The last two Interglacials in an expanded biological proxy record from the coastal northern Adriatic (Istria, Croatia)

Investigating forest successions from biological proxies in high resolution sedimentary records allows to reconstruct the climatic structure of interglacials. Here we present the first detailed centennial record of vegetation change for the Last Interglacial (LIG; i.e. MIS 5.5) and the Holocene in the northern Adriatic basin. Numerical techniques (MAT, WA-PLS, fxTWA-PLS) were applied on selected intervals of the fossil pollen record to obtain quantitative reconstructions of those climate parameters accounting for most part of the variance in the calibration set. We compared the obtained time series of climate parameters during the LIG and the Holocene from the same stratigraphic archive, to disentangle the differences in the fine climate structure between the last two interglacials. Site and stratigraphy - The Istria Peninsula is located in the northern-eastern corner of the Adriatic Sea and it's dissected by deep karst valleys that during the marine high-stands have been transformed in rias. Part of these karst canyons was infilled by long amphibious sedimentary records, yet largely unexplored, and the valley of Mirna River represents the largest and thickest one. The infill was successfully cored providing a 120 m long record (MIR1) of sedimentary environments, ranging from marine shelf to lagoonal to alluvial plain. The most complete transgression sequence, from 74 to 45 m depth, proved to contain an expanded record of the LIG with an exceptional potential of co-registered continental and marine biological proxies. So far, we analysed in detail microbotanical and sedimentary proxies. Interestingly, charcoal peaks mark fire events affecting plant communities developed on the limestone cliffs facing the coring site. The Last Glacial is almost missing due to the low-stand erosional phase, but the uppermost 32 m record the Holocene transgression. Termination II is represented by a vegetation dynamic from semi-desert and steppe to mixed deciduous-conifer forests. Indeed, high pollen percentages of Pinus sp. and of xerophytic taxa (Artemisia, Juniperus, Chenopodiaceae) are followed by a sharp expansion of temperate forest pollen taxa and the development of a typical southern European LIG forest succession, clustered into two main zones. The lower one displays the maximum abundance of dry temperate broad-leaved trees (mainly Quercus robur-type), gradually replaced by moisture-demanding broad-leaved species (e.g., Carpinus betulus and Ulmus). A moderate expansion of evergreen Mediterranean sclerophylls (evergreen oaks and Oleaceae) is co-recorded in this upper main zone. These Mediterranean communities likely developed in the dry extreme of the edaphic gradient connecting the moist alluvial lowland to the dry cliffs. Termination I is mostly not recorded. The hiatus is terminated by transgressional lagoonal facies dated to 10.4 ka, covered by a continuous expanded marine Early to Middle Holocene record and topped by the Late-Holocene coastal plain. Overall, the Holocene pollen record exhibits high percentages of deciduous oaks, evergreen oaks and Fagus, suggesting significant moisture availability and the return of Mediterranean elements after the Last Glacial.