Thursday, April 14, 2016, 12:30PM - 1:30PM
SEEC room 225
Dissolved black carbon in Antarctic lakes and other regions of the cryosphere: Identifying chemical signatures of past and present sources
The perennially ice-covered, closed-basin lakes in the McMurdo Dry Valleys, Antarctica, serve as sentinels for understanding the fate of dissolved black carbon (DBC) from glacial sources in aquatic ecosystems. Here we show that DBC can persist in freshwater and saline surface waters for thousands of years, while preserving the chemical signature of the original source materials. The ancient brines of the lake bottom waters have retained DBC with a woody chemical signature, representing long-range transport of black carbon (BC) from wildfires. In contrast, the surface waters are enriched in contemporary BC from fossil fuel combustion. Comparison of samples collected 25 years apart from the same lake suggests the enrichment in anthropogenic BC is recent. Differences in the chemical composition of DBC among the lakes is likely due to biogeochemical processing such as photochemical degradation and sorption on metal oxides.
The second part of this study presents data from diverse regions of the cryosphere including Antarctica, the Arctic (Greenland and Svalbard), and major mountain ranges including the Himalayas, Rockies, Andes, and Alps. The samples were collected from snow, snowmelt, glacialmelt, proglacial lakes, as well as supra-glacial lakes and streams. The samples in this dataset appear similar in composition, with the exception of samples collected on the Greenland Ice Sheet, which show a distinctive signature of DBC derived from wildfires. Those samples were collected in June 2014 as wildfires raged in boreal forests of northern Canada. The similarity in the rest of the dataset suggests that DBC in polar and alpine regions is similar in composition due to comparable exposure to sunlight resulting in photodegradation of the DBC. However, the similarity could also be due to other physical processes such as atmospheric transport, regional wind and climate patterns, as well as solubility controls on particulate black carbon.