25th International Meeting on Organic Geochemistry IMOG 2011

P-214
Crenarchaeotal tetraether index of TEX86 as an indicator of
subsurface temperatures in the South China Sea
Guodong Jia 1 , Jie Zhang 1 , Jianfang Chen 2
1 Guangzhou Institute of Geochemistry, Guangzhou, China, 2 Second Institute of Oceanography, Hangzhou,
China (corresponding author:jiagd@gig.ac.cn)
Global core-top calibrations of the organic
paleothermometer, TEX86, have been performed
extensively. However, few data from the global
dataset were from the pacific, and some studies have
suggested the importance of local calibrations due to
the spatiality and seasonality of marine crenarchaeota
production. Here, we examined and calibrated the
TEX86 index in 32 surface sediments in the South
China Sea (SCS), a tropical marginal sea in the
western Pacific. Another widely used
paleothermometer, U37 K′ , having been calibrated
previously to reflect 0-30 m sea surface temperature
(SST) in the SCS, was also examined. TEX86 and
U37 K′ indices were correlated with averaged
temperatures of various depth levels and seasons.
Our results revealed a contrast that U37 K′ correlated
significantly with spring, autumn and winter SSTs,
whereas TEX86 showed strong correlations with
summer and autumn subsurface temperatures
(sSST). However, the strong signals of annual mean
temperatures in both the indices indicated that
seasonality in coccolith and marine crenarchaeota
growth seemed unlikely to bias them towards a
certain seasonal temperatures. The best curve fittings
of the TEX86 measurements were obtained for the
annual mean 30-125 m water column temperatures,
providing a linear equation of sSSTannual =
38.73*TEX86–5.04. Due to their indexing temperatures
of different water column intervals, the difference
between U37 K′ - and TEX86-derived temperatures
(ΔTAlkenone-GDGT) was hypothesized as a novel proxy
for upper ocean vertical thermal gradient in the SCS.
This hypothesis was confirmed by a strong correlation
between ΔTAlkenone-GDGT and the depth of thermocline
defined as the 18°C isothermal depth (Fig. 1).
Fig. 1 Correlation of the difference between U37 k′ - and
TEX86-derived temperatures (ΔTAlkenone-GDGT) with the
depth of thermocline (DOT) defined as the 18°C
isothermal depth.
353