The 26 December 2004 Sumatra tsunami recorded on the coast of West Africa

Analysis of sea-level data obtained from the Atlantic Global Sea Level Observing System (GLOSS) sea-level station at Takoradi, Ghana, West Africa, clearly reveals a tsunami signal associated with the M_w = 9.3 Sumatra earthquake of 26 December 2004 in the Indian Ocean. The tsunami arrived at this location on 27 December 2004 at approximately 01:38 UTC (which is close to the expected tsunami arrival time at that site), after travelling for more than 24 hours. The first wave was negative (trough), in contrast with the South African stations where the first wave was mainly positive (crest). The dominant observed period at Takoradi was about 42 minutes. The maximum trough-to-crest wave height (41cm) was observed on 28 December at 00:15 UTC. There were two distinct tsunami 'bursts', separated in time by about 14 hours, the larger being the second burst. A small residual lowering of the sea level (～15cm) during the tsunami and for several days afterwards, and a delayed (～4.5 days) lowering of seawater temperature (up to ～4.5°C), was observed, possibly indicating the presence of internal waves through the Gulf of Guinea associated with propagating tsunami waves. The prominent tsunami signal found in the Takoradi record suggests that tsunami waves could also be found at other sites off the West African coast.     

Impacts of the 26 December 2004 tsunami in Eastern Africa

The tsunami of 26 December 2004 was the largest ever recorded in the Indian Ocean, triggered by the 3rd largest earthquake in 100 years measuring 9.2 moment magnitude. The epicenter of the earthquake was off Banda Aceh on the Indian Ocean coast of the island of Sumatra in Indonesia, centered at 3.316°N, 95.854°E. A sudden upward movement of the seafloor that averaged ∼6 m occurred along almost 1300 km of the north-east Indian Ocean plate at 0059 Coordinated Universal Time (UTC) and lasted 8 min. Because of the lack of preparedness and absence of warning systems in the Indian Ocean the tsunami spread silently across the ocean over a span of 8 h causing massive destruction including the deaths of over 250,000 people, with maximum damages occurring in Indonesia, Thailand, Sri Lanka, India and the Maldives. Moderate to low damages were recorded in the Seychelles, Socotra (Yemen) and Somalia, though in the latter a highly vulnerable town was impacted resulting in over 300 deaths. Most of eastern Africa was spared massive damages from the waves due to (a) distance from the epicenter (>6000 km), (b) the dissipation of energy of the tsunami by shallow banks in the middle of the Indian Ocean (the Seychelles banks, Saya de Malha and Cargados Carajos Shoals) and (c) at least for Kenya and Tanzania, the first and largest waves hit at low tide. In Kenya and Tanzania these factors resulted in the waves being experienced as tidal surges of 1–1.5 m amplitude lasting 5–10 min. Damages recorded for eastern Africa include 11 deaths in Tanzania and 1 in Kenya, of people walking and swimming over shallow intertidal flats being trapped by the advancing and receding tidal surges, damage to boats anchored in shallow water and inundation in Mauritius and Rodrigues. Official information, warning and response networks were nonexistent, and even when an official response was generated in Kenya the public demonstrated no faith or willingness to act on warnings from officials such as the police. Importantly, information on the tsunami and the generation of an official response was dependent on two technologies, satellite television and mobile telephony, and these should be built into future warning systems as key mechanisms and backups to official information and warning networks.     

基于Landsat遥感数据的长岛南部岛群景观格局演化研究

为了了解长岛南部岛群在经济发展背景下的景观格局及未来变化趋势,利用1990~2015年6景Landsat TM5、TM7和OLI8影像数据源,基于地理信息系统(GIS)平台采用决策树分类的方法对长岛南部岛群的景观类型进行了分类,并结合Frag-stats软件提取7种不同的景观格局指数,对长岛南部岛群的景观格局演化特征进行了系统分析。结果显示,人为活动是近年来长岛南部岛群景观格局演化的主要驱动力,该岛群景观类型变化以建设用地、水产养殖用地增加和林地减少为特征,建设用地斑块聚集度指数较高,斑块的聚集度指数逐年增加,整体上斑块的聚集度和连通性很好。不同景观指数(SHDI(景观斑块多样性)、PAFRAC(周长面积分维数)、PD(斑块密度指数)、LSI(斑块形状指数)、CA(斑块面积指数)、AI(景观聚集度指数)、COHESION(斑块结合度指数))对人为扰动因子均具有良好的表征。相关研究结论可为长岛南部岛群综合管理和生态红线划定提供有效依据。     

