Organic Carbon in Antarctic Snow W

GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L02501, doi:10.1029/2006GL028150, 2007 Click Here for Full Article Organic carbon in Antarctic snow W. Berry Lyons,1,2 Kathleen A. Welch,1 and J. Kenneth Doggett3 Received 12 September 2006; revised 23 October 2006; accepted 5 December 2006; published 16 January 2007. [1] Little information exists about the concentration and 2. Location and Methods temporal variations of organic components in Antarctic [3] The McMurdo Dry Valleys of Southern Victoria Land precipitation. We present results of TOC (total organic are one of the largest expanses of ice-free area in Antarctica. carbon) analyses from snowpits that were sampled on alpine The valleys are a mosaic of bedrock, soils, seasonally glaciers in the Taylor Valley, Southern Victoria Land, flowing streams, ice-covered closed-basin lakes, and Antarctica, at 78°S. The snowpits represent snow glaciers [Fountain et al., 1999]. Taylor Valley ( 78°S lat.) accumulation from the 1990s and the TOC concentrations is one of the largest of these valleys and in the 2000–2001 are very low; most of the analysis yielded values below austral summer, a series of 2 m snow pits were dug and 8 mM. These values are some of the lowest ever reported for precipitation or snowpack and indicate that TOC in glacial sampled in the accumulation zones of three of the alpine snow in coastal Antarctica is little influenced by terrestrial glaciers flowing from the Asgard Range into the Taylor and anthropogenic emissions of organic carbon. The Valley floor (Figure 1). These glaciers, the Commonwealth, sources of the TOC are still not known, however the TOC the Canada and the Rhone, are 10, 20 and 35 km inland variation is negatively correlated to ClÀ and the other major from the McMurdo Sound portion of the Ross Sea, respec- ions in the snow suggesting a different source or timing of tively (Figure 1). deposition than the seasalt aerosols and terrestrial dust. [4] Snow samples were collected in a similar manner as described by Twickler et al. [1986] in that the snow pit wall Citation: Lyons, W. B., K. A. Welch, and J. K. Doggett (2007), was carefully scraped using a precleaned Plexiglas instru- Organic carbon in Antarctic snow, Geophys. Res. Lett., 34, ment by an individual wearing a non-particulating ‘‘clean L02501, doi:10.1029/2006GL028150. suit’’. Samples were collected at 3 cm intervals although not all of the samples were analyzed for TOC. The snow was 1. Introduction collected in 1 L plastic (HDPE) containers with snap-on [2] The preservation of atmospheric deposition in glacier lids. The containers were soaked with distilled-deionized ice provides a powerful method to investigate past atmo- water (DDIW) for 24 hours and then rinsed five times with spheric conditions [e.g., Delmas, 1995]. To date in the polar DDIW prior to use. The samples were stored frozen. In the regions, long and detailed histories of atmospheric and Crary Laboratory at McMurdo Station, the samples were precipitation chemistry obtained from ice cores have led melted and transferred to combusted amber glass bottles to important new insights into past climate changes and/or with Teflon caps. The samples were not filtered. One biogeochemical cycling [Legrand and Mayewski, 1997]. percent by volume phosphoric acid was added to drive off Yet, the vast majority of these investigations have focused inorganic carbon and the samples were stored at 4°C until on inorganic constituents. Little information exists on var- analysis at the Crary Lab. TOC was determined using a iations in organic components, especially in the Antarctic, Shimadzu TOC-5000 with a high sensitivity catalyst. The and most of this previous work reflects individual com- instrument was set so that if the precision of replicate pounds, such as low molecular weight organic acids, standards reached 10%, the instrument is recalibrated. The methanesulfonate or formaldehyde [Staffelbach et al., relative standard deviation of most measurements was 1991; Legrand and DeAngelis, 1995]. More recent work 3%. The detection limit was determined to be 8.3 mM. has added information on the distribution of both humic Chloride concentrations were measured on all snow pit substances and organic pollutants in modern Antarctic snow samples using a modification of the analytical techniques [Calace et al., 2005; Cincinelli et al., 2005]. Only a small of Welch et al. [1996]. Samples were analyzed using a data set of the concentrations of total organic carbon (TOC) Dionex DX-120 instrument with a 400 mL sample loop and in glacier ice and snow exists. In this paper we report some Dionex IonPac AS14 analytical column (4 Â 250 m) and an of the first TOC data from Antarctic glaciers and provide AG14 guard column (4 Â 50 mm). The eluent was a 1.0 mM information about the temporal variation of TOC preserved NaHCO3 and 3.5 mM Na2CO3 solution. An ASRS Ultra in the snowpack. Anion Self-Regenerating Suppressor was used. Precision of the ClÀ data determined by analysis of duplicates was always better than 3.5% for the Commonwealth Glacier samples. 