Glacier meltwater hydrochemistry

Glacierised areas present an ideal environment in which to study water-rock interaction, since chemical weathering rates are high and anthropogenic impacts are often minimal. Detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles. Most notably, the role of meltwaters in CO₂ sequestration during episodes of deglaciation has attracted considerable attention, since this may impact on climate at glacial-interglacial timescales. However, there is still considerable uncertainty surrounding estimates of CO₂ drawdown by meltwaters which remains to be resolved. Water flow through glaciers exerts an important control on ice mass dynamics, and influences the quantity and quality of water delivered to environments downstream of glacierised basins. Thus, the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding, but also to allow effective water resource utilisation in glacierised headwater catchments. Bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment. Here, significant advances have been made in understanding the controls on chemical weathering reactions, based on the identification of key dissolved indicator species. This has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations. As a result, this area of glaciology has received considerable attention in recent years, utilising an increasing range of dissolved ions, and integrating field and laboratory studies. However, uncertainty still surrounds certain areas of meltwater quality science, including the role of microorganisms in a system which to date has largely been viewed as abiotic. A better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment, and to facilitate the exploitation of water quality variations for both scientific and applied objectives. In this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed, and problems and future directions identified. This will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications.