02981nas a2200253 4500008004100000022001400041245011200055210006900167260001200236300001400248490000700262520216600269653002102435653002602456653002602482100002802508700002202536700002202558700002102580700002202601700001802623700001502641856007102656 2021 eng d a1523-043000aThe magnitude and climate sensitivity of isotopic fractionation from ablation of Antarctic Dry Valley lakes0 amagnitude and climate sensitivity of isotopic fractionation from c12/2021 a352 - 3710 v533 a

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.

10aDry Valley lakes10aisotope fractionation10astable water isotopes1 aBellagamba, Anthony, W.1 aBerkelhammer, Max1 aWinslow, Luke, A.1 aDoran, Peter, T.1 aMyers, Krista, F.1 aDevlin, Shawn1 aHawes, Ian uhttps://www.tandfonline.com/doi/full/10.1080/15230430.2021.200189902072nas a2200193 4500008004100000245010300041210006900144260005100213490000900264520138000273653003401653653004201687653002201729653002401751653001201775100002401787700002201811856004501833 2016 eng d00aModeling Surface Photosynthetic Active Radiation in Taylor Valley, McMurdo Dry Valleys, Antarctica0 aModeling Surface Photosynthetic Active Radiation in Taylor Valle aChicago, ILbUniversity of Illinois at Chicago0 vM.S.3 a

Understanding primary productivity is a core research area of the National Science Foundation’s Long-Term Ecological Research Network. This study maps surface Photosynthetically Active Radiation (PAR) using long term data collected by a meteorological network in the McMurdo Dry Valleys. Four stations with ~20 years of records were used to correct T-sPAR, a topographic surface PAR model. Maximum expected daily surface PAR at meteorological stations was calculated for Taylor Valley, through statistical analysis of location records using a local regression model that included 84% of all observations. Expected values represent daily surface PAR under cloudless conditions. Daily measured and expected PAR was used to model cloud coverage at each location, corroborating that overcast conditions are positively correlated with proximity to the ocean. Ground-truth data collected for TaylorValley’s major lakes during the 2015/2016 field season were used to validate T-sPAR estimates. The final model approximates total seasonal surface PAR for the Taylor Valley basin. Bi- monthly maps estimate total surface PAR by lake to assist in future sampling site selection. Finally, a user interface was developed to estimate total daily surface PAR by coordinate or surface based on a user input date.

 

10adigital elevation model (DEM)10ageographical information system (GIS)10aice-covered lakes10ameteorological data10aR model1 aAcosta, Dimitri, R.1 aBerkelhammer, Max uhttp://indigo.uic.edu/handle/10027/21180