Holocene environmental change in coastal Denmark: interactions between land, sea and society

In this study a multiproxy approach (including sedimentary techniques, diatoms, molluscs, foraminifera, sedimentary pigments, isotopes, pollen and plant macrofossils) has been adopted to assess environmental change over the last ~9,000 years at three Danish coastal sites (Kilen, Norsminde Fjord and Korup Sø). Particular focus has been placed on periods of intense human coastal occupation, identifiable in Denmark’s rich coastal archaeological record (i.e. shell midden accumulation periods), to test critically, hypotheses that changes in the marine environment were contemporary with major cultural and societal changes over the last ~9,000 years. For example, it has been proposed that a decrease in salinity was responsible for the widespread oyster decline, apparent in the Neolithic layers of a number of Danish shell middens. This hypothesis, however, remains speculative to date, lacking any high-resolution and quantitative salinity data covering the Mesolithic-Neolithic transition. Inside the agricultural era, two more phases of shell midden accumulation occur (i.e. during the Pitted Ware/Single Grave cultural period and the Iron Age), suggesting that people must have returned to the sea at these times for increased exploitation of its resources. A diatom-based salinity transfer function (WAPLS-C3 model, r2 boot = 0.923, RMSEP= 0.36 square root salinity units) based on a trans-Baltic training set has been applied to fossil diatom datasets from each site for quantitative assessment of salinity change over the study period. The multiproxy results presented in this study demonstrate a close connection between environmental change and human exploitation of marine resources over the Holocene. This relationship, however, is complex, with the individual fjord systems often exhibiting spatially different responses (i.e. variations in the sedimentary regime, salinity, productivity and nutrient status) to changes in key forcing mechanisms such as sea level change, climate change and human impact upon the catchment (following the introduction of agriculture). Environmental hypotheses for cultural change are reviewed on the basis of the evidence presented in this study. Diatomenvironmental relationships have also been modelled (using multivariate techniques) at Korup Sø and Norsminde Fjord using proxy data as ‘predictor’ variables for changes in the terrestrial and marine environment. These results suggest that a variety of marine, climatic, human and catchment related processes are important in explaining a proportion of the variation in the fossil diatom datasets, but these influences tend to vary temporally throughout the profile (e.g. human impact becomes important after ~3,900 BC).