PROJECT SUMMARY Intellectual Merit: Climate change predictions have long emphasized decay of the Greenland Ice Sheet (GIS). Ice loss will decrease albedo, raise sea level, and potentially impact ocean circulation. Given the close association between the water and carbon cycles, decay of the GIS could also have important carbon cycle feedbacks within human timescales. Freshwater runoff from the GIS ranks among the 12th and 13th largest rivers of the world, yet analyses of its geochemistry are surprisingly sparse. Insufficient data are available to identify what carbon cycle feedbacks presently occur and how they might change in the future. Preliminary research suggests that rivers draining the GIS yield a previously unknown flux of CO2 to the atmosphere. Water emerging from beneath the Russell Glacier in West Greenland has CO2 partial pressures 3 - 10X supersaturated with respect to atmospheric equilibrium. This CO2 likely originates from subglacial microbial metabolism. During downstream transport, the chemical weathering of glacial till sequesters much of the excess CO2 as HCO3 (a carbon sink on human timescales), and the remainder evades to the atmosphere. With this initial insight, key questions concern if, how, and to what extent CO2 evasion will either increase or decrease as the ice sheet decays in a warmer world. For example, worst-case model predictions suggest that by the year 2100, CO2 evasion from the GIS could equal ~25% of the CO2 flux anticipated for permafrost thaw. Through comprehensive seasonal samplings and targeted hypothesis testing, this proposal aims to improve our understanding of modern-day processes, a critical first step toward better predicting future effects. We will focus on a source to sink characterization of the Akuliarusiarsuup Kuua River, from its origin at the GIS margin to its mouth at the head of the Kangerlussuaq Fjord. Our objective is to measure and model downstream gradients for pH, major ions (Ca, Mg, Na, K, and SO4), dissolved organic carbon (DOC), carbonate system parameters (CO2, HCO3, and DIC), and the stable carbon isotope composition of dissolved inorganic carbon (ä13C-DIC). We will also measure the oxygen and hydrogen isotope composition of water (ä18O- and äD-H2O) to identify water sources and flowpaths, and we will analyze the radiocarbon content (14C) of DIC and DOC to constrain the age of inorganic and organic carbon, respectively. In this context, we will test five hypotheses designed to elucidate how microbial activity, hydrologic processes, and chemical weathering regulate the rate and extent of CO2 evasion. We will collect water, sediment, and bedrock samples.
|Effective start/end date||1/1/14 → 12/31/18|
- National Science Foundation (PLR-1304686/002)
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