Geology topics

Research about Cook Inlet

Source-linked reports with geographic coverage including Cook Inlet.

At least 19 recordsLinked to original sources

USGS2026

Cook Inlet beluga whale calling varies by group characteristics, behavior, and tidal state

Communication allows social species to exchange information among group members. In aquatic environments, acoustic signals are among the most effective forms of communication and are important for many species, including cetaceans. Beluga whales ( Delphinapterus leucas ) are highly social and vocal, yet little is known about the functionality of their social calls. To examine context-dependent vocal behavior in belugas, we collected passive acoustic data and fine-scale behavioral observations for the endangered Cook Inlet beluga population. The resulting dataset includes 1,720 annotated vocalizations collected over 21 behaviorally encoded encounters. We fit generalized linear mixed models to these data to investigate the effect of behavioral state, group size, calf presence, and tidal state on (1) calling rate (number of calls/minute) and (2) call category (whistles, pulsed calls, combined calls). Belugas were more likely to call when traveling and had higher calling rates during flood tides. Group-level calling rate increased sublinearly with group size, suggesting that individuals called less in larger groups, possibly reflecting increased listening, vocal coordination, or a strategy to avoid acoustic masking. Group calling rate increased before transitions between traveling and milling, suggesting a possible link between communication and behavioral transitions. Whistles were more prevalent when traveling, while pulsed calls were more prevalent when milling. Combined calls occurred only when calves were present, indicating the importance of these calls in communication with calves. Identifying these communication patterns and the contexts in which they occur can enhance our understanding of beluga whale ecology and aid in conservation efforts via passive acoustic monitoring.

Alaska↗

USGS2025

Paralytic shellfish toxins and seabirds: Evaluating sublethal effects, behavioral responses, and ecological implications of saxitoxin ingestion by common murres (Uria aalge)

Paralytic shellfish toxins (PSTs), including saxitoxin (STX) and its congeners, are neurotoxins that can be produced during harmful algal blooms and cause illness or death in humans, fish, seabirds, and marine mammals. Since 2014, multiple large-scale seabird mortality events have occurred in Alaska waters, with STXs detected in some carcasses. To investigate the sublethal behavioral and ecological effects of STX on seabirds, we conducted captive dosing trials with common murres ( Uria aalge ). We gavaged purified STX (dehydrated STX dihydrocholoride, STX-diHCl) or an Alexandrium catenella culture extract into murres, monitored behavioral responses and recovery times, and assessed tissue concentrations in individuals that died or were euthanized. Using a modified up-and-down dose-finding scheme, we estimated a median effective dose (ED 50 ) of 89 µg STX-equivalents (eq) kg -1 for STX-diHCl and 366 µg STX-eq kg -1 for the A. catenella extract based on ecologically relevant behavior. Differences between the ED 50 estimates could reflect uncertainties in toxin equivalency factors for PST congeners, which are based on studies using purified toxins in mice and may vary across taxa or toxin matrices. Post-dosing concentrations of STX varied by tissue type across individuals, with quantifiable levels ranging from 3 to 379 µg STX-eq 100g -1 . Evidence of biotransformation of STX in A. catenella extract-dosed birds was observed. We also measured the chronic effects of dosing with sublethal levels of STX-diHCl over seven-days, which resulted in lower fish intake among treatment birds compared to controls (-187 g day -1 ). This investigation improves our understanding of the ecological effects of PSTs on seabird health.

Alaska↗

USGS2025

Quantifying sea otter abundance, distribution, habitat use, and foraging intake in Cook Inlet, Alaska

