Climate changes and human impacts in the North Atlantic over the last 2,000 years inferred from organic geochemical proxies and lacustrine archives

Richter, Nora

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Year:: 2020
Contributor:: Richter, Nora (creator); Russell, James M. (Advisor); Herbert, Timothy (Reader); Milliken, Ralph (Reader); Castañeda, Isla (Reader); Amaral-Zettler, Linda A. (Advisor); Brown University. Department of Earth, Environmental, and Planetary Sciences (sponsor)
Genre:: theses
Subject:: Paleoclimatology; Azores; Iceland; Paleoecology
Extent:: xvi, 225 p.
DOI: https://doi.org/10.26300/22d6-j695

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Abstract:: In the coming decades to centuries drastic changes in temperature and precipitation patterns pose new challenges for societies and ecosystems in the North Atlantic region. However, our understanding of both forced and unforced climate variability on multi-decadal to centennial timescales is fraught with uncertainty, particularly during the cold season (i.e. winter and spring). Climate change also adds a new threat to ecosystems under pressure from human land use changes. Thus, there we need to understand how climate and humans have altered the sensitivity of these ecosystems over time. This dissertation aims to (1) refine our mechanistic understanding of cold season climate variability in the high North Atlantic region and precipitation in the sub-tropical North Atlantic over the last 2,000 years and (2) to assess the role of humans and climate in shaping the landscapes of Iceland and the Azores. First, we characterize the algal producers of alkenones, a proxy commonly used for temperature reconstructions, in Northern Hemisphere freshwater lakes. We find that these algal producers, i.e. Group I Isochyrsidales, are extremely diverse, yet the alkenone signatures and response to cold season temperatures is conserved. We develop a record of cold season temperatures from a lake in Iceland using alkenones produced by Group I Isochrysidales. We find that cold season temperatures gradually warm over the last 2,000 years in response to increasing orbital insolation during the winter and spring season, however, on multi-decadal timescales temperatures are strongly modulated by unforced climate variability. A complementary paleoecological record suggests that the Icelandic landscape was resilient to natural climate variability, whereas the arrival of humans c. 870 CE led to a major shift in vegetation but no permanent changes in the lake. In contrast, in the Azores Archipelago human-driven changes in vegetation composition and erosion led to eutrophication in lake Funda. Hydroclimate in the Azores is also strongly modulated by unforced climate variability, namely the North Atlantic Oscillation, over the last 2,000 years. Overall, this work demonstrates the importance of unforced climate variability in the North Atlantic region, and the role of human impacts in shaping present-day terrestrial and lacustrine ecosystems.
Notes:: Thesis (Ph. D.)--Brown University, 2020

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Rights: In Copyright
Restrictions on Use: Collection is open for research.

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Richter, Nora, "Climate changes and human impacts in the North Atlantic over the last 2,000 years inferred from organic geochemical proxies and lacustrine archives" (2020). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.26300/22d6-j695

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Earth, Environmental and Planetary Sciences Theses and Dissertations

Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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