Late glacial and deglacial palaeoceanographic changes at Vestnesa Ridge, Fram Strait: Methane seep versus non-seep environments

Abstract

Two cores from 1200m water depth from Vestnesa Ridge on the western Svalbard margin have been investigated for the distribution of benthic and planktic foraminiferal assemblages, oxygen and carbon isotopes, geochemical and sedimentological parameters including magnetic susceptibility, total organic carbon (TOC) and CaCO3 content of the sediment. Vestnesa Ridge is known for the presence of numerous pockmarks, where methane gas is bubbling out from the seafloor. One core was taken from a pockmark with active seepage of methane, while the second core was taken just outside the seepage area for comparison. The purpose of the study is to reconstruct the palaeoceanography and compare to published palaeoceanographic records from the area and evaluate if seepage of methane have had any impact on the distribution patterns of benthic foraminiferal species and the sedimentary environments through time. The results indicate almost continuous presence of Atlantic water throughout the last 43,000years. During the Heinrich H1 interval ca. 18,000–15,300years Atlantic water flowed subsurface along the bottom and the period stands out with the highest bottom-water temperatures of the last 43,000years. Settlement of a community of chemo-synthesizing bivalves indicates increase in the release of methane beginning during H1. However, in both records of seep versus non-seep environments, the distribution patterns of benthic foraminiferal species, diversity, and productivity of the specimens were the same, indicating that seepage of methane had no influence on the foraminiferal faunas. Our results show that the palaeoceanographic development at Vestnesa Ridge was similar to the development over the western Svalbard margin and the Fram Strait confirming previously published results. We conclude that the benthic foraminifera at the methane seep site were mainly controlled by palaeoceanographic changes and associated changes in the sedimentary environment and palaeoproductivity overprinting any eventual influence of seepage of methane.