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At least 235 records · Page 13Linked to original sources

USGS2017

Continuously amplified warming in the Alaskan Arctic: Implications for estimating global warming hiatus

Historically, in situ measurements have been notoriously sparse over the Arctic. As a consequence, the existing gridded data of surface air temperature (SAT) may have large biases in estimating the warming trend in this region. Using data from an expanded monitoring network with 31 stations in the Alaskan Arctic, we demonstrate that the SAT has increased by 2.19°C in this region, or at a rate of 0.23°C/decade during 1921–2015. Meanwhile, we found that the SAT warmed at 0.71°C/decade over 1998–2015, which is 2 to 3 times faster than the rate established from the gridded data sets. Focusing on the “hiatus” period 1998–2012 as identified by the Intergovernmental Panel on Climate Change (IPCC) report, the SAT has increased at 0.45°C/decade, which captures more than 90% of the regional trend for 1951–2012. We suggest that sparse in situ measurements are responsible for underestimation of the SAT change in the gridded data sets. It is likely that enhanced climate warming may also have happened in the other regions of the Arctic since the late 1990s but left undetected because of incomplete observational coverage.

Alaska↗

USGS2018

Nutrient dynamics in partially drained arctic thaw lakes

Thaw lakes are ubiquitous on arctic coastal plains (ACPs). While many thaw lakes have steep banks, stable water levels, and static surface areas, others only partially fill their basins and vary in area over the summer. These partially drained lakes (PDLs) are hydrologically connected to the wetlands immediately surrounding them. Heat and nutrient availability limit aquatic productivity on ACPs, and we hypothesized that shallow shorelines and greater hydrologic connectivity with the landscape should result in greater nutrient concentrations and biogeochemical cycling in PDLs. We tested this by monitoring water chemistry in lakes with varying levels of seasonal drainage in sandy and silty peaty lowland sites on the ACP of Alaska. One highly drained lake (N1) was significantly warmer than minimally drained lakes (minDLs) related to earlier ice off, reaching temperatures as high as 16 °C in June when minDLs still contained ice. Ammonia, total dissolved phosphorus, and dissolved organic carbon and nitrogen concentrations were higher in lakes with greater drainage, and concentrations in N1 rivaled those in the small, biologically productive ponds. Many PDLs displayed a midsummer decrease in nutrients consistent with assimilation by the aquatic ecosystem, and a late‐summer increase most likely related to runoff from drained lake margins following precipitation. N1 exported kilograms of ammonium and total dissolved phosphorus to the stream network over the summer. Given increased warming and drying in the arctic, the proportion of PDLs may be changing, which in turn may affect nutrient and organic matter availability in arctic lakes and export to downstream environments.

Journal of Geophysical Research: Biogeosciences↗

USGS2023

Effects of vehicle traffic on space use and road crossings of caribou in the Arctic

Assessing the effects of industrial development on wildlife is a key objective of managers and conservation practitioners. However, wildlife responses are often only investigated with respect to the footprint of infrastructure, even though human activity can strongly mediate development impacts. In Arctic Alaska, there is substantial interest in expanding energy development, raising concerns about the potential effects on barren-ground caribou ( Rangifer tarandus granti ). While caribou generally avoid industrial infrastructure, little is known about the role of human activity in moderating their responses, and whether managing activity levels could minimize development effects. To address this uncertainty, we examined the influence of traffic volume on caribou summer space use and road crossings in the Central Arctic Herd within the Kuparuk and Milne Point oil fields on the North Slope of Alaska. We first modeled spatiotemporal variation in hourly traffic volumes across the road system from traffic counter data using gradient-boosted regression trees. We then used generalized additive models to estimate nonlinear step selection functions and road-crossing probabilities from collared female caribou during the post-calving and insect harassment seasons, when they primarily interact with roads. Step selection analyses revealed that caribou selected areas further from roads (~1–3 km) during the post-calving and mosquito seasons and selected areas with lower traffic volumes during all seasons, with selection probabilities peaking when traffic was <5 vehicles/h. Using road-crossing models, we found that caribou were less likely to cross roads during the insect seasons as traffic increased, but that response dissipated as insect harassment became more severe. Past studies suggested that caribou exhibit behavioral responses when traffic exceeds 15 vehicles/h, but our results demonstrate behavioral responses at much lower traffic levels. Our results illustrate that vehicle activity mediates caribou responses to road infrastructure, information that can be used in future land-use planning to minimize the behavioral responses of caribou to industrial development in sensitive Arctic landscapes.

