Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Arctic”

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 919 records · Page 51Linked to original sources
USGS1988

Size differences in migrant sandpiper flocks: Ghosts in ephemeral guilds

Scolopacid sandpipers were studied from 1980 until 1984 during spring migration in North Dakota. Common species foraging together in mixed-species flocks differed in bill length most often by 20 to 30 percent (ratios from 1.2:1 to 1.3:1). Observed flocks were compared to computer generated flocks drawn from three source pools of Arctic-nesting sandpipers. The source pools included 51 migrant species from a global pool, 33 migrant species from a Western Hemisphere pool, and 13 species that migrated though North Dakota. The observed flocks formed randomly from the available species that used the North Dakota migration corridor but the North Dakota species were not a random selection from the Western Hemisphere and global pools of Arctic-nesting scolopacid sandpipers. In short, the ephemeral, mixed-species foraging flocks that we observed in North Dakota were random mixes from a nonrandom pool. The size-ratio distributions were consistent with the interpretation that use of this migration corridor by sandpipers has been influenced by some form of sizerelated selection such as competition

North Dakota↗
USGS2011

Projected status of the Pacific walrus (Odobenus rosmarus divergens) in the twenty-first century

Extensive and rapid losses of sea ice in the Arctic have raised conservation concerns for the Pacific walrus ( Odobenus rosmarus divergens ), a large pinniped inhabiting arctic and subarctic continental shelf waters of the Chukchi and Bering seas. We developed a Bayesian network model to integrate potential effects of changing environmental conditions and anthropogenic stressors on the future status of the Pacific walrus population at four periods through the twenty-first century. The model framework allowed for inclusion of various sources and levels of knowledge, and representation of structural and parameter uncertainties. Walrus outcome probabilities through the century reflected a clear trend of worsening conditions for the subspecies. From the current observation period to the end of century, the greatest change in walrus outcome probabilities was a progressive decrease in the outcome state of robust and a concomitant increase in the outcome state of vulnerable. The probabilities of rare and extirpated states each progressively increased but remained <10% through the end of the century. The summed probabilities of vulnerable, rare, and extirpated (P(v,r,e)) increased from a current level of 10% in 2004 to 22% by 2050 and 40% by 2095. The degree of uncertainty in walrus outcomes increased monotonically over future periods. In the model, sea ice habitat (particularly for summer/fall) and harvest levels had the greatest influence on future population outcomes. Other potential stressors had much smaller influences on walrus outcomes, mostly because of uncertainty in their future states and our current poor understanding of their mechanistic influence on walrus abundance.

Polar Biology↗
USGS2026

Nest site and habitat changes over 15 years in a predicted climate refugium in Beluga, AK, USA, have a positive impact on Hudsonian godwit (Limosa haemastica) nest survival

Climate change is transforming the Arctic and sub-Arctic at a pace that threatens many taxa with population declines and extinction. However, some habitats–such as muskeg bogs–can serve as climatic refugia and lessen the effects of a changing climate on the species that rely on them. Hudsonian Godwits ( Limosa haemastica ) are a species of migratory shorebird that utilizes the muskeg bogs of Alaska and Canada to breed. Our study focused on a muskeg bog in Beluga, Alaska, USA to see if it had changed from 2009 to 2023, if the availability of Godwit nests sites in the bogs changed in concert, and if Godwit nest survival was affected by any of these changes. We found that, overall, the bog dried and became more vegetated, with the proportional cover of graminoids, shrubs, and forbs all increasing during our study. Godwit nest sites also changed, with the proportion of shrubs and graminoids around nests increasing over time. Nonetheless, these changes did not negatively impact Godwit nest survival. Instead, nest survival increased ~ 22% during our study period, and we observed no decline in the number of potential nests sites available to Godwits. Taken together, these results suggest that while muskeg bogs are changing, they are also currently acting as climate refugia for Godwits. However, it is unclear for how long muskeg bogs can continue to buffer Godwits and other species from the effects of climate change.

