Biogeochemistry of streams draining to Kobbefjord, Greenland, 2019

We sampled streams draining to Kobbefjord, Greenland during two periods in July 2019. Sampled streams drain glacial meltwater and lake outlets, plus soil water sources that were collected from small seep-fed tributaries to the mainstream channels that lack any glacial meltwater. We utilized variations in water isotopes (d18O, dD) at the watershed outlet stream compared to putative water source end members (seep-fed streams draining soil water, lakes, glacial meltwater) to determine variations in the source of water to the watershed outlet between sampling periods. Period 1 was characterized by higher contributions from the glacial meltwater due to higher insolation and temperature than Period 2, which was characterized by higher contributions from soil water sources. The concentrations of greenhouse gases (CO2 and CH4), as well as products of mineral weathering reactions (as determined by a mass balance model utilizing major cation and anion concentrations in stream water) varied between sampling periods. Period 1 had greater export of mineral weathering products and lower exports of dissolved CH4, making the net carbon balance negative, while Period 2 had lower exports of mineral weathering products and high exports of CH4, making the net carbon balance positive. Our results indicate that weathering of fresh comminuted sediment dominates in glacial meltwater during glacial to interglacial transitions, resulting in net CO2 sinks, as exemplified by Period 1 sampling. In contrast, deglaciated landscapes that form OC rich soils are sites of biogeochemical reactions with more mature weathering that enhances CO2 and CH4 production and limits CO2 consumption.