Popular Science: Tracking Paleoclimate in High Central Andes
Under the hands of scientists from the Physical Geography Department and Geochemical Dept. of the Faculty of Nature (Charles University in Prague) along with the collaboration of workers from the West Australian Biogeochemistry Centre, a study of the paleoclimate conditions on the Western side of the Central Andes was prepared. A peat bog core sample of 755 cm was done in the site area; then using radiocarbon methods the authors dated the profile to be 4300 years old. The whole profile was cut into 302 samples of 2.5 cm each, which were thereafter analyzed under laboratory conditions. The authors also acknowledged the relative temperature changes during the last 4300 years (the upper Holocene period) thanks to the measurements of stable carbon isotope content in the samples. This data was then compiled with information about humidity changes in the study area, which were taken using an analysis of the organic carbon content. The studied profile was sampled in an area that was formed by a glacier that modeled the Carhuasanta River valley, 4800 m a. s. l. The annual air temperature is close to 0°C; however day-night differences in winter can be over 30°C. Because of this, only plants well-adapted to repeated freezing and melting are able to survive in areas such as this study site. One of these plants is Distichia muscoides (Juncaceae), which is a dominant plant species of peat bogs in valleys of the Andes and it is therefore no wonder that its remains comprise 99% of the organic matter in the samples.
In the discussion, the authors differentiate 7 periods. They also compare their findings about relative changes in moisture levels and temperatures with other paleoclimate records from area of the Central Andes. The first one (2300–1990 BC) was a relatively warm and humid period during which a little cooling happened (2180–1900 BC), followed by a decrease in moisture, which also corresponded with changes in the stable oxygen isotope content in the significant sediment record of Pumacocha lake. In the following period, the most prominent climate change in the last 4300 years occurred. Firstly, there was some warming between the years 1090 and 800 BC, followed by a massive cooling of the air temperature of 2°C lower than the mean temperature for whole Upper Holocene period. This observed change corresponded nicely with the global climatic event dated 2.8 t. of years BP, which is often contributed to changes in solar activity as well as in ocean currents. After a predominantly dryer period with more stable temperatures (800 to 0 BC), the conditions began to be more variable. During the first century we can clearly see some fluctuating in the air temperature (-0.8 to 1.7°C to the mean) and, according to the authors, this period matches with the beginning of an unstable phase of Niño activity that affects the area. A relative decrease in the level of humidity at the end of the first century indicates a more weakened South-American monsoon that brings precipitations to the area from the Amazonia basin. From the end of the 10th century and far to the beginning of the 14th century, the regional air temperature was mostly under the mean, with only exceptionally short warmer fluctuations that appeared in a period of regional temperature anomaly (Medieval Warm Period). The following phase (1310–1795) was surprisingly characterized by a gradual warming, which was in contradiction with the assumedly cold conditions in the period of the regional little ice age (delineated in the Central Andes on the basis of the glacier advance, from the 14th to 17th centuries). The period from the end of 18th century was observed as the second coldest phase with temperatures up to 2°C lower that the mean. A gradual decrease and fluctuations in temperature continued until 1960 when we can see a clear change in this trend, featuring a rapid warming which is also documented by historical temperature records.
Beyond the climate changes, the authors of the paper also observed a positive influence of warmer and moister conditions on the mass amount of accumulated plant remains – which supports the positive influence of a warmer temperature and water column on primary production and decomposition.
The authors were focused on an area where paleo-environmental research work is limited. Therefore, they present a new approach of significant potential for further fieldwork, as peat bogs in the Andes valleys are widely extended. Paleo-environmental studies are not only important for the understanding of widely-discussed global climate change, but also for modeling future developments.
Z článku: Engel, Z., Skrzypek, G., Chuman, T., Šefrna, L. & Mihaljevič, M. (2014). Climate in the Western Cordillera of the Central Andes over the last 4300 years. Quaternary Science Reviews, Vol. 99, 60-77.