Alaska↗
USGS2020

Drivers and consequences of apex predator diet composition in the Canadian Beaufort Sea

Polar bears ( Ursus maritimus ) rely on annual sea ice as their primary habitat for hunting marine mammal prey. Given their long lifespan, wide geographic distribution, and position at the top of the Arctic marine food web, the diet composition of polar bears can provide insights into temporal and spatial ecosystem dynamics related to climate-mediated sea ice loss. Polar bears with the greatest ecological constraints on diet composition may be most vulnerable to climate-related changes in ice conditions and prey availability. We used quantitative fatty acid signature analysis (QFASA) to estimate the diets of polar bears ( n = 419) in two western Canadian Arctic subpopulations (Northern Beaufort Sea and Southern Beaufort Sea) from 1999 to 2015. Polar bear diets were dominated by ringed seal ( Pusa hispida ), with interannual, seasonal, age- and sex-specific variation. Foraging area and sea ice conditions also affected polar bear diet composition. Most variation in bear diet was explained by longitude, reflecting spatial variation in prey availability. Sea ice conditions (extent, thickness, and seasonal duration) declined throughout the study period, and date of sea ice break-up in the preceding spring was positively correlated with female body condition and consumption of beluga whale ( Delphinapterus leucas ), suggesting that bears foraged on beluga whales during entrapment events. Female body condition was positively correlated with ringed seal consumption, and negatively correlated with bearded seal consumption. This study provides insights into the complex relationships between declining sea ice habitat and the diet composition and foraging success of a wide-ranging apex predator.

Northwest Territories, Yukon↗
USGS2023

Elodea mediates juvenile salmon growth by altering physical structure in freshwater habitats

Invasive species introductions in high latitudes are accelerating and elevating the need to address questions of their effects on Subarctic and Arctic ecosystems. As a driver of ecosystem function, submerged aquatic vegetation is one of the most deleterious biological invasions to aquatic food webs. The aquatic plant Elodea spp. has potential to be a widespread invader to Arctic and Subarctic ecosystems and is already established in 19 waterbodies in Alaska, USA. Elodea spp. has been found to alter ecosystem processes through multiple pathways; yet little is known about the impact of Elodea spp. on fish life history. A primary concern is the effect of Elodea spp. on juvenile Pacific salmon ( Oncorhynchus spp.), because this invading plant can form dense stands in littoral zones, potentially impacting important freshwater rearing habitats used by juvenile fish for foraging and refuge from predators. We used a field experiment to test the effect of Elodea spp. on juvenile coho salmon ( O. kisutch ) growth in an infested lake near Cordova, Alaska, USA. We found that Elodea spp. stands result in reduced growth and a lower trophic position for juvenile coho salmon over the summer compared to habitats dominated by a native assemblage of aquatic plants. While infested sites were not associated with significant changes in water condition or primary productivity compared to sites dominated by native vegetation, zooplankton densities were reduced, and Elodea spp. height and vegetation richness increased macroinvertebrate densities. Combined, these results indicate that Elodea spp. may alter the flow of energy to juvenile salmon by restructuring space and affecting prey resources for rearing fish. Furthermore, these results suggest that widespread establishment of Elodea spp. may alter the quality of habitat for juvenile salmon and, by affecting juvenile fish growth, could lead to population-level impacts on salmon returns.

Biological Invasions↗
USGS1993

The role of permafrost and seasonal frost in the hydrology of northern wetlands in North America

Wetlands are a common landscape feature in the Arctic, Subarctic, and north Temperate zones of North America. In all three-zones, the occurrnce of seasonal frost results in similar surface-water processes in the early spring. For example, surface ice and snow generally melt before the soil frost thaws, causing melt water to flow into depressions, over the land surface and at times, across low topographic divides. However, evapotranspiration and ground-water movement differ among the three climatic zones because they are more affected by permafrost than seasonal frost. The water source for plants in the Arctic is restricted to the small volume of subsurface water lying above the permafrost. Although this is also true in the Subarctic where permafrost exists, where it does not, plants may receive and possibly reflect, more regional ground-water sources. Where permafrost exists, the interaction of wetlands with subsurface water is largely restricted to shallow local flow systems. But where permafrost is absent in parts of the Subarctic and all of the Temperature zone, wetlands may have a complex interaction with ground-water-flow systems of all magnitudes.