Following near extirpation from the fur trade, sea otters ( Enhydra lutris ) have returned to occupy lower Cook Inlet since the 1950s, or earlier, with numbers increasing to ~11,000 and ~9,000 on the west and east side, respectively, by 2017. Northward range expansion on the west side has been negligible for decades with few animals found north of Kamishak Bay, while northward expansion on the east side has been more pronounced in recent decades. The reasons for these contrasting distribution patterns are not certain. Possible explanations for lack of expansion on the west side included 1) poor sea otter habitat north of Kamishak Bay; 2) adequate habitat north of Kamishak Bay but no incentive for sea otters to move north because of abundant food in Kamishak Bay, and/or sea otters discouraged from moving north of Kamishak Bay; 3) seasonal ice formation; or 4) seasonal presence of killer whales. This project was designed to document current sea otter abundance and distribution in lower Cook Inlet, including seasonal variation, and evaluate drivers of habitat use and foraging conditions, including how these overlap with Bureau of Ocean Energy Management (BOEM) Lease Sale blocks. We found that the probability of sea otter presence in lower Cook Inlet was significantly related to depth and distance from shore with the highest probabilities of sea otter presence in areas ~7–8 kilometers (km) from shore in water ~20–30 meters (m) deep. Historical survey data suggest sea otter distribution has not changed dramatically since 2002, and while we detected significant seasonal changes including due to presence of heavy sea ice, the seasonal changes were modest and primarily related to locations with consistent winter ice formation on the west side of lower Cook Inlet. Overall, throughout the year, sea otters appeared to be utilizing most of the habitat within the 40-m depth contour on the east side of lower Cook Inlet, including Kachemak Bay. Sea otters on the west side reside largely within Kamishak Bay. Because of the shallow bathymetry of lower Cook Inlet, sea otters consistently occurred farther offshore than in many other areas of Alaska. The presence of sea otters, including females with pups, in these offshore waters indicates that sea otters can forage productively in these open water areas. Importantly, we documented that sea otters, including females with pups, occurred in most of the eastern BOEM lease blocks including the original Lease Sale 244 blocks 7064, 7114, 6162, 6310, 6360, 6410, 6458 and 6457. The relinquishments for these 7 leases were effective September 17, 2024: OCS-Y-02434 (block # 7064), OCS-Y-02435 (7114), OCS-Y-02436 (6162), OCS-Y-02438 (6357), OCS-Y-02442 (6407), OCS-Y02446 (6457), OCS-Y-02447 (6458) https://www.boem.gov/sites/default/files/documents/environment/Map%20of%20Active%20Leases%20 Cook%20Inlet%20OCS_0.pdf Regarding differential northward expansion on the east and west side of lower Cook Inlet, we found that wind and water circulation patterns make winter sea ice more prominent on the west side, but this had minimal effects on sea otter distribution. In addition, although there have been observations of killer whale ( Orcinus orca ) predation on sea otters in Cook Inlet, we did not see behavioral or distributional evidence that it was prevalent enough to have strong effects on sea otter habitat use. Benthic surveys using a remotely operated vehicle (ROV) indicated that epibenthic substrate and biological community heterogeneity differed between areas with and without otters, suggesting that these factors may explain the current distribution of otters within lower Cook Inlet. However, ROV surveys cannot assess infaunal prey abundance, making assessments of the role of prey availability difficult. The existence of a healthy Pacific razor clam ( Siliqua patula ) fishery along western lower Cook Inlet along the Lake Clark coast north of Kamishak Bay suggests there may still be a resource base for eventual expansion of sea otters into this area. Our shore-based forage observations indicated that sea otters exist near carrying capacity densities relative to nearshore prey resources. However, our distribution model suggests the bulk of the population lives offshore beyond our ability to observe their feeding activity. The fact that sea otters are a consistent presence in offshore areas suggests that prey resources in these areas were relatively abundant in comparison to nearshore prey resources, making foraging in offshore areas, with water depths of 0–40 m, energetically profitable. Prey types in these offshore areas of lower Cook Inlet likely included epifauna such as crabs and large urchins, in addition to infaunal clams based on the soft substrate habitat types that characterize lower Cook Inlet. Collectively, our results suggest that sea otters occupy most areas of lower Cook Inlet with appropriate benthic habitat types and prey resources, which includes areas within BOEM Lease Sale blocks. With the exception of the Lake Clark coast, sea otters may be approaching a food- and habitat-limited distribution and carrying capacity, suggesting that the current status of sea otters in lower Cook Inlet is likely to remain similar in the absence of significant changes to prey, habitat, predation, or anthropogenic disturbance.

