Ion concentrations in discrete water column samples collected from lakes in the McMurdo Dry Valleys, Antarctica (1991-2019, ongoing)

As part of the Long Term Ecological Research (LTER) project in the McMurdo Dry Valleys of Antarctica, a systematic aqueous geochemical sampling program has been undertaken. A series of terrestrial water samples have been collected and analyzed for major ion chemistry by ion chromatography. The concentrations of ions cover a wide range of total dissolved solids from fresh to hypersaline lake waters. This dataset shows concentrations of lithium, sodium, potassium, magnesium, calcium, chloride, bromide, silicon, fluoride, SO4, found in various depths of Taylor Valley lakes.

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Lake sampling was carried out by lowering a Niskin bottle through a hole in the ice cover of the lake to specified depths. Samples were then collected in precleaned plastic bottles. Separate aliquots were collected in serum vials for pH and dissolved inorganic carbon (DIC) measurements. Samples were returned to field laboratories for processing and for time-sensitive analyses such as pH. Dedicated sampling equipment for each lake has been important for maintaining the integrity of the samples. For example, the range of Cl- concentration in the investigated lakes varies by more than three orders of magnitude. This carryover between samples becomes a potential problem. Carryover can also be a potential problem during analysis, and therefore analytical blanks are run to monitor this. The initial sample processing was carried out in field laboratories. A 100-ml sample aliquot was filtered for each anion and cation sample. All samples were filtered through 0.4-microm Nucleopore filters, usually within 12h of collection. The cation samples were filtered into acid-washed polyethylene bottles which had been rinsed with DI water, while the anion samples were filtered into DI-washed bottles. The cation samples were acidified by adding 0.5% (v/v) of concentrated HCl. Quality control was maintained by carefully rinsing all filtration apparatus with DI between samples and by processing filtration blanks which were later run as samples. The majority of water chemistry samples were returned to the Crary Laboratory, McMurdo Station, Antarctica, for analysis. Some of the samples were returned to the laboratory at the University of Alabama (pre 2000) or the Ohio State University (post 2000) for analysis owing to time constraints during the field season. DX-300 ion chromatographic system was used for the major ion analyses. The system included a gradient pump module, high-pressure injection valve with a 25-microm sample loop, a Dionex conductivity detector (CDM-3) advanced computer interface and automated sampler. The timed events and data collection were controlled by the Dionex AI-450 chromatography software for Windows. The same ion chromatographic system was used but was switched back and forth between anion and cation configurations. Appropriate dilutions of the stock standards were used to prepare a range of standards for calibration. Owing to the high salt concentrations in many of the samples, dilutions were made before the samples were run. Dilutions ranged from 1:2 for Lake Hoare surface water up to 1:6000 for the Lake Bonney deep water. The samples were diluted by serial dilution, using plastic microbeakers and adjustable pipettors. Replicate and duplicate samples were run daily. Usually, each sample was injected twice and samples from each batch were run in duplicates to check the precision of the dilutions. In almost every case, the relative standard deviation of the duplicates was less than 1%, even with dilutions of 1:6000. In addition, analytical blanks and filtration blanks were analyzed to check the quality control. Dissolved Silica analyses were done with the molybdate blue method. After the 2007-2008 season silica analysis were done on a Skalar nutrient analyzer at the OSU Lake water samples were analyzed in the field laboratories for DIC with an infrared gas analyzer. The DIC data was used with the other major ion data to calculate ionic balances as a further check on the data