Journal of Hydrology↗
USGS1977

Biogeography of late Silurian and devonian rugose corals

Three marine benthic faunal realms can be recognized in the Early and Middle Devonian. The Eastern Americas Realm consisted of most of the eastern half of North America and South America north of the Amazon. This realm extended in a southwest direction from the Devonian equator to approximately 35??S and was an isolated epicontinental sea during much of its history. The Eastern Americas Realm was bounded on the west by the Transcontinental Arch, on the north by the Canadian Shield and on the east and southeast by a peninsular extension of the Old Red Continent. These barriers were emergent during much, but not all, of Devonian time. Seaways beyond these barriers belonged to the Old World Realm. The Malvinokaffric Realm that was farther south was apparently temperate to arctic in climate and latitudinal position and contained few corals. Rugose corals in the Eastern Americas Realm show increasing generic-level endemism from the Late Silurian through the Early Devonian; during the late Early Devonian, 92% of the rugosan genera are not known anywhere else in the world. Endemism decreased through the Middle Devonian to zero in the early Late Devonian. The Early Devonian increase in endemism paralleled, and was probably related to, the development of the Old Red Continent as a barrier between America and Africa-Europe. The waning of endemism in the Middle Devonian reflects the breaching of the land barriers. This permitted some migration in and out of the realm in early Middle Devonian time but greatest movements were in late Middle Devonian time. Principal migration directions were from western or Arctic North America into the Michigan-Hudson Bay area and from the southern Appalachian area into Africa. ?? 1977.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2017

Middle pleistocene mollusks from St. Lawrence Island and their significance for the paleo-oceanography of the Bering Sea

Drift, evidently of Illinoian age, was deposited on St. Lawrence Island at the margin of an ice cap that covered the highlands of the Chukotka Peninsula of Siberia and spread far eastward on the continental shelf of northern Bering Sea. Underlying the drift on the northwestward part of the island are mollusk-bearing beds deposited during the Kotzebuan Transgression. A comparison of mollusk faunas from St. Lawrence Island, Chukotka Peninsula, and Kotzebue Sound suggests that the present northward flow through Bering and Anadyr Straits was reversed during the Kotzebuan Transgression. Cold arctic water penetrated southward and southwestward bringing an arctic fauna to the Gulf of Anadyr. Warmer Pacific water probably entered eastern Bering Sea, passed eastward and northeastward around eastern and northern St. Lawrence Island, and then became entrained in the southward currents that passed through Anadyr Strait.

Alaska↗
USGS2017

Plant and insect remains from the Wisconsinan interstadial/stadial transition at Wedron, north-central Illinois

Organic material exposed within a small swale fill in Pit 6 of the Wedron Silica Sand Co. near Wedron in LaSalle County, Illinois, includes well-preserved pollen, plant macrofossils, and insect remains. This material occurs in slackwater sediment in the lower part of the Peddicord Formation, which was deposited as existing valleys were dammed by fluvial aggradation during the initial late Wisconsinan advance of Laurentide ice into the Wedron area. Wood from the organic horizon has a radiocarbon age of 21,460 ?? 470 yr B.P. (ISGS-1486). The pollen spectrum is dominated by Picea, Pinus, and Cyperaceae. Plant macrofossils comprise a mix of boreal-forest taxa, including Picea, Larix laricina, and the moss Campylium stellatum; subarctic species including Betula glandulosa, Empetrum nigrum, and Selaginella selaginoides; along with the predominantly arctic Vaccinium uliginosum var. alpinum, Dryas integrifolia, and Rhododendron lapponicum. The insect fauna contains the western montane ground beetle Opisthius richardsoni; several arctic-subarctic ground beetles including Diacheila polita, Helophorus sibiricus, and Pterostichus (Cryobius) caribou; and a diverse assemblage of insects that today inhabit the boreal forest. We interpret the biotic record to record a phase in the transition from closed boreal forest to open tundra as climatic conditions deteriorated in advance of continental glaciation. ?? 1990.

