Upwelling off the coast of Peru

Geographical distributions of upwelling centers off the coast of Peru are studied on the basis of monthly mean wind data during 17 years from 1939 through 1955. Three remarkable upwelling centers are found near 5°S, 11°S and 15°S, from the analyses. With regard to the negative surface divergence found in the offing of Huacho-Callao (near 11°S) in August, it is pointed out that a local high pressure cell is generated in the atmosphere.     

Fish scales in sediments from off Callao,central Peru

We study fish scales as a proxy of fish abundance and preservation biases together with phosphorus from fish remains (P_fish) in a sediment core retrieved off Callao, Peru (12°1′S, 77°42′W; water depth=179 m; core length=52 cm). We interpret our results as a function of changing redox conditions based on ratios of redox-sensitive trace elements (Cu/Al, Mo/Al, Ni/Al, Zn/Al, V/Al), terrigenous indicators (Fe in clays, Ti, Al), and biogenic proxies (CaCO₃, biogenic opal, total nitrogen, organic carbon, barite Ba). The core covers roughly 700 years of deposition, based on ²¹⁰Pb activities extrapolated downcore and ¹⁴C dating at selected intervals. Our fish-scale record is dominated by anchovy (Engraulis ringens) scales followed by hake (Merluccius gayii) scales.The core presented an abrupt lithological change at 17 cm (corresponding to the early 19th century). Above that depth, it was laminated and was more organic-rich (10–15% organic carbon) than below, where the core was partly laminated and less organic-rich (<10%). The lithological shift coincides with abrupt changes in dry bulk density and in the contents of terrigenous and redox-sensitive trace elements, biogenic proxies, and fish scales. The remarkable increase in redox-sensitive trace elements in the upper 17 cm of the core suggests more reducing conditions when compared with deeper and older horizons, and is interpreted as an intensification of the oxygen minimum zone off Peru beginning in the early 19th century. Higher fish-scale contents and higher P_fish/P_total ratios were also observed within the upper 17 cm of the core. The behavior of biogenic proxies and redox-sensitive trace elements was similar; more reduced conditions corresponded to higher contents of CaCO₃, C_org, total nitrogen and fish scales, suggesting that these proxies might convey an important preservation signal.     

Numerical investigation of the effects of upwelling on harmful algal blooms off the west Florida coast

The initiation of the toxic harmful algal bloom (HAB), Karenia brevis, along the west Florida coast has been associated with upwelling events. Upwelling processes may be responsible for the transport of nutrients or algae from deep offshore locations across the Florida shelf to the coast. The influence of coastal wind-driven upwelling on the onset and occurrences of K. brevis in this region was numerically investigated using Rutgers University's Regional Ocean Modeling System. Computations were carried out in an idealized model domain, a two-dimensional slice in the cross-shore and vertical directions. The surface forcing data used was from several offshore meteorological buoys. The motion of the algae was simulated using Lagrangian particles and a passive tracer. The numerical simulations of three K. brevis events in 2000–2002 showed that the particles respond (with upwelling/downwelling) to the along-shore wind stresses as expected and some upwelling was present during the events. Comparison of the passive tracer fields with measured fluorescence data exposed the model's sensitivity to the particular surface forcing data employed and the relatively more significant role played by surface forcing over initial conditions. The present model set-up constitutes a useful predictive tool for conditions conducive to the onset of HABs. It is planned to be used in a real-time mode to aid the NOAA HAB monitoring and forecasting system.     

