Collaborative Research: Quantitative Estimates of Holocene Warmth and Climate Variability Derived from Icelandic Lake Sediments

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This award will evaluate the role of polar amplification, and derive quantitative estimates of warmth through the Holocene of Iceland. Iceland occupies a strategic position to monitor North Atlantic climate, as it is situated at the boundary between major oceanic and atmospheric circulation systems. Consequently, Iceland records the status of much of the northern North Atlantic region. This award will address Arctic warmth by reconstructing the status of Iceland's ice caps from changes in the physical properties of sediment accumulating in glacier-dominated lakes. Ice-cap modeling will provide quantitative estimates of past summer warmth consistent with reconstructions of the ice cap derived from the lake sediment study. The oxygen isotopic ratio (delta18O) of precipitation will be determined from the delta18O of chironomid (midge) head capsules, a common constituent of arctic lake sediment. The delta18O of Arctic precipitation is highly correlated with mean annual air temperature, providing quantitative temperature reconstructions. Chironomid delta18O provides quantitative estimates of past air temperatures from Arctic lakes, and circumvents persistent problems with low pollen productivity at high latitudes and with plant immigration delays. Changes in chironomid assemblages in the same sediment cores, tied to an Icelandic training set, will provide an independent estimate of summer temperature.Three U.S. PhD students will be involved in this project. In addition, two Icelandic graduate students and one postdoc will be involved in a companion study with Icelandic collaborators. Film footage of the Hvitarvatn coring may be used in a proposed public television program on climate change. Thermohaline circulation is the greatest non-linearity in the climate system. By providing quantitative data on Holocene warmth and status of ice caps, this work will provide a key benchmark for General Circulation Models, especially those attempting to simulate thermohaline circulation. Results will be of great interest to Icelanders, who depend on their ice caps for hydroelectric power and as major tourist attractions. If Iceland's ice caps are at risk from projected global warming, this will have substantial economic impacts. This research will help constrain those risks.