Tracing winter temperatures over the last two millennia using a north-east Atlantic coastal record

摘要

We present 2500 years of reconstructed bottom water temperatures (BWT) using a fjord sediment archive from the north-east Atlantic region. The BWT represent winter conditions due to the fjord hydrography and the associated timing and frequency of bottom water renewals. The study is based on a ca. 8 m long sediment core from Gullmar Fjord (Sweden), which was dated by sup210/supPb and AMS sup14/supC and analysed for stable oxygen isotopes (δsup18/supO) measured on shallow infaunal benthic foraminiferal species Cassidulina laevigata d'Orbigny 1826. The BWT, calculated using the palaeotemperature equation from McCorkle et al.?(1997), range between 2.7 and 7.8 °C and are within the annual temperature variability that has been instrumentally recorded in the deep fjord basin since the 1890s. The record demonstrates a warming during the Roman Warm Period (?～?350 BCE–450 CE), variable BWT during the Dark Ages (?～?450–850 CE), positive BWT anomalies during the Viking Age/Medieval Climate Anomaly (?～?850–1350 CE) and a long-term cooling with distinct multidecadal variability during the Little Ice Age (?～?1350–1850 CE). The fjord BWT record also picks up the contemporary warming of the 20th century (presented here until 1996), which does not stand out in the 2500-year perspective and is of the same magnitude as the Roman Warm Period and the Medieval Climate Anomaly.