Browsing by Subject "Beaufort Sea"
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Item Assessing the Predictability of the Beaufort Sea Minimum Ice Extent in a Changing Arctic Climate Regime(2014-04-25) Quirk, Laura MarieUnderstanding the climatic drivers of changes in sea ice extent in the Arctic has become increasingly important as record minima in the September sea ice extent continue to be reached. This research therefore addresses the question of which synoptic scale climatological features are most important in affecting changes in sea ice extent in the Beaufort Sea. First, three measures of sea ice extent?the Barnett Severity Index, the Beaufort Sea minimum sea ice extent, and the Arctic-wide minimum sea ice extent?are compared to assess their degree of agreement and consistency using goodness of fit techniques. Secondly, a number of atmospheric predictor variables are analyzed using a composite approach to identify the most relevant predictors of sea ice in the region. Thirdly, monthly statistical forecast models are created based on multiple regressions and classification and regression trees (CART) to predict the minimum sea ice extent beginning in October of the previous year. Many differing measures have been used to quantify sea ice conditions in the Beaufort Sea, although no study has assessed these measures for consistency. When compared, all three measures indicate the same level of agreement according to the goodness of fit tests. This indicates that the choice of measure can be determined based on the specific application, as no measure outperforms another. In addition to differing measures of sea ice extent, differing predictor variables have been utilized to predict summer sea ice conditions. This study assesses all potentially relevant predictor variables and indicates that upper atmospheric air temperatures at 850 hPa, 700 hPa, and 500 hPa, monthly mean surface air temperatures, freezing degree days, thawing degree days, sea level pressure, total ice concentration, and multiyear ice concentration showed the strongest relationships with sea ice. Various teleconnection patterns including the Arctic Oscillation, the North Atlantic Oscillation, and the Pacific-North American pattern also showed strong relationships with these variables and are therefore believed also have some predictive utility. Finally, monthly multiple linear regression and CART models are created to predict the September sea ice extent using a number of climatic predictor variables. The results of these models suggest that antecedent sea ice conditions (total and multiyear ice concentration) and surface air temperature are the most important variables in predicting summer sea ice extent. The potential predictive power of the forecasts increases as predictions are made closer to the September minimum sea ice extent, with the most precise predictions made during July. This research confirms previous studies and provides a useful compilation of the state of the knowledge on the drivers of sea ice changes in the Beaufort Sea.Item Paleoreconstruction of Particulate Organic Carbon Inputs to the High-Arctic Colville River Delta, Beaufort Sea, Alaska(2013-01-09) Schreiner, Kathryn 1983-High Arctic permafrosted soils represent a massive sink in the global carbon cycle, accounting for twice as much carbon as what is currently stored as carbon dioxide in the atmosphere. However, with current warming trends this sink is in danger of thawing and potentially releasing large amounts of carbon as both carbon dioxide and methane into the atmosphere. It is difficult to make predictions about the future of this sink without knowing how it has reacted to past temperature and climate changes. This dissertation summarizes the results of the first study to look at long term, fine scale organic carbon delivery by the high-Arctic Colville River into Simpson?s Lagoon in the near-shore Beaufort Sea. Modern delivery of organic carbon to the Lagoon was determined to come from a variety of sources through the use of a three end-member mixing model and sediment biomarker concentrations. These sources include the Colville River in the western area of the Lagoon near the river mouth, marine sources in areas of the Lagoon without protective barrier islands, and coastal erosional sources and the Mackenzie River in the eastern area of the Lagoon. Downcore organic carbon delivery was measured on two cores in the Lagoon, one taken near the mouth of the Colville River (spans about 1800 years of history) and one taken on the eastern end of the Lagoon (spans about 600 years of history). Bulk organic parameters and biomarkers were measured in both cores and analyzed with Principle Component Analysis to determine long-term trends in organic carbon delivery. It was shown that at various times in the past, highly degraded organic carbon inputs of what is likely soil and peat carbon were delivered to the Lagoon. At other times, inputs of fresher, non-degraded, terrestrially-derived organic carbon inputs of what are likely higher amounts of plant and vegetative material was delivered to the Lagoon. Inputs of degraded soil carbon were also shown to correspond to higher temperatures on the North Slope of Alaska, likely indicating that warmer temperatures lead to a thawing of permafrost and in turn organic carbon mobilization to the coastal Beaufort Sea.Item Reconstructing late Holocene Artctic climate change using high resolution sediment records from Simpson Lagoon, Alaska and the Colville River alluvial valley(2015-12) Hanna, Andrea Jo Miller; Goff, John A.; Shanahan, Timothy M.; Allison, Mead A. (Mead Ashton),; Quinn, Terrence M; Mohrig, David; Marcantonio, FrancoArctic nearshore environments proximal to large rivers, like Simpson Lagoon, Alaska, potentially contain high-resolution sediment archives that can be utilized to reconstruct paleoclimate variability over the late Holocene. The ongoing, rapid environmental changes recently observed in the Arctic highlight the need for high-resolution records of pre-industrial climate change in this climatically sensitive region; such records are fundamental for understanding recent anthropogenic changes in the context of natural variability. This dissertation utilizes a suite of geochemical and sedimentological proxies in combination with age-constrained, shallow acoustic reflection data to demonstrate that these underutilized coastal sediment archives are capable of generating high-resolution paleoclimate records on par with other terrestrial climate archives (i.e. lake sediments, ice cores, tree rings) and provides the first ~1650-year long record of climate variability from the inner shelf of the Alaskan Beaufort Sea. An analysis of sedimentation patterns within Simpson Lagoon using CHIRP seismic data and radioisotope