赤道西太平洋冬季浮游有孔虫分布与壳体同位素特征

通过对2009年1月在赤道西太平洋暖池区6个站位、28个垂直分层拖网浮游有孔虫样品进行分析,在0~250m水层内共鉴定出14个浮游有孔虫属种,以热带暖水种为主、广适应性冷水种仅零星出现。表层种Globigerinoides ruber平均生活深度较Globigerinoides sacculifer深,可能是由于赤道地区强烈的太阳光照射或两个种食物来源差别的缘故。G.ruber与Pulleniatina obliquiloculata壳体氧碳同位素协同变化,反映出海水碳酸盐化学体系是同位素变化的控制因子之一。此外,浮游有孔虫壳径也是壳体同位素值的重要影响因素,因而为了减小壳体壳径对壳体同位素值的影响,进行浮游有孔虫同位素分析时应尽量挑选壳径相近的壳体。

DISTRIBUTION OF WINTER LIVING PLANKTONIC FORAMINIFERS AND CHARACTERISTICS TO THEIR SHELL'S STABLE ISOTOPIC IN THE WESTERN EQUATORIAL PACIFIC

Planktonic foraminifera keep records of the upper ocean environments in their assemblage and individual tests.In order to attain the information of the vertical distribution and stable isotopic characteristics of planktonic foraminifera,we collected samples in MultiNet mediate plankton tow(aperture opening 0.25m2; 154μm mesh size)in the upper 250m of the water column which divided into five depth intervals(0~50,50~100,100~150,150~200,and 200~250m)from 6 sites in the western equatorial Pacific in January 2009. The species fauna analysis showed that totally 14 species were identified in the water of upper 250m,and they were most tropic warm water species(Globigerinoides ruber,G.sacculifer,Pulleniatina obliquiloculata,Neogloboquadurina dutertrei and Globorotalia menardii widespread distributed there)and cold water species only occurred sparsely,which indicates the warm-dwelling species are dominated in the study areas. G.ruber (s.s.)accounted for the majority of G.ruber(two morphotypes G.ruber s.s.and G.ruber s.l.)in the study stations,with sedimentary records probably reflecting G.ruber s.l.predominant in lower temperature or deeper surface waters.In terms of vertical distribution,G.sacculifer had an average shallower habitat than G.ruber,probably related to the light intensity and food supply.Besides,an interesting feature is the main depth habitat of G.aequilateralis with symbiotic algae within the lower mixed layer and upper thermocline in the region.The maximum abundance of P.obliquiloculata occurred at the lower mixed layer(50~100m)among the water column. G.menardii showed a relatively high abundance in the marginal western equatorial sites compared with others,and indicative of larger and thicker shells at the greater depth,probably related with vertical transport in the life cycle.The oxygen and carbon isotopes of G.ruber and P.obliquiloculata parallelly vary as the result of the similar sea water carbonate effect.In addition,it has been shown that the size of planktonic foraminiferal shells was an important influencing factor to the stable isotopes,which suggest that we should pick up the shells with the same size fraction for the stable isotopic analysis.