Eastern Prince William Sound Research Articles

Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska

Abstract We present new marine seismic‐reflection profiles and bathymetric maps to characterize Holocene depositional patterns, submarine landslides, and active faults beneath eastern and central Prince William Sound (PWS), Alaska, which is the eastern rupture patch of the 1964 M w 9.2 earthquake. We show evidence that submarine landslides, many of which are likely earthquake triggered, repeatedly released along the southern margin of Orca Bay in eastern PWS. We document motion on reverse faults during the 1964 Great Alaska earthquake and estimate late Holocene slip rates for these growth faults, which splay from the subduction zone megathrust. Regional bathymetric lineations help define the faults that extend 40–70 km in length, some of which show slip rates as great as 3.75 mm/yr. We infer that faults mapped below eastern PWS connect to faults mapped beneath central PWS and possibly onto the Alaska mainland via an en echelon style of faulting. Moderate ( M w >4) upper‐plate earthquakes since 1964 give rise to the possibility that these faults may rupture independently to potentially generate M w 7–8 earthquakes, and that these earthquakes could damage local infrastructure from ground shaking. Submarine landslides, regardless of the source of initiation, could generate local tsunamis to produce large run‐ups along nearby shorelines. In a more general sense, the PWS area shows that faults that splay from the underlying plate boundary present proximal, perhaps independent seismic sources within the accretionary prism, creating a broad zone of potential surface rupture that can extend inland 150 km or more from subduction zone trenches.

A Comprehensive Study of the Seismicity of the Kenai Peninsula-Cook Inlet Region, South-Central Alaska

Abstract We compare 30 yr of background seismicity of the Kenai Peninsula–Cook Inlet region (extending from eastern Prince William Sound–Kayak Island to west of the Cook Inlet volcanic arc) to potential field (gravity, magnetics), tomographic, Global Positioning System–geodesy, and geologic information to better determine factors controlling seismicity. We also compare the occurrence of M w >5 events over the past 80–100 yr to background seismicity in an effort to determine how reflective background seismicity is of the regional seismic hazard. Our results indicate that contrasts in upper plate rheology leading to changes in density, magnetic susceptibility, and velocity of the upper plate serve to concentrate seismicity. The southwestern edge of the subducting Yakutat microplate has a strong influence on both upper and lower plate seismicity. Density and velocity contrasts also indicate changes in lower plate rheology that influence the location of deeper (>30 km) seismicity and the occurrence of a double seismic zone within the subducting Pacific plate.

INFECTIOUS DISEASE AND THE DECLINE OF STELLER SEA LIONS (EUMETOPIAS JUBATUS) IN ALASKA, USA: INSIGHTS FROM SEROLOGIC DATA

Serologic data were examined to determine whether infectious disease may have played a role in the decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands, USA. Available published data, unpublished data, and recent collections (1997-2000) were compared and reviewed. Data were stratified by geography to compare the declining western Alaskan population in the Aleutian Islands through eastern Prince William Sound to the increasing population in southeastern Alaska. Prevalences of antibodies from the 1970s to the early 1990s were noted for Leptospira interrogans, Chlamydophila psittaci, Brucella spp., phocid herpesvirus-1, and calciviruses. Serum samples collected from 1997-2000 were tested for antibodies to these agents as well as to marine mammal morbilliviruses, canine parvovirus, and canine adenovirus-1 and -2. Conclusions could not be drawn about changes in antibody prevalence to these agents during the decline of Steller sea lions, however, because data were incomplete or not comparable as a result of inconsistencies in testing techniques. Despite these shortcomings, results provided no convincing evidence of significant exposure of Steller sea lions to morbilliviruses, Brucella spp., canine parvovirus, or L. interrogans. Steller sea lions have been exposed to phocid herpesviruses, caliciviruses, canine adenovirus, and C. psittaci or to cross-reactive organisms in regions of both increasing and decreasing sea lion abundance. Based on similar antibody prevalence estimates from the increasing and decreasing populations, these agents are unlikely to have been the primary cause of the population decline. They may have contributed to the decline or impeded population recovery, however, because of undetected mortality and morbidity or reductions of fecundity and body condition in animals under other stresses. Systematic monitoring for disease agents and their effects is needed to determine whether infectious disease currently plays a role in the decline and lack of recovery of Steller sea lions.

