A study of cross-shore maximum upwelling intensity along the Northwest Africa coast

Satellite images of sea surface temperature (SST) show that the location of cross-shore SST minimum (LCSM) stretches along the isobaths in the Northwest Africa Upwelling System. To understand and interpret these observations better, we set up a two-dimensional analytical model that takes into account the surface and bottom Ekman transport and the alongshore geostrophic current, as well as bottom friction and variations in bottom topography. The structure of vertical velocity with a realistic topography clearly illustrates the variations of SST drop in a sample cross-shore section. Some idealized theoretical model experiments are carried out to examine the effects of eddy viscosity, Coriolis force, and cross-shore wind on the location of the cross-shore maximum upwelling intensity. The results show that the cross-shore wind largely impacts on the location where the coldest water outcrops to the surface through an adjustment of the cross-shore pressure gradient. This is also verified by the remotely sensed data, which indicate that the maximum correlation coefficient between cross-shore wind stress and the depth of LCSM is ?0.65 with a lag of approximately 1 day.     

Study on the upwelling along the east coast of Guangdong

-There is a wind-caused upwelling along the east coast of Guangdong in summer. Its central position is above the depth of 20 m, and its annual variation is quite large. In August 1982, the velocity of the upwelling was 1.2 ×10-3 cm/s, the vertical flux of active phophate, 1.5m mol/(m2·d); and the primary productivity, 1558 mg/(m2·d), in the area outside the bay of Jieshi. Inside the up-welling facing the shore, a phenomenon of lacking oxygen existed at the sea bottom above 5 m depth. In the area outside the upwelling center, there was a phenomenon of upward water temperature inversion. The physical and chemical characteristics in the area of the upwelling are as follows: temperature, 22.13℃; salinity, 34.19, dissolved oxygen, 3.72 ml/1; oxygen saturation degree, 74.6%; pH value, 8.14; and active phosphate, 1.10 m mol/m3.     

Water level changes along the Norwegian coast

The water level records of 11 stations from the Norwegian coast having the recording interval 1971–1972 in common have been analysed with a least squares algorithm. The results for the harmonic constants are compared to open ocean tide models and a good agreement is found. The variation of tidal parameters and mean sea level are calculated from a 70 years water level record from Bergen. An 18.6 yearly variation in amplitude and phase of the fortnightly tide Mf could be identified. Cross correlation techniques are used to investigate the nontidal part of the water level changes. Correlating the residuals of the analyses with each other, the main nontidal water level changes are found to be moving from south to north along the Norwegian coast, taking 20 hours to reach from Stavanger to Vadsø. The effect of local air pressure on sea level is modelled using transfer functions. Mean sea level changes in Bergen are found to correlate with changes in length of day and changes in global surface temperature.     

福建沿海全新世高温期的气候与海面变化

本文综合分析了福建沿海全新世高温期的孢粉资料和海平面变化资料,建立了气温和海平面变化曲线.结果表明,8ka,B.P.前为气温和海平面上升期,8ka,B.P.以来为高温期和高海平面期,海平面升降与气温升降几乎同步.     

Coastal upwelling events along the southern coast of Java during the 2008 positive Indian Ocean Dipole

To understand the coastal upwelling system along the southern coast of Java, we investigated ocean temperature and salinity obtained from an Argo float. In 2008, a positive Indian Ocean Dipole (IOD) event began to develop in early May and anomalously cool SST developed around south of Java from May to September. During the peak of the IOD, an Argo float successfully observed vertical structure of temperature and salinity within 90 km from Java. The float observed two intraseasonal-scale temperature cooling events in July and August, with significant upward movements of the thermocline more than 90 m. Concurrent with the signals, anomalous southeasterly alongshore winds, lowering of local SST and sea level, and upward expansion of high-salinity water were also observed. During the event in August, vertical velocity estimated by the anomalous wind stress agreed well with the observations. These results indicate that the Argo float observed the coastal upwelling, which was enhanced by the 2008 positive IOD, along the southern coast of Java.     

Plankton dynamics and carbon flux in an area of upwelling off the coast of Morocco

