AMQ abs Marchegiano et al PALCOM 147-150.pub Available online http://amq.aiqua.it ISSN (online): 2279-7335 Alpine and Mediterranean Quaternary, Vol. 31 (Quaternary: Past, Present, Future - AIQUA Conference, Florence, 13-14/06/2018), 147 - 150 RAPID LATE PLEISTOCENE CLIMATE CHANGE RECONSTRUCTED FROM A LACUSTRINE OSTRACOD RECORD IN CENTRAL ITALY (LAKE TRASIMENO, UMBRIA): PRELIMINARY RESULTS Marta Marchegiano 1, David J. Horne 2, Elsa Gliozzi 3, Daniel Ariztegui1 1 Department of Earth Sciences, University of Geneva, Geneva, Switzerland 2 School of Geography, Queen Mary University of London, London, UK 3 Department of Science, University Roma Tre, Roma, Italy Corresponding author: M. Marchegiano ABSTRACT: An 8.59 m long sediment core was retrieved from Lake Trasimeno (central Italy) with the aim of performing a palaeoclimatic and palaeoenvironmental reconstruction. In this study we present, for the first time in central Italy, a quantitative palaeotemperatures reconstruction based on ostracod assemblages. The mean winter (January) and summer (July) palaeotemperatures were estimated from 44,000 to 9,000 cal yr BP by using the Mutual Ostracod Temperature Range (MOTR) method. Of the total of 19 ostracod species recovered, 13 of them were used as reliable palaeotemperature proxies on the base of their living temperature ranges. KEYWORDS: Palaeotemperatures, palaeoclimatology, ostracoda, central Mediterranean, Quaternary 1. INTRODUCTION The Late Quaternary climate has been affected by numerous and rapid fluctuations and different tech- niques have been developed to reveal their extent and associated effects on the environment. Here we present for the first time the application of the Mutual Ostracod Temperature Range (MOTR) method (Horne, 2007) on an 8.59 m long sediment core from Lake Trasimeno (central Italy) with the aim of reconstruct the palaeotem- perature variations in central Italy. The provisional age model proposed by Marchegiano et al. (2017a) sug- gests the Co1320 Trasimeno sediment core covers the last 47,000 cal yr BP. The MOTR analysis was per- formed within the interval from 44,000 to 9,000 cal yr BP. This period encompassed a long mild period (MIS 3), followed by a colder one (MIS 2) and ended with the beginning of the Holocene, characterised by the abrupt restoration of warmer conditions. The MIS 3 and 2 en- closed high-frequency climate variations characterised by warmer (interstadial) and colder (stadial) periods (Abrantes et al., 2012). These features were recognized for the first time in the ice-core record from Greenland (Grootes & Stuiver, 1997; Johnsen et al., 1992) and subsequently documented in climate records all over the world (Voelker, 2002). In central Italy, several paly- nological studies (summarized in Fletcher et al., 2010), revealed that the Greenland Interstadials (GI) were characterised by relatively humid conditions, whereas dry ones prevailed during Greenland Stadials (GS). This trend has been further confirmed at Lake Trasimeno (43°09’N; 12°06’E, Umbria Region, central Italy) (Fig. 1) by the repeated changes of the ostracod assemblages that suggested frequent lake level variations that mir- rored the alternation of dry and humid phases (Marchegiano et al. 2017a). Due to its very shallow depth (maximum depth of 6 m), its smooth bathymetry (Ludovisi et al., 2005) and its endorheic nature, Lake Trasimeno revealed to be particularly suitable to detect the changes in the lacustrine environment driven by cli- mate, since its hydrological system strictly depends on climatically-governed precipitation/evaporation changes (Dragoni et al., 2012). The continuous presence of fossil ostracods throughout the entire succession (Marchegano et al., 2017a), allowed to fruitfully apply the MOTR method Fig. 1 - Map of Lake Trasimeno showing the location of core Co1320. Legend: A. natural catchment area; B. artificially-joined basins; C. sluice gates of the artificially-joined channels (modified from Marchegiano et al., 2017). https://doi.org/10.26382/AIQUA.2018.AIQUAconference along the sediment core, trying to depict, for the first time, the palaeotemperature variations based on ostra- cods. In fact, until today, only few continental records provided high-resolution analyses of Late Quaternary climatic changes, mainly based on pollen [e.g. Lago di Lagaccione (Magri & Sadori 1999), Lago di Vico (Magri 1999, Magri & Parra 2002), Lago di Albano (Ariztegui et al., 2001), Valle di Castiglione (Magri, 1994), Lago di Monticchio (Allen et al., 1999), Lake Ohrid (Wagner et al., 2017)]. 