geochronology reveals that sediment infilling in Simpson Lagoon began ~3500 y BP, creating a primary depocenter with mm/y sediment accumulation in western Simpson Lagoon. The interbedded sediments suggest that major sediment reworking from ice processes, a common occurrence in Arctic shelf environments, does not disrupt the sediment archive contained within the lagoon. Quantitative reconstructions of surface air temperature are obtained using the brGDGT-derived MBT’/CBT paleothermometer. A comprehensive study of lagoon and river sediments and catchment soils demonstrate that brGDGTs are primarily soil-derived, and yield reconstructed temperatures consistent with instrumental summer temperature observations from Alaska’s North Slope. Temperature reconstructions from Simpson Lagoon also show similarities with regional and pan-Arctic climate records over the last few millennia, with evidence of temperature departures correlative with noted climate events (i.e., Little Ice Age, Medieval Climate Anomaly). In addition, temporal variability in sediment sourcing to the lagoon, determined using a multi-proxy approach (i.e., granulometry, elemental analysis, clay mineralogy), broadly corresponds with temperature fluctuations, indicating relative increases in fluvial sediment discharge during colder intervals and decreased river discharge/increased coastal erosion during warmer periods. This paleoclimate variability may be driven by variations in solar output and/or shifts in the regional ocean-atmosphere circulation patterns (e.g., the Aleutian Low).Item Tracing organic matter pathways in marine food webs using fatty acids and compound specific stable isotope analysis(2015-08) Smith, Stephanie Denise; McClelland, James W.; Dunton, Kenneth H; Walther, Benjamin DOrganic matter inputs to the marine environment vary over seasonal and spatial scales, altering the type and availability of food sources for marine consumers. It is important to identify diet in order to understand basic ecology, characterize trophic interactions, and predict consequences of biotic and abiotic change within a community. Methods of direct observation of diet and feeding can be difficult, so indirect methods have been developed such as analysis of gut contents and fecal pellets. However, these methods only represent a snapshot of the last meal, and provide information about what was ingested, but not what was actually incorporated into consumer tissues. Therefore, biogeochemical approaches such as fatty acid (FA) and stable isotope analyses have been developed, which provide a time-integrated measure of diet. Further, stable isotope measurements of specific FA markers can be used to identify carbon sources, and can be applied to a variety of food web studies (Iverson et al., 2004). The purpose of this research is to examine the linkages between organic carbon sources and trophic transfer by consumers. To achieve this, we use FA biomarkers and compound specific stable isotope analysis (CSIA) to trace carbon cycling. This study has two main components: environmental sampling and experimental research. Chapter 1 demonstrates the use of these tools for elucidating seasonal trophic linkages in invertebrates collected from the Alaskan Arctic coast. Overall, invertebrate diets were characterized by terrestrial, detrital, and carnivorous sources in winter and spring, with a shift toward autochthonous diatom-based diets in summer. Our results demonstrate the importance of terrestrial organic carbon as a subsistence food source in winter, whereas in situ production in summer was critical for accumulating FA stores rich in essential FAs. Chapter 2 is an experimental feeding study designed to quantify the incorporation rates of 18:2n-6 from diet to tissue in Atlantic croaker. Liver tissues accumulated FAs more quickly than muscle tissues, but both tissues reached equilibrium at 5 to 7 weeks. From these experiments, quantitative assessments of diet sources can be made with confidence when using FAs to understand trophic interactions of Atlantic croaker and other similar species.Item Trophodynamics of the benthic food webs in the Chukchi and Beaufort Seas, Alaska(2013-12) McTigue, Nathan David; Dunton, Kenneth H.The Chukchi and Beaufort Sea shelves host diverse and productive seafloor ecosystems important for carbon and nitrogen cycling for the Arctic Ocean. The benthic food web transfers energy from primary producers to high trophic level organisms (e.g., birds, fish, and mammals), which are important for cultural practices and subsistence hunting by Native Alaskans. This work focuses on the trophic ecology of arctic food webs through use of several different approaches. First, variation in the natural abundance of stable carbon and nitrogen isotopes facilitated the identification of trophic pathways and, subsequently, allowed the comparison of trophic guilds and food webs from the Chukchi and Beaufort Seas. Compared to water column and sedimentary organic matter end-members, second trophic level grazers and suspension feeders were conspicuously ¹³C-enriched throughout the Chukchi Sea, which supports the hypothesis that microbial degradation of organic matter occurred prior to metazoan assimilation. Second, food web recovery from disturbances caused by exploratory oil drilling at the seafloor that had occurred approximately 20 years prior were assessed in both the Chukchi and Beaufort Seas. Based on isotopic trophic niche overlap between organisms common to drilled and reference sites in the Chukchi and Beaufort Seas, the oil drilling sites had similar food web structure, indicating recovery from the activity associated with the drilling process. Third, photosynthetic pigment biomarkers were used to better understand the diagenetic process, specifically focusing on how both microbial and metazoan grazing pathways degrade organic matter in relation to seasonal sea ice retreat in the Chukchi Sea. The benthic macrofaunal and microbial food web caused rapid degradation of organic matter upon the initial pulse of microalgal food sources to the seafloor. These diagenetic pathways are linked to the ¹³C-enrichment of residual organic matter, which corresponds to the stable isotope values measured in the benthic macrofauna. Lastly, high-precision liquid chromatography and spectrophotometry were compared for estimating sedimentary pigments in the marine environment. Substantial differences in pheopigment (chlorophyll degradation products) concentrations were observed between the two techniques, suggesting the need for revisions to the monochromatic spectrophotometric equation that relates absorbance to pigment concentrations. One pheopigment, pheophorbide, was found to interfere with the accuracy of the spectrophotometric equation and caused the overestimation of pheopigments.