Chironomid-inferred Holocene temperature changes in the South Carpathians (Romania)

Abstract

We present a Holocene summer air temperature reconstruction based on fossil chironomids from Lake Brazi (1740 m a.s.l.), a shallow mountain lake in the South Carpathians. Summer air temperature reconstruction was performed using transfer functions based on the Swiss (Sw-TF) and the merged Norwegian-Swiss calibration dataset (NS-TF). Our results suggest that summer air temperatures increased rapidly from the onset of the early Holocene onwards years, reconstructed temperatures showed again an increasing trend at Lake Brazi. Short-term temperature declines of 0.6-1.2°C were observed between ca 10,350-10,190, 9750-9500, 8700-8500, 7600-7300, 7100-6900 and 4400-4000 cal yr BP. These temperature declines are however within the estimated error of prediction of the chironomid-based inferences.Generally, our reconstructed temperatures complied with the summer insolation curve at 45°N, with other proxy records (i.e. pollen and diatoms) from the same sediment and with other records from the Carpathians and from Western Europe.

Identification of Floral Relicts Based on Spatial Distance of Isolation

“…There are no species with an MATD > 2.2 • C in the whole interval. These findings did not confirm that paleontological estimates with large maximum values of HTM MATD [30,41] were the only supported scenarios. Nevertheless, we could not exclude higher values.…”

“…As another important criterion we specified that the isolated occurrence should be the northernmost one at least on a regional scale (in Central Europe), as the supposed northernmost HTM-edge of the area is fundamentally important in our approach. Interglacial relicts (indicating a MATD greater than 2.5 • C) are not dealt with in our research, as an MATD value of 2.5 • C is the highest reliable paleontological estimation in most paleontological reconstructions [29,30,40,41] of the HTM. A higher MATD probably indicates an origin from a warmer, interglacial period.…”

“…The HTM was followed by a cooling period which resulted in the retreat of the area of the investigated thermophilic species. Established estimates for MATD (Mean Annual Temperature Difference) between the HTM and recent times range between 1 and 2.5 °C [29,30], thus a gap of 150-300 km satisfies the requirement of a distant, isolated occurrence with a potential HTM origin. If the regression left relict and patchy occurrences, the latitudinal component of the distance between the relict patch and the continuous regressed area indicates the minimal northern extent of the original distribution during the HTM.…”

“…We divided the interval of 1-2.5 • C into two equal subintervals: 1-1.7 • C, corresponding to the HTM MATD estimates of Feurdean et al [40] and Molnár and Végvári [29], and 1.8-2.5 • C, corresponding to the HTM MATD estimates of Magyari et al [41] and Tóth et al [30], and compared the number of observations from the two intervals. The lack of observations from the second subinterval does not imply that the HTM MATD estimates with larger maximum values are necessarily wrong, because the MATD values in the current analysis are minimum values.…”

Limnological changes in South Carpathian glacier-formed lakes (Retezat Mountains, Romania) during the Late Glacial and the Holocene: A synthesis

“…Catalan et al, 2009;Heiri et al, 2014) started. Within the multiproxy paleoecological project PROLONG (Magyari et al, 2009a) several biotic and abiotic proxies have been studied on sediment cores of four mountain lakes including sediment organic matter (as loss on ignition) and biogenic silica content, geochemical element concentrations, diatoms, chrysophycean cysts, cladocera, ostracods and chironomids (Korponai et al, 2011;Braun et al, 2012;Buczkó et al, 2012;Iepure et al, 2012;Tóth et al, 2012;Buczkó et al, 2013;Soróczki-Pintér et al, 2014;Tóth et al, 2015). In this study we concentrate on proxy records from two lakes on the northern slopes of the Retezat Mountains.…”