Quaternary Research↗
USGS1979

Geology and tectonic development of the continental margin north of Alaska

The continental margin north of Alaska, as interpreted from seismic reflection profiles, is of the Atlantic type and consists of three sectors of contrasting structure and stratigraphy. The Chukchi sector, on the west, is characterized by the deep late Mesozoic and Tertiary North Chukchi basin and the Chukchi Continental Borderland. The Barrow sector of central northern Alaska is characterized by the Barrow arch and a moderately thick continental terrace build of Albian to Tertiary clastic sediment. The terrace sedimentary prism is underlain by lower Paleozoic metasedimentary rocks. The Barter Island sector of northeastern Alaska and Yukon Territory is inferred to contain a very thick prism of Jurassic, Cretaceous and Tertiary marine and nonmarine clastic sediment. Its structure is dominated by a local deep Tertiary depocenter and two regional structural arches. We postulate that the distinguishing characteristics of the three sectors are inherited from the configuration of the rift that separated arctic Alaska from the Canadian Arctic Archipelago relative to old pre-rift highlands, which were clastic sediment sources. Where the rift lay relatively close to northern Alaska, in the Chukchi and Barter Island sectors, and locally separated Alaska from the old source terranes, thick late Mesozoic and Tertiary sedimentary prisms extend farther south beneath the continental shelf than in the intervening Barrow sector. The boundary between the Chukchi and Barrow sectors is relatively well defined by geophysical data, but the boundary between the Barrow and Barter Island sectors can only be inferred from the distribution and thickness of Jurassic and Cretaceous sedimentary rocks. These boundaries may be extensions of oceanic fracture zones related to the rifting that is postulated to have opened the Canada Basin, probably beginning during the Early Jurassic.

Alaska↗
USGS1991

Stratigraphy and paleoceanography of Pliocene deposits of Karaginsky Island, eastern Kamchatka, U.S.S.R.

The lithology and paleontology of Pliocene deposits from Karaginsky Island, off eastern Kamchatka Peninsula, U.S.S.R., are described in order to provide a paleoceanographic reconstruction of this region of the eastern North Pacific Ocean. The stratigraphic sequence is divided into three suites — the Limimtevayamian, the Ust-Limimtevayamian, and the Tusatuvayamian, which correspond to three standard Pacific diatom zones — the Thalassiosira oestrupii, Neodenticula koizumi-N. kamtschatica , and N. koizumi . The entire sequence is further subdivided into six members and 18 distinct beds on the basis of molluscan assemblages and three members and seven beds on the basis of benthic foraminiferal assemblages. Marine ostracodes are described from the Limimtevayamian suite. The marine invertebrate assemblages from Karaginsky Island provide evidence that: (1) ocean water temperatures were warmer than today about 4 Ma and again about 3.5-3.0 Ma; (2) several Arctic-Atlantic species of molluscs and ostracodes migrated to the eastern North Pacific between 4.2−3.0 Ma, presumably through the proto-Bering Strait; (3) many species found in the Karaginsky Island Pliocene represent Pacific taxa which migrated through the Arctic into the North Atlantic during the late Pliocene.

eastern Kamchatka, Karaginsky Island↗
USGS1993

Initiation and development of the Laurentide and Cordilleran Ice Sheets following the last interglaciation

