TY - JOUR T1 - The magnitude and climate sensitivity of isotopic fractionation from ablation of Antarctic Dry Valley lakes JF - Arctic, Antarctic, and Alpine Research Y1 - 2021 A1 - Bellagamba, Anthony W. A1 - Berkelhammer, Max A1 - Winslow, Luke A. A1 - Peter T. Doran A1 - Myers, Krista F. A1 - Devlin, Shawn A1 - Ian Hawes KW - Dry Valley lakes KW - isotope fractionation KW - stable water isotopes AB -

There has been extensive research on the effects of evaporation on the isotopic ratio of lacustrine and marine water bodies; however, there are limited data on how ablation or sublimation from lake or sea ice influences the isotopic ratio of the residual water body. This is a challenging problem because there remains uncertainty on the magnitude of fractionation during sublimation and because ablation can involve mixed-phase processes associated with simultaneous sublimation, melting, evaporation, and refreezing. This uncertainty limits the ability to draw quantitative inferences on changing hydrological budgets from stable isotope records in arctic, Antarctic, and alpine lakes. Here, we use in situ measurements of the isotopic ratio of water vapor along with the gradient diffusion method to constrain the isotopic ratio of the ablating ice from two lakes in the McMurdo Dry Valleys, Antarctica. We find that during austral summer, the isotopic fractionation of ablation was insignificant during periods of boundary layer instability that are typical during midday when latent heat is highest. This implies that the loss of mass during these periods did not yield any isotopic enrichment to the residual lake mass. However, fractionation increased after midday when the boundary layer stabilized and the latent heat flux was small. This diurnal pattern was mirrored on synoptic timescales, when following warm and stable conditions latent heat flux was low and dominated by higher fractionation for a few days. We hypothesize that the shifting from negligible to large isotopic fractionation reflects the development and subsequent exhaustion of liquid water on the surface. The results illustrate the complex and nonlinear controls on isotopic fractionation from icy lakes, which implies that the isotopic enrichment from ablation could vary significantly over timescales relevant for changing lake volumes. Future work using water isotope fluxes for longer periods of time and over additional perennial and seasonal ice-covered lake systems is critical for developing models of the isotopic mass balance of arctic and Antarctic lake systems.

VL - 53 UR - https://www.tandfonline.com/doi/full/10.1080/15230430.2021.2001899 IS - 1 JO - Arctic, Antarctic, and Alpine Research ER - TY - JOUR T1 - Year‐round and long‐term phytoplankton dynamics in Lake Bonney, a permanently ice‐covered Antarctic lake JF - Journal of Geophysical Research: Biogeosciences Y1 - 2021 A1 - Patriarche, Jeffrey D. A1 - John C. Priscu A1 - Cristina D. Takacs-Vesbach A1 - Winslow, Luke A. A1 - Myers, Krista F. A1 - Heather N. Buelow A1 - Rachael M. Morgan-Kiss A1 - Peter T. Doran KW - algae KW - Antarctic KW - fluorometry KW - ice KW - lakes KW - light KW - profiling KW - winter AB -

Lake Bonney (McMurdo Dry Valleys, east Antarctica) represents a year‐round refugium for life adapted to permanent extreme conditions. Despite intensive research since the 1960s, due to the logistical constraints posed by 4‐months of 24‐h darkness, knowledge of how the resident photosynthetic microorganisms respond to the polar winter is limited. In addition, the lake level has risen by more than 3 m since 2004: impacts of rapid lake level rise on phytoplankton community structure is also poorly understood. From 2004 to 2015 an in situ submersible spectrofluorometer (bbe FluoroProbe) was deployed in Lake Bonney during the austral summer to quantify the vertical structure of four functional algal groups (green algae, mixed algae, and cryptophytes, cyanobacteria). During the 2013–2014 field season the Fluoroprobe was mounted on autonomous cable‐crawling profilers deployed in both the east and west lobes of Lake Bonney, obtaining the first daily phytoplankton profiles through the polar night. Our findings showed that phytoplankton communities were differentially impacted by physical and chemical factors over long‐term versus seasonal time scales. Following a summer of rapid lake level rise (2010–2011), an increase in depth integrated chlorophyll a (chl‐a) occurred in Lake Bonney caused by stimulation of photoautotrophic green algae. Conversely, peaks in chl‐a during the polar night were associated with an increase in mixotrophic haptophytes and cryptophytes. Collectively our data reveal that phytoplankton groups possessing variable trophic abilities are differentially competitive during seasonal and long‐term time scales owing to periods of higher nutrients (photoautotrophs) versus light/energy limitation (mixotrophs).

VL - 126 UR - https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JG005925 IS - 4 JO - J Geophys Res Biogeosci ER - TY - JOUR T1 - Subglacial brine flow and wind-induced internal waves in Lake Bonney, Antarctica JF - Antarctic Science Y1 - 2020 A1 - Lawrence, Jade A1 - Peter T. Doran A1 - Winslow, Luke A. A1 - John C. Priscu KW - Dry valleys KW - hypersalinity KW - lakes KW - proglacial KW - temperature AB -

Brine beneath Taylor Glacier has been proposed to enter the proglacial west lobe of Lake Bonney (WLB) as well as from Blood Falls, a surface discharge point at the Taylor Glacier terminus. The brine strongly influences the geochemistry of the water column of WLB. Year-round measurements from this study are the first to definitively identify brine intrusions from a subglacial entry point into WLB. Furthermore, we excluded input from Blood Falls by focusing on winter dynamics when the absence of an open water moat prevents surface brine entry. Due to the extremely high salinities below the chemocline in WLB, density stratification is dominated by salinity, and temperature can be used as a passive tracer. Cold brine intrusions enter WLB at the glacier face and intrude into the water column at the depth of neutral buoyancy, where they can be identified by anomalously cold temperatures at that depth. High-resolution measurements also reveal under-ice internal waves associated with katabatic wind events, a novel finding that challenges long-held assumptions about the stability of the WLB water column.

UR - https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102020000036 ER - TY - JOUR T1 - Autonomous Year-Round Sampling and Sensing to Explore the Physical and Biological Habitability of Permanently Ice-Covered Antarctic Lakes JF - Marine Technology Society Journal Y1 - 2014 A1 - Winslow, Luke A. A1 - Hilary A. Dugan A1 - Heather N. Buelow A1 - Cronin, Kyle D. A1 - John C. Priscu A1 - Cristina D. Takacs-Vesbach A1 - Peter T. Doran AB -

The lakes of the McMurdo Dry Valleys, Antarctica, are some of the only systems on our planet that are perennially ice-covered and support year-round metabolism. As such, these ecosystems can provide important information on conditions and life in polar regions on Earth and on other icy worlds in our solar system. Working in these extreme environments of the Dry Valleys poses many challenges, particularly with respect to data collection during dark winter months when logistical constraints make fieldwork difficult. In this paper, we describe the motivation, design, and challenges for this recently deployed instrumentation in Lake Bonney, a lake that has been the subject of summer research efforts for more than 40 years. The instrumentation deployed includes autonomous water, phytoplankton, and sediment samplers as well as cable-mounted profiling platforms with dissolved gas and fluorometry sensors. Data obtained from these instruments will allow us, for the first time, to define the habitability of this environment during the polar night. We include lessons learned during deployment and recommendations for effective instrument operation in these extreme conditions.

VL - 48 UR - http://openurl.ingenta.com/content/xref?genre=article&issn=0025-3324&volume=48&issue=5&spage=8http://www.ingentaconnect.com/content/mts/mtsj/2014/00000048/00000005/art00002 IS - 5 JO - mar technol soc j ER -