Physical Limnology of the Mcmurdo Dry Valleys Lakes

Depth profiles of solar ultraviolet radiation (UVR), photosynthetically available radiation (PAR), and related variables were measured beneath the thick, permanent ice cover of four lakes in the McMurdo Dry Valleys (77°S, 162°E). These lakes span a range of phytoplankton concentrations (0.1-10 μg Chl a liter ') but receive little input of chromophoric dissolved organic matter (CDOM) from their barren, polar desert catchments. The diffuse attenuation coefficients for downwelling radiation (K d ) in the upper water column of the lakes were at or below those for clear natural waters elsewhere, with minimum values in Lake Vanda of 0.080 (305 nm), 0.055 (320 nm), 0.036 (340 nm), 0.023 (380 nm) and 0.034 (PAR) m -1 . The attenuation lengths (1/K d ) for these lakes and for a set of high latitude lakes in the northern hemisphere (tundra and boreal forest catchments) showed a close log-log relationship with dissolved organic carbon (DOC) concentrations (r 2 ≥ 0.90; n = 20); dry valley lakes were at the high transparency end of this polar-subpolar continuum. Phytoplankton exposure to UVR relative to PAR is known to rise steeply with decreasing DOC in the concentration range 2-4 g m -3 ; the addition of the dry valley lakes data shows the continuation of this upward, markedly nonlinear trend at lower DOC concentrations. Calculation of the biologically effective UVR dosage rate for the upper phytoplankton community of Lake Vanda indicated that sufficient UVR penetrates through the 3.5-m-thick lake ice to cause inhibition of algal growth. These results show that polar desert lakes are optical extremes in terms of their water-column transparency to UVR, and that their dilute, mostly autochthonous CDOM offers little protection against the ultraviolet-B radiation flux that is continuing to increase over the polar regions.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1998.43.4.0618

Transparency of antarctic ice-covered lakes to solar UV radiation

[1] Soluble salt accumulations in soils of Taylor Valley, Antarctica, provide a history of paleolakes and the advance of the Ross Sea Ice Sheet (RSIS). In western Taylor Valley, soluble salt accumulations are relatively high and are composed primarily of Na+, Ca2+, Cl–, and SO42–. In eastern Taylor Valley, soluble salt accumulations are much lower and are composed primarily of Na+ and HCO3–. Na-HCO3-rich compositions in eastern Taylor Valley are formed through leaching, calcite dissolution, and cation exchange reactions and appear to influence the chemistry of nearby streams and lakes. The data presented here support hypotheses that a lobe of the RSIS expanded into eastern Taylor Valley and dammed proglacial paleolakes. However, in contrast to previous studies, our findings indicate that the RSIS advanced deeper into Taylor Valley and that paleolakes were less extensive. By comparing soluble salt distributions across Taylor Valley, we conclude that a lobe of the RSIS filled all of eastern Taylor Valley and dammed paleolakes in western Taylor Valley up to approximately 300 m elevation. Following ice retreat, smaller paleolakes formed in both western and eastern Taylor Valley up to about 120 m elevation, with prominent still-stands controlled by the elevation of major valley thresholds. At higher elevations, soluble salt accumulations are consistent with older soils that have not been affected by the most recent RSIS advance.

Soluble salt accumulations in Taylor Valley, Antarctica: Implications for paleolakes and Ross Sea Ice Sheet dynamics

Our paper describes the ecological controls on algal-mat diatom communities in the dynamic stream ecosystems of the McMurdo Dry Valleys in Antarctica. Dry Valley diatom communities are relatively diverse, and nearly ½ of the taxa found in these mats are considered endemic. Diatom community composition was examined in 5 streams in Taylor Valley during a 15-y cooling period that included a discrete flood event. Two hydrologic variables, total annual discharge and historical variation in discharge, gave the most parsimonious model of among-stream and interannual variation in diatom communities. Algal-mat biomass and chlorophyll a concentrations decreased after the flood, which occurred during the 2001/2002 summer season. Most algal-mat diatom communities recovered quickly after the flood. However, Green Creek, a relatively high-flow stream with low historical variation in discharge, appears to have experienced a persistent diatom community shift toward increased relative abundance of small, generalis...

/pdf/hydrologic-processes-influence-diatom-community-composition-2sgwcf6htz.pdf

Hydrologic processes influence diatom community composition in Dry Valley streams

In the McMurdo Dry Valleys of Antarctica, stream biota is limited by the brief availability of liquid water. The benthic microbial mats harbor diatoms that have adapted to hydrologic stresses, including numerous endemic species. We found a strong relationship between diatom community composition and flow intermittency in a data set including seven streams that spanned a gradient in flow intermittency. In particular, two genera represented by numerous endemic species in Dry Valley habitats, Hantzschia and Luticola, had high abundances in moderately and highly intermittent streams, respec- tively. The Shannon Index of diversity was greatest in streams with intermediate flow intermittency, with lower diversity in more stable streams resulting from lower evenness, and lower diversity in highly intermittent streams resulting from lower richness. These results indicate that multiple metrics of biodiversity may be useful in assessing the response of diatom com- munities to changing hydrologic regime. We propose that flow intermittency acts as a species filter that increases habitat heterogeneity in Dry Valley streams and may allow endemic species to persist. Future Antarctic warming may alter diatom community composition and habitats that act as refugia for desiccation-tolerant taxa. Resume : Dans les vallees seches de McMurdo de l'Antarctique, les organismes des cours d'eau sont limites par la courte disponibilite d'eau liquide. Les tapis microbiens benthiques contiennent des diatomees, dont de nombreuses especes endemi- ques, qui se sont adaptees aux stress hydrologiques. Il existe une forte relation entre la composition de la communaute de diatomees et l'intermittence du debit dans un ensemble de donnees qui inclut sept cours d'eau qui couvrent un gradient de discontinuite du debit. En particulier, deux genres qui contiennent de nombreuses especes endemiques dans les habitats des vallees seches, Hantzschia et Luticola, atteignent de fortes abondances, respectivement dans les cours d'eau moyennement et fortement intermittents. L'indice de diversite de Shannon est maximal dans les cours d'eau qui ont un debit moderement discontinu; la diversite est plus basse dans les cours d'eau plus stables a cause d'une equitabilite plus faible et aussi plus basse dans les cours d'eau fortement intermittents a cause d'une richesse reduite. Ces resultats indiquent que l'utilisation de plusieurs metriques de la biodiversite peuvent etre utiles pour evaluer la reaction des communautes de diatomees aux chan- gements de regime hydrologique. Nous croyons que la discontinuite du debit sert de filtre des especes, augmente l'heteroge- neite des habitats dans les cours d'eau des vallees seches et peut permettre aux especes endemiques de survivre. Un rechauffement futur de l'Antarctique modifiera peut-etre les communautes de diatomees et les habitats qui servent de refuges pour les taxons tolerants a la dessiccation. (Traduit par la Redaction)

Extreme streams: flow intermittency as a control on diatom communities in meltwater streams in the McMurdo Dry Valleys, Antarctica 1

Geochemical Linkages Among Glaciers, Streams and Lakes Within the Taylor Valley, Geochemical Linkages Among Glaciers, Streams And Lakes Within The Taylor Valley, Antartica

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Geochemical Linkages Among Glaciers, Streams and Lakes Within the Taylor Valley, Geochemical Linkages Among Glaciers, Streams And Lakes Within The Taylor Valley, Antartica