Palaeoclimate, vegetation and coastal lake developement, from Upper Pleniglacial until Early Holocene, in the northern Adriatic Valun Bay (Isle of Cres, Croatia)

Abstract

A multi proxy approach study (cladocerans, foraminifers, ostracods, pollen, geochemistry/mineralogy) was performed on a core sequence from the northern Adriatic Valun bay (Isle of Cres, Croatia) Since the whole core section was dominated by pine pollen, the differentiation of pine pollen types improved climate interpretations. Dating at the present stage of investigations, however, is tentative. At the core base, a period was observed, which was dominated by pollen of pine, and to a lesser extent of spruce and deciduous trees (Tilia). Freshwater conditions exhibiting a slightly brackish influence, occurred towards the top of the section. The overall picture of this interstadial period is the shift from cold to moderately warm, humid conditions. This interstadial was compared with the vegetation development of the middle Wurmian period (isotope stages 3 and 4) known from sites south of the Alps. It was followed by a period rich in P. mugo types. The high abundances of these pine pollen types indicate a situation comparable with the present subalpine P. mugo belt. A cold period rich in snow-cover was inferred. Because of the lowest inferred temperatures throughout the core, it was related to the last glacial maximum (LGM). Freshwater and/or brackish ostracods occurred, some of which are only known as fossils in the present-time Adriatic region. The subsequent shift from P. mugo-types to P. Haloxylon-type indicates rise in timberline. It was followed again by an at least temporarly wet period with fluctuating timberlines. The subsequent pollen increase in P. sylvestris-types and low abundances of oak indicates climate amelioration. Ostracods indicate lake salinity and water temperature increase. This development was related to a period of expansion of alpine shrubs and pines at Langsee, Carinthia (Längsee oscillation, Prä-Bölling?), with an upper boundary of about 15.5 14C ky BP. At Valun it was followed by a pine-rich period of climate regression (Oldest Dryas la). Higher values of P. mugo-types at the lower part of the section, and catchment erosion indicate more wet conditions relative to the upper part with the highest pollen abundances of Haploxylon pine throughout the core. The subsequent pollen shift from alpine pines towards P. sylvestris-tfpes together with an increase in elements of the mixed oak forest, was related to late glacial climate amelioration. During this time the marine ingression into the basin took place. Subsequent to a Lateglacial climate fluctuation, as indicated by increased abundances of P. mugo- types, enhanced pollen abundances of oak together with submediterranean pine indicate that summer became warmer and drier. The lower boundary of the Younger Dryas biozone was drawn according to the distinct decline of foraminifer abundances concurrent with increasing values of the P. mugo-types. In this case, and supported by a 14C date, the YD biozone appeared as a multiphase period. During early Holocene, the expansion of a vegetation favoured by humidity, was related with the onset of a pluvial period in the Adriatic at about 8.4 14C ky BP. During the lower Younger Dryas and the Holocene pluvial period, increased freshwater incursions were assumed to result in lowered salinity in the bay of Valun.