Late Quaternary hydrological variability in southeastern Patagonia – 45,000 years of terrestrial evidence from Laguna Potrok Aike

Torsten Haberzettl

Geoscience Center Göttingen, Dept. of Sedimentology/Environmental Geology

Talk by Torsten Haberzettl in MN 16, on Tuesday, 28th November 2006, 16:15
(in German)

The maar lake Laguna Potrok Aike is located in the dry Patagonian steppe, an area with hitherto only scarce paleoenvironmental information. Within the project SALSA (South Argentinean Lake Sediment Archives and modelling) Laguna Potrok Aike turned out to be the key site for paleoenvironmental reconstruction in that area. With a continuous, high-resolution multi-proxy approach applied to the well radiocarbon and tephra dated sediments it was possible to distinguish between lake level high and low stands. Those do not only give information about the hydrological state of climatic periods like the Little Ice Age or the Medieval Climate Anomaly but also reflect hydrological variations for southern Patagonia during the past 16,000 cal. BP as well as Oxygen Isotope Stage 3. In this context the total inorganic carbon content was identified as a sensitive lake level indicator which was supported by various other proxies for lake level changes, minerogenic input or redox-conditions which are also suited for reconstructing paleoenvironmental conditions.
Proxies suggest a high lake level during Oxygen Isotope Stage 3 for Laguna Potrok Aike. At least similar, probably higher lake levels are assumed for the period between 16,000 and 13,100 cal. BP that possibly resulted in a Late Glacial surface outflow. From 13,100 until 11,400 cal. BP the lake level lowered. Contemporaneously, between 12,800 until 11,400 cal. BP the record suggests warm conditions. A transgression starting at 11,400 cal. BP lasted until 8,650 cal. BP when the lake level dropped to the lowest position of the record. After a transgression, shortly before 6,750 cal. BP, the lake level was variable with humid intervals. The last wet period ascribed to the Little Ice Age, was the most extended humid period since early Holocene high lake levels at Laguna Potrok Aike before 8,650 cal. BP.
Data also contain a signal of European impact which started earlier in Patagonia than previously assumed. Most obvious signals for the presence of Europeans in southern Patagonia become evident with the beginning of sheep farming.
In general, the record from Laguna Potrok Aike is consistent with the further north located record from Lago Cardiel suggesting a response to the same forcing mechanisms and a similar climatic history of today's Patagonian steppe, maybe slightly shifted in time. In contrast, comparisons with Andean archives revealed an opposite hydrological pattern which is probably based on the fact that an intensification of Southern Hemisphere Westerlies results in a precipitation increase west of the Andes and a precipitation decrease in the steppe. This is due to blocking of precipitation carrying easterly winds responsible for most of the precipitation at Laguna Potrok Aike.