Alaska↗

USGS2024

Where east meets west: Phylogeography of the high Arctic North American brant goose

Genetic variation in Arctic species is often influenced by vicariance during the Pleistocene, as ice sheets fragmented the landscape and displaced populations to low- and high-latitude refugia. The formation of secondary contact or suture zones during periods of ice sheet retraction has important consequences on genetic diversity by facilitating genetic connectivity between formerly isolated populations. Brant geese ( Branta bernicla ) are a maritime migratory waterfowl (Anseriformes) species that almost exclusively uses coastal habitats. Within North America, brant geese are characterized by two phenotypically distinct subspecies that utilize disjunct breeding and wintering areas in the northern Pacific and Atlantic. In the Western High Arctic of Canada, brant geese consist of individuals with an intermediate phenotype that are rarely observed nesting outside this region. We examined the genetic structure of brant geese populations from each subspecies and areas consisting of intermediate phenotypes using mitochondrial DNA (mtDNA) control region sequence data and microsatellite loci. We found a strong east–west partition in both marker types consistent with refugial populations. Within subspecies, structure was also observed at mtDNA while microsatellite data suggested the presence of only two distinct genetic clusters. The Western High Arctic (WHA) appears to be a secondary contact zone for both Atlantic and Pacific lineages as mtDNA and nuclear genotypes were assigned to both subspecies, and admixed individuals were observed in this region. The mtDNA sequence data outside WHA suggests no or very restricted intermixing between Atlantic and Pacific wintering populations which is consistent with published banding and telemetry data. Our study indicates that, although brant geese in the WHA are not a genetically distinct lineage, this region may act as a reservoir of genetic diversity and may be an area of high conservation value given the potential of low reproductive output in this species.

Ecology and Evolution↗

USGS2012

Hybridization among Arctic white-headed gulls (Larus spp.) obscures the genetic legacy of the Pleistocene

We studied the influence of glacial oscillations on the genetic structure of seven species of white-headed gull that breed at high latitudes ( Larus argentatus, L. canus, L. glaucescens, L. glaucoides, L. hyperboreus, L. schistisagus, and L. thayeri ). We evaluated localities hypothesized as ice-free areas or glacial refugia in other Arctic vertebrates using molecular data from 11 microsatellite loci, mitochondrial DNA (mtDNA) control region, and six nuclear introns for 32 populations across the Holarctic. Moderate levels of genetic structure were observed for microsatellites ( F ST = 0.129), introns ( Φ ST = 0.185), and mtDNA control region ( Φ ST = 0.461), with among-group variation maximized when populations were grouped based on subspecific classification. Two haplotype and at least two allele groups were observed across all loci. However, no haplotype/allele group was composed solely of individuals of a single species, a pattern consistent with recent divergence. Furthermore, northernmost populations were not well differentiated and among-group variation was maximized when L. argentatus and L. hyberboreus populations were grouped by locality rather than species, indicating recent hybridization. Four populations are located in putative Pleistocene glacial refugia and had larger t estimates than the other 28 populations. However, we were unable to substantiate these putative refugia using coalescent theory, as all populations had genetic signatures of stability based on mtDNA. The extent of haplotype and allele sharing among Arctic white-headed gull species is noteworthy. Studies of other Arctic taxa have generally revealed species-specific clusters as well as genetic structure within species, usually correlated with geography. Aspects of white-headed gull behavioral biology, such as colonization ability and propensity to hybridize, as well as their recent evolutionary history, have likely played a large role in the limited genetic structure observed.

