Synchronous Changes of Nitrogen and Carbon Isotopic Ratios and Nannoplankton Assemblage in Marine Sediments off Peru at 250 ka: A Role of Phytoplankton in Primary Ocean Productivity
Synchronous Changes of Nitrogen and Carbon Isotopic Ratios and Nannoplankton Assemblage in Marine Sediments off Peru at 250 ka: A Role of Phytoplankton in Primary Ocean Productivity
复制标题
DOI：
10.4236/ojg.2013.32015
复制
发表时间：
2013-04
期刊：
影响因子：
--
通讯作者：
H. Hasegawa;I. Kita;S. Tsukamoto;S. Chiyonobu;Y. Kuwahara
中科院分区：
文献类型：
--
作者：
H. Hasegawa;I. Kita;S. Tsukamoto;S. Chiyonobu;Y. Kuwahara
我们根据过去 50 万年赤道太平洋秘鲁 ODP 846B 孔岩心样本中钙质超小型浮游生物组合的变化，报告了控制海洋有机质 δ15Norg 和 δ13Corg 值变化的机制。 δ15Norg值波动范围为2.1‰至6.7‰，自250ka左右开始急剧增加，老年期和年轻期平均值分别为3.8‰和5.0‰。 δ13Corg 值的变化范围为 23.5‰ 至 20.1‰，与 δ15Norg 值呈负相关，描述了 250 ka 时平均值的增加以及 δ15Norg 值的增加。总有机碳含量在年轻时期和老年时期的平均值分别为 0.6% 和 0.3%。与较早时期相比，较年轻时期钙质超小型浮游生物深部栖息物种（Florisphaera profunda）数量的增加表明，这些与海洋沉积物中超小型浮游生物组合变化同步的化学和同位素跳跃是由约250ka以来该海域信风强度突然下降导致透光区深层生物活动引起的。将 δ15Norg 和 δ13Corg 值与超微浮游生物组合相结合的研究可以成为评估透光带分层程度以及浮游植物表层和深层居民在产生初级有机质中的作用的有用方法。
We report the mechanism controlling changes of δ15Norg and δ13Corg values of marine organic matter, based on the change of calcareous nannoplankton assemblage during the last 500,000 years in core samples from ODP Hole 846B off Peru in the equatorial Pacific Ocean. The δ15Norg values fluctuate in a range from 2.1‰ to 6.7‰, giving an abrupt increase since about 250 ka with the averages of 3.8‰ and 5.0‰ during the older and younger periods, respectively. The δ13Corg values change in a range from ?23.5‰ to ?20.1‰ in an inverse correlation with δ15Norg values, describing an increase of average values at 250 ka as well as those of δ15Norg values. The total organic carbon content also shows averages of 0.6% and 0.3% during the younger and older periods, respectively. The numerical increase of deep dwelling species (Florisphaera profunda) of calcareous nannoplankton during the younger period in comparison with the older period indicates that these chemical and isotopic jumps synchronized with nannoplankton assemblage changes in marine sediments are caused by activity of deep dwellers in photic zone more stratified by an abrupt decline of trade wind strength on this sea area since about 250 ka. A study coupling δ15Norg and δ13Corg values and nannoplankton assemblage can be a useful method for evaluating the extent of stratification of photic zone and the roles of surface and deep dwellers of phytoplankton in producing primary organic matter.