Fossil records from sites overridden by or adjacent to the Laurentide Ice Sheet indicate that the climate of the last interglaciation (Oxygen-Isotope Substage 5e, ca. 130-116 ka) was warmer than today. Following the last interglaciation, the Laurentide Ice Sheet first developed during Stage 5 over Keewatin, Quebec and Baffin Island. Along its northern margin, the ice sheet reached its maximum extent of the last glaciation during Stage 5. The ice sheet advanced across Baffin Island onto the continental shelf early during Stage 5 (5d?), whereas the advance into the western Canadian Arctic occurred late during Stage 5 (5b?). The ice sheet also may have advanced into the St Lawrence Lowland during Substage 5b, although this event may be younger (Stage 4). The Hudson Bay lowland became ice-free during Substage 5a. Retreat of the ice sheet on Baffin Island occurred during late Stage 5, probably Substage 5a. The exact timing of retreat from the western Canadian Arctic is unknown, but it occurred before 48 ka. The southern sector, including the St Lawrence Lowland, was ice-free during late Stage 5. The Hudson Bay lowland may have remained ice free through Stage 4 and much of Stage 3. Because of conflicting chronologies, however, it is more likely that this area was glaciated throughout Stage 3 and perhaps Stage 4. Nevertheless, the data demonstrate that the lowland was ice-free during part of the last glaciation. An independent ice cap developed over the Appalachian Uplands and advanced across Nova Scotia during Stage 4, perhaps as far as the edge of the continental shelf. The ice cap remained active over Nova Scotia as a setellite to the Laurentide Ice Sheet throughout the remainder of the last glaciation. The ice sheet advanced into the St Lawrence Lowland during Stage 4 and subsequently overwhelmed the local ice cap in the Appalachian Uplands, advancing perhaps into northern New England, but not farther south. The Lowland remained covered by the ice sheet until late Stage 2. The ice sheet may also have advanced into the Lake Ontario basin during Stage 4. The position of the northern margin of the Laurentide Ice Sheet during Stage 4 is not known, but it remained an unknown distance behind its maximum position reached during Stage 5. Cores from Baffin Bay indicate a substantial decrease in high-latitude glaciation during Stage 4. Following retreat, the Keewatin sector of the ice sheet may have remained over much of northwestern Canada as a quasi-stable ice mass until it readvanced during Stage 2. Similarly, the Baffin Island sector of the ice sheet may have remained largely intact. The southern margin of the ice sheet may have advanced into the Lake Ontario basin and upper Mississippi Valley during the middle of Stage 3 (ca. 50 ka), reaching its maximum extent of the last glaciation during Stage 2 (ca. 18–21 ka). Advance of the northern margin was younger (ca. 8–13 ka) than that of the southern margin; this advance was less extensive than the penultimate advance (Stage 5). Paleoenvironmental records indicate that the last interglaciation in areas covered by and near the Cordilleran Ice Sheet was as warm as, or warmer than, present. The Cordilleran Ice Sheet appears to have developed during Stage 5 or 4. At that time, it advanced over southern British Columbia and into the northern Puget Lowland. There is no record of this event in northern areas that were later covered by the ice sheet. The ice sheet disappeared before 59 ka, at the beginning of a lengthy nonglacial interval. Paleoenvironmental records indicate that climate was similar to the present during part of this interval. The ice sheet was absent, and glaciers probably were confined to mountain areas, throughout Stage 3. Climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka. By 14–15 ka, the ice sheet had achieved its maximum extent of the last glaciation. Because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted, we consider this synthesis as tentative and subject to significant revision as dating methods improve. Nevertheless, this perspective of the North American ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume.

Quaternary Science Reviews↗
USGS2024

Diversity, distribution, and methodological considerations of haemosporidian infections among Galliformes in Alaska

