Editorial: Late Holocene oceanographic and climate change from the western European margin: the results of the HOLSMEER project

Abstract

The underlying aim of the HOLSMEER project has been to improve our understanding of natural climate variability through the search for, interpretation and quantification of, climatic variability in very high-resolution shallow marine records from Atlantic Europe covering the last 2000 years. This has been achieved through detailed analyses of a series of coastal and shallow marine sites spanning the Atlantic seaboard from Iberia to western Norway, and extending across to Iceland. HOLSMEER partners have documented pronounced instability in the thermohaline circulation (THC) during the period immediately prior to the recent significant anthropogenic impact on the environment. For the first time we have been able to document that these changes in the coastal ocean are correlated with significant changes in terrestrial palaeoclimate proxies, notably during the last 1000 years. The notable changes are the significance of warm sea surface temperatures (SST) associated with active THC between AD 700 and 1000, a transition phase to much colder SST and reduced THC between AD 1000 and AD 1300, colder SST through to AD 1900 followed by an active re-establishment of warm surface water circulation during the twentieth century. These switch-like reorganizations of the climate system have influenced the entire seaboard from western Iberia to western Norway, and have forced changes in ocean productivity, iceberg frequency and sea ice coverage. These changes have also directly influenced sea level through steric effects. The project has also resulted in significant advances in the establishment of new palaeoclimate proxies, including transfer functions related to benthic foraminifera, diatoms and dinoflagellate cysts. Annual growth band series from fossil specimens of the long-lived bivalve mollusc Arctica islandica from the northern North Sea have been successfully cross-matched, and independently verified by radiocarbon dating, to provide the longest Arctica chronology, and the first floating chronology constructed entirely from marine fossils.