Ecology and Evolution↗

USGS2021

Life-history attributes of Arctic-breeding birds drive uneven responses to environmental variability across different phases of the reproductive cycle

Animals exhibit varied life-history traits that reflect adaptive responses to their environments. For Arctic-breeding birds, traits related to diet, egg nutrient allocation, clutch size, and chick growth are predicted to be under increasing selection pressure due to rapid climate change and increasing environmental variability across high-latitude regions. We compared four migratory birds (black brant [ Branta bernicla nigricans ], lesser snow geese [ Chen caerulescens caerulescens ], semipalmated sandpipers [ Calidris pusilla ], and Lapland longspurs [ Calcarius lapponicus ]) with varied life histories at an Arctic site in Alaska, USA, to understand how life-history traits help moderate environmental variability across different phases of the reproductive cycle. We monitored aspects of reproductive performance related to the timing of breeding, reproductive investment, and chick growth from 2011 to 2018. In response to early snowmelt and warm temperatures, semipalmated sandpipers advanced their site arrival and bred in higher numbers, while brant and snow geese increased clutch sizes; all four species advanced their nest initiation dates. During chick rearing, longspur nestlings were relatively resilient to environmental variation, whereas warmer temperatures increased the growth rates of sandpiper chicks but reduced growth rates of snow goose goslings. These responses generally aligned with traits along the capital-income spectrum of nutrient acquisition and altricial–precocial modes of chick growth. Under a warming climate, the ability to mobilize endogenous reserves likely provides geese with relative flexibility to adjust the timing of breeding and the size of clutches. Higher temperatures, however, may negatively affect the quality of herbaceous foods and slow gosling growth. Species may possess traits that are beneficial during one phase of the reproductive cycle and others that may be detrimental at another phase, uneven responses that may be amplified with future climate warming. These results underscore the need to consider multiple phases of the reproductive cycle when assessing the effects of environmental variability on Arctic-breeding birds.

Alaska↗

USGS2014

Morphology-dependent water budgets and nutrient fluxes in arctic thaw ponds

Thaw ponds on the Arctic Coastal Plain of Alaska are productive ecosystems, providing habitat and food resources for many fish and bird species. Permafrost in this region creates unique pond morphologies: deep troughs, shallow low-centred polygons (LCPs) and larger coalescent ponds. By monitoring seasonal trends in pond volume and chemistry, we evaluated whether pond morphology and size affect water temperature and desiccation, and nitrogen (N) and phosphorus (P) fluxes. Evaporation was the largest early-summer water flux in all pond types. LCPs dried quickly and displayed high early-summer nutrient concentrations and losses. Troughs consistently received solute-rich subsurface inflows, which accounted for 12 to 42 per cent of their volume and may explain higher P in the troughs. N to P ratios increased and ammonium concentrations decreased with pond volume, suggesting that P and inorganic N availability may limit ecosystem productivity in older, larger ponds. Arctic summer temperatures will likely increase in the future, which may accelerate mid-summer desiccation. Given their morphology, troughs may remain wet, become warmer and derive greater nutrient loads from their thawing banks. Overall, seasonal- to decadal-scale warming may increase ecosystem productivity in troughs relative to other Arctic Coastal Plain ponds.

Alaska↗

USGS2017

Variation in δ15N and δ13C values of forages for Arctic caribou: Effects of location, phenology and simulated digestion

Rationale The use of stable isotopes for dietary estimates of wildlife assumes that there are consistent differences in isotopic ratios among diet items, and that the differences in these ratios between the diet item and the animal tissues (i.e., fractionation) are predictable. However, variation in isotopic ratios and fractionation of δ 13 C and δ 15 N values among locations, seasons, and forages are poorly described for arctic herbivores especially migratory species such as caribou ( Rangifer tarandus ). Methods We measured the δ 13 C and δ 15 N values of seven species of forage growing along a 200-km transect through the range of the Central Arctic caribou herd on the North Slope of Alaska over 2 years. We compared forages available at the beginning (May; n = 175) and the end ( n = 157) of the growing season (September). Purified enzymes were used to measure N digestibility and to assess isotopic fractionation in response to nutrient digestibility during simulated digestion. Results Values for δ 13 C declined by 1.38 ‰ with increasing latitude across the transect, and increased by 0.44 ‰ from the beginning to the end of the season. The range of values for δ 15 N was greater than that for δ 13 C (13.29 vs 5.60 ‰). Differences in values for δ 13 C between graminoids ( Eriophorum and Carex spp.) and shrubs ( Betula and Salix spp.) were small but δ 15 N values distinguished graminoids (1.87 ± 1.02 ‰) from shrubs (−2.87 ± 2.93 ‰) consistently across season and latitude. However, undigested residues of forages were enriched in 15 N when the digestibility of N was less than 0.67. Conclusions Although δ 15 N values can distinguish plant groups in the diet of arctic herbivores, variation in the digestibility of dietary items may need to be considered in applying fractionation values for 15 N to caribou and other herbivores that select highly digestible items (e.g. forbs) as well as heavily defended plants (e.g. woody browse).

