Late Holocene coastal hydrographic and climate changes in the eastern North Sea

Abstract

We present a high-resolution palaeoenvironmental reconstruction covering the late Holocene from the Skagerrak and other sites in the North Sea area. The data, which are based on the analyses of marine sediment cores, reveal a marked environmental shift that took place between AD 700 and AD 1100, with the most pronounced changes occurring at AD 900. Both surface and bottom waters in the Skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of Atlantic waters to the North Sea marking the beginning of the 'Mediaeval Warm Period' (MWP). The observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 BC. At the transition to the 'Little Ice Age' (LIA) the bottom current strength remains at a high level, now probably forced by atmospheric circulation. Thus, despite opposite temperature forcing, these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the Skagerrak than observed in the preceding 2000 years, and demonstrate the significance of climatic forcing in shaping the marine environment. Indeed, both the MWP and the LIA are reported as strong climatic signals in northwest Europe, being the warmest (except the late twentieth century) and coldest periods, respectively, during at least the last 2000 years.

Coastal primary productivity changes over the last millennium: a case study from the Skagerrak (North Sea)

“…The high oxygen and favourable nutrient conditions were likely associated with an intense mixing of the water column and enhanced productivity. Gil et al 15 (2006) and Hebbeln et al (2006) suggested increased storminess that entailed intense mixing of the water column at this time (Erbs-Hansen et al, 2011), in line with our results. The colder BWTs at both sites can be indicative of weaker Atlantic water inflow.…”

“…This interpretation is 30 supported by a study from the Northern North Sea, where Klitgaard-Kristensen and Sejrup (1996) argued that the Atlantic water is favourable for planktonic foraminifera, while the low salinity of the NCC reduces their abundance. Our interpretation is further supported by previous studies based on foraminiferal (Erbs-Hansen et al, 2011) and diatom assemblages, as well as a multiproxy study by Hebbeln et al (2006), which all report on an onset of enhanced Atlantic water advection to the Skagerrak at ~ CE 900. Gil et al (2006), documented an increase in diatom species associated with high 5 salinity water in the Skagerrak and argued for enhanced productivity caused by inflow of nutrient-rich, high-salinity water via the NJC.…”

Variations in sediment provenance during the past 3000 years off the Tagus River, Portugal

“…Additionally, variations in sediment properties appear to be synchronous to environmental changes, that have been reconstructed from eastern North Atlantic records (e.g. Hebbeln et al, 2006), evidenced by complementary patterns in sediment parameters, such as grain-size, in records from these locations. This emphasises the significance of the GeoB 8903 record despite the high spatial variability of sediment properties and although the chronology of Little Ice Age, Medieval Warm Period, Dark Ages or Roman Warm Period, which is commonly applied to the Portuguese shelf records, can not be implemented here.…”

Late Weichselian deglaciation and early Holocene development of a cold-water coral reef along the Lopphavet shelf (Northern Norway) recorded by benthic foraminifera and ostracoda

“…1), the Norwegian Atlantic Current (NwAC) which is mainly a continuation of the North Atlantic Current (NAC) and the Norwegian Coastal Current (NCC), which has its main source in the Skagerrak region (Hebbeln et al, 2006). The warm and saline Atlantic water (temperature¼ 6-9 1C, salinity ¼ 435) enters the Norwegian Sea through two major pathways, from the southwestern part by passing the Iceland-Faroe Ridge and from the southeast along the FaroeShetland Channel (Orvik et al, 2001;Orvik and Niiler, 2002).…”