Late Holocene Climate Variability in the Norwegian Sea

Hayo, Kathryn Marie

Graduate Thesis Or Dissertation

Late Holocene Climate Variability in the Norwegian Sea Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/5d86p054d

Abstract

Understanding late Holocene climate variability is essential for the creation of accurate predictive climate models. Most of our understanding of pre-instrumental climate variability comes from highly temporally resolved terrestrial proxy records. As much of the Earth's surface is covered by ocean, this leads to a great deal of uncertainty in global reconstructions of Holocene climate variability. In this study I present two highly resolved records of alkenone derived paleoclimate variability from the Norwegian Sea. The first focuses on the last ~550 years and uses alkenone derived records of sea surface temperature and phytoplankton productivity to investigate regional controls on climate variability. Through a comparison with previously published records of δ18O variability in planktonic foraminifera, my results show that sea surface (alkenone) and near surface (foraminifera) temperature variability are decoupled and reflect the influence of two separate water masses. Previous studies suggest that near surface temperature variability is controlled by the strength of the Norwegian Atlantic Slope Current (NwASC), the primary source of warm Atlantic inflow water to the Norwegian Sea. Sea surface temperatures are thought to reflect the seasonal formation of a wedge-shaped cap of warm, fresh water resulting from the westward advection of the Norwegian Coastal Current (NCC) over the NwASC. Analysis of the phytoplankton productivity record suggests seasonal bloom size reflects the stability of the water column and is anti-correlated with the North Atlantic Oscillation (NAO) Index. The second record compares alkenone and foraminifera derived proxy reconstructions to investigate the influence of abrupt changes in solar irradiance, centered on the 2.8 kyr event, on regional climate and atmospheric modes of variability. Surface and near surface temperatures are once again decoupled and show strong and opposite responses to the reduction in solar irradiance while the productivity record remains relatively unaffected. The reconstructed temperature variability is consistent with a negative NAO-type mode of atmospheric variability triggered by the sudden reduction in incoming solar radiation.

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