The influence of near-surface sediment hydrothermalism on the TEX 86 tetraether-lipid-based proxy and a new correction for ocean bottom lipid overprinting

[摘要] The diversity and relative abundances of tetraether lipids produced byarchaea and bacteria in soils and sediments are increasingly used to assessenvironmental change. For instance, the TetraEther indeX of 86 carbon atoms(TEX 86 ), based on archaeal isoprenoidal glycerol dialkyl glyceroltetraether (iGDGT) lipids, is frequently applied to reconstruct pastsea-surface temperatures (SSTs). Yet, it is unknown how the ratio fullyresponds to environmental and/or geochemical variations and if the producedsignals are largely the adaptive response by Thaumarchaeota to oceanographiceffects associated with climate or seasonal temperature changes in the upperwater column. We present the results of a four push-core transect study ofsurface sediments collected along an environmental gradient at the CathedralHill hydrothermal-vent system in Guaymas Basin, Gulf of California. Thetransect crosses a region where advecting hydrothermal fluids reach 155  ∘ C within the upper 21 cm below the seafloor (cm b.s.f.) close to thevent center to near-ambient conditions at the vent periphery. The recoverediGDGTs closest to the vent center experienced high rates of turnover with upto 94 % of the lipid pool being lost within the upper 21 cm b.s.f. Here, weshow that the turnover is non-selective across TEX 86 GDGT lipids anddoes not affect the ratio independently. However, as evident by TEX 86 ratios being highly correlated to the Cathedral Hill vent sediment porewatertemperatures ( R 2 =0.84 ), the ratio can be strongly impacted by thecombination of severe lipid loss coupled with the addition of in situ iGDGTproduction from archaeal communities living in the vent sediments. Theresulting overprint produces absolute temperature offsets of up to 4  ∘ C based on theTEX 86 H calibration relative to modernclimate records of the region. The overprint is also striking given the fluxof iGDGTs from the upper water column is estimated to be ∼  93 % of the combined intact polar lipid (IPL) and core GDGT lipid poolinitially deposited on the seafloor. A model to correct the overprint signalusing IPLs is therefore presented that can similarly be applied to allnear-surface marine sediment systems where calibration models or climatereconstructions are made based on the TEX 86 measure.

[学科分类] 大气科学