Wave hindcasting off the coast of Portugal

A study was conducted applying a second-generation wave model to predictions in coastal zones. The model was calibrated with wave measurements conducted off the Portuguese coast, for a period of 6 months. The wind fields used in the calculation were supplied by the European Centre for Medium Range Weather Forecast (ECMRWF). The calibrated model allows good predictions of significant wave height. Satisfactory comparisons have been made with predictions of the WAM model     

Phytoplankton community structure in Otsuchi Bay,northeastern Japan,after the 2011 off the Pacific coast of Tohoku Earthquake and tsunami

The tsunami caused by the 2011 off the Pacific coast of Tohoku Earthquake seriously damaged the Pacific coast of northeastern Japan. In addition to its direct disturbance, a tsunami can indirectly affect coastal pelagic ecosystems via topographical and environmental changes. We investigated seasonal changes in the phytoplankton community structure in Otsuchi Bay, northeastern Japan, from May 2011, which was 2 months after the tsunami, to May 2013. The phytoplankton species composition in May 2011 was similar to that observed in May 2012 and 2013. The present results are consistent with the dominant species and water-mass indicator species of phytoplankton in past records. These results suggest that there was no serious effect of the tsunami on the phytoplankton community in Otsuchi Bay. Community analysis revealed that two distinct seasonal communities appeared in each year of the study period. The spring–summer community was characterized by warm-water Chaetoceros species, and dinoflagellates appeared from May to September. The fall–winter community was characterized by cold neritic diatoms, which appeared from November to March. The succession from the spring–summer community to the fall–winter community took place within a particular water mass, and the fall–winter community appeared in both the surface water and the Oyashio water mass, suggesting that water-mass exchange is not the only factor that determines the phytoplankton community structure in Otsuchi Bay.     

A preliminary investigation of the feeding ecology of squaloid sharks off the west coast of southern Africa

The diets of 15 species of squaloid sharks caught between Walvis Bay and Cape Agulhas over a depth range of 50–1 016 m are analysed. The most common prey items were fish and cephalopods. Hake Merluccius spp. were common in the diets of Centrophorus squamosus, Squalus acanthias, and S. cf. mitsukurii. Myctophids were extensively preyed on by Centroscyllium fabricii, Deania calcea, D. profundorum, Etmopterus cf. brachyurus, E. compagnoi, S. acanthias and S. megalops, among others. The most common cephalopods in shark stomachs were Histioteuthis miranda, Lycoteuthis ?diadema, Octopus vulgaris and Todarodes angolensis. Crustaceans were uncommon prey of most species, except for Centroscyllium fabricii and Etmopterus cf. granulosus. Centroscymnus coelolepis was the only squaloid with cetacean remains in the stomach. That species appears to parasitize its cetacean victims.     

Continental shelf waves off the Fukushima coast

Numerical experiments are performed on shelf waves forced by wind stress with a spectral peak around a period of 100 hr. Water depth in the numerical model is a function of offshore distance only and resembles a bathymetric profile off the Fukushima coast. A pair of vortices alined in the offshore direction and a large vortex are reproduced and they propagate southward outside the forced region. Judging from the propagation speed, the former corresponds to the second-mode and the latter to the first-mode shelf waves. In the forced region, the propagation speed of a trough and a ridge is slow, 3–5km hr^–1. These propagation characteristics reproduce those observed along the Fukushima coast and this propagation speed corresponds to that of second-and third-mode shelf waves. Thus, it is concluded that the periodical current fluctuations observed in the inshore region along the Fukushima coast are due to motions associated with the second-and third-mode shelf waves.     

Continental shelf waves off the Fukushima coast

Past observations and theories have indicated the importance of the constitution of the lowest-mode of shelf waves to the velocity field. However, significant contributions of the higher mode waves to current velocity fluctuations in the vicinity of the coast are suggested in observational results obtained along the Fukushima coast in Pt. I of this study (Kubota et al., 1981). To understand the importance of the higher modes, the generation of shelf waves is investigated theoretically by two methods. First, the generation of long shelf waves by monochromatic forcing is examined, and it is concluded that near the coast the second mode's contribution to the longshore velocity is the largest for the Fukushima coast. Second, the response of shelf waves to broad-band forcing is investigated by taking the dispersive characteristics of shelf waves into consideration. It is concluded that shelf waves with zero group velocity are selectively excited if the forcing has a broad-band spectrum. According to observational results obtained along the Fukushima coast, the wind spectrum has a broad peak at about 100 hours (Kubota et al., 1981). Since the third mode of shelf waves has zero group velocity around the period of 100 hours, the third mode can be selectively generated off the Fukushima coast. From this it is suggested that the Fukushima coast is in the forced region and that observed current fluctuations are motions associated with the second- and third-mode shelf waves.     

