Premium
Fossilization and degradation of archaeal intact polar tetraether lipids in deeply buried marine sediments ( P eru M argin)
Author(s) -
Lengger Sabine K.,
Hopmans Ellen C.,
Sinninghe Damsté Jaap S.,
Schouten Stefan
Publication year - 2014
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/gbi.12081
Subject(s) - glycosidic bond , lability , polar , geology , chemistry , oceanography , biochemistry , physics , astronomy , enzyme
Glycerol dibiphytanyl glycerol tetraether ( GDGT ) lipids are part of the cellular membranes of T haumarchaeota, an archaeal phylum composed of aerobic ammonia oxidizers, and are used in the paleotemperature proxy TEX 86 . GDGT s in live cells possess polar head groups and are called intact polar lipids ( IPL ‐ GDGT s). Their transformation to core lipids ( CL ) by cleavage of the head group was assumed to proceed rapidly after cell death, but it has been suggested that some of these IPL ‐ GDGT s can, just like the CL ‐ GDGT s, be preserved over geological timescales. Here, we examined IPL ‐ GDGT s in deeply buried (0.2–186 mbsf, ~2.5 Myr) sediments from the P eru M argin. Direct measurements of the most abundant IPL ‐ GDGT , IPL ‐crenarchaeol, specific for T haumarchaeota, revealed depth profiles, which differed per head group. Shallow sediments (<1 mbsf) contained IPL ‐crenarchaeol with both glycosidic and phosphate head groups, as also observed in thaumarchaeal enrichment cultures, marine suspended particulate matter and marine surface sediments. However, hexose, phosphohexose‐crenarchaeol is not detected anymore below 6 mbsf (~7 kyr), suggesting a high lability. In contrast, IPL ‐crenarchaeol with glycosidic head groups is preserved over timescales of Myr. This agrees with previous analyses of deeply buried (>1 m) marine sediments, which only reported glycosidic and no phosphate‐containing IPL ‐ GDGT s. TEX 86 values of CL ‐ GDGT s did not markedly change with depth, and the TEX 86 of IPL ‐derived GDGT s decreased only when the proportions of monohexose‐ to dihexose‐ GDGT s changed, likely due to the enhanced preservation of the monohexose GDGT s. Our results support the hypothesis that in situ GDGT production and differential IPL degradation in sediments is not substantially affecting TEX 86 paleotemperature estimations based on CL – GDGT s and indicates that likely only a small amount of IPL ‐ GDGT s present in deeply buried sediments is part of cell membranes of active archaea. The amount of archaeal biomass in the deep biosphere based on these IPL s may have been substantially overestimated.