Browsing by Subject "Gulf of Alaska"
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Item Characterizing the winter movements and diving behavior of subadult Steller sea lions (eumetopias jubatus) in the north-central Gulf of Alaska(Texas A&M University, 2007-04-25) Briggs, Holly BethRecent 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.Item The impact of climate and tectonics on sedimentary and deformational processes, Gulf of Alaska(2012-12) Reece, Robert Sherman; Gulick, Sean P. S.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.Item Seismic and morphologic analysis of the Gulf of Alaska Yakutat margin : evidence for recent trough mouth fan growth(2014-08) Swartz, John Marshall; Gulick, Sean P. S.; Goff, John; Catania, GinnyThe active St. Elias Orogen in southern Alaska was created by collision of the offshore Yakutat Terrane with North America. These mountains exhibit the highest coastal relief in the world and also are home to temperate tidewater glaciers, one of the most powerful erosive agents known. Glaciation in Southern Alaska has occurred since the Miocene, but climatic shifts associated with the intensification of Northern Hemisphere glaciation at ~2.5 Ma and the mid-Pleistocene transition at ~1 Ma have led to drastic increases in glacial erosion and associated offshore sediment transport and deposition. The Yakutat continental shelf has hosted ice streams during glacial advances since the mid-Pleistocene, but it is only recently that ice has reached the continental shelf edge itself. Quantitative morphologic analysis finds significant variability along the slope, with an relatively gentle gradient trough mouth fan building off the Yakutat Sea Valley, a shelf-crossing glacial trough, due to massive sediment supply from the heart of the St. Elias Orogen, while farther to the east the extremely steep continental margin is heavily gullied and sediment bypasses the slope reaching the offshore Surveyor fan. Seismic stratigraphy indicates that ice streams first reached the shelf edge with the mid-Pleistocene climate transition, a shift from 41 ka to 100 ka glacial-interglacial climate cycles. This increase in glacial durations allowed not only the ice to sustain advances to the shelf edge, but led to amplified erosion and climate-tectonic feedback effects.Item Seismic stratigraphy and paleo-glaciology of Sabrina Coast, East Antarctica and Bering Trough, Gulf of Alaska(2015-05) Montelli, Aleksandr; Gulick, Sean P.S.; Blankenship, Donald; Mohrig, DavidExamination of the sedimentary record in areas occupied by fast flowing outlet glaciers and ice streams is critical for understanding ice sheet dynamics on millennial timescales. We use high-resolution seismic data together with log data and foraminiferal- based radiocarbon and isotope data from Integrated Ocean Drilling Program (IODP) Expedition 341 cores to examine the evolution of the Cordilleran Ice Sheet (CIS) in southeast Alaska. Evidence for at least seven advances of the Bering Glacier to the shelf break since the end of Middle Pleistocene Transition (MPT) are interpreted from the seismic data. Seismic data demonstrate two distinctive patterns of slope sedimentation, which are: (1) dominated by sediments bypassing a steep paleo-slope or (2) dominated by glacigenic debris flows (GDFs) that form a trough mouth fan (TMF) on a lower slope. Integration of seismic, well, and age data suggests that the TMF was formed as a result of three advances to the shelf break since ca. 140 ka, implying extreme (average > 4m/ka) rates of sediment delivery. Extraordinarily high sediment flux played a key role in the development of the margin architecture resulting from a temperate, highly aggressive Bering Glacial System and abundant source of erodible bedrock onshore (St. Elias orogeny). We use the first high-resolution seismic data acquired on the Sabrina Coast, East Antarctica, together with core data, to examine major transitions in glacial regime of East Antarctic Ice Sheet. Three large-scale megasequences represent changes in the dominant pattern of sedimentation: Megasequence I shows signs of Eocene fluvial and possibly glacio-fluvial sedimentation; Megasequence II provides evidence of Oligocene-Miocene polythermal glacial sedimentation with significant amount of meltwater; Megasequence III overlies the regional erosional surface that marks major Miocene ice sheet expansion and transition into polar (cold- based) ice sheet glacial regime with no significant evidence of subglacial meltwater preserved. Megasequence II exhibits preserved record of EAIS evolution starting from its first expansion. Seismic stratigraphic analysis suggests a dynamic glacial late Paleogene-early Neogene evolution including expansions of the EAIS across the shelf at least eight times, which is marked by erosional surfaces and chaotic acoustic character of overlying strata. We report on finding the first conclusive seismic evidence of deep, extensive tunnel valley systems incised into sedimentary substrate from Antarctic continental margins. The Sabrina Coast tunnel valley system was presumably formed during Oligocene as a result of the second major EAIS shelf expansion. Shallower erosion events observed in the upper part of Megasequence II suggest more extensive glaciations in the Oligocene compared to the Miocene.