The response of the Gulf of Alaska (GOA) circulation to large-scale North Pacific climate variability is explored using three high resolution (15 km) regional ocean model ensembles over the period 1950-2004. On interannual and decadal timescales the mean circulation is strongly modulated by changes in the large scale climate forcing associated with PDO and ENSO. Intensification of the model gyre scale circulation occurs after the 1976-1977 climate shift, as well as during 1965-1970 and 1993-1995. From the model dynamical budgets we find that when the GOA experiences stronger southeasterly winds, typical during the positive phase of the PDO and ENSO, there is net large-scale Ekman convergence in the central and eastern coastal boundary. The geostrophic adjustment to higher sea surface height (SSH) and lower isopycnals lead to stronger cyclonic gyre scale circulation. The opposite situation occurs during stronger northwesterly winds (negative phase of the PDO). Along the eastern basin, interannual changes in the surface winds also modulate the seasonal development of high amplitude anticyclonic eddies (e.g. Hada and Sitka eddies). Large interannual eddy events during winter-spring, are phase-locked with the seasonal cycle. The initial eddy dynamics are consistent with a quasi-linear Rossby wave response to positive SSH anomalies forced by stronger downwelling favorable winds (e.g. southwesterly during El Nio). However, because of the fast growth rate of baroclinic instability and the geographical focusing associated with the coastal geometry, most of the perturbation energy in the Rossby wave is locally trapped until converted into large scale nonlinear coherent eddies. Coastally trapped waves of tropical origin may also contribute to positive SSH anomalies that lead to higher amplitude eddies. However, their presence does not appear essential. The model ensembles, which do not include the effects of equatorial coastally trapped waves, capture the large Hada and Sitka eddy events observed during 1982 and 1997 and explain most of the variance of tidal gauges along the GOA coast. In the western basin, interannual eddy variability located south of the Alaskan Stream is not correlated with large scale forcing and appears to be intrinsic. A comparison of the three model ensembles forced by NCEP winds and a multi-century-long integration forced only with the seasonal cycle, shows that the internal variability alone explains most of the eddy variance. The asymmetry between the eddy forced regime in the eastern basin, and the intrinsic regime in the western basin, has important implications for predicting the GOA response to climate change. Eastern boundary eddies transport important biogeochemical quantities such as iron, oxygen and chlorophyll-a into the gyre interior, therefore having potential upscale effects on the GOA high-nutrient-low-chlorophyll region.

Recent studies indicate a 70% decrease in the Alaskan Steller sea lion (SSL) population (ca. 5% per year) since the early 1980's. In accordance with a 1997 status classification of the Western Steller sea lion (WSSL) stock as endangered, the "critical habitat" for the species was to be defined. This habitat has now been designated to include 10-20 nautical mile buffer zones around most rookeries and haulouts in the Gulf of Alaska (GOA) and Aleutian Islands. However, these zones were based on limited, summer, foraging data. The primary objective of this study was to characterize juvenile SSL diving behavior and habitat use along the Kenai Peninsula and Prince William Sound (PWS) from winter to spring. Fifteen free ranging, subadult SSL of both sexes were captured and equipped with satellite telemeters at five haulout sites in PWS and Resurrection Bay, Alaska. Telemeters transmitted for an average of 122 days (range 38-181 days). A total of 11,692 locations were received and 217,419 dives recorded. All sea lions exhibited localized movements parallel or close to shore (3-15 km offshore). Young of the year (YOY) exhibited high site fidelity. Older juvenile sea lion lions were less restricted in their movements and traveled greater distances (200-400km) visiting a variety of islands, buoys, and other locations in PWS. Most dives were short (mean duration = 1.1 min) and shallow (mean depth = 10.8 m), with animals diving to an average maximum depth of 193 m. During winter (January and February), many dives (>40%) occurred during the daytime (0900-1500 LT). However, by April and May this pattern shifted and the animals made most of their dives (>40%) during the night (2100-0300 LT). This relationship was more pronounced for dives deeper than 20 m and coincided with the seasonal increase in photoperiod. Subadult SSL, especially YOY, remained within the 20 nautical mile coastal zone during winter and spring. Shallow, nearshore waters provide important habitat during this critical period of transition to nutritional independence. However, more conclusive data on SSL foraging ecology is necessary to better understand locations and depths preferred by the species.

Collision of the Yakutat Terrane with North America in southern Alaska has driven growth of the Chugach-St. Elias orogen. Glaciation of the St. Elias Range has periodically increased since the Miocene, but began dominating erosion and spurred enhanced exhumation since the mid-Pleistocene transition at ~1 Ma. Ice associated with this glacial intensification carved cross-shelf sea valleys that connect the St. Elias Range to the deep-sea Surveyor Fan. A newly increased terrigenous sediment flux into the fan triggered the formation and growth of the Surveyor Channel. The change in geomorphology observed throughout Fan sequences allows us to characterize the influence that a glaciated orogen can have in shaping margin processes and the sediment pathways from source to sink. Seismic data also reveal an isolated, large, short runout, mass-transport deposit (MTD) buried in the Surveyor Fan. The MTD geometry, size and location on a convergent margin lend support to recent studies suggesting seismic strengthening and infrequent sediment failure on active margins. This study provides insight into the magnitude and scope of events required to cause submarine mega-slides and overcome higher than normal sediment shear strength, including the influence of climate and sea level change. Beneath the Surveyor Fan, integrated geophysical data reveals massive intraplate shearing, and a lack of oceanic crust magnetic lineaments in regions of Pacific Plate crust. We argue that stress from the Yakutat-North America collision transferred outboard to the Pacific Plate is the major driver for the deformation causing these features. This stress would have resulted in significant strain in the NE corner of the Pacific Plate, creating pathways for sill formation in the crust and Surveyor Fan. The collision further intensified as the thickest Yakutat portion began to subduct during the Pleistocene, possibly providing the impetus for the creation of the Gulf of Alaska Shear Zone, a >200 km zone of shear extending out into the Pacific Plate. This study highlights the importance of farfield stress from complex tectonic regimes in consideration of large-scale oceanic intraplate deformation. / text

