25th International Meeting on Organic Geochemistry IMOG 2011

P-220
A multiproxy high-resolution approach for the reconstruction of
sea surface temperatures of the last 500 years at the southern
Italian shelf
Arne Leider 1 , Anna-Lena Grauel 2 , Kai-Uwe Hinrichs 1 , Stefano M. Bernasconi 2 , Gerard
J.M. Versteegh 1
1 Org. Geochemistry Group, MARUM Center for Marine Environmental Sci. & Department of Geosciences,
University of Bremen, Bremen, Germany, 2 Geological Institute, ETH Zürich, Zürich, Switzerland
(corresponding author:arneleider@uni-bremen.de)
The southern Italian shelf harbors excellent sites for
high-resolution paleoenvironmental reconstructions [1
and references therein]. Furthermore, Italy provides a
unique archive of instrumental and historical records
of climate and environment in the Mediterranean.
Previous core-top calibrations along the southern
Italian shelf showed clear discrepancies between sea
surface temperature (SST) proxies based on the U K‘ 37
and TEX86 indices as well as � 18 O of the planktic
foraminifer G. ruber (white) (Fig. 1A-D). The
alkenone-based SSTs reflect maxima in haptophyte
production during colder seasons. The TEX86-derived
temperatures increase with distance from shore, so
that at least offshore TEX86-derived SSTs reflect
summer temperatures in the stratified and oligotrophic
water column of the Ionian Sea [2]. � 18 O based
temperatures of G. ruber (white) also reflect a
summer signal but variations seem to be influenced
offshore by changes in water depth habitat and
salinity of Ionian Sea waters [3].
In this study we have extended the previous
temperature proxy comparison [2] to a time series
using a core from the southern Italian shelf covering
the last 500 years with a 3-year sample resolution
(39.76°N, 17.89°E, 173 m water depth).
The SST proxy signals show a high variability during
the last 500 years with amplitudes of up to 3°C that
could not be explained by variations in regional
instrumental temperature records alone. The
alkenone-based temperatures (14.6-19.4°C; Fig. 1E)
are up to 5°C lower compared to TEX86 temperatures
(18.0-22.0°C). However, both proxies show covariations
with maxima at 1500 AD, 1800 AD and a
decrease in SST during the last century which
contrasts with the global temperature trend [e.g., 4]. In
general, � 18 O based temperatures (15.9-21.9°C)
agree with TEX86 SST estimates, but show periods
with opposing trends. We speculate that these reflect
variations in the balance between near-coastal and
more saline Ionian Sea waters from the Eastern
Mediterranean partly affecting the � 18 O composition
and carrying a high TEX86 temperature signal.
References
[1] Versteegh, G.J.M., de Leeuw, J.W., Tarricco, C.,
Romero, A. (2007) Geochem. Geophys. Geosyst. 8,
doi:10.1029/2006GC001543.
[2] Leider, A., Hinrichs, K.-U., Mollenhauer, G., Versteegh,
G.J.M., (2010) Earth Planet. Sci. Lett. 300, 112-124.
[3] Grauel, A.L., Bernasconi, S.M., (2010) Mar.
Micropaleontology 77, 175-186.
[4] IPCC (2007) WG1, Cambridge Univ. Press, New York.
Fig. 1. Distribution of sea surface temperatures (A-D) based on annual mean satellite data and the temperature proxies
U K‘ 37, TEX86 and � 18 O of G. ruber (white) in surface sediments at the southern Italian shelf [adapted from 2, 3]. E) Depth
profile of alkenone-based SSTs in core GeoB 10709-4, black curve indicates 3-point running mean.
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