Alaska↗

USGS2018

An interferometric synthetic aperture radar (InSAR) habitat suitability model to identify overwinter conditions for coregonine whitefishes in Arctic lagoons

Lagoons provide critical habitats for many fishes, including coregonine whitefishes, which are a mainstay in many subsistence fisheries of rural communities in Arctic Alaska. Despite their importance, little is known about the overwintering habits of whitefishes in Arctic Alaska due to the challenges associated with sampling during winter. We developed a habitat suitability (HS) model to understand the potential range of physical conditions that whitefishes experience during the Arctic winter, using three indicator lagoons that represent a range of environmental characteristics. The HS model was built using a three-step approach. First, remote sensing that uses interferometric synthetic aperture radar (InSAR) identified areas of floating and bottomfast ice. Second, through in-field ground-truthing, we confirmed the presence and quality of liquid water (water depth, temperature, and dissolved oxygen) beneath the ice cover. Third, we assessed the suitability of that liquid water as habitat for whitefishes based on published literature and expert interpretation of water quality parameters. InSAR determined that 0, 65.4, and 88.2% of the three lagoons were composed of floating ice corresponding with areas of liquid water beneath a layer of ice. The HS model indicated that all three lagoons had reduced suitability as whitefish habitat in winter than in summer due to the loss of habitat because of the presence of bottomfast ice and a reduction in the quality of liquid water due to cold temperatures, high salinities, and low dissolved oxygen levels. However, only the shallowest lagoon had lethal conditions and zero suitability as whitefish habitat. The methods outlined here provide a simple, cost-effective method to identify habitats that consistently provide critical winter habitat and integrate remote sensing in a HS model framework.

Alaska↗

USGS2011

Contaminant loading in remote Arctic lakes affects cellular stress-related proteins expression in feral charr

The remote Arctic lakes on Bjørnøya Island, Norway, offer a unique opportunity to study possible affect of lifelong contaminant exposure in wild populations of landlocked Arctic charr ( Salvelinus alpinus ). This is because Lake Ellasjøen has persistent organic pollutant (POP) levels that are significantly greater than in the nearby Lake Øyangen. We examined whether this differential contaminant loading was reflected in the expression of protein markers of exposure and effect in the native fish. We assessed the expressions of cellular stress markers, including cytochrome P4501A (Cyp1A), heat shock protein 70 (hsp70), and glucocorticoid receptor (GR) in feral charr from the two lakes. The average polychlorinated biphenyl (PCB) load in the charr liver from Ellasjøen was approximately 25-fold higher than in individuals from Øyangen. Liver Cyp1A protein expression was significantly higher in individuals from Ellasjøen compared with Øyangen, confirming differential PCB exposure. There was no significant difference in hsp70 protein expression in charr liver between the two lakes. However, brain hsp70 protein expression was significantly elevated in charr from Ellasjøen compared with Øyangen. Also, liver GR protein expression was significantly higher in the Ellasjøen charr compared with Øyangen charr. Taken together, our results suggest changes to cellular stress-related protein expression as a possible adaptation to chronic-contaminant exposure in feral charr in the Norwegian high-Arctic.

