THE PLANETARY DECADAL SURVEY (2011) RECOGNIZED THE IMPORTANCE OF MARS HYDROTHERMAL ENVIRONMENTS: IN ALL EPOCHS THE COMBINATION OF VOLCANISM AND WATER-RICH CONDITIONS MIGHT HAVE SUSTAINED HYDROTHERMAL SYSTEMS IN WHICH LIFE COULD HAVE THRIVED. WHILE PERVASIVE EVIDENCE EXISTS FOR EXTENDED HYDROTHERMAL SYSTEMS AT MARS CHLORINE ENHANCEMENT AND INTERACTION OF MAGMAS WITH CHLORINE-RICH BRINES NO RESEARCH TO DATE HAS DETAILED MARS ANALOG HYDROTHERMAL SYSTEMS AND THE EFFECTS OF CL-ENRICHMENT OF THE FLUIDS AND ITS IMPACT ON BIOTA WHICH IS THE PRIMARY OBJECTIVE OF THIS PROPOSED WORK. OUR STUDY WILL INVESTIGATE TWO NEARBY HIGH TEMPERATURE (~573K) HYDROTHERMAL FIELD SITES IN ICELAND: (1) GUNNUHVER BEING COASTAL WITH SEAWATER SOURCE WATER AND (2) KR SUVIK AN INLAND HYDROTHERMAL VENT OF SIMILAR TEMPERATURE RANGE AND SAME BASEMENT THOLEIITIC BASALT (11.15% FE2O3T) BUT WITH METEORIC SOURCE WATER. WE WILL SURVEY AQUEOUS CHEMISTRIES MICROBIAL COMMUNITIES AND ASSOCIATED MINERALOGIES FROM BOTH GUNNUHVER (1 MAIN GEYSER AND APPROXIMATELY 12 FUMAROLES) AND KR SUVIK (APPROXIMATELY 12 SPRINGS AND 10S OF FUMAROLES). WE WILL SAMPLE OVER A RANGE OF TEMPERATURES AND PH AS WELL AS CHARACTERIZE CO-LOCATED MINERALOGIES AND MICROBIAL COMMUNITIES. COLLECTIVELY THE RESULTS FROM THIS STUDY WILL ESTABLISH MICROBIAL RELATIONSHIPS TO BOTH AQUEOUS CHEMISTRY AND MINERALOGIES OF TWO ICELANDIC MARS ANALOGUE HYDROTHERMAL SYSTEMS GUNNUHVER AND KR SUVIK INFORMING FUTURE MARS SAMPLE RETURN BIOSIGNATURE ANALYSIS. THIS PROPOSED RESEARCH IS DIRECTLY RELEVANT TO MULTIPLE NASA SMD GOALS AND PROGRAMS. SMD OBJECTIVE REFERENCED IN CHAPTER 4.3 OF THE SMD 2014 SCIENCE PLAN EXPLORE AND FIND LOCATIONS WHERE LIFE COULD HAVE EVOLVED OR COULD EXIST TODAY IS SATISFIED BY THIS STUDY. A SECOND SMD OBJECTIVE WHICH IS SATISFIED IS LIKEWISE CLARIFIED IN CHAPTER 4.3 OF THE SMD 2014 SCIENCE PLAN SPECIFICALLY IMPROVE OUR UNDERSTANDING OF THE ORIGIN OF LIFE ON EARTH TO GUIDE OUR SEARCH FOR LIFE ELSEWHERE. THIS PROPOSED EFFORT IS RELEVANT TO THE FOLLOWING SMD PROGRAMS: NASA HABITABLE WORLDS (MINERALOGY/AQUEOUS CHEMISTRY STUDIES OF MARS ANALOG ENVIRONMENTS) AND EXOBIOLOGY (MICROBIOLOGICAL SURVEYS OF MARTIAN ANALOG ENVIRONMENTS).