Barium as a tracer to study the paleoproductivity variation of Nansha Islands sea area

During the cruise of Nansha Islands sea areas investigation in 2002,three sediments cores were obtained using gravity box method,then barium,titanium,REE and other trace elements in these samples were examined on ICPMS,at the same time the sedimentage was measured with AMS-¹⁴C_orc(organic carbon) method.The distribution characteristics of barium and titanium both in plane and vertical direction were studied.It is found that biobarium variation at NS02-21 and NS02-50 is obvious,begining to increase at about 2 800 a BP.However,the situation is fairly complex and no obvious trend is found at another site(NS02-1),combining with related REE data and other trace element tracers,may be due to its high contents of terrigenous substance in this core.The paleoproductivity using bariumas a reconstructing proxy was calculated adapting Francois model subsequently.The paleoproductivity(export productivity) at Site NS02-21 is 0.78~2.41 g/(cm²·a),the average value is 1.06 g/(cm²·a).The paleoproductivity at NS02-50 site is 3.72~4.57 g/(cm²·a),the average value is 4.13 g/(cm²·a).Lots of researches have indicated that the variations of paleopro ductivity in Nansha Islands sea area are mainly caused by variation of paleo monso on and sea level.Here the paleo productivity records at Sites NS02-21 and NS02-50 mainly reflect the paleo ecological environment variation since Mid Holocene.During that period there was an obvious cold period between 4 000 a BP and 2 000 a BP according to related resear chresults,and the winter trade wind streng thened at that time.The increasing of paleoproductivity in these two sam pling sites mainly corresponds to the cold period in the late Holocene.