东海断面调查数据的最优插值同化试验

以World Ocean Atlas(WOA)气候态月平均资料作为数据同化的背景场,以断面调查数据作为数据同化的观测场,采用最优插值法,对WOA数据进行同化处理,得到分析场,并通过一维搜索方法获得最优相关距离尺度,对分析场进行优化。将调整得到的分析场作为现场观测数据的补充,然后对其网格化并绘制等值线图。两组试验结果表明,经过同化处理后绘制得到的等值线图既保留了区域的气候态特征,又体现了观测期间的特点,在一定程度上可以避免因数据空间分辨率不足所导致的插值结果异常,较单纯使用实测数据或将实测数据与WOA数据简单叠加得到的等值线分布更合理。最优相关距离尺度的大小依同化对象数据类型的不同而不同,一维搜索方法可以较便捷的获得最优相关距离尺度,提高数据同化的效果。     

Dissolved organic matter cycling in the confluence of the Atlantic and Indian oceans south of Africa

The boundary between the Atlantic and Indian sectors of the Southern Ocean is a key spot of the thermohaline circulation, where the following water masses mix up: Indian Central water (ICW), South Atlantic Central Water (SACW), Antarctic Intermediate Water (AAIW), Circumpolar Deep Water (CDW), North Atlantic Deep Water (NADW), Weddell Sea Deep Water (WSDW) and Antarctic Winter Water (WW). An optimum multiparameter analysis based on the distributions of potential temperature, salinity, NO (=O₂+9.3×NO₃) and silicate during the GoodHope 2004 (GH04) cruise allowed us to (i) define the realms of these water masses; (ii) obtain the water mass proportion weighted-average (archetypal) apparent oxygen utilization (AOU) and dissolved organic carbon (DOC) concentrations of each water mass; and (iii) estimate the contribution of DOC to the oxygen demand of the study area. WW represented only 5.2% of the water volume sampled during GH04, followed by WSDW with 10.8%, NADW with 12.7%, SACW with 15.3%, AAIW with 23.1% and CDW with 32.8%. The distributions of DOC and AOU were mainly explained by the mixing of archetypal concentrations of these variables, 75±5% and 65±3% respectively, which retained the variability due to the basin-scale mineralization from the formation area to the barycentre of each water mass along the GH04 line. DOC accounted for 26±2% and 12±5% of the oxygen demand of the meso- and bathypelagic ocean, respectively. Conversely, local mineralization processes, retained by the residuals of the archetypal concentrations of DOC and AOU, did not contribute to improve significantly the mixing model of DOC.     

The prediction of traveling jet trenching in stiff clay based on the erosion failure mechanism

The performance of traveling jet trenching in stiff clay was tested. All the key parameters varied in the experiment, including the jet velocity, the shear strength of clay, the diameter of the nozzle, and the translational velocity of the nozzle. The jet–soil interface was found to be an arc. An equation was given to describe the interface. On the basis of the erosion failure mechanism, a new method is presented for predicting jet trenching depth. We first calculated the trajectory of the jet–soil interface and then predicted the distribution of the boundary layer shear stress along the jet–soil interface. The point where the wall shear stress was equal to the critical shear strength of clay was the ultimate trenching depth. The predictive results were found to fit the experimental results well.     

Analysis of the landscape structure in the tundra zone for western Siberia based on satellite data

The landscape structure are investigated for typical and southern tundra subzones of western Siberia based on satellite images from Landsat and WorldView. The microlandscape types for the considered regions are selected and areas of microlandscapes are defined on the basis of satellite information and accounting data of field studies. The areas of the main wetland landscapes in the different types of bogs in northwestern Siberia are defined.     

Mass mortality and recolonization of Pyura stolonifera (Heller) on the south coast of South Africa

The fauna and flora of two sublittoral communities situated in close proximity on the west coast of South Africa are described and shown to be radically different, despite the fact that both experience similar physical conditions. One of these communities, at Marcus Island, has prolific beds of the black mussel Choromytilus meridionalis (35 954 g wet weight·m^?2) accompanied by a large number of other species, notably sea urchins, holothurians, brittle stars, whelks and barnacles. In contrast, the other site, Malgas Island, is dominated by a large population of rock lobsters Jasus lalandii together with a dense seaweed flora (3 866 and 4 402 g wet weight·m^?2 respectively). The numbers of species are similar at both sites (102 at Malgas Island and 107 at Marcus Island) but only 34 per cent are common to both localities. Although preliminary research indicates that the two sites have fairly similar physical conditions and bottom topography, they maintained their contrasting communities for the whole research period (1983–1986) and have probably done so for at least nine years, suggesting that they represent two stable alternative states of the same ecosystem. In the absence of rock lobsters at Marcus Island, wave action and inter/intraspecific competition are the main forces structuring the benthic community. Stability is maintained here by the resilience and rapid recovery of the mussel population after disturbance by storms. Where rock lobsters are abundant, as at Malgas Island, intense predation pressure is the main force controlling the structure of the benthos, and it is continually maintained because the rock lobsters are resistant to the effect of storms. Therefore, the presence or absence of high densities of rock lobsters is fundamental to the maintenance of these two contrasting communities.     

