Ocean Model Simulation of Southern Indian Ocean Surface Currents

The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N–60°S and 30°E–120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.     

Ocean Model Simulation of Southern Indian Ocean Surface Currents

The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N-60°S and 30°E-120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.     

Bio-Optical Relationship of Case I Waters: The Difference between the Low- and Mid-Latitude Waters and the Southern Ocean

Both historic and currently operational chlorophyll algorithms of the satellite-borne ocean color sensors, such as SeaWiFS, were evaluated for in situ spectral radiation and chlorophyll data in some Case I waters, including the waters in the Indian Ocean sector of the Southern Ocean. Chlorophyll a concentration of the data set (n = 73) ranged from 0.04 to 1.01 mg m^–3. The algorithms had higher accuracy for the low- and mid-latitude waters (RMSE: 0.163–0.253), specifically the most recently developed algorithms of OCTS and Sea WiFS showed 0.163 and 0.170 of Root Mean Square Errors, respectively. However, these algorithms had large errors (0.422–0.621) for the Southern Ocean data set and underestimated the surface chlorophyll by more than a factor of 2.6. The absorption coefficients in the blue spectral region retrieved from remote sensing reflectance varied in a nonlinear manner with chlorophyll a concentration, and the value in the Southern Ocean was significantly lower than that in the low- and mid-latitude waters for each chlorophyll a concentration. The underestimation of chlorophyll a concentration in the Southern Ocean with these algorithms was caused by the lower specific absorption coefficient in the region compared with the low- and mid-latitude waters under the same chlorophyll a concentration.     

南大洋环流动力学研究动态

本文基于南大洋环流研究最新资料，从资料来源、动力模式以及有待解决的问题几个方面较详细地阐述南大洋环流动力学研究动态。     

5000 aBP南部大洋南大西洋区南极表层水温急剧下降和浮冰扩张

我们根据南部大洋大西洋区南纬 53°活塞岩心分析结果重建南大西洋全新世南极表层水变化史。此岩心沉积速率较高 (全新世平均值为50 cm/ 1 0 3a) ,且位于亚南极的南大西洋 ,适用于古气候研究。钻位位于现代极地前缘带( PFZ)以南约 3°,冬季海冰边界以北约 2°。利用硅藻转换函数、硅藻内有机质的碳和氮同位素、粗粒沉积物 ( >1 50 μm～ 2 mm)中放射虫、有孔虫和浮冰碎屑相对丰度 ,对硅藻和有孔虫的氧同位素、二月表层海水和海冰盖层温度进行了测定 ,提供了 50 0 0 a BP表层水特征急剧变化的证据。1 0 0 0 0～ 550 0 a BP粗粒沉积物 ( >1…     

Accumulation and Export of Dissolved Organic Carbon in Surface Waters of Subtropical and Tropical Pacific Ocean

Dissolved organic carbon (DOC) concentrations in surface waters of the Pacific Ocean during October–November, 1995, were determined using a high-temperature combustion method. The DOC in the surface mixed-layer was approximately homogeneous with a concentration between 55 and 89 μmol C l⁻¹. This homogeneity indicates that there is a strong control of the vertical distribution of DOC by mixing processes. The DOC concentrations in the mixed-layer in the subtropical region were up to 27 μmol C l⁻¹ higher than in the tropical region. This difference reflects the subtropical accumulation and the tropical export of DOC. There is a significant positive correlation between DOC and chlorophyll a concentrations in the mixed-layer of the North Pacific subtropical region, suggesting that phytoplankton is the primary source of DOC accumulated in this region. Calculations using simple box models suggest that DOC export in the tropical region (0–50 m depth, 10°N-10°S, along 160°W) occurs primarily by poleward advection at a rate of 0.5–3 mmol C m⁻²day⁻¹. A comparison with estimates of the export rate of particulate organic carbon published in previous studies leads us to conclude that DOC export may contribute less to the carbon budget in the tropical region than has recently been supposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Biosiliceous particle flux in the Southern Ocean

The flux of diatom valves and radiolarian shells obtained during short-term and annual sediment trap experiments at seven localities in the Atlantic sector of the Antarctic Ocean (in the Drake Passage, Bransfield Strait, Powell Basin, NW and SE Weddell Sea and the Polar Front north of Bouvet Island) is summarized and discussed. The deployment of time-series sediment traps provided annual flux records between 1983 and 1990. The biosiliceous particle flux is characterized by significant seasonal and interannual variations. Flux pulses, accounting for 70–95% of the total annual flux, occur during austral summer, with a duration ranging between about 2 and 9 weeks. The annual values of vertical diatom and radiolarian flux range between 0.26 × 10⁹ and more than 26 × 10⁹ valves m⁻² and between 0.21 × 10⁴ and 70 × 10⁴ shells m⁻², respectively. Interannual differences in the particle flux range over a factor of 10. Grazers play an important role in controlling the quantity, timing and pattern of the vertical biosiliceous particle flux.The flux pattern of diatoms and radiolarians is similar at most of the sites investigated and shows a close relationship between the production of siliceous phytoplankton and proto-zooplankton. At some sites, however, the radiolarian flux pattern indicates probably phytoplankton production which is not documented by direct signals in the trap record.During their transfer through the water column to the ocean floor, the composition of the biosiliceous particles is altered mechanically (breakdown by grazing Zooplankton) and by dissolution, which significantly affects especially diatoms and phaeodarians in the upper portion of the water column and at the sediment-water interface.Significant lateral transport of suspended biosiliceous particles was observed in the bottom water layer in regions adjacent to shelf areas (Bransfield Strait), and in the vicinity of topographic elevations (Maud Rise), indicating considerable redistribution of biogenic silica in these regions.     