Bjørnøya Island↗

USGS2014

Spatio-temporal patterns of ptarmigan occupancy relative to shrub cover in the Arctic

Rock and willow ptarmigan are abundant herbivores that require shrub habitats in arctic and alpine areas. Shrub expansion is likely to increase winter habitat availability for ptarmigan, which in turn influence shrub architecture and growth through browsing. Despite their ecological role in the Arctic, the distribution and movement patterns of ptarmigan are not well known, particularly in northern Alaska where shrub expansion is occurring. We used multi-season occupancy models to test whether ptarmigan occupancy varied within and among years, and the degree to which colonization and extinction probabilities were related to shrub cover and latitude. Aerial surveys were conducted from March to May in 2011 and April to May 2012 in a 21,230 km 2 area in northeastern Alaska. In areas with at least 30 % shrub cover, the probability of colonization by ptarmigan was >0.90, indicating that moderate to extensive patches of shrubs (typically associated with riparian areas) had a high probability of becoming occupied by ptarmigan. Occupancy increased throughout the spring in both years, providing evidence that ptarmigan migrated from southern wintering areas to breeding areas north of the Brooks Range. Occupancy was higher in the moderate snow year than the high snow year, and this was likely due to higher shrub cover in the moderate snow year. Ptarmigan distribution and migration in the Arctic are linked to expanding shrub communities on a wide geographic scale, and these relationships may be shaping ptarmigan population dynamics, as well as rates and patterns of shrub expansion.

Alaska↗

USGS2020

The influence of snow cover, air temperature, and groundwater flow on the active-layer thermal regime of Arctic hillslopes drained by water tracks

Permafrost in Arctic watersheds limits soil biological activity to a thin, seasonally thawed active layer that contributes water to streams. In many hillslopes, relatively wet drainage features called water tracks have distinct freeze-thaw patterns that affect groundwater flow and storage, and thus the export of heat and solutes to Arctic streams. This study uses groundwater flow and energy transport models to examine potential controls on the timing and duration of freeze–thaw conditions and the magnitude of temperature fluctuations within water tracks and their adjacent hillslopes. The simulated length of the active-layer thaw season varies by 1 month over the range of snow-cover and mean annual air-temperature scenarios simulated. The timing and duration of freezing is particularly sensitive to depth and duration of snow cover. Thus, the deeper snowpack covers that can accumulate in water tracks contribute to their more persistent thaw conditions and their ability to conduct groundwater downslope. A three-dimensional simulation shows that during the summer thaw season, the water track captures groundwater laterally from half way across the hillslope. The models presented here elucidate key mechanisms driving small-scale variation in the active-layer thermal regime of tundra hillslopes, which may be responsible for changes in drainage-network geometry and Arctic biogeochemical fluxes under a warming climate.

Alaska↗

USGS2012

Relationships between ecosystem metabolism, benthic macroinvertebrate densities, and environmental variables in a sub-arctic Alaskan river

Relationships between environmental variables, ecosystem metabolism, and benthos are not well understood in sub-arctic ecosystems. The goal of this study was to investigate environmental drivers of river ecosystem metabolism and macroinvertebrate density in a sub-arctic river. We estimated primary production and respiration rates, sampled benthic macroinvertebrates, and monitored light intensity, discharge rate, and nutrient concentrations in the Chena River, interior Alaska, over two summers. We employed Random Forests models to identify predictor variables for metabolism rates and benthic macroinvertebrate density and biomass, and calculated Spearman correlations between in-stream nutrient levels and metabolism rates. Models indicated that discharge and length of time between high water events were the most important factors measured for predicting metabolism rates. Discharge was the most important variable for predicting benthic macroinvertebrate density and biomass. Primary production rate peaked at intermediate discharge, respiration rate was lowest at the greatest time since last high water event, and benthic macroinvertebrate density was lowest at high discharge rates. The ratio of dissolved inorganic nitrogen to soluble reactive phosphorus ranged from 27:1 to 172:1. We found that discharge plays a key role in regulating stream ecosystem metabolism, but that low phosphorous levels also likely limit primary production in this sub-arctic stream.

