25th International Meeting on Organic Geochemistry IMOG 2011

P-449
Glycerol dialkyl glycerol tetraethers and the TEX86 index in
sinking particles in the western North Pacific
Masanobu Yamamoto 1 , Yuichiro Tanaka 2 , Akifumi Shimamoto 3
1 Hokkaido University, Sapporo, Japan, 2 Geological Survey of Japan, AIST, Tsukuba, Japan, 3 the General
Environmental Technos, Osaka, Japan (corresponding author:myama@ees.hokudai.ac.jp)
Seasonal and depth variations in the flux of
glycerol dialkyl glycerol tetraethers (GDGTs) and the
TEX86 values in sinking particles were examined
using a 21-month time-series sediment trap
experiment at a mooring station WCT-2 (39°N, 147°E)
in the mid-latitude NW Pacific to understand the
delivery process of GDGTs produced in surface water
to the deeper water column. A study of the same trap
samples was conducted for alkenones and U K 37‘
(Yamamoto et al., 2007), and we tried to understand
the behavior of GDGTs by comparing with that of
alkenones. Lateral advection of particles is negligible
at the study site (Yamamoto et al., 2007).
Alkenone sinking flux and U K 37‘–based
temperature showed strong seasonal variability. The
variations at three different depths were synchronous.
Alkenone fluxes were higher from spring to fall than
they were from fall to spring. During periods of high
alkenone flux, the U K 37‘–based temperatures were
lower than the contemporary SSTs, suggesting
alkenone production in a well-developed thermocline
(shallower than 30m). During low alkenone flux
periods, the U K 37‘–based temperatures were nearly
constant and were higher than the contemporary
SSTs, suggesting that fresh and labile particles sank
from spring to fall, while old and stable particles sank
from fall to spring (Yamamoto et al., 2007).
Isoprenoid GDGT sinking flux showed strong
temporal variability at the shallow traps (~1300 m),
whilst the fluxes at the deeper traps (~2500–4800 m)
did not vary in harmony with that at the shallow trap.
In contrast to U K 37‘, TEX86 did not show seasonal
variability. The average value of TEX86 corresponds to
the sea surface temperature in cooler seasons. The
sinking flux of isoprenoid GDGTs decreased with
increasing depth. The half depth, the depth interval in
which sinking flux becomes half, of total isoprenoid
GDGTs is ~3100 m, which is higher than that of
alkenones (~1700 m). The sinking fluxes of isoprenoid
GDGTs showed a good correlation with those of
organic carbon. The TEX86 values in sinking particles
at all depths were nearly identical and correspond to
sea surface temperatures.
These results suggest that the GDGTs
produced in surface water are suspended and
homogenized over annual cycles in the uppermost
water column and delivered to the deeper water
column along with the bulk organic particles. TEX86
values are stable during vertical transportation. The
above delivery mechanism is consistent with that
proposed by Wuchter et al. (2005). We also suggest
that isoprenoid GDGTs are relatively stable
(Yamamoto and Polyak, 2009), in contrast to a
suggestion by previous studies on the stability of
GDGTs, and they are preserved in oxic surface water
in a certain period, at least more than one year.
References
Wuchter, C., Schouten, S., Wakeham, S.G., Sinninghe
Damsté, J.S., 2005. Temporal and spatial variation
in tetraether membrane lipids of marine
Crenarchaeota in particulate organic matter:
Implications for TEX86 paleothermometry.
Paleoceanography, 20, PA3013.
Yamamoto, M., Shimamoto, A., Fukuhara, T.,
Naraoka, H., Tanaka, Y., Nishimura, A., 2007.
Seasonal and depth variations in molecular and
isotopic alkenone composition of sinking particles
from the western North Pacific. Deep-Sea
Research Part I, 54, 1571-1592.
Yamamoto,M., Polyak, L., 2009. Changes in
terrestrial organic matter input to the Mendeleev
Ridge, western Arctic Ocean, during the Late
Quaternary. Global and Planetary Change, 68, 30–
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