Worst scenarios of tsunami effects along the Mediterranean coast of Egypt

Scenarios of tsunami effects represent a very useful technique for the definition and evaluation of tsunami hazard and risk for the Egyptian coast. This paper is an attempt to develop different worst scenarios of tsunamigenesis toward the Egyptian Coast for five segment localities along three different sub-regions (Hellenic Arc, Cyprean Arc and Levantine Coast) in the eastern Mediterranean Sea. These segments are the southwest Hellenic Arc, southeast Hellenic Arc, northeast Hellenic Arc, west of Cyprean Arc and Levantine. For each of them, the scenario takes into account a seismic fault capable of generating an earthquake with magnitude equal to or larger than the highest magnitude registered in that region in historical times. Then the ensuing tsunamis are simulated numerically, highlighting the basic features of the wave propagation and roughly identifying the coastal sectors that are expected to suffer the heaviest tsunami effects. The output data indicated that the first wave of tsunamis from different segments attacked the nearest reference localities (city located nearest each segment) along the Egyptian shore between 28 and 50 min after an earthquake. Tsunamis from these earthquake scenarios produced maximum run-up heights ranging from 1.7 to 9.4 m at the shore. A Beirut Thrust scenario (Levantine segment) included the fact that only a small portion of the fault extended out into the sea, leading to a small effective tsunami source area. In contrast, the southwest Hellenic Arc segment (as in the A.D. 365 earthquake) has high displacement (15 m) and a long extensional fault, forming a highly effective tsunami source area.     

2016年春季浙江中部海域温、盐、密度的断面分布特征

厦门大学海洋与地球学院,近海海洋环境科学国家重点实验室。摘要：本文通过分析2016年春季航次在浙江中部海域3条断面的观测资料,结果表明：（1）在断面的10~25米层左右观测到了"中层冷水"现象以及在上层观测到微弱的上升流;（2）在浙江中部海域的上层观测到较弱的上升流;（3）春季,在浙江中部海域观测到了丰富的温跃层、逆温跃层以及盐跃层现象。（4）台湾暖流水向上爬坡对跃层的变化有一定的影响,使得跃层厚度变小,跃层强度加强,但是强度并不足以冲破跃层到达表层。     

Complex BSR pattern in the Yaquina Basin off Peru

The distribution of gas and gas hydrate within the central Yaquina Basin, a forearc basin at the Peru convergent margin, can be estimated from the interpretation of high-resolution reflection seismic data. The strongest bottom simulating reflector (BSR) is observed where the base of gas hydrate stability (BGHS) parallels strata. Where the BGHS crosscuts strata, only a small amount of gas is present beneath the BGHS. Anisotropic permeability plays a key role in controlling methane supply. Where present-day tectonic activity is observed, faults and, consequently, gas reach up to the seafloor where chemoherms formed. The warm fluids contort the BGHS and, consequently, the BSR is shifted upward. Increased heat flux and/or sediment interval velocity in this region is likely. Bright spots align beneath the actual BGHS and mark the depth of a paleo-BSR, which can be correlated with sedimentation of a particular sequence. There is clear evidence for free gas being present within the gas hydrate stability zone.     

海啸地震震源机制解统计

为探索海啸地震发震时的规律,统计分析了1976-2010年的美国全球CMT地震矩心矩张量数据,并结合美国海洋与大气局的海啸灾害数据库,从海啸事件和较大海啸事件两个方面对震源机制解展开了对比统计分析,给出了海啸地震在震源方面的统计特征。     

Real-time wave forecasts off the western Indian coast

The wave observations at three locations off the west coast of India have been analyzed using artificial neural network (ANN) to obtain forecasts of significant wave heights at intervals of 3, 6, 12 and 24 h. The most appropriate training method requiring an input of four observations spread over previous 24 h has been selected after considerable trials. Further, the networks are trained after filling in the missing information. Larger gaps in data are filled in using spatial mapping involving observations at nearby locations, while relatively smaller gaps are accounted for by the statistical technique of multiple regressions in temporal mode. It is found that by doing so the long-interval forecasting is tremendously improved, with corresponding accuracy levels becoming close to those of the short-interval forecasts. If the amount of gaps is restricted to around 2% per year or so it is possible to obtain 12 h ahead forecasts with 0.08 m accuracy on an average and 24 h ahead forecast with a mean accuracy of 0.13 m. However, in harsher environments the prediction accuracy can change.     

