Arctica islandica shell growth and geochemical records from northern Norway as North Atlantic marine climate proxies for the last millennium

Paleoclimate proxy records are needed to better understand the behavior of various components of Earth’s complex climate system across major climate transitions of the past. Such records can also provide benchmarks to test climate models and interpret the evolution of climate forcing, feedbacks, and interactions in the past, present, and future. Development of high-resolution, high-latitude records of climate change such as those presented in this dissertation, provide insight to highly sensitive regions where very few lengthy instrumental records exist. This dissertation presents shell growth and geochemical records from the long-lived marine bivalve, Arctica islandica, from northern Norway to investigate major North Atlantic marine climate of the past millennium. A 112-year Master Shell Growth Chronology and oxygen isotope time series were tested against instrumental climate indices (including the Atlantic Multidecadal Oscillation, the North Atlantic Oscillation, and Atlantic meridional overturning circulation) and local to regional sea surface temperature records. Shell growth rate and oxygen isotopic composition were found to reflect regional sea surface temperatures across a broad swath of the North Atlantic in a pattern mimicking the path of the North Atlantic Current, suggesting a causal mechanism for coherence between marine variability in northern Norway and North Atlantic climate, namely, the influence of the North Atlantic Current in the Barents Sea. Statistically robust relationships were found between the Atlantic Multidecadal Oscillation and the shell-based MultiproxyAMO Index over the instrumental record, suggesting lengthy shell-based records from northern Norway may skillfully reconstruct AMO variability of the past. Spectral analysis of a 455-year Master Shell Growth Chronology constructed by crossdating dead-collected material with the modern chronology revealed significant periodicity in the ~60 year band, reminiscent of that of Atlantic multidecadal variability. Spectral analysis of oxygen isotope ratios from the Little Ice Age, Late Little Ice Age, and Modern periods also suggest multidecadal periodicity, suggesting that multidecadal oscillations in Atlantic sea surface temperatures have persisted for at least the past five centuries. A statistically significant decrease in δ18Oshell of 0.25‰ since the Little Ice Age suggests warming or strengthening of the North Atlantic Current into the Modern climate period. Additionally, this thesis presents an investigation of variability in replicated oxygen isotope measurements and the potential for the influence of sampling imprecision. Our findings suggest that natural proxy variability combined with analytical uncertainty, and not human-related sampling error, are the primary contributors to larger than expected variability among replicated measurements. This work has important implications for previously published isotope records from biogenic archives and provides a template for estimating isotopic variability on an individual case basis