Northeastern Gulf Of Alaska Research Articles

Clarifying Subspecies of Peregrine Falcons Along the Lost Coast of Alaska

Abstract The concept of subspecies is an important tool to help categorize and conserve biodiversity; thus, delineating the range of subspecies can have important management and conservation implications. The Peregrine Falcon (Falco peregrinus) is a widespread species that occurs throughout North America, where three subspecies are recognized: F. p. anatum, F. p. pealei, and F. p. tundrius. In Alaska, all three subspecies breed and their general distributions during the breeding season are well documented. However, the limits of their distributions were unclear or unconfirmed, especially those of F. p. anatum and F. p. pealei along the Lost Coast in the northeastern Gulf of Alaska. We describe plumage, morphology, and/or movements of Peregrine Falcons known to have nested (n = 6) or hatched (n = 3) within the Lost Coast and used this information to determine their subspecific group. For all nine birds, we found these characteristics to be consistent with F. p. anatum. Our results underscore the import...

A Climatology of Precipitating Open-Cell Convection over the Northeast Gulf of Alaska

AbstractThis brief paper addresses the frequency of precipitating open-cell convection over the northeastern Gulf of Alaska during a 5-yr period (2002–06). The research employs 154 previously documented satellite synthetic aperture radar–derived wind speed (SDWS) images that contain open-cell convection signatures. Each SDWS image is paired with a near-in-time, National Weather Service Weather Surveillance Radar-1988 Doppler Level-III 0.5°-elevation-angle short-range base reflectivity image from coastal Alaska for which coverage spatially overlaps open-cell convection signatures. The time difference between any two images of a single pair is typically a few minutes or less. For 65% of the image pairs, at least one SDWS open-cell convection signature in the overlap region is associated with precipitation. That percentage may be conservative given the method used in this research. Thus, the results of this research support a suggestion that has been posed in previous studies that the organization of open-cell convection can be controlled by the interaction of the environmental vertical wind shear and precipitation-driven cold pools.

Glider observations of kinematics in a Gulf of Alaska eddy

The depth‐radial structure of a Gulf of Alaska (GoA) eddy is investigated using observations from an autonomous winged buoyancy‐driven glider, drifters, and satellite altimeters. The eddy formed when Sitka and Yakutat eddies merged in June 2005. Sitka and Yakutat eddies form in the northeastern GoA and travel westward carrying anomalous energy, temperature, and chemical properties. The glider crossed the eddy seven times from mid‐August to late October 2005. A temperature maximum, at 130 m depth near the eddy's center, is indicative of coastal water. The strongest azimuthal current is 0.35 m s−1, occurring at 270 m depth and 17.5 km radius. The eddy's Rossby (Burger) number is 0.16 (0.47). Using a model with nonzero constant potential vorticity anomaly only within each depth's radius of strongest current, a function is fit to azimuthal current. The fit explains a large percentage of the current's radial variance, with a squared correlation coefficient of ≥0.9 at the depths of strongest current (270 m) and weakest stratification (360 m). Temporal trends in azimuthal volume transport rate and depth mean potential vorticity are not observed during the glider survey.

AN OVERVIEW OF THE LATE CENOZOIC BIVALVE PANOMYA IN JAPAN

Abundant fossil and modern specimens of the bivalve Panomya collected from Hokkaido, northern Japan, belong to five extant species, including P. norvegica and P. trapezoidis (both no longer present in Japan), and P. beringiana, P. nipponica, and P. ampla for modern specimens. I examine the taxonomy for these species around Japan and also for the extinct P. simotomensis and P. izumo from Japan and discuss the geographic history of Panomya. Panomya originated during the latest Oligocene to middle Miocene in the northeastern Gulf of Alaska. Subsequently, P. simotomensis and P. beringiana appeared in the early to late Miocene of northeastern Asia, while P. izumo and P. trapezoidis appeared in the middle to late Miocene of northeastern Asia and Alaska. Panomya nipponica, P. ampla, and P. norvegica appeared during the Plio–Pleistocene in northern Japan and Bering regions. All extant species evolved in the North Pacific; Panomya trapezoidis and P. norvegica extended their ranges to the North Atlantic in the middle Pliocene and early Pleistocene, respectively, and P. beringiana and P. ampla migrated into the Arctic Ocean in the late Pleistocene to Holocene.