Alaska↗

USGS2012

Reconstruction of past methane availability in an Arctic Alaska wetland indicates climate influenced methane release during the past ~12,000 years

Atmospheric contributions of methane from Arctic wetlands during the Holocene are dynamic and linked to climate oscillations. However, long-term records linking climate variability to methane availability in Arctic wetlands are lacking. We present a multi-proxy ~12,000 year paleoecological reconstruction of intermittent methane availability from a radiocarbon-dated sediment core (LQ-West) taken from a shallow tundra lake (Qalluuraq Lake) in Arctic Alaska. Specifically, stable carbon isotopic values of photosynthetic biomarkers and methane are utilized to estimate the proportional contribution of methane-derived carbon to lake-sediment-preserved benthic (chironomids) and pelagic (cladocerans) components over the last ~12,000 years. These results were compared to temperature, hydrologic, and habitat reconstructions from the same site using chironomid assemblage data, oxygen isotopes of chironomid head capsules, and radiocarbon ages of plant macrofossils. Cladoceran ephippia from ~4,000 cal year BP sediments have δ13C values that range from ~−39 to −31‰, suggesting peak methane carbon assimilation at that time. These low δ13C values coincide with an apparent decrease in effective moisture and development of a wetland that included Sphagnum subsecundum. Incorporation of methane-derived carbon by chironomids and cladocerans decreased from ~2,500 to 1,500 cal year BP, coinciding with a temperature decrease. Live-collected chironomids with a radiocarbon age of 1,640 cal year BP, and fossil chironomids from 1,500 cal year BP in the core illustrate that ‘old’ carbon has also contributed to the development of the aquatic ecosystem since ~1,500 cal year BP. The relatively low δ13C values of aquatic invertebrates (as low as −40.5‰) provide evidence of methane incorporation by lake invertebrates, and suggest intermittent climate-linked methane release from the lake throughout the Holocene.

Alaska↗

USGS2025

Observing northern high-latitude river systems to understand changes in a warming Arctic

Purpose of Review Streams and rivers are undergoing rapid change as the Arctic warms and thaws. We review recent observations in Arctic stream systems to identify ubiquitous changes and the most useful tools for observing change and exploring the underlying processes. Recent Findings Recent literature indicates increasingly significant trends in river hydrology and chemistry due to persistent warming in the Arctic and longer observational records for analysis. However, regional differences in the magnitude and direction of these trends persist. We also observe thresholds in ground thaw and surface–groundwater interactions that can impact river hydrology and chemistry. Summary Warming and thaw are occurring rapidly at high latitudes, resulting in increasing, yet variable responses in stream systems across regions and scales. These differences highlight the need for long-term records and an interdisciplinary approach to explain trends and predict future states. Stream systems respond to multiple landscape changes related to hydrology (changing precipitation and subsurface flow), geology (ground thaw dynamics), and ecology (vegetation change).

Current Climate Change Reports↗

USGS2016

Impacts of shore expansion and catchment characteristics on lacustrine thermokarst records in permafrost lowlands, Alaska Arctic Coastal Plain

Arctic lowland landscapes have been modified by thermokarst lake processes throughout the Holocene. Thermokarst lakes form as a result of ice-rich permafrost degradation, and they may expand over time through thermal and mechanical shoreline erosion. We studied proximal and distal sedimentary records from a thermokarst lake located on the Arctic Coastal Plain of northern Alaska to reconstruct the impact of catchment dynamics and morphology on the lacustrine depositional environment and to quantify carbon accumulation in thermokarst lake sediments. Short cores were collected for analysis of pollen, sedimentological, and geochemical proxies. Radiocarbon and 210 Pb/ 137 Cs dating, as well as extrapolation of measured historic lake expansion rates, were applied to estimate a minimum lake age of ~1400 calendar years BP. The pollen record is in agreement with the young lake age as it does not include evidence of the “alder high” that occurred in the region ~4000 cal yr BP. The lake most likely initiated from a remnant pond in a drained thermokarst lake basin (DTLB) and deepened rapidly as evidenced by accumulation of laminated sediments. Increasing oxygenation of the water column as shown by higher Fe/Ti and Fe/S ratios in the sediment indicate shifts in ice regime with increasing water depth. More recently, the sediment source changed as the thermokarst lake expanded through lateral permafrost degradation, alternating from redeposited DTLB sediments, to increased amounts of sediment from eroding, older upland deposits, followed by a more balanced combination of both DTLB and upland sources. The characterizing shifts in sediment sources and depositional regimes in expanding thermokarst lakes were, therefore, archived in the thermokarst lake sedimentary record. This study also highlights the potential for Arctic lakes to recycle old carbon from thawing permafrost and thermokarst processes.

