Variability of the North Pacific Current and its bifurcation

The North Pacific Current (NPC) bifurcates approaching the west coast of North America into a subpolar branch that forms the Alaska Current, and a subtropical branch that includes the California Current. The variability of this current system is discussed using numerical results from a wind-driven, reduced-gravity model. Indices of the strength of the subpolar and subtropical components of the NPC are examined based on output from multi-decadal simulations with the numerical model. This shows periods of both correlated and anti-correlated variability of the subpolar and subtropical gyres. A decomposition of the gyre transport time series indicates that the dominant mode of variability is a “breathing” mode in which the subpolar and subtropical gyres co-vary in response to fluctuations in the strength of the NPC. This finding is consistent with an analysis of dynamic height data of limited duration from the array of Argo drifting floats.The variability of the NPC is also examined using sea surface height (SSH) data from satellite altimetry over the period 1993-2005. The leading mode of SSH over the northeast Pacific dominates the variability of the NPC and is shown to be associated with in-phase variations in the transport of the subtropical and subpolar gyres. A strong correlation is found between time-dependent fluctuations in SSH across the NPC and variations in the strength of the transport of the NPC in the model. This agreement provides evidence for variability of the NPC occuring in direct response to large-scale atmospheric forcing.     

Suspended matter transport in coral reef waters of the Abrolhos Bank, Brazil

The coral reef system of the Abrolhos Bank, Brazil, is located between 10 and 65 km off the coast. Suspended particulate matter between the coast and the inner arc of the reef was mainly composed of kaolinite clay and reworked fossil carbonate fragments, resuspended from nearshore shoals. Strong permanent and tidal alongshore currents in the nearshore channel together with the geomorphological configuration of the inner arc formed an efficient hydrodynamic and topographic barrier to offshore transport of land-derived material. Most of the material was being transported alongshore. Suspended particulate matter between the inner and outer arcs was dominated by carbonate shells, coral fragments, and needle-shaped biogenic opal, and the reef system was in large part being dominated by the oligotrophic waters of the Brazil Current.     

North Brazil current: vertical structure

On the basis of the data ofin situ measurements of the velocities of currents and basic hydrophysical parameters (such as temperature and salinity) carried out during Cruise 41 of the R/VAkademik Vernadsky, we analyze the structure of the North Brazil Current near the continental slope and in the equatorial abyssal part of the ocean in winter, establish the regularities of changes in the current velocity with depth, and compare the structures of the North Brazil and Guiana Currents. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Modulation of the inflow into the Caribbean Sea by North Brazil Current rings

A two-year long record from a triangular mooring array between the Lesser Antilles islands Tobago, Barbados, and St. Lucia is used to investigate the inflow into the Caribbean Sea, the amount of South Atlantic Water (SAW) carried with the inflow, and the role of North Brazil Current (NBC) rings in the observed variability. The data set consists of time series from temperature/conductivity recorders and current meters in the moorings, bottom-mounted inverted echo sounders at the Tobago and St. Lucia mooring positions, and supplementary shipboard measurements. The acoustic travel time measurements of the inverted echo sounders and the conductivity/temperature time series are used for continuous estimation of dynamic height profiles and geostrophic currents between the surface and 1000 dbar as well as the amount of SAW found at the mooring positions.The observations show a domination of intraseasonal variability between 0 and 15 Sv, superimposed on the long-term fluctuations. With time scales of one to three months, these represent the signature of the NBC rings. The baroclinic transport time series shows nine periods of increased variability, indicative of the rings interacting with the Lesser Antilles island arc; with the exception of one, these periods were associated with corresponding sea surface height anomalies. No marked seasonality was observed in the transport variability or the ring frequency.The arrival of individual rings leads to a weakening of the inflow into the Caribbean. Nevertheless, the rings carry large amounts of SAW into the area, and the immediate increase of the transport towards the end of a ring event suggests a subsequent flow of this SAW-rich water into the Caribbean. At St. Lucia, rings sometimes cause a short-term decrease of SAW content, indicative of an influx of northern hemispheric water and a blocking situation. The average transport of SAW into the Caribbean south of St. Lucia during the observations amounted to 5.5 Sv, with no significant seasonal cycle, but a small positive trend in SAW fraction as well as in transport of about 15% and 1 Sv, respectively; a corresponding trend in the baroclinic volume transport was not observed.     

