We propose the development and testing of a new instrument for the rapid in situ measurement of heat generation as an indicator of the total metabolic activity of microbes residing in marine and lacustrine sediments, soils and ultimately at hydrocarbon reservoir depths. We will demonstrate the feasibility of our approach by a controlled field experiment designed to measure both oxygen consumption of benthic organisms as a direct indicator of metabolic activity and the corresponding contribution to the total heat flux across the sediment/water interface. A natural hydrocarbon seep area in the Gulf Of Mexico will serve as the phase i test site. Work will focus on confirming theoretical relations between heat generation and metabolism while optimizing thermal sensor design and array for development of the prototype in situ instrument. Theoretical calculations based on realistic values of the critical parameters support the feasibility of the heat flux approach to direct measurement proposed herein. In the past, this has been laboriously pursued by indirect methods or by calorimetric measurements on samples returned to laboratories, resulting in an undoubted lack of accounting for and/or altering of in situ conditions. Future phases of this work will stress field measurements over a range of ambient conditions including downhole measurements. In the process of optimizing the in situ instrument we anticipate making a significant contribution to our present knowledge of the metabolic responses of the organisms to varied in situ conditions.
