Seasonal and spatial variations in settling manganese fluxes in the Northern Arabian Sea

Particulate manganese (Mn) fluxes measured with six time series sediment traps showed that the annual settling fluxes were 3–6 times higher in the west compared to those in the east and central Arabian Sea. Annual detrital Mn (Mn_dt) flux was nearly the same in the eastern and western Arabian Sea, but excess Mn (Mn_ex) fluxes were much higher (>4 times) in the western Arabian Sea. Atmospheric inputs cannot account for these high-Mn fluxes. Central and eastern Arabian Sea traps are overlain by a thick and intense denitrification layer, which may cause reductive dissolution of Mn oxides from settling particles and consequently low Mn_ex fluxes. As the exchange of intermediate waters between the Arabian Sea and the rest of the Indian Ocean is confined largely to the western Arabian Sea, relatively more oxic and dynamic conditions prevail in this region. Increased oxidizing conditions coupled with higher inputs of dissolved Mn through intermediate and surface advective processes might have led to in situ oxidation of Mn, thus resulting in higher vertical fluxes of Mn_ex. Mn_ex fluxes in traps at ∼1000 m depth exhibited seasonal variability with a minimum during the winter monsoon (January–February) and maximum during the pre- and early- south-west monsoon (March–June). This variation is correlated with water mass movements and bacterial abundance observed during the Joint Global Ocean Flux Study (JGOFS). The possible involvement of bacteria and the microbial loop is suggested for the concentration and vertical transport of excess Mn.     

Seasonal variations in the distribution of Fe and Al in the surface waters of the Arabian Sea

Concentrations of dissolved Al and Fe in the surface mixed layer were measured during five cruises of the 1995 US JGOFS Arabian Sea Process Study, Concentrations of both Al and Fe were relatively uniform between January and April, the NE Monsoon and the Spring Intermonsoon period, ranging from 2 to 11 nM Al (mean 5.3 nM) and 0.5 to 2.4 nM Fe (mean 1.0 nM). In July/August, after the onset of the SW Monsoon, surface water Al and Fe concentrations increased significantly (Al range 4.5–20.1 nM; mean=10 nM, Fe range 0.57–2.4 nM; mean=1.3 nM), particularly in the NE part of the Arabian Sea, as the result of the input and partial dissolution of eolian dust. Using the enrichment of Al in the surface waters, we estimate this is the equivalent to the deposition of 2.2–7.4 g m⁻² dust, which is comparable to values previously estimated for this region. Approximately one month later (August/September), surface water concentrations of both Al and Fe were found to have decreased significantly (mean Al 7.4 nM, mean Fe 0.90 nM) particularly in the same NE region, as the result of export of particulate material from the euphotic zone. Fe supply to the surface waters is also affected by upwelling of sub-surface waters in the coastal region of the Arabian Sea during the SW Monsoon. Despite the proximity of high concentrations of Fe in the shallow sub-oxic layer, freshly upwelled water is not drawn from this layer and the NO₃/Fe ratio in the initially upwelled water is below the value at which Fe limitation is through to occur. Continued deposition of eolian Fe into the upwelled water as it advects offshore provides the Fe required to raise this ratio above the Fe limitation value.     

Seasonal variations of sound speed in the Arabian Gulf

Sound-speed computations from CTD casts in the Arabian Gulf during 1992, reveal spatial and temporal variations in acoustic properties. Hydrographic conditions affecting sound speed propagation were seasonally investigated. A monotonic decrease in sound speed profiles with depth was commonly observed at almost all the stations in the Gulf. However, an exception occurred at Hormuz strait during winter. The water exchange pattern between the Gulf of Oman and the Arabian Gulf seems to influence the sound-speed structure, especially in the southern part of the latter. Winter profiles along the Gulf axis showed almost vertically homogenous sound speed. Maximum speeds are observed in summer, with a strong gradient associated with the development of the summer thermocline layer. Horizontal distributions in both winter and summer show a decreasing trend in sound speed from the Strait of Hormuz to the head of the Gulf. The resultant profiles provide a more comprehensive and reliable data set than any that have been reported in the literature. Shallowness and multiple refraction and reflection in the Arabian Gulf may cause sound speed energy to be trapped. No sound channel was detected inside the Gulf. A correlation analysis shows that sound speed is closely correlated with temperature throughout the Gulf, except in winter in the southern half where salinity effects, as a result of inversion and water exchange at the entrance, are found to be dominant.     