The structure of the incoherent sediments in the Ita Mai Tai Guyot (Pacific Ocean) based on geoacoustic profiling data

The results of geoacoustic studies carried out by the acoustic MAK-1M system in the southeastern Ita Mai Tai Guyot (Magellan Seamounts, Pacific Ocean) are discussed. The obtained geoacoustic sections characterize the incoherent part of the sedimentary sequence with high resolution. The geoacoustic stratification is well correlative with the deep-sea drilling data: the acoustic units are reliably correlated with the lithostratigraphic units defined in the cores of DSDP holes 200 and 202. Three geoacoustic units are distinguished in the sedimentary section (from the top downward): unit I corresponding in age to the terminal Miocene (Messinian)-Quaternary; unit II correlated with the Late Miocene (Tortonian); unit III accumulated in the Early Eocene-Early Miocene. The acoustic basement is composed of reefogenic limestones that were formed at different stages of the guyot’s development through the Aptian-Turonian to Late Paleocene-Eocene. The sonar images allow the distribution of the incoherent carbonate sediments to be contoured along the periphery of the summit’s plateau.     

卫星高度计资料揭示的冬季南海吕宋冷涡的双涡结构

吕宋冷涡是南海海洋环流系中最重要的涡旋之一。利用卫星高度计资料时空较高分辨率的优势,发现冬季吕宋冷涡有可能是由2个气旋式涡旋所组成的,一个气旋式涡旋位于吕宋岛的西侧(LCE1),另一个位于吕宋岛的西北(LCE2)。利用相关分析、功率谱分析等,估计了局地风应力和黑潮在形成吕宋冷涡过程中各自的贡献。研究结果表明,LCE1只存在于冬季,与吕宋岛西侧局地的风应力旋度有关;LCE2位于进入吕宋海峡的黑潮的西侧,全年存在,可能是由黑潮所诱生的气旋式涡旋,其变化主要周期为季节内振荡。     

On the occurrence of oxygen-depleted water south of Africa and its implications for Agulhas-Atlantic mixing

Data obtained during the Agulhas Retroflection cruise of the Knorr in November/December 1983 suggested the presence of an oxygen-depleted water layer at the boundary of the Agulhas Current/Return Current system. An analysis of historical data shows that such a layer is present off the edge of the Agulhas Bank during much of the year and may be found off the West Coast as far north as 32°S during summer. The origins, temporal and spatial variations and hydrography of this low-oxygen water mass are described, and its influence on the biology of the Western Cape upwelling region is discussed. It is considered that the presence of this low-oxygen water mass can be used to show penetration of Agulhas water into the South-East Atlantic.     

基于单片机的海洋要素垂直剖面测量系统的控制电路设计

设计了一种基于AT89C2051单片机的海洋要素垂直剖面测量系统(简称“海马”)的控制电路。实验表明,该控制电路实现了“海马”的核心部件——棘爪机构单向抓紧、阻尼锁定和自由上浮3个状态的控制,方法简单新颖,同时实现了“海马”下潜运动的能量全部来自波浪,上浮依靠自身浮力的目标。     