Correlates to survival of juvenile sea otters in Prince William Sound, Alaska, 1992–1993

We estimated survival of sea otters (Enhydra lutris) for 1 year post weaning during 1992–1993 in Prince William Sound (PWS), location of the 1989 Exxon Valdez oil spill. We sampled 38 pups in eastern PWS (EPWS), an unoiled area occupied by sea otters for <15 years, and 33 pups from oiled western PWS (WPWS), occupied for >25 years. We compared survival between areas, sexes, and condition groups. We also examined the relation of blood parameters to survival. Survival was estimated at 0.74 in EPWS and 0.52 in WPWS. Female survival was 0.86 in EPWS and 0.64 in WPWS, whereas male survival was lower, 0.61 in EPWS and 0.44 in WPWS. Sea otters from EPWS were in better condition (mass/length) than WPWS sea otters. Pups in better condition had higher survival in EPWS but not in WPWS. Foraging success was greater in EPWS than in WPWS, consistent with either an effect of length of occupation or the effects of oil on the prey base or a combination of these effects. Area differences in blood parameters suggested liver damage in WPWS sea otters, perhaps resulting from continued exposure to oil. Thus, both length of occupation and oiling history likely influenced juvenile survival in PWS.

A synthesis of the life history and ecology of juvenile Pacific herring in Prince William Sound, Alaska

AbstractPhysical and biological variables affecting juvenile Pacific herring (Clupea pallasi) in Prince William Sound (PWS) from 1995 to 1998 were investigated as part of a multifaceted study of recruitment, the Sound Ecosystem Assessment (SEA) program. Though more herring larvae were retained in eastern PWS bays, ages‐0 and ‐1 herring used bays throughout PWS as nursery areas. Water transported into PWS from the Gulf of Alaska (GOA) contributed oceanic prey species to neritic habitats. Consequently, variations in local food availability resulted in different diets and growth rates of herring among bays. Summer food availability and possible interspecific competition for food in nursery areas affected the autumn nutritional status and juvenile whole body energy content (WBEC), which differed among bays. The WBEC of age‐0 herring in autumn was related to over‐winter survival. The limited amount of food consumption in winter was not sufficient to meet metabolic needs. The smallest age‐0 fish were most at risk of starvation in winter. Autumn WBEC of herring and winter water temperature were used to model over‐winter mortality of age‐0 herring. Differences in feeding and energetics among nursery areas indicated that habitat quality and age‐0 survival were varied among areas and years. These conditions were measured by temperature, zooplankton abundance, size of juvenile herring, diet energy, energy source (GOA vs. neritic zooplankton), WBEC, and within‐bay competition.

A REASSESSMENT OF THE IMPACT OF THEEXXON VALDEZOIL SPILL ON HARBOR SEALS (PHOCA VITULINA RICHARDSI) IN PRINCE WILLIAM SOUND, ALASKA

AbstractAnalyses of population trends and movements of harbor seals in Prince William Sound (PWS) casts doubt on published findings that 302 seals were killed by theExxon Valdezoil spill in 1989. Assumptions that seals have 100% fidelity to a haul‐out, that they were not displaced by the spill and associated disturbances, and that population trends throughout PWS varied similarly, except for oil spill effects, are not supported. Survey efforts to account for missing seals in 1989 were incomplete, too late in the year, and geographically limited. Basic assumptions required for statistical comparisons of oiled and unoiled haul‐outs were violated. Fourteen dead seals, mostly pups, were recovered in PWS. Cause of death in most instances could not be determined, nor could the proportion that would have died naturally. Evidence does not support high unsubstantiated mortality, but is more consistent with seals avoiding or moving away from some oiled haul‐outs. Interpretation of survey results requires consideration of temporal and regional variation. “Route A” surveys of central and eastern PWS do not represent population trends in western PWS or at glacial haul‐outs. To adequately monitor population trends of PWS as a whole, broader sampling must be conducted on a routine basis.