Alaska↗

USGS1996

Character, paleoenvironment, rate of accumulation, and evidence for seismic triggering of Holocene turbidites, Canada Abyssal Plain, Arctic Ocean

Four box cores and one piston core show that Holocene sedimentation on the southern Canada Abyssal Plain for the last 8010 ± 120 yr has consisted of a continuing rain of pelagic organic and ice-rafted clastic sediment with a net accumulation rate during the late Holocene of ⩽10 mm/1000 yr, and episodically emplaced turbidites 1–5 m thick deposited at intervals of 830 to 3450 yr (average 2000 yr). The average net accumulation rate of the mixed sequence of turbidites and thin pelagite interbeds in the cores is about 1.2 m/1000 yr. Physiography suggests that the turbidites originated on the Mackenzie Delta or its clinoform, and δ 13 C values of −27 to −25%. in the turbidites are compatible with a provenance on a delta. Extant displaced neritic and lower slope to basin plain calcareous benthic foraminifers coexist in the turbidite units. Their joint occurence indicates that the turbidites originated on the modern continental shelf and entrained sediment from the slope and rise enroute to their final resting place on the Canada Abyssal Plain. The presence of Middle Pleistocene diatoms in the turbidites suggests, in addition, that the turbidites may have originated in shallow submarine slides beneath the upper slope or outer shelf. Small but consistent differences in organic carbon content and δ 13 C values between the turbidite units suggest that they did not share an identical provenance, which is at least compatible with an origin in slope failures. The primary provenance of the ice-rafted component of the pelagic beds was the glaciated terrane of northwestern Canada; and the provenance of the turbidite units was Pleistocene and Holocene sedimentary deposits on the outer continental shelf and upper slope of the Mackenzie Delta. Largely local derivation of the sediment of the Canada Abyssal Plain indicates that sediment accumulation rates in the Arctic Ocean are valid only for regions with similar depositional sources and processes, and that these rates cannot be extrapolated regionally. The location of an elliptical zone of active seismicity over the inferred provenance of the turbidites suggests that they were triggered by large earthquakes. Distal turbidite sediment accumulation rates were more than two orders of magnitude greater than pelagic sediment accumulation rates on the Canada Abyssal Plain during the last 8000 years. This disparity reconciles the discrepancy between the high accumulation rates assumed by some for the Arctic Ocean because of the numerous major rivers and large ice sheets that discharge into this small mediterranean basin and the low pelagic sedimentation rates that have been reported from the Arctic Ocean.

Marine Geology↗

USGS2023

Investigating effects of climate-induced changes in water temperature and diet on mercury concentrations in an Arctic freshwater forage fish

The amount of mercury (Hg) in Arctic lake food webs is, and will continue to be, affected by rapid, ongoing climate change. At warmer temperatures, fish require more energy to sustain growth; changes in their metabolic rates and consuming prey with potentially higher Hg concentrations could result in increased Hg accumulation. To examine the potential implications of climate warming on forage fish Hg accumulation in Arctic lakes, we quantified growth and Hg accumulation in Ninespine Stickleback Pungitius pungitius under different temperature and diet scenarios using bioenergetics models. Four scenarios were considered that examined the role of climate, diet, climate × diet, and climate × diet × elevated prey Hg. As expected, annual fish growth increased with warmer temperatures, but growth rates and Hg accumulation were largely diet dependent. Compared to current growth rates of 0.3 g⋅y −1 , fish growth increased at least 200% for fish consuming energy-dense benthic prey and decreased at least 40% for fish consuming pelagic prey. Compared to baseline levels, the Hg burden per kilocalorie of Ninespine Stickleback declined up to 43% with benthic consumption – indicating strong somatic growth dilution – but no more than 4% with pelagic consumption; elevated prey Hg concentrations led to moderate Hg declines in benthic-foraging fish and Hg increases in pelagic-foraging fish. Bioenergetics models demonstrated the complex interaction of water temperature, growth, prey proportions, and prey Hg concentrations that respond to climate change. Further work is needed to resolve mechanisms and rates linking climate change to Hg availability and uptake in Arctic freshwater systems.

Alaska↗