Seasonal and Regional Variability in Dissolved and Particulate Iron Fluxes via Glacial Runoff Along the West Greenland Coast

Choquette, K., Hagedorn, B., Sletten, R.S., Harrold, Z., Liu, L., Dieser, M., Cameron, K.A. , Christner, B.C. and Junge, K. (2012) Seasonal and Regional Variability in Dissolved and Particulate Iron Fluxes via Glacial Runoff Along the West Greenland Coast. AGU Fall Meeting, San Francisco, CA USA, 3-7 Dec 2012.

Abstract

Subglacial weathering, due to biogeochemical and physical weathering processes, can affect the chemical evolution of subglacial waters and release dissolved and particulate iron via glacial runoff. Iron is a growth limiting nutrient and plays a critical role in the biogeochemical cycles of coastal and marine waters. More recently, dissolved and colloidal iron derived from subglacial sources have been considered an important contributor of Fe fluxes to the ocean; however, their dependency on lithology, grain size, and microbial activity is not well understood. This study characterizes the solute chemistry, in particular iron mineralogy and dissolved iron concentrations, released from beneath the Greenland Ice Sheet (GrIS), from two locations along the West Greenland coast, Thule (76°N, 68°W) and Kangerlussuaq (67°N, 50°W). We hypothesize that the subglacial lithology has a control on Fe fluxes from the GrIS to coastal and marine systems. The underlying bedrock in Thule is the Precambrian Dundas and Narssarssuk sedimentary formations which include sandstone, siltstone, and shale. The bedrock in Kangerlussuaq is dominated by Archean granodioritic gneiss and amphibolite within the Nagssugtoqidian Orogen. Supra and subglacial meltwater samples were collected directly in front of the Ice Sheet over an entire melt season in 2011 (North River, Thule) and 2012 (Akuliarusiarsuup Kuua River, Kangerlussuaq). In situ parameters such as temperature, pH, dissolved oxygen, and electrical conductivity were recorded in order to interpret meltwater chemistry. Dissolved Fe(II) and Fe(III) species were fixed immediately and analyzed within 24 hours after sampling in the field laboratory using a spectrophotometer and 10 cm cell. Total dissolved iron (FeT) of different size fractions (<0.22 and <0.05 μm) of iron were determined back in the home laboratory using reaction cell ICP MS. Preliminary results demonstrate that subglacial meltwater of North River has average FeT concentrations of 200 nM and 10 nM in the <0.22 and <0.05 μm size fraction, respectively, indicating that FeT in the <0.22 μm fraction is mostly (95%) in form of colloidal iron. In comparison, data from Kangerlussuaq show an average FeT of 580 nM in the <0.22 μm size fraction and 150 nM in the <0.05 μm fraction. Suspended load in North River increased throughout the ablation period in concurrence with variation in discharge, from an average of 0.08 g/L in the early melt stages (June), 0.21 g/L during the high melt (July-August), and 0.15 g/L during the late melt (end of August-September). Initial estimates for the suspended load for subglacial flow in Kangerlussuaq are 0.30 g/L on average. The suspended load will be analyzed for iron by sequential extraction in order to characterize how iron partitions between oxide and (oxyhydr)oxide minerals in the sediment. This comprehensive study will allow us to identify biogeochemical processes involved in the mobilization of iron and to evaluate how increased melting of GrIS will affect Fe fluxes to coastal and marine environments.

• Item Type: Conference or Workshop Item
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Cameron, Dr Karen
• Authors: Choquette, K., Hagedorn, B., Sletten, R.S., Harrold, Z., Liu, L., Dieser, M., Cameron, K.A., Christner, B.C., and Junge, K.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences