As a frequently-observed phenomenon in the northern South China Sea(nSCS),subsurface chlorophyll maximum(SCM)evolution from summer to winter remains unclear,neither the associated hydrographic control.In this study,on...As a frequently-observed phenomenon in the northern South China Sea(nSCS),subsurface chlorophyll maximum(SCM)evolution from summer to winter remains unclear,neither the associated hydrographic control.In this study,on the basis of in-situ data of fall-season cruises in 2004–2006,we characterized the depth,thickness and intensity of the SCM in the nSCS using a general Gaussian-function fitting approach,and investigated a linkage to the corresponding ocean vertical buoyance properties.Our results show that the SCM becomes deeper,thicker and less intense offshore-wards in the nSCS during fall seasons.In parallel,a correlation between the SCM variation and mixed layer depth exists in the nSCS,and it becomes pronounced in the shelf region compared to the slope and basin areas in autumn.Physically,once warmer surface ocean and thus stronger thermo-determined stratification,the SCM layer goes deeper and becomes thicker and less intense in the nSCS,especially in the shelf area of the nSCS.Moreover,the impact of water temperatures at deeper layers on the vertical stratification exerts more consequent roles on the spatial variability of SCM,compared to surface temperatures in the nSCS.Specifically,the isotherm line of 22℃ acts as crucial indicator for variations of the SCM in the nSCS during autumns.展开更多
dOn the basis of the CTD data obtained by the two cruises before and after summer monsoon burst (25th May, 1998), several significant hydrographic characteristics, their variation and formation mechanism in the South ...dOn the basis of the CTD data obtained by the two cruises before and after summer monsoon burst (25th May, 1998), several significant hydrographic characteristics, their variation and formation mechanism in the South China Sea (SCS) are analyzed. The results show that the Kuroshio water intrudes into the SCS in the form of loop current, and its main part is limited to the east of 118degreesE near the Luzon Strait. Then it continuously extends westwards under the influence of the large-scale circulation, and has a distinct impact on the area north of 16degreesN. There are two high temperature and low salinity regions: west off Luzon and east off Vietnam respectively. One region west off Luzon strengthens obviously after summer monsoon burst, the other east off Vietnam shows a tendency of weakening in the north and strengthening in the south. The formation of these two high temperature and low salinity regions is related to the anti-cyclonic eddies existing in this area, besides, it is also related to the high temperature feature west of Luzon, the influx of Sulu Sea water and the influence of the large-scale air circulation. There is a cold region below the depth of 50 m in the south of Zhongsha Islands, and it strengthens after monsoon burst. The formation of cold water is related to the upwelling there.展开更多
Methods for studying oceanic circulation from hydrographic data are reviewed in the context of their applications in the South China Sea. These methods can be classified into three types according to their different d...Methods for studying oceanic circulation from hydrographic data are reviewed in the context of their applications in the South China Sea. These methods can be classified into three types according to their different dynamics as follows: (1) descriptive methods, (2) diagnostic methods without surface and bottom forcing, and (3) diagnostic methods with the above boundary forcing. The paper discusses the progress made in the above methods together with the advancement of study in the South China Sea circulation.展开更多
This article is part of our long-term study on the quantitative at-sea distribution of the marine "upper trophic levels"—seabirds and marine mammals—in polar ecosystems, aiming at quantifying the factors i...This article is part of our long-term study on the quantitative at-sea distribution of the marine "upper trophic levels"—seabirds and marine mammals—in polar ecosystems, aiming at quantifying the factors influencing their distribution as well as detecting possible spatial and temporal changes, with special attention to hydrography and to global climate changes. During an expedition of icebreaking RV Polarstern in February 2010, along the North–South transect between New Zealand and the Ross Gyre, off the Ross Sea, 3200 seabirds belonging to 22 identified pelagic species were recorded during 338 half-hour transect counts. Four major hotspots were identified. These were in Sub-tropical Water off New Zealand(up to 300 birds per count), and at the main Southern Ocean fronts: the Sub-Antarctic Front(up to 240 per count), the Antarctic Front(up to 150 per count) and the Polar Front(up to 200 per count), representing the vast majority of recorded seabirds. The most numerous species in the three frontal zones were: prions—mainly slender-billed Pachyptila belcheri—and Salvin’s albatross Thalassarche [cauta]salvini. The eight more abundant species represented 2650 birds, i.e. more than 80% of the total. A random forest clustering method identified four groups of seabird species occupying similar oceanographic niches.展开更多
The differences of temperature, salinity distribution characteristics and structure of circulation in the upper layer of the South China Sea (SCS) are analyzed, based on the CTD and ADCP data from the two intensive su...The differences of temperature, salinity distribution characteristics and structure of circulation in the upper layer of the South China Sea (SCS) are analyzed, based on the CTD and ADCP data from the two intensive surveyed cruises (IOP1: April 10 - May 5; IOP2: June 12 - July 6) and carried out before and after the Asian monsoon burst (May 25) during the South China Sea Monsoon Experiment (SCSMEX) in 1998. The results showed that field of temperature in the upper layer of the SCS distinctly changed before and after the monsoon burst, the average surface temperature increased by 0.75℃ , with its influence down to the depth of 500 m. The interaction of the local circulation in some areas resulted in the complexity and variability of the temperature and salinity structure in the upper layer, and the alternating distribution of cold and warm water regions (blocks). The high salinity subsurface water obviously intruded into the SCS from the Northwest Pacific, but only limited to the area of southwest of Taiwan Island, and the low salinity intermediate water flowed from the SCS to the Northwest Pacific. The circulation field of the SCS in the summer mainly consisted of cyclonic and anticyclonic eddies (rings). With the burst of the monsoon, the intensity and amount of the anticyclonic or the cyclonic eddies (rings) would vary, showing the complex distribution patterns and variations. The result analyzed by the isopycnic surface method coincided extremely with those by in situ survey (ADCP), which showed that the formation of circulation in the SCS was mainly controlled by the internal mass field, that is, dominated by the geostrophic component.展开更多
Hydrographical parameters and phytoplankton assemblages were determined along the Pondicherry, Parangipettai and Nagapattinam coastal waters, southeast coast of India. All the hydrographical parameters such as sea sur...Hydrographical parameters and phytoplankton assemblages were determined along the Pondicherry, Parangipettai and Nagapattinam coastal waters, southeast coast of India. All the hydrographical parameters such as sea surface temperature, salinity, p H, total alkalinity, dissolved oxygen and nutrients like nitrate, nitrite, inorganic phosphate and reactive silicate, chlorophyll a and phytoplankton assemblages were studied for a period of five months(May, August, September 2010, March and November 2011). Over 121 species of phytoplankton represented by 93 species of diatoms, 16 species of dinoflagellates, 9 species of blue-green algae, 2 species of greens and 1 species of silicoflagellate were recorded. High phytoplankton species diversity was found in March 2011 when salinity and nitrate concentrations were low and reactive silicate and inorganic phosphates were moderate. Species diversity was low during May 2010 when increased sea surface temperature, salinity and low nutrients availability were observed. Coscinodiscus centralis, Diatoma vulgaris and Proboscia alata were dominant, especially Coscinodiscus sp. distributed in all stations whereas Skeletonema costatum, Odontella sinensis and Ditylum brightwellii were abundant in August and September 2010. From principal component analysis and multiple regression analysis, it is evident that variables like sea surface temperature and dissolved oxygen are the most important factors influencing the seasonal pattern of phytoplankton population.展开更多
-On the basis of the hydrographic data observed within the Canary Basin in autumn 1985, temperature-salinity properties, distributions of water masses and barocltne flow field, as well as the volume transports in this...-On the basis of the hydrographic data observed within the Canary Basin in autumn 1985, temperature-salinity properties, distributions of water masses and barocltne flow field, as well as the volume transports in this area are described more detailly. The analyses indicate that the activity in the waters of the Canary Basin is mainly attributed to the interleaving and mixing between the originated water masses (e. g. Surface Water, North Atlantic Central Water, Mediterranean Water and Deep Water) and the modified water masses (Subpolar Mode Water, Labrador Sea Water and Antarctic Intermediate Water) from the outside of the study area and the variation of themselves. The east recirculation of the Subtropic Gyre in the North Atlantic consists of Azores Current and Canary Current.Azores Current is formed with several flow branches around the Azores Island, while the main flow lies at 35?N south of the Azores Island. It begins to diverge near the 15?W. The return flow found off the Portugal coast may be its northern branch. The southern invasion of the Labrador Sea Water and the Subpolar Mode Water are prevented by Azores front which serves an obvious boundary separating the North Western Atlantic (Central) Water and the North Eastern Atlantic (Central) Water.展开更多
This article demonstrates how currently available digital elevation (NASA SRTM;30 m resolution) and hourly global precipitation data (rain, snow;5 and 10 km resolution) can be used to hydrographically quantify the reg...This article demonstrates how currently available digital elevation (NASA SRTM;30 m resolution) and hourly global precipitation data (rain, snow;5 and 10 km resolution) can be used to hydrographically quantify the regional watershed management context across northern Chile. This is done through comprehensive derivations of flow direction, flow accumulation, flow channels, floodplain extent, depressions, and upslope watershed outlines. In turn, these derivations allow for estimating potential precipitation accumulations within any watershed, and turn these into subsequent storm-averaged discharge estimates at, e.g., at any road—flow-channel crossing points. This article elaborates on this by modelling and mapping hydrological conditions and subsequent storm damage at the regional scale and at select locations in terms of recent flood events on March 2015, May 2017, and June 2017. It was found that modelled flood extent and storm-estimated discharge volumes and rates generally conform to reported values including storm-caused damages within communities along the Huasco, Elqui, Limari, Copiapó and Salado rivers. This included the storm response assessment of six water reservoirs as these varied, as quantified, from normal (Puclaro, La Laguna, Cogoti), at capacity (La Paloma, Cogoli), and overflowing (Recoleta). The details of the local to regional assessments are presented in the form hydrologically explicit maps, figures and tables. Together, these attest to the general validity of the framework as introduced. Hydrometrically based stream-discharge calibrations would assist in further refining the approach, especially in terms of estimating local to regional run-off coefficients.展开更多
Hydrographic surveying in reservoirs is a key activity in order to collect data for a variety of purposes like estimation of storage capacity, rate and pattern of sediment deposition, movement of underwater sediment d...Hydrographic surveying in reservoirs is a key activity in order to collect data for a variety of purposes like estimation of storage capacity, rate and pattern of sediment deposition, movement of underwater sediment delta and reservoir routing, etc. These parameters play a pivotal role in any planning, management and operation activity of the reservoirs. Traditional approaches to perform hydrographic surveying in Indus Basin are time consuming, laborious, comparatively inaccurate and costly. As water resources are under immense pressure due to a variety of factors, such inefficient methods are not acceptable for efficient water management. In this study, an integrated approach for hydrographic surveying is introduced and evaluated in terms of its efficiency in comparison with the traditional methods of hydrographic surveying. The approach develops an integrated environment of hydrographic surveying comprising human, hardware and software. The process of surveying starts from in-house planning using specialized geo-spatial softwares. Then, on site a combination of computer hardware, echosounder, differential global positioning system (DGPS), survey vessel and survey crew is made. Post-processing is performed after conducting a survey in order to improve quality of data by filtering errors and producing the end product like reservoir underwater terrain, development of reservoir stage-area and stage-storage relationships, etc. The study was applied to Tarbela Reservoir, Pakistan.展开更多
Study of CTD data collected by the R/V DONG FANG HONG 2 in a 1997 summercruise in the ocean region around the Ryukyu Islands showed: 1) the existence, in the upper layer, of ahigh salinity water (HSW) core at about 20...Study of CTD data collected by the R/V DONG FANG HONG 2 in a 1997 summercruise in the ocean region around the Ryukyu Islands showed: 1) the existence, in the upper layer, of ahigh salinity water (HSW) core at about 200 dbar, and a low salinity water (LSW) core, centered atabout 700 dbar on the Pacific Ocean side of the Ryukyu Ridge, and located shallower on the East Chinafor (ECS) side; 2) the existence, in the upper layer, of warm water regions (WWR) west of Amami Is-land and Ishigaki Island, and a cold water region (CWR) east of Okinawa Ieland; in the lower layer, ofa CWR (WWR) southwest (southeast) of Okinawa Island; 3) the intrusion of North Pacific IntermediateWater into the ECS through the Kerama Trench located south of Okinawa Island and the strait east of Tai-wan Island.展开更多
This study evaluates the ocean climatology simulated by the Beijing Climate Center Climate System Models(BCC-CSMs)participating in phases 5 and 6 of the Coupled Model Intercomparison Project(CMIP5 and CMIP6).CMIP6 BCC...This study evaluates the ocean climatology simulated by the Beijing Climate Center Climate System Models(BCC-CSMs)participating in phases 5 and 6 of the Coupled Model Intercomparison Project(CMIP5 and CMIP6).CMIP6 BCC models generally outperform CMIP5 ones in reproducing ocean states.The CMIP6 high-resolution model,BCC-CSM2-HR,with an enhanced ocean component,exhibits the best simulation performance overall.Specifically,only BCC-CSM2-HR can accurately reproduce the southern equatorial current in the Pacific Ocean,implying the benefits of an enhanced ocean component.Persistent biases are also identified in BCC models across CMIP5 to CMIP6,including substantial biases in sea surface salinity in the Arctic Ocean,warm biases in the intermediate and deep ocean,and notable salinity biases in the northern Indian Ocean.These biases are also commonly presented in other CMIP5 and CMIP6 models.Furthermore,this study evaluates how BCC models simulate modes of climate variability,such as ENSO(El Niño-Southern Oscillation),PDO(Pacific Decadal Oscillation),and NPGO(North Pacific Gyre Oscillation).Future plans are also outlined,including the online integration of an ocean surface wave model and the refinement of model resolution,for development efforts aimed at bolstering the accuracy and reliability of BCC model simulations of ocean climatology.展开更多
This study focuses on the mapping of lineaments using remote sensing techniques and Geographic Information Systems.The aim is to carry out a statistical analysis of the lineaments in order to better understand the org...This study focuses on the mapping of lineaments using remote sensing techniques and Geographic Information Systems.The aim is to carry out a statistical analysis of the lineaments in order to better understand the organization of fracturing in the Batie district,and to identify areas of high fracturing density and their relationship with the hydrographic network.The methodology implemented to achieve these objectives is based on the processing and analysis of Landsat 9 Operational Land Imager/Thermal Infrared Sensor(OLI/TIRS)satellite imagery and Shuttle Radar Topography Mission(SRTM)data covering the study area.After essential pre-processing of data,the following processing techniques were applied:Principal Component Analysis,Sobel Directional Filter with a 3×3 matrix and shaded relief of SRTM data with a sun azimuth of 345°,altitude of 45 m and an elevation factor of 3,followed by manual lineament extraction.The results reveal a total of 176 lineaments,ranging in size from 0.002 to 2.461 km,with an average length of 840.66 km.The projection of these lineaments on a Rose diagram shows a predominance of the North East–South-West(NE-SW)direction,which is the direction of the major tectonic fractures that affect the basement of Central Africa.These lineaments are organized into networks and corridors that define large fracture zones or corridors that control the drainage of the study area.The zones with networks show medium and high densities.This fracturing density gives good aquifer and reservoir potential to the study area.展开更多
Bamako’s geographic and demographic expansion is sure to increase the need for water, and the slow development of the water supply network seems unable to meet this need. The knowledge of the approximate quantity of ...Bamako’s geographic and demographic expansion is sure to increase the need for water, and the slow development of the water supply network seems unable to meet this need. The knowledge of the approximate quantity of water reaching the groundwater is crucial, given the high dependence of this city and its surrounding area on groundwater. The aim of this study is to estimate the average groundwater recharge on a monthly scale, based on measurements taken over a 24-month period by using Water Table Fluctuation (WTF). The monthly recharge values obtained from the 15 piezometers in the study area by using WTF method vary from 1.04 to 38.81 mm with an average value of 9.74 mm. As part of the precipitations, these values represent respectively 1.29%, 48.52% and 12.17% of monthly average precipitation. It appears in this study that despite the piezometers belonging to the same climatic zone, the recharge rate can be different because of many factors such as the thickness of the aquifers, the soil and geology type, the local land cover and land use activities.展开更多
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 b...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.展开更多
Antarctic Bottom Water(AABW)plays an important role in the meridional overturning circulation and contributes significantly to global heat transport and sea level rise(SLR).Based on the Global Ocean(1/12)°Physica...Antarctic Bottom Water(AABW)plays an important role in the meridional overturning circulation and contributes significantly to global heat transport and sea level rise(SLR).Based on the Global Ocean(1/12)°Physical Reanalysis(GLORYS12V1)products and conductivity-temperature-depth instrument data from the World Ocean Circulation Experiment hydrographic program,we analyzed the trends in the thickness,volume,temperature,salinity,and neutral density of the AABW in the Amundsen Sea from 1993 to 2017.Over the past 25 years,the volume has decreased by 3.45×10^(12) m^(3)/a,thinning at a rate of 5 m/a.In the vertical direction,the contraction of the AABW is compensated by the volume expansion of the Circumpolar Deep Water.As the volume of AABW decreases,the temperature of the AABW increases by about 0.002℃/a.This warming is equivalent to a heat flux of 0.27 W/m^(2).A local SLR is produced due to thermal expansion of 0.35 mm/a.During the study period,the neutral density decreased by 0.0003 kg/(m^(3)·a)due to warming.In the horizontal direction,the volume of AABW flowing from the Ross Sea into the Amundsen Sea gradually decreases and the temperature of the AABW increases continuously.The horizontal transport loss of the AABW volume is 4.07×10^(14) m^(3) and the horizontal heat transport results in a 0.03℃ increase in the temperature of the AABW.展开更多
Small surface reservoirs play an important role of providing ready and convenient source of water for various uses in semi-arid areas which are characterized by erratic and low rainfall. Lack of current data on reserv...Small surface reservoirs play an important role of providing ready and convenient source of water for various uses in semi-arid areas which are characterized by erratic and low rainfall. Lack of current data on reservoir capacity loss due to sedimentation is one of the challenges to the sustainable management of surface reservoirs. The study investigated the capacity loss due to sedimentation from 2000-2012, and estimated the trap efficiency of the Mutangi reservoir which is located in semi-arid Chivi, Southern of Zimbabwe. Hydrographic surveys, grab sampling and water depth-capacity methods were used to determine the capacity of the dam as of 2012. To compute capacity loss from 2000 to 2012, the 2000 and 2012 dam capacities were compared whilst the trap efficiency of the reservoir was determined using a set of empirical models that relates trap efficiency to the capacity-watershed area ratio and capacity-inflow ratio. The results show that Mutangi reservoir has a trap efficiency of 95% - 98% (av = 96.4%) and has lost 37% of its capacity due to sedimentation in 12 years (2000 and 2012). Rates of sedimentation were 8539 t·yr-1, 9110?t·yr-1 and 8265 t·yr-1 for the hydrographic survey, grab sampling and water depth-capacity method respectively, and the little difference in these figures demonstrates that any method can be used to determine sedimentation rates. The area specific sediment yield (ASY) ranged from 14 - 15.5 t·ha-1·yr-1 (av = 14.956 t·ha-1·yr-1). At the current rate of sedimentation the projected dead level of the reservoir will be lost to sedimentation in 8 years while the useful life of the reservoir is estimated to be 30 years. Capacity loss due to sedimentation is further complicating the already strained water scarcity situation in semi-arid areas and management decisions should be made based on the current sedimentation rates estimated by different methods. These results imply that management practices that reduce erosion, hence sedimentation in these small reservoirs should be practiced in order to prolong their lifespan.展开更多
The BR （Ba River） basin is one of 9 main river basins in Vietnam. In the past 20 years, natural hazards such as flood andinundation have been complex and increased dramatically in both frequency and intensity in the...The BR （Ba River） basin is one of 9 main river basins in Vietnam. In the past 20 years, natural hazards such as flood andinundation have been complex and increased dramatically in both frequency and intensity in the BR basin. Recently, there have beenapproximately 198 large and small operating reservoirs which lead to increase natural hazards in the river basin. An Khe reservoir,one of big reservoirs in the upstream of the Ba river, impacts significantly on flooding in the downstream. This paper useshydrological model to simulate the flows as a basic for the safety operation of An Khe reservoir in order to prevent the downstreamfloods. The results indicate the Nash-Sutcliffe coefficient higher than 0.8 is stable and reliable parameter.展开更多
Improving the accuracy of digital elevation is essential for reducing hydro-topographic derivation errors pertaining to, e.g., flow direction, basin borders, channel networks, depressions, flood forecasting, and soil ...Improving the accuracy of digital elevation is essential for reducing hydro-topographic derivation errors pertaining to, e.g., flow direction, basin borders, channel networks, depressions, flood forecasting, and soil drainage. This article demonstrates how a gain in this accuracy is improved through digital elevation model (DEM) fusion, and using LiDAR-derived elevation layers for conformance testing and validation. This demonstration is done for the Province of New Brunswick (NB, Canada), using five province-wide DEM sources (SRTM 90 m;SRTM 30 m;ASTER 30 m;CDED 22 m;NB-DEM 10 m) and a five-stage process that guides the re-projection of these DEMs while minimizing their elevational differences relative to LiDAR-captured bare-earth DEMs, through calibration and validation. This effort decreased the resulting non-LiDAR to LiDAR elevation differences by a factor of two, reduced the minimum distance conformance between the non-LiDAR and LiDAR-derived flow channels to ± 10 m at 8.5 times out of 10, and dropped the non-LiDAR wet-area percentages of false positives from 59% to 49%, and of false negatives from 14% to 7%. While these reductions are modest, they are nevertheless not only consistent with already existing hydrographic data layers informing about stream and wet-area locations, they also extend these data layers across the province by comprehensively locating previously unmapped flow channels and wet areas.展开更多
Neotectonic activity can be deduced from stream network patterns and as an outcome of its evolution. The objective of this study is to investigate the use of the stream network morphology and morphometric methods to a...Neotectonic activity can be deduced from stream network patterns and as an outcome of its evolution. The objective of this study is to investigate the use of the stream network morphology and morphometric methods to assess neotectonic signatures in Nefza region situated in North-West of Tunisia. For this aim, a Digital Elevation Model (DEM), hydrographic layers extracted from Nefza topographic map (1/25,000), lithology and tectonic lineament parameters extracted from the geologic map (1/50,000) were used. The objective of this paper is to map structural and lithological discontinuities of the study area, by the morphostructural analysis of the topography extracted of DEM as well as the drainage anomalies. This work allowed the characterization of discontinuities of lithologic and structural origin. The previously conducted studies in the study area, confirm that is crossed by lineaments at several directions E-W, N-S, NE-SW and NW-SE. Based on the results obtained from this study regarding the correlation between tectonic and hydrographic network, we can highlight a regional rejuvenation tendency of the most mapped lineaments.展开更多
The formation of mesoscale eddies and the structure of the surface flow field in the Luzon Strait area were examined using in-situ CTD data, Argo float data, and multi-satellite remote sensing data collected from May ...The formation of mesoscale eddies and the structure of the surface flow field in the Luzon Strait area were examined using in-situ CTD data, Argo float data, and multi-satellite remote sensing data collected from May to August 2009. The results show that vigorous water exchange between Kuroshio water and South China Sea （SCS） water began to emerge over the 200 m water column throughout the strait. Based on an objective definition of surface currents, float A69 tracked an anti-cyclonic eddy southwest of Taiwan Island under a Lagrangian current measurement. The salinity inside the anti-cyclonic eddy was higher than in typical SCS water but lower than in Kuroshio mainstream water, indicating that this eddy was induced by Kuroshio frontal intrusion through the Luzun Strait and into the SCS. From hydrographic data, we propose that continuous horizontal diffusion with high-salinity characteristics in the subsurface layer could extend to 119°E or even further west. The high-temperature filament, large positive sea level anomaly and clockwise geostrophic current all confirmed the existence of this warm eddy in May and June. A strongly negative wind stress curl maintained the eddy until it died. The surface flow field during July and August was rather complicated. Float A83 described an east-west orientated shuttle run in the 20°N section that was not reported by previous studies. At the same time, float A80 indicated a Kuroshio bend into the north-central region of Luzon Strait but it did not cross 120.5°E. The water mass rejoining the Kuroshio mainstream from the southern tip of Taiwan Island was less saline, indicating an entrainment of water from SCS by the Kuroshio bend.展开更多