Dynamics of a Wave Packet on the Surface of an Inhomogeneously Vortical Fluid (Lagrangian Description)

A nonlinear Schrödinger equation (NSE) describing packets of weakly nonlinear waves in an inhomogeneously vortical infinitely deep fluid has been derived. The vorticity is assumed to be an arbitrary function of Lagrangian coordinates and quadratic in the small parameter proportional to the wave steepness. It is shown that the modulational instability criteria for the weakly vortical waves and potential Stokes waves on deep water coincide. The effect of vorticity manifests itself in a shift of the wavenumber of high-frequency filling. A special case of Gerstner waves with a zero coefficient at the nonlinear term in the NSE is noted.     

大洋在冰川动力学中的作用

加拿大数学模拟专家与美国冰川学家以及加拿大地球物理学家共同得出了结论：约14700年前,由南极冰川区进入南大洋海区的融化水巨浪,成为最近25ka来地球上最大的气候剧变的原因。     

Chlorophyll a Biomass of Netplankton in Surface Waters of the Northern North Pacific Ocean and the Adjacent Seas from Summer to Autumn

Chlorophyll a concentrations of net (retained on 30 m mesh net) and total plankton in surface waters were determined along cruise tracks in an area of the northern North Pacific Ocean and the adjacent Bering Sea and the Gulf of Alaska from summer to autumn. Total chlorophyll a concentrations were high with a great areal and temporal variations in the western northern North Pacific compared to the eastern part. Chlorophyll a concentrations of netplankton varied from 0.001 to 0.230 g chl a l^–1 (average, 0.029 ± 0.040 g chl a l^–1), and showed a positive relation but a weak regression coefficient (r ² = 0.551) against the "average total chlorophyll a" (average of total chlorophyll a at the beginning and at the end during sampling of netplankton). However there were several data points showing high "average total chlorophyll a" but low netplankton and vice versa. Average percentage share of netplankton in the total chlorophyll a was estimated to be as large as 4.26%.     

Hydrocarbon gas in sediment of the Southern Pacific Ocean

Methane, ethane, ethene, propane, and propene are common hydrocarbon gases in near-surface sediment from offshore areas in the southern Pacific Ocean near Papua New Guinea, the Solomon Islands, Vanuatu, Tonga, New Zealand, and Antarctica. Sea floor sites for sampling of sediment were selected on the basis of anomalies in marine seismic records, and the samples were intentionally biased toward finding possible thermogenic hydrocarbon gases. In none of the areas, however, were thermogenic hydrocarbons clearly identified. The hydrocarbon gases that were found appear to be mainly the products ofin situ microbial processes.     

山东南部近海秋季长蛇鲻相对资源量的分布及其影响因素

为探究长蛇鲻(Saurida elongate)的生态习性和分布规律,并为长蛇鲻资源的合理利用与养护提供科学依据,本文根据2016年秋季在山东南部近海进行的渔业资源与环境调查数据,分析了该海域长蛇鲻的分布特征,研究长蛇鲻成体、幼体的分布差异,并利用广义可加模型(GAM)研究其分布与生物因子和环境因子的关系。结果表明,长蛇鲻成体与幼体的分布存在差异,成体分布范围广,幼体主要分布在30 m等深线及以浅水域。GAM模型的结果表明,饵料生物、底层水温、水深和底层盐度是影响长蛇鲻相对资源量分布的主要因子。成体、幼体的分布与影响因子的关系差异极显著(P<0.01)。长蛇鲻成体的相对资源量随饵料生物和底层水温的增加表现为先上升后下降的趋势,而幼体呈现一致上升趋势;成体和幼体的相对资源量随水深增加均呈下降趋势;幼体相对资源量随底层盐度增加有明显上升趋势,而盐度对成体的影响不显著。本研究认为山东南部近海是长蛇鲻的重要栖息地,水温和盐度是成体和幼体分布差异的可能原因。     

Energy of the Jets of the Antarctic Circumpolar Current and of Their Eddies in the Surface Layer of the Southern Ocean

Oceanology - The kinetic energy of six jets of the Antarctic Circumpolar Current (ACC) and of the cyclonic and anticyclonic mesoscale eddies generated by these jets is studied in application to the...     

