Holocene shelf sea evolution offshore northeast England

Spatial and temporal changes of tidally mixed and stratified water conditions during the Holocene are poorly understood and constrained within the North Sea region. This study investigates the changing tidal conditions at a core site from offshore northeast England through the Holocene. A continuous Holocene sedimentary record in British Geological Survey vibrocore 54/-02/97 (54degrees53.05'N. 1degrees3,88'W: water depth 55 m) collected from a natural trough in the North Sea has been investigated. A multiproxy approach. including the interpretation of magnetic susceptibility values. bulk sedimentological characteristics. benthic foraminifera faunal and isotopic data is adopted. The chronology of this record is constrained by a total of ten accelerator mass spectrometry C-14 dates obtained from molluscs and mixed benthic foraminiferal samples. The age derived from benthic foraminifera and molluscs obtained at the same core depth are statistically the same. These results suggest that benthic foraminifera tests do not undergo significant post-mortem reworking at this shallow site and that the foraminifera-based proxy records are reliable. Sedimentary characteristics indicate that tidally mixed waters between 11 150 and 5869 calendar (cal) yr BP affected the core site. The core site was bathed by tidally mixed water conditions indicated by the presence of Ammonia batavus Hofker with stratified conditions and associated frontal systems developing at or close to the core site between 5869 and 2032 cal yr BP. based on the presence of Stainforthia fusiformis (Williamson). Finally, species that are indicative of fully stratified water such as Bulimina marginata d'Orbigny, Hyalinea balthica (Schroter) and S. fusiformis record the transition from mixed-frontal to stratified conditions at 1158 cal yr BP. This site records a faunal change in the last 500 years that may be a consequence of fully stratified conditions and enhanced phytodetritus delivery to the sea floor. Alternatively, supported to some extent by heavy metal concentrations, the fauna may be responding to eutrophication of coastal waters through anthropogenic influences. (C) 2002 Elsevier Science B.V. All rights reserved.