Recent sediment accumulation in the Skagerrak, Northeastern North Sea

Abstract

Recent sedimentation and sediment accumulation rates calculated from downcore 210Pb excess activity profiles in 16 boxcores from the Skagerrak show great variations. Highest sedimentation rates, in excess of 0.40 cm·y −1, are found in the northeastern Skagerrak. Intermediate values (∼0.20 cm·y −1) occur both along the southern and northern slopes of the basin. The central basin is characterized by values of ∼0.10 cm·y −1. These sedimentation rates evidence that 28.4 million tons (dry weight) of sediment accumulate annually in the Skagerrak, of which some 59% (16.7 million tons) are finer than 63 μm. The organic carbon content of the bottom sediments is 2.5% of dry weight in the deepest part of the basin where the finest sediment settles, around 2% in the northern and eastern sectors and on average around 1.5% in the southern part of the study area. Downcore deviations from the logarithmic decrease of 210Pb with depth could generally be attributed to biological disturbance causing reworking of the sediment, as shown by ETS measurements and X-radiography. The Skagerrak is evidently the major depository of fine-grained sediments in the North Sea. The role of sea-floor erosion as an additional source of sediment has most probably been highly underestimated in mass budget studies so far.