Geochemistry of Greenland Ice Sheet Melt Water

The Greenland Ice Sheet (GrIS) is melting at an alarming rate. Supraglacial melt water flows into moulins that drain to the base of the ice sheet, and enhances basal flow. Ultimately, large quantities of melt water are expelled into the ocean contributing to rising sea level, as well as nutrient fertilization of the North Atlantic Ocean. The presence of residual melt water in a warm-based polythermal glacier creates conditions for chemical weathering of the subglacial till which is expected to lead to a higher dissolved load in the basal melt water. Supraglacial melt arriving during the start of the melting season flushes out the basal melt water. Despite this important window, little work has been done to measure trace element concentrations in the early melt season. To examine the effect of supraglacial melt water input on the chemistry of basal melt waters, we performed a time series of supraglacial and proglacial sampling collected daily for four weeks at the start of the melt season in 2016 in southwest Greenland following GEOTRACES trace element-clean protocols. Briefly, glacial melt water samples were vacuum-filtered through 0.45 um acid-washed Supor filters under Class-10 HEPA-filtered laminar air flow and analyzed for major and trace element concentrations by High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS). The daily sampling regime captured trace element concentrations throughout the first seasonal pulse of melt water discharge. Concentrations of a variety of trace elements, including Ba, Mg, Mn, and Sr, closely followed the melt water discharge pulse, increasing in concentration during the main pulse event (which lasted <5 days). The abundances of REEs and Fe exhibited no discernable temporal relationship, however Fe concentrations fell between 15-120 ppb, below a recent study implying that the melting GrIS is a significant source of bioavailable Fe. Also notable is that toxic metals never exceeded EPA primary and secondary drinking water quality standards, even during the pulse peak, demonstrating the potential of seasonal glacial melt waters as viable sources of drinking water.