Abstract
Abstract. Integrated Ocean Drilling Program (IODP) Expedition 336 addressed questions concerning subseafloor microbial life and its relation to seawater circulation and basalt–seawater reactions in the basaltic ocean crust. Sediment and basement samples were recovered at three drill sites located in the North Pond area, an 8 × 15 km large sediment pond on the 8 Ma western flank of the Mid-Atlantic Ridge around 22°45' N and 46°05' W in roughly 4450 m water depth. The average core recovery rate in basement was approx. 31%. The subseafloor depth of the basement holes ranges from 90 to 332 m; sediment thickness is between 36 and 90 m. Two of the holes (U1382A, and U1383C) were equipped with advanced Circulation Obviation Retrofit Kit (CORK) observatories, employing – for the first time – fiberglass casing. Another CORK string was deployed in Deep Sea Drilling Project (DSDP) Hole 395A, but the wellhead broke off upon final installment. Nonetheless, the North Pond observatory is fully operational and post-cruise observatory research is already underway. Combined geochemical and microbiological studies of the drill core samples and experimental CORK materials will help understand (1) the extent and activity of microbial life in basalt and its relation to basalt alteration by circulating seawater, and (2) the mechanism of microbial inoculation of an isolated sediment pond.
Highlights
The upper ocean crust constitutes a permeable and hydrologically active aquifer holding as much as 1–2 % of the ocean’s water (e.g., Fisher, 2005)
It is well known that the geochemical changes associated with basalt alteration in the uppermost oceanic crust play an important role in setting ocean chemistry
Fsiugubrseecaapfltioonosr microbiological communities in young igneous Foicg.e1a:nBacthryumsettraicnmdapthoef tihrerNoolrethiPnonodcaereaan(dcatraufrsotmaSltcehmraidtti-oSnchiwerhaosrnaetparl.i,2m01a2r)yonothbejwecesttievrnef.laSnkpoefcthifie Mcaidl-lAyt,lawntiec Rwidagen(tseede intsoet)t.e(sctomthmenths yonpothfeigsuirse)that microbes play an active role in ocean crust alteration, while exploring broad-based ecological questions such as how hydrological structure and geochemistry influence microbial community structures
Summary
The upper ocean crust constitutes a permeable and hydrologically active aquifer holding as much as 1–2 % of the ocean’s water (e.g., Fisher, 2005). Seawater circulation within this volcanic crust is well documented, but the extent to which microbes colonize, alter, and evolve in subsurface rock is essentially not known (e.g., Edwards et al, 2012a). Fsiugubrseecaapfltioonosr microbiological communities in young igneous Foicg.e1a:nBacthryumsettraicnmdapthoef tihrerNoolrethiPnonodcaereaan(dcatraufrsotmaSltcehmraidtti-oSnchiwerhaosrnaetparl.i,2m01a2r)yonothbejwecesttievrnef.laSnkpoefcthifie Mcaidl-lAyt,lawntiec Rwidagen(tseede intsoet)t.e(sctomthmenths yonpothfeigsuirse)that microbes play an active role in ocean crust alteration, while exploring broad-based ecological questions such as how hydrological structure and geochemistry influence microbial community structures. We intended to study the biogeography and dispersal of microbial life in subseafloor sediments
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