A carbon flux study was carried out off the coast of Morocco, at 31°N, in a region characterized by the presence of a persistent cyclonic eddy. Two short-term (4 and 3 day) deployments of free-floating sediment traps were combined with water column sampling and rate process measurements as the ship followed the traps. For a period of 36 h between trap deployments, a hydrographic section was run along 31°30'N as part of a larger scale survey being carried out simultaneously on the R.V. A. von Humboldt. The first trap deployment was near the eastern margin of the eddy and the traps moved to the north and west in a frontal jet associated with its northern boundary. After the second deployment, which was at the recovery point of the first, the traps moved to the west and then to the southwest. Throughout the study, chlorophyll concentrations varied between 27 and 125 mg m⁻² (0–100 m), with highest concentrations in the upwelled water nearest the coast and in upwelled water generated within the cyclonic eddy. Particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations were relatively uniform (13.6±1.8 and 1.63±28 g m⁻² with phytoplankton carbon accounting for 16–85% of total POC. Bacterial carbon was 5% of total POC and mesozooplankton carbon concentrations were equivalent to 9% of total POC. Microzooplankton biomass was not assessed but POC:PON ratios in the water column were often high, suggesting there was sometimes a large detrital component in the POC. Primary production rates varied between 1.0 and 2.5 g C m⁻² day⁻¹. Bacterial consumption accounted for 50% of primary production. Metabolic rates suggested that copepods were ingesting more than 0.4 g C m⁻² day⁻¹. while filtration rates suggested that ingestion of phytoplankton carbon was only 0.2 g C m⁻²day⁻¹, even when phytoplankton constituted 85% of the POC. f-ratios (based on uptake rates for ¹⁵N-nitrate and ammonia) were between 0.1 and 0.4, and excretion by mesozooplankton could account for 40% of the daily ammonium uptake by phytoplankton. HPLC pigment analysis showed that when chlorophyll biomass was high, diatoms were dominant, whereas when it was low, small prymnesiophytes, chlorophytes and diatoms were all important. The composition of the fluoresecent pigments in material in the sediment traps indicated that intact phytoplankton and copepod faecal pellets were the main sources but the relative rates of sedimentation of pigment, POC and PON for the two trapping periods did not reflect differences that were observed in the overlying water column. This was likely to be the result of spatial heterogeneity and strong horizontal currents heterogeneity and strong horizontal currents within the euphotic zone. Thus, material collected at 100 m probably did not originate in the water column immediately overlying the traps and trapping efficiencies might also have been variable.     

Variability in plankton community structure, metabolism, and vertical carbon fluxes along an upwelling filament (Cape Juby, NW Africa)

The variability in dissolved and particulate organic matter, plankton biomass, community structure and metabolism, and vertical carbon fluxes were studied at four stations (D₁–D₄), placed along a coastal-offshore gradient of an upwelling filament developed near Cape Juby (NW Africa). The filament was revealed as a complex and variable system in terms of its hydrological structure and distribution of biological properties. An offshore shift from large to small phytoplankton cells, as well as from higher to lower autotrophic biomass, was not paralleled by a similar gradient in particulate (POC) or dissolved (DOC) organic carbon. Rather, stations in the central part of the filament (D₂ and D₃) presented the highest organic matter concentrations. Autotrophic carbon (POC_Chl) accounted for 53% (onshore station, D₁) to 27% (offshore station, D₄) of total POC (assuming a carbon to chlorophyll ratio of 50), from which nano- and pico-phytoplankton biomasses (POC_{A < 10 μm}) represented 14% (D₁) to 79% (D₄) of POC_Chl. The biomass of small hetrotrophs (POC_{H < 10 μm}) was equivalent to POC_{A < 10 μm}, except at D₁, where small autotrophs were less abundant. Dark community respiration (R_d) in the euphotic zone was in general high, almost equivalent to gross production (P_g), but decreasing offshore (D₁–D₄, from 108 to 41 mmol C m⁻² d⁻¹). POC sedimentation rates (POC_sed) below the euphotic zone ranged from 17 to 6 mmol C m⁻² d⁻¹. Only at D₄ was a positive carbon balance observed: P_g−(R_d + POC_sed) = 42 mmol C m⁻² d⁻¹. Compared to other filament studies from the NE Atlantic coast, the Cape Juby filament presented lower sedimentation rates and higher respiration rates with respect to gross production. We suggest that this is caused by the recirculation of the filament water, induced by the presence of an associated cyclonic eddy, acting as a trapping mechanism for organic matter. The export capacity of the Cape Juby filament therefore would be constrained to the frequency of the interactions of the filament with island-induced eddies.     

Monthly mean sea level variability along the west coast of southern Africa

Principal components analysis was used to examine monthly data on sea level obtained from tide-gauge records from the west coast of southern Africa over the period 1957—1975. After a simple correction had removed the effect of local atmospheric pressure, this statistical analysis revealed the structure of nearshore ocean variability over time periods of months to years. The first principal component, accounting for over 55 per cent of the variability in monthly mean sea level, was a near uniform rise and fall everywhere along the west coast of southern Africa. The spectrum of this large-scale structure showed a strong interannual trend, which correlated well with long-term trends of temperature anomaly over the entire South-East Atlantic, and a high-frequency term, which could not be resolved at a time period of one month. The second principal component showed the contrasting response of the northern and southern sites on a seasonal scale, and it could be correlated with seasonal wind data. These results compared well with similar analysis carried out in the North Pacific Ocean.     

