02147nas a2200193   4500008004100000022001400041245007800055210006900133260001200202490000700214520142200221653002201643653001801665653002001683653002501703100002801728700002101756856017601777       2019                        eng d  a0954-102000aInorganic carbon fixation in ice-covered lakes of the McMurdo Dry Valleys0 aInorganic carbon fixation in icecovered lakes of the McMurdo Dry  c04/20190 v723 a<p>Inorganic carbon fixation, usually mediated by photosynthetic microorganisms, is considered to form the base of the food chain in aquatic ecosystems. In high-latitude lakes, lack of sunlight owing to seasonal solar radiation limits the activity of photosynthetic plankton during the polar winter, causing respiration-driven demand for carbon to exceed supply. Here, we show that inorganic carbon fixation in the dark, driven by organisms that gain energy from chemical reactions rather than sunlight (chemolithoautotrophs), provides a significant influx of fixed carbon to two permanently ice-covered lakes (Fryxell and East Bonney). Fryxell, which has higher biomass per unit volume of water, had higher rates of inorganic dark carbon fixation by chemolithoautotrophs than East Bonney (trophogenic zone average 1.0 &micro;g C l<sup>&minus;1</sup> d<sup>&minus;1&nbsp;</sup>vs 0.08 &micro;g C l<sup>&minus;1</sup> d<sup>&minus;1</sup>, respectively). This contribution from dark carbon fixation was partly due to the activity of ammonia oxidizers, which are present in both lakes. Despite the potential importance of new carbon input by chemolithoautotrophic activity, both lakes remain net heterotrophic, with respiratory demand for carbon exceeding supply. Dark carbon fixation increased the ratio of new carbon supply to respiratory demand from 0.16 to 0.47 in Fryxell, and from 0.14 to 0.22 in East Bonney.</p>10aammonia oxidation10acarbon budget10achemoautotrophy10achemolithoautotrophy1 aVick-Majors, Trista, J.1 aPriscu, John, C.  uhttps://www.cambridge.org/core/journals/antarctic-science/article/inorganic-carbon-fixation-in-icecovered-lakes-of-the-mcmurdo-dry-valleys/4B5CA9E91C85B307EFDA69F8D7B5BFD9