Submitted by Phyllis
I am wondering about the purity of the oldest water that makes up the oldest glaciers. That is, if a very old (pre-Homo-sapiens) sample of ice is taken from a glacier in Antarctica, what is found in there? It’s not salty, I would guess, but is it extremely pure? Does it hold small life forms? How does it compare to a similar UNFROZEN water sample today, i.e., a sample from a relatively pure source like a remote lake?
Thanks for a fascinating question! To answer this, we’ll take a look at some ice cores. Ice cores are long, continuous samples of ice obtained by drilling down deep into an ice sheet. The oldest ice recovered from a continuous ice core is around 800,000 years old, from Dome C of the East Antarctic Ice Sheet1, drilled by the European Project for Ice Coring in Antarctica. This ice is more than old enough to be before any significant human influence!
Ice sheets accumulate through the evaporation of sea water, which falls as snow on the ice sheet, and builds up. The evaporation process cleans most of the impurities from the snow, so ice-sheet ice is nearly pure, but still contains trace amounts of sea salts, and other things like dust and ash from volcanoes and forest fires. Once humans came, more pollutants were added, such as the spike in Caesium-137 concentrations due to nuclear weapons testing in the 1950s2.
No life has been recorded living within ice sheets, as it’s an extreme place to live. However, bacteria have been found living in snow in polar regions3 and dead microbes are found within ice at the bottom of the Antarctic Ice Sheet4. Even subglacial lakes have been found to contain life in the form of bacteria5.
Even the remotest of lakes, by comparison, are far less pure. Although lake water is generally fresh water, it arrives in the lake as runoff from the land, via streams, or from glacial meltwater. The salinity of lakes is relatively low, except endorheic lakes – lakes that have no outlet, which can become salty through evaporation and concentration of salts. Lakes are also open to atmospheric pollution, and human pollutants, as well as dust and ash from natural sources, can become dissolved or trapped within the lake waters.
Hope that answers your questions!
- Augustin, L. et al. Eight glacial cycles from an Antarctic ice core. Nature 429, 623–628 (2004).
- Pourchet, M., Magand, O., Frezzotti, M., Ekaykin, A. & Winther, J. G. Radionuclides deposition over Antarctica. J. Environ. Radioact. 68, 137–158 (2003).
- Redeker, K. R., Chong, J. P. J., Aguion, A., Hodson, A. & Pearce, D. A. Microbial metabolism directly affects trace gases in (sub) polar snowpacks. J. R. Soc. Interface 14, (2017).
- Priscu, J. C. et al. Geomicrobiology of subglacial ice above Lake Vostok, Antarctica. Science (80-. ). 286, 2141–2144 (1999).
- Christner, B. C. et al. A microbial ecosystem beneath the West Antarctic ice sheet. Nature 512, 310–313 (2014).