The Laurentian Fan: Sohm abyssal plain

The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust. Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to the fan is glacial in origin, and in part results from seismically triggered slumping on the upper continental slope. Sandy turbidity currents, such as the 1929 Grand Banks earthquake event, probably erode the fan-valley floors; but thick muddy turbidity currents build up the high levees.     

Morphology,sedimentation processes,and growth pattern of the Amazon Deep-Sea Fan

The Amazon Deep-Sea Fan began to form in the Early Miocene and is characterized by a highly meandering distributary channel system. On the middle fan, these leveed channels coalesce to form two broad levee complexes. Older, now buried levee complexes are also observed within the fan. These levee complexes grow through channel migration, branching, and avulsion. Probably only one or two channels are active at any given time. Sediments reach the fan only during glacio-eustatic low stands of sea level. Coarse sediments largely by-pass the upper and middle fan via the channels and are deposited on the lower fan.     

Morphology, sedimentation processes, and growth pattern of the Amazon Deep-Sea Fan

The Amazon Deep-Sea Fan began to form in the Early Miocene and is characterized by a highly meandering distributary channel system. On the middle fan, these leveed channels coalesce to form two broad levee complexes. Older, now buried levee complexes are also observed within the fan. These levee complexes grow through channel migration, branching, and avulsion. Probably only one or two channels are active at any given time. Sediments reach the fan only during glacio-eustatic low stands of sea level. Coarse sediments largely by-pass the upper and middle fan via the channels and are deposited on the lower fan. Margin setting represents fan and/or source area     

Variation of sediment geotechnical properties between the greater antilles outer ridge and the nares abyssal plain

Abstract

It is clear from morphology alone that distinctly different dynamic and sedimentary processes can be expected to be associated with the Greater Antilles Outer Ridge relative to those of the adjacent Nares Abyssal Plain. This difference is further substantiated by seismic reflection data which show the ridge to be a very large prism of acoustically transparent sediment in contrast to the stratified deposits of the abyssal plain. An examination of the geotechnical properties of the near‐surface (0 to 2.4m) deposits of the two areas also reveals distinct differences in their sedimentological characteristics. The outer ridge sediments, of more or less homogenous clay‐size material, display much higher water contents, porosities, sensitivities, plasticity, and organic carbon contents in contrast to the abyssal plain deposits which are much less homogenous owing to the presence of turbidite sequences. The turbidites themselves are uniquely contrasted to the other abyssal plain sediments by their higher silt content, wet bulk density, shear strength, and sensitivity.     

Sequence boundaries and salt diapirism in the Balearic abyssal plain, western Mediterranean

 Unconformities and lapout structures in seismic profiles from the Balearic abyssal plain northeast of Menorca are apparently related to salt dome movements. Six sequence boundaries, observed around different salt structures, could be correlated throughout the area surveyed. The synchronous episodic movements are interpreted to be related to glacial/interglacial sea level fluctuations. During periods of low stand, more material is eroded from the continental shelf than during high stand, and it is deposited in the deep sea, in turn loading the Miocene salts and activating diapirism. DSDP site 372 and site survey seismic lines were used to define the Pliocene–Pleistocene boundary and to date the sequence boundaries.     

Distribution and abundance of the Weddell seal in the western Ross Sea,Antarctica

The distribution and abundance of the Weddell seal (Leptonychotes weddelli Lesson) in the fast ice and pack ice of the western Ross Sea, Antarctica, were investigated during 1967 and 1968 from icebreakers and accompanying helicopters. It was estimated that there were about 50,000 Weddell seals in the western Ross Sea between Cape Adare and McMurdo Sound. Weddell seals appear to breed mainly in the fast ice along the Victoria Land coast and less frequently in some nearby areas of pack ice. Fast ice is preferred to pack ice. Most Weddell seals in the pack ice were adults. General observations on the distribution of crabeater, leopard, and Ross seals are included.     

Major and trace element distributions in manganese nodules and micronodules as well as abyssal clay from the Clarion-Clipperton abyssal plain,Northeast Pacific

The contents of seven major components (TiO₂, Fe₂O₃, MgO, CaO, Na₂O, K₂O and P₂O₅) and 15 trace elements (Sc, V, Cr, Ni, Cu, Sr, Y, Zr, Ba, La, Ce, Nd, Eu, Yb and Th) were determined by ICP-AE spectrometry in 27 samples of manganese nodules, micronodules as well as abyssal clay collected by dredging from an area of nearly 1,9802 nautical miles in the central Clarion-Clipperton abyssal plain at a depth of about 4,500 m. Statistical analyses were used to compare among individual as well as pooled datasets, in addition to different indicators such as La/Th, Ni/Cu and LREE/HREE ratios for the Clarion-Clipperton samples, as well as between these and corresponding values for the upper continental crust (UCC), North America Shale Composite (NASC), and igneous Indian and Pacific Mid-Ocean Ridge Basalts (MORBs). The results show significant correlations between major components in the Clarion-Clipperton samples and Pacific Ocean MORB, whereas trace elements (excepting Ni and Cu) correlate better with the UCC and NASC. There is also depletion in LREEs, together with a Ce negative anomaly for all Clarion-Clipperton samples. The nodule, micronodule and abyssal clay datasets each reveal typical clusters of components such as P₂O₅ and Y, La, Nd, Eu, Tb, or Ni and Cu. Compared to abyssal clay, the nodule as well as micronodules show significant enrichment in Ni and Cu; nevertheless, an essentially constant Ni/Cu ratio indicates that all samples come from the sediment surface. The distributions of major components as well as trace elements for the Clarion-Clipperton samples present, to different degrees, characteristics common to both the upper continental crust and Mid-Ocean Ridge Basalt, strongly implying a hydrothermal origin, most probably from East Pacific Rise material transported by the Pacific North Equatorial Current.     