Sea surface height anomaly and geostrophic circulation variations in the South China Sea from TOPEX/POSEIDON altimetry

The sea surface height anomaly (SSHA) and geostrophic circulation in the South ChinaSea (SCS) are studied using TOPEX/POSE1DON (T/P) altimetry data. The SSHA, which is obtained after tidal correction based on the tidal results from T/P data, is predominated by seasonal alternating monsoons. The results reveal that the SSHA in the central part of the SCS is positive in spring and summer, but negative in autumn and winter. It is also found that the SSHA in the SCS can be approached with the sum of tidal constituents SA and SSA. The geostrophic circulations in the SCS are calculated according to sea surface dynamic topography, which is the sum of SSHA and mean sea surface height. It is suggested that the circulation in the upper layer of the SCS is generally cyclonic and notably western intensified during autumn and winter, while the western intensification is weak during spring and summer. It is also indicated that the Kuroshio intrudes into the northeastern SCS throuth the Luzon Strait in winter. But ther     

阿拉伯海淡水输运量的季节变化特征研究

本文利用简单海洋模式同化再分析产品等资料,阐述了阿拉伯海与赤道西印度洋,阿拉伯海与阿曼湾之间淡水输运量的季节变化特征,揭示了阿拉伯海淡水输运量的基本平衡和季节变化特征。结果表明,阿拉伯海得到的淡水输运量(包括来自赤道西印度洋、河流)和失去的淡水输运量(包括降水量减蒸发量、向阿曼湾输运)基本相当。阿拉伯海通过海气交换失去的淡水(降水量减蒸发量)主要由来自赤道西印度洋(包括孟加拉湾)的淡水输运来补偿,赤道西印度洋向阿拉伯海的淡水输运对维持阿拉伯海的盐度基本平衡起到至关重要的作用。阿拉伯海的淡水输运量在1?6月和12月为负值,失去淡水;7?11月为正值,9月最大,得到淡水。阿拉伯海的净淡水输运量的季节变化特征表现为单峰现象。阿拉伯海与赤道西印度洋(9°N断面）的淡水输运量主要出现在表层至约200 m层,多年平均约为0.1×106 m3/s,向阿拉伯海输运。从10月至翌年3月,来自孟加拉湾的低盐水向阿拉伯海输运,该输运主要出现在印度半岛西南端近海约60 m层以浅区域。夏季和秋季,出现在索马里半岛东部海域的涡旋(大回旋)引起的输运(涡旋的西部低盐水向北输运,东部高盐水向南输运),不仅输运量是一年当中最大的,而且影响的深度可达约300 m。该输运从6月开始形成,8?9月最强,11月迅速减弱。阿拉伯海与阿曼湾的淡水输运量较小,其垂直分布呈现3层结构,表层至10 m层,高盐水向阿拉伯海输运;15～170 m层,低盐水向阿曼湾输运;175～400 m层,高盐水向阿拉伯海输运。阿曼湾湾口断面多年平均淡水输运量约为0.39×104 m3/s,向阿曼湾输运。     

阿拉伯海东南海域盐度收支的季节变化

采用SODA海洋同化产品的月平均资料,本文分析了阿拉伯海东南海域表层盐度的季节变化特征,发现局地海面淡水通量不能解释盐度的变化。两个典型区域的表层海水盐度收支分析表明,海洋的平流输送是造成阿拉伯海东南海域盐度冬季降低、夏季升高的主要原因,而淡水通量仅在夏季印度西侧沿岸区域造成盐度降低。冬季,东北季风环流将孟加拉湾北部的低盐水沿同纬度输送到阿拉伯海,然后向北输送,使表层海水盐度降低;夏季,西南季风环流把阿拉伯海西北部的高盐水向南、向东输送,使阿拉伯海东南海域盐度升高。受地理位置因素的影响,阿拉伯海东南海域表层盐度的变化冬季明显强于夏季。     

Seasonal circulation in the southeastern Huanghai Sea

The seasonal circulation in the southeastern Huanghai Sea has been studied with hydrographic data,which were observed in February and June 1994 and bimonthly during 1970-1990,and numerical model results.Horiwntal distributions of temperature and salinity in 1994 are quite different due to strong tidal mixing so that we need a analysis to see the real distributions of water masses.The mixing ratio analysis with the data of 1970-1990 shows the connection of the waters in the west coasts of Kotea Peninsula with warm and saline waters from the south in summer,which means northward inflows along the west coasts of Korea Peninsula in summer.With this flow,the seasonal circulations,which are deduced from the seasonal change of water mass distributions in the lower layer,are warm inflows in winter and mld outflows in summer in the central Huanghai Sea,and cold outflows in winter and warm inflows in summer along the west coasts of Korea Peninsula.The seasonally changed inflows might be the Huanghai Sea Warm Current.The monsoon winds can drive such circulations.However,summer monsoon winds are weak and irregular.As one of other possible dynamics,the variation of Kuroshio transport is numerically studied with allowing sea level fluctuations.Although it should be studied more,it possibly drives the summer circulations.The real circulations seem to be driven by both of them.     

Seasonal variability of sonic layer depth in the Central Arabian Sea

The seasonal variability of sonic layer depth (SLD) in the central Arabian Sea (CAS) (0 to 25°N and 62-66°E) was studied using the temperature and salinity (T/S) profiles from Argo floats for the years 2002–2006. The atmospheric forcing responsible for the observed changes was explored using the meteorological data from NCEP/NCAR and Quickscat winds. SLD was obtained from sound velocity profiles computed from T/S data. Net heat flux and wind forcing regulated SLD in the CAS. Up-welling and down-welling (Ekman dynamics) associated with the Findlater Jet controlled SLD during the summer monsoon. While in winter monsoon, cooling and convective mixing regulated SLD in the study region. Weak winds, high insolation and positive net heat flux lead to the formation of thin, warm and stratified sonic layer during pre and post summer monsoon periods, respectively.     

Seasonal variation of pteropods from the Western Arabian Sea sediment trap

Sediment trap samples collected from the Western Arabian Sea yielded a rich assemblage of intact and non-living (opaque white) pteropod tests from a water depth of 919 m during January to September 1993. Nine species of pteropods were recorded, all (except one) displaying distinct seasonality in abundance, suggesting their response to changing hydrographical conditions influenced by the summer/winter monsoon cycle. Pteropod fluxes increased during the April–May peak of the intermonsoon, and reached maximum levels in the late phase of the southwest summer monsoon, probably due to the shallowing of the mixed layer depth. This shallowing, coupled with enhanced nutrient availability, provides ideal conditions for pteropod growth, also reflected in corresponding fluctuations in the flux of the foraminifer Globigerina bulloides. Pteropod/planktic foraminifer ratios displayed marked seasonal variations, the values increasing during the warmer months of April and May when planktic foraminiferal fluxes declined. The variation in fluxes of calcium carbonate, organic carbon and biogenic opal show positive correlations with fluxes of pteropods and planktic foraminifers. Calcium carbonate was the main contributor to the total particulate flux, especially during the SW monsoon. In the study area, pteropod flux variations are similar to the other flux patterns, indicating that they, too could be used as a potential tool for palaeoclimatic reconstruction of the recent past.     

Regional and seasonal variations of recent benthic deep-sea foraminifera in the Arabian Sea

Assemblages of living deep-sea benthic foraminifera, their densities, vertical distribution pattern, and diversity, were investigated in the intermonsoon period after the northeast monsoon in the Arabian Sea in spring 1997. Foraminiferal numbers show a distinct gradient from north to south, with a maximum of 623 foraminifera in 50 cm³ at the northern site. High percentages of small foraminifera were found in the western and northern part of the Arabian Sea. Most stations show a typical vertical distribution with a maximum in the first centimeter and decreasing numbers with increasing sediment depths. But at the central station, high densities can be found even in deeper sediment layers. Diversity is very high at the northern and western sites, but reduced at the central and southern stations. Data and faunal assemblages were compared with studies carried out in 1995. A principal component analysis of intermonsoon assemblages shows that the living benthic foraminifera can be characterized by five principal component communities. Dominant communities influencing each site differ strongly between the two years. In spring 1997, stations in the north, west and central Arabian Sea were dominated by opportunistic species, indicating the influence of fresh sedimentation pulses or enhanced organic carbon fluxes after the northeast monsoon.     

Seasonal and spatial variability in N2O distribution in the Arabian Sea

Extensive measurements of nitrous oxide (N₂O) were made in the central and eastern Arabian Sea during the northeast monsoon (February–March), intermonsoon (April–May) and southwest monsoon (July–August) seasons. The latitudinal and longitudinal variations, along with seasonal changes with respect to winter convection and coastal upwelling, are clearly discernible. Vertical profiles collected down to 1000 m show that the Arabian Sea water column is supersaturated with N₂O at all depths. However, N₂O consumption at intermediate depths, coincident with the oxygen minimum and associated with sediment–water interfaces, and in the denitrifying zone, coincident with NO^-₂ secondary maxima, are also apparent. The N₂O concentration varies from ∼10 nM near the surface to about 80 nM in the secondary peak region (≈800 m). Interrelationships with chemical parameters suggest nitrification to be the main process for the production of N₂O in the oceanic water. Plots of apparent oxygen utilization vs production of N₂O indicate a consistent linear relationship for AOU between 0 and 200 μM.     

Seasonal and annual variability of vertically migrating scattering layers in the northern Arabian Sea

A 30-month time series of mean volume backscattering strength (MVBS) data obtained from moored acoustic Doppler current profilers (ADCPs) is used to analyze the evolution of vertically migrating scattering layers and their seasonal and annual variability in the Arabian and Oman Seas. Substantial diel vertical migration (DVM) is observed almost every day at all three mooring sites. Two daytime layers (Layers D1 and D2) and one nighttime layer (Layer E1) are typically present. The greatest biomass is observed near the surface during the night in Layer E1 and at depth between 250 and 450 m during the daytime in Layer D2. All layers are deepest during the spring inter-monsoon and shallowest during the summer/fall southwest monsoon (SWM). Seasonal modulation of the D2 biomass change is evident in our high-resolution data. The lowest biomass in D2 is measured in the early summer (May or June) followed by a rapid biomass increase during the SWM (June–November) until the biomass reaches a maximum at the end of the SWM season. Short-period oscillations in D2 biomass are often seen with periods ranging from days to one month. Occasionally, a lower nighttime layer E2 is formed between 180 and 270 m, mostly near the time of full moons. The upper daytime layer D1 is centered at 200 m and densely concentrated. It is only formed during the winter northeast monsoon (NEM) and the spring inter-monsoon. The influence of physical processes on layer distribution is also investigated. Interestingly, the two daytime layers are found to be formed at the two boundaries of the Persian Gulf outflow water (PGW) and follow the seasonal depth change of the PGW. The timing of the DVM and the formation, persistence, decay and reformation of the deep scattering layers seem to be governed by light, both solar and lunar. The scattering strength, the layer depth and the layer thickness are likewise closely related to the Moon phase at night. Cloud coverage, the isotherm and the isohaline also appear to affect the distribution and depth of the scattering layers. The continuous multiple-year acoustic data from ADCPs allow us, for the first time, to study the seasonal and annual variations of scattering layers in this region.     

Seasonal variations of the ocean surface circulation in the vicinity of Palau

The surface circulation in the western equatorial Pacific Ocean is investigated with the aim of describing intra-annual variations near Palau (134°30′ E, 7°30′ N). In situ data and model output from the Ocean Surface Currents Analysis—Real-time, TRIangle Trans-Ocean buoy Network, Naval Research Laboratory Layered Ocean Model and the Joint Archive for Shipboard ADCP are examined and compared. Known major currents and eddies of the western equatorial Pacific are observed and discussed, and previously undocumented features are identified and named (Palau Eddy, Caroline Eddy, Micronesian Eddy). The circulation at Palau follows a seasonal variation aligned with that of the Asian monsoon (December–April; July–October) and is driven by the major circulation features. From December to April, currents around Palau are generally directed northward with speeds of approximately 20 cm/s, influenced by the North Equatorial Counter-Current and the Mindanao Eddy. The current direction turns slightly clockwise through this boreal winter period, due to the northern migration of the Mindanao Eddy. During April–May, the current west of Palau is reduced to 15 cm/s as the Mindanao Eddy weakens. East of Palau, a cyclonic eddy (Palau Eddy) forms producing southward flow of around 25 cm/s. The flow during the period July to September is disordered with no influence from major circulation features. The current is generally northward west of Palau and southward to the east, each with speeds on the order of 5 cm/s. During October, as the Palau Eddy reforms, the southward current to the east of Palau increases to 15 cm/s. During November, the circulation transitions to the north-directed winter regime.     