2. METHODS The MOTR is a non-analogue method (Horne, 2007) for reconstructing palaeotemperature using fresh- water fossil ostracod assemblages, based on the spe- cies still living today with a known climatic distribution. The temperature ranges, which enclose all the living records of the species, are determined by fitting World- Clim database (version1.3) (Hijmans et al., 2001) to the mapped coordinate points of the species’ distribution and are expressed in terms of the maximum and mini- mum values of July and January temperature ranges. The temperature reconstruction for a given interval is provided by the mutual temperature range of all the species in the fossil assemblage. (i.e. the T interval in which they could have co-existed Fig 2.). 3. RESULTS A total of three hundred and fifty samples were analysed to perform the MOTR method in the Tra- simeno sedimentary core. The ostracod analyses (Marchegiano et al., 2017a) enabled recognition of 19 different species of ostracods referable to 15 genera: Cyprideis torosa, Candona angulata, Candona neglecta, Candona candida, Heterocypris incongruens, Cythero- morpha fuscata, Sarscypridopsis aculeata, Heterocypris salina, Ilyocypris sp., Eucypris mareotica, Darwinula stevensoni, Limnocythere inopinata, Limnocythere blankenbergensis, Potamocypris paludum, Trajancypris serrata, Amnicythere sp., Herpetocypris helenae, Cypri- dopsis vidua, Plesiocypridopsis newtoni. Among all of the recovered species, Cyprideis torosa was not taken into account because is a typically brackish water spe- cies (although it occurs sometimes in freshwater) while the MOTR method is developed only for freshwater species. Other species were also excluded: Amni- cythere sp. and Ilyocypris sp., for reasons of taxonomic uncertainty, and Trajancypris serrata, Potamocypris paludum and Herpetocypris helenae, which are still not calibrated. The temperature ranges were calculated for all the samples from 7.4 to 3.1 m depth in the Co1320 Tra- simeno core to obtain the palaeotemperature variations during the whole sequence, represented by recon- structed palaeotemperature ranges to which maxima and minima curves can be fitted. 4. DISCUSSION AND CONCLUSIONS Although the Mutual Ostracod Temperature Range method has been frequently applied to infer past climate conditions (Horne, 2007; Horne et al., 2012; Pint et al., 2015; Cosentino et al. 2017; Benvenuti et al. 2017), in this contribution it was used, for the first time, to recon- struct a palaeotemperature curve similar to those de- rived from other usual proxies (e.g. isotopes, pollen and beetles (inter alia Atkinson et al., 1987-1986; Allen et al., 1999; Pross et al., 2000; Pross & Klotz, 2002). Notwithstanding uncertainties regarding where (within the reconstructed ranges) the actual tempera- tures were located, a preliminary inspection of the MOTR results suggests rapid temperature changes in central Italy in the interval from 44,000 to 9,000 cal yr BP. In order to compare the global temperature changes of this period with the ones that affect central Italy, the MOTR-derived curves have been compared with the Greenland Isotopic Palaeotemperature recon- struction (NGRIP-members, 2004). Despite limitations of the use of a provisional age-depth model, the January 148 Marchegiano M. et al. Fig. 2 - Example of the application of the MOTR method on sample 374 of the Co1320. 149 and July temperature curves show a remarkable corre- spondence with features of the NGRIP-record, demon- strating their ability to record the millennial climate varia- tions. The Trasimeno MOTR reconstruction also reveals the possible occurrence of rapid climate changes, which could be considered equivalent to those observed at Monticchio Lake by Allen et al. (1999) using pollen- based reconstruction methods. 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