Johanna A. A. Bos

Preboreal climate oscillations in Europe: Wiggle-match dating and synthesis of Dutch high-resolution multi-proxy records

Abstract In order to compare environmental and inferred climatic change during the Preboreal in The Netherlands, five terrestrial records were analysed. Detailed multi-proxy analyses including microfossils (e.g., pollen, spores, algae, and fungal spores), macroremains (e.g., seeds, fruits, wood, mosses, etc.), and loss on ignition measurements were carried out with high temporal resolution. To link the five Preboreal records, accurate chronologies were produced by AMS 14C wiggle-match dating. The Dutch records show that following the Lateglacial/Holocene climate warming, birch woodlands expanded between 11,530 and 11,500xa0calxa0BP during the Friesland Phase of the Preboreal. After the Friesland Phase, two distinct climatic shifts could be inferred: (1) around 11,430–11,350xa0calxa0BP the expansion of birch forests was interrupted by a dry continental phase with open grassland vegetation, the Rammelbeek Phase. This phase was coeval with the coldest part of the Preboreal oscillation (PBO) as observed in the δ18O record of the Greenland ice-core records and has been attributed to a large meltwater flux that resulted in a temporary decrease of the thermohaline circulation in the North Atlantic. (2) At the start of the Late Preboreal, between 11,270 and 11,210xa0calxa0BP, a sudden shift to a more humid climate occurred and birch forests expanded again. A simultaneous increase in the cosmogenic nuclides 14C and 10Be suggests that these changes in climate and vegetation were forced by a sudden decline in solar activity. Expansion of pine occurred during the later part of the Late Preboreal. At the onset of the Boreal, between 10,770 and 10,700xa0calxa0BP, dense woodlands with hazel, oak, elm and pine started to develop in The Netherlands.

The influence of environmental changes on local and regional vegetation patterns at Rieme (NW Belgium): implications for Final Palaeolithic habitation

Late-glacial vegetation changes were studied at Rieme, NW Belgium. Human occupation of this cover sand area occurred from the Final Palaeolithic onwards. The research area is situated on the northern side of a large cover sand ridge in an undulating landscape with small ridges and depressions. The past landscape was reconstructed using a multi-disciplinary approach, including geomorphological, sedimentological, loss-on-ignition, botanical (micro- and macrofossil) and zoological analyses. AMS 14C dating provided an accurate chronology for the sediments. Analyses were performed on three sequences located ~200–300xa0m apart. Our study shows that during the Bølling (GI-1e) wet meadows developed on the sandy soils and groundwater levels increased probably as result of permafrost melting. Shallow pools formed in depressions. During the Older Dryas (GI-1d) shrubs with juniper, sea-buckthorn and willow developed. Many shallow depressions were overblown with sand and deposition of organic material almost ceased. In the early Allerød (GI-1c) open birch woodlands developed. Due to the final melting of permafrost, groundwater levels rose further and ponds with floating-leaved open water vegetation developed. Large water level fluctuations occurred in one of the ponds. Accumulation of organic deposits ceased during the mid-Allerød. Indirect evidence for human occupation during the Allerød (GI-1c) was found in indications of burning of the reed-swamps in combination with the presence of large herbivores. Final Palaeolithic people probably used the northern side of the cover sand ridge as hunting area, while they settled their temporary (base) camps on the steep southern side along the extensive and deeper Moervaart lake.

Early Holocene environmental change and the presence of Mesolithic people in the Tungelroyse Beek valley near Mildert, the Netherlands

An archaeological excavation in the Tungelroyse Beek valley revealed the remains of two red deer specimens (Cervus elaphus) of Early Mesolithic age that possibly were the victims of hunter-gatherers. The find of animal remains of this age is unique in the Netherlands. In this respect, a sediment core taken close to the remains was investigated, i.e. to reconstruct the vegetation and landscape development of the site and to find more evidence for human activity at this site during the Early Mesolithic. The sediment core shows a typical Early Holocene palynological sequence from the Younger Dryas into the Middle Atlantic, which is supported by AMS dating. The microscopic charcoal record shows peaks in fire activity during the Younger Dryas and Friesland phase, probably wildfire related. Records of spores of coprophilous fungi indicate that the Tungeroyse Beek valley was a favourable place for large herbivores (game) to visit during the investigated period. However, around the age of the oldest red deer remains, no significant peak in fire activity or spores of coprophilous fungi is visible in the investigated record. The pollen diagram does not show disturbed or open vegetation around this age either. This study therefore suggests the impact of Early Mesolithic people on their environment was very low.

The Younger Dryas and Preboreal landscape in the Moervaart area (northwestern Belgium) and the apparent decrease in human occupation

This paper presents the results of multi-disciplinary research carried out on the deposits of a residual channel (“Peerdemeers”) of the Kale/Durme River in the Moervaart depression, NW Belgium. The combination of physical, botanical, zoological and chemical analyses allowed a detailed reconstruction of the channel ecosystem and the vegetation in the surrounding landscape during the Younger Dryas and Early Holocene. A chronology for the record was provided by radiocarbon dating. Vegetation patterns were influenced by major climate changes that occurred during this period. During the early Younger Dryas, the river channel was active and vegetation was open with scattered birch copses, shrubs, grasses and herbs. The channel was cut-off in the late Younger Dryas, while some heath developed in the area. The Friesland Phase is characterised by a lithological change and increase in water level in the residual channel. Dwarf birch disappeared and boreal forests developed. The area however, remained relatively open compared to other coversand areas in NW Europe. The Rammelbeek Phase is considered as a drier, more continental climate phase in which forest expansion was temporarily interrupted and grasslands became more abundant. Also at the “Peerdemeers” site an increase in grasses is recorded. During the entire period (ca. 1,000xa0years) there is no hard evidence for human activity. The absence of archaeological evidence is in sharp contrast with the preceding (Allerød) and succeeding periods (Boreal). This suggests that environmental conditions during the YD and PB were probably too unfavourable for hunter-gatherers to remain in the Moervaart area.