Variations in organic carbon flux and stagnation periods during the last 2400 years in a Skagerrak fjord basin, inferred from benthic foraminiferal δ13C

Abstract

AbstractA well-dated high-resolution δ13C record of the last 2400 a, based on the benthic foraminifer Cassidulina laevigata, is presented for Gullmar Fjord, Sweden. The time interval covers the Roman Warm Period (RWP), the Viking Age/Medieval Warm Period (VA/MWP), the Little Ice Age (LIA) and the most recent warming. There is little variation in the δ13C record until the early Viking Age (AD 800), when the δ13C signal becomes significantly more negative and continues to decrease throughout the VA/MWP. The δ13C signal increases both at the beginning and at the end of the LIA but is marked by more negative values during the larger part of the period. Since about 1970, the δ13C values are more negative than the long-term average. This general negativity of the record may result from a higher flux of organic matter, possibly of terrestrial origin due to land-use changes together with moderate changes in stagnation periods since the VA/MWP. In most recent times, the oceanic Suess effect together with increased number of extended stagnation periods are probably the main causes of the shift towards more negative δ13C values.