Millennial-scale paleoceanography in Okinawa Trough during Late Quaternary period

Based on the analyses of foraminifer and accelerator mass spectrometer radiocarbon dating in DGKS9603 core from mid-Okinawa Trough close to bottom, oscillation curve, which expressed the relation between the surface water temperature and the depth, has been obtained by using foraminifer analysis and calculation of FP-12E transfer function. The whole core indicated seven cold phases and eight warm phases. Obvious expression of low temperature event during Middle and Late Holocene, YD,H1,H2,H3 and H4 events, as well as the short cold phase during the middle last glacial period, implied that short shifts since 50 kaBP would have been global significance. Sedimentation rate during cold phases is usually faster than that in warm stages, with the lowest rate in Holocene, which may be connected with rising sea level and principal axial of Kuroshio Current moving to west. Volcanic activities highly developed in Okinawa Trough during the Quaternary period, thus abundant volcanic glass and pumice were well preserved.

Last deglaciation in the Okinawa Trough: Subtropical northwest Pacific link to Northern Hemisphere and tropical climate

IEECAS SKLLQG

Phylogeography of the Northern Atlantic species Chondrus crispus (Gigartinales, Rhodophyta) inferred from nuclear rDNA internal transcribed spacer sequences

Eighteen isolates of the red algae Chondrus crispus were collected from Northern Atlantic sites, together with C. ocellatus, C. yendoi and C. pinnulatus from the North Pacific. The nuclear rDNA internal transcribed spacer (ITS) was sequenced and compared, spanning both the ITS regions and the 5.8S rRNA gene. Percentage of nucleotide variation for C. crispus ranged from 0.3% to 4.0%. Phylogenetic analyses were performed using maximum parsimony (MP), neighbor-joining (NJ) and minimum evolution methods. They showed that two main clades existed within the C. crispus samples examined and that suggested C. crispus had a single Atlantic origin. The clustering however did not follow the geographic origin. We hypothesized that the current distribution of C. crispus populations might be a result of three main factors: temperature boundaries, paleoclimate and paleoceanography. ITS data exhibited abundant molecular information not only for phylogeographical investigation but also for systematics studies.

Paleoceanographic records in the sedimentary cores from the middle Okinawa Trough

Two gravity piston cores (Cores 155 and 18) involved in this study were collected from the middle Okinawa Trough. Stratigraphy of the two cores was divided and classified based on the features of planktonic foraminifera oxygen isotope changes together with depositional sequence, millennium-scale climatic event comparison, carbonate cycles and AMS(14)C dating. Some paleoclimatic information contained in sediments of these cores was extracted to discuss the paleoclimatic change rules and the short-time scale events presented in interglacial period. Analysis on the variation of oxygen isotope values in stage two shows that the middle part of the Okinawa Trough may have been affected by fresh water from the Yellow River and the Yangtze River during the Last Glacial Maximum (LGM). The oxygen isotope value oscillating ranges of the cores have verified that the marginal sea has an amplifying effect on climate changes. The delta(13)C of benthic foraminifera Uvigerina was lighter in the glacial period than that in the interglacial period, which indicates that the Paleo-Kuroshio's main stream moved eastward and its influence area decreased. According to the temperature difference during the "YD" period existing in Core 180 and other data, we can reach the conclusion that the climatic changes in the middle Okinawa Trough area were controlled by global climatic changes, but some regional factors had also considerable influence on the climate changes. Some results in this paper support Fairbanks's point that the "YD" event was a brief stagnation of sea level rising during the global warming up procession. Moreover, the falling of sea level in the glacial period weakened the exchange between the bottom water of the Okinawa Trough and the deep water of the northwestern Pacific Ocean and resulted in low oxygen state of bottom water in this area. These procedures are the reasons for carbonate cycle in the Okinawa Trough area being consistent with the "Atlantic type" carbonate cycle.

Sea surface temperature reconstruction for the middle Okinawa Trough during the last glacial-interglacial cycle using C-37 unsaturated alkenones

C-37 unsaturated alkenones were analyzed on a core retrieved from the middle Okinawa Trough. The calculated U-37(K') displays a trend generally parallel with those of the oxygen isotopic compositions of two planktonic foraminiferal species, Neogloboquadrina dutertrei and Globigerinoides sacculifer, suggesting that in this region, SST has varied in phase with global ice volume change since the last glacial -interglacial cycle. The U-37(K')-derived SST ranged from ca. 24.0 to 27.5 degrees C, with the highest value 27.5 degrees C occurring in marine isotope stage 5 and the lowest similar to 24.0 degrees C in marine isotope stage 2. This trend is consistent with the continental records from the East Asian monsoon domain and the marine records from the Equatorial Pacific. The deglacial increase of the U-37(K')-derived SST is similar to 2.4 degrees C from the Last Glacial Maximum to the Holocene. (c) 2007 Elsevier B.V. All rights reserved.

