Steinar Gulliksen

Changes in North Atlantic Radiocarbon Reservoir Ages During the Allerød and Younger Dryas

Estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late Quaternary climate. We radiocarbon-dated marine shells and terrestrial plant remains deposited in two bays on Norways west coast between 11,000 and 14,000 years ago, a time of large and abrupt climatic changes that included the Younger Dryas (YD) cold episode. The radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early YD, stabilized for 900 years, and dropped by 300 years within a century across the YD-Holocene transition.

A calendar age estimate of the Younger Dryas-Holocene boundary at Kråkenes, western Norway

The Younger Dryas/Holocene transition (YD/H) in the sediments of Kråkenes Lake, western Nor way, is well marked both lithologically and palaeobiologically at 756.5 cm in the investigated core. A series of 70 AMS radiocarbon dates on terrestrial plant macrofossils and the NaOH-soluble fraction of lake sediment was measured between 585 and 840 cm, covering the time span c. 10 440 to 7915 BP on the radiocarbon timescale. Forty-three of these dates above 760 cm were wiggle-matched against the German oak-pine dendro calibration curve (IntCal 93) with recent corrections in both the oak and the pine sections. With an increase in age of the pine dendro-series of 200 6 20 yr, the calendar age of the YD/H lithostratigraphic boundary at Kråkenes is estimated to 11 530+40 -60 cal. BP. By using a date of 9750 BP (11 170 cal. BP) on the transition between the 10 000 and 9600 14C plateaux as a time marker, this result is compared with recent results from other archives. It is consistent with many of them, including the GRIP ice core, German pine series, Lake Gościaz, south Swedish lakes, and Baltic varves, suggesting that the Younger Dryas-Holocene transition in the North Atlantic region occurred within the range 11 500–11 600 cal. BP.

The marine 14C age of the Vedde Ash Bed along the west coast of Norway

Articulated molluscs, sea urchins and barnacle fragments close to the Vedde Ash Bed in a shallow marine deposit on the west coast of Norway have been 14C dated. The weighted mean of four dates from a sediment slice 8 cm thick centred on the Vedde Ash Bed is 10920 ± 24 14C yr BP. The most accurate 14C age of the Vedde Ash from terrestrial plant macrofossils is 10310 ± 50 yr BP. The difference is the 14C reservoir age for coastal water at the west coast of Norway during the mid-Younger Dryas and equals 610 ± 55 yr. This is 230 yr older than the reservoir age for the Bolling/Allerod and for the present day in this area. The result supports earlier conclusions of a higher reservoir age for the Younger Dryas in the North Atlantic and Nordic Seas, although our reservoir age of 610 ± 55 yr is a few hundred years younger. This suggests that the 14C reservoir age at Vedde Ash time may increase from coastal water towards the open North Atlantic and Nordic Seas. Copyright

The Krakenes late-glacial palaeoenvironmental project

Kråkenes is the site of a small lake on the west coast of Norway that contains a long sequence of late-glacial sediments. The Younger Dryas is well represented, as a cirque glacier developed in the catchment at this time. This site offers unique opportunities to reconstruct late-glacial environments from independent sources of evidence; physical evidence (glacial geomorphology, sedimentology, palaeomagnetism, radiocarbon dating), and biological evidence from the remains of animals and plants derived from both the terrestrial and aquatic ecosystems. This report describes the background to the site, and the international multidisciplinary project to reconstruct late-glacial and early Holocene environmental and climatic changes at Kråkenes.

Paleomagnetic correlations between scandinavian ice-sheet fluctuations and greenland dansgaard–oeschger events, 45,000–25,000 yr B.P.

Abstract Two paleomagnetic excursions, the Skjong correlated with the Laschamp (about 41,000 GISP2 yr B.P.) and the Valderhaug correlated with the Mono Lake (about 34,000 GISP2 yr B.P.), have been identified in stratigraphic superposition in laminated clay deposited in ice-dammed lakes in three large caves in western Norway. During both periods the margin of the Scandinavian Ice Sheet advanced and reached the continental shelf beyond the outermost coastline. The mild, 4000-yr-long Alesund interstade, when the coast and probably much of the hinterland were ice-free, separated the two glacial advances. The two paleomagnetic excursions have also been indirectly identified as increased fluxes of 36Cl and 10Be in the GRIP ice core, Greenland. This article presents a correlation between ice-margin fluctuations of the Scandinavian Ice Sheet and the stratigraphy of GRIP/GISP cores, using the paleomagnetic excursions and the 36Cl and 10Be peaks and thus circumventing the application of different dates or time scales. Some of the fluctuations of the Scandinavian Ice Sheet were of the “Allerod/Younger Dryas type” in the sense that its margin retreated during mild interstades on Greenland and readvanced during cold stades. However, some fluctuations were apparently not in phase with the Greenland climate.

First Generation Christians, Second Generation Radiocarbon Dates: The Cemetery at St. Clement's in Oslo

The archaeological material from the site of St. Clements Church in Oslo, one of the earliest Christian cemeteries in Norway, is important for studying the Christianisation process in this country. Radiocarbon dates from 1972 generated discussions on the typology of early Christian burials, the architecture of early medieval stone churches, the role of churches dedicated to St. Clement, the relation between the church and the urban settlement, and the age of the city. The celebration of Oslos 1000‐year anniversary in 2000 was based on the results from 1972 and the discussions that followed. The material from St. Clements in Oslo is still playing an important role in relevant discussions. However, in the light of information gained since then, the reliability of the radiocarbon dates from 1972 can be questioned. This paper discusses improvements in the radiocarbon dating methods and illustrates the necessity to be sceptical of old results. New radiocarbon dates are presented. They show in particular that the earliest possible range in the previous results is no longer tenable. The article also discusses the consequences of this result for the theories regarding the Christianisation process in Norway and for the age of Oslo.

Calibration of radiocarbon dates: A review

Dendrochronologic calibration of radiocarbon dates, which is of vital importance when such dates are compared with historical records, is discussed. The nature and causes of variations in the past atmospheric radiocarbon content are briefly described. Different calibration curves are compared with available high‐precision data on radiocarbon in tree rings, and also with preliminary results from the joint efforts of U.S. scientists to establish an optimal calibration scheme.