A note on cross-shelf exchange in the northern Gulf of Alaska

The continental shelf of the Gulf of Alaska (GOA) is a complex system characterized by large freshwater runoff and strong winds. The GOA supports one of the world's richest ecosystems, including numerous species of fishes, marine mammals and sea birds. The mechanisms that provide nutrients to support this ecosystem are not well understood. The rivers and streams that provide freshwater to the shelf are low in nitrate, and the regional winds favor downwelling. High concentrations of nitrate are available in the deep basin of the GOA, but these must be introduced to the shelf in order to support the high productivity. We present evidence for cross-shelf exchange due to three different mechanisms. Episodes of downwelling relaxation result in a flux of saline, nutrient-rich water onto the shelf at depth. Eddies, formed in the northeastern GOA, propagate along the shelf-break influencing cross-shelf exchange by carrying shelf-origin water from the formation region into the basin and by interacting with the shelf-break circulation. Bathymetric steering in the many canyons that incise the GOA shelf results in flow into the canyons where strong tidal mixing results in cross-isobath movement of water properties.

Foraminiferal sequence biostratigraphy and seismic stratigraphy of a tectonically active margin; the Yakataga Formation, northeastern Gulf of Alaska

Upper Miocene through Recent glacial-marine deposits of the Yakataga Formation, which underlie the northern Gulf of Alaska continental shelf, are the focus of an integrated study to understand the depositional and climatic history of the upper Cenozoic Gulf of Alaska. Biostratigraphic, lithologie, and multichannel seismic data were integrated in a sequence stratigraphic analysis of the Yakataga continental margin. A paleontologically based approach to sequence stratigraphy, known as sequence biostratigraphy, was used to define eight seismic stratigraphic sequences on this tectonically active, glaciated continental margin. Foraminifera provide information on the age, paleoenvironments, and paleoclimates of strata within these eight sequences. Lithologic evidence is used to infer the presence and influence of tidewater glaciers.The three oldest sequences, arbitrarily labeled Brown, Red, and Orange (early Pliocene, mid-Pliocene, late Pliocene, respectively), were deposited in mainly outer neritic through upper bathyal environments. Planktic foraminiferal assemblages show that sea surface temperatures during deposition of these sequences were mainly cool temperate in the Gulf of Alaska at this time, yet benthic assemblages indicate cold bottom waters and dropstones indicate glacial-marine sedimentation during the late Pliocene.The five youngest sequences (labeled Yellow, Green, Aqua, Blue, Violet), which are Pleistocene to Recent in age, were deposited in deeper environments on average (upper bathyal to middle bathyal) than the older sequences. Glacial-marine sedimentation was common during deposition of these sequences (abundant dropstones) and foraminiferal assemblages indicate both cold sea surface and bottom water temperatures.

Intertidal boulder pavements in the northeastern Gulf of Alaska and their geological significance

Striated boulder pavements, consisting of planar concentrations of clasts having striated upper surfaces, are a common feature of glacigenic deposits but their origin is not well understood. Laterally extensive pavements are currently forming in the intertidal zone west of Icy Bay in the Gulf of Alaska. Pavements comprise “armoured” layers of interlocking boulders, one clast thick, that have been eroded from underlying outcrops of Late Cenozoic glaciomarine diamictites; they originate essentially as lag surfaces along a high energy, storm-dominated, mesotidal shoreline. Boulder pavements are either flat or show a “nucleated” plan form where successively smaller boulders have been accreted around a large core boulder. Nucleation imparts a hummocky surface topography to the pavements and suggests that some form of size sorting of clasts has occurred. Packing is promoted by repeated tamping of the clast lag by floating masses of glacier ice which become grounded across the intertidal zone at low tide. Repeated abrasion of the pavement surface by debris contained within ice blocks produces smooth, flattened clast upper surfaces and short, randomly oriented striations. Data from Icy Bay can be used to constrain the origin of laterally extensive boulder pavements exposed in Late Cenozoic glaciomarine sediments on Middleton Island. The significance of such pavements in the geologic record is that they form along erosional unconformities and may identify sequence boundaries.

Molluscan evidence for early middle Miocene marine glaciation in southern Alaska

Profound cooling of Miocene marine climates in southern Alaska culminated in early middle Miocene coastal marine glaciation in the northeastern Gulf of Alaska. This climatic change resulted from interaction of the Yakutat terrane with southern Alaska beginning in late Oligocene time. The ensuing extreme uplift of the coastal Chugach and St. Elias Mountains resulted in progressive regional cooling that culminated in coastal marine glaciation beginning in the early middle Miocene (15-16 Ma) and continuing to the present. The counterclockwise flow of surface water from the frigid northeastern Gulf of Alaska resulted in a cold-temperate shallow-marine environment in the western Gulf of Alaska, as it does today. Ironically, dating of Gulf of Alaska marine glaciation as early middle Miocene is strongly reinforced by the presence of a few tropical and subtropical mollusks in western Gulf of Alaska faunas. Shallow-marine waters throughout the Gulf of Alaska were cold-temperate to cold in the early middle Miocene, when the world ocean was undergoing peak Neogene warming.