A preliminary investigation of the feeding ecology of catsharks (Scyliorhinidae) off the west coast of southern Africa

The diets of six species of catsharks (Carcharhiniformes: Scyliorhinidae) caught between Walvis Bay and Cape Agulhas at depths between 50 and 1 016 m were analysed. The most common prey items were teleosts and crustaceans. Lanternfish (Myctophidae) were common in the diets of Apristurus microps, A. saldanha, Apristurus spp. and Holohalaelurus regani, whereas the Cape anchovy Engraulis capensis was preyed on extensively by Scyliorhinus capensis. The most common crustaceans in the diet were Parapagurus spp., Mursia cristimanus and Euphausia lucens. Cephalopods were uncommon prey items, except in A. microps, A. saldanha, Apristurus spp. and H. regani.     

海南东方近岸海底活动沙波的地球物理特征及其迁移机制

海南东方近岸海底发育有大量沙波,利用多波束测深、侧扫声呐、浅地层剖面、单道地震资料综合分析了活动沙波的地球物理特征,探讨了沙波的分布特征、迁移机制、活动性及形态演变特征。结果表明,研究区海底沙波分布和规模具有显著空间差异性,大中型沙波主要发育于沙脊上,小型沙波主要发育于沙脊两侧,坑槽区发育近对称沙波,研究区西南部沙波不发育。受潮流和科氏力约束,在海底沙脊西侧沙波迁移方向主要为向北（略偏东）,在沙脊东侧主要为向南（略偏西）;受地形制约,坑槽区近对称沙波迁移可能停止或方向发生改变。沙波活动性强的标志主要包括：① 形态呈不对称的“脊尖槽缓”,② 叠置小沙波与沙纹发育,③ 浅部有透明层,④ 陡坡面反射模糊,⑤ 内部斜交前积结构。分析认为,沙波活动性与其形态密切相关,包括弱运动、强运动、不运动3个演变阶段。     

Forecasting of tsunami wave heights at the Russian coast of the Black Sea

Forecasting of tsunami wave heights at the Russian coast of the Black Sea is discussed. Prognostic numerical calculations of tsunamis were carried out for the tsunami sources uniformly distributed in the Black Sea basin (a total of 55 events). Their results are compared with the results of numerical modeling of the historical events (in 1939 and 1966) and the data of not numerous measurements. A preliminary forecast is made on this basis for the tsunami wave heights along the Russian coast of the Black Sea.     

Demersal communities off the west coast of South Africa

To describe demersal communities off the west coast of South Africa, collections of all species of fish, cephalopods and crustaceans made during four cruises in the area during January and July have been analysed. Hierarchical classification methods were employed to determine species and sample associations. The results showed that the species could be split into two main groups, the first containing Merluccius paradoxus (the dominant species both in abundance and frequency of occurrence) and other species normally found in deep (> 380 m) water. The second group is represented by species that live on the continental shelf, M. capensis being the most abundant. The boundary separating the deep-sea community from that of the shelf follows approximately the 385-m isobath. Seasonal variations in the number of main associations as well as in their spatial location are documented.     

Pollen analysis of marine sediments off the Washington coast

Pollen diagrams of postglacial sediments from the continental terrace off the Washington coast reveal trends similar to those observed in continental sections of postglacial age from the Pacific Northwest and appear sufficient for correlation with terrestrial deposits. The absolute pollen frequency (APF) varies from 3000 to 15000 grains/g. Maximum number of pollen grains (500–800/cm²/year) accumulated during the Hypsithermal.