| Summary: | If unabated, the continued anthropogenic release of carbon dioxide is expected to lead to warming and acidification of ocean waters, with widespread and detrimental impacts on marine ecosystems. Proxy records stored in biomineralized shells and skeletons of long-lived paleoclimate archives are essential for understanding long-term climate variability - previously unresolvable based on spatiotemporally limited observations. In this dissertation, geochemical and physical proxies from Clathromorphum spp. crustose coralline algae (CCA) are used for interpreting past climatic and environmental changes in the subarctic North Pacific and North Atlantic Oceans. Micro-computed tomography techniques are used to examine the algal skeleton, and reveal changes in skeletal density in relation to recently observed acidification off the Aleutian Islands, Alaska. Metabolic trade-offs associated with continued growth and calcification in acidifying seawaters may have resulted in the production of weaker (less-dense) skeletons since 1980. However, correlations indicate that in addition to acidification, sunlight availability and temperature stress are also important factors influencing the ability of CCA to calcify. Furthermore, barium-to-calcium (Ba/Ca) ratios are utilized as proxies for phytoplankton productivity in northern Labrador, Canada, such that: Higher (lower) algal Ba/Ca values are interpreted as decreased (increased) productivity coinciding with the expansion (melting) of sea-ice. This multi-centennial record of algal Ba/Ca indicates a long-term increase in North Atlantic productivity that is unprecedented in the last 365 years. Conversely, in mountainous coastal regions surrounding the Gulf of Alaska where high sediment loads are present in seasonal runoff, algal Ba/Ca is used as an indicator for freshwater runoff. Ba/Ca is inversely correlated to instrumental salinity, and indicates a unique period of freshening (2001 â 2006) that is related to increasing glacial melt and precipitation on mainland Alaska. The results presented here illustrate the physiological responses of coralline algae to acidification, and provides much-needed data for future projections of climate and environmental change. Ph.D. 2018-06-23 00:00:00
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