Award: OPP-1115245

The McMurdo Dry Valleys (MDVs) represent the largest (4500 km2) ice-free area of Antarctica. The MDV landscape is a mosaic of glaciers, soil and exposed rock, and stream channels that connect glaciers to mostly closed-basin (no outflow), permanently ice-covered lakes. The climate is cold (mean annual air temperatures from -15 to -30C), and dry (~50 mm annual water equivalent as snow), yet life persists, and evolves in this polar desert ecosystem. Lake water columns are liquid and biologically active year-round, but glacial meltwater streams flow and soils thaw only during the austral summer. The ecosystem is dominated by microorganisms, there are no vascular plants. Microbial mats composed primarily of cyanobacteria are abundant in lakes and streams. Mat organisms are transported by wind onto glacier and lake ice surfaces where they melt into the ice and actively metabolize in liquid water pockets that form during the summer. The stream mats host many diatoms, with sparse numbers of invertebrates. Lakes provide a habitat for diverse plankton communities that are adapted to annual light-dark cycles and subzero temperatures. Soils are inhabited by diverse bacteria, nematodes, rotifers, and tardigrades, all of which are metabolically active during summer. The McMurdo LTER (MCM) began studying this cold desert ecosystem in 1993 and showed that its biological complexity is very closely linked to past and present climatic conditions. The focus of our research on this project was how physical, chemical, and biological connections (i.e., connectivity) across the landscape would change as projected regional warming was expected to melt more ice, creating more streamflow, more wet soils, and higher lake levels. The MDVs are physically linked by wind (year-round) and by streamflow from glaciers to lakes during the austral summer. We continued to monitor several critical processes in the MDVs including meteorology (at 12 stations), streamflow (17 stream gauges), stream mat biomass and diversity, lake chemical, physical, and biological properties, soil communities, and glacial mass balance. Our hypotheses followed from our observations of synchronous and uniform ecosystem response to the cooling period of 1987-2001, which dampened connectivity among landscape units. In the decade since the end of that cooling trend, streamflows and aeolian transport of material have increased, amplifying connectivity. Contrary to the predictions of some of our hypotheses, not all ecosystem responses to increased connectivity have been synchronous or monotonic. We investigated the biological connectivity among MDV landscape units by determining the biodiversity, distribution, and functional roles of the microbial communities within the environment, and their responses to climate driven pulses and presses (warm/cold, long/short changes). Results showed that bacterial diversity is greatest in streams, followed by lakes and soils, indicating limited biological connectivity among habitats, despite clear physical connectivity. For example, during flood events the stream microbial mats are scoured from the streambed and the mat material is transported to the nearshore lake sediments. Regrowth of the stream mats occurs over several years. We also found significant biogeographic patterns that include a range of connectivity among organisms from very broadly dispersed organisms (e.g., nematodes) to fine-scale, stream by stream, habitat sorting in cyanobacteria and diatom communities. A hillslope wetting experiment was initiated to test whether soil biogeochemical cycling and biodiversity were positively impacted by the addition of water. Our results suggest that the addition of water leads to more homogeneity of soil biological communities and does not enhance biogeochemical cycling (i.e., of nitrogen, carbon, and phosphorous). In a new initiative for this long-term project, we included the expertise of an environmental historian to explore the connections between people and the MDVs. In these efforts we went beyond the heroic age of exploration (early 1900s) to document and quantify the human activity in the MDVs which has increased from 1957 to present. Our outreach and education activities leveraged the publication of our children?s book, "The Lost Seal", with several curriculum guides, many classroom visits (both in-person and virtual), and museum presentations made. The book was also translated into several different languages in an effort to reach more diverse audiences. We also gave TEDX talks on the MDVs, and worked in the field with several artists and writers supported by the NSF to translate and amplify our science to the public. Last Modified: 02/16/2018 Submitted by: Michael N Gooseff