Petrographic and Geochemical Records of Climate Perturbation in Carbonates from a Perennially Ice-Covered Antarctic Lake

• Main Author: Clance, Jared
• Format: Text
• Language: English
• Published: UNM Digital Repository 2022
• Subjects: Antarctic carbonates; McMurdo Dry Valleys; Lake Fryxell; carbonate oxygen isotopes; paleoclimate; carbonate redox; Biogeochemistry; Sedimentology; Antarctic; Fryxell; Antarc*; Antarctica
• Online Access: https://digitalrepository.unm.edu/eps_etds/301; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1323&context=eps_etds

Carbonate precipitation in perennially ice-covered Lake Fryxell, McMurdo Dry Valleys, Antarctica produces a modern analog for Antarctic paleolake carbonates. Lake Fryxell contains a steep oxycline in the photic zone, where dissolved oxygen falls from supersaturation to zero. In the lake’s benthic microbial mats, oxygen concentrations are higher than in the water column due to microbial photosynthesis. These mats contain carbonate cements that precipitated in a discrete episode from mat pore waters. Precipitation continued through seasonal fluctuations in oxygenation, demonstrated by variable concentrations of oxidized and reduced manganese and iron within carbonates. Carbonates precipitated out of isotopic equilibrium with the lake water column and are enriched in 18O relative to expected values. Carbonate δ18O varies by >20‰ across μm to mm; carbonate triple oxygen isotopes suggest mixing of a modified marine water with lake water as an explanation for both isotopic heterogeneity and a possible trigger for this episodic carbonate precipitation.