Stable carbon isotopic compositions of archaeal lipids constrain terrestrial, planktonic, and benthic sources in marine sediments

• Published in: Geochimica et cosmochimica acta 2021-08, Vol.307, p.319-337
• Main Authors: Zhu, Qing-Zeng, Elvert, Marcus, Meador, Travis B., Becker, Kevin W., Heuer, Verena B., Hinrichs, Kai−Uwe
• Format: Article
• Language: English
• Subjects: Archaea; Butanetriol dibiphytanyl glycerol tetraethers; Geochemical zones; Glycerol dibiphytanyl glycerol tetraethers; In situ production; Intact polar lipids; Marine sediments; Stable carbon isotopes; Terrestrial input
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2021.04.037

•Constraining sources of core and intact archaeal lipids with stable C isotopic ratios.•No evidence for sedimentary sources of IPL crenarchaeol.•Evidence of sedimentary production of IPL caldarchaeol and BDGT-0.•Higher organic matter content promotes higher activity of sedimentary archaea.•Archaeol is a sensitive indicator of sedimentary archaea. Archaea occupy an important niche in the global carbon cycle and their lipids are widely used as indicators of environmental conditions in both paleoenvironmental and modern biogeochemical studies. The principal sources of archaeal lipids in marine sediments are benthic archaea, fossil remnants of planktonic archaea, and allochthonous sources such as soils. However, the relative contributions of these sources to the sedimentary lipid pool have not been comprehensively constrained, complicating a mechanistic understanding of archaeal lipid proxies. In order to provide insights into the relative contributions of these sources and identify signals derived from sedimentary activity, we performed a systematic survey of stable carbon isotopic compositions (δ13C) of both core and intact archaeal lipids via analyses of their phytanyl (Phy) and biphytanyl (BP) moieties in diverse marine sediments. The sample set consisted of 44 sediment horizons from the Mediterranean and adjacent basins and represented diverse sources of organic matter and depositional conditions. Complementary geochemical data enabled the comparison of lipid distributions and carbon isotopic signatures with prevailing redox conditions. The δ13C of tricyclic BP (BPcren) from the core and intact forms of crenarchaeol ranged from −19.1 to −28.6‰ and −18.1 to −27.4‰, respectively. δ13C values of core and intact BPcren did not differ, suggesting that intact crenarchaeol is either a fossil relic from planktonic archaea or a product of lipid recycling by benthic archaea, as opposed to being synthesized de novo by sedimentary archaea. δ13C values of BP0 derived from core and intact forms of glycerol and butanetriol dibiphytanyl glycerol tetraethers (GDGTs and BGDTs, respectively), but predominantly from caldarchaeol (GDGT-0), ranged from −19.4 to −32.0‰ and −20.9 to −37.0‰, respectively. In contrast to BPcren, intact-lipid derived BP0 was often 13C-depleted relative to its core counterpart, consistent with in situ production by sedimentary archaea. This relative depletion was most pronounced in sulfate reduction zones, likely due to heterotrophic activity. Core