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Abstract. The relative abundance of individual archaeal membranelipids, namely of glycerol dialkyl glycerol tetraethers (GDGTs) withdifferent numbers of cyclopentane rings, varies with temperature, whichenables their use as a paleotemperature proxy index. The firstGDGT-based index in marine sediments called TEX86 is believed to reflect mean annual sea surface temperature (maSST). The TEX 86 L is an alternative temperatureproxy for “low-temperature” regions ( ∘ C), where the original TEX86 proxycalibration shows a larger scatter. However, TEX 86 L -derived temperatures stilldisplay anomalous estimates in polar regions. In order to elucidate thepotential cause of the disagreement between the TEX 86 L estimate and SST, we analyzedGDGT fluxes and TEX 86 L -derivedtemperatures in sinking particles collected with time-series sediment trapsin high-northern- and high-southern-latitude regions. At 1296 m depth in theeastern Fram Strait (79 ∘  N), a combination of various transportingmechanisms for GDGTs might result in seasonally different sinking velocitiesfor particles carrying these lipids, resulting in strong variability in the TEX 86 L signal. The similarity of flux-weighted TEX 86 L temperatures fromsinking particles and surface sediments implies an export of GDGTs withoutalteration in the Fram Strait. The estimated temperatures correspond totemperatures in water depths of 30–80 m, where nitrification might occur,indicating the favorable depth habitat of Thaumarchaeota. In the AntarcticPolar Front of the Atlantic sector (50 ∘  S), TEX 86 L -derived temperatures displayedwarm and cold biases compared to satellite-derived SSTs at 614 m depth, andits flux-weighted mean signal differs from the deep signal at 3196 m. TEX 86 L -derived temperatures at 3196 mdepth and the surface sediment showed up to 7  ∘ C warmertemperatures relative to satellite-derived SST. Such a warm anomaly might becaused by GDGT contributions from Euryarchaeota, which are known to dominatearchaeal communities in the circumpolar deep water of the Antarctic PolarFront. The other reason might be that a linear calibration is notappropriate for this frontal region. Of the newly suggested SST proxiesbased on hydroxylated GDGTs (OH-GDGTs), only those with OH-GDGT–0 andcrenarchaeol or the ring index (RI) of OH-GDGTs yield realistic temperatureestimates in our study regions, suggesting that OH-GDGTs could be applied asa potential temperature proxy in high-latitude oceans.

biogeosciences

Seasonality of archaeal lipid flux and GDGT-based thermometry in sinking particles of high-latitude oceans: Fram Strait (79° N) and Antarctic Polar Front (50° S)