海平面变化对冲绳海槽沉积有机质来源、14C年龄组成及其碳汇效应的影响

Sediment organic carbon burial removes CO2 from the ocean–atmosphere pool, playing an important role in regulating climate changes. It has been reported that the accumulation rate of marine sediment organic carbon was 47±18% higher during the last glacial maximum than during the Holocene. However, sources and 14C age compositions of the glacial buried organic carbon remains ambiguous, hindering our understanding on marine carbon cycle. By carrying out RPO-14C analysis on total organic carbon from sediment cores derived from the Okinawa Trough, this study aims to estimate the contributions from contemporary, pre-aged and petrogenic organic carbon during the last glacial maximum. Combined with 14C ages of long-chain fatty acids and alkenones, as well as biomarker loadings on hydrodynamic-sensitive mineral surface, from the same core, effort will be focused on the mechanisms controlling organic carbon burial efficiency and variation of 14C ages. Results from this study are expected to improve our understanding about the effect of sea level change on the source-sink process of sedimentary organic carbon in the western Pacific margin.

末次冰盛期全球海洋有机碳埋藏通量相比晚全新世增加了约47±18%，解析该有机碳来源和年龄组成，有助于认知其对大气CO2浓度变化的调控作用。然而，有关末次冰盛期有机质14C组成的资料匮乏，对该时期有机质埋藏碳汇效应及其调控机制的认识尚不清楚。针对这一问题，本项目聚焦末次冰盛期与晚全新世典型背景下，拟对冲绳海槽沉积岩芯开展有机质14C年龄组成的研究。利用总有机质升温热裂解-14C技术量化评估有机质的来源、通量和年龄特征；结合长链正构脂肪酸、直链烯酮的14C年龄及其在敏感粒级矿物单位比表面的载荷量，探讨陆架水动力搬运过程对陆源有机质埋藏效率及14C年龄的影响。通过末次冰盛期与晚全新世的资料对比，尝试梳理海平面变化对西太平洋边缘陆坡沉积有机质的源—汇过程及其碳汇效应的影响。

本项目计划应用先进14C技术方法，开展海平变化背景下冲绳海槽有机质来源和14C年龄组成变化的研究。通过三年的工作开展，项目基本完成了计划书拟定的任务；此外，在项目书所列研究材料的基础上，增加了南黄海泥质区和济州岛泥质区岩芯并开展了有机碳含量及同位素、脂肪酸单体碳同位素等参数的测定。通过陆架与陆坡相结合，更加客观的评估了海平面变化对西太平洋边缘海有机碳埋藏的影响，回答了项目书中所列的科学问题。主要结论如下：（1）海平面变化显著改变了陆架沉积体系中陆源有机碳的比例（冰消期高、全新世低），但是对冲绳海槽南部和中部区域的影响并不显著。（2）伴随冰消期海平面上升，南黄海和冲绳海槽沉积岩芯中（南部和中部）陆源有机碳年龄逐渐变老，而东海陆架陆的源有机碳年龄变年轻。（3）东海陆架强的水动力过程造成了陆源有机碳在陆架侧向传输过程中发生了显著的降解与老化，进而调控了冲绳海槽的有机碳埋藏通量及特征。（4）相比于高海平面时期，冲绳海槽埋藏的有机碳在低海平面时期具有年龄小、碳通量大的特征，因此具有更高的碳汇能力。项目负责人以第一/通讯作者发表项目标注SCI论文4篇（项目预期结果为发表论文2-3篇），其中包括《Geochimica et Cosmochimica Acta》和《Geophysical Research Letters》等TOP期刊论文；另有2篇（第一标注）已经投稿至TOP期刊《Global Biogeochemical Cycles》(under review)和《Palaeogeography, Palaeoclimatology, Palaeoecology》(under review)。培养了2名博士生，1名硕士生。