末次盛冰期以来冲绳海槽中部沉积物有机碳和磷的地球化学研究

Characterizing the geochemical properties of organic carbon and phosphorus in the sediments of the middle Okinawa Trough since the Last Glacial Maximum for clarity

利用元素及同位素地球化学方法研究了冲绳海槽中部沉积物岩芯中有机碳及磷的地球化学特征及影响因素。结果表明,冲绳海槽沉积速率(16.5~32.5 cm/ka)变化小,不是沉积物中有机碳埋藏的重要影响因素。相对于全新世氧化性底水环境,末次盛冰期/冰消期冲绳海槽缺氧底水环境提高了沉积物对有机碳的埋藏效率。冲绳海槽沉积物中各形态磷的相对含量与其他边缘海沉积物中的相似。交换态磷(Ex-P)含量低、变化小。末次盛冰期/冰消期缺氧底水环境下铁氧化物的还原溶解导致铁结合磷(Fe-P)释放以及自生磷矿物(Au-P)的形成。全新世氧化性底水条件有利于铁氧化物的有效再生及对磷的再吸附,但不利于Au-P的保存。总有机碳(TOC)和有机磷(Org-P)之间良好的相关性表明TOC埋藏对Org-P含量的重要控制作用。冲绳海槽沉积物中碎屑磷(De-P)含量低于长江口及东海陆架沉积物中的含量,这与陆源碎屑向外海传输减弱有关。在约9.3 ka BP(岩芯200 cm深度),TOC、Fe-P、Org-P、De-P以及FeHR均出现的极小值可能由物质坡移造成。

We employed elemental and isotope geochemical methods to investigate the geochemical characteristics and influencing factors of organic carbon(OC)and phosphorus(P)in the sediment cores collected from the middle Okinawa Trough.The results showed that the sedimentation rates(16.5~32.5 cm/ka)had only small variations,thereby having no significant effect on the burial of OC.The anoxic bottom water conditions during the last Glacial/Deglacial Maximum promoted the sediment burial of OC as compared the conditions under the oxidative bottom water conditions during the Holocene.The middle sediments of Okinawa Trough have percent fractions of various forms of P that are similar to the sediments present in other marginal seas.The contents of exchangeable or loosely absorbed P(Ex-P)were lower and present at an invariable depth.The anoxic bottom water conditions during the last Glacial/Deglacial Maximum facilitated the reductive dissolution of iron(Fe)oxides,thus leading to the release of Fe-bound P(Fe-P)and the formation of authigenic P(Au-P)forms.Oxic conditions during the Holocene favored the oxidative regeneration of Fe(Ⅲ)oxides and re-adsorption of P,but dampened the burial of Au-P.A significant linear correlation between total OC(TOC)and organic P(Org-P)indicates that the sediment burial/remineralization of OC exerted an important control on the content of Org-P.The contents of detrital phosphorus(De-P)in the sediments of Okinawa Trough were lower than those in the sediments of the Yangtze Estuary and the East China Sea shelf;this observation could be ascribed to the gradual decrease in the transport of De-P particles from the nearshore areas to the open sea.At about 9.3 ka(depth of 200 cm),mass wasting may have caused abrupt changes in the contents of TOC,Fe-P,Org-P,De-P,and reactive iron.