Seasonal fields of tangenital wind stress over the Black Sea

Tangential wind stress fields with a 40×60 spatial step are calculated from the data on atmospheric pressure distribution over the Black Sea over a decade. Their space-time variability is studied. It is shown that maximum values of the tangential wind stress in all seasons are located in the areas southwest of the Crimea and south of the Taman Peninsula. The tangenital wind stress retrieved from wind measurements is compared with the one determined from the atmospheric pressure data.Translated by V. Puchkin.     

中国近海海面高度异常资料再处理

卫星海面高度异常产品再处理的研究多集中在欧洲和美国近海,中国近海尚未有过。在产生AVISO(Archiving Validation and Interpolation of Satellite Oceanographic Data)全球0.25°多颗卫星海面高度异常产品时,只用了1/3~1/2的部分沿轨资料,给区域海洋动力学研究造成了一定的限制。本研究尝试利用多颗卫星的所有沿轨资料及25个测潮站的观测资料,通过最优插值方法产生一份新的中国近海海面高度异常资料。新资料的空间分辨率仍为0.25°,但使用了来自3颗卫星(Jason-1、Jason-2、Cryo Sat-2)的所有沿轨资料及25个测潮站的观测资料。新资料的范围为10°S~50°N、90°~160°E。新资料与AVISO资料的对比分析表明新资料更接近沿轨海面高度异常观测,同时也更接近测潮站资料。与AVISO资料相比,新资料与沿轨海面高度异常观测的均方根误差降低了10.03%,与测潮站资料的均方根误差降低了9.6%。     

渤、黄海颗粒有机碳空间分布及交换通量的季节性变化

海洋是地球上最大的碳库,对大气中的CO2起着调控作用,在减缓全球变暖过程中起着重要作用。渤、黄海是典型的封闭-半封闭型陆架海,深入探讨渤、黄海颗粒有机碳（POC）变化特征和输运通量,对区域碳循环和海洋碳通量研究具有重要意义。通过2010年春秋两季、2016年夏季和2012年冬季渤、黄海的大面积实测数据,结合MODIS卫星遥感影像反演的叶绿素a（Chl-a）,探讨了渤、黄海POC空间分布、影响因素、碳库及交换通量的季节性差异。结果表明：春季POC浓度最高,平均浓度0.34 mg/L;夏季次之,平均浓度0.30 mg/L;秋季平均浓度0.27 mg/L;冬季最低,平均浓度0.17 mg/L。不同季节POC空间分布基本一致,整体呈现“近岸高、离岸低,表层低、底层高”的特点,高值区主要位于黄河三角洲、山东半岛东侧和苏北浅滩-长江口北附近水域,低值区主要集中在南黄海中部深水区。不同季节影响POC分布的因素不同,春、秋两季受径流输入、沉积物再悬浮和浮游植物共同影响,夏季主要受控于浮游植物初级生产,沉积物再悬浮是影响冬季POC分布的主要原因。渤、黄海POC碳库呈明显的季节性变化,春季碳库最高,渤海与黄海分别为1.32×106 t和6.71×106 t;冬季碳库最低,渤海与黄海分别为7.21×105 t和3.39×106 t。约有6.55×105 t/a POC通过渤海海峡由渤海进入黄海,POC输运主要集中在夏季。     