Alaska↗

USGS2024

Lingering impacts of the 2014-2016 northeast Pacific marine heatwave on seabird demography in Cook Inlet, Alaska (USA)

A protracted period (2014-2016) of anomalously warm water in the northeast Pacific Ocean precipitated an extensive die-off of common murres Uria aalge (hereafter ‘murres’) during 2015-2016, accompanied by reduced colony attendance and reproductive success of murres and black-legged kittiwakes Rissa tridactyla (‘kittiwakes’) starting in 2015. Most murres died of starvation following a large-scale reduction in abundance and quality of forage fish. To assess murre and kittiwake recovery following the marine heatwave, we monitored their demographics at 2 colonies (Chisik and Gull Islands) in Cook Inlet, Alaska (USA), from 2016 to 2019. Compared to historic data (1995-1999), we observed declines and increased variability in colony attendance and productivity across species and colonies, and predation was widespread. At Chisik, where food limitations were common during historic studies, both species experienced substantial population declines and reproductive failures in all 4 years (2016-2019) following the heatwave. At Gull, a typically productive colony during historic studies, murres failed to fledge chicks for 3 years (2016-2018) following the heatwave. By 2019, murre productivity recovered to about half that observed during historic studies (0.28 vs. 0.54 chicks per pair), but populations had declined by half. Kittiwake population size at Gull declined a quarter from historic counts, and reproduction alternated between complete breeding failures (2016/2018) and high productivity (2017/2019). These multi-year demographic impacts indicate lingering effects of the heatwave on kittiwakes and murres through forage fish depletion and increased predator disturbance, and possibly other stressors. It remains unknown whether populations can rebound to historic levels. If so, recovery would likely take decades.

Alaska↗

USGS2024

Predator disturbance contributed to Common Murre Uria aalge breeding failures in Cook Inlet, Alaska following the 2014–2016 Pacific marine heatwave

The 2014-2016 Pacific marine heatwave caused unprecedented die-offs and multi-year reproductive failures for Common Murres Uria aalge along the west coast of North America. Lingering impacts, such as declines in colony attendance and productivity, have persisted at some colonies following the heatwave and are attributed largely to changes in prey availability and quality. Here, we present evidence of an additional, top-down mechanism contributing to Common Murre breeding failures on Gull Island (Alaska): disturbance of nesting birds by aerial predators and associated egg depredation. We collected time-lapse images over five murre breeding seasons (2016-2020) on Gull Island to document the frequency, duration, and intensity of disturbances caused by aerial predators, as well as to quantify disturbance-associated egg depredation. To identify seasonal and inter-annual variability of disturbances, we calculated a daily disturbance index and compared years using generalized additive models. In all years, Bald Eagles Haliaeetus leucocephalus were the primary cause of disturbance, which led to periods of prolonged colony abandonment by murres and facilitated high levels of murre egg depredation by Glaucous-winged Gulls Larus glaucescens and Herring Gulls L. argentatus . We found that the seasonality of disturbance was an important factor in determining egg depredation rates. In years when disturbance levels were high and persisted later in the season, the colony experienced complete breeding failures due to disturbance-associated egg depredation. Our study revealed that the response of nesting murres to a strong environmental perturbation, such as the Pacific marine heatwave, can be complex and involve multiple stressors from both bottom-up and top-down factors.

Alaska↗

USGS2018

Secular changes in Cenozoic arc magmatism recorded by trends in forearc-basin sandstone composition, Cook Inlet, southern Alaska

A robust set of modal composition data (238 samples) for Eocene to Pliocene sandstone from the Cook Inlet forearc basin of southern Alaska reveals strong temporal trends in composition, particularly in the abundance of volcanic lithic grains. Field and petrographic point-count data from the northwestern side of the basin indicate that the middle Eocene West Foreland Formation was strongly influenced by nearby volcanic activity. The middle Eocene to lower Miocene Hemlock Conglomerate and Oligocene to middle Miocene Tyonek Formation have a more mature quartzose composition with limited volcanic input. The middle to upper Miocene Beluga Formation includes abundant argillaceous sedimentary lithic grains and records an upward increase in volcanogenic material. The up-section increase in volcanic detritus continues into the upper Miocene to Pliocene Sterling Formation. These first-order observations are interpreted to primarily reflect the waxing and waning of nearby arc magmatism. Available U-Pb detrital zircon geochronologic data indicate a dramatic reduction in zircon abundance during the early Eocene, and again during the Oligocene to Miocene, suggesting the arc was nearly dormant during these intervals. The reduced arc flux may record events such as subduction of slab windows or material that resisted subduction. The earlier hiatus in volcanism began ca. 56 Ma and coincided with a widely accepted model of ridge subduction beneath south-central Alaska. The later hiatus (ca. 25–8 Ma) coincided with insertion of the leading edge of the Yakutat terrane beneath the North American continental margin, resulting in an Oligocene to Miocene episode of flat-slab subduction that extended farther to the southwest than the modern seismically imaged flat-slab region. The younger tectonic event coincided with development of some of the best petroleum reservoirs in Cook Inlet.

