Reconstruction of the Iberian Holocene temperature from the study of subfossil insects
Reconstruction of the Iberian Holocene temperature from the study of subfossil insects
Reconstruction of the Iberian Holocene temperature from the study of subfossil insects
Subfossil remains of chironomids, a type of insect similar to mosquitoes, have served for researchers from the University of Barcelona, the Pyrenean Institute of Ecology (IPE-CSIC) (Spain) and the University of Bern to reconstruct the temperature of the peninsula Iberian in the Holocene, the geological period that goes from 11,000 years ago to the present. The results of the study confirm some of the Holocene weather patterns contributed by other methodologies: a tendency to increase temperatures at the beginning of the period, higher temperatures coinciding with the so-called climatic optimum and a decrease from the beginning of the late Holocene.
The work, published in the scientific journal The Holocene, is the first reconstruction of the temperature of the Peninsula during this period that uses this indicator. According to the researchers, it is a promising tool to understand the evolution of climate throughout history and the main climatic changes of both natural and anthropic nature that have modeled ecosystems before instrumental records.
The researcher Pol Tarrats, of the Research Group Freshwater Ecology, Hydrology and Management (FEHM) of the UB, is the first author of the article. The researchers of the FEHM-UB Miguel Cañedo-Argüelles, Narcís Prat and Maria Rieradevall have also participated in the study; Blas Valero-Garcés and Penelope González-Sampériz, of the Pyrenean Institute of Ecology (IPE-CSIC), and Oliver Heiri, of the University of Bern (Switzerland).
Extraction of the sequence of the Basa de la Mora by the Quaternary Paleoenvironments group of the IPE-CSIC. (Photo: Anchel Belmonte)
The chironomids (Chironomidae) are a family of nematode diptera, similar to mosquitoes. These are very abundant insects throughout the world and they vary in number and gender according to the temperature in which they live, so they are a good indicator of this climatic variable. The investigation began in the Basa de la Mora (Huesca), from where the sediments necessary to carry out the study were extracted. «Regarding the registration of chironomids, the objective in any study of paleoenvironmental reconstruction is to obtain the cephalic capsules of the larvae, since it is the larval phase of these insects that develops in the sediments and from which the subfossil remains remain », Explains Miguel Cañedo-Argüelles, postdoctoral researcher at the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB. The subfossils are biological remains whose fossilization process is not complete due to the way they were buried in the sediments and still contain organic matter that can be analyzed.
These witnesses were extracted by the Quaternary Paleoenvironment Group of IPE-CSIC to obtain a sequence covering the entire Holocene period. The temperature estimate is obtained by comparing the insect composition obtained in the samples of the sediments along the study sequence with a calibration base composed of numerous samples of chironomids obtained at present that are related to temperature changes . «In our case we did not have this comparison element of the study area (Pyrenees), so the sequence obtained in Basa de la Mora was compared with the results of a study -the most developed and used in Europe-, carried out in 274 lakes in Switzerland and Norway, "explains Pol Tarrats.
The results of the study show an increase in temperatures at the beginning of the Holocene, which reached the highest values during the so-called climatic optimum (about 7,800 years ago). High temperatures are also observed until approximately 6,000 years ago, when a temperature drop begins that gives rise to the lowest values in the first part of the late Holocene (approximately between 4,200 and 2,000 years ago). Finally, researchers have detected an increasing temperature rise in the last two millennia, data on which they are cautious: "We dare not assure that the increase observed in the reconstruction is the result of only the increase in temperature. There could be other covariates that were influencing to a greater or lesser extent in this result. For example, a progressive increase in anthropic activity in the area that would have modified the community of chironomids towards species adapted to higher temperatures, but also to other indicators of human influence, "says Narcís Prat.
Although these conclusions coincide with other paleoclimatic reconstructions, the results also highlight some divergences at the regional level. "These differences may be due to the fact that each type of indicator tells us about different seasonal signals. Thus, chironomids are indicators of temperature in summer, while others, such as chrysophytes or alquenones, are related to winter, spring or annual temperatures, "says the researcher.
The reconstruction of past climate in general and of temperatures in particular is a very relevant tool when evaluating current climate trends within a context of climate change. For researchers, the methodology followed in this work is "a very interesting tool to contrast, confirm or deny patterns about the evolution of temperature in the Holocene". It also allows "add other indicators to rebuild temperatures and be able to progress in this field of study."
In this sense, the objective of the research team is to be able to develop a base of comparison that relates the communities of chironomids present in different geographical areas of the Iberian Peninsula with temperature. "This would allow us, on the one hand, to confirm the influence of temperature when explaining the distribution of different species and, on the other hand, to be able to use specific transfer functions for each zone, which would give greater robustness and accuracy to the following studies aimed at reconstructing temperatures from the chironomids in the Peninsula ", concludes Miguel Cañedo-Argüelles. (Source: U. Barcelona)
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