Sediment accumulation rates in the southern Barcelona continental margin (NW Mediterranean Sea) derived from Pb-210 and Cs-137 chronology

Sediment cores were collected from the southern Barcelona continental margi n, including the Foix canyon, in order to study sediment accumulation in th is area. For this purpose, Pb-210, Cs-137 and, to a lesser extent, Pu-239,P u-240 and heavy metals, were determined in sediment sections using state-of -the-art techniques. Pb-210 concentration profiles and Cs-137, Pu-239,Pu-24 0 and heavy metals profile features were used to establish the sediment chr onologies. Further information was also obtained from granulometric analyse s. The magnitudes studied and correlated in this work included surface activit ies, mixing rates, accumulation rates and inventories. Sediments on the con tinental shelf showed a varied degree of mixing (except possibly CN-23), se dimentation rates were relatively small and the sedimentary material probab ly had a common origin. Cores from the slope showed less mixing and, in cor es CN-36 and EB-2, located in the Foix canyon axis, the Cs-137 Signal vs. d epth was clear and well preserved. Accumulation rates and total Pb-210 inve ntories were maximum in core CN-36 at mid-slope of the canyon, which was co nsidered to be an active depocenter. Core CN-38, collected on the open slop e, showed a much smaller accumulation rate. Therefore, it was concluded tha t shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon, which is acting as a natural trap. With in the canyon this material is preferentially deposited at a mid-slope depo center. Little extra material reaches the lower canyon area. In this area, core EB-2 appeared to show signs of the presence of resuspended material, p ossibly derived from the canyon walls, Finally, observed changes in sedimen tation rates during the 1930s could not be explained on the basis of curren t knowledge and this is suggested to be an important subject for further re search. (C) 1999 Elsevier Science Ltd. All ri hts reserved.