Alaska↗

USGS2017

Energetic solutions of Rock Sandpipers to harsh winter conditions rely on prey quality

Rock Sandpipers Calidris ptilocnemis have the most northerly non-breeding distribution of any shorebird in the Pacific Basin (upper Cook Inlet, Alaska; 61°N, 151°W). In terms of freezing temperatures, persistent winds and pervasive ice, this site is the harshest used by shorebirds during winter. We integrated physiological, metabolic, behavioural and environmental aspects of the non-breeding ecology of Rock Sandpipers at the northern extent of their range to determine the relative importance of these factors in facilitating their unique non-breeding ecology. Not surprisingly, estimated daily energetic demands were greatest during January, the coldest period of winter. These estimates were greatest for foraging birds, and exceeded basal metabolic rates by a factor of 6.5, a scope of increase that approaches the maximum sustained rate of energetic output by shorebirds during periods of migration, but far exceeds these periods in duration. We assessed the quality of their primary prey, the bivalve Macoma balthica , to determine the daily foraging duration required by Rock Sandpipers to satisfy such energetic demands. Based on size-specific estimates of M. balthica quality, Rock Sandpipers require over 13 h/day of foraging time in upper Cook Inlet in January, even when feeding on the highest quality prey. This range approaches the average daily duration of mudflat availability in this region ( c . 18 h), a maximum value that annually decreases due to the accumulation of shore-fast ice. Rock Sandpipers are likely to maximize access to foraging sites by following the exposure of ice-free mudflats across the upper Cook Inlet region and by selecting smaller, higher quality M. balthica to minimize foraging times. Ultimately, this unusual non-breeding ecology relies on the high quality of their prey resources. Compared with other sites across their range, M. balthica from upper Cook Inlet have relatively light shells, potentially the result of the region's depauperate invertebrate predator community. Given the delicate balance between environmental and prey conditions that currently make Cook Inlet a viable wintering area for Rock Sandpipers, small variations in these variables may affect the suitability of the site in the future.

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USGS2015

Stratigraphic reconnaissance of the Middle Jurassic Red Glacier Formation, Tuxedni Group, at Red Glacier, Cook Inlet, Alaska

The Alaska Division of Geological & Geophysical Surveys (DGGS) and U.S. Geological Survey (USGS) are implementing ongoing programs to characterize the petroleum potential of Cook Inlet basin. Since 2009 this program has included work on the Mesozoic stratigraphy of lower Cook Inlet, including the Middle Jurassic Tuxedni Group between Tuxedni and Iniskin bays (LePain and others, 2013; Stanley and others, 2013; fig. 5-1). The basal unit in the group, the Red Glacier Formation (fig. 5-2), is thought to be the principal source rock for oil produced in upper Cook Inlet, and available geochemical data support this contention (Magoon and Anders, 1992; Magoon, 1994). Despite its economic significance very little has been published on the formation since Detterman and Hartsock’s (1966) seminal contribution on the geology of the Iniskin–Tuxedni area nearly 50 years ago. Consequently its stratigraphy, contact relations with bounding formations, and source rock characteristics are poorly known. During the 2014 field season, a nearly continuous stratigraphic section through the Red Glacier Formation in its type area at Red Glacier was located and measured to characterize sedimentary facies and to collect a suite of samples for analyses of biostratigraphy, Rock-Eval pyrolysis, vitrinite reflectance, and sandstone composition (fig. 5-3). The poorly known nature of the Red Glacier Formation is likely due to its remote location, steep terrain, and the fact that the type section is split into two segments that are more than 3 km apart. The lower 375 m segment of the formation is on the ridge between Red Glacier and Lateral Glacier and the upper 1,009 m segment is on the ridge between Red Glacier and Boulder Creek (fig. 5-3). Structural complications in the area add to the difficulty in understanding how these two segments fit together.