Flow Cytometric Determination of Genotoxic Effects of Exposure to Petroleum in Mink and Sea Otters

Three experiments were conducted to investigate the genotoxic effects of crude oil on mink and sea otters. In the first experiment, the effects on mink of chronic exposure to weathered Prudhoe Bay crude oil were studied. Female mink were fed a diet that included weathered crude oil for a period of 3 weeks prior to mating, during pregnancy and until weaning. Kits were exposed through lactation and by diet after weaning until 4 months of age. Kidney and liver tissues of the kits were examined using flow cytometry (FCM) and it was found that the genome size was increased in kidney samples from the experimental group compared to the control group. This effect was probably due to some type of DNA amplification and it could have been inherited from the exposed mothers or have been a somatic response to oil exposure in the pups. No evidence of clastogenic effects, as measured by the coefficient of variation (CV) of the G1 peak, was found in kidney or liver tissue. In the second experiment, yearling female mink were exposed either by diet or externally to crude oil or bunker C fuel oil. Evidence for clastogenic damage was found in spleen tissue for the exposure groups, but not in kidney tissue. No evidence of increased genome size was observed. In the third experiment, blood was obtained from wild-caught sea otters in Prince William Sound. The sea otters represented two populations: one from western Prince William Sound that was potentially exposed to oil from the Exxon Valdez oil spill and a reference population from eastern Prince William Sound that did not receive oil from the spill. The spill had occurred 1.5 years prior to obtaining the blood samples. Although the mean CVs did not differ between the populations, the exposed population had a significantly higher variance of CV measurements and five out of 15 animals from the exposed population had CVs higher than the 95% confidence limits of the reference population. It is concluded that FCM is a sensitive indicator of the clastogenic effects of oil exposure and that haematopoietic tissues and blood are best for detecting clastogenic damage. Moreover, the observed differences in the genome size of the kidney cells were possibly heritable effects, but this needs further investigation. Lastly, sea otters exposed to spilled oil 1.5 years earlier showed evidence of clastogenic damage in one-third of the individuals sampled.

Fatty acid signatures reveal fine scale structure of foraging distribution of harbor seals and their prey in Prince William Sound, Alaska

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 151:255-271 (1997) - doi:10.3354/meps151255 Fatty acid signatures reveal fine scale structure of foraging distribution of harbor seals and their prey in Prince William Sound, Alaska Iverson SJ, Frost KJ, Lowry LF Fatty acid signature analysis was used to investigate the diet and the spatial scales of foraging in harbor seals Phoca vitulinarichardsi in Prince William Sound (PWS) and elsewhere in the Gulf of Alaska. Blubber samples collected in 1994 and 1995 from 104 harbor seals from PWS, Kodiak Island, and southeast Alaska were analyzed for fatty acid composition. A total of 163 potential prey samples representing 10 taxa were collected and individually analyzed for total fat content and fatty acid composition. Approximately 70 fatty acids and isomers were found in both harbor seals and their prey. Classification and regression tree analysis was used to classify seals and prey according to their fatty acid signatures. Large differences were found in the fatty acid composition of blubber from seals sampled at Kodiak, southeast Alaska and PWS, over a broad geographical scale of 400 to 800 km. Additionally, fatty acid signatures distinguished seals from different regions within PWS, as well as on fine-scale resolutions of specific haulout sites within 9 to 15 km of one another. These findings suggest that seals forage site-specifically. These conclusions are supported by prey fatty acid patterns, which also differed on similarly small spatial scales within PWS. Not only could prey species such as herring Clupea pallasi and pollock Theragra chalcogramma be differentiated from one another using fatty acid signatures, but they could also be distinguished by size-class and location within PWS, reflecting differences in diet with age and as well as with fine-scale habitat. Results from this study are consistent with both satellite data from tagged harbor seals and stomach content analyses of forage fish species in PWS. Although preliminary, analyses suggest that large herring and pollock, as well as flatfish, may have dominated the diet of seals in southern PWS, whereas diets of seals in northern and eastern PWS may have been comprised more of small size classes of herring and pollock, and perhaps other items such as cephalopods, sandlance Ammodyteshexapterus, cod Gadus macrocephalus, and shrimp. We conclude that fatty acid signature analysis will be an important contribution to understanding marine food webs in estuarine and other marine environments. Foraging ecology · Fatty acid signatures · Harbor seals · Fish · Spatial scales Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 151. Publication date: May 22, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Strike‐slip faulting and block rotation along the contact fault system, eastern Prince William Sound, Alaska