Sediment Instability in the Northeastern Gulf of Alaska: A Retrospective: ABSTRACT

Sediment Instability in the Northeastern Gulf of Alaska: A Retrospective: ABSTRACT

Causes of two slope-failure types in continental-shelf sediment, northeastern Gulf of Alaska: Schwab, W C; Lee, H J J Sediment PetrolV58, N1, Jan 1988, P1–11

Causes of two slope-failure types in continental-shelf sediment, northeastern Gulf of Alaska: Schwab, W C; Lee, H J J Sediment PetrolV58, N1, Jan 1988, P1–11

New Species of Limpets from the Neogene of Alaska (Patellogastropoda: Mollusca)

Two new species of patellogastropod limpets from the Miocene-Pliocene of Alaska are described - Patelloida gradatus new species from the Unga Conglomerate Member of the Bear Lake Formation at Cape Aliaksin, Alaska Peninsula, southwestern Alaska, and Niveotectura myrakeenae new species from the Yakataga Formation in the northeastern Gulf of Alaska. A third species from the Narrow Cape Formation of Kodiak Island may be referrable to Patelloida sookensis Clark and Arnold, 1923, a species previously known only from Vancouver Island, Canada. These and other species of Patelloidinae dominated the northeastern Pacific patellogastropod fauna for over 60 m/y. The presence in Alaska of these three warm-water limpet species may be related to the middle Miocene warm-water event that is well documented elsewhere in the North Pacific. However, regional cooling during the late Neogene drove this predominantly tropical group from higher latitudes, leaving them poorly represented in the Holocene boreal fauna.Key words: paleontology, historical biogeography, paleoecology, fossil gastropods, Miocene, Patellogastropoda, Patelloida, limpets

Causes of Two Slope-Failure Types in Continental-Shelf Sediment, Northeastern Gulf of Alaska

ABSTRACT Slumps and sediment-gravity flows have been identified in Holocene glaciomarine sediment on declivities less than 1.3° on the Gulf of Alaska continental shelf. Geologic and geotechnical investigation suggest that the processes responsible for these slope failures are earthquake and storm-wave loading, coupled with cyclic degradation of the sediment-shear strength. We propose that the failure type is related to the nature of the failure load. For example, a slump that occurs approximately 30 km seaward of Icy Bay in water depth of 70 to 150 m was most likely caused by earthquake loading, whereas sediment-gravity flows on the Alsek prodelta, which occur in water depths of 35 to 80 m, probably were caused primarily by storm-wave loading. Sediment remolding and redistribution and inco poration of water, which occurs more readily during wave loading from a long storm than during the limited number of loading cycles generated by an earthquake, reduces the shear strength and increases the fluidity of the failed sediment mass. Wave-induced slope failures thereby tend to transform into sediment-gravity flows.

Clay Mineralogy of a Glacially Dominated, Subarctic Continental Shelf: Northeastern Gulf of Alaska

ABSTRACT Glaciation is the single most important process responsible for contributing sediment to the northeastern Gulf of Alaska continental shelf. Over 75 percent of the northeastern gulf's drainage basin is presently ice-covered or only recently has emerged from beneath Holocene glacial ice. Many glaciers terminate in rivers that drain into the gulf or terminate in tidewater bays. This study examines the mineralogy of the northeastern Gulf of Alaska continental shelf clay minerals in light of the glacially dominant nature of the area. Analyses of 110 bottom samples from the Gulf of Alaska continental shelf between Icy Point and Prince William Sound show an average clay mineral assemblage of 61 percent kaolinite + chlorite, 37 percent illite, and 2 percent smectite. Over most of the shelf deviations from the average composition are generally <10 percent. One significant exception is an area south of the Copper River where illite content is as high as 65 percent and kaolinite + chlorite ranges from 35 to 48 percent. Suspended-sediment and bottom samples collected in successive years from the Copper River, the largest sediment source to the gulf, have variations in clay mineralogy suggesting that different tributaries and hence different source areas control the composition of the river's mineralogy during different years. Upper river sources are rich in kaolinite + chlorite whereas illite-rich sediment is introduced in the lower 100 km. Transportation of sediment south of the Copper River, across the shelf, and into Prince William Sound is documented by a decrease in illite from a continental shelf point source south of the river's mouth. In addition to modern fluvial input, a second source of the modern shelf sediment appears to be the glacially derived Miocene to Quaternary Yakataga Formation. Older formations such as the Poul Creek and Katalla Formations show fewer compositional similarities to nearby shelf sediment.

The chemistry and vertical flux of particles in the northeastern Gulf of Alaska

The physical and chemical compositions of settling particles and underlying sediments collected from a pristine coastal environment south of Icy Bay in the northeastern Gulf of Alaska were compared to investigate the processes affecting the compositions, flux, and early diagenesis of the materials. Settling particles were collected with three self-closing sediment traps moored vertically approximately 30 km offshore. Sediments collected by gravity coring at the site were dated by 210Pb geochronology. Total particulate Al, Si, Cr, Mn, Fe, Ni, Cu, Zn, and Pb were determined on all samples by flameless atomic absorption and standard colorimetric procedures. Total C and N were determined by dry combustion gas chromatography. A dilute hydrogen peroxide oxidation dissolution treatment was used to study element associations with labile particulate organic matter. A selective biogenic SiO 2 dissolution treatment also was employed to determine the biogenic SiO 2 fraction. Results suggest that the sediment traps efficiently collected settling particles. The elemental accumulation rates, remineralization of particulate organic matter, and remobilization of trace elements, notably Cu, were quantified by comparing the composition of the trapped materials with the underlying sediments. The majority of the remineralization appears to occur within the sediments below the zone influenced by resuspension, presumably as a result of biological activity.

Holocene Slump on Continental Shelf Off Malaspina Glacier, Gulf of Alaska

Bottom features on the earthquake- and storm-prone continental shelf of the northeastern Gulf of Alaska indicate mass movement of about 1,080 sq km of the seafloor. A total of 29 high-resolution seismic reflection lines was run across the area south of Icy Bay and the Malaspina Glacier on five cruises between September 1974 and June 1976. The reflection profiles show disrupted bedding and irregular topography, characteristics associated with submarine slides and slumps. The slump structures are in water depths of 70 to 150 m on a slope of less than 0.5°, are about 0.5 km long (front to back), have a relief of 2 to 5 m, and consist of low-strength, poorly sorted, clayey silt. The base of individual slump blocks lies at a depth in the Holocene sediment of 35 to 50 m. A the landward edge of the slump area, side-scan sonar records show small irregular, curvilinear features approximately parallel with the contours. These features are interpreted as incipient scarps and suggest a headward growth of the slump mass. The most likely triggering mechanism for this mass movement is one or more of the numerous earthquakes that have occurred in this highly seismic region. The slump features cannot be related to a specific earthquake; however, the presence of numerous faults on the continental shelf and adjacent coastal area plus the abundance of historic earthquakes in the region indicate that prolonged ground shaking is common and of sufficient intensity to cause the mass movement of the unstable sediment.

Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska: Discussion and reply

Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska: Discussion and reply

Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska: Discussion and reply

Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska: Discussion and reply

Late Cenozoic volcanism in the Aleutian Arc: Information from ash layers in the northeastern Gulf of Alaska

A sequence of ash layers recovered from site 178 of the Deep Sea Drilling Project in the Gulf of Alaska was studied to determine the nature of highly explosive volcanic eruptions associated with the Aleutian Arc and Alaskan Peninsula during the last 8 m.y. The major-element chemistry of 25 distinct ash layers was determined. When the analyses are plotted on conventional major-element variation diagrams, the unusual, highly evolved, calc-alkalic characteristics of the ashes are apparent. Perhaps more significantly, there is a good correlation of certain indices of the degree of chemical evolution of each ash (SiO2 content and Larsen index) with sample age. Both parameters vary cyclically, with maximum values of both indices occurring at present, 2.5, and about 5.0 m.y. ago. The cause of the cyclic activity, as well as discontinuous volcanic activity reported for other areas by other investigators, is not precisely known. However, we suggest that variable rates of subduction provide a viable hypothesis for discontinuous volcanic activity associated with convergent plate boundaries.

Sedimentation on Gravel Outwash Fans, Malaspina Glacier Foreland, Alaska

ABSTRACT Three depositional facies occur on the outwash fans of Fountain Stream and Alder Stream, which presently drain portions of the Malaspina Glacier along the northeastern Gulf of Alaska. Deposition of longitudinal bars occurs during high-flow stage and consists of plane-bedded, imbricate, very poorly sorted pebble and cobble gravels. The sediment of the bars decreases in mean size downstream. Some bars terminate in avalanche slip faces of poorly sorted, silty, medium to coarse sand. Paleocurrent directions suggest that stream flow diverges across bar surfaces. Deposition in channels occurs in two morphologically distinct areas, riffles and pools. Sediment deposited in pools consists primarily of ripple cross-laminated, poorly sorted, silty, medium to coarse sand, commonly capped by draped lamination. Ripple crests vary from straight to cuspate. Sediment in riffles consists of gravel laid down under upper flow regime conditions as transverse ribs and stone cells. Both apparently are relict antidune bedforms. During late-stage flow, thin patches of horizontally bedded sand are deposited between transverse ribs and adjacent stone-cell borders. The longitudinal bar facies and channel pool facies are common in cutbank sections. The channel riffle facies was not recognized in cutbank sections. Scour pits, commonly observed on some bar surfaces, are produced by currents scouring around grounded ice blocks. Ice-block trails are produced by ice blocks dragged through soft sediment. Neither of these sedimentary structures have been reported in the literature. If found in ancient sediments, both structures would indicate a nearby source of ice.