Fryxell Basin Research Articles

Habitat suitability of biocrust communities in a cold desert ecosystem.

Drylands are unique among terrestrial ecosystems in that they have a significant proportion of primary production facilitated by non-vascular plants such as colonial cyanobacteria, moss, and lichens, i.e., biocrusts, which occur on and in the surface soil. Biocrusts inhabit all continents, including Antarctica, an increasingly dynamic continent on the precipice of change. Here, we describe in-situ field surveying and sampling, remote sensing, and modeling approaches to assess the habitat suitability of biocrusts in the Lake Fryxell basin of Taylor Valley, Antarctica, which is the main site of the McMurdo Dry Valleys Long-Term Ecological Research Program. Soils suitable for the development of biocrusts are typically wetter, less alkaline, and less saline compared to unvegetated soils. Using random forest models, we show that gravimetric water content, electrical conductivity, and snow frequency are the top predictors of biocrust presence and biomass. Areas most suitable for the growth of dense biocrusts are soils associated with seasonal snow patches. Using geospatial data to extrapolate our habitat suitability model to the whole basin predicts that biocrusts are present in 2.7 × 105 m2 and contain 11-72 Mg of aboveground carbon, based on the 90% probability of occurrence. Our study illustrates the synergistic effect of combining field and remote sensing data for understanding the distribution and biomass of biocrusts, a foundational community in the carbon balance of this region. Extreme weather events and changing climate conditions in this region, especially those influencing snow accumulation and persistence, could have significant effects on the future distribution and abundance of biocrusts and therefore soil organic carbon storage in the McMurdo Dry Valleys.

The hydrologic and geochemical contributions from snow to streamflow in the McMurdo Dry Valleys of Antarctica

AbstractThe glacial meltwater streams in the McMurdo Dry Valleys (MDVs), Antarctica only flow during the austral summer and contain abundant algal mats which grow at the onset of flow. Their relative abundance in stream channels of this polar desert make the streams biogeochemical hot spots. The MDVs receive minimal precipitation as snow, which is redistributed by wind and deposited in distinct locations, some of which become persistent snow patches each year. Previous studies identified that MDV streamflow comes from a combination of glacier ice and snow, although snow was assumed to contribute little to the overall water budget. This study uses a combination of satellite imagery, terrain analysis, and field measurements to determine where snow patches accumulate and persist across MDV watersheds, and to quantify the potential hydrologic and biogeochemical contributions of snow patches to streams. Watersheds near the coast have the highest snow‐covered area and longest snow persistence. Many of these snow patches accumulate within the stream channels, which results in the potential to contribute to streamflow. During the summer of 2021–2022, stream channel snow patches had the potential to contribute anywhere between <1% and 90% of the total annual discharge in Lake Fryxell Basin streams, and may increase with different hydrometeorological conditions. On average the potential inputs from snow patches to streamflow was between 12% and 25% of the annual discharge during the 2021–2022 season, as determined by snow area and SWE. Snow patches in the majority of the watersheds had higher nitrogen and phosphorous concentrations than stream water, and six streams contained snow with higher N:P ratios than the average N:P in the stream water. This suggests that if such patches melt early in the summer, these nutrient and water inputs could occur at the right time and stoichiometry to be crucial for early season algal mat growth.

The Distribution of Surface Soil Moisture over Space and Time in Eastern Taylor Valley, Antarctica

Available soil moisture is thought to be the limiting factor for most ecosystem processes in the cold polar desert of the McMurdo Dry Valleys (MDVs) of Antarctica. Previous studies have shown that microfauna throughout the MDVs are capable of biological activity when sufficient soil moisture is available (~2–10% gravimetric water content), but few studies have attempted to quantify the distribution, abundance, and frequency of soil moisture on scales beyond that of traditional field work or local field investigations. In this study, we present our work to quantify the soil moisture content of soils throughout the Fryxell basin using multispectral satellite remote sensing techniques. Our efforts demonstrate that ecologically relevant abundances of liquid water are common across the landscape throughout the austral summer. On average, the Fryxell basin of Taylor Valley is modeled as containing 1.5 ± 0.5% gravimetric water content (GWC) across its non-fluvial landscape with ~23% of the landscape experiencing an average GWC > 2% throughout the study period, which is the observed limit of soil nematode activity. These results indicate that liquid water in the soils of the MDVs may be more abundant than previously thought, and that the distribution and availability of liquid water is dependent on both soil properties and the distribution of water sources. These results can also help to identify ecological hotspots in the harsh polar Antarctic environment and serve as a baseline for detecting future changes in the soil hydrological regime.

