary short- and long-term effects on the well-being of a particular caribou herd. Furthermore, despite a general acceptance that body condition and fecundity of the females are functionally related for reindeer and caribou, it seemed unlikely that any single model would apply to all subspecies of Rangifer , and perhaps not even within a subspecies in different geographic regions. We therefore lacked a complete understanding of the behavioral responses of arctic caribou to industrial development, the manner in which access to habitats might be affected, and how changes in habitat use might translate into measurable effects on fecundity and herd growth rate. Our study addressed the following objectives: 1) estimate variation in the size and productivity of the Central Arctic herd; 2) estimate changes in the distribution and movements of Central Arctic herd caribou in relation to the oil field development; 3) estimate the relationships between body condition and reproductive performance of female Central Arctic herd caribou, and 4) compare the body condition, reproductive success, and offspring survival of females under disturbance-free conditions (i.e., east of the Sagavanirktok River) with the status of those exposed to petroleum-related development (i.e., west of the Sagavanirktok River).

Alaska, Northwest Territories, Yukon Territory

Spatial integration of biological and social objectives to identify priority landscapes for waterfowl habitat conservation

Waterfowl population management and habitat conservation compose one of the oldest and most successful adaptive management frameworks in the world. Since its inception, the North American Waterfowl Management Plan (NAWMP) has emphasized strategically targeted conservation investments in regions that most affect waterfowl population dynamics. By 2012, regional conservation had progressively become more science-based and strategic: many migratory bird partnerships had initiated or completed projects on mapping and modeling waterfowl distribution and abundances using geospatial techniques. However, when developing a map depicting and titled “Areas of Greatest Continental Significance to North American Ducks, Geese, and Swans” for the 2012 NAWMP Revision, waterfowl professionals articulated the need for improved decision frameworks and use of consistent datasets for refining large-scale spatial products depicting priority areas for waterfowl and people. This report describes a framework for developing a spatial value model to support the identification of North American geographies of importance to waterfowl during the breeding and non-breeding periods and to resource users who could potentially support (financially and (or) politically) waterfowl habitat conservation. Objectives used to identify priority geographies were determined through a collaborative process of the NAWMP Science Support Team, Priority Landscapes Committee (PLC), and other experts in the fields of waterfowl biology and ecology, environmental science, and human dimensions. ArcGIS Desktop was used as the platform for managing, analyzing, combining and displaying the spatial data as well as producing new data through spatial analysis functions. Thirty-eight spatial layers were developed, and several composite spatially explicit products (maps of North America) were produced based on PLC recommendations. The composite products have extensive similarities to the 2012 NAWMP map depicting areas of greatest continental significance to North American waterfowl. There are also some differences, especially in regions of the high Arctic and in Mexico. These differences between spatial value model maps and the 2012 NAWMP output likely arose from inclusion of social objectives, reduced dependence on expert opinion to generate abundance estimates, lack of population surveys in some regions and availability of expanded survey data in other regions, and use of model-based waterfowl population estimates for some unsurveyed areas. The structured decision-making framework application in this study is discussed, and the appropriate use of the products and their limitations are outlined. Additionally, options for future improvements are presented by identifying gaps in data collection, waterfowl-habitat association assumptions, and uncertainties related to social objectives. These spatial products are intended for use by national, regional, and province/state level wildlife professionals to aid their decisions in targeting waterfowl habitat conservation.

Open-File Report

Assessment of undiscovered oil and gas in the Arctic

Among the greatest uncertainties in future energy supply and a subject of considerable environmental concern is the amount of oil and gas yet to be found in the Arctic. By using a probabilistic geology-based methodology, the United States Geological Survey has assessed the area north of the Arctic Circle and concluded that about 30% of the world’s undiscovered gas and 13% of the world’s undiscovered oil may be found there, mostly offshore under less than 500 meters of water. Undiscovered natural gas is three times more abundant than oil in the Arctic and is largely concentrated in Russia. Oil resources, although important to the interests of Arctic countries, are probably not sufficient to substantially shift the current geographic pattern of world oil production.