The Bengal Fan: morphology, geometry, stratigraphy, history and processes

The Bengal Fan is the largest submarine fan in the world, with a length of about 3000 km, a width of about 1000 km and a maximum thickness of 16.5 km. It has been formed as a direct result of the India–Asia collision and uplift of the Himalayas and the Tibetan Plateau. It is currently supplied mainly by the confluent Ganges and Brahmaputra Rivers, with smaller contributions of sediment from several other large rivers in Bangladesh and India.The sedimentary section of the fan is subdivided by seismic stratigraphy by two unconformities which have been tentatively dated as upper Miocene and lower Eocene by long correlations from DSDP Leg 22 and ODP Legs 116 and 121. The upper Miocene unconformity is the time of onset of the diffuse plate edge or intraplate deformation in the southern or lower fan. The lower Eocene unconformity, a hiatus which increases in duration down the fan, is postulated to be the time of first deposition of the fan, starting at the base of the Bangladesh slope shortly after the initial India–Asia collision.The Quaternary of the upper fan comprises a section of enormous channel-levee complexes which were built on top of the preexisting fan surface during lowered sea level by very large turbidity currents. The Quaternary section of the upper fan can be subdivided by seismic stratigraphy into four subfans, which show lateral shifting as a function of the location of the submarine canyon supplying the turbidity currents and sediments. There was probably more than one active canyon at times during the Quaternary, but each one had only one active fan valley system and subfan at any given time. The fan currently has one submarine canyon source and one active fan valley system which extends the length of the active subfan. Since the Holocene rise in sea level, however, the head of the submarine canyon lies in a mid-shelf location, and the supply of sediment to the canyon and fan valley is greatly reduced from the huge supply which had existed during Pleistocene lowered sea level. Holocene turbidity currents are small and infrequent, and the active channel is partially filled in about the middle of the fan by deposition from these small turbidity currents.Channel migration within the fan valley system occurs by avulsion only in the upper fan and in the upper middle fan in the area of highest rates of deposition. Abandoned fan valleys are filled rapidly in the upper fan, but many open abandoned fan valleys are found on the lower fan. A sequence of time of activity of the important open channels is proposed, culminating with formation of the one currently active channel at about 12,000 years BP.     

Navy Fan, California Borderland: Growth pattern and depositional processes

Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland. The middle fan, characterized by one active and two abandoned “distributary” channels and associated lobe deposits, at present onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene depositional processes. Margin setting represents fan and/or source area     

Navy Fan,California Borderland: Growth pattern and depositional processes

Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland. The middle fan, characterized by one active and two abandoned “distributary” channels and associated lobe deposits, at present onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene depositional processes.     

Distribution of chlorophyll a and diatom in the sea ice of the Weddell Sea, Antarctica

Diatoms are major primary producers of microbial biomass in the Antarctica. They are found in the water and sea ice. The distribution, abundance of the ice diatoms and their relation to the environmental factors inside and outside the ice have been studied for its special role in the Antarctic Ocean ecology. In this paper we describe the abundance, distribution and composition of diatom assemblages in     

Mississippi Fan: Internal structure and depositional processes

The Mississippi Fan is a Quarternary accumulation composed of more than seven elongated fan lobes. Isopach and structure maps show frequent shifting of these lobes. The Mississippi Canyon, formed by retrogressive slumping, connects to the youngest fan lobe. The upper fan-lobe is characterized by a large, incised, partially infilled, leveed channel. The middle fan-lobe is aggradational, convex in cross section, with a channel-levee complex on its apex. The lower fan-lobe contains a recently active small channel and several abandoned ones. Depositional patterns can be explained by several processes: “fluvial,” debris flows, and turbidity currents. Margin setting represents fan and/or source area     

Mississippi Fan: Internal structure and depositional processes

The Mississippi Fan is a Quarternary accumulation composed of more than seven elongated fan lobes. Isopach and structure maps show frequent shifting of these lobes. The Mississippi Canyon, formed by retrogressive slumping, connects to the youngest fan lobe. The upper fan-lobe is characterized by a large, incised, partially infilled, leveed channel. The middle fan-lobe is aggradational, convex in cross section, with a channel-levee complex on its apex. The lower fan-lobe contains a recently active small channel and several abandoned ones. Depositional patterns can be explained by several processes: “fluvial,” debris flows, and turbidity currents.     

