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)

Park, Eunmi; Hefter, Jens; Fischer, Gerhard; Iversen, Morten Hvitfeldt; Ramondenc, Simon; Nöthig, Eva-Maria; Mollenhauer, Gesine

The relative abundance of individual archaeal membrane lipids, namely of glycerol dialkyl glycerol tetraethers (GDGTs) with different numbers of cyclopentane rings, varies with temperature, which enables their use as a paleotemperature proxy index. The first GDGT-based index in marine sediments called inline-formulaTEX86 is believed to reflect mean annual sea surface temperature (maSST). The inline-formula M4inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimg506c31356df3d4d1ee627292e6343e00 bg-16-2247-2019-ie00001.svg32pt17ptbg-16-2247-2019-ie00001.png is an alternative temperature proxy for “low-temperature” regions (inline-formula<15inline-formulaC), where the original inline-formulaTEX86 proxy calibration shows a larger scatter. However, inline-formula M8inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimgc8229702bb877f286ac5dc06585d9567 bg-16-2247-2019-ie00002.svg32pt17ptbg-16-2247-2019-ie00002.png -derived temperatures still display anomalous estimates in polar regions. In order to elucidate the potential cause of the disagreement between the inline-formula M9inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimg3033545652db2f76301491c4b4d8ae24 bg-16-2247-2019-ie00003.svg32pt17ptbg-16-2247-2019-ie00003.png estimate and SST, we analyzed GDGT fluxes and inline-formula M10inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimge4b57ce73663c24ae05588f7afdd61fd bg-16-2247-2019-ie00004.svg32pt17ptbg-16-2247-2019-ie00004.png -derived temperatures in sinking particles collected with time-series sediment traps in high-northern- and high-southern-latitude regions. At 1296 m depth in the eastern Fram Strait (79inline-formula N), a combination of various transporting mechanisms for GDGTs might result in seasonally different sinking velocities for particles carrying these lipids, resulting in strong variability in the inline-formula M12inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimge9e27c6fdbebfdec574f03c1bec9f596 bg-16-2247-2019-ie00005.svg32pt17ptbg-16-2247-2019-ie00005.png signal. The similarity of flux-weighted inline-formula M13inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimg6a412767e13b5e7c78b7739f62338cc2 bg-16-2247-2019-ie00006.svg32pt17ptbg-16-2247-2019-ie00006.png temperatures from sinking particles and surface sediments implies an export of GDGTs without alteration in the Fram Strait. The estimated temperatures correspond to temperatures in water depths of 30–80 m, where nitrification might occur, indicating the favorable depth habitat of Thaumarchaeota. In the Antarctic Polar Front of the Atlantic sector (50inline-formula S), inline-formula M15inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimgfa9316b81ba1ec61e5b75fc334bcfab9 bg-16-2247-2019-ie00007.svg32pt17ptbg-16-2247-2019-ie00007.png -derived temperatures displayed warm and cold biases compared to satellite-derived SSTs at 614 m depth, and its flux-weighted mean signal differs from the deep signal at 3196 m. inline-formula M16inlinescrollmathml normal TEX normal 86 normal L 32pt17ptsvg-formulamathimga69d239fad4cd272b9fda3456220f7fd bg-16-2247-2019-ie00008.svg32pt17ptbg-16-2247-2019-ie00008.png -derived temperatures at 3196 m depth and the surface sediment showed up to 7 inline-formulaC warmer temperatures relative to satellite-derived SST. Such a warm anomaly might be caused by GDGT contributions from Euryarchaeota, which are known to dominate archaeal communities in the circumpolar deep water of the Antarctic Polar Front. The other reason might be that a linear calibration is not appropriate for this frontal region. Of the newly suggested SST proxies based on hydroxylated GDGTs (OH-GDGTs), only those with OH-GDGT–0 and crenarchaeol or the ring index (RI) of OH-GDGTs yield realistic temperature estimates in our study regions, suggesting that OH-GDGTs could be applied as a potential temperature proxy in high-latitude oceans.

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Park, Eunmi / Hefter, Jens / Fischer, Gerhard / et al: 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). 2019. Copernicus Publications.

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