Seminars Archive

Tracing methane emissions with benthic foraminifera

Abstract
Coupling of methane emissions with global climate throughout the recent geological history of the Earth is well established. However, the contribution of different methane sources in the global budget is still a matter of debate. Marine and terrestrial methane both contribute to atmospheric methane, but the intensity, duration, episodicity, and areal distribution of these emissions are poorly understood, particularly in the marine environment. One of the problems in the investigation of methane emissions in the sedimentary record is the scarcity of well-defined proxies that can be used to establish the timing of such events. Benthic foraminifera are an important component of biomass in the present oceans. In addition to their interest as indicator species living in the largest habitat on Earth, their tests have been used in isotope and trace element analysis aimed at reconstructing past environments. Carbon isotope (delta13C) of foraminiferal tests affected by release of large volumes of isotopically light methane from the seafloor are much lower than those observed in non-seep environments. The hypothesis that benthic foraminifera could be used as proxies of local methane emissions from the seafloor has been verified by several studies. However, additional work is needed to better understand how seep foraminifera secrete carbonates with delta13C values that are so far out of equilibrium with ambient pore water values.