Sedimentation and climate-induced sediments on Feni Ridge, Northeast Atlantic Ocean

Abstract

Feni Ridge has been studied in detail in the area between 54 and 56°N and 12 and 16°W by using high-resolution profiling, water column sampling with transmissometer and CTD, and by piston and box core sampling. The crest of Feni Ridge is absent in the north of the study area, but on passing towards the south it begins to take shape and to increase in height; its distance from the Rockall slope also increases towards the south. On the lower southeastern flank a secondary ridge crest has locally developed, and sediment waves along the flanks have amplitudes of up to 45 m. The highest and steepest waves are found in the south, the waves in the north being somewhat lower. Bottom nepheloid layers of 175 m near the foot of Rockall Plateau and 125 m near the crest are attributed to a Norwegian Sea Overflow Water current with a core at 2100 m. Bottom nepheloid layers of 75–100 m on the lower flanks of the ridge are thought to have been caused by Northeast Atlantic Deep Water. Piston cores reflect alternations of glacial and interglacial periods. Interglacials have a high carbonate and C org content, a positive Eu anomaly and negative Ce anomaly, and a low Rb La ratio. They are dominated by a subpolar and transitional foraminiferal assemblage. Glacials show a low carbonate and C org content, a reduced Eu anomaly and a high Rb La ratio, suggesting increasingly continental sediment sources. These deposits are dominated by a polar planktonic foraminiferal assemblage characterized by N. pachyderma (s) and G. quinqueloba. Sedimentation rates reflect differential deposition. At crestal station NA 87-25 rates are 17.1 cm/k.y. for stage 1, 14.6 cm/k.y. for stage 2, 3.4 cm/k.y. for stage 3 and 5.4 cm/k.y. for stage 4. Stage 5a–e has a mean sedimentation rate of 6.1 cm/k.y. Over the last 125 k.y. the development of Feni Ridge has taken place under a relatively low energy current regime.