Counting Carbon: Quantifying Biomass in the McMurdo Dry Valleys through Orbital & Field Observations

ABSTRACT We use correlative field studies and high-resolution multispectral remote sensing data from the WorldView-2 instrument to estimate the abundance of photosynthetically active biomass (photoautotrophs consisting primarily of microbial mats and mosses) in Canada Stream in Taylor Valley, McMurdo Dry Valleys (MDV), Antarctica. In situ field investigations were performed to (1) acquire ground validation targets for atmospherically correcting satellite imagery, (2) derive spectra of “pure” geologic and biological endmembers, (3) estimate photoautotroph cover from remote sensing data, and (4) convert these coverage estimates to biomass using data collected in the field. Our results suggest that, on the morning of 12 December 2018, the Canada Stream system contained more than 3,800 kg of photosynthetically active carbon. Extrapolating our unmixing results to the entirety of the Fryxell basin of Taylor Valley, Antarctica, we model the presence of more than 750,000 kg of photosynthetically active carbon across the landscape and carbon fixation rates roughly equivalent to five hectares of tropical rainforest. The ability to spatially and temporally quantify the amount of photosynthetically active biomass using remote sensing data in the MDV of Antarctica is a revolutionary development that will help elucidate the ecological drivers and environmental responses in this cold desert landscape.

Thermal legacy of a large paleolake in Taylor Valley, East Antarctica, as evidenced by an airborne electromagnetic survey

Abstract. Previous studies of the lakes of the McMurdo Dry Valleys have attempted to constrain lake level history, and results suggest the lakes have undergone hundreds of meters of lake level change within the last 20 000 years. Past studies have utilized the interpretation of geologic deposits, lake chemistry, and ice sheet history to deduce lake level history; however a substantial amount of disagreement remains between the findings, indicating a need for further investigation using new techniques. This study utilizes a regional airborne resistivity survey to provide novel insight into the paleohydrology of the region. Mean resistivity maps revealed an extensive brine beneath the Lake Fryxell basin, which is interpreted as a legacy groundwater signal from higher lake levels in the past. Resistivity data suggest that active permafrost formation has been ongoing since the onset of lake drainage and that as recently as 1500–4000 years BP, lake levels were over 60 m higher than present. This coincides with a warmer-than-modern paleoclimate throughout the Holocene inferred by the nearby Taylor Dome ice core record. Our results indicate Mid to Late Holocene lake level high stands, which runs counter to previous research finding a colder and drier era with little hydrologic activity throughout the last 5000 years.

Evaluating Alternative Metacommunity Hypotheses for Diatoms in the McMurdo Dry Valleys Using Simulations and Remote Sensing Data

Diatoms are diverse and widespread freshwater Eukaryotes that make excellent microbial subjects for addressing questions in metacommunity ecology. In the McMurdo Dry Valleys of Antarctica, the simple trophic structure of glacier-fed streams provides an ideal outdoor laboratory where well-described diatom assemblages are found within two cyanobacterial mat types, which occupy different habitats and vary in coverage within and among streams. Specifically, black mats of Nostoc spp. occur in marginal wetted habitats, and orange mats (Oscillatoria spp. and Phormidium spp.) occur in areas of consistent stream flow. Despite their importance as bioindicators for changing environmental conditions, the role of dispersal in structuring dry valley diatom metacommunities remains unclear. Here, we use MCSim, a spatially explicit metacommunity simulation package for R, to test alternative hypotheses about the roles of dispersal and species sorting in maintaining the biodiversity of diatom assemblages residing in black and orange mats. The spatial distribution and patchiness of cyanobacterial mat habitats was characterized by remote imagery of the Lake Fryxell sub-catchment in Taylor Valley. The available species pool for diatom metacommunity simulation scenarios was informed by the Antarctic Freshwater Diatoms Database, maintained by the McMurdo Dry Valleys Long Term Ecological Research program. We used simulation outcomes to test the plausibility of alternative community assembly hypotheses to explain empirically observed patterns of freshwater diatom biodiversity in the long-term record. The most plausible simulation scenarios suggest species sorting by environmental filters, alone, was not sufficient to maintain biodiversity in the Fryxell Basin diatom metacommunity. The most plausible scenarios included either (1) neutral models with different immigration rates for diatoms in orange and black mats or (2) species sorting by a relatively weak environmental filter, such that dispersal dynamics also influenced diatom community assembly, but there was not such a strong disparity in immigration rates between mat types. The results point to the importance of dispersal for understanding current and future biodiversity patterns for diatoms in this ecosystem, and more generally, provide further evidence that metacommunity theory is a useful framework for testing hypotheses about microbial community assembly.