海水中微量元素-碳酸钙共沉淀现象模拟：古海洋环境指标的实验研究

本文主要阐述运用稳定加液-反应系统，在实验室环境下模拟海水中方解石和文石形成时微量元素共沉淀现象，主要研究微量元素固-液体系中的迁移、转化和分配。进而在对其定量描述的前提下，研究各靶元素的共沉淀行为对各种反应条件的响应，从中提取出可以用于古海洋研究的替代性指标。所研究的微量元素和部分常量元素包括非金属元素硼和砷、碱土金属元素镁、过渡金属元素(锰、钴、镍、铜、和镉)、铀系元素(铀、钍和铅)以及钇和稀土元素。 本实验首先运用pH测试、高精度滴定分析等手段测定了实验的一些基本参数，如[H+]、碱度和[Ca2+]，根据计算获得了各碳酸体系要素，并以此为基础建立了5℃、15℃和25℃及pCO2=0.0015 atm.=0.0030atm.下的人工海水中方解石或文石的沉淀动力学方程。研究表明： 1)在各个条件下，方解石或文石的沉淀速率(R)和其在海水中过饱和度(Ω)存在很好的相关性，可基本表达为Log R=k*Log(Ω-1)+b； 2) pCO2对会严重改变海水中的碳酸钙过饱和度，进而影响相应的沉淀速率，但对方解石或文石的沉淀动力学方程没有明显影响； 3)不同温度下所得的方解石或文石各自的沉淀动力学方程存在明显差异，表明这一过程受热力学元素控制。 在方解石和文石沉淀实验中，通过人为添加各种微量元素对它们的共沉淀行为进行模拟。首先通过直接溶解稀释法结合ICP-MS或采用离线螯合系统前处理结合ICP-MS测定海水、固体样品中各靶元素的浓度。在此基础之上通过换算得出各靶元素在海水([Me]sol’n)和方解石或文石沉淀([XMe]overg)中的含量，然后 计算出单个实验中各靶元素介于碳酸钙沉淀和海水之间的分异系数。 实验中通过改变晶核类型(方解石和文石)、温度、pCO2、碳酸钙过饱和度(2-12，以方解石计)、沉淀速率和靶元素起始浓度等参数，得到在不同反应条件下各靶元素的分异系数。基于分异系数之间的差异，各靶元素在方解石和文石沉淀过程中的共沉淀行为被加以分类和界定。在方解石中Mn、Co、Ni、Pb、Th、Cd、Cu、Mg等表现为相容元素。而在文石中Mn、Co、Ni、Cd等都属不相容元素。B、As、U与其他金属离子不同的是这三种元素是以BO33-、AsO33-、UO22+等基团的形式参予共沉淀的，其中BO33-和AsO33-是替代CO32-而UO22+取代Ca2+。 进一步总结各靶元素和反应条件的关系，初步得出碳酸钙沉淀动力学机制、温度、离子半径、碳酸钙矿物的晶格结构、溶液化学组成及其变化是影响微量元素随方解石和文石共沉淀过程的重要因素，并对各靶元素共沉淀模式进行了探讨。最后我们结合实际工作主要是文献中报导的有孔虫、珊瑚等生物钙质壳体或骨架中各靶元素的结果，对比我们的实验从中提取出了一些可应用于古海洋研究的潜在替代性指标，如： 1) 海水中CO32-浓度代用指标——文石U/Ca、Cd/Ca比，方解石U/Ca比； 2) 海水pH 代用指标——文石B/Ca、As/Ca 比； 3) 氧化还原代用指标——方解石Mn/Ca 比； 4) 海水化学代用指标——方解石Co/Ca 比、U/Ca 比文石Cu/Ca、Pb/Ca 比。 5）稀土元素代用指标——方解石质载体中的YREE/Ca比。 还有几种元素组合也非常具有价值，如Mn-Co-Ni 组合、B-U 组合。此外指出了现有微量元素古海洋指标应用过程中被忽略了的一些关键性因素，如文石Mg/Ca比受到文石沉淀速率的限制、方解石Cd/Ca 比受到沉淀速率和温度的双重影响等。