Multi-Proxy Reconstructions of Holocene Environmental Change and Catchment Biogeochemistry Using Algal Pigments and Stable Isotopes Preserved in Lake Sediment from Baffin Island and Iceland

Lake sediments provide a continuous record of environmental change, integrating information about multiple biogeochemical processes occurring within the lake and catchment. Much of this is recorded by the chemical characteristics of sedimentary organic matter, which can be used as a proxy for past conditions. This dissertation examines Holocene lake sediment records from Baffin Island and Iceland, which, as a result of Arctic amplification feedbacks, are particularly sensitive to changes in climate. We integrated sedimentary algal pigments with more commonly used proxies such as stable isotopes, C:N ratio, and biogenic silica in order to derive a more complete understanding of local climate history and catchment biogeochemistry. Contrasting modern climate conditions between the Eastern Canadian Arctic and Iceland allows us to examine proxy response across different environments. The climate records developed in this study broadly agree with other regional records, with coherent shifts in biogeochemical proxies occurring in response to Holocene climate evolution. The nature, magnitude, and timing of proxy response vary between locations, underscoring the need to account for the distinct environmental factors of each lake system when reconstructing climate history. This study is the first to develop Holocene records of sedimentary algal pigments in each study area which distinctly characterize changes in lacustrine algal group assemblage through time. In Baffin Island, green algae and higher plants are most abundant during the early Holocene, with increased diatom relative abundance during the late Holocene and Little Ice Age. This is followed by a return to increased green algae and higher plants during recent times. This pattern is not replicated in Icelandic lakes, where cyanobacteria show the strongest temperature response and are more abundant during warm times. More complete progression of seasonal algal group succession during longer ice-free seasons is the proposed mechanism controlling algal group relative abundance. Recent trends in Icelandic lakes from this study do not show as strong of a response to Anthropogenic warming as on Baffin Island, where many proxies abruptly return to a Holocene Thermal Maximum-like state. The results of this dissertation characterize the biogeochemical regimes which occur during climatic extremes of the Holocene, and can be used to predict future conditions influencing water quality and the carbon cycle in a warming Arctic