Alaska↗

USGS2013

Coping with the cold: An ecological context for the abundance and distribution of rock sandpipers during winter in upper Cook Inlet, Alaska

Shorebirds are conspicuous and abundant at high northern latitudes during spring and summer, but as seasonal conditions deteriorate, few remain during winter. To the best of our knowledge, Cook Inlet, Alaska (60.6˚ N, 151.6˚ W), is the world’s coldest site that regularly supports wintering populations of shorebirds, and it is also the most northerly nonbreeding location for shorebirds in the Pacific Basin. During the winters of 1997–2012, we conducted aerial surveys of upper Cook Inlet to document the spatial and temporal distribution and number of Rock Sandpipers (Calidris ptilocnemis) using the inlet. The average survey total was 8191 ± 6143 SD birds, and the average of each winter season’s highest single-day count was 13 603 ± 4948 SD birds. We detected only Rock Sandpipers during our surveys, essentially all of which were individuals of the nominate subspecies (C. p. ptilocnemis). Survey totals in some winters closely matched the population estimate for this subspecies, demonstrating the region’s importance as a nonbreeding resource to the subspecies. Birds were most often found at only a handful of sites in upper Cook Inlet, but shifted their distribution to more southerly locations in the inlet during periods of extreme cold. Two environmental factors allow Rock Sandpipers to inhabit Cook Inlet during winter: 1) an abundant bivalve (Macoma balthica) food source and 2) current and tidal dynamics that keep foraging substrates accessible during all but extreme periods of cold and ice accretion. C. p. ptilocnemis is a subspecies of high conservation concern for which annual winter surveys may serve as a relatively inexpensive population-monitoring tool that will also provide insight into adaptations that allow these birds to exploit high-latitude environments in winter.

Alaska↗

USGS2013

Ecological correlates of variable organ sizes and fat loads in the most northerly-wintering shorebirds

Shorebirds at northern latitudes during the nonbreeding season typically carry relatively large lipid stores and exhibit an up-regulation of lean tissues associated with digestion and thermogenesis. Intraspecific variation in these tissues across sites primarily reflects differences in environmental conditions. Rock (Calidris ptilocnemis (Coues, 1873)) and Purple (Calidris maritima (Brünnich, 1764)) sandpipers are closely related species having the most northerly nonbreeding distributions among shorebirds, living at latitudes up to 61°N in Cook Inlet, Alaska, and up to 71°N in northern Norway, respectively. Cook Inlet is the coldest known site used by nonbreeding shorebirds, and the region’s mudflats annually experience extensive coverage of foraging sites by sea and shore-fast ice. Accordingly, Rock Sandpipers increase their fat stores to nearly 20% of body mass during winter. In contrast, Purple Sandpipers exploit predictably ice-free rocky intertidal foraging sites and maintain low (<6.5%) fat stores. Rock Sandpipers increase the mass of lean tissues from fall to winter, including contour feathers, stomach, and liver components. They also have greater lean pectoralis and supracoracoideus muscle and liver and kidney tissues compared with Purple Sandpipers in winter. This demonstrates a combined emphasis on digestive processes and thermogenesis, whereas Purple Sandpipers primarily augment organs associated with digestive processes. The high winter fat loads and increased lean tissues of Rock Sandpipers in Cook Inlet reflect the region’s persistent cold and abundant but sporadically unavailable food resources.

