title: Influence of ammonia oxidation rate on thaumarchaeal lipid composition and the TEX86 temperature proxy.
abstract: Archaeal membrane lipids known as glycerol dibiphytanyl glycerol tetraethers (GDGTs) are the basis of the TEX86 paleotemperature proxy. Because GDGTs preserved in marine sediments are thought to originate mainly from planktonic, ammonia-oxidizing Thaumarchaeota, the basis of the correlation between TEX86 and sea surface temperature (SST) remains unresolved: How does TEX86 predict surface temperatures, when maximum thaumarchaeal activity occurs below the surface mixed layer and TEX86 does not covary with in situ growth temperatures? Here we used isothermal studies of the model thaumarchaeon Nitrosopumilus maritimus SCM1 to investigate how GDGT composition changes in response to ammonia oxidation rate. We used continuous culture methods to avoid potential confounding variables that can be associated with experiments in batch cultures. The results show that the ring index scales inversely (R(2) = 0.82) with ammonia oxidation rate (ϕ), indicating that GDGT cyclization depends on available reducing power. Correspondingly, the TEX86 ratio decreases by an equivalent of 5.4 °C of calculated temperature over a 5.5 fmol·cell(-1)·d(-1) increase in ϕ. This finding reconciles other recent experiments that have identified growth stage and oxygen availability as variables affecting TEX86 Depth profiles from the marine water column show minimum TEX86 values at the depth of maximum nitrification rates, consistent with our chemostat results. Our findings suggest that the TEX86 signal exported from the water column is influenced by the dynamics of ammonia oxidation. Thus, the global TEX86-SST calibration potentially represents a composite of regional correlations based on nutrient dynamics and global correlations based on archaeal community composition and temperature.
authors.affiliation: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138; shurley@fas.harvard.edu felling@uni-bremen.de pearson@eps.harvard.edu.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Hurley
authors.affiliation: Organic Geochemistry Group, MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen 28359, Germany; Department of Geosciences, University of Bremen, Bremen 28359, Germany; shurley@fas.harvard.edu felling@uni-bremen.de pearson@eps.harvard.edu.
authors.forename: Felix J
authors.initials: FJ
authors.lastname: Elling
authors.affiliation: Organic Geochemistry Group, MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen 28359, Germany; Department of Geosciences, University of Bremen, Bremen 28359, Germany;
authors.forename: Martin
authors.initials: M
authors.lastname: Könneke
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543; Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, MD 21613.
authors.forename: Carolyn
authors.initials: C
authors.lastname: Buchwald
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543;
authors.forename: Scott D
authors.initials: SD
authors.lastname: Wankel
authors.affiliation: Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, MD 21613.
authors.forename: Alyson E
authors.initials: AE
authors.lastname: Santoro
authors.affiliation: Organic Geochemistry Group, MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen 28359, Germany; Department of Geosciences, University of Bremen, Bremen 28359, Germany;
authors.forename: Julius Sebastian
authors.initials: JS
authors.lastname: Lipp
authors.affiliation: Organic Geochemistry Group, MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen 28359, Germany; Department of Geosciences, University of Bremen, Bremen 28359, Germany;
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Hinrichs
authors.affiliation: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138; shurley@fas.harvard.edu felling@uni-bremen.de pearson@eps.harvard.edu.
authors.forename: Ann
authors.initials: A
authors.lastname: Pearson
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D001105:Archaea / Q000378:metabolism*; D046508:Culture Techniques; D004734:Energy Metabolism; D005995:Glyceryl Ethers / Q000378:metabolism*; D050356:Lipid Metabolism; D009792:Oceans and Seas; D010084:Oxidation-Reduction; D010163:Paleontology / Q000379:methods*; D013696:Temperature
chemical_list: D005995:Glyceryl Ethers; D000641:Ammonia
keywords: GDGT; TEX86; Thaumarchaeota; continuous culture; nitrification