Remote characterization of photosynthetic communities in the Fryxell basin of Taylor Valley, Antarctica

AbstractWe investigate the spatial distribution, spectral properties and temporal variability of primary producers (e.g. communities of microbial mats and mosses) throughout the Fryxell basin of Taylor Valley, Antarctica, using high-resolution multispectral remote-sensing data. Our results suggest that photosynthetic communities can be readily detected throughout the Fryxell basin based on their unique near-infrared spectral signatures. Observed intra- and inter-annual variability in spectral signatures are consistent with short-term variations in mat distribution, hydration and photosynthetic activity. Spectral unmixing is also implemented in order to estimate mat abundance, with the most densely vegetated regions observed from orbit correlating spatially with some of the most productive regions of the Fryxell basin. Our work establishes remote sensing as a valuable tool in the study of these ecological communities in the McMurdo Dry Valleys and demonstrates how future scientific investigations and the management of specially protected areas could benefit from these tools and techniques.

Local and Regional Scale Heterogeneity Drive Bacterial Community Diversity and Composition in a Polar Desert.

The distribution of organisms in an environment is neither uniform nor random but is instead spatially patterned. The factors that control this patterning are complex and the underlying mechanisms are poorly understood. Soil microbes are critical to ecosystem function but exhibit highly complex distributions and community dynamics due in large part to the scale-dependent effects of environmental heterogeneity. To better understand the impact of environmental heterogeneity on the distribution of soil microbes, we sequenced the 16S rRNA gene from bacterial communities in the microbe-dominated polar desert ecosystem of the McMurdo Dry Valleys (MDV), Antarctica. Significant differences in key edaphic variables and alpha diversity were observed among the three lake basins of the Taylor Valley (Kruskal–Wallis; pH: χ2 = 68.89, P < 0.001, conductivity: χ2 = 35.03, P < 0.001, observed species: χ2 = 7.98, P = 0.019 and inverse Simpson: χ2 = 18.52, P < 0.001) and each basin supported distinctive microbial communities (ANOSIM R = 0.466, P = 0.001, random forest ratio of 14.1). However, relationships between community structure and edaphic characteristics were highly variable and contextual, ranging in magnitude and direction across regional, basin, and local scales. Correlations among edaphic factors (pH and soil conductivity) and the relative abundance of specific phyla were most pronounced along local environmental gradients in the Lake Fryxell basin where Acidobacteria, Bacteroidetes, and Proteobacteria declined while Deinococcus–Thermus and Gemmatimonadetes increased with soil conductivity (all P < 0.1). Species richness was most strongly related to the soil conductivity gradient present within this study system. We suggest that the relative importance of pH versus soil conductivity in structuring microbial communities is related to the length of edaphic gradients and the spatial scale of sampling. These results highlight the importance of conducting studies over large ranges of key environmental gradients and across multiple spatial scales to assess the influence of environmental heterogeneity on the composition and diversity of microbial communities.

