Diagenetic disturbances of marine sedimentary records from methane‐influenced environments in the Fram Strait as indications of variation in seep intensity during the last 35 000 years

Abstract

T. L. 2017 (April): Diagenetic disturbances of marine sedimentary records from methane-influenced environments in the Fram Strait as indications of variation in seep intensity during the last 35 000 years.The effect of seeping of methane on marine sediment records has been studied in four gravity cores from Vestnesa Ridge, Svalbard margin. The area shows acoustic signs in the form of flares indicating active methane gas seepage. For a better understanding of the timing and variability of the flux of methane in the past and the effects on potential proxies, a detailed study of the diagenetic processes that may affect the composition and structure of both sediments and foraminiferal shells is needed. Here we discuss deep-sea records from methane-influenced environments in three cores from an active and very heterogeneous seep-area (pockmark) and one core from outside the pockmark for background. The results include the distribution and stable isotopes of authigenic carbonates and of benthic and planktonic foraminifera, magnetic susceptibility, AMS-14 C dates, sedimentary data and biostratigraphy. Extremely low d 13 C values recorded in both benthic and planktonic foraminifera during the Bølling-Allerød interstadials indicate possible increased methane flux beginning at late Heinrich event H1. The recorded low values are mainly a result of diagenetic overprint by methane-derived authigenic carbonates. The d 18 O signals of authigenic carbonates are close to those of foraminiferal calcite and thus the d 18 O records remain a valid stratigraphical tool in methane seep sites, except in the case of severely encrusted samples. In addition, the records from the active pockmark show nearly constant values of low magnetic susceptibility in contrast to higher and more variable magnetic susceptibility values from the control station and other published records from normal sediments west of Svalbard. This phenomenon is probably caused by dissolution of magnetic minerals in the reducing environmental conditions of methane seep sediments, associated with anaerobic oxidation of methane and formation of paramagnetic minerals (pyrite). This process enables magnetic susceptibility to be used as a common diagnostic tool for identifying methane-related palaeo-reductive environments.

Ice‐rafting patterns on the western Svalbard slope 74–0 ka: interplay between ice‐sheet activity, climate and ocean circulation

“…The magnetic susceptibility records show that both the mass‐transport deposits and the IRD layer on top have very low magnetic susceptibility values all along the western Svalbard slope (Jessen et al . ; Sztybor & Rasmussen ) including the Yermak Plateau, northwest Svalbard (Chauhan et al . ).…”

Methane cold seeps as biological oases in the high‐Arctic deep sea

“…Plaza‐Faverola et al () documented the history of methane seepage for the last ∼ 2.7 My along VR identifying multiple historical events of seepage. There have also been methane seepage events identified in the stratigraphic record through analysis of fossil marine fauna (Ambrose et al ; Sztybor and Rasmussen ). Hong et al () document vigorous biogeochemical processing and transformations in the surface sediments at VR consistent with high methane consumption via microbial AOM.…”

Geophysical and geochemical controls on the megafaunal community of a high Arctic cold seep

“…Intriguingly, this separation between Arctic seeps and seeps in other parts of the world with respect to large, chemosymbiotic species, is likely only a modern trend. The shells of large bodied chemosymbiotic bivalves (thyasirids and vesicomyids) have been recovered in cores from the pingo 15 study site (Åström et al, 2017a), Vestnesa Ridge (Ambrose et al, 2015;Hansen et al, 2017;Sztybor and Rasmussen, 2017) and methane seep deposits on the Gakkel Ridge (Kim et al, 2006) and in the Laptev Sea (Sirenko et al, 1995). Shells from the pingo site have been estimated to be up to 7-14 thousand years old (M. Carroll, unpublished data), and based on the Vestnesa and Gakkel Ridge samples, the extinction event for these animals has been estimated to have taken place around 15,000 years ago (Ambrose et al, 2015;Hansen et al, 2017;Kim et al, 2006;Sztybor and Rasmussen, 2017).…”

“…The shells of large bodied chemosymbiotic bivalves (thyasirids and vesicomyids) have been recovered in cores from the pingo 15 study site (Åström et al, 2017a), Vestnesa Ridge (Ambrose et al, 2015;Hansen et al, 2017;Sztybor and Rasmussen, 2017) and methane seep deposits on the Gakkel Ridge (Kim et al, 2006) and in the Laptev Sea (Sirenko et al, 1995). Shells from the pingo site have been estimated to be up to 7-14 thousand years old (M. Carroll, unpublished data), and based on the Vestnesa and Gakkel Ridge samples, the extinction event for these animals has been estimated to have taken place around 15,000 years ago (Ambrose et al, 2015;Hansen et al, 2017;Kim et al, 2006;Sztybor and Rasmussen, 2017). This coincides 20 with deglaciation following the Heinrich H1 cold event and the accompanying environmental changes, including extensive releases of methane such as is hypothesized to have created the pingos at the study site This could have led to the local extinction of large chemosymbiotic bivalves in the Arctic.…”