Decoupling short- and long-term methane seepage dynamics: high-resolution insights from Pyrgo spp. δ¹³C records at Woolsey Mound, Gulf of Mexico

Abstract

Oceanic methane seepage plays a critical role in the global carbon cycle, yet reconstructing transient seepage variability remains challenging due to the complex interplay of environmental dynamics and biogeochemical processes. Here, we demonstrate that stable carbon isotopes from individual Miliolida foraminifera, particularly Pyrgo spp., offer a reliable high-resolution proxy for short-lived, episodic seafloor methane discharge. Using sediment cores from Woolsey Mound, a cold seep/methane gas hydrate system in the northern Gulf of Mexico, we analyzed individual foraminiferal δ¹³C signatures alongside bulk geochemical proxies to assess methane flux variability over the last ∼50 kyrs. Our results reveal a pronounced temporal decoupling, with short-term δ¹³C excursions in Pyrgo spp. (years) distinct from longer-term bulk sedimentary trends (centuries to millennia), reflecting different temporal resolutions. Notably, while sedimentary proxies reflect longer-term, integrated dynamics, the preservation of primary methane-derived carbon signals in Pyrgo spp. due to minimal diagenetic alteration, enables the detection of short-lived methane seepage events with high temporal precision. These findings highlight the value of species-specific foraminiferal δ¹³C analyses for resolving episodic methane release and highlight the complementary insights gained from integrating individual foraminiferal records with bulk geochemical proxies. This approach advances our ability to reconstruct past methane cycling at cold seeps, providing a framework for understanding methane release dynamics under changing climatic conditions.