浙南近海虾类群落结构及其多样性分析

作者根据2015年11月(秋季)、2016年2月(冬季)、2016年5月(春季)和2016年8月(夏季)对浙南近海进行的渔业资源调查数据,用生物量作为虾类资源分布的数量指标,对该海域虾类的组成、数量分布以及季节变化进行分析。结果显示:该区域共鉴定出虾类30种,隶属于10科21属,以对虾科(Penaeidae)虾类最多,其次为管鞭虾科(Solenoceridae),长臂虾科(Palaemonida)位居第3位。按季节来看,秋季共鉴定虾类27种,各站位平均生物量为6.97 kg/km2,优势种为凹陷管鞭虾(Solenocera koelbeli)、中国毛虾(Acetes chinensis)和中华管鞭虾(Solenocera crassicornis)等3种;冬季鉴定出虾类25种,平均生物量为1.65 kg/km2,优势种为凹陷管鞭虾、扁足异对虾(Atypopenaeus stenodactylus)、日本鼓虾(Alpheus japonicus)、鲜明鼓虾(Alpheus digitalis)、中国毛虾、中华管鞭虾和周氏新对虾(Metapenaeus joyneri)等7种;春季20种,平均生物量为2.22 kg/km2,优势种为戴氏赤虾(Metapenaeopsis dalei)、东海红虾(Metapenaeopsis dalei)和中华管鞭虾等3种;夏季16种,平均生物量为10.36 kg/km2,优势种有鹰爪虾(Trachysalambria curvirostris)和中华管鞭虾等2种。Margalef丰富度指数(D)、Shannon-Wiener多样性指数(H′)和Pielou均匀度指数(J′)秋季均低于冬季。秋冬季受到浙闽沿岸流影响,温度、盐度相对较低,夏季受到台湾暖流外侧影响,温度、盐度相对较高,且各季节间由于瓯江、椒江、飞云江、鳌江等陆源性冲淡水的影响,盐度、温度变化相对较大,使得该区域的物种不得不适应一个跨度较大的温盐范围,广温广盐性种类为主。     

The feeding ecology of skates (Batoidea: Rajidae) off the Cape south coast,South Africa

Six species of skates were trawled commonly on the continental shelf off the Southern Cape during routine surveys of demersal fish between 1986 and 1990. Raja miraletus is a small skate found principally in shallow (<50 m) water that feeds mainly on small crustaceans, such as mysids and macrurans. The large Raja alba occurs over most of the continental shelf, is a piscivore throughout its life and preys heavily on flatfish, especially Cynoglossus zanzibarensis. R. cf. clavata is ubiquitous on the shelf but most abundant between 50 and 150 m deep. Feeding predominantly on crustaceans, this skate switches from carids, penaeids and mysids when small to brachyurans and small benthic fish when larger. R. pullopunctata is found over a similar depth range but attains a much larger size. It eats small mysids and macrurans when small, but brachyurans and fish become more important in the diet with increasing size of the predator. R. wallacei is most commonly taken at depths of 80–>200 m, feeds initially on small crustaceans, but switches to fish, including eels, as it grows. The small Cruriraja parcomaculata is found at the edge of the continental shelf and over the upper slope; it preys on small crustaceans, including mysids, isopods and macrurans. The distribution pattern of the skates and their prey suggest overlap in prey taken, the overlap being greatest in those species which feed on crustaceans. The large biomass of skates in the area suggests that they are an important component of the demersal faunal assemblage of the continental shelf there, and also that they may have a significant impact on the benthic fauna.     

A 450-kyr record of hydrological conditions on the western Agulhas Bank Slope, south of Africa

The Agulhas Bank region, south of Africa, is an oceanographically important and complex area. The leakage of warm saline Indian Ocean water into the South Atlantic around the southern tip of Africa is a crucial factor in the global thermohaline circulation. Foraminiferal assemblage, stable isotope and sedimentological data from the top 10 m of core MD962080, recovered from the western Agulhas Bank Slope, are used to indicate changes in water mass circulation in the southeastern South Atlantic for the last 450 kyr. Sedimentological and planktonic foraminiferal data give clear signals of cold water intrusions. The benthic stable isotope record provides the stratigraphic framework and indicates that the last four climatic cycles are represented (i.e. down to marine isotope stage (MIS) 12). The planktonic foraminiferal assemblages bear a clear transitional to subantarctic character with Globorotalia inflata and Neogloboquadrina pachyderma (dextral) being the dominant taxa. Input of cold, subantarctic waters into the region by means of leakage through the Subtropical Convergence, as part of Agulhas ring shedding, and a general cooling of surface waters is suggested by increased occurrence of the subantarctic assemblage during glacial periods. Variable input of Indian Ocean waters via the Agulhas Current is indicated by the presence of tropical/subtropical planktonic foraminiferal species Globoquadrina dutertrei, Globigerinoides ruber (alba) and Globorotalia menardii with maximum leakage occurring at glacial terminations. The continuous presence of G. menardii throughout the core suggests that the exchange of water from the South Indian Ocean to the South Atlantic Ocean was never entirely obstructed in the last 450 kyr. The benthic carbon isotope record and sediment textural data reflect a change in bottom water masses over the core location from North Atlantic Deep Water to Upper Southern Component Water. Planktonic foraminiferal assemblages and sediment composition indicate a profound change in surface water conditions over the core site approximately 200–250 kyr BP, during MIS 7, from mixed subantarctic and transitional water masses to overall warmer surface water conditions.     

