Climatically induced depositional dynamics - Results of an areal sediment survey at Laguna Potrok Aike, Argentina
Abstract
The ca. 770 ka old maar lake Laguna Potrok Aike (51°S, 70°W) is an ICDP site within the “Potrok Aike maar lake Sediment Archive Drilling prOject” (PASADO) and was drilled in 2008. The lake - situated in the dry steppe environment of south-eastern Patagonia - is a palaeolimnological key site for the reconstruction of terrestrial climatic and environmental conditions in the Southern Hemisphere. Climate patterns are characterized by high sensitivity to variations in westerly wind and pressure systems. Depositional changes inferred from the lacustrine sediment sequence and lake level terraces provide detailed information about the water budget of the lake which is related to the variability of the Southern Hemispheric Westerlies. In addition to the existing high-resolution and long-term multi-proxy investigation this study focuses on the understanding of depositional dynamics, which control the characteristics and spatial distribution of the lake’s sediment infill. This areal information will improve the interpretations of the long sediment record recovered within the PASADO project. A dense grid of 63 gravity cores and 40 near-shore surface samples were recovered to survey the spatial sediment distribution. Using X-ray fluorescence and magnetic susceptibility scanning data the cores were correlated and linked to a previously established age model. Samples of the 2005 sediment surface were taken from all cores. The scanning profiles do not allow unequivocal correlation of basin and littoral cores across the steep slopes. Thus, sub-sampling of five selected older time intervals covering distinctive hydrological settings back to AD 1380 was restricted to well correlated deep central basin cores. Distribution maps of multi-proxy datasets were created for every time slice using kriging. Sediment deposition in the lake is not only sensitive to lake level changes but also controlled by the dominant westerly winds. The longest wind fetch occurs at the eastern lake side and results in strong wave action, internal currents and polymictic conditions. Furthermore, influence of episodic inflows, ground water springs and of the surrounding geology is observed. The surficial sediments point to frequent relocation of littoral sediment at the eastern shore followed by transport to profundal accumulation areas. The sub-recent spatial sediment distribution is interpreted in context of these modern processes. Changing wind patterns and varying lake levels are assumed to cause modifications of depositional dynamics during the selected late Holocene time intervals. Low lake levels prior to the Little Ice Age and strengthened winds result in sediment distribution patterns comparable to modern times. In contrast, high lake levels during the Little Ice Age and extenuated westerly winds result in a more homogeneous sediment distribution indicating strengthened influence of the tributaries.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP14A..11K
- Keywords:
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- 0473 BIOGEOSCIENCES / Paleoclimatology and paleoceanography;
- 1620 GLOBAL CHANGE / Climate dynamics;
- 1637 GLOBAL CHANGE / Regional climate change