Seasonal and interannual variations in the velocity field of the South China Sea

A three-dimensional numerical model is used to simulate sea level and velocity variations in the South China Sea for 1992–1995. The model is driven by daily wind and daily sea surface temperature fields derived from the NCEP/NCAR 40-year reanalysis project. The four-year model outputs are analyzed using time-domain Empirical Orthogonal Functions (EOF). Spatial and temporal variations of the first two modes from the simulation compare favorably with those derived from satellite altimetry. Mode 1, which is associated with a southern gyre, shows symmetric seasonal reversal. Mode 2, which contributes to a northern gyre, is responsible for the asymmetric seasonal and interannual variations. In winter, the southern and northern cyclonic gyres combine into a strong basin-wide cyclonic gyre. In summer, a cyclonic northern gyre and an anticyclonic southern gyre form a dipole with a jet leaving the coast of Vietnam. Interannual variations are particularly noticeable during El Niño. The winter gyre is generally weakened and confined to the southern basin, and the summer dipole structure does not form. Vertical motions weaken accordingly with the basin-wide circulation. Variations of the wind stress curl in the first two EOF modes coincide with those of the model-derived sea level and horizontal velocities. The mode 1 wind stress curl, significant in the southern basin, coincides with the reversal of the southern gyre. The mode 2 curl, large in the central basin, is responsible for the asymmetry in the winter and summer gyres. Lack of the mode 2 contribution during El Niño events weakens the circulation. The agreement indicates that changes in the wind stress curl contribute to the seasonal and interannual variations in the South China Sea.     

Sea level variations in the regional seas around Taiwan

The patterns and trends of sea level rise in the regional seas around Taiwan have been investigated through the analyses of long-term tide-gauge and satellite altimetry data. Series of tide-gauge data extending over 50 years reveal decadal and interannual variations and spatially-inhomogeneous patterns of generally rising sea level. The East Asia tide-gauge stations around Taiwan show an average trend of +2.4 mm/yr from 1961–2003, which is larger than the reported global rate of +1.8 mm/yr for the same period. These stations also show significantly larger sea level rise rates (+5.7 mm/yr) than global values (+3.1 mm/yr) during the period from 1993–2003. Consistent with the coastal tide-gauge records, satellite altimetry data show similar increasing rates (+5.3 mm/yr) around Taiwan during the same period. Comparisons with temperature anomalies in the upper ocean suggest that thermal expansion and heat advection in the upper layer contribute significantly to the long-term sea level variations in this area with correlations >0.9 for observations after 1992. Thermosteric sea level variations may also explain the interannual and decadal variations of the observed sea level rises around Taiwan. Our analysis also indicates that the altimetry data are only part of a long-term, larger-scale signal. Finally, we have found that a non-linear smoother, LOESS, is more suitable for extracting long-term trends in sea level than the traditional linear regression approach.     

东海和黄海二甲基亚砜（DMSO）的季节和空间变化

Seasonal and spatial distributions of dissolved and particulate dimethylsulfoxide(DMSOd,DMSOp)were measured in the East China Sea and the Yellow Sea during March–April 2011 and October–November 2011.The concentrations of DMSOd and DMSOp in the surface water were 20.6(5.13–73.8)and 8.90(3.75–29.6)nmol/L in spring,and 13.4(4.17–42.7)and 8.18(3.44–22.6)nmol/L in autumn,respectively.Both DMSOd and DMSOp concentrations revealed similar seasonal changes with higher values occurring in spring,mainly because of the higher phytoplankton biomass observed in spring.Moreover,the ratios of DMSOp/chlorophyll a also exhibited an apparent seasonal change with higher values in autumn(35.7 mmol/g)and lower values in spring(23.4 mmol/g),thereby corresponding with the seasonal variation in the proportion of DMSO producers in the phytoplankton community between spring and autumn.In addition,DMSOd and DMSOp concentrations in the surface seawater revealed obvious diurnal variations with the maxima appearing in the afternoon.     

南海混合层深度的季节和年际变化特征

利用1871-2008年SODA资料和月平均的Levitus资料计算了南海混合层深度(MLD)的季节及年际变化特征.资料分析表明:季风通过流场调整对南海MLD的时空分布特征有显著的影响.南海MLD的距平变化总体上呈上升趋势,南海南部MLD的距平变化趋势和北部的有显著差异,特别在1955年后北部整体呈下降趋势而南部呈上升趋势,二者的显著周期北部为2-3年,南部与整个区域平均的基本相似有2-6年的显著周期.SOI指数对滞后的南海各个区域有较好的相关性.EOF分析表明第一模态整体呈单极型最大变率分布在南海南部,由南往北逐渐减小显著周期2-3年变化为主;第二模态呈偶极子型,显著周期以2-5年变化为主.回归分析表明南海南部深水区域呈现增深的趋势,而吕宋海峡至南海北部陆架区呈变浅趋势,滑动t检验表明南海MLD有6个显著的突变年份.