Decadal variations of the transport and bifurcation of the Pacific North Equatorial Current

Decadal variations of the transport and bifurcation latitude of the North Equatorial Current (NEC) in the northwestern tropical Pacific Ocean over 1959–2011 are investigated using outputs of the Ocean Analysis/Reanalysis System 3 prepared by the European Centre for Medium-Range Weather Forecasts. The results indicate that the NEC transports at different longitudes have different decadal fluctuations, which are strongest around 139°E. The NEC bifurcation latitude (NBL) has its largest decadal variations around 150 m. Extremes of the decadal NEC transport and NBL before 1975 correspond to different circulation anomalies from those after 1975. The regression map against decadal NBL exhibits negative sea surface height (SSH) anomalies and a cyclonic gyre anomaly over the northwestern tropical Pacific Ocean, while that against the decadal NEC transport exhibits a dipole structure, with positive/negative SSH anomalies to the north/south of about 13°N. Furthermore, decadal variations of the NEC transport and NBL over the whole period have different correlations with Pacific Decadal Oscillation (PDO) and Tropical Pacific Decadal Variability (TPDV). Generally, the decadal NEC transport shows higher correlations with PDO than with TPDV, while the NBL has higher correlations with TPDV than with PDO. The high correlation of decadal NEC transport with PDO mainly comes from that of its northern branch with PDO, while its southern branch shows higher correlation with TPDV.     

Suspended sediment transport in surface waters of the California Current off southern California: 1977–78 floods

Floods in southern California during the rainy season of 1977–78 followed four years of severe drought when vegetative cover of drainage areas was at a minimum. LANDSAT Band 5 analyses following these floods suggest extensive transport of suspended sediment to 80 to 100 km from the coastline. Current patterns can be explained by a decaying Davidson Current situation and a large semipermanent cyclonic gyre that controls distribution of surface suspended sediment throughout the California Borderland. This gyre, and associated spinoff eddies, produce three distinct cells of suspended sediment in surface waters. These cells may control sedimentation patterns of terrigenous silt and clay.     

Absolutely referenced geostrophic velocity and transport on a section across the North Atlantic Current

A transect of CTD profiles crossing the North Atlantic Current (NAC) along WOCE line ACM6 near 42.5°N during August 1–7, 1993, provides geostrophic shear velocity profiles, which were absolutely referenced using simultaneous POGO transport float measurements and velocity measurements from a ship-mounted acoustic doppler current profiler (ADCP). The NAC absolute transport was 112±23×10⁶ m³ s⁻¹, which includes a portion of the transport of the Mann Eddy, a large permanent anticyclonic eddy commonly adjacent to the NAC. The NAC transport estimated relative to a level of no motion at the bottom would have underestimated the true total absolute transport by 20%. A surprisingly large 58×10⁶ m³ s⁻¹ flowed southward just inshore of the NAC. This flow, centered near 1500 dbars about 200 km offshore of the shelf-break, was fairly barotropic with a peak velocity of greater than 20 cm s⁻¹, and the water mass characteristics were of Labrador Sea Water. These absolute transport observations suggest southward recirculation inshore of the NAC at 42.5°N and a stronger NAC than has previously been observed.     

Analysis of horizontal and vertical ring structure based on analytical model and satellite data: Application to the North Brazil Current Rings

A theoretical analysis of the principal oceanic ring parameters (tangential and angular velocities, shape function, horizontal and vertical scale of the ring) is described. The theoretical model consists of a reduced gravity model of the lens-like vortices with solid body rotation. The application of this approach is tested by comparison with data from the North Brazil Current Rings Experiment and remote sensing data. Specifically, we used the data corresponding to the surfaceintensified North Brazil Current ring (R-3) surveyed in February–March 1999, using direct velocity and hydrographical measurements. The theoretical model was used for evaluating the geometrical structure of the surface-intensified rings that produce remarkable signals in satellite data. The principal ring parameters from the model were compared with those from satellite data (altimetry and drifter information), which were estimated by using the method of minimization of the multivariable objective functions. Although the proposed model is linear in its conception, a good agreement was observed between the model and the primary characteristics of the observed rings. The model, however, allows for improvement in its assumptions, since its application is rather limited to intense ocean rings.     