The geological significance of kelp-rafted rock along the west coast of South Africa

Angular to well-rounded pebbles and cobbles have been observed along the southwest coast of South Africa, attached to holdfasts of three species of kelp:Ecklonia maxima, Laminaria pallida, andLaminaria schinzii. A kelp-rafted clast has been dredged from the outer shelf and other clasts have been observedin situ in up to 5 m of water near Cape Town. The clasts have been found on both rocky and sandy shores as well as in a large backshore lagoon on the exposed Atlantic coast of the Cape Peninsula. Isolated clasts in a mid-Holocene lagoon were probably rafted ashore during winter storms in the mid-Holocene.     

Southward extension of the reproductive range of Macroramphosus scolopax in the upwelling area off North-West Africa

Ichthyological literature gives the distribution of M. scolopax as along the whole coast of West Africa. However, analysis of this literature and the results of trawling surveys in the North-East Atlantic suggest only exceptional occurrences in the tropics. Plankton surveys off N.W. Africa, up to and including 1977, rarely yielded M. scolopax larvae off the coast of the southern Sahara and not at all off Mauritania, though a few specimens were collected after having been swept southwards in the open ocean by the Canary Current. Larvae did occur off northern Mauritania in February 1983. Details of distribution, abundance and length composition of early stages caught during the period January–April 1983 are given. It is concluded that the reproductive range of M. scolopax (as well as that of some other temperate species) extends south of that documented and that its spawning season there may be shorter than in the centre of this species' distribution. The findings are discussed in relation to interannual variation of upwelling intensity and the current system off N.W. Africa.     

福建沿海晚更新世以来的海平面变化

本文选择了六类７９个具有＾１４Ｃ年龄和准确高程的古海面标志物，按北，中，南三个岸段分别建立了三条相对海平面变化曲线，讨论了福建沿海晚更新世以来的海平面变化特征和规律，通过比较也分析了不同岸段新构造差异升降情况。     

浙江沿岸春季上升流的数值研究

采用三维斜压非线性数值模式ROMS(Regional Ocean Modeling System),在浙江沿岸特殊地形的基础上综合考虑风场、台湾暖流、潮流以及长江径流等可变因子,对春季浙江沿岸上升流进行了数值研究。研究结果表明,浙江沿岸春季存在上升流,且上升流以带状分布在浙江近岸海域,在渔山列岛附近(28.40°N,122.00°E)以及舟山群岛附近(30.70°N,122.60°~123.00°E)存在2个上升流中心。风、台湾暖流和潮动力是影响浙江沿岸春季上升流的重要因子,其中风和台湾暖流对浙江沿岸整条上升流带均有影响;潮动力仅对28.60°N 纬度线以北至舟山群岛附近的上升流以及2个上升流中心的强度存在影响;长江径流对2个上升流中心、舟山群岛及长江口附近的上升流有一定影响。通过对浙江沿岸海域流场的分析可以发现,舟山群岛附近底层各等深线上水体向岸运动的速度比周围海域的大,跨越底层各等深线向上涌升的趋势更明显,间接反映了舟山群岛附近的上升流强度相对较强。对于舟山群岛附近的上升流而言,30 m深度以浅的海域,科氏力、水平平流作用与垂直粘性力是上升流形成的主要动力, 30 m深度以深的海域,上升流形成的主要动力为科氏力与压强梯度力,此时水平平流作用和垂直粘性力对上升流的影响较弱。     

Comparative analysis of the diets of smaller odontocete cetaceans along the coast of southern Africa

The diets of 20 species of smaller Odontoceti were investigated. The material was collected along the southern African coast between 1966 and 1990 and included 158 strandings, 29 animals killed incidentally and 49 animals caught under permit. In total, 57 species in 34 families of fish and 89 species in 24 families of cephalopods were identified from remains in the 236 stomachs investigated. Most Odontoceti fed on commercially unexploited cephalopods and fish, or on fish below commercially utilized sizes. However, the average sizes of anchovy and pilchard eaten by Delphinus delphis and Lagenorhynchus obscurus were larger than the sizes most frequently taken commercially. The species composition of the prey items reflected the onshore-offshore distribution (and possibly the foraging depths) of different Odontoceti. Tursiops truncatus and Cephalorhynchus heavisidii were closest to shore and D. delphis and L. obscurus over the continental shelf. The rest were distributed around the shelf-edge and just off the edge. A comparison of the stomach contents of stranded and non-stranded D. delphis, L. obscurus and C. heavisidii demonstrated that results from stranded animals are biased.     