Science

Impacts of petroleum development in the Arctic

In their article “Cumulative impacts of oil fields on northern Alaskan landscapes.” D. A. Walter et al . (1) document some direct and indirect impacts of petroleum development in the Arctic on selected portions of the Prudhoe Bay Oil field. While most of the kinds of impacts they discuss are valid points to consider in designing an arctic oil field, the magnitude of what they describe is not representative of the Prudhoe Bay field, in general, or of newer oil fields, such as Kuparuk to the west of Prudhoe. It is even less applicable in areas of higher topographic relief, such as the coastal plain of the Arctic National Wildlife Refuge (ANWR). Any development will cause an impact to the land. In the Arctic, as noted by Walker et al. , gravel roads and pads have been built that are thick enough to support facilities while the thermal integrity of the underlying permafrost is maintained. Decision-makers must evaluate whether or not the gains of development are worth the impacts incurred. Accurate assessment of both direct and indirect impacts is essential.

Alaska

USGS Alaska Tissue Archival Projects: An update on FY02 activities

The banking of environmental specimens under cryogenic conditions for future retrospective analysis has been recognized for many years as an important part of environmental monitoring programs. Since 1987, the Alaska Marine Mammal Tissue Archival Project (AMMTAP) has been collecting tissue samples from marine mammals for archival in the National Biomonitoring Specimen Bank (NBSB) at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, USA. The USGS, Alaska Biological Science Center (ABSC), the NOAA Fisheries, Office of Protected Resources (NMFS), and the NIST conduct this partnership project, which began under the Mineral Management Service (MMS) Outer Continental Shelf Environmental Assessment Program. MMS remains the primary client agency for the AMMTAP providing programmatic guidance and review. The purpose of the project is to collect tissue samples from Alaska marine mammals and to store these specimens under the best conditions so that they can be analyzed for environmental contaminants and other constituents. A substantial part of the sample collection is from Arctic species and, since most of the animals sampled are from Alaska Native subsistence harvests, the project relies on cooperation and collaboration with several Alaska Native organizations and local governmental agencies. Although a substantial amount of recent research has been conducted on contaminants in Alaskan marine mammals, few data exists on colonial seabirds nesting in Alaska. Like marine mammals, seabirds are an important group of upper trophic level marine organisms with a potential for accumulating lipophilic contaminants and are identified by MMS as species of interest for monitoring activities. More than 95% of the seabirds breeding in the continental United States nest at colonies in the Bering and Chukchi seas and Gulf of Alaska (see USFWS 1992). Realizing the value of colonial seabirds in environmental monitoring and the lack of recent data from Alaskan seabird colonies, the U.S. Fish and Wildlife Service Alaska Maritime National Wildlife Refuge (USFWS-AMNWR), the U.S. Geological Survey Biological Resources Division (USGS-BRD), and the National Institute of Standards and Technology (NIST) initiated the Seabird Tissue Archival and Monitoring Project (STAMP) in 1998. The project was designed as a 100-year-long program to monitor long-term trends in environmental quality by collecting eggs at nesting colonies using standardized protocols, banking the egg contents under conditions that ensure chemical stability during long-term (decadal) storage, and analyzing subsamples of the stored material to establish baseline levels for persistent bioaccumulative contaminants (e.g., chlorinated pesticides, PCBs, mercury).

Conference Paper

The chemical, physical and structural properties of estuarine ice in Great Bay, New Hampshire

The purpose of this study was to provide general information on the chemical, physical and structural properties of estuarine ice and show how it compares with sea ice found at higher latitudes in order to determine whether the ice in Great Bay can be used as an analog in the study of arctic sea ice. Ice cores and water samples were collected during the 1983–1984 winter season at Adams Point in Great Bay, New Hampshire. Concentrations of chloride, nitrogen (as nitrate and nitrite), bromide, phosphate, sulfate and silicate were determined for samples chosen on the basis of identifiable stratigraphic layers (i.e. bubble size and shape, sediment layers, etc.). Similarities between ice formation in Great Bay and those in the arctic regions include the nature of the freezing process and the ice types produced. In addition, the distribution and concentration of chemical constituents were found to be similar to those observed in arctic sea ice. Factors affecting the chemistry of the ice in Great Bay include rainfall during the freezing season, the presence of sediment layers in the ice cores, the nature of incorporation of brine into the crystal structure of the ice and the drainage of brine.