Copper, lead and cadmium in coastal waters of the western North Sea

Cadmium, lead and copper have been determined in both dissolved and particulate phases for 130 surface-water samples from the coastal zone of Scotland and England in the western North Sea. The concentrations reported are, in general, lower than those published previously for the same area.The distribution of total metal concentration between the dissolved and particulate phases varies for the three elements. The lead distribution is dominated by its associations with particulate material while cadmium shows the reverse behaviour, existing almost totally in the dissolved phase. Copper is intermediate in behaviour, with the dissolved phase generally being dominant.An inverse relationship between salinity and dissolved copper concentration suggests a freshwater origin for this element. It is suggested that sedimentary and/or anthropogenic sources affect dissolved copper concentrations in coastal waters. The dissolved lead distribution reveals plumes of contaminated coastal water. The lead distribution is, however, dominated by associations with particulate material and sediments which produce a sharp concentration gradient close to the coast. The Humber estuary is identified as a significant source of cadmium to the North Sea.     

Characterizing Observed Environmental Variability With HF Doppler Radar Surface Current Mappers and Acoustic Doppler Current Profilers: Environmental Variability in the Coastal Ocean

A network of high-frequency (HF) radars is deployed along the New Jersey coast providing synoptic current maps across the entire shelf. These data serve a variety of user groups from scientific research to Coast Guard search and rescue. In addition, model forecasts have been shown to improve with surface current assimilation. In all applications, there is a need for better definitions and assessment of the measurement uncertainty. During a summer coastal predictive skill experiment in 2001, an array of in situ current profilers was deployed near two HF radar sites, one long-range and one standard-range system. Comparison statistics were calculated between different vertical bins on the same current profiler, between different current profilers, and between the current profilers and the different HF radars. The velocity difference in the vertical and horizontal directions were then characterized using the observed root-mean-square (rms) differences. We further focused on two cases, one with relatively high vertical variability, and the second with relatively low vertical variability. Observed differences between the top bin of the current profiler and the HF radar were influenced by both system accuracy and the environment. Using the in situ current profilers, the environmental variability over scales based on the HF radar sampling was quantified. HF radar comparisons with the current profilers were on the same order as the observed environmental difference over the same scales, indicating that the environment has a significant influence on the observed differences. Velocity variability in the vertical and horizontal directions both contribute to these differences. When the potential effects of the vertical variability could be minimized, the remaining difference between the current profiler and the HF radar was similar to the measured horizontal velocity difference (~2.5 cm/s) and below the resolution of the raw radial data at the time of the deployment     

Isotopic,trace element and nutrient characterization of coastal waters from Ubatuba inner shelf area,south-eastern Brazil

Stable isotopes, tritium, radium isotopes, radon, trace elements and nutrients data were collected during two sampling campaigns in the Ubatuba coastal area (south-eastern Brazil) with the aim of investigating submarine groundwater discharge (SGD) in the region. The isotopic composition (δD, δ¹⁸O, ³H) of submarine waters was characterised by significant variability and heavy isotope enrichment. The stable isotopes and tritium data showed good separation of groundwater and seawater groups. The contribution of groundwater in submarine waters varied from a few % to 17%. Spatial distribution of ²²²Rn activity concentration in surface seawater revealed changes between 50 and 200 Bq m⁻³ which were in opposite relationship with observed salinities. Time series measurements of ²²²Rn activity concentration in Flamengo Bay (from 1 to 5 kBq m⁻³), obtained by in situ underwater gamma-spectrometry showed a negative correlation between the ²²²Rn activity concentration and tide/salinity. This may be caused by sea level changes as tide effects induce variations of hydraulic gradients, which increase ²²²Rn concentration during lower sea level, and opposite, during high tides where the ²²²Rn activity concentration is smaller. The estimated SGD fluxes varied during 22–26 November between 8 and 40 cm d⁻¹, with an average value of 21 cm d⁻¹ (the unit is cm³/cm² per day). The radium isotopes and nutrient data showed scattered distributions with offshore distance and salinity, which implies that in a complex coast with many small bays and islands, the area has been influenced by local currents and groundwater–seawater mixing. SGD in the Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater), which claims for potential environmental concern with implications on the management of freshwater resources in the region.     

