|Biological source and provenance of deep-water derived isoprenoid tetraether lipids along the Portuguese continental margin|Kim, J.-H.; Villanueva, L.; Zell, C.; Sinninghe Damsté, J.S. (2016). Biological source and provenance of deep-water derived isoprenoid tetraether lipids along the Portuguese continental margin. Geochim. Cosmochim. Acta 172: 177–204. dx.doi.org/10.1016/j.gca.2015.09.010
In: Geochimica et Cosmochimica Acta. Elsevier: Oxford,New York etc.. ISSN 0016-7037; e-ISSN 1872-9533, meer
There is increasing evidence that nitrifying Thaumarchaeota in the deep ocean waters may contribute to the sedimentarycomposition of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs), impacting TEX86 paleothermometry. We investigatedthe potential effect of deep-water dwelling Thaumarchaeota in the warm and saline Mediterranean Outflow Water(MOW) on the distribution of isoGDGTs by analysing suspended particulate matter (SPM) and surface sediments collectedalong five land-ocean transects along the southern Portuguese continental margin. To this end, we directly compared for thefirst time the composition of intact polar lipid (IPL)-derived isoGDGTs of SPM with the diversity, abundance, and activity ofThaumarchaeota based on the genetic analysis of the genes coding for the archaeal ammonia monooxygenase (amoA) and thegeranylgeranylglyceryl phosphate (GGGP) synthase involved in the isoGDGT biosynthetic pathway. Our results revealed astrong positive relationship between water depth and TEXH86 values for both SPM and surface sediments. The increasingTEXH86 trends for both core lipid (CL) and IPL-derived fractions were accompanied by increasing fractional abundances ofGDGT-2 and crenarchaeol regio-isomer and decreasing fractional abundances of GDGT-1 and GDGT-3 with increasingwater depth. Phylogenetic analyses based on the archaeal amoA and the GGGP synthase proteins showed that Thaumarchaeotapopulations detected at 1 m and 50 m water depth were different from those detected in 200 m and 1000 m waterdepth, which had an increased contribution of so-called ‘deep water’ Thaumarchaeota. The differences in the fractional abundancesof isoGDGTs with water depth were compatible with the increasing contribution of ‘deep water’ Thaumarchaeota harboringa different GGGP synthase enzyme which has been suggested to relate to changes in the relative proportion ofsynthesized isoGDGTs. Accordingly, it appears that the sedimentary distribution of CL isoGDGTs used in TEXH86 alongthe Portuguese margin is primarily influenced by water depth due to the increasing contribution of the deep-water populationof Thaumarchaeota residing in the MOW. Our study also reveals that the effect of deep water Thaumarchaeotal communitieson sedimentary isoGDGT distributions should be considered globally.