Evolution of the South China Sea and monsoon history revealed in deep-sea records

As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropale-ontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkabl ediagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ～3 Ma.     

The identity of Yoldia micrometrica Seguenza, 1877 and three new deep-sea protobranchs from the Mediterranean (Bivalvia)

Three new species are described from the relatively well-known deep Mediterranean protobranch fauna. Yoldiella wareni n. sp. is a miniaturized species so far misidentified as Yoldiella micrometrica (Seguenza, 1877), which is a Pleistocene species (neotype here designated). Yoldiella ovulum n. sp. is similar to Y. micrometrica, of which it may represent a descendant species. Ledella marisnostri n. sp. is the second species known for the genus in the Mediterranean. These three species are thought to be endemic to the Mediterranean, where they may represent either persisting Plio-Pleistocene species which survived the changes from psychrospheric to homeothermic conditions, or newly adapted species, evolved from Plio-Pleistocene ancestors. In the second case, they seem to be the result of an ongoing differentiation of the deep Mediterranean protobranch fauna from the North-East Atlantic one, due to the physical isolation of the Mediterranean basin.     

On Liljeborgia fissicornis (M. Sars, 1858) and three related new species from Scandinavia,with a hypothesis on the origin of the group fissicornis

The large and common Scandinavian amphipod Liljeborgia fissicornis (M. Sars) is split into four species: the deep-water L. caliginis sp. nov. and L. charybdis sp. nov., and the shallow-water L. fissicornis and L. ossiani sp. nov. The poorly known species L. polosi Barnard and Karaman, recorded from the deep Canadian Basin of the Arctic Ocean, is considered as belonging to the same group. All those northern species are completely devoid of eyes, while similar species from the Antarctic and sub-Antarctic continental shelf do have eyes. It is hypothesized that the group fissicornis, which is specific to cold waters, derives from ancestors living on the continental shelf of the Southern Ocean. These ancestors would have adapted to deep-sea environments, losing their eyes completely. Then they would have migrated northwards through the cold abyss, and reached the cold but shallow waters of the Arctic/sub-Arctic continental shelf, without redeveloping visual organs.     

深海风暴的原位观测

 深海风暴是高悬浮颗粒浓度水体在深海近海底的快速运动,能够损坏甚至摧毁一切障碍物,改变海底地形,影响深海底栖生态环境,但对其发生过程和沉积记录的认识尚缺乏原位观测研究。选择南海东北部台湾岸外高屏海底峡谷堤岸,通过布放锚系原位观测了2016年9月一次由浊流活动引发深海风暴的沉积物弥散发生过程,发现其表现为近海底悬浮颗粒浓度快速增加,并伴随温度升高和盐度降低。研究认为,深海风暴的沉积物弥散是海底峡谷沉积纹层形成的主要动力过程。     

南海浊流地貌

 南海深海底部浊流地貌十分发育。陆坡区有大量的海底峡谷，部分峡谷的谷底、越岸区或出口部位分布有超临界流成因的大型沉积物波和周期阶坎底形。多数峡谷在陆坡脚的出口处并未形成像样的海底扇，而深海平原中却保有高丰度的浊流沉积。这可能暗示，南海峡谷浊流的能量较高，即使在经历陆坡脚的减速之后仍有足够的能量维持其沿平缓的深海平原作较长距离的搬运。浊流地貌的出现大多始于晚中新世，其成因与南海及周缘强烈的构造活动有关。     

海底沉积物剪切强度的试验研究

通过在船上现场测试,对勘探海域沉积物剪切强度进行了测试和分析.并从力学特征等方面对海底沉积物进行了综合工程地质特性研究,发现测试区域剪切强度特征随含水量的变化而变化.当含水量较高时,具有抗剪切强度小的力学特性.同时结果也表明沉积物剪切强度随深度加大而增大,到一定深度后强度趋于平稳.不同站位的沉积物由于其类型不同其剪切强度随深度的变化也不一样,有的甚至还有较大的差别.图2,表1,参9.     

Morphology and composition of the internal axis in two morphologically contrasting deep-water sea pens (Cnidaria: Octocorallia)

Umbellula encrinus Linnaeus, 1758 and Anthoptilum grandiflorum (Verrill, 1879) are two species of deep-water sea pens (Cnidaria: Octocorallia) commonly found in the Northwest Atlantic. These sea pens are frequently caught as fishing bycatch, but little is known about their biology. Here we characterise the internal skeleton (axis) of these two morphologically contrasting species, in terms of axis carbonate composition and proportion, morphology and metrics (i.e. cross-sectional area and weight) through gradients along their lengths. Using the conspicuous growth rings present in the axis of U. encrinus we also estimated intra-colonial variation in radial growth rates for this species. X-ray diffraction (XRD) analyses revealed that the carbonate portion of the axis is composed of magnesian calcite (Ca, Mg)CO₃ in both species. On average, the axis is composed of 71% carbonate material in U. encrinus, and 65% carbonate in A. grandiflorum. The carbonate proportion was greatly reduced from base (71%) to tip (33%) in the axis of U. encrinus, while in A. grandiflorum changes were less abrupt (~6% difference from base to tip). In U. encrinus, the axis is quadrangular in shape through its whole length, twisting longitudinally. Twisting can occur in both clockwise and anti-clockwise directions. The axis of A. grandiflorum varied from elliptical near the base to cylindrical through most of the remaining length, with no twisting observed. Axes’ cross-sectional areas also decreased with distance from the base in both species, being the largest near the base. Estimated radial growth rates in U. encrinus were variable within a single colony, ranging between 0.04 and 0.08 mm.yr^?1. This is the first study to describe changes along the axes of sea pens, and to characterise the axes in the studied species. It provides a baseline for studies considering sea pens’ skeletons (e.g. ocean acidification and palaeoceanography).     

深海采矿履带式集矿机行走可行性仿真研究

履带式行走平台作为深海采矿集矿机子系统的工作平台行走在海底沉积物上进行深海采矿作业。分析了履带式行走平台简单数学模型,基于大型机械系统动力学分析软件履带车辆专用模块(ADAMS/ATV),构建了深海履带式集矿机多刚体系统模型。通过分析软件仿真了履带式集矿机虚拟样机在四种典型海泥路面上行走的过程,分析了仿真实验结果,履带式集矿机的深海行驶性能被证明比较满意。这种软泥上行走履带式车辆的建模和仿真研究方法被证明是一种有效的新方法。