25th International Meeting on Organic Geochemistry IMOG 2011

O-20
Organic aerosol transport and deposition over the Southern
Ocean
Susanne Fietz 1 , Alfredo Martínez-Garcia 2 , Bastian Hambach 1 , Sze Ling Ho 3 , Frank
Lamy 3 , Walter Geibert 4,5 , Antoni Rosell-Melé 1,6
1 Institut de Ciència i Tecnologia Ambientals (ICTA), Universitat Autònoma de Barcelona (UAB), Barcelona,
Spain, 2 ETH Zürich, Zürich, Switzerland, 3 Alfred Wegener Institute, Bremerhaven, Germany, 4 School of
Geosciences, University of Edinburgh, Edinburgh, United Kingdom, 5 Dunstaffnage Marine Laboratory,
Scottish Association for Marine Science, Oban, United Kingdom, 6 Institució Catalana de Recerca i Estudis
Avançats (ICREA), Barcelona, Spain (corresponding author:susanne.fietz@uab.cat)
The Southern Ocean plays a critical role in the
regulation of Earth‘s climate and atmospheric CO2
concentrations. The westerly winds drive the world‘s
largest current system, the Antarctic Circumpolar
Current, which connects the Atlantic, Pacific, and
Indian Oceans, and control the upwelling of CO2-rich
deep ocean waters to the surface. In addition, the
westerly winds are also responsible for the transport
of iron-rich terrestrial material into the Southern
Ocean, a process that can largely affect ocean
biogeochemical cycles. Indeed, windblown iron can
stimulate biological productivity in the Subantarctic
region, potentially affecting atmospheric CO2 uptake
through time.
In order to evaluate biomarker proxies to trace dust
inputs and the westerlies we have investigated the
importance and pathways of transport and deposition
of lithogenic material and associated biomarkers. We
focussed in the distribution of n-alkanes (derived from
plant waxes) and branched GDGTs (derived from soil
bacteria) in samples from the Atlantic and Pacific
sectors of the Southern Ocean (Fig. 1). Samples
investigated comprised air filters, particulate material
in surface and deep ocean waters, and surface
sediments. The n-alkane and GDGT export fluxes
towards the sea bottom were compared to proxies of
in-situ marine production (e.g., chlorins, alkenones,
and crenarchaeol).
Figure 1. Sample locations (black dots: aerosol filters,
surface water, deep water, and/or surface sediment;
red circle: ODP Site 1090, cf. Fig.2)
A further aim was to investigate the potential of nalkanes
and branched GDGTs as paleoclimatic
proxies of dust deposition over the Southern Ocean.
For that purpose, we also report a paleoceanographic
reconstruction from ODP site 1090 (see Fig. 1 for
location and Fig. 2 for record). We show that in this
record both biomarkers indicate an increase in dust
deposition during the glacial periods (Fig. 2) that is
closely linked to an increase in marine phytoplankton
(Fig. 2) and Archaea productivity.
Figure 2. Reconstructed SST (based on alkenone
unsaturation index UK37´), dust deposition (inferred
from branched GDGT and n-alkane concentrations),
and in-situ phytoplankton production (inferred from
chlorophyll transformation products, i.e. chlorins, and
alkenones) for the last 500 ky in the Subantarctic
Atlantic (ODP Site 1090)
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