New insights into the transport processes controlling the sulfate-methane-transition-zone near methane vents.

Nabil Sultan,Livio Ruffine,Sébastien Garziglia

doi:10.1038/srep26701

Abstract

Over the past years, several studies have raised concerns about the possible interactions between methane hydrate decomposition and external change. To carry out such an investigation, it is essential to characterize the baseline dynamics of gas hydrate systems related to natural geological and sedimentary processes. This is usually treated through the analysis of sulfate-reduction coupled to anaerobic oxidation of methane (AOM). Here, we model sulfate reduction coupled with AOM as a two-dimensional (2D) problem including, advective and diffusive transport. This is applied to a case study from a deep-water site off Nigeria’s coast where lateral methane advection through turbidite layers was suspected. We show by analyzing the acquired data in combination with computational modeling that a two-dimensional approach is able to accurately describe the recent past dynamics of such a complex natural system. Our results show that the sulfate-methane-transition-zone (SMTZ) is not a vertical barrier for dissolved sulfate and methane. We also show that such a modeling is able to assess short timescale variations in the order of decades to centuries.

Highlights

Dynamical interactions were taken from the coexistence of free gas within the gas hydrate occurrence zone (GHOS) and, most from the presence of methane hydrates with a bubble-type fabric[15]
The top of the gas hydrate occurrence zone (GHOZ) is located at depths ranging from 2.3 to 7.6 m below seabed, with a tendency to deepen towards the periphery of pockmark A20
The driving factor of this relatively high lateral advection velocity seems to be related to an over-pressured intermediate gas reservoir rather than to the hydrate dissolution/dissociation[26] processes where the methane advection velocity is Figure 5. 2D modeling of sulfate-reduction coupled to AOM

Summary

Introduction

Chloride and alkalinity data acquired from GMMB01 and GMMB02 and presented in Fig. 2c–e seem more to be the result of a complex advection/diffusion transport processe controlling the sulfate-methane-transition-zone near methane vents.

Results

Conclusion