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https://doi.org/10.5194/bg-2019-34
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-34
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Jan 2019

Research article | 30 Jan 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Biogeosciences (BG).

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

Eunmi Park1,2,3, Jens Hefter1, Gehard Fischer2,3, Morten H. Iversen1,2, Simon Ramondenc1,2, Eva-Maria Nöthig1, and Gesine Mollenhauer1,2,3 Eunmi Park et al.
  • 1Alfred-Wegener-Institute, Helmholtz-Center for Polar and Marine Sciences, 27570 Bremerhaven, Germany
  • 2MARUM Centre for Marine Environmental Sciences, University of Bremen, 28334 Bremen, Germany
  • 3Department of Geosciences, University of Bremen, 28334 Bremen, Germany

Abstract. The relative abundance of individual archaeal membrane lipids, namely of glycerol dialkyl glycerol tetraethers (GDGTs) with the different number of cyclopentane rings, varies with temperature, which enabled their use as paleotemperature proxy. The first GDGT-based index in marine sediments called TEX86 is believed to reflect mean annual sea surface temperature (maSST). The TEX86L is an alternative temperature proxy for low temperature regions (< 15 °C), where the original TEX86 proxy suffers from scattering in a linear calibration with SSTs. However, TEX86L-derived temperatures still display anomalous estimates in polar regions. In order to elucidate the potential cause of the disagreement between TEX86L estimate and SST, we analyzed GDGT fluxes and TEX86L-derived temperatures in sinking particles collected with time-series sediment traps in high northern and southern latitude regions. At 1296 m depth in the eastern Fram Strait (79° 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 TEX86L signal. The similarity of flux weighted TEX86L temperatures from sinking particles and surface sediments implies an export of GDGTs without alteration during transport 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 (50° S), TEX86L-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. TEX86L-derived temperatures at 3196 m depth and the surface sediment showed up to 7 °C 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.

Eunmi Park et al.
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Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Eunmi Park et al.
Data sets

Fractional abundances and concentrations of GDGT collected by sediment trap moored in two latitude regions of the Atlantic Ocean: in the eastern Fram Strait (FEVI16) and in the Antarctic Polar Front (PF3) E. Park, J. Hefter, G. Fischer, G. Iversen, M. Hvitfeldt, S. Ramondenc, E.-M. Nöthig, and G. Mollenhauer https://doi.pangaea.de/10.1594/PANGAEA.897268

Eunmi Park et al.
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Short summary
We analyzed GDGT based proxy temperatures in the polar oceans. In the eastern Fram Strait (79° N), the nutrient distribution may determine the depth habit of Thaumarchaeota and thus the proxy temperature. In the Antarctic Polar Front (50° S), the contribution of Euryarchaeota or the nonlinear correlation between the proxy values and temperatures may cause the warm biases of the proxy temperatures relative to SSTs.
We analyzed GDGT based proxy temperatures in the polar oceans. In the eastern Fram Strait...
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