In November 2012, Oregon State University initiated the project entitled: Application of Crunch-Flow routines to constrain present and past carbon fluxes at gas-hydrate bearing sites. Within this project we developed Crunch-Flow based modeling modules that include important biogeochemical processes that need to be considered in gas hydrate environments. Our modules were applied to quantify carbon cycling in present and past systems, using data collected during several DOE-supported drilling expeditions, which include the Cascadia margin in US, Ulleung Basin in South Korea, and several sites drilled offshore India on the Bay of Bengal and Andaman Sea. Specifically, we completed modeling efforts that: 1) Reproduce the compositional and isotopic profiles observed at the eight drilled sites in the Ulleung Basin that constrain and contrast the carbon cycling pathways at chimney (high methane flux) and non-chimney sites (low methane, advective systems); 2) Simulate the Ba record in the sediments to quantify the past dynamics of methane flux in the southern Hydrate Ridge, Cascadia margin; and 3) Provide quantitative estimates of the thickness of individual mass transport deposits (MTDs), time elapsed after the MTD event, rate of sulfate reduction in the MTD, and time required to reach a new steady state at several sites drilled in the Krishna-Godavari (K-G) Basin off India. In addition we developed a hybrid model scheme by coupling a home-made MATLAB code with CrunchFlow to address the methane transport and chloride enrichment at the Ulleung Basins chimney sites, and contributed the modeling component to a study focusing on pore-scale controls on gas hydrate distribution in sediments from the Andaman Sea. These efforts resulted in two manuscripts currently under review, and contributed the modeling component of another pare, also under review. Lessons learned from these efforts are the basis of a mini-workshop to be held at Oregon State University (Feb 2014) to instruct graduate students (OSU and UW) as well as DOE staff from the NETL lab in Albany on the use of Crunch Flow for geochemical applications.iii routines to constrain present and past carbon fluxes at gas-hydrate bearing sites, we developed Crunch-Flow based modules to simulate important biogeochemical processes that need to be considered in gas hydrate environments. Kinetic model nodules were developed to: 1) Fully characterize the methane cycling at the sulfate-methane transition zone in systems in both diffusive and advective (chimney sites) flux regimes; 2) Reconstruct paleo-methane fluxes; and 3) Quantify the effect of sediment slumping on pore water profiles. We show the applicability of these modules by contributing to an additional study led by Kelly Rose, on pore-scale effects of gas hydrate distribution in the Andaman Sea.Our efforts within the scope of this project have allowed us to better quantify the reactions involved in generation and cycling or methane in present day system, both those controlled by purely diffusive fluxes as well as ...