Guiana current over North Brazil shelf and continental slope

Using thein situ currents measurements conducted during Cruise 41 of the R/VAkademik Vernadsky, we have considered the structure of the Guiana Current in winter over the shelf, continental slope and in the deep-water part of the ocean, adjoining the Brazilian coast. Regular variations of the current velocity with depth have been identified, and the current velocity's stability and variability determined. The paper examines how the barocline component of the hydrostatic pressure horizontal drop influences the current velocity's vertical profile. An attempt has been made to evaluate the current's transport. Translated by Vladimir A. Puchkin.     

Fishery-seal interactions in Irish waters: Current perspectives and future research priorities

Interactions between seals and the fishing industry are an on-going problem in Ireland and indeed globally across the range of most seal species. These interactions occur at both the operational (seal damage to catches and fishing gear) and biological (competition for shared resources) level. With declines in fish stocks there has been increased interest in the extent of competition for resources between commercial fisheries and seals. High levels of seal damage perceived by the fishing industry has led to frequent calls for seal culls, highlighting the significance of the problem. However, the scale of interaction between seals and commercial fishing and aquaculture in Ireland heretofore remained unclear. A comprehensive review of existing data, augmented with data from key stakeholders on the current state of play is presented to provide a realistic and representative account of the situation. This suggests that seal interactions with commercial fisheries in Ireland are most significant in inshore (<12 nautical miles from shore) static-net (or passive) fisheries (e.g. gill/tangle nets) and have increased following the driftnet ban in 2006, which suggests displacement of seal interactions from salmon to other fisheries. The industry highlighted pollack, angler fish, cod, and turbot fisheries as the main inshore fisheries currently impacted by operational damage to gear and catch by seals. Seal damage to line-caught salmon continues, with industry feedback suggesting large geographical variation in the range of damage levels reported. Salmon farming installations are also increasingly being targeted by seals, with significant losses due to seal depredation being reported. In the absence of robust data on seal depredation, the extent to which changes in fishing gear and practices have reduced damage levels, or resulted in displacement of seal foraging effort, is unknown. Recommendations are made to suggest how research efforts should be focused to address critical data gaps identified in the study.     

长江口北支的沉积物输运趋势

2007年9月在长江口北支采集表层沉积物样品,进行粒度和重矿分析,并利用Gao-Collins粒径趋势分析模型计算沉积物净输运趋势。结果显示,北支上口的沉积物有向下游输运的趋势;大新港至河口处,沉积物大致呈由北支下段向中、上段输运的趋势;北支河口外的沉积物,存在着向河口内输运的趋势。重矿物中稳定矿物与不稳定矿物比值的变化也显示,北支上口、下口处沉积物均向北支内输运,与粒径趋势分析的结果基本吻合。上述结果均显示,沉积物向北支内净输运,导致北支河段逐渐淤积。     

北太平洋副热带模态水盐度的年代际变化

副热带模态水(Subtropical Mode Water;STMW)在气候变化中起着重要作用。本文利用全球高分辨率数值模拟结果,研究了北太平洋STMW核心层盐度(Core Layer Salinity;CLS)的年代际变化及其物理机制。结果表明,CLS存在显著的年代际变化,其空间分布则与背景流场分布特征有关。侵蚀区CLS滞后生成区CLS约1~2年,这主要是海流平流输运引起的。生成区内,STMW的季节循环一般可分为生成期(12-4月)、隔离期(5-6月)和侵蚀期(7-11月),生成期混合层盐度(Mixed Layer Salinity;MLS)决定着隔离期和侵蚀期的CLS,而MLS年代际变化则主要由同太平洋年代际涛动存在负相关性的海表面淡水通量的变化引起。     

