Limnological properties of Antarctic ponds during winter freezing

Abstract

Two shallow ponds at Cape Evans, Ross Island, were sampled at 1–2 week intervals, during winter freezing throughout the winter and during the subsequent melt period, to examine the physical and chemical conditions imposed on the biota during the year. Liquid water was first detected at the base of the ponds in late December. During the main summer melt period conductivities were less than 10 mS cm−1 with maximum daily temperatures around 5°C. The bottom waters became increasingly saline during freezing and water temperatures decreased below 0°C; by June the remaining water overlying the sediments had conductivities >150 mS cm−1 and temperatures of −13°C. Calcium carbonate, then sodium sulphate precipitated out of solution during early freezing. The dominant nitrogen species was dissolved organic-N which reached 12 g m−3 in Pond 1 just prior to final freeze up. The organic and inorganic forms of nitrogen and dissolved reactive phosphorus increased with increasing conductivity in the ponds. The behaviour of particulate-N and particulate-P mirrored that of chlorophyll a with a peak in March-April and a second higher peak just before final freeze-up. This study provides clear evidence that organisms which persist throughout the year in Antarctic coastal ponds must be capable of surviving much more severe osmotic, pH, temperature and redox conditions than those measured during the summer melt. Deoxygenation, pH decline and H2S production, however, point to continued respiratory activity well into the dark winter months.

Metagenomic Analysis of Stress Genes in Microbial Mat Communities from Antarctica and the High Arctic

“…Aqueous temperatures may occasionally rise above 5°C but are more typically around 0°C. During freeze-up, salts are excluded from the ice and the resultant brines may have temperatures that fall well below zero (13,14,29,48). Calculations based on production-to-biomass ratios have shown that the ice shelf mats are perennial, with the standing stock representing many years of microbial biomass accumulation (29).…”

Colored dissolved organic matter and dissolved organic carbon exclusion from lake ice: Implications for irradiance transmission and carbon cycling

“…CDOM exclusion likely results from the same process that affects other solutes-that is the tendency for ice to grow pure ice crystals, rejecting impurities during the process (Adams 1981;Welch and Legault 1986;Schmidt et al 1991;Wharton et al 1993). The lowest a CDOM in the ice covers was observed in the clear ice, although the bottom section of ice often had an exclusion factor slightly lower than the remaining clear ice (Fig.…”

Biodiversity in extreme aquatic environments: Lakes, ponds and streams of the Ross Sea sector, Antarctica

“…Many of these are enriched by skuas and/or penguins, as well as sea spray. A study of the winter limnology of two such ponds has shown that the benthos experiences especially harsh conditions during freeze-up (Schmidt et al, 1991). These ponds had conductivities of a few hundred ktS cm -1 during summer, but salts were oncentrated into the remaining water during ice formation, ultimately resulting .in a chloride-rich brine with conductivities more than five times that of seawater and liquid water temperaaues below -10°C.…”

“…Most of the ponds are lined with cohesive mats of cyanobacteria, and planktonic chlorophyll a concentrations range from less than 1 ~g 1-1, to more than 100~tg 1 -I (Howard-Williams et al, 1991). A detailed survey of the algal benthos revealed 58 taxa, with 17 of these occurring in more than 25% of the samples (Howard-Williams et ai., 1990).…”

“…Another species of Navicula as well as Tropidoneis laevissima were restricted to the highest salinity waters (11-60 mS cm-1). The measurements of Schmidt et al (1991) on Ross Island suggest that winter salinities during freeze-up may be extreme in these environments which remain saline even after melt-out, and could be a factor excluding many of the species found in the freshwater pond environments.…”