1Byrd Polar Research Center, Ohio State University, Columbus, Ohio, 3. Results and Discussion USA. 2 À Also at Department of Geological Sciences, Ohio State University, [5] The Cl and TOC profiles for the Commonwealth Columbus, Ohio, USA. Glacier snow pit are shown in Figure 2. Only one sample 3Department of Oceanography, University of Hawaii, Honolulu, Hawaii, USA. from the Canada Glacier had a TOC value above our limits of detection; the sample from 9 cm had a TOC concentra- Copyright 2007 by the American Geophysical Union. tion of 15 mM. The Rhone Glacier had measurable TOC 0094-8276/07/2006GL028150$05.00 L02501 1of4 L02501 LYONS ET AL.: ORGANIC CARBON IN ANTARCTIC SNOW L02501 Figure 1. Map of Taylor Valley. Based on U.S. Geological Survey 1:50,000 maps: Lake Fryxell, Antarctica, 1977; and Lake Bonney, Antarctica, 1977. concentrations at 27, 96, 103, 167 and 185 cm depth, which [6] Previous work in both Antarctica and Greenland has were 10, 11, 9, 22 and 10 mM, respectively. These concen- demonstrated that in regions with low snow accumulation À trations from Taylor Valley glacier snow are generally lower rates, NO3 is lost from the snowpack [Jones et al., 2001; than TOC and dissolved organic carbon (DOC) concentra- Ro¨thlisberger et al., 2002]. This post depositional loss is tions from samples collected in other remote and/or polar caused by the release of nitric acid by volatilization and/or regions. Marine precipitation yields a mean value of 23 mM photolysis, with the latter being more important at the [Willey et al., 2000] where there was no difference between lowest snow accumulations [Ro¨thlisberger et al., 2002]. DOC and TOC. Kieber et al. [2002] recently determined Empirical and/or laboratory work in both the Arctic and at DOC values in oceanic-dominated precipitation from New South Pole indicate that snowpacks can be sources of Zealandtobe24mM. Twickler et al. [1986] found a monocarboxylic acids as well as aldehydes and acetone to mean DOC concentration of 9 mM in snow pit samples the overlying atmosphere [Dibb and Arsenault, 2002; from southern Greenland. Samples of snowpack collected from the Canadian Rockies had DOC concentrations of 23–34 mM[Lafreniere and Sharp, 2004]; Alaskan glacier snow and ice had concentrations of 33 and 12 mM, respectively [Skidmore et al., 2005; Loder and Hood, 1972], while Ellesmere Island glacier snow had a mean value of 24 mM[Skidmore et al., 2005]. Recent work at Alert, Nunavut, Canada, and Summit, Greenland yielded mean values in snow to be 37 and 41 mM respectively, with higher concentrations occurring in the spring/summer months in both locations [Grannas et al., 2004]. Data from these two locations and snow/ice from Franz Josef Land in the Russian Arctic, indicate that the majority of the TOC is <1000 daltons in size, low in black carbon and contains less than 20% particulate OC [Grannas et al., 2004, 2006]. The data also suggest that the TOC is derived from a variety of sources, but terrestrial sources, including humic-like materials, comprise a large portion. The TOC concentrations from the Commonwealth Glacier snow pit essentially bracket the range outlined above, but with many samples Figure 2. Depth profiles of TOC and ClÀ concentrations below detection, or a range from 23 to less than 8 mM from the 2-m snowpit on the Commonwealth Gl. Dates have (Figure 2). been determined using seasonal signals in ClÀ. 2of4 L02501 LYONS ET AL.: ORGANIC CARBON IN ANTARCTIC SNOW L02501 Guimbaud et al., 2002; Grannas et al., 2004]. Because of than in coastal East Antarctica [Legrand and DeAngelis, the lack of data from polar snowpacks, it is impossible at 1995]. À this stage to evaluate if our very low TOC concentrations [8] The Cl time series from the Commonwealth Glacier represent low levels of depositional input or if they are snow pit was used to date the snow pit. The ClÀ concen- partially due to post-depositional loss of the more volatile trations are thought to be higher in the austral fall into the carbon species. Recent work by Barker et al. [2006] winter period when low sea-ice extent and high winds presents DOC data from glacier and basal ice samples that deposit sea-salt aerosols [Legrand and Mayewski, 1997]. were taken along a 180 cm transect across the glacier ice/ The highest TOC values generally occur when the ClÀ basal ice contact at Victoria Upper Glacier, 50 km north of values are lowest, suggesting that the highest concentrations Commonwealth Glacier. The maximum DOC concentration of TOC in these glaciers occur during the spring to summer is right above the glacier-basal ice transition with a value of period, when the annual sea-ice extent is decreasing.

Load more