Alaska↗

USGS2013

Constructing a reference tephrochronology for Augustine Volcano, Alaska

Augustine Volcano is the most historically active volcano in Alaska's populous Cook Inlet region. Past on-island work on pre-historic tephra deposits mainly focused on using tephra layers as markers to help distinguish among prevalent debris-avalanche deposits on the island (Waitt and Beget, 2009, USGS Prof Paper 1762), or as source material for petrogenetic studies. No comprehensive reference study of tephra fall from Augustine Volcano previously existed. Numerous workers have identified Holocene-age tephra layers in the region surrounding Augustine Island, but without well-characterized reference deposits, correlation back to the source volcano is difficult. The purpose of this detailed tephra study is to provide a record of eruption frequency and magnitude, as well as to elucidate physical and chemical characteristics for use as reference standards for comparison with regionally distributed Augustine tephra layers. Whole rock major- and trace-element geochemistry, deposit componentry, and field context are used to correlate tephra units on the island where deposits are coarse grained. Major-element glass geochemistry was collected for use in correlating to unknown regional tephra. Due to the small size of the volcanic island (9 by 11 km in diameter) and frequent eruptive activity, on-island exposures of tephra deposits older than a couple thousand years are sparse, and the lettered Tephras B, M, C, H, I, and G of Waitt and Beget (2009) range in age from 370-2200 yrs B.P. There are, however, a few exposures on the south side of the volcano, within about 2 km of the vent, where stratigraphic sections that extend back to the late Pleistocene glaciation include coarse pumice-fall deposits. We have linked the letter-named tephras from the coast to these higher exposures on the south side using physical and chemical characteristics of the deposits. In addition, these exposures preserve at least 5 older major post-glacial eruptions of Augustine. These ultra-proximal sites, along with an off-island section 20 km to the west, provide the first continuous tephrochronology for Augustine that extends from the earliest to latest Holocene. Because examined pumice-fall exposures are limited to a narrow azimuth on the south side of the volcano, the on-island record is likely an incomplete catalog of major eruptions. It is possible however, that the coarse-grained near vent exposures (within 2 km) represent large eruptions that blanketed the entire island in tephra and are representative of the entire Holocene record. The major Holocene tephra units exposed on-island are composed of coarse-grained (cm-scale) pumice ranging in color from white to cream (variably oxidized), and light to medium gray as well as banded varieties. Accidental lithic assembles are highly variable and often unique for individual eruptions. Pumices range from 60-66 wt % SiO2 in whole-rock composition and are distinguishable using trace and minor element abundances and field context. Glass geochemistry is often distinguishable between tephras, but more overlap exists among deposits and presents challenges for correlating to regional tephras.

Alaska↗

USGS2012

Geologic map of the Cook Inlet region, Alaska, including parts of the Talkeetna, Talkeetna Mountains, Tyonek, Anchorage, Lake Clark, Kenai, Seward, Iliamna, Seldovia, Mount Katmai, and Afognak 1:250,000-scale quadrangles

In 1976, L.B. Magoon, W.L. Adkinson, and R.M. Egbert published a major geologic map of the Cook Inlet region, which has served well as a compilation of existing information and a guide for future research and mapping. The map in this report updates Magoon and others (1976) and incorporates new and additional mapping and interpretation. This map is also a revision of areas of overlap with the geologic map completed for central Alaska (Wilson and others, 1998). Text from that compilation remains appropriate and is summarized here; many compromises have been made in strongly held beliefs to allow construction of this compilation. Yet our willingness to make interpretations and compromises does not allow resolution of all mapping conflicts. Nonetheless, we hope that geologists who have mapped in this region will recognize that, in incorporating their work, our regional correlations may have required some generalization or lumping of map units. Many sources were used to produce this geologic map and, in most cases, data from available maps were combined, without generalization, and new data were added where available. A preliminary version of this map was published as U.S. Geological Survey Open-File Report 2009–1108. The main differences between the versions concern revised mapping of surfical deposits in the northern and eastern parts of the map area. Minor error corrections have been made also.

Alaska↗

USGS2011

Gas emissions from failed and actual eruptions from Cook Inlet Volcanoes, Alaska, 1989-2006

