Glaciers supply coastal oceans with substantial quantities of organic carbon, which is utilized by downstream heterotrophic bacteria and other consumers. The Greenland Ice Sheet contributes the greatest amount of glacially-derived carbon on Earth, and of this, the larger particulate fraction (POC) is approximately double that of the dissolved (DOC). Despite its importance, POC has been only sparsely investigated due to logistical challenges associated with its collection. However, as summer melt seasons continue to expand and intensify in Greenland, investigation into the source and export of this larger carbon size fraction is timely.
In a new study led by Tyler, recently published in Geophysical Research Letters, we collected POC samples from the Leverett Glacier river at 10 discreet time points within the 2015 summer, and 14C-dated them to gain insight into trends in the source of POC over a melt season. We found that during the early part of the summer, associated with a rapidly expanding subglacial drainage system, the age of POC increased in tandem from about 5,000 to about 9,000 years old. After the last outburst of the summer, POC ages fluctuated widely, which we interpreted to reflect changes in subglacial hydrologic pressure and possible sediment depletion. These results show POC export is inextricably linked to the evolution of the subglacial drainage system, and future changes in meltwater generation are likely to impact POC flux as well by potentially tapping different sediment reservoirs.
This study is part of our subglacial carbon project.
Kohler TJ, Žárský JD, Yde JC, Lamarche-Gagnon G, Hawkings JR, Tedstone AJ, Wadham JL, Box JE, Beaton AD, Stibal M (2017) Carbon dating reveals a seasonal progression in the source of particulate organic carbon exported from the Greenland Ice Sheet. Geophysical Research Letters 44, doi: 10.1002/2017GL073219