Integrating novel molecular techniques to disentangle the roles of climate, time, and human agency on the evolution of the Icelandic landscape

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Project AbstractNon-Technical Description:Significant uncertainties remain in our ability to predict how ecosystems will respond and landscapes will change as the Arctic continues to warm faster than the global average. We can look to past warm times in recent Earth history to better constrain how the Earth system will respond to warming over the coming century. At the end of the last ice age Earth's orbit was such that the Northern Hemisphere received nearly 10% more solar energy in summer than at present. That extra energy was sufficient to melt almost all Iceland's glaciers, and the Sagas say birch forests extended from the shores to the mountains. Molecular compounds that track changes in temperature, aridity, and vegetation history are contained within the sediment deposited in Icelandic lakes and nearby composite soils over the past 12,000 years. These "proxies" provide a means to accurately reconstruct a continuous history of climate and ecosystem status across Iceland since the end of the last ice age. This research benefits from recent advances in the recovery of DNA from sedimentary archives and in organic geochemistry to isolate biomarkers that track temperature and moisture balance. A pervasive feature of the contemporary Icelandic landscape is widespread soil erosion, but whether that erosion is a result of human settlement and pastoral activity or climate change remains debated. Geochemical proxies related to soil erosion preserved in well-dated lake sediment are targeted to disentangle the roles of climate and humans in Iceland's soil erosion history. This project helps launch an early-career Latino scientist, provides international exposure to a recent PhD as postdoc in a DNA laboratory in Norway, and supports a new PhD student, as well as supporting and mentoring motivated undergraduate students, who gain research experience in a highly relevant field. With an embedded journalist communicating the potential effects of climate change derived from this research to the wider public is enhanced. Technical Description:The Arctic is currently warming twice as fast as the global average with summer temperatures predicted to be 4 to 6 degrees C above late 20th Century averages by the year 2100. Amplified warming in the Arctic is expected to result in a northward shift in woody plants. The increase in woody vegetation will reduce surface albedo and increase atmospheric water vapor, positive feedback mechanisms that are currently poorly constrained in climate models. In Iceland, stratified, securely-dated, lake sediment records span the current interglacial (Holocene) and contain a rich archive of sedimentary ancient DNA (sedaDNA) and lipid biomarker proxies for temperature (brGDGTs), hydrology (delta2-Hwax) and human agency (fecal sterols and PAHs). The analysis of modern soil and lake surface sediment networks will provide calibrations that enhance the community's understanding of these promising new molecular proxies and facilitate the development of regional training sets. Merging the local calibrations with similar measurements downcore in lake sediment and stratified aeolianites will enable reliable reconstructions of past ecosystems and their dependence on summer temperature and hydroclimate. The novel integration of these datasets will provide transformative new insights into 1) how much warmer was the early Holocene in Iceland relative to today, 2) when and to what elevation woody plants established themselves during early Holocene warmth, and 3) to what extent climate, volcanism and/or Norse settlement led to the widespread soil erosion apparent across the Icelandic landscape today. Anticipated results from this project provide key datasets needed to inform policy and improve forecasts of a rapidly warming Arctic.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.