Surface drift in the South-East Atlantic Ocean

Surface drift in the South-East Atlantic Ocean is described using historical shipdrift data. The Benguela Current has a width of 200 km in the south and 750 km in the north. The mean speeds of the current vary from <11 cm·s^?1 to a maximum of 23 cm·s^?1 The highest current speeds occur during summer in the southern regions and during winter in the northern regions, and this seasonality corresponds well with seasonal wind speeds. Eddy kinetic energy is enhanced in the Subtropical Convergence zone and is highest in the general vicinity of the Agulhas Current retroflection. The Subtropical Convergence is evident as a line where northward Ekman drift terminates.     

长江口南部水域次级羽状锋

1994年11月24-25日（枯季）,在长江口南部水域内,对2个定点,2个段面（24个站位）进行了水流流速,盐度及悬沙浓度观测,而后,分别绘制出：（1）水流流速、盐度和悬沙浓度沿水深,时间变化过程组;（2）各层水流流速、流向随时间变化过程图。结果表明：1）实测水流流速、盐度及悬沙浓度垂向,水平分布具不连续性,表明了次级羽状锋的存在;2）在枯季,相对于径流、波浪而言,外海潮流对长江口次级羽状锋的影响占主导作用;3）次级羽状锋可能使得悬沙在南汇东滩附近大量淤积;4）次级羽状锋在长江口与杭州湾之间的水沙交换中起着一定作用。     

Geostrophic Circulation of Waters in the South Atlantic Ocean and Its Seasonal Variability

Based on an analysis of the monthly average diagrams of dynamic topography, we reveal some specific features of the geostrophic circulation of waters in the South Atlantic Ocean. We present an improved picture of the structure and annual variability of the climatic large-scale circulations. They are compared with similar climatic cells of the large-scale circulation of waters in the north part of the ocean. Quantitative estimates of the characteristics of seasonal oscillations of the field of dynamic heights are obtained.     

Detection of Intermediate Mediterranean Waters in the Atlantic Ocean by ARGO Floats Data

Peculiarities of the spatial distribution of intermediate Mediterranean waters (MW), which are the main source to maintain the heat and salt budgets at depths of 600–1500 m in the Atlantic Ocean, have been studied using the ARGO floats measurements database. About 75000 temperature and salinity profiles recorded by 900 ARGO floats in 2005–2014 in the Atlantic Ocean for latitudes from 20° to 50° N were used. To process these data, we used the ARGO-Based Model for Investigation of the Global Ocean (AMIGO). This technique allowed us for the first time to obtain a complete set of oceanographic characteristics up to a depth of 2000 m for different time averaging intervals (month, season, years). Joint analysis of the temperature, salinity, and velocity distributions at 700–1000 m depths made it possible to revise the distribution of MW and their penetration into the western part of the ocean across the Mid-Atlantic Ridge (MAR). It is shown that at depths of 700 and 1000 m, the Mid-Atlantic Ridge is a barrier to advective propagation of salty waters (>35.5 PSU) to the west and is transparent to fragments of destroyed intrathermocline lenses (ITL) with lower salinity (<35.4 PSU). In the Atlantic region, from 20° to 35° N and from 30° to 70° W, individual lens profiles with an anomalous salinity distribution were sought using ARGO measurements to detect ITL and its separate fragments. About 24 000 measurements from 370 ARGO floats were analyzed, and only about 3% of them showed weak salinity anomalies at 800–1200 m depths. No ITL were found from these observations. Analysis of long-term drifting of individual floats recording temperature and salinity profiles with anomalous layers made it possible to study the nature of MW transport through the MAR.     

A Comparison of Sea Surface Fluxes over Southern Indian Ocean Cruise Expedition Observation and NCEP Reanalysis

Surface layer atmospheric and ocean observations have been collected along the cruise track from a special scientific expedition to Antarctica. Bulk estimates of surface momentum flux, sensible heat flux and latent heat flux have been computed applying bulk algorithms from the data collected along cruise track during the time period January 27 to March 31, 2006, and compared the results with National Centre for Environmental Prediction (NCEP) reanalysis. Underestimation of surface momentum flux in roaring forties (40°S–50°S) area of Indian Ocean is seen from NCEP reanalysis. Systemic differences in sensible and latent heat fluxes between observed and NCEP reanalysis have been found. Along the cruise track, the average sensible (latent) heat flux was 9.45 Wm^?2 (67.46 Wm^?2) and 3.75 Wm^?2 (64.45 Wm^?2) from the direct measurement and NCEP reanalysis, respectively. The NCEP reanalysis is being widely used in numerical modeling studies, and the discrepancies shown in the NCEP reanalysis in present study will be of immense use to the modeling community of the Indian Ocean in general and Southern Indian Ocean in particular.