Short-term variations and influencing factors of suspended sediment concentrations at the Heisha Beach,Guangdong, China

Knowledge of sediment variation processes is essential to understand the evolution mechanism of beach morphology changes. Thus, a field measurement was conducted at the Heisha Beach, located on the west coast of the Zhujiang River(Pearl River) Estuary, to investigate the short-term variation in suspended sediment concentrations(SSCs) and the relationship between the SSC and turbulent kinetic energy, bottom shear stress(BSS), and relative wave height. Based on extreme event analysis results, extr...     

Glacial morphology and post-glacial contourites in northern Prince Gustav Channel (NW Weddell Sea,Antarctica)

We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation.     

椒江流域水沙变化特征及人类活动影响

在人类活动的影响下,径流和泥沙过程的变化受到越来越多人的关注。研究椒江流域水沙变化特征及人类活动影响因素,对椒江流域生态保护和高质量发展具有重要意义。利用椒江流域降水、径流、输沙和遥感影像等长期监测数据,采用多种方法综合分析椒江流域降水、径流和输沙演变特征,包括对椒江流域水文观测资料进行线性回归趋势分析,使用Mann-Kendall突变检验法、滑动t检验法、距平累积曲线法和双累积曲线法进行水文序列的突变检验,使用小波和功率谱进行水文序列的周期分析。在此基础上,采用线性回归方法估算人类活动和气候变化对椒江流域输沙变化的贡献率,最后讨论了人类活动对椒江流域水沙变化的影响。结果表明：椒江降水量存在2～3、4～5、8～9和15～18 a周期;径流量存在2～3、8～9、14～15和18 a周期;输沙量存在2～3、8、12～15和19 a周期。永安溪、始丰溪年降水量、年径流量和始丰溪年输沙量没有显著变化,永安溪输沙量显著减少,63 a间下降了28%。人类活动对永安溪输沙减少的贡献率为86.5%～98.7%,对始丰溪输沙变化的贡献率为50.3%～83.2%。椒江流域水库建设使得年内流量高峰期由6月份向8、9月份发生转移,起到了很好的“蓄峰”作用。流域内土地利用/覆被发生的显著变化以及植被覆盖度的上升降低了流域产沙能力、减少了河流输沙量。     

Physical structure and vertical distribution of chlorophyll a in winter sea ice from the northwestern Weddell Sea, Antarctica

The investigation on sea-ice biology in combination with physics, chemistry and ecology was carried out in the northwestern Weddell Sea, Antarctica, during the cruise ANT/XX III-7 on board POLARSTERN in the austral winter (August-October) in 2006. The distribution of chlorophyll a was measured and related to sea ice texture. The mean concentrations of chlorophyll a in the sea ice varied considerably with ice texture. The concentration of chlorophyll a per core ranged from 2.10– 84.40 μg/dm 3 with a mean of 16.56 μg/dm 3 . And the value of R (chlorophyll a / gross chlorophyll) ranged from 0.79–0.83. These high winter chlorophyll values indicate that primary production is considerable and confirms that there is significant primary production in Antarctic sea ice during winter. Thus this constitutes a major proportion of southern ocean primary production and carbon flux before the sea ice retreats.     

半日潮流作用下悬移质泥沙的运动特征及其影响因素研究

本文通过建立一维水深平均悬沙模型,对典型潮流控制的水道内悬沙运动特征进行研究。模型以泥沙再悬浮、沉降和平流为主要物理过程,动力因素包含M₂、S₂分潮及余流,采用湄洲湾2007年8月潮位、潮流、悬沙、底质同步观测资料进行分析和验证。通过三角傅里叶分析,将悬沙的时间序列分解为12个主要的谐波分量,其中主要分量包括:M₂分潮作用下产生的具有M₂倍潮角速度的1/4日分潮项,M₂与S₂分潮共同作用下且角速度为两分潮角速度之和的1/4日分潮项,及水平悬沙梯度、余流与M₂分潮共同作用下具有M₂分潮角速度的半日潮项。悬沙在时间上的平均值受到余流、悬沙水平梯度、M₂分潮流及悬沙起动条件等因素控制。余流导致了悬沙序列中相邻周期之间的不对称性。反映泥沙特性的参量对悬沙的曲线特征具有重要影响,泥沙沉降速度影响悬沙的相位,并影响其振幅;再悬浮有关的参量仅影响各谐波分量的振幅,但不影响相位。     

青岛市灵山湾海水浴场沉积物分布特征与影响因素

针对灵山湾海水浴场海滩沉积物进行了粒度测试,探讨了沉积物分布特征并分析了其输运趋势。测试结果表明,沉积物类型均为砂,分选好至较好,其沉积作用受相对稳定的水动力条件控制,主要受到波浪、潮汐和沿岸流的影响。灵山湾海水浴场东北侧偏粗,分选略差,西南侧偏细,分选较好。粒度趋势分析显示,研究区沉积物有北东-南西向的沿岸搬运趋势,东北部为侵蚀区,西南部为沉积区。随着青岛西海岸经济新区的大规模开发,灵山湾海水浴场侵蚀可能将会更加严重。日后持续的调查研究,将为本区和其他地区的海滩砂研究和保护提供基础资料和参考。