25th International Meeting on Organic Geochemistry IMOG 2011

P-197
Sediment trap and core top study of organic (UK’37 and TEX86)
and inorganic � 18 O, Mg/Ca) sea surface temperature proxies in
the Mozambique Channel
Isla Castañeda, Ulrike Fallet, Geert-Jan Brummer, Jaap Sinninghe Damsté, Stefan
Schouten
NIOZ Royal Netherlands Institute for Sea Research, Den Burg, Netherlands (corresponding
author:isla.castaneda@nioz.nl)
Proxies for reconstructing past sea surface
temperatures (SST) are critical for paleoceanographic
and paleoclimatic studies; however, several factors
can influence their reliability. Here, we examine
organic (U K‘ 37 and TEX86) and inorganic (� 18 O and
Mg/Ca) SST proxies from a deep moored sediment
trap and surface sediments in the Mozambique
Channel (SW Indian Ocean). To evaluate
environmental factors influencing each proxy, we
compare this data to satellite-derived SST and to insitu
measurements of a number of physical properties
including salinity, current velocity and direction,
oxygen and nutrient concentrations.
A time series of sinking particles was collected at 21
day intervals from Nov. 2003 to April 2009 from a
deep sediment trap (2250 m depth; 250 m above the
seafloor) in the mid-Mozambique Channel. While the
Mg/Ca of surface dwelling foraminifer G. ruber
captured the seasonal variability in SST, the organic
proxies did not (Fig. 1). However, flux weighted mean
SSTs of all proxies (28.1 °C for Mg/Ca, 28.1 °C for
U K‘ 37 and 27.9 °C for TEX86) are in close agreement
with mean annual SST (27.6 °C). Times-series
analysis of all geochemical parameters examined
revealed a dominant peak at four to six cycles per
year, which is attributed to the passage of anticyclonic
meso-scale eddies (―Agulhas rings‖) through
the Mozambique Channel. The lack of seasonality in
the organic SST proxies is hypothesized to result from
eddy transport of organic carbon; however, this
material must be derived from a nearby location
because the reconstructed SSTs are in good
agreement with measured SST.
Radionuclide ( 14 C, 210 Pb, 234 Th) analysis of an E-W
transect of surface sediments extending across the
Mozambique Channel revealed that core top
sediments contain a mixture of pre-aged material and
fresh sediment. 14 C AMS ages of foraminiferal calcite
and TOC in surface sediments yielded ages of
977±35 yr BP and 887±30 yr BP, respectively, while
the 210 Pb profile displays a diffusive mixing pattern
and the 234 Th profile displays high activity in the
surface sediments (