Determination of residence time and mixing processes of the Ubatuba,Brazil, inner shelf waters using natural Ra isotopes

Coastal waters contain elevated dissolved activities of short-lived radium isotopes, ²²³Ra and ²²⁴Ra, having half-lives of 11.4 and 3.66 days, respectively. The input of these isotopes near the coast must be balanced by decay and mixing into the open ocean, where excess activities are zero. Since the decay rate is known, in the ideal case the mixing rate may be determined from the offshore distribution of these isotopes. This study found that samples collected in June 2000 followed the expected exponential decrease with distance offshore. We assign a dispersion coefficient of 28–39 m² s⁻¹ for this study. During January 2002 and November 2003, there was not a consistent decrease of activity with distance offshore. This is likely due to the ruggedness of the coastline, where many bays and small islands interrupt simple mixing patterns. To estimate exchange rates during 2002 and 2003, we used a model based on the decrease in the ²²⁴Ra/²²³Ra activity ratio (AR) with time for samples isolated from fresh inputs of Ra. This model yielded residence times of 1–2 weeks for samples collected within 20 km of the coast. We used this residence time to calculate the flux of ²²⁸Ra (half-life = 5.7 years) to the study area necessary to maintain the enrichment relative to ocean water. This enrichment is a factor of ten greater than the flux of ²²⁸Ra expected from submarine groundwater discharge (SGD) occurring within 50 m of shore.     

北太平洋经向翻转环流和热盐输送研究综述

北太平洋经向翻转环流是北太平洋所有经向翻转环流圈的总称,目前它拥有五个环流圈,即副热带环流圈(the subtropical cell,STC)、热带环流圈(the tropical cell,TC)、副极地环流圈(the subpolar cell,SPC)、深层热带环流圈(the deep tropical cell,DTC)和温跃层环流圈(the thermohaline cell,THC)。这些环流圈是北太平洋经向物质和能量交换的重要通道,它们的变化对海洋上层热盐结构和气候变化皆有重要影响。迄今,人们已对STC、TC和DTC的结构形态、变化特征与机理开展了广泛而深入的研究,并对STC的极向热输送特征也做了一些初步分析。但应指出的是,关于SPC和THC的研究仍较少,迄今尚不清楚这两个环流圈的三维结构和变异机理;而且,对北太平洋经向翻转环流的热盐输送研究尚处于起步阶段,目前对各环流圈的热盐输送特征、变化规律和变异机理仍知之甚少,这些科学问题亟待深入研究。     

Coastal currents adjacent to the Caeté Estuary,Pará Region,North Brazil

We examined and compared tidal currents and water column structure between a near-shore station (12 km from the coast) and an offshore station (32 km from the coast) adjacent to the Caeté River, Pará Region, Brazil. Although the coastal system of Pará is largely influenced by local tides and wind, we found substantial differences in the dominant forcing agents between stations. Water column dynamics at the near-shore station were largely affected by local tidal processes, while differences between surface and bottom layer flows also indicated the importance of gravitational circulation at this station and a substantial influence of the adjacent Caeté River discharge. In comparison, at the offshore station, water column structure was largely influenced by a semi-diurnal tidal flow, an along-coastal current flow (mainly associated with the North Brazil Current) and the dynamics of local wind flow. The near-shore station at low tide showed a high level of stratification; at high tide such stratification was reduced. In comparison, stratification was only apparent within the upper 6 m at the offshore station, the rest of the water column was relatively well-mixed. The stratification within Station 1 at low tide was a result of the bi-directional movement of water discharged from the Caeté River, with lower salinity surface water and high salinity bottom water resulting in an estuarine-like circulation environment. The spatial variability and lack of correlation in current flow and water column structure between the near-shore and offshore stations suggest that a flow field resulting from differences in local circulation, tidal variability and wind persistence separate areas. We argue that this separation may indicate that the offshore station is located in a transition region between the Caeté River waters and the local coastal area.