南海冬季之西边界流：1998年2月的水文结构与体积输运

The unique survey in December 1998 mapped the entire western boundary area of the South China Sea(SCS),which reveals the three-dimensional structure and huge volume transport of the swift and narrow winter western boundary current of the SCS(SCSwwbc) in full scale. The current is found to flow all the way from the shelf edge off Hong Kong to the Sunda Shelf with a width around 100 km and a vertical scale of about 400 m. It appears to be the strongest off the Indo-China Peninsula, where its volume transport reached over 20×10~6 m~3/s. The current is weaker upstream in the northern SCS to the west of Hong Kong. A Kuroshio loop or detached eddy intruded through the Luzon Strait is observed farther east where the SCSwwbc no more exists. The results suggest that during the survey the SCSwwbc was fed primarily by the interior recirculation of the SCS rather than by the"branching" of the Kuroshio from the Luzon Strait as indicated by surface drifters, which is likely a near-surface phenomenon and only contributes a minor part to the total transport of the SCSwwbc. Several topics related to the SCSwwbc are also discussed.     

Dissolved iron in the Australian sector of the Southern Ocean (CLIVAR SR3 section): Meridional and seasonal trends

We report measurements of dissolved iron (dFe, <0.4 μm) in seawater collected from the upper 300 m of the water column along the CLIVAR SR3 section south of Tasmania in March 1998 (between 42°S and 54°S) and November–December 2001 (between 47°S and 66°S). Results from both cruises indicate a general north-to-south decrease in mixed-layer dFe concentrations, from values as high as 0.76 nM in the Subtropical Front to uniformly low concentrations (<0.1 nM) between the Polar Front and the Antarctic continental shelf. Samples collected from the seasonal sea-ice zone in November–December 2001 provide no evidence of significant dFe inputs from the melting pack ice, which may explain the absence of pronounced ice-edge algal blooms in this sector of the Southern Ocean, as implied by satellite ocean-color images. Our data also allow us to infer changes in the dFe concentration of surface waters during the growing season. South of the Polar Front, a comparison of near-surface with subsurface (150 m depth) dFe concentrations in November–December 2001 suggests a net seasonal biological uptake of at least 0.14–0.18 nM dFe, of which 0.05–0.12 nM is depleted early in the growing season (before mid December). A comparison of our spring 2001 and fall 1998 data indicates a barely discernible seasonal depletion of dFe (0.03 nM) within the Polar Frontal Zone. Further north, most of our iron profiles do not exhibit near-surface depletions, and mixed-layer dFe concentrations are sometimes higher in samples from fall 1998 compared to spring 2001; here, the near-surface dFe distributions appear to be dominated by time-varying inputs of aerosol iron or advection of iron-rich subtropical waters from the north.     

An analysis of mixing in the frontal zone of South and North Atlantic Central Water off North-West Africa

Multi-parameter mixing analysis is applied to 26 stations of Auftrieb 75, a joint expedition of R.R.S. Discovery and FS Meteor. North Atlantic Central Water (NACW) and South Atlantic Central Water (SACW) are represented by two water types each, and phosphate, silicate and nitrate are all used as an additional parameter with temperature and salinity, yielding three sets of independent solutions. Solutions from different parameters show similar vertical distributions but can differ considerably in absolute terms. This is believed to be caused by insufficient knowledge of nutrient values of pure NACW and SACW and by low range/precision ratios of nutrient determination.It is shown that isopycnal mixing analysis correctly describes the water mass distribution to lowest order, i.e. there is agreement between results from isopycnal and multi-parameter analysis at most stations within the error bounds which are inherent in the method and which are presently very high. Significant non-isopycnal mixing could be confirmed for only one station, situated on the continental slope in the area of the undercurrent of the Canary Current upwelling regime, and may be caused by active upwelling, increased lateral and vertical shear in the under-current, or internal waves interacting with the bottom. Five stations do not yield oceanographically acceptable solutions, and an attempt is made to include a coastal water mass in the analysis in order to improve the result for these stations, i.e. three-parameter analysis for NACW and SACW is replaced by four-parameter analysis for NACW, SACW and coastal water by combining temperature and salinity with phosphate and silicate or with nitrate and silicate simultaneously (the combination phosphate and nitrate is degenerate because both nutrients are linearly correlated). This indeed improves the results, indicating the presence of coastal water at those stations, but accumulation of errors inhibits quantitative conclusions.