Biogeochemical weathering of soil apatite grains in the McMurdo Dry Valleys, Antarctica

The biogeochemical weathering of the mineral apatite links the lithosphere to the biosphere by releasing the essential nutrient phosphorus (P) into the soil ecosystem. In Taylor Valley, Antarctica, faster rates of apatite weathering may be responsible for the higher concentrations of bioavailable soil P that exist in the Fryxell Basin as compared to the Bonney Basin. In this study, we use scanning electron microscopy to quantify the morphology and surface etching of individual apatite grains to determine whether the degree of apatite weathering differs between the Fryxell and Bonney Basins as well as saturated and dry soil sediments. We show that apatite grains from the Fryxell Basin are rounder, have fewer intact crystal faces, and are more chemically etched than grains from the Bonney Basin. In the Bonney Basin, apatite grains from dry soils show few signs of chemical dissolution, suggesting that soil moisture is a stronger control on the rate of apatite weathering in the Bonney Basin than in the Fryxell Basin. In addition, etch-pit morphologies in the Bonney Basin are more clearly controlled by the hexagonal crystal structure of apatite, while in the Fryxell Basin, etch pits demonstrate a wide range of morphologies without clear crystallographic control. Higher rates of apatite weathering in the Fryxell Basin may be due to the legacy of the physical abrasion of apatite grains during transport by a warm-based ice sheet, as well as the higher levels of precipitation and soil moisture closer to the coast. Our grain-scale approach provides a new perspective on P cycling in the McMurdo Dry Valleys and has implications for apatite weathering and P dynamics in the early stages of soil development.

Strontium Isotopic Signatures of Streams from Taylor Valley, Antarctica, Revisited: The Role of Carbonate Mineral Dissolution

We have collected and analyzed a larger set of stream waters for major ions and strontium isotopes in Taylor Valley, McMurdo Dry Valleys, Antarctica. These new data substantiate the concept that the dissolution of carbonate minerals is a significant source of strontium, even in polar desert environments where liquid water is primarily limited to stream channels. In Taylor Valley, most of the carbonate minerals present are the result of secondary processes, such as mineral precipitation and/or eolian deposition, and not through primary geologic sources, such as bedrock or till sources. In Von Guerard Stream (Lake Fryxell basin) and Andersen Creek (Lake Hoare basin), water samples were collected during the austral summer to determine short-term 87Sr/86Sr patterns. The observed variability in both time and space may be dependent on the relative amounts of primary and secondary carbonates present in the streambeds and hyporheic zone as well as contingent on the relative proportions of carbonate and aluminosilicate weathering.

A diatom record of environmental change in Fryxell Basin, Taylor Valley, Antarctica, late Pleistocene to present

We present a diatom record from a sediment core taken in Lake Fryxell, Taylor Valley, Antarctica. Six zones were defined using diatom assemblage changes that indicate varying limnological conditions. The early lake stage, ca. 35,000 cal years BP, is characterized by Mayamea atomus f. permitis, a species rarely reported in modern Antarctic Dry Valley environments. An extended period from ca. 35,000 to 19,000 cal years BP is characterized by low diatom abundance, with dominant taxa Luticola spp., Muelleria spp., and Diadesmis contenta. The modern assemblage was established ca. 13,000 cal years BP, after two relatively brief transitional stages. One key species for this recent period, Navicula lineola var. perlepida, is absent in surface sediments and the modern environment, indicating an environmental change within the last several centuries. The diatom assemblage is compared to modern diatom communities in Dry Valley streams, which provide the most complete information on diatom distributions in this region. Although precise environmental interpretation of the core is hampered by limited knowledge of environmental constraints on many of the diatom taxa present in the lake core, the data provide important new insights into the history of Glacial Lake Washburn.

Glacial and postglacial sedimentation in the Fryxell basin, Taylor Valley, southern Victoria Land, Antarctica

A 9.14 m long sediment sequence was recovered from Lake Fryxell, Taylor Valley, southern Victoria Land, Antarctica, and investigated for its chronology and sedimentological, mineralogical, and biogeochemical changes. The basal part of the sequence is dominated by coarse clastic matter, i.e., mainly sand. The sediment composition suggests that a lake existed in Fryxell basin during the Middle Weichselian by ca. 48,000 cal. year BP. After a short period of lake-level lowstand ca. 43,000 cal. year BP, lower Taylor Valley became occupied by the proglacial Lake Washburn, which was at least partly supplied by meltwater and sediments from the Ross Ice Sheet that was advanced to the mouth of Taylor Valley. Evaporation of Lake Washburn to lower levels started during the Last Glacial Maximum at ca. 22,000 cal. year BP, long before the Ross Ice Sheet retreated significantly. Lake-level lowering was discontinuous with a series of high and low stands. From ca. 4000 cal. year BP environmental conditions were similar to those of today and lower Fryxell basin was occupied by a small lake. This lake evaporated to a saline or hypersaline pond between ca. 2500 and 1000 cal. year BP and refilled subsequently.