New Hampshire

The arctic water resource vulnerability index: An integrated assessment tool for community resilience and vulnerability with respect to freshwater

People in the Arctic face uncertainty in their daily lives as they contend with environmental changes at a range of scales from local to global. Freshwater is a critical resource to people, and although water resource indicators have been developed that operate from regional to global scales and for midlatitude to equatorial environments, no appropriate index exists for assessing the vulnerability of Arctic communities to changing water resources at the local scale. The Arctic Water Resource Vulnerability Index (AWRVI) is proposed as a tool that Arctic communities can use to assess their relative vulnerability-resilience to changes in their water resources from a variety of biophysical and socioeconomic processes. The AWRVI is based on a social-ecological systems perspective that includes physical and social indicators of change and is demonstrated in three case study communities/watersheds in Alaska. These results highlight the value of communities engaging in the process of using the AWRVI and the diagnostic capability of examining the suite of constituent physical and social scores rather than the total AWRVI score alone. ?? 2008 Springer Science+Business Media, LLC.

Environmental Management

Mercury export from Arctic great rivers

Land–ocean linkages are strong across the circumpolar north, where the Arctic Ocean accounts for 1% of the global ocean volume and receives more than 10% of the global river discharge. Yet estimates of Arctic riverine mercury (Hg) export constrained from direct Hg measurements remain sparse. Here, we report results from a coordinated, year-round sampling program that focused on the six major Arctic rivers to establish a contemporary (2012–2017) benchmark of riverine Hg export. We determine that the six major Arctic rivers exported an average of 20 000 kg y –1 of total Hg (THg, all forms of Hg). Upscaled to the pan-Arctic, we estimate THg flux of 37 000 kg y –1 . More than 90% of THg flux occurred during peak river discharge in spring and summer. Normalizing fluxes to watershed area (yield) reveals higher THg yields in regions where greater denudation likely enhances Hg mobilization. River discharge, suspended sediment, and dissolved organic carbon predicted THg concentration with moderate fidelity, while suspended sediment and water yields predicted THg yield with high fidelity. These findings establish a benchmark in the face of rapid Arctic warming and an intensifying hydrologic cycle, which will likely accelerate Hg cycling in tandem with changing inputs from thawing permafrost and industrial activity.

Environmental Science & Technology

Science foundation Chapter 5 Appendix 5.1: Case study diving ducks

Diving ducks are the most abundant group of waterfowl that overwinter in the open bays and ponds of San Francisco Bay (SFB). Species within this group are primarily benthivores that dive to obtain their macroinvertebrate prey in bottom sediments, although at times they may eat plant matter or forage in the water column. These migratory species include bay ducks (lesser scaup Aythya affinis , greater scaup A. marila , canvasback A. valisineria ), sea ducks (surf scoter Melanitta perspicillata and bufflehead Bucephala albeola ), and a stiff-tailed duck (ruddy duck Oxyura jamaicensis ). These species vary from largest to smallest body mass: canvasback, greater scaup, surf scoter, lesser scaup, ruddy duck, and bufflehead. Their breeding grounds range from Central Valley grasslands, intermountain wetlands, prairie potholes, boreal forest, and Arctic tundra. Their wintering populations in SFB are most abundant between October and April, and SFB comprises up to 50% of the number counted during midwinter surveys on the lower Pacific coast. Species are found in all SFB regions, but greater scaup and surf scoter are most often seen in subtidal to intertidal waters and are not commonly found in baylands. In contrast, ruddy duck and bufflehead populations are most abundant in baylands, particularly in managed ponds. Canvasbacks are commonly found at estuaries or creek mouths.

California

Geologic studies in Alaska by the U.S. Geological Survey, 1999

The collection of nine papers that follow continue the series of U.S. Geological Survey (USGS) investigative reports in Alaska under the broad umbrella of the geologic sciences. The series presents new and sometimes preliminary findings that are of interest to earth scientists in academia, government, and industry; to land and resource managers; and to the general public. Reports presented in Geologic Studies in Alaska cover a broad spectrum of topics from various parts of the State (fig. 1), serving to emphasize the diversity of USGS efforts to meet the Nation's needs for earth-science information in Alaska. The papers in this volume are organized under the topics: Hazards, Geologic Framework, Environment and Climate, and Resources. This organization is intended to reflect the scope and objectives of USGS geologic programs currently active in Alaska. The two Hazards studies discuss volcano-related topics in the seismically active southcentral Alaska region. The first paper revisits the eruptive events of Redoubt Volcano that occurred more than a decade ago and the subsequent development of the Alaska Volcano Observatory (AVO). This treatise documents the historic impact of this eruption and briefly summarizes the state of our knowledge of the other Cook Inlet, Alaska Peninsula, and Aleutian Island volcanoes. Finally, it discusses the recent role that AVO has had in seismic station installation and hazard assessment at volcanically active sites throughout the world. The second paper discusses the eruptive history of Snowy Mountain in the upper Alaska Peninsula. Because subsets of its 25-30 lava flows erupted as packages in short episodes, calculation of the volcano's lifetime average volumetric eruption rate is problematic. A portion of the cone was hydrothermally weakened and collapsed in the late Holocene producing a 22-km2 debris avalanche. Geologic Framework studies provide background information that is the scientific basis for present and future earth science investigations. The first paper compares and contrasts the Insular-Intermontane suture zone (IISZ) of southeast Alaska with the Adria-Europe suture zone (AESZ) of Switzerland and Hungary. The study develops the hypothesis that the zones have distinct differences as well as similarities and neither is a simple lithotectonic terrane boundary. The second paper discusses the relation among volcanic, glacial, and tectonic activity in the Cold Bay and False Pass 1 :250,000-scale quadrangles on the Alaska Peninsula. During Pleistocene time, continental-shelf glaciations and two massive volcanic centers were the dominant controls over landscape development. The third paper gives detailed geologic information for Paleozoic rocks within the Taylor Mountains D-1 quadrangle portion of the Holitna Lowland of southwestern Alaska. Because of the excellent preservation of megafossils, these Silurian and Ordovician strata lend themselves to detailed statigraphic investigations. Further, low thermal alteration indices of this area have made them a potential target of petroleum exploration. The final report in this section discusses the development of a new spectral enhancement approach for interpreting Multispectral Scanner (MSS) and Thematic Mapper (TM) satellite images. This technique enhances the use of remote sensing data in identifying geologic units in areas that have been poorly investigated. This study used this technique to better define the distribution of a JMtu (mafic, ultramafic, and sedimentary) unit and a PzZrqs (pelitic and quartzitic schist) unit. Environment and climate studies are the emphasis of two papers. One presents the first radiocarbon-dated postglacial vegetation history of the Kenai Mountains of southcentral Alaska. This reconstruction is the result of the analysis of pollen assemblages and peat from sediments collected in Tern Lake and presents a minimum age for deglaciation of these interior valleys at 9,31 0±200 yr B .P. Current vegetation, however, developed within the past ca. 2,500 years. A second study discusses the cycling of arsenic and cadmium in sub-arctic boreal forest ecosystems typical of interior Alaska and defines the importance of various natural (geogenic) sources. The transport and uptake into vegetation of these elements from soils developed from loess as well as soils developed from the major rock units is presented. The bioaccumulation of cadmium in willow (Salix sp.) and its potential consequence to the health of browsing animals is discussed. Papers related to resource issues comprise the topic of the final report. This paper presents a brief statistical summary of the geochemistry of rock samples collected in the east-central portion of the Eagle 1 :250,000-scale quadrangle. This study helps define the rock unit source of both resource- and environmental-based chemical elements of interest in the Fortymile mining district. Two bibliographies at the end of the volume list reports covering Alaska earth science topics in USGS publications during 1999 and reports about Alaska by USGS authors in non-USGS publications during the same period.

Alaska

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

Alaska