A study developed at the Unicamp Geosciences Institute during Adriana Mercedes Camejo Aviles' master's thesis, supervised by professor Fresia Soledad Ricardi Torres Branco, revealed important data on the evolution of climate change in the Campinas region over the last 25 thousand years. The discovery was published in a article in mid-November in Brazilian Journal of Geology and is also signed by researchers Marie-Pierre Ledru, from the French Institute for Development Research (IRD), which maintains a partnership with the IG, and by Luís Carlos Bernacci, from the Center for Research and Development of Plant Genetic Resources at the Agronomic Institute of Campinas (IAC). The results show a sequence of changes in vegetation and climate, revealing the evolution from a drier period to a wetter one.
The research was carried out at Fazenda Santa Elisa, of the Agronomic Institute of Campinas, close to Campo dos Amarais, in Campinas. Although drier climate conditions were recorded 25 years ago, there were peaks of humidity capable of maintaining an open forest. “In that area, there is a riparian forest with a stream that is part of the Quilombo stream. The curves form lakes, where organic matter accumulates. Plant pollens and pieces of leaves and trunks are deposited and, over thousands of years, record the vegetation that existed in the area”, explains professor Fresia Ricardi. Registration is done by levels, from oldest to youngest. By analyzing centimeter by centimeter, due to slow deposition, it is possible to identify what the vegetation was like in different periods of time.
“As it is material from a recent period, it was possible to date them by C14, which records data from up to 60 thousand years ago. C14 is a radioactive isotope of Carbon that degrades over time and transforms into another isotope. By measuring the age of the parent isotope and the daughter isotope, it is possible to assess how much time has passed according to the drop in the radioactive decay rate”, reveals Fresia. According to the teacher, in the collection carried out in the IAC forest, it was possible to recover a testimonial measuring 182 cm. “We dated it to C14 and analyzed pollen in the first 90 cm and the stable isotopes of Carnabo13 and Nitrogen 15 throughout the record. We identified changes in vegetation and compared them with current vegetation, which allowed us to analyze this evolution,” she says.
Palynological records make it possible to infer climate changes. “Depending on the type of pollen assemblage identified, there is one or another type of forest. From 25 thousand to 13 thousand years ago the river changed. The isotopic results indicated a dry climate”, explains Fresia. Family plants arecaceae, which are palm trees, exist today in the area, but during the drier period there were almost none. From 4 thousand years to the present day it was possible to identify an increase in humidity. The climate has changed and has intervals with drier and wetter parts. “Today we are in a wetter period, but there is a possibility of a drier period coming due to climate fluctuations”, he highlights.
According to Fresia, it is not possible to carry out this type of analysis in any location where there are meanders, as it is necessary to have preserved natural vegetation, which has not suffered human intervention. IAC's collaboration was fundamental to the discovery. The researchers had an ongoing FAPESP project (“Water in soil morphology associated with the physiognomic gradient Riparian Forest — Cerrado in Campinas, SP”) which allowed the drilling of the testimony.
The discovery also included the collaboration of the Herbarium of the Unicamp Biology Institute. The IG group identified plants in the region, collected flowers and identified the types of pollen that could be found in the sediments. “The flowers of these pollens were correctly identified in the systematics by the IB Herbarium, which kindly collaborated with the research”, he concludes.
