INTRODUCTION
Ice core records provide a rich record of climate change across much of
Antarctica, but a similar record has not been thoroughly constructed for
the ice-free regions of the continent. In ice-free areas like the
McMurdo Dry Valleys (MDV) in West Antarctica, modern and ancient
lacustrine carbonate deposits provide a means to develop such a record.
Lacustrine carbonate deposits are useful sedimentary archives, often
preserving rich multi-proxy records of changes in local climate,
hydrology, and biogeochemistry. The physical and geochemical information
contained in lacustrine carbonates can aid in detailed reconstruction of
past local environmental conditions. The rich lacustrine carbonate
record has been most thoroughly recognized and explored in low- and
mid-latitude lakes, including both open- and closed-basin lakes (e.g.
DeMott et al. 2019, Hudson et al. 2017, Petryshyn et al. 2015, Talbot
1990). In Antarctic closed-basin lakes, where processes of sedimentation
differ considerably from those at lower latitudes, the carbonate record
has not yet been thoroughly characterized. Sedimentation in Antarctic
lakes is impacted by factors such as transport of sediment through
permanent ice covers on lakes, restricted liquid water input due to
sub-freezing temperatures, low weathering rates, prevalence of freeze
concentration over evaporative concentration, and limitation of primary
productivity by the seasonal light-dark cycle and low nutrient
availability (Craig et al. 1992, Green et al. 1988, Rivera-Hernandez et
al. 2019, Vincent et al. 2008 and references therein). Thus, it is
necessary to explore modern carbonate deposition in order to more
accurately interpret drivers of carbonate precipitation in paleolake
deposits (e.g. Doran et al. 1994) and their implications for terrestrial
Antarctic climate records.
At present, the MDV contain a number of perennially ice-covered lakes
which contain liquid water year-round. Many of these lakes contain
abundant benthic carbonate deposits (e.g. Lawrence and Hendy 1985,
Mackey et al. 2018); the fraction of the total sediment represented by
these carbonates varies among the lakes (Lawrence and Hendy 1985, Mackey
et al. 2015, Sutherland and Hawes 2008). Modern benthic carbonates in
Lake Fryxell (Taylor Valley, MDV) comprise a record of modern climate,
hydrology, and biogeochemistry in the lake and its surroundings. Lake
Fryxell carbonates are found in close spatial association with
metabolically active microbial mats on the lake floor (Wharton et al.
1982), and sediment cores indicate that carbonate precipitation occurred
through changes in regional climate and hydrology over tens of thousands
of years (Lawrence and Hendy 1985; 1989). This study assesses the
distribution, texture, and composition of carbonates in modern microbial
mats of Lake Fryxell to better interpret the roles of climate,
hydrology, and biology in carbonate precipitation in this perennially
ice-covered lake. Such terrestrial carbonates present a promising
sedimentary archive that can enhance scientific understanding of
terrestrial Antarctic environmental change.