Luminescence Dating: a new Chronometer for Arctic Ocean Sediments

Late Cenozoic sediments from the Arctic Ocean contain a record of variable ice cover and of related paleoclimatic conditions. However, a common chronostratigraphy has been elusive, especially in the range 30-780 ka. Attempts at stratigraphic correlations within this age range depend on assumptions about sedimentation rate, and about correlations with more southern ocean sediments. Luminescence sediment dating potentially can provide direct burial ages of siliclastic mineral grains within such sediment cores. Forty-six "known-age", fine-silt samples from 20 cores along a transect from the northern slope of Alaska to near Fram Strait were analyzed by thermally-stimulated (TL) and infrared-stimulated (IRSL) luminescence sediment-dating procedures. Unsupported ("excess") Th-230 and Pa-231were measured by thick-source alpha-particle counting. The cores represent water depths from 400 m to 4200 m. Compared to C-14 ages from core-top material, IRSL ages are too old by variable amounts, ranging from 4 kyr (insignificant when dating samples > 50 ka) at the Northwind Ridge (western Arctic Ocean) to ca. 10 kyr over some ridge tops, and to 190 kyr from the deepest sample (near the Gakkel Ridge). The geographically variable age overestimates indicate the spatial irregularity of "inherited" luminescence, attributable to the diverse effects of ice-rafting and other processes, such as turbidity and bottom-current resuspension. Samples likely as old as ca. MIS 5 were analyzed at the Northwind Ridge site. An IRSL age of 85±5 ka was obtained just above the penultimate foram (N. pachyderma) abundance peak, while TL and IRSL ages of 99±9 ka were obtained for the younger part of the next deepest abundance peak. These results indicate the great potential for various versions of luminescence sediment dating in some regions of the Arctic Ocean. The TL method has the potential to reach back beyond 500 ka. Interglacial-stage (foram-'rich') sediments from ridge tops are probably most suitable for luminescence dating.