Neglected fluxes: Understanding the evolution of weathering as continental ice sheets retreat

点击翻译按钮获取中文摘要

The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. However, as the arctic warms the ice sheet has been retreating, and as a result, altering the fundamental nature of weathering and the delivery of nutrients and elements to the ocean. The proposed work is focused on the hydrological, biological, biogeochemical, and the isotopic signatures of proglacial watersheds, which are watershed that convey dilute but high volume glacial meltwater from the top and underneath the ice sheet to the ocean, and deglacial watersheds, which are watersheds that are no longer physically connected to the ice sheet and sourced only by annual precipitation and permafrost melt. The PIs contend that while deglacial watersheds have received less attention, preliminary work suggests they may be equally or more important than proglacial watersheds for oceanic and atmospheric fluxes. Moreover, as the ice sheet melts, the area contributing to meltwater and constituent fluxes will increasingly be from deglacial watersheds. The understanding gained from this work will provide a context for the prediction of future land-ocean and land-atmosphere fluxes in response to continued ice sheet retreat. Results of the project have the potential to change our understanding of global CO2, nutrient, and isotope cycling in response to ice sheet collapse and permit predictions of the future responses to global warming and ice sheet retreat. Results will also provide a context to interpret past high latitude ice sheet retreat and climate change based on marine isotope records. The project includes training for undergraduate, graduate, and postdoctoral researchers, as well as a collaboration with students and faculty at a Greenlandic academic institution.The proposed study will test the hypotheses that (1) deglacial and proglacial watersheds contribute distinct elemental, isotopic, and nutrient fluxes to the ocean and atmosphere as a result of evolving weathering patterns, and (2) these reactions and associated fluxes will change within and between watersheds as the Greenland Ice Sheet retreats. The project focuses on three field areas: deglacial and proglacial watersheds near Kangerlussuaq and Narsasuaq and a deglacial watershed near Sisimiut. Each area has a distinct water balance, exposure age, and weathering characteristics, and will be sampled three times over two melt seasons to evaluate intra-seasonal and inter-annual variations. Mass balance models and PHREEQc modeling of solute data will be used to identify and assess extents of weathering reactions. Weathering extents will also be estimated based on trends in proportional contributions of minerals and offsets between dissolved and bedload strontium and lead isotope ratios, and will be linked to phosphorous fluxes and organic carbon lability and degradation. This holistic approach will provide a broad view of the relative elemental, nutrient and isotopic fluxes in proglacial and deglacial environments. These results will provide magnitudes, time scales, and drivers of weathering reactions, with a goal of linking fluxes to past records and future predictions of global climate change associated with continental ice sheet collapse.