The Chugach and Prince William terranes compose a Mesozoic through Paleogene accretionary complex rimming the Gulf of Alaska. In eastern Prince William Sound, we studied the Contact fault system, which juxtaposes flysch of the latest Cretaceous Valdez Group (Chugach terrane) with flysch of the late Paleocene through early Eocene Orca Group (Prince William terrane). Near Valdez, we found three lithotectonic belts separated by right‐lateral strike‐slip faults. Anomalous structural trends between the two faults appear to be the result of clockwise block rotation in response to dextral shear. In a second area, to the east near Cordova, early formed folds were rotated clockwise before burial to depths sufficient to form axial‐planar cleavage. Apparently, synchronous thrusting and dextral‐slip faulting occurred during accretion. The relations above, combined with earlier studies, suggest that the fundamental nature of motion on faults composing the Contact fault system is dextral. Near Cordova, deposition, accretion, and block rotation occurred between early Eocene and early middle Eocene time. Near Valdez, block rotation appears to have occurred prior to accretion of the rocks near Cordova. Current plate tectonic models show that convergence became progressively more oblique during Eocene time, correlating well with the initiation of strike‐slip faulting. The presence of early Tertiary dextral‐slip faults, such as these, helps account for the northward displacement of the Chugach‐Prince William terrane with respect to the Peninsular and Wrangellia terranes suggested by paleomagnetic and geologic studies.

Tectonic implications of out‐of‐sequence faults in an Accretionary Prism, Prince William Sound, Alaska

The Chugach and Prince William terranes constitute a Mesozoic through Tertiary accretionary complex bordering the Gulf of Alaska. Faults of the Contact fault system juxtapose the two terranes. Across the previously mapped trace of the Contact fault in western Prince William Sound, we studied three belts of alternately higher and lower deformation intensity and metamorphism. Out‐of‐sequence reverse faults separate these belts. Until recently, researchers assumed that the Prince William terrane was accreted to the Chugach terrane along the Contact fault. However, our work supports an emerging view that the Chugach and Prince William terranes represent older and younger parts of a continuously evolved accretionary prism, best considered a single terrane. We found that we cannot distinguish the Chugach from the Prince William terrane on the basis of lithology, deformation, or metamorphism; therefore, we cannot precisely identify the local strand of the Contact fault system. Furthermore, the major faults in the study area are relatively late‐stage features, related not to initial accretion but rather to internal deformation of the prism. West‐northwest shortening characterizes the deformation along the Contact fault system in western Prince William Sound, whereas dextral‐slip faulting characterizes the deformation along the Contact fault system in eastern Prince William Sound. We ascribe this difference to development of the Alaska orocline coeval with changes in plate motions during Eocene time, which resulted in convergence in western Prince William Sound remaining relatively orthogonal while convergence in eastern Prince William Sound became increasingly oblique.

Pollen Profiles from Prince William Sound and Southeastern Kenai Peninsula, Alaska

Two earlier papers discussed the pollen and peat stratigraphy of southeastern Alaska muskegs and its relation to postglacial phytogeography, climate, glacier variation, land-sea level fluctuation, and vulcanism (Heusser 1952, 1954). In an effort to extend these studies to the northwest along the border of the Gulf of Alaska, five peat sections were taken from muskegs in coastal southern Alaska, on southeastern Kenai Peninsula, and on eastern Prince William Sound. The localities at which muskegs have been sampled are shown by number on the accompanying sketch map (Fig. 1). One of the objectives of this paper is to trace the postglacial dispersal of the trees of the Coast Forest Formation in this district. Furthermore, since the district is at present part of an ecotone or transition between tundra and the coast forest (Cooper 1942), another objective is to show the postglacial relation of these two formations. The study region is also of interest in that it represents the northern terminus for two members of the coast forest. Western hemlock (Tsuga heteroPhvllal), which comprises almost 75 per cent of this forest in the Alexander Archipelago (Taylor 1932), 500 to 800 rniles southeastward, and Alaska yellow cedar (Chamaecyparis nootkatensis) extend as far as western Prince Williamn Sound. Recent palynological investigations by Livingstone (1953), Hansen (1953), and the Alaska Terrain and Permafrost Section of the U. S. Geological Survey (William S. Benninghoff, personal communication) and those made earlier by Bowman (1934) and Knox (Judson 1946) are gradually unfolding the postglacial and earlier Pleistocene events in the Territory. Geologists, in addition, are making a concerted effort to map the Pleistocene glaciations and construct a chronology (Pewe, et al. 1953). It is the purpose of this paper to add to this evolving store of information and at the same time to augment our knowledge of the postglacial development of the Coast Forest Formation as we know it today. Field work connected with this study was supported by a Sigma Xi-Resa Grant-in-Aid and a grant from the Glacier Study Project of the American Geographical Society. Travel to the Territory was afforded by the Juneau Ice Field ResearclhL Project which is administered by the 'Nomenclature follows Hulten (1941-1950) ; in some cases plant names given in references cited in the text have been changed to follow Hulte'n.