In:
Biogeosciences, Copernicus GmbH, Vol. 16, No. 11 ( 2019-06-04), p. 2247-2268
Abstract:
Abstract. 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 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
calibration shows a larger scatter. However,
TEX86L-derived temperatures still
display anomalous estimates in polar regions. In order to elucidate the
potential cause of the disagreement between the
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 high-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 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.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-16-2247-2019
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2158181-2
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