基金Supported by the Ministry of Science and Technology of the People’s Republic of China(No.2019 YFE 0125000)the National Natural Science Foundation of China-Shandong Joint Fund(No.U 1906215)+1 种基金the National Natural Science Foundation of China(No.41406010)partially by the Key Laboratory of Coastal Environmental Processes and Ecological Remediation,Chinese Academy of Sciences Opening Fund(No.2020 KFJJ 04)。
文摘As a frequently-observed phenomenon in the northern South China Sea(nSCS),subsurface chlorophyll maximum(SCM)evolution from summer to winter remains unclear,neither the associated hydrographic control.In this study,on the basis of in-situ data of fall-season cruises in 2004–2006,we characterized the depth,thickness and intensity of the SCM in the nSCS using a general Gaussian-function fitting approach,and investigated a linkage to the corresponding ocean vertical buoyance properties.Our results show that the SCM becomes deeper,thicker and less intense offshore-wards in the nSCS during fall seasons.In parallel,a correlation between the SCM variation and mixed layer depth exists in the nSCS,and it becomes pronounced in the shelf region compared to the slope and basin areas in autumn.Physically,once warmer surface ocean and thus stronger thermo-determined stratification,the SCM layer goes deeper and becomes thicker and less intense in the nSCS,especially in the shelf area of the nSCS.Moreover,the impact of water temperatures at deeper layers on the vertical stratification exerts more consequent roles on the spatial variability of SCM,compared to surface temperatures in the nSCS.Specifically,the isotherm line of 22℃ acts as crucial indicator for variations of the SCM in the nSCS during autumns.
文摘dOn the basis of the CTD data obtained by the two cruises before and after summer monsoon burst (25th May, 1998), several significant hydrographic characteristics, their variation and formation mechanism in the South China Sea (SCS) are analyzed. The results show that the Kuroshio water intrudes into the SCS in the form of loop current, and its main part is limited to the east of 118degreesE near the Luzon Strait. Then it continuously extends westwards under the influence of the large-scale circulation, and has a distinct impact on the area north of 16degreesN. There are two high temperature and low salinity regions: west off Luzon and east off Vietnam respectively. One region west off Luzon strengthens obviously after summer monsoon burst, the other east off Vietnam shows a tendency of weakening in the north and strengthening in the south. The formation of these two high temperature and low salinity regions is related to the anti-cyclonic eddies existing in this area, besides, it is also related to the high temperature feature west of Luzon, the influx of Sulu Sea water and the influence of the large-scale air circulation. There is a cold region below the depth of 50 m in the south of Zhongsha Islands, and it strengthens after monsoon burst. The formation of cold water is related to the upwelling there.
基金supported by the National key program for Derelop-ing Basic Sciences(G 1999043805 and G19999043810)the National Natural Science Foundation of China(Grant No.40076009)the Chinese Academny of Sciences(KZCX1-SW-01-16).
文摘Methods for studying oceanic circulation from hydrographic data are reviewed in the context of their applications in the South China Sea. These methods can be classified into three types according to their different dynamics as follows: (1) descriptive methods, (2) diagnostic methods without surface and bottom forcing, and (3) diagnostic methods with the above boundary forcing. The paper discusses the progress made in the above methods together with the advancement of study in the South China Sea circulation.
文摘This article is part of our long-term study on the quantitative at-sea distribution of the marine "upper trophic levels"—seabirds and marine mammals—in polar ecosystems, aiming at quantifying the factors influencing their distribution as well as detecting possible spatial and temporal changes, with special attention to hydrography and to global climate changes. During an expedition of icebreaking RV Polarstern in February 2010, along the North–South transect between New Zealand and the Ross Gyre, off the Ross Sea, 3200 seabirds belonging to 22 identified pelagic species were recorded during 338 half-hour transect counts. Four major hotspots were identified. These were in Sub-tropical Water off New Zealand(up to 300 birds per count), and at the main Southern Ocean fronts: the Sub-Antarctic Front(up to 240 per count), the Antarctic Front(up to 150 per count) and the Polar Front(up to 200 per count), representing the vast majority of recorded seabirds. The most numerous species in the three frontal zones were: prions—mainly slender-billed Pachyptila belcheri—and Salvin’s albatross Thalassarche [cauta]salvini. The eight more abundant species represented 2650 birds, i.e. more than 80% of the total. A random forest clustering method identified four groups of seabird species occupying similar oceanographic niches.
基金This study was supported by the National Key Foundation Research Program under contract No. G1999043805 the National Climbing Project A: "South China Sea Monsoon Experiment " the State Oceanic Administration.
文摘The differences of temperature, salinity distribution characteristics and structure of circulation in the upper layer of the South China Sea (SCS) are analyzed, based on the CTD and ADCP data from the two intensive surveyed cruises (IOP1: April 10 - May 5; IOP2: June 12 - July 6) and carried out before and after the Asian monsoon burst (May 25) during the South China Sea Monsoon Experiment (SCSMEX) in 1998. The results showed that field of temperature in the upper layer of the SCS distinctly changed before and after the monsoon burst, the average surface temperature increased by 0.75℃ , with its influence down to the depth of 500 m. The interaction of the local circulation in some areas resulted in the complexity and variability of the temperature and salinity structure in the upper layer, and the alternating distribution of cold and warm water regions (blocks). The high salinity subsurface water obviously intruded into the SCS from the Northwest Pacific, but only limited to the area of southwest of Taiwan Island, and the low salinity intermediate water flowed from the SCS to the Northwest Pacific. The circulation field of the SCS in the summer mainly consisted of cyclonic and anticyclonic eddies (rings). With the burst of the monsoon, the intensity and amount of the anticyclonic or the cyclonic eddies (rings) would vary, showing the complex distribution patterns and variations. The result analyzed by the isopycnic surface method coincided extremely with those by in situ survey (ADCP), which showed that the formation of circulation in the SCS was mainly controlled by the internal mass field, that is, dominated by the geostrophic component.
