Slope Water Intrusions Onto Canadian Atlantic Continental Shelf During the Past 1800 Years

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Abstract
Warm Slope Water (WSW), with a large Gulf Stream component, and cold Labrador Slope Water (LSW), with a strong Arctic contribution, fill deep shelf basins off southeastern Canada such as Emerald, on the Scotian Shelf, and Jordan in the Gulf of Maine. These slope waters leave their imprint in the stable isotope ratio of benthic foraminifera. We present a simple method for estimating the WSW/LSW blend using hydrographic data, the predicted equilibrium δ 18 O in benthic foraminiferal calcite, and the assumption that the dominant control on δ 18 O is temperature. Our results show that for most of the past 1800 years in deep Jordan Basin (deposition rate ∼235 cm kyr −1 ; temporal resolution ∼25 years), the slope waters were variable but generally consisted of a 60/40 mixture of LSW and WSW. About 800 years ago, LSW dominated (74% average contribution, 100% maximum contribution) Jordan and Emerald Basins for many decades, about the time that the climate was cooled by volcanic eruptions. During the Little Ice Age from ∼500 to 300 and ∼200 to ∼150 years ago, the LSW contribution was about 84% and 78%, respectively. The most extreme event, a strong trend in δ 18 O of −0.006‰ yr −1 (corresponding to ∼3.2°C increase in temperature), occurred during the Industrial Era warming beginning about 140 years ago. While hydrographic data indicate that the North Atlantic Oscillation can force short term slope water dynamics, it does not seem to be a primary driver of long‐term variability seen in the core data.
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  • Office of Nuclear Energy

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