Shoreline changes and beach-sand sorting along the northern Sinai coast of Egypt

 Changing shoreline positions along the Sinai coast of Egypt were determined by comparing aerial photographs and historical charts with present-day conditions. The analyses identify longshore patterns wherein erosion along a protruding stretch of the coast gives way to accretion in an adjacent major embayment. This pattern defines two coastal subcells consisting of source/sink couplets. There is a general correspondence between the mineral variation, grain sizes of beach sand, and the patterns of shoreline changes. Associated with erosion/ accretion shoreline change is a selective transport of different minerals according to their densities and grain sizes. Two heavy-mineral groups were obtained by applying Q-mode factor analysis on the heavy-mineral data. These two groups are influenced by transport processes, including sediment provenance from different sources: eroded Nile delta west of Sinai, relict sediments from the former Nile distributaries, and sediment supply by land valleys and from wind-blown sand. Received: 2 June 1995 / Revision received: 29 May 1996     

Analysis of year-to-year variation of water temperature along the coast of the Japan sea

Mean monthly records of coastal sea surface temperature data (CSST) obtained from stations along the Japanese coasts of the Japan Sea and from those in the related seas for the period 1941–1984 were analyzed by using various methods of time series analysis, for the purpose of clarifying the nature of the year-to-year variations of the state of the Japan Sea. The year-to-year variations in the Japan Sea were found to be closely related to those in the East China Sea and in the western North Pacific. Specific results are as follows. (1) A sudden cooling in the early 1960's occurred in the southern stations of the Japan Sea and continued to the end of the analyzed data. (2) Variations, with about a 6-year periodicity, were observed at most stations, and were especially dominant in the southern stations of the Japan Sea (3) These variations could be traced back to the Kuroshio region of the East China Sea. (4) Variations, with about a 10-year periodicity, were also observed in the northern stations of the Japan Sea.     

北大西洋沿岸过去2000年海平面变化的若干重要特征

北大西洋沿岸是世界上最容易受海平面上升影响的地区之一。了解该区域过去海平面变化历史和特征,对认识现代海平面变化过程、预估未来海平面变化趋势具有重要科学意义,同时也有助于最大限度地减小预测结果的不确定性。基于此,我们以北大西洋沿岸1 350个验潮站观测记录和已发表的1 604个海平面数据为基础,进行系统分析和集成研究,尝试建立北大西洋沿岸过去2000年海平面的变化历史,并分析北大西洋沿岸过去2000年海平面变化的主要过程与特征、区域差异和存在的问题。结果表明：①北大西洋沿岸过去2000年海平面变化具有显著的时空差异性,海平面的变化幅度、变化时间、波动次数等均具有区域差异性。②北大西洋沿岸过去2000年以来海平面总体上呈现出波动上升趋势,但不同地区海平面上升高程相差较大,北大西洋西岸北美洲东部海平面上升超过2.5 m,格陵兰岛-冰岛、欧洲和美国南部和东南部海平面上升幅度约1.9 m,北海和地中海海平面上升幅度约1 m。③公元1900年以来,北大西洋东西沿岸海平面上升速率普遍加快,并呈现出明显的纬度差异,即北大西洋东岸从地中海到欧洲沿岸再到格陵兰岛-冰岛,随着纬度增加,海平面上升速率逐渐增加。类似的,北大西洋西岸美国南部和东南部到美国东部再到加拿大东部,随着纬度的增加,海平面上升速率也依次增加。④过去2000年北大西洋沿岸海平面变化及其时空差异性是多种因素综合作用的结果,气候冷暖交替、冰川均衡调整、大气-海洋动力学、区域构造以及沿岸地形的变化、沉积物压实和潮汐范围变化等可能是主要原因。     

Kinematics of the upwelling front off southern Africa

Mesoscale circulation features have been shown to play an important role in the cross-frontal mixing of upwelling cells, their frontal morphology and in their interaction with oceanic water masses. With three years of detailed thermal infra-red satellite information on the South-East Atlantic upwelling system available, it proved possible to present a preliminary study of four prevalent frontal features intrinsic to the short-term behaviour of upwelling in this area. Upwelling filaments are shown to extend between 50 and 600 km seawards of the main front and are found, as are upwelling plumes, predominantly off the recognized major upwelling cells. Frontal eddies have a range of diameters and are found distributed over the full area of upwelling and on both sides of the main upwelling front. Warm filaments of Agulhas Current origin are advected preferentially along the western border of the Agulhas Bank and follow closely the front of the southernmost upwelling cells, where they may play a catalytic role in the creation of frontal turbulence.     

用沿岸上升流指数分析中国东南沿岸风生上升流的特征

对1968年1月到2007年12月中国东南沿海(17°N～30°N,109°E～123°E)上升流指数月平均数据进行分析,结论如下:(1)风生沿岸上升流主要在4-8月间发生于海南岛东部、雷州半岛东部、汕头以北至浙江沿岸.(2)风生沿岸上升流的强度具有时空分布变化特征,其中海南岛东部沿岸上升流最强,浙江沿岸其次;整个中国...