Cook Inlet volcanoes that experienced an eruption between 1989 and 2006 had mean gas emission rates that were roughly an order of magnitude higher than at volcanoes where unrest stalled. For the six events studied, mean emission rates for eruptions were ~13,000 t/d CO 2 and 5200 t/d SO 2 , but only ~1200 t/d CO 2 and 500 t/d SO 2 for non-eruptive events (‘failed eruptions’). Statistical analysis suggests degassing thresholds for eruption on the order of 1500 and 1000 t/d for CO 2 and SO 2 , respectively. Emission rates greater than 4000 and 2000 t/d for CO 2 and SO 2 , respectively, almost exclusively resulted during eruptive events (the only exception being two measurements at Fourpeaked). While this analysis could suggest that unerupted magmas have lower pre-eruptive volatile contents, we favor the explanations that either the amount of magma feeding actual eruptions is larger than that driving failed eruptions, or that magmas from failed eruptions experience less decompression such that the majority of H 2 O remains dissolved and thus insufficient permeability is produced to release the trapped volatile phase (or both). In the majority of unrest and eruption sequences, increases in CO 2 emission relative to SO 2 emission were observed early in the sequence. With time, all events converged to a common molar value of C/S between 0.5 and 2. These geochemical trends argue for roughly similar decompression histories until shallow levels are reached beneath the edifice (i.e., from 20–35 to ~4–6 km) and perhaps roughly similar initial volatile contents in all cases. Early elevated CO 2 levels that we find at these high-latitude, andesitic arc volcanoes have also been observed at mid-latitude, relatively snow-free, basaltic volcanoes such as Stromboli and Etna. Typically such patterns are attributed to injection and decompression of deep (CO 2 -rich) magma into a shallower chamber and open system degassing prior to eruption. Here we argue that the C/S trends probably represent tapping of vapor-saturated regions with high C/S, and then gradual degassing of remaining dissolved volatiles as the magma progresses toward the surface. At these volcanoes, however, C/S is often accentuated due to early preferential scrubbing of sulfur gases. The range of equilibrium degassing is consistent with the bulk degassing of a magma with initial CO 2 and S of 0.6 and 0.2 wt.%, respectively, similar to what has been suggested for primitive Redoubt magmas.

Alaska↗

USGS2004

Testing archival tag technology in coho salmon

Archive tags with temperature and light-geolocation sensors will be monitored for post-smolt coho salmon in Cook Inlet. Light/location relationships specific to the Gulf of Alaska developed under Project 00478 will be applied in this study of movement and migration paths for coho salmon during maturation in ocean environments in Cook Inlet. Salmon for this study will be reared in captivity (at the Alaska Department of Fish and Game hatchery at Fort Richardson) to 1+ year of age (200-250mm) and released in Cook Inlet as part of the department's Ship Creek sport-fishing hatchery release. FY 01 includes pilot studies of tag retention, behavior, and growth for coho in captivity. Ship Creek coho will be tagged mid-May. A spring release experiment in the first year will be contingent on the successful implementation and retention of these tags. Surveys for early jack recoveries will be done at the Ship Creek weir and among sport fishers. Monitoring for adult tag recoveries will be done in the coho commercial fishery in Cook Inlet and the derby sport fishery on Ship Creek. Archive tagged fish will be used to document coho salmon use of marine habitats, migration routes, contribution to the sport fishery, and hatchery/wild interactions for salmon in Cook Inlet.

Alaska↗

USGS2002

Nitrogen dynamics in an Alaskan salt marsh following spring use by geese

Lesser snow geese ( Anser caerulescens caerulescens ) and Canada geese ( Branta canadensis ) use several salt marshes in Cook Inlet, Alaska, as stopover areas for brief periods during spring migration. We investigated the effects of geese on nitrogen cycling processes in Susitna Flats, one of the marshes. We compared net nitrogen mineralization, organic nitrogen pools and production in buried bags, nitrogen fixation by cyanobacteria, and soil and litter characteristics on grazed plots versus paired plots that had been exclosed from grazing for 3 years. Grazed areas had higher rates of net nitrogen mineralization in the spring and there was no effect of grazing on organic nitrogen availability. The increased mineralization rates in grazed plots could not be accounted for by alteration of litter quality, litter quantity, microclimate, or root biomass, which were not different between grazed and exclosed plots. In addition, fecal input was very slight in the year that we studied nitrogen cycling. We propose that trampling had two effects that could account for greater nitrogen availability in grazed areas: litter incorporation into soil, resulting in increased rates of decomposition and mineralization of litter material, and greater rates of nitrogen fixation by cyanobacteria on bare, trampled soils. A path analysis indicated that litter incorporation by trampling played a primary role in the nitrogen dynamics of the system, with nitrogen fixation secondary, and that fecal input was of little importance.

