Marine Crenarchaeota are the most abundant single group of prokaryotes in the ocean, but their physiology and role in marine biogeochemical cycles are unknown. Recently, a member of this clade was isolated from a sea aquarium and shown to be capable of nitrification, tentatively suggesting that Crenarchaeota may play a role in the oceanic nitrogen cycle. We enriched a crenarchaeote from North Sea water and showed that its abundance, and not that of bacteria, correlates with ammonium oxidation to nitrite. A time series study in the North Sea revealed that the abundance of the gene encoding for the archaeal ammonia monooxygenase alfa subunit ( amoA ) is correlated with a decline in ammonium concentrations and with the abundance of Crenarchaeota. Remarkably, the archaeal amoA abundance was 1–2 orders of magnitude higher than those of bacterial nitrifiers, which are commonly thought to mediate the oxidation of ammonium to nitrite in marine environments. Analysis of Atlantic waters of the upper 1,000 m, where most of the ammonium regeneration and oxidation takes place, showed that crenarchaeotal amoA copy numbers are also 1–3 orders of magnitude higher than those of bacterial amoA . Our data thus suggest a major role for Archaea in oceanic nitrification.

Large impacts provide a mechanism for resurfacin g planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peak s transition to peak ri ngs. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Ex pedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust

[1] Recently, a new geochemical temperature proxy, the TEX 86 , was introduced. This proxy is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraethers (GDGTs) of the membrane lipids of marine Crenarchaeota, which changes as a response to temperature. However, until now, only sediment data have been used to establish this proxy, and experimental work is missing. We performed mesocosm studies with marine Crenarchaeota incubated at temperatures ranging from 5 to 35°C and salinities of 27 and 35% to test the validity of the TEX 86 proxy. Growth of marine Crenarchaeota in these mesocosms was evident from the substantial increase in the concentration of marine Crenarchaeotal membrane lipids with amounts up to 3400 ng/L. With increasing temperature, an increase in the number of cyclopentane moieties in the crenarchaeotal membrane lipids was observed. Different salinities did not show any effect on the GDGT distribution. The TEX 86 showed a significant linear correlation to incubation temperature: TEX 86 = 0.015 Â T + 0.10 (r 2 = 0.79). This equation has a similar slope to the correlation obtained from core tops but differs in the intersection (TEX 86 = 0.015 Â T + 0.28, r 2 = 0.92). This difference is mainly determined by the smaller amount of the regioisomer of crenarchaeol in the incubation series compared to core top samples. These incubation experiments indicates that water temperature is indeed the major controlling factor for the membrane distribution of marine Crenarchaeota and confirms that the TEX 86 proxy depends on a physiological response to regulate membrane fluidity.

Within the upper 400 m at western, central, and eastern stations in the world's largest stratified basin, the Black Sea, we studied the qualitative and quantitative distribution of putative nitrifying Archaea based on their genetic markers (16S rDNA, amoA encoding for the alfa-subunit of archaeal ammonia monooxygenase), and crenarchaeol, the specific glycerol diphytanyl glycerol tetraether (GDGT) of pelagic Crenarchaeota within the Group I.1a.Marine Crenarchaeota were the most abundant Archaea (up to 98% of the total archaeal 16S rDNA copies) in the suboxic layers with oxygen levels as low as 1 µM including layers where previously anammox bacteria were described (Kuypers et al., 2003). Different marine crenarchaeotal phylotypes (both 16S rDNA and amoA) were found at the upper part of the suboxic zone as compared to the base of the suboxic zone and the upper 15-30 m of the anoxic waters with prevailing sulfide concentrations of up to 30 µM. Crenarchaeol concentrations were higher in the sulfidic chemocline as compared to the suboxic zone. These results indicate an abundance of putative nitrifying Archaea at very low oxygen levels within the Black Sea and might form an important source of nitrite for the anammox reaction.2