Hydrogeochemistry of Greenlandic proglacial and nonglacial streams, 2017-2018

This project assesses how weathering varies across deglaciated and proglacial watersheds in western and southern Greenland to evaluate the impact of ice sheet retreat on isotopic and nutrient fluxes to the ocean and atmospheric carbon dioxide (CO 2 ) and methane (CH 4 ) exchange. Deglaciated watersheds are separated from the ice sheet by hydrologic divides and drain precipitation and permafrost meltwater, while proglacial watersheds include also glacial meltwater. Previous studies of high latitude weathering focused almost exclusively on proglacial and subglacial systems; however, preliminary work suggests deglaciated watersheds in western Greenland have similar specific discharge (discharge normalized to drainage area) but solute concentrations distinct from proglacial system. Distinct solute concentrations results from increasing weathering extent from inland to the coast. Greenland Ice Sheet (GrIS) retreat will increase the areal extent of deglaciated watersheds, particularly those with coastal weathering characteristics, and thus should weathering fluxes. This project aims to test the hypothesis that differences in weathering reactions and extent within deglaciated watershed, and between deglaciated and proglacial environments, will produce predictable changes in isotopic, solute, and nutrient fluxes as the ice sheet retreats. We compare stream discharge and water chemistry between Greenlandic proglacial and nonglacial streams during the spring (2017), summer (2018) and fall (2017) melt seasons between two rivers draining the Greenland Ice Sheet (proglacial rivers) and six streams draining deglaciated watersheds (nonglacial streams). This dataset includes major cations and anions, biogeochemical solute concentrations, trace metals, radiogenic isotopes, Dissolved Organic Carbon (DOC) and Colored Dissolved Organic Matter (CDOM) characteristics analyzed with spectroscopic (UV (ultraviolet) absorbance and fluorescence) measurement, and stream discharge information.

本项目旨在探究格陵兰西部与南部地区冰消流域（deglaciated watersheds）及冰前流域（proglacial watersheds）的风化作用差异，以评估冰盖退缩对海洋同位素与营养盐通量、大气二氧化碳（CO₂）及甲烷（CH₄）交换过程的影响。冰消流域以水文分界与冰盖相隔，仅汇集降水与多年冻土融水；而冰前流域则额外纳入冰川融水径流。此前针对高纬度风化作用的研究几乎仅聚焦于冰前与冰下（subglacial）系统；但前期研究表明，格陵兰西部的冰消流域虽比流量（specific discharge，即归一化至汇水面积的径流量）与冰前流域相近，但其溶质浓度却与冰前流域存在显著差异。这种溶质浓度差异源于从内陆到海岸带的风化程度逐步升高。格陵兰冰盖（Greenland Ice Sheet, GrIS）的退缩将扩大冰消流域的面积范围，尤其是具备海岸带风化特征的流域，进而改变风化通量。本项目旨在验证如下假说：随着冰盖退缩，冰消流域内部以及冰消与冰前环境之间的风化反应与风化程度差异，将导致同位素、溶质及营养盐通量出现可预测的变化。本研究在2017年春季、2018年夏季与2017年秋季的融季期间，对两类溪流展开对比：一类是汇入格陵兰冰盖的2条冰前河流（proglacial rivers），另一类是流经冰消流域的6条非冰川溪流（nonglacial streams），对比二者的径流量与水化学特征。本数据集涵盖主要阳离子与阴离子、生物地球化学溶质浓度、痕量金属、放射性同位素、溶解性有机碳（Dissolved Organic Carbon, DOC）及有色溶解性有机质（Colored Dissolved Organic Matter, CDOM）的光谱分析（紫外（UV）吸光度与荧光光谱）特征，以及径流量相关信息。