Fungal diversity in soils and historic wood from the Ross Sea Region of Antarctica

Microorganisms play a dominant role in Antarctic ecosystems, yet little is known about how fungal diversity differs at sites with considerable human activity as compared to those that are remote and relatively pristine. Ross Island, Antarctica is the site of three historic expedition huts left by early explorers to the South Pole, Robert F. Scott and Ernest Shackleton. The fungal diversity of these wooden structures and surrounding soils was investigated with traditional culturing methods as well as with molecular methodology including denaturing gradient gel electrophoresis (DGGE) using the internal transcribed spacer (ITS) regions of ribosomal DNA for identification. From historic wood and artifact samples and soils adjacent to the huts as well as soil samples obtained from the Lake Fryxell Basin, a remote Dry Valley location, and remote sites at Mt. Fleming and the Allan Hills, 71 fungal taxa were identified. The historic huts and associated artifacts have been colonized and degraded by fungi to various extents. The most frequently isolated fungal genera from the historic woods sampled include Cadophora, Cladosporium and Geomyces. Similar genera were found in soil samples collected near the huts. Sampling of soils from locations in the Transantarctic Mountains and Lake Fryxell Basin at considerable distances from the huts and with different soil conditions revealed Cryptococcus spp., Epicoccum nigrum and Cladosporium cladosporioides as the most common fungi present and Cadophora species less commonly isolated. DGGE revealed 28 taxa not detected by culturing including four taxa which possibly have not been previously described since they have less than 50% ITS sequence identity to any GenBank accessions. Fungi capable of causing degradation in the wood and artifacts associated with the expedition huts appear to be similar to those present in Antarctic soils, both near and at more remote locations. These species of fungi are likely indigenous to Antarctica and were apparently greatly influenced by the introduction of organic matter brought by early explorers. Considerable degradation has occurred in the wood and other materials by these fungi.

Experimental investigations into processes controlling stream and hyporheic temperatures, Fryxell Basin, Antarctica

Glacial meltwater streams in the McMurdo Dry Valleys, Antarctica exhibit daily cycles in temperature with maxima frequently reaching 10–15 °C, often 10 °C above air temperatures. Hydrologic and biogeochemical processes occurring in these streams and their hyporheic zones strongly influence the flux of water, solutes, and sediment to the ice-covered lakes on the valley bottoms. The purpose of this study was to identify the dominant processes controlling water temperature in these polar desert streams and to investigate in particular the role of hyporheic exchange. In order to do this, we analyzed stream temperature patterns on basin-wide, longitudinal, and reach scales. In the basin-wide study, we examined stream temperature monitoring data for seven streams in the Lake Fryxell Basin. For the longitudinal study, we measured temperatures at seven sites along a 5-km length of Von Guerard Stream. Maximum temperatures in the Fryxell Basin streams ranged from 8 to 15 °C. Daily temperature changes in the streams averaged 6–9 °C. Stream temperature patterns showed strong diel cycles peaking at roughly the same time throughout the lake basin as well as along the longitudinal gradient of Von Guerard Stream. Further, temperature patterns closely matched the associated net shortwave radiation patterns. Von Guerard Stream experienced its greatest amount of warming, 3–6 °C, in a playa region and cooled below snowfields. Temperatures in several streams around Lake Fryxell converged on similar values for a given day as did temperatures in downstream reaches of Von Guerard Stream not influenced by snowfields suggesting that at a certain point instream warming and cooling processes balance one another. The reach-scale investigation involved conducting two dual-injection conservative tracer experiments at mid-day in a 143-m reach of Von Guerard Stream instrumented with temperature and specific conductance probes. In one experiment, snow was added to the stream to suppress the temperature maximum. Chloride data from monitoring wells installed in the streambed showed that streamwater was infiltrating into the streambed and was reaching the frozen boundary. Temperatures in the hyporheic zone were always cooler than temperatures in the stream. OTIS-P modeling of tracer experiment data indicated that significant hyporheic exchange occurred in both experiments. Reach and cross-sectional heat budgets were established with data obtained from the tracer experiments and from a nearby meteorological station. The budgets showed that net radiation accounted for 99% of the warming taking place in the experimental reach. This result, together with the streams’ shallow depths and hence rapid response to meteorological conditions, explains the close linkage between stream temperature and net shortwave radiation patterns. Cross-sectional heat budgets also indicated that evaporation, convection, conduction, and hyporheic exchange contributed to 30%, 25–31%, 19–37%, and 6–21%, respectively, of the non-radiative heat losses in the experimental reach. Thus these processes all worked in conjunction to limit stream temperatures in the Dry Valleys’ highly exposed environment. This contrasts with other streams in which convection and conduction may play a warming role. The cooling impact of hyporheic exchange was greater in a losing reach than in a gaining one, and increased hyporheic exchange may have lessened the contribution of conduction to the thermal budgets by decreasing streambed temperature gradients. The cooling contributions of evaporation and convection increased with stream temperature and may thus play a role in constraining stream temperature maxima. Finally, our data indicate that streams act as vectors of heat in the Lake Fryxell basin, not only warming the hyporheic zone and eroding the frozen boundary underlying the streams but also accumulating and carrying heat downstream, sending a thermal wave into the lake once a day.

