Preprints
https://doi.org/10.5194/bg-2021-245
https://doi.org/10.5194/bg-2021-245

  18 Nov 2021

18 Nov 2021

Review status: this preprint is currently under review for the journal BG.

The influence of near surface sediment hydrothermalism on the TEX86 tetraether lipid-based proxy and a new correction for ocean bottom lipid overprinting

Jeremy N. Bentley1, Gregory T. Ventura1, Clifford C. Walters2, Stefan M. Sievert3, and Jeffrey S. Seewald3 Jeremy N. Bentley et al.
  • 1Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada
  • 2Bureau of Economic Geology, University of Texas at Austin, USA
  • 3Woods Hole Oceanographic Institution, Woods Hole, USA

Abstract. The diversity and relative abundances of tetraether lipids produced by Thaumarchaeota in soils and sediments increasingly is used to assess environmental change. For instance, the TetraEther indeX of 86 carbon atoms (TEX86), based on archaeal isoprenoidal glycerol dialkyl glycerol tetraether (iGDGT) lipids, is frequently applied to reconstruct past sea-surface temperatures (SST). Yet, it is unknown how the ratio fully responds to environmental and or geochemical variations and if the produced signals are the adaptive response by Thaumarchaeota to climate driven temperature changes in the upper water column. We present the results of a four push-core transect study of surface sediments collected along an environmental gradient at the Cathedral Hill hydrothermal vent system in Guaymas Basin, Gulf of California. The transect crosses a region where advecting hydrothermal fluids reach 155 °C within the upper 21 cm below the seafloor (cmbsf) close to the vent center to near ambient conditions at the vent periphery. The recovered iGDGTs closest to the vent center experienced high rates of turnover with up to 94 % of lipid pool being lost within the upper 21 cmbsf. Here, we show that turnover is non-selective across TEX86 GDGT lipid classes and does not independently affect the ratio. However, as evident by TEX86 ratios being highly correlated to the Cathedral Hill vent sediment porewater temperatures (R2 = 0.84), the ratio can be strongly impacted by the combination of severe lipid loss when it is coupled to the addition of in situ iGDGT production from archaeal communities living in the vent sediments. The resulting signal overprint produces absolute temperature offsets of up to 4 °C based on the TEX86H-calibration relative to modern climate records of the region. The overprint is also striking given the flux of GDGTs from the upper water column that is estimated to represent ~93 % of the combined intact polar lipid (IPL) and core GDGT lipid pool initially deposited on the seafloor. A model to correct the overprint signal using IPLs is therefore presented that can similarly be applied to all near-surface marine sediment systems where calibration models or climate reconstructions are made based on the TEX86 measure.

Jeremy N. Bentley et al.

Status: open (until 30 Dec 2021)

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Jeremy N. Bentley et al.

Jeremy N. Bentley et al.

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Short summary
For this study, we demonstrate the commonly used TEX86 paleoclimate proxy can become heavily impacted by the ocean floor archaeal community. The impact result from a combination of source inputs, their diagenetic and catagenetic alteration, and further overprint by the additions of lipids from the ocean floor sedimentary archaeal community. We then present a method to correct the overprints by both water column and subsurface archaeal community’s using IPLs extracted from both of these sources.
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