Date of Award

2007

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Karl J. Kreutz

Second Committee Member

Daniel F. Belknap

Third Committee Member

Harold W. Borns Jr.

Abstract

Understanding regional patterns of interannual to decadal-scale climate variability over the past 1000 years is critical for evaluating recently observed trends in atmosphere/ocean conditions, particularly in highly-productive ecosystems such as the Gulf of Maine (GOM) that are sensitive to minor changes in climate and/or changes in slope water input. To develop quantitative relationships between bivalve shell chemistry (d18Oc) and growing conditions, aquaculture-based experiments were developed using Mytilus edulis collected in the GOM and Greenland. These experiments yielded a highly accurate and precise paleothermometer [e.g., T °C = 16.28 (± 0.10) - 4.57 (± 0.15) {d18Oc VPBD – d18Ow VSMOW} + 0.06 (± 0.06) {d18Oc VPBD – d 18Ow VSMOW}2; r2 = 0.99; N= 323; p < 0.0001] for M. edulis, and the techniques were applied to the long-lived bivalve species Arctica islandica. To examine ocean variability in the Western GOM during the last millennium, a 142-year-old living A. islandica and three fossil A. islandica shells (corrected 14CAMS = 1030 ± 78 AD; 1320 ± 45 AD; 1357 ± 40 AD) were collected for d18O and growth increment analysis. The standardized annual growth index (SGI) of the modern shell is significantly correlated with continuous GOM plankton recorder data (1961 – 2003; Calanus finmarchicus; r2 = 0.55; p < 0.0001), and SGIs during the late Holocene contain significant periods of 2-6 years, suggesting that slope water variability coupled with North Atlantic Oscillation (NAO) dynamics is primarily responsible for productivity variability. Mean shell-derived isotopic changes were + 0.47 ‰ from 1000 AD to present, and likely reflect a 2 °C cooling caused by an increase in Labrador Current (LC) transport of ~ 0.7 Sv (1 Sv = 106 m3 s-1) and a corresponding decrease in Gulf Stream influence on GOM water temperatures during the past millennium. This hypothesis is consistent with modern observational relationships among the LC, GOM water temperatures, NAO, and Atlantic Multi-Decadal Oscillation (AMO). These results corroborate recent evidence of a large-scale cooling of slope waters and/or dynamical oceanographic changes outside the GOM during the Holocene, and suggest that a direct link exists between the GOM and Northwestern Atlantic.

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