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| Titel |
Geochemical composition of surface sediments from the fjords of Northern Chilean Patagonia (44-47∘S): Spatial variability and implications for paleoclimate reconstructions |
| VerfasserIn |
S. Bertrand, K. Hughen, J. Sepulveda, S. Pantoja, C. Lange |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250020759
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| Zusammenfassung |
| High-resolution paleoclimate records from the Southern Hemisphere are essential to improve
our understanding of the interhemispheric pattern of paleoclimate changes. Due to their
intermediate location between the terrestrial and marine realms of southern South
America, the sediments deposited in the fjords of Southern Chile contain a high
resolution (i.e., sub-decadal) record of paleoclimate changes that occurred in the area
since the last deglaciation. Here we investigate the geochemical and mineralogical
composition of surface sediment samples collected in the fjords of Northern Chilean
Patagonia (44-47S) in order to better understand the processes that are responsible for
changes in sediment composition. PCA analysis of multi-proxy geochemical and
mineralogical variables demonstrates that the sediment composition in the fjords primarily
reflects the distance from/to the main tributaries, and therefore mirrors the nature and
degree of terrestrial sediment discharge. Proximal locations are characterized by
high contents in dense minerals such as amphibole, and high Zr/Ti, Ti/Fe, Zr/Al,
Fe/Al and C/N ratios, while more distal locations are enriched in biogenic particles
and have high Na/Al, Sr/Al and low C/N ratios. These proxies are therefore well
suited for estimating changes in terrestrial supply into the fjords through time. The
application of these proxies to a 2-m long sediment core from the Quitralco fjord
(PC29A, 46S, 1400 years) shows an increased terrestrial supply between ~1400
and 1900 AD, clearly marked by an increase in the Fe/Al ratio, as well as by a
strong increase in total Ti and Fe concentrations. These results are interpreted as an
increased river runoff, most likely linked to an increase in precipitation intensity and/or
wetter climate conditions between ~1400 AD and the beginning of the 20th century.
This wet period is coeval with a 1C decrease in SST, and is therefore believed to
represent a northward shift of the Southern Westerlies over Northern Patagonia
during the Little Ice Age. Finally, a similar approach is now being applied to long
sedimentary records from the fjords of Northern and Southern Patagonia (45-55S,
~15,000 years), from which preliminary results will be presented (Palmer 0505 cores). |
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