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Dissolved Carbon Dynamics in Meltwaters From the Russell Glacier, Greenland Ice Sheet
Author(s) -
Andrews M. Grace,
Jacobson Andrew D.,
Osburn Magdalena R.,
Flynn Theodore M.
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004458
Subject(s) - dissolved organic carbon , greenland ice sheet , glacier , carbon cycle , ice sheet , heterotroph , geology , carbonate , oceanography , hydrology (agriculture) , geomorphology , chemistry , ecology , ecosystem , biology , paleontology , geotechnical engineering , organic chemistry , bacteria
Melting of the Greenland Ice Sheet (GrIS) has accelerated in recent decades. Given the close association between the water and carbon (C) cycles, melting of the GrIS may also drive local and global C cycle feedback. However, few studies have quantified such feedback, which may have important implications for predicting future climate or understanding linkages between ice sheet destabilization and climate change in the geologic past. Here we investigate seasonal and interannual dissolved C cycling at the margin of the Russell Glacier, west Greenland. By synthesizing isotopic analyses of water (δ 18 O) and C (δ 13 C and Δ 14 C) with geomicrobiological observations, we present evidence for previously unknown connections between the GrIS's supraglacial and subglacial dissolved C cycles. Supraglacial streams have variable concentrations of dissolved organic carbon (DOC) and are the dominant source of DOC in subglacial discharge. Supraglacial stream dissolved inorganic carbon (DIC) concentrations are uniform and sourced from a spatially and temporally constant mixture of organic C (~25%) respired by aerobic heterotrophs inhabiting the GrIS surface and dissolved atmospheric C (~75%). Supraglacial inputs account for ~50% of subglacial discharge DIC. The remaining subglacial DIC derives from carbonate weathering and microbial CO 2 production, with the latter attributable to abundant anaerobic heterotrophic communities observed in subglacial discharge. Furthermore, we find that supraglacial streams deliver young DOC to the subglacial environment during snowmelt and rain events. These pulses of organic C may drive heterotrophic microbial respiration, with the cumulative effect being a seasonal shift in the source of basal DIC, from microbial‐ to carbonate‐dominated.