Using samples spanning 10-degrees of latitude in Alaska, we provide the first comparative assessment of avian haemosporidia distribution of Arctic Alaska with subarctic host populations for four species of grouse and three species of ptarmigan (Galliformes). We found a high overall prevalence for at least one haemospordian genus (88%; N = 351/400), with spruce grouse ( Canachites canadensis ) showing the highest prevalence (100%; N = 54/54). Haemoproteus and Plasmodium lineages were only observed within grouse, while Leucocytozoon species were found within both grouse and ptarmigan. Further, different Leucocytozoon lineages were obtained from blood and tissue samples from the same individual, potentially due to the differential timing and duration of blood and tissue stages. Using different primer sets, we were able to identify different Leucocytozoon lineages within 55% (N = 44/80) of sequenced individuals, thereby detecting coinfections that may have otherwise gone undetected. The commonly used Haemoproteus / Plasmodium primers amplified Leucocytozoon for 90% (N = 103/115) of the products sequenced, highlighting the potential value of alternate primers to identify intra-genus coinfections and the importance of obtaining sequence information rather than relying solely on PCR amplification to assess parasite diversity. Overall, this dataset provides baseline information on parasite lineage distributions to assess the range expansion associated with climate change into Arctic regions and underscores methodological considerations for future studies.

Alaska↗
USGS2016

Seasonal response of ghrelin, growth hormone, and insulin-like growth factor I in the free-ranging Florida manatee ( Trichechus manatus latirostris )

Seasonal changes in light, temperature, and food availability stimulate a physiological response in an animal. Seasonal adaptations are well studied in Arctic, Sub-Arctic, and hibernating mammals; however, limited studies have been conducted in sub-tropical species. The Florida manatee ( Trichechus manatus latirostris ), a sub-tropical marine mammal, forages less during colder temperatures and may rely on adipose stores for maintenance energy requirements. Metabolic hormones, growth hormone (GH), insulin-like growth factor (IGF)-I, and ghrelin influence growth rate, accretion of lean and adipose tissue. They have been shown to regulate seasonal changes in body composition. The objective of this research was to investigate manatee metabolic hormones in two seasons to determine if manatees exhibit seasonality and if these hormones are associated with seasonal changes in body composition. In addition, age related differences in these metabolic hormones were assessed in multiple age classes. Concentrations of GH, IGF-I, and ghrelin were quantified in adult manatee serum using heterologous radioimmunoassays. Samples were compared between short (winter) and long (summer) photoperiods ( n = 22 male, 20 female) and by age class (adult, juvenile, and calf) in long photoperiods ( n = 37). Short photoperiods tended to have reduced GH ( p = 0.08), greater IGF-I ( p = 0.01), and greater blubber depth ( p = 0.03) compared with long photoperiods. No differences were observed in ghrelin ( p = 0.66). Surprisingly, no age related differences were observed in IGF-I or ghrelin concentrations ( p > 0.05). However, serum concentrations of GH tended ( p = 0.07) to be greater in calves and juveniles compared with adults. Increased IGF-I, greater blubber thickness, and reduced GH during short photoperiod suggest a prioritization for adipose deposition. Whereas, increased GH, reduced blubber thickness, and decreased IGF-I in long photoperiod suggest prioritization of lean tissue accretion. Hormone profiles in conjunction with difference in body composition between photoperiods indicate seasonal adjustments in manatee nutrient partitioning priorities.

Mammalian Biology↗
USGS2011

Examination of core samples from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope: Effects of retrieval and preservation

Collecting and preserving undamaged core samples containing gas hydrates from depth is difficult because of the pressure and temperature changes encountered upon retrieval. Hydrate-bearing core samples were collected at the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well in February 2007. Coring was performed while using a custom oil-based drilling mud, and the cores were retrieved by a wireline. The samples were characterized and subsampled at the surface under ambient winter arctic conditions. Samples thought to be hydrate bearing were preserved either by immersion in liquid nitrogen (LN), or by storage under methane pressure at ambient arctic conditions, and later depressurized and immersed in LN. Eleven core samples from hydrate-bearing zones were scanned using x-ray computed tomography to examine core structure and homogeneity. Features observed include radial fractures, spalling-type fractures, and reduced density near the periphery. These features were induced during sample collection, handling, and preservation. Isotopic analysis of the methane from hydrate in an initially LN-preserved core and a pressure-preserved core indicate that secondary hydrate formation occurred throughout the pressurized core, whereas none occurred in the LN-preserved core, however no hydrate was found near the periphery of the LN-preserved core. To replicate some aspects of the preservation methods, natural and laboratory-made saturated porous media samples were frozen in a variety of ways, with radial fractures observed in some LN-frozen sands, and needle-like ice crystals forming in slowly frozen clay-rich sediments. Suggestions for hydrate-bearing core preservation are presented.

Alaska↗
USGS2012

Resource and hazard implications of gas hydrates in the Northern Gulf of Mexico: Results of the 2009 Joint Industry Project Leg II Drilling Expedition

In the 1970's, Russian scientists were the first to suggest that gas hydrates, a crystalline solid of water and natural gas, and a historical curiosity to physical chemists, should occur in abundance in the natural environment. Since this early start, the scientific foundation has been built for the realization that gas hydrates are a global phenomenon, occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide. Recent field testing programs in the Arctic (Dallimore et al., 2008; Yamamoto and Dallimore, 2008) have indicated that natural gas can be produced from gas hydrate accumulations, particularly when housed in sand-rich sediments, with existing conventional oil and gas production technology (Collett et al., 2008) and preparations are now being made for the first marine field production tests (Masuda et al., 2009). Beyond a future energy resource, gas hydrates in some settings may represent a geohazard. Other studies also indicate that methane released to the atmosphere from destabilized gas hydrates may have contributed to global climate change in the past.

Northern Gulf Of Mexico↗
USGS2016

Holocene climate changes in eastern Beringia (NW North America) – A systematic review of multi-proxy evidence

Reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate change. This review summarizes available information from diverse Holocene paleoenvironmental records across eastern Beringia (Alaska, westernmost Canada and adjacent seas), and it quantifies the primary trends of temperature- and moisture-sensitive records based in part on midges, pollen, and biogeochemical indicators (compiled in the recently published Arctic Holocene database, and updated here to v2.1). The composite time series from these proxy records are compared with new summaries of mountain-glacier and lake-level fluctuations, terrestrial water-isotope records, sea-ice and sea-surface-temperature analyses, and peatland and thaw-lake initiation frequencies to clarify multi-centennial- to millennial-scale trends in Holocene climate change. To focus the synthesis, the paleo data are used to frame specific questions that can be addressed with simulations by Earth system models to investigate the causes and dynamics of past and future climate change. This systematic review shows that, during the early Holocene (11.7–8.2 ka; 1 ka = 1000 cal yr BP), rather than a prominent thermal maximum as suggested previously, temperatures were highly variable, at times both higher and lower than present (approximate mid-20th-century average), with no clear spatial pattern. Composited pollen, midge and other proxy records average out the variability and show the overall lowest summer and mean-annual temperatures across the study region during the earliest Holocene, followed by warming over the early Holocene. The sparse data available on early Holocene glaciation show that glaciers in southern Alaska were as extensive then as they were during the late Holocene. Early Holocene lake levels were low in interior Alaska, but moisture indicators show pronounced differences across the region. The highest frequency of both peatland and thaw-lake initiation ages also occurred during the early Holocene. During the middle Holocene (8.2–4.2 ka), glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka, as reflected in most proxy types. Following the middle Holocene thermal maximum, temperatures decreased starting between 4 and 3 ka, signaling the onset of Neoglacial cooling. Glaciers in the Brooks and Alaska Ranges advanced to their maximum Holocene extent as lakes generally rose to modern levels. Temperature differences for averaged 500-year time steps typically ranged by 1–2 °C for individual records in the Arctic Holocene database, with a transition to a cooler late Holocene that was neither abrupt nor spatially coherent. The longest and highest-resolution terrestrial water isotope records previously interpreted to represent changes in the Aleutian low-pressure system around this time are here shown to be largely contradictory. Furthermore, there are too few records with sufficient resolution to identify sub-centennial-scale climate anomalies, such as the 8.2 ka event. The review concludes by suggesting some priorities for future paleoclimate research in the region.

Quaternary Science Reviews↗