Alaska↗

USGS2000

Historic and current use of Lower Cook Inlet, Alaska, by Belugas, Delphinapterus leucas

Dedicated at-sea surveys for marine birds and mammals conducted in lower Cook Inlet in late July and early August from 1995–99 failed to locate any belugas, Delphinapterus leucas . Surveys covered a total of 6,249 linear km and were conducted in both nearshore and offshore habitats. Sightings included 791 individual marine mammals of 10 species. Both historical data and local knowledge indicate that belugas were regularly seen in summer in nearshore and offshore areas of lower Cook Inlet up until the early 1990’s. Diminished presence of belugas in lower Cook Inlet may be a direct function of reduced numbers but may also indicate changes in habitat quality that may inhibit recovery.

Alaska↗

USGS1999

Seasonal shorebird use of intertidal habitats in Cook Inlet, Alaska

Seasonal shorebird use of intertidal habitats of Cook Inlet, Alaska, was studied from February 1997 to February 1999 using aerial surveys as the principal method of assessment. On-ground studies were conducted to validate aerial survey results and to assess shorebird use of vegetated habitats, especially during the breeding season. Twenty-eight species of shorebirds were recorded using the area, ranging from all being present during spring to a single species present during winter. The annual pattern of use was characterized by the sudden occurrence and rapid increase in numbers of birds during early May and their abrupt departure in mid- to late-May. During this period, survey totals frequently exceeded 150,000 birds per day. Comparatively little use occurred during summer and autumn, but use was significant from late autumn to early spring when Rock Sandpipers ( Calidris ptilocnemis ) resided in the Inlet. A single species, the Western Sandpiper ( C. maun ), was by far the numerically dominant shorebird, accounting for three-fourths of all birds recorded. The Pacific flyway population of this species numbers 2-3 million birds of which we estimated 20-47% used Cook Inlet embayments, especially southern Redoubt Bay. Cook .Inlet also supported between 11 and 21% of the Pacific flyway population of Dunlin ( C. alpina pacifica ) and what may be the entire population (ca. 20,000 birds) of the nominate race of the Rock Sandpiper ( C. p. ptilocnemis ). Several areas along the west side of Cook Inlet proved to be extremely important to shorebirds. Southern Redoubt Bay supported 73% of all shorebirds during spring (average 32,000 per day) while Susitna Flats accounted for 82% of use during winter (8,400 per day). International criteria used to assess the conservation importance of particular wetland sites to shorebirds not only place Cook Inlet at the highest level of recognition but afford similar recognition to several individual embayments therein. The large human population and the extent of oil and natural gas production facilities occurring in the Cook Inlet region potentially pose serious risks to shorebirds and intertidal habitats.

Alaska↗

USGS1999

Biological effects of the 1997/98 ENSO in Cook Inlet, Alaska

We have been conducting detailed studies of the biology of seabirds in relation to oceanography and forage fish ecology in lower Cook Inlet, Alaska, since 1995. This fortuitously allowed us to document biological effects of the 1997/98 ENSO in this region. Anomalously warm sea surface temperatures (SSTs) were observed in the Gulf of Alaska (GOA) beginning in June of 1997, but not in Cook Inlet until September, 1997. Warm temperature anomalies at the surface and at depth persisted until May of 1998, when temperatures returned to average in the GOA and Cook Inlet. Thus, temperature anomalies occurred outside the core window of productivity (June–August) for forage fish and seabirds in both 1997 and 1998. Abundance or production of phytoplankton, zooplankton, fish, and seabirds in lower Cook Inlet varied among years, and overall appeared to be depressed in 1998. We observed a few biological anomalies that might be attributed to ENSO effects: (1) a significant die-off of Common Murres occurred in March–May of 1998, (2) murres and Black-legged Kittiwakes were physiologically stressed during the 1998 breeding season, (3) murres failed to reproduce at one colony in 1998, (4) kittiwake breeding success was lower than usual at colonies in 1998, and (5) phenology of breeding was later in 1998 for both murres and kittiwakes. We presume that seabird die-offs, reduced productivity and delayed phenology were linked to a reduction or delay in food availability, but the mechanism by which anomalously warm water temperatures in winter reduce forage fish availability during the summer breeding season for seabirds is not known.

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