Canada Stream: A Glacial Meltwater Stream in Taylor Valley, South Victoria Land, Antarctica

The McMurdo Dry Valleys of South Victoria Land, Antarctica, form the largest of the desert oases found along the coast of Antarctica. Although this region is an extreme cold desert, glacial meltwater streams, which flow for 6-10 wk during the austral summer, are a prominent feature of the landscape. Canada Stream is in Taylor Valley and is one of 3 major streams draining Canada Glacier. The surrounding landscape is characterized by an absence of plant life, an underlying permafrost at a depth of 0.5 m, and prominent "patterned ground" features, which are large (3-5 m across) polygonal patterns formed through freeze/thaw cycles. In contrast to the barren landscape, many of the streams contain perennial algal mats and mosses, illustrating that the presence of liquid water allows for a photosynthetically based ecosystem even under the harshest conditions. Canada Stream is one of 10 streams that flow into Lake

Carbonate deposition and Ross Sea ice advance, Fryxell basin, Taylor Valley, Antarctica

Abstract Mechanisms of carbonate deposition in Lake Fryxeli, Taylor Valley, Antarctica (75° 35′S, 163° 35′E) have been investigated. The lake lies within an area once covered by Ross Sea 1 ice (c. 20 000 years ago) and its proglacial lake. Lake sediments consist of five units, unit A being the lowermost deposit cored and unit E the uppermost. Three phases of carbonate deposition are evident in these sediments and result from climate changes associated with ice advances and retreat. 1. About 20 000 years ago, a calcareous mud (unit B) was deposited in a deep proglacial Lake Washburn. The carbonate is of biogenic origin, and mixed calcite/ aragonite mineralogy. Aragonite is the dominant phase. 2. About 10 000 years ago the ice had retreated beyond the basin margins and the large volume of water then covered areas once under ice. This spreading of lake waters increased the ablation surface, resulting in evaporative concentration of lake waters, and a reduction in lake levels. Brine concentration caused the p...

Quaternary stratigraphy and glacial history of the Lower Taylor Valley, Antarctica

Abstract Well⋅bedded glacioaqueous sediments exposed in Lower Taylor Valley meltwater streams are informally defined as lithofacies by texture and lithology, and assigned to chronozones. One litho⋅ logically distinct marker, the Basalt Granule Bed, is particularly useful in assigning Chronozone III Thick-bedded Facies within Lake Fryxell Basin (0 the latest proglacial lake episode. Early Chronozone III Interbed Facies (lake marginal) is well exposed together with older sediments in New Harbour Stream. Chmnozone II Sand Facies was deposited on a previous shoreline and Chronozone I, interbedded clayey silt and sand, was deposited marginal to a still older lake. Chronozone I, II, and III sediments are provisionally correlated with the upper units (Units 1, 2, 3) of DVDP II. All three depositional episodes are consequent on grounding of ice within New Harbour. Chronozones I and II are provisionally assigned to Ross Sea Glaciation II; Chronozone III is assigned to Ross Sea Glaciation I, during which coarse det...