Vegetation and climate history in the Westeifel Volcanic Field (Germany) during the past 11 000 years based on annually laminated lacustrine maar sediments

Abstract

Lakes Holzmaar and Meerfelder Maar are located in the Westeifel Volcanic Field less than 10 km apart. Both maar lakes are well known for their annually laminated (varved) sediments covering the past 15 000 years. Here, we focus on reconstructing the history of Holocene vegetation, human impact and climate using high‐resolution pollen data. Detailed correlation between the two records using palynologically defined tie‐points provides for the first time a test of the precision of the individual varve chronologies. The high‐resolution pollen records of both Holzmaar and Meerfelder Maar show continuous natural successions of vegetation during the early and mid‐Holocene controlled by the development of soil, climate, immigration and competitive expansion of thermophilous tree species. From 6500 varve yr BP onwards, human impact became an increasingly more important factor. Given the high chronological precision of both records, regional similarities, but also local differences of anthropogenically influenced vegetation changes, can be recognized. The reconstructed July temperature between 8500 and 5000 varve yr BP is around 1 °C higher than today, most likely in response to higher summer insolation related to orbital forcing. High variability of reconstructed July and January temperatures as well as annual precipitation around 5000 varve yr BP is a prominent climatic signal. This is consistent with other records in several areas of Europe which also identify this period as climatically highly variable.

Strengths and Weaknesses of Quantitative Climate Reconstructions Based on Late-Quaternary Biological Proxies

“…The pdf climate reconstructions have been compared, in many cases, with climate reconstructions based on quantitative pollen assemblage data using a modern analogue technique (see The Assemblage Approach below). These comparisons suggest that the pdf method generally underestimates past climate variability but may provide robust estimates of long-term climate trends rather than of climate variability of small amplitude (Litt et al 2009;). This is not surprising as the bioclimatic envelopes of many central European trees and shrubs are very broad so that presence/absence data can only provide palaeoclimate information when the site in question is near the range margins of some of the 'key' indicator taxa (e.g.…”

“…The reconstructed climate is based on the complete distribution and climate data of all the taxa included and because it is a multiplicative technique, no single taxon is decisive (Kühl & Litt 2003). The pdf approach has been used to reconstruct Holocene (Litt et al 2009; and last interglacial and early Weichselian climate from pollen assemblages (expressed as presences and absences) (Kühl 2003;Kühl & Litt 2003;Kaspar et al 2005). The pdf climate reconstructions have been compared, in many cases, with climate reconstructions based on quantitative pollen assemblage data using a modern analogue technique (see The Assemblage Approach below).…”

A method for climate and vegetation reconstruction through the inversion of a dynamic vegetation model

“…For the interpretation of climate reconstruction results we divide the 11 to 0 cal ky BP chronology in four periods. A more comprehensive discussion can be found in Litt et al (2009). The earliest period (11 to 10 cal ky BP) corresponds to the end of the glacial period and is characterised by a rapid decrease of Grass-Shrub group, Pinus and Betula.…”

“…The sediment core (Litt et al 2009) was taken from the lake Meerfelder Maar (50.1°N, 6.75°E, see Figure 1) located within the Westeifel Volcanic Field. The uppermost 180 cm of the core, corresponding to approximately the last 1.6 cal ky BP (calendar kilo-years Before Present; which refers to the number of years before 1950), are not continuously varved and were dated using two AMS 14 C dates and extrapolated sedimentation rates based on varve data.…”

“…(3) The method is validated using 30 modern pollen samples distributed across Europe. (4) The temporal feature of the approach is fully exploited by reconstructing Holocene climate from the high resolution Meerfelder Maar sediment core (data from Litt et al 2009). …”