Showing papers on "Ocean current published in 1988"

The dispersal of the Amazon's water

Abstract: New information obtained with NASA's Coastal Zone Color Scanner and with drifting buoys reveals that the discharge of the Amazon is carried offshore around a retroflection of the North Brazil Current and into the North Equatorial Countercurrent towards Africa between June and January each year. From about February to May, the countercurrent and the retroflection weaken or vanish, and Amazon water flows northwestward toward the Caribbean Sea.

A simulation of the global ocean circulation with resolved eddies

Abstract: A multilevel primitive-equation model has been constructed for the purpose of simulating ocean circulation on modern supercomputing architectures. The model is designed to take advantage of faster clock speeds, increased numbers of processors, and enlarged memories of machines expected to be available over the next decade. The model allows global eddy-resolving simulations to be conducted in support of the World Ocean Circulation Experiment. Furthermore, global ocean modeling is essential for proper representation of the full range of oceanic and climatic phenomena. The first such global eddy-resolving ocean calculation is reported here. A 20-year integration of a global ocean model with ½° grid spacing and 20 vertical levels has been carried out with realistic geometry and annual mean wind forcing. The temperature and salinity are constrained to Levitus gridded data above 25-m depth and below 710-m depth (on time scales of 1 month and 3 years, respectively), but the values in the main thermocline are unconstrained for the last decade of the calculation. The final years of the simulation allow the spontaneous formation of waves and eddies through the use of scale-selective viscosity and diffusion. A quasi-equilibrium state shows many realistic features of ocean circulation, including unstable separating western boundary currents, the known anomalous northward heat transport in the South Atlantic, and a global compensation for the abyssal spread of North Atlantic Deep Water via a long chain of thermocline mass transport from the tropical Pacific, through the Indonesian archipelago, across the Indian Ocean, and around the southern tip of Africa. This chain of thermocline transport is perhaps the most striking result from the model, and eddies and waves are evident along the entire 20,000-km path of the flow. The modeled Gulf Stream separates somewhat north of Cape Hatteras, produces warm- and cold-core rings, and maintains its integrity as a meadering thermal front as far east as the Mid-Atlantic Ridge. The Florida Current near the Yucatan peninsula sheds warm-core rings into the Gulf of Mexico. The East Australia Current produces warm rings which travel southward where the main current turns eastward. The Kuroshio and Oyashio currents are modeled as separate and distinct, each capable of producing warm and cold rings, but neither of them being distinguishable more than 1500 km offshore. A number of frontal regions in the Antarctic Circumpolar Current also exhibit spontaneous variability. Some specific areas of vigorous eddy activity have been identified in the South Atlantic by examining regional enlargements of the southwest Atlantic and of the southeast Atlantic over a simulated span of 225 days, using color raster animations of the volume transport stream function and of the temperature at 160-m depth. The Agulhas Current spawns mainly warm-core rings which enter the large-scale gyre circulation of the South Atlantic after rounding the tip of Africa and moving to the northwest. The Drake Passage has two thermal fronts, the northern of which is strongly unstable and generates ring pairs at about a 140-day period, whose net effect is to transport heat poleward. The confluence of the Brazil Current and the Malvinas (Falkland) Current forces each to turn abruptly eastward and exhibit ring formation near the continental shelf break, with unstable meandering farther downstream. It appears that each separated jet has a distinct core for generating unstable waves with periods of roughly 60 days. More quantitative results on global dynamics will be forthcoming as seasonally forced simulations, including ones with ⅓° × ⅖° grid spacing, are obtained and as the simulated variability and eddy transports are analyzed in a systematic fashion.

Instability and multiple steady states in a meridional-plane model of the thermohaline circulation

Abstract: A meridional-plane model of the thermohaline circulation with a simple friction force and advection and vertical diffusion of the T-S field has been used to demonstrate the instability and existence of multiple steady states associated with “mixed” T-S boundary conditions (specified temperature, flux condition for salinity). With forcing and geometry symmetric to the equator, the symmetric solution was found to be unstable to infinitesimal perturbations, and an asymmetric pole-to-pole circulation was the end-result in all cases. The structure obtained for the meridional-plane stream function and for the poleward heat flux are in qualitative agreement with those obtained by Bryan (1986). Convective overturning caused by static instability was not found to be essential for the transition to the asymmetric steady state. The study suggests that certain aspects of the ocean circulation, in particular those related to the ocean climate, may be profitably explored by use of two-dimensional, zonally averaged models. DOI: 10.1111/j.1600-0870.1988.tb00414.x

A deep hydrological front between intermediate and deep-wafpr , masses in the glacial Indian Ocean

Abstract: Ocean circulation and climate are strongly interconnected. Under climatic conditions very different from those of today, deep and intermediate water circulation was subject to drastic changes1–7. For instance, during the last glacial maximum (LGM), deep ocean water was cooler than now by several degrees8. These temperature changes in the deep ticean were associated with striking variations in chemical characteristics of the intermediate and deep water masses of the Atlantic and Pacific Oceans3,8–13. Here we reconstruct the hydrological structure of the deep and intermediate water of the Indian Ocean during LGM (∼18,000yr BP). The carbon and oxygen isotope analyses of the benthic foramiriifira genus Cibicides show that the water-column structure of the Indian Ocean during; LGM was marked by the presence of a deep front separating intermediate and deep-water masses with very different characteristics: Intermediate-water mass temperatures and §13C were similar to those of today. By contrast, the Jeep water was cooler than iiow by at least 1.5 °C, more depleted in 13C and poorly oxygenated.

An Ocean Basin Scale Model of plankton dynamics in the North Atlantic: 1. Solutions For the climatological oceanographic conditions in May

Abstract: Mathematical equations describing marine plankton dynamics are solved for the climatological oