SCIENCE GOALS&OBJECTIVES WE SEEK TO CHARACTERIZE THE MOLECULAR AND ISOTOPIC BIOSIGNATURES OF MICROBIAL ECOSYSTEMS OF THE DIRTY ICE ENVIRONMENTS OF THE MCMURDO ICE SHELF (MIS) OF ANTARCTICA. THESE ARE LITTLE-STUDIED MELT-WATER PONDS PROTECTED FROM ANTHROPOGENIC DISTURBANCE AND WITH UNIQUE ENVIRONMENTAL CONSTRAINTS. THEY ARE NEAR TO FREEZING EVEN IN SUMMER HAVE DIVERSE CHEMISTRIES WATERS OF MIXED ORIGIN AND AN UNUSUAL LIGHT REGIME. THEY ARE ALSO OASES OF MICROBIAL BIODIVERSITY IN A LANDSCAPE THAT IS OTHERWISE LARGELY LACKING LIQUID WATER AND POORLY SUPPORTIVE OF LIFE. THE PRIMARY OBJECTIVES OF OUR RESEARCH ARE TO CHARACTERIZE THE BIOSIGNATURES OF A SUITE OF MIS PONDS AND TO DETERMINE WHICH HAVE THE POTENTIAL TO BE PREDICTIVE FOR ANALOG ENVIRONMENTS. THESE DATA WILL INFORM STUDIES OF A VARIETY OF ICEBOUND ECOSYSTEMS POTENTIALLY INCLUDING THOSE OF ICY MOONS. MOREOVER THE PHYSIOGRAPHY OF THE MCMURDO DIRTY ICE SYSTEM IS SUCH THAT SIMILAR ENVIRONMENTS WERE LIKELY WIDESPREAD DURING THE CRYOGENIAN (720 TO 635 MA). THE BIOSIGNATURES WE IDENTIFY COULD THUS HAVE PARTICULAR IMPACT ON OUR UNDERSTANDING OF THE PERSISTENCE AND EVOLUTION OF LIFE THROUGH THE SNOWBALL EARTH GLACIATIONS. HYPOTHESES&MEASUREMENTS THE ENVIRONMENTAL CONSTRAINTS OF THE MIS PONDS LEAD TO UNIQUE BIOLOGICAL COMMUNITIES AND WE HYPOTHESIZE UNIQUE BIOSIGNATURES. PRIOR WORK HAS SHOWN THAT THE CHEMISTRIES OF THE PONDS VARY WIDELY; PRIMARY PRODUCTION IS DOMINATED BY CYANOBACTERIA COEXISTING WITH ALGAL PROTISTS; AND THE COMMUNITIES FACE PERENNIAL COLD AND POTENTIALLY LIMITING LIGHT CO2 AND FIXED N. BASED ON THESE CHARACTERISTICS WE HYPOTHESIZE A NUMBER OF LIKELY BIOSIGNATURES:1) VERY HIGH RATIO OF BACTERIAL/ALGAL LIPIDS 2) ABUNDANT CYANOBACTERIAL LIPIDS DISTINCT FROM THOSE OF TROPICAL TO TEMPERATE MATS 3) LIPIDS REFLECTING ADAPTATION TO PERENNIAL COLD AND FREEZE/THAW SURVIVAL 4) HEAVY ?13C AND ?15N VALUES REFLECTING CO2-LIMITATION AND N-FIXATION RESPECTIVELY; 5) POSITIVE ORGANIC AND/OR PYRITE ?34S VALUES REFLECTING CONSUMPTION OF MARINE SULFATE IN A CLOSED SYSTEM; 6) VARIABLE WATER AND LIPID ?2H VALUES DUE TO MIXING OF SEAWATER AND GLACIAL ICE. MORE GENERALLY WE WILL SEARCH FOR RELATIONSHIPS AND CORRELATIONS AMONG ENVIRONMENTAL VARIABLES COMMUNITY COMPOSITIONS AND THEIR DIAGNOSTIC LIPID AND ISOTOPIC ASSEMBLAGES TO ASSESS THE PROCESSES INFLUENCING BIOSIGNATURE FORMATION PRESERVATION AND DESTRUCTION. WE PROPOSE TO TEST THESE HYPOTHESES BY APPLYING STATE-OF-THE-ART METHODS OF LIPID CHARACTERIZATION (HPLC-MS-MS GCMS) AND STABLE ISOTOPE ANALYSIS (GC-IRMS EA-IRMS AND MC-ICP-MS) TO SAMPLES FROM 16 PONDS AND 4 CRYOCONITE PANS THAT WERE PREVIOUSLY COLLECTED BY PI SUMMONS AND COLLABORATORS JUNGBLUT AND HAWES. NO FIELD WORK IS REQUESTED BY THIS PROPOSAL ALTHOUGH OUR COLLABORATORS WILL BE RETURNING TO MIS IN 2019 AND COULD COLLECT FURTHER SAMPLES IF NEEDED. COLLABORATOR JUNGBLUT WILL ALSO BE CONDUCTING FURTHER GENOMIC CHARACTERIZATION OF SPLITS FROM THE SAME SAMPLES ALLOWING US TO DIRECTLY COMPARE LIPID AND STABLE ISOTOPE DATA WITH PHYLOGENETIC IDENTITIES. SIGNIFICANCE&RELEVANCE A PRIME FOCUS FOR FUTURE RESEARCH OUTLINED IN THE NASA ASTROBIOLOGY STRATEGY 2015 DOCUMENT IS THE STUDY OF HABITABILITY INDICATORS INCLUDING BIOSIGNATURES AND THEIR INTERPRETATION WITHIN PLANETARY AND ENVIRONMENTAL CONTEXTS. OUR RESEARCH WILL CHARACTERIZE THE DIRTY ICE MICROBIAL ECOSYSTEMS THE RANGE OF PARAMETERS THAT INFLUENCE THEIR HABITABILITY AND WAYS IN WHICH THEY MAY BE PRESERVED DETECTED AND CHARACTERIZED IN THE ANCIENT ROCK RECORD AND POTENTIALLY ON OTHER ICY WORLDS. A SECOND FOCUS OF THE ASTROBIOLOGY STRATEGY (SECTION 4) IS THE CO-EVOLUTION OF LIFE AND THE PHYSICAL ENVIRONMENT INCLUDING MAJOR CHANGES IN THE PHYSICAL STATE OF THE PLANET SUCH AS SNOWBALL EARTH EPISODES WITH HYPOTHESIZED LINKS TO BIOLOGICAL INNOVATION. THE BIOSIGNATURES WE SEEK WILL PROVIDE A DIRECT PATH TO INVESTIGATING LINKS BETWEEN THE CRYOGENIAN AND EVOLUTION OF COMPLEX LIFE.