基金the University Grants Commission,Govt.of India,New Delhi for financial support through UGCResearch Award(No.F.30-1/2014(SA-II)/RA-2014-16-SCTAM-4364 dated 05/02/2015)
文摘Hydrographical parameters and phytoplankton assemblages were determined along the Pondicherry, Parangipettai and Nagapattinam coastal waters, southeast coast of India. All the hydrographical parameters such as sea surface temperature, salinity, p H, total alkalinity, dissolved oxygen and nutrients like nitrate, nitrite, inorganic phosphate and reactive silicate, chlorophyll a and phytoplankton assemblages were studied for a period of five months(May, August, September 2010, March and November 2011). Over 121 species of phytoplankton represented by 93 species of diatoms, 16 species of dinoflagellates, 9 species of blue-green algae, 2 species of greens and 1 species of silicoflagellate were recorded. High phytoplankton species diversity was found in March 2011 when salinity and nitrate concentrations were low and reactive silicate and inorganic phosphates were moderate. Species diversity was low during May 2010 when increased sea surface temperature, salinity and low nutrients availability were observed. Coscinodiscus centralis, Diatoma vulgaris and Proboscia alata were dominant, especially Coscinodiscus sp. distributed in all stations whereas Skeletonema costatum, Odontella sinensis and Ditylum brightwellii were abundant in August and September 2010. From principal component analysis and multiple regression analysis, it is evident that variables like sea surface temperature and dissolved oxygen are the most important factors influencing the seasonal pattern of phytoplankton population.
文摘-On the basis of the hydrographic data observed within the Canary Basin in autumn 1985, temperature-salinity properties, distributions of water masses and barocltne flow field, as well as the volume transports in this area are described more detailly. The analyses indicate that the activity in the waters of the Canary Basin is mainly attributed to the interleaving and mixing between the originated water masses (e. g. Surface Water, North Atlantic Central Water, Mediterranean Water and Deep Water) and the modified water masses (Subpolar Mode Water, Labrador Sea Water and Antarctic Intermediate Water) from the outside of the study area and the variation of themselves. The east recirculation of the Subtropic Gyre in the North Atlantic consists of Azores Current and Canary Current.Azores Current is formed with several flow branches around the Azores Island, while the main flow lies at 35?N south of the Azores Island. It begins to diverge near the 15?W. The return flow found off the Portugal coast may be its northern branch. The southern invasion of the Labrador Sea Water and the Subpolar Mode Water are prevented by Azores front which serves an obvious boundary separating the North Western Atlantic (Central) Water and the North Eastern Atlantic (Central) Water.
文摘This article demonstrates how currently available digital elevation (NASA SRTM;30 m resolution) and hourly global precipitation data (rain, snow;5 and 10 km resolution) can be used to hydrographically quantify the regional watershed management context across northern Chile. This is done through comprehensive derivations of flow direction, flow accumulation, flow channels, floodplain extent, depressions, and upslope watershed outlines. In turn, these derivations allow for estimating potential precipitation accumulations within any watershed, and turn these into subsequent storm-averaged discharge estimates at, e.g., at any road—flow-channel crossing points. This article elaborates on this by modelling and mapping hydrological conditions and subsequent storm damage at the regional scale and at select locations in terms of recent flood events on March 2015, May 2017, and June 2017. It was found that modelled flood extent and storm-estimated discharge volumes and rates generally conform to reported values including storm-caused damages within communities along the Huasco, Elqui, Limari, Copiapó and Salado rivers. This included the storm response assessment of six water reservoirs as these varied, as quantified, from normal (Puclaro, La Laguna, Cogoti), at capacity (La Paloma, Cogoli), and overflowing (Recoleta). The details of the local to regional assessments are presented in the form hydrologically explicit maps, figures and tables. Together, these attest to the general validity of the framework as introduced. Hydrometrically based stream-discharge calibrations would assist in further refining the approach, especially in terms of estimating local to regional run-off coefficients.
文摘Hydrographic surveying in reservoirs is a key activity in order to collect data for a variety of purposes like estimation of storage capacity, rate and pattern of sediment deposition, movement of underwater sediment delta and reservoir routing, etc. These parameters play a pivotal role in any planning, management and operation activity of the reservoirs. Traditional approaches to perform hydrographic surveying in Indus Basin are time consuming, laborious, comparatively inaccurate and costly. As water resources are under immense pressure due to a variety of factors, such inefficient methods are not acceptable for efficient water management. In this study, an integrated approach for hydrographic surveying is introduced and evaluated in terms of its efficiency in comparison with the traditional methods of hydrographic surveying. The approach develops an integrated environment of hydrographic surveying comprising human, hardware and software. The process of surveying starts from in-house planning using specialized geo-spatial softwares. Then, on site a combination of computer hardware, echosounder, differential global positioning system (DGPS), survey vessel and survey crew is made. Post-processing is performed after conducting a survey in order to improve quality of data by filtering errors and producing the end product like reservoir underwater terrain, development of reservoir stage-area and stage-storage relationships, etc. The study was applied to Tarbela Reservoir, Pakistan.
文摘Study of CTD data collected by the R/V DONG FANG HONG 2 in a 1997 summercruise in the ocean region around the Ryukyu Islands showed: 1) the existence, in the upper layer, of ahigh salinity water (HSW) core at about 200 dbar, and a low salinity water (LSW) core, centered atabout 700 dbar on the Pacific Ocean side of the Ryukyu Ridge, and located shallower on the East Chinafor (ECS) side; 2) the existence, in the upper layer, of warm water regions (WWR) west of Amami Is-land and Ishigaki Island, and a cold water region (CWR) east of Okinawa Ieland; in the lower layer, ofa CWR (WWR) southwest (southeast) of Okinawa Island; 3) the intrusion of North Pacific IntermediateWater into the ECS through the Kerama Trench located south of Okinawa Island and the strait east of Tai-wan Island.
基金supported by the National Natural Science Foundation of China(Grant No.42230608)the National Key Research and Development Program of China(Grant No.2022YFC3004203)+1 种基金the Key Program of the National Natural Science Foundation of China(Grant No.U2242214)the S&T Development Fund of the Chinese Academy of Meteorological Sciences(2024KJ013).
文摘This study evaluates the ocean climatology simulated by the Beijing Climate Center Climate System Models(BCC-CSMs)participating in phases 5 and 6 of the Coupled Model Intercomparison Project(CMIP5 and CMIP6).CMIP6 BCC models generally outperform CMIP5 ones in reproducing ocean states.The CMIP6 high-resolution model,BCC-CSM2-HR,with an enhanced ocean component,exhibits the best simulation performance overall.Specifically,only BCC-CSM2-HR can accurately reproduce the southern equatorial current in the Pacific Ocean,implying the benefits of an enhanced ocean component.Persistent biases are also identified in BCC models across CMIP5 to CMIP6,including substantial biases in sea surface salinity in the Arctic Ocean,warm biases in the intermediate and deep ocean,and notable salinity biases in the northern Indian Ocean.These biases are also commonly presented in other CMIP5 and CMIP6 models.Furthermore,this study evaluates how BCC models simulate modes of climate variability,such as ENSO(El Niño-Southern Oscillation),PDO(Pacific Decadal Oscillation),and NPGO(North Pacific Gyre Oscillation).Future plans are also outlined,including the online integration of an ocean surface wave model and the refinement of model resolution,for development efforts aimed at bolstering the accuracy and reliability of BCC model simulations of ocean climatology.
文摘This study focuses on the mapping of lineaments using remote sensing techniques and Geographic Information Systems.The aim is to carry out a statistical analysis of the lineaments in order to better understand the organization of fracturing in the Batie district,and to identify areas of high fracturing density and their relationship with the hydrographic network.The methodology implemented to achieve these objectives is based on the processing and analysis of Landsat 9 Operational Land Imager/Thermal Infrared Sensor(OLI/TIRS)satellite imagery and Shuttle Radar Topography Mission(SRTM)data covering the study area.After essential pre-processing of data,the following processing techniques were applied:Principal Component Analysis,Sobel Directional Filter with a 3×3 matrix and shaded relief of SRTM data with a sun azimuth of 345°,altitude of 45 m and an elevation factor of 3,followed by manual lineament extraction.The results reveal a total of 176 lineaments,ranging in size from 0.002 to 2.461 km,with an average length of 840.66 km.The projection of these lineaments on a Rose diagram shows a predominance of the North East–South-West(NE-SW)direction,which is the direction of the major tectonic fractures that affect the basement of Central Africa.These lineaments are organized into networks and corridors that define large fracture zones or corridors that control the drainage of the study area.The zones with networks show medium and high densities.This fracturing density gives good aquifer and reservoir potential to the study area.
文摘Bamako’s geographic and demographic expansion is sure to increase the need for water, and the slow development of the water supply network seems unable to meet this need. The knowledge of the approximate quantity of water reaching the groundwater is crucial, given the high dependence of this city and its surrounding area on groundwater. The aim of this study is to estimate the average groundwater recharge on a monthly scale, based on measurements taken over a 24-month period by using Water Table Fluctuation (WTF). The monthly recharge values obtained from the 15 piezometers in the study area by using WTF method vary from 1.04 to 38.81 mm with an average value of 9.74 mm. As part of the precipitations, these values represent respectively 1.29%, 48.52% and 12.17% of monthly average precipitation. It appears in this study that despite the piezometers belonging to the same climatic zone, the recharge rate can be different because of many factors such as the thickness of the aquifers, the soil and geology type, the local land cover and land use activities.
基金The National Basic Research Program(973 Program)of China under contract Nos 2009CB421205 and 2011CB40350the National Key Research and Development Program of China under contract No.2016YFC1402607the State Oceanic Administration Special Grant of China under contract No.HY126-04-02-03
文摘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.
基金The Impact and Response of Antarctic Seas to Climate Change Program under contract No.RFSOCC2020-2022-No.18the National Key Research and Development Program of China under contract No.2016YFA0601301。
文摘Antarctic Bottom Water(AABW)plays an important role in the meridional overturning circulation and contributes significantly to global heat transport and sea level rise(SLR).Based on the Global Ocean(1/12)°Physical Reanalysis(GLORYS12V1)products and conductivity-temperature-depth instrument data from the World Ocean Circulation Experiment hydrographic program,we analyzed the trends in the thickness,volume,temperature,salinity,and neutral density of the AABW in the Amundsen Sea from 1993 to 2017.Over the past 25 years,the volume has decreased by 3.45×10^(12) m^(3)/a,thinning at a rate of 5 m/a.In the vertical direction,the contraction of the AABW is compensated by the volume expansion of the Circumpolar Deep Water.As the volume of AABW decreases,the temperature of the AABW increases by about 0.002℃/a.This warming is equivalent to a heat flux of 0.27 W/m^(2).A local SLR is produced due to thermal expansion of 0.35 mm/a.During the study period,the neutral density decreased by 0.0003 kg/(m^(3)·a)due to warming.In the horizontal direction,the volume of AABW flowing from the Ross Sea into the Amundsen Sea gradually decreases and the temperature of the AABW increases continuously.The horizontal transport loss of the AABW volume is 4.07×10^(14) m^(3) and the horizontal heat transport results in a 0.03℃ increase in the temperature of the AABW.
文摘Small surface reservoirs play an important role of providing ready and convenient source of water for various uses in semi-arid areas which are characterized by erratic and low rainfall. Lack of current data on reservoir capacity loss due to sedimentation is one of the challenges to the sustainable management of surface reservoirs. The study investigated the capacity loss due to sedimentation from 2000-2012, and estimated the trap efficiency of the Mutangi reservoir which is located in semi-arid Chivi, Southern of Zimbabwe. Hydrographic surveys, grab sampling and water depth-capacity methods were used to determine the capacity of the dam as of 2012. To compute capacity loss from 2000 to 2012, the 2000 and 2012 dam capacities were compared whilst the trap efficiency of the reservoir was determined using a set of empirical models that relates trap efficiency to the capacity-watershed area ratio and capacity-inflow ratio. The results show that Mutangi reservoir has a trap efficiency of 95% - 98% (av = 96.4%) and has lost 37% of its capacity due to sedimentation in 12 years (2000 and 2012). Rates of sedimentation were 8539 t·yr-1, 9110?t·yr-1 and 8265 t·yr-1 for the hydrographic survey, grab sampling and water depth-capacity method respectively, and the little difference in these figures demonstrates that any method can be used to determine sedimentation rates. The area specific sediment yield (ASY) ranged from 14 - 15.5 t·ha-1·yr-1 (av = 14.956 t·ha-1·yr-1). At the current rate of sedimentation the projected dead level of the reservoir will be lost to sedimentation in 8 years while the useful life of the reservoir is estimated to be 30 years. Capacity loss due to sedimentation is further complicating the already strained water scarcity situation in semi-arid areas and management decisions should be made based on the current sedimentation rates estimated by different methods. These results imply that management practices that reduce erosion, hence sedimentation in these small reservoirs should be practiced in order to prolong their lifespan.
文摘The BR （Ba River） basin is one of 9 main river basins in Vietnam. In the past 20 years, natural hazards such as flood andinundation have been complex and increased dramatically in both frequency and intensity in the BR basin. Recently, there have beenapproximately 198 large and small operating reservoirs which lead to increase natural hazards in the river basin. An Khe reservoir,one of big reservoirs in the upstream of the Ba river, impacts significantly on flooding in the downstream. This paper useshydrological model to simulate the flows as a basic for the safety operation of An Khe reservoir in order to prevent the downstreamfloods. The results indicate the Nash-Sutcliffe coefficient higher than 0.8 is stable and reliable parameter.
文摘Improving the accuracy of digital elevation is essential for reducing hydro-topographic derivation errors pertaining to, e.g., flow direction, basin borders, channel networks, depressions, flood forecasting, and soil drainage. This article demonstrates how a gain in this accuracy is improved through digital elevation model (DEM) fusion, and using LiDAR-derived elevation layers for conformance testing and validation. This demonstration is done for the Province of New Brunswick (NB, Canada), using five province-wide DEM sources (SRTM 90 m;SRTM 30 m;ASTER 30 m;CDED 22 m;NB-DEM 10 m) and a five-stage process that guides the re-projection of these DEMs while minimizing their elevational differences relative to LiDAR-captured bare-earth DEMs, through calibration and validation. This effort decreased the resulting non-LiDAR to LiDAR elevation differences by a factor of two, reduced the minimum distance conformance between the non-LiDAR and LiDAR-derived flow channels to ± 10 m at 8.5 times out of 10, and dropped the non-LiDAR wet-area percentages of false positives from 59% to 49%, and of false negatives from 14% to 7%. While these reductions are modest, they are nevertheless not only consistent with already existing hydrographic data layers informing about stream and wet-area locations, they also extend these data layers across the province by comprehensively locating previously unmapped flow channels and wet areas.
文摘Neotectonic activity can be deduced from stream network patterns and as an outcome of its evolution. The objective of this study is to investigate the use of the stream network morphology and morphometric methods to assess neotectonic signatures in Nefza region situated in North-West of Tunisia. For this aim, a Digital Elevation Model (DEM), hydrographic layers extracted from Nefza topographic map (1/25,000), lithology and tectonic lineament parameters extracted from the geologic map (1/50,000) were used. The objective of this paper is to map structural and lithological discontinuities of the study area, by the morphostructural analysis of the topography extracted of DEM as well as the drainage anomalies. This work allowed the characterization of discontinuities of lithologic and structural origin. The previously conducted studies in the study area, confirm that is crossed by lineaments at several directions E-W, N-S, NE-SW and NW-SE. Based on the results obtained from this study regarding the correlation between tectonic and hydrographic network, we can highlight a regional rejuvenation tendency of the most mapped lineaments.
基金Supported by the National Natural Science Foundation of China(Nos.41306019,U1133001)the open grant of LTO SCSIO/CAS(No.LTO201305)+4 种基金the Sanya and CAS Cooperation Project(No.2013YD77)the NSFC Innovative Group(No.41421005)the NSFC-Shandong Joint Fund for Marine Science Research Centers(No.U1406401)the Pilot Strategic Project of CAS(No.XDA11020101)the Knowledge Innovation Engineering Frontier Project of SIDSSE(No.SIDSSE-201205)
文摘The formation of mesoscale eddies and the structure of the surface flow field in the Luzon Strait area were examined using in-situ CTD data, Argo float data, and multi-satellite remote sensing data collected from May to August 2009. The results show that vigorous water exchange between Kuroshio water and South China Sea （SCS） water began to emerge over the 200 m water column throughout the strait. Based on an objective definition of surface currents, float A69 tracked an anti-cyclonic eddy southwest of Taiwan Island under a Lagrangian current measurement. The salinity inside the anti-cyclonic eddy was higher than in typical SCS water but lower than in Kuroshio mainstream water, indicating that this eddy was induced by Kuroshio frontal intrusion through the Luzun Strait and into the SCS. From hydrographic data, we propose that continuous horizontal diffusion with high-salinity characteristics in the subsurface layer could extend to 119°E or even further west. The high-temperature filament, large positive sea level anomaly and clockwise geostrophic current all confirmed the existence of this warm eddy in May and June. A strongly negative wind stress curl maintained the eddy until it died. The surface flow field during July and August was rather complicated. Float A83 described an east-west orientated shuttle run in the 20°N section that was not reported by previous studies. At the same time, float A80 indicated a Kuroshio bend into the north-central region of Luzon Strait but it did not cross 120.5°E. The water mass rejoining the Kuroshio mainstream from the southern tip of Taiwan Island was less saline, indicating an entrainment of water from SCS by the Kuroshio bend.