High latitude mountain environments are experiencing disproportionately adverse effects in a currently changing climate. The Gulf of Alaska (GoA) region is an exemplar of this. Dramatic shifts are occurring in the region’s freshwater reservoirs as glaciers retreat more with each passing year. Research in the region places much focus on observing and predicting climate driven shifts in glacier mass balance, surface discharge, and associated nutrient fluxes to the ocean. On the other hand, coastal groundwater discharge (CGD) is given very little attention. Global and near-global estimates of CGD indicate variable results spanning an order of magnitude. Focusing on regionally specific processes may provide more reliable estimates of CGD and allow isolation of CGD hotspots. This is of particular importance in the GoA region where complex topography, geology, and climate are coupled with recharge derived from rain, snow, and ice. I estimate CGD to the GoA with a water balance that integrates high temporal and spatial resolution recharge inputs and distinguishes between high conductivity surficial deposit and bedrock catchments. I find that CGD contributes nearly 3% of the total freshwater flux to the GoA, equivalent to a mean annual flux of 20.8 km3, and that CGD has been increasing by 0.5%/year over the past 4 decades. Although freshwater discharge to the GOA is well-constrained, the importance of fresh CGD to the GoA has, thus far, been overlooked.

The Kittlitz's murrelet (Brachyramphus brevirostris) is a species of conservation concern over the entirety of its known range, which spans coastal Alaska and northeastern Russia. Concerns about the status of the species have been raised due to evidence of population declines in key breeding areas, low reproductive output, and perceived threats to adult survival. A general lack of information related to vital rates and natural history for this species has hampered efforts to address potential threats and drivers of population decline. This thesis addresses the hypothesis that foraging conditions and nutritional stress may be related to the observed low reproductive output and apparent population declines. I used stable isotope analysis of Kittlitz's murrelet feathers and blood to assess foraging habits during four separate periods across the annual cycle. I also used stable isotope signatures (δ¹⁵N and δ¹³C) in feathers from museum specimens collected in southeastern Alaska during 1907–1984 to investigate potential long-term trends in food habits and foraging ecology. I found that δ¹⁵N progressively increased by 5‰ between the vernal pre-alternate molt and the autumnal pre-basic molt, equivalent to an increase of 1.5 trophic levels for assimilated prey, whereas seasonal patterns in δ¹³C suggest shifts in foraging habitat between breeding and non-breeding periods. These results indicate that the pre-breeding diet was comprised primarily of low trophic level prey from offshore habitats, such as macrozooplankton and/or larval fish. During the summer breeding season, Kittlitz's murrelets gradually switched to consuming higher proportions of planktivorous fish from nearshore habitats. By the post-breeding period, during the pre-basic molt, the diet was comprised almost exclusively of higher trophic level prey, presumably forage fish, from offshore habitats. Based on stable isotope signatures of murrelet feathers from museum specimens, these seasonal patterns were evident during the past century (1907-2009). δ¹³C in feathers grown during pre- and post-breeding (pre-alternate and pre-basic molts, respectively) became significantly more depleted over the last century, however, suggesting either a gradual change in diet and/or foraging habitat or a long-term shift in the isotopic composition of prey. I investigated potential energy constraints on reproduction in Kittlitz's murrelets by constructing a bioenergetics model to estimate energy budgets for breeding adult Kittlitz's murrelets under different scenarios of prey energy content and commuting distance between foraging areas and nest sites. Estimated field metabolic rate (FMR) of breeding Kittlitz's murrelets during the chick-rearing period exceeded the hypothetical maximum sustainable working capacity (MSWC; 4 times basal metabolic rate [BMR]) under empirically derived scenarios of prey energy content and commuting distance. This suggests that, under conditions of low energy content in available prey and/or long commuting distances to inland nest sites, Kittlitz's murrelets would be required to expend energy at a rate that, if maintained over an extended period, could be detrimental to subsequent adult survival and overall fitness. In addition, energy expenditure rates at the high end of the estimated range may exceed the rate at which food energy can be assimilated by adult murrelets. Metabolism of fat reserves, as indicated by mass loss during the breeding season, may be a partial, although limited, solution to periods of high energy demand for breeding adults. This thesis research is the first to indicate that Kittlitz's murrelets rely on distinctly different prey resources during different periods of the annual cycle. The previously unappreciated seasonal complexity of Kittlitz's murrelet foraging ecology offers a new perspective on potential factors limiting survival and reproduction in this species of conservation concern. In addition, my research suggests an adaptive explanation for the low breeding frequency and low reproductive output of Kittlitz's murrelets that is related to the exceptionally high energy expenditure rates required to raise young at nest sites as much as 70 km inland from the coast and up to 2,500 m above sea level. Because of their high level of reproductive effort, Kittlitz's murrelets may be more dependent on the high availability of high-lipid marine prey than other seabirds. / Graduation date: 2012

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