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 ~200–300 m 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, seabuckthorn 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

Synchronous vegetation response to the last glacial-interglacial transition in northwest Europe

<jats:title>Abstract</jats:title><jats:p>The North Atlantic region experienced abrupt high-amplitude cooling at the onset of the Younger Dryas stadial. However, due to chronological uncertainties in the available terrestrial records it is unclear whether terrestrial ecosystem response to this event was instantaneous and spatially synchronous, or whether regional or time-transgressive lags existed. Here we use new palynological results from a robustly dated lake sediment sequence retrieved from lake Hämelsee (north Germany) to show that vegetation change started at 12,820 cal. yr BP, concurrent with the onset of changes in local climate. A comparison of the Hämelsee results to a compilation of precisely dated palynological records shows instant and, within decadal-scale dating uncertainty, synchronous response of the terrestrial plant community to Late-Glacial climate change across northwest Europe. The results indicate that the environmental impact of climate cooling was more severe than previously thought and illustrates the sensitivity of natural terrestrial ecosystems to external forcing.</jats:p&gt

Biodiversity responses to Lateglacial climate change in the subdecadally-resolved record of Lake Hämelsee (Germany)

Anthropogenically-driven climate warming and land use change are the main causes of an ongoing decrease in global biodiversity. It is unclear how ecosystems, particularly freshwater habitats, will respond to such continuous and potentially intensifying disruptions. Here we analyse how different components of terrestrial and aquatic ecosystems responded to natural climate change during the Lateglacial. By applying a range of analytical techniques (sedimentology, palaeoecology, geochemistry) to the well-dated sediment archive from Lake Hämelsee (Germany), we show evidence for vegetation development, landscape dynamics and aquatic ecosystem change typical for northwest Europe during the Lateglacial. By particularly focussing on periods of abrupt climate change, we determine the timing and duration of changes in biodiversity in response to external forcing. We show that onsets of changes in biodiversity indicators (e.g. diatom composition, Pediastrum concentrations) lag changes in environmental records (e.g. loss-on-ignition) by a few decades, particularly at the Allerød/Younger Dryas transition. Most biodiversity indicators showed transition times of 10–50 years, whereas environmental records typically showed a 50–100 year long transition. In some cases, transition times observed for the compositional turnover or productivity records were up to 185 years, which could have been the result of the combined effects of direct (e.g. climate) and indirect (e.g. lake stratification) drivers of ecosystem change. Our results show differences in timing and duration of biodiversity responses to external disturbances, suggesting that a multi-decadal view needs to be taken when designing effective conservation management of freshwater ecosystems under current global warming

Centennial-scale lake-level lowstand at Lake Uddelermeer (The Netherlands) indicates changes in moisture source region prior to the 2.8-kyr event

The Uddelermeer is a unique lake for The Netherlands, containing a sediment record that continuously registered environmental and climatic change from the late Pleistocene on to the present. A 15.6-m-long sediment record was retrieved from the deepest part of the sedimentary basin and an age–depth model was developed using radiocarbon dating, 210Pb dating, and Bayesian modeling. Lake-level change was reconstructed using a novel combination of high-resolution palaeoecological proxies (e.g. pollen, non-pollen palynomorphs, chironomids), quantitative determinations of lake-level change (ground-penetrating radar), and estimates of changes in precipitation (lipid biomarker stable isotopes). We conclude that lake levels were at least as high as present-day water levels from the late glacial to 3150 cal. yr BP, with the exception of at least one lake-level lowstand during the Preboreal period. Lake levels were ca. 2.5 m lower than at present between 3150 and 2800 cal. yr BP, which might have been the result of a change in moisture source region prior to the so-called 2.8-kyr event. Increasing precipitation amounts around 2800 cal. yr BP resulted in a lake-level rise of about 3.5–4 m to levels that were 1–1.5 m higher than at present, in line with increased precipitation levels as inferred for the 2.8-kyr event from nearby raised bog areas as well as with reconstructions of higher lake levels in the French Alps, all of which have been previously attributed to a phase of decreased solar activity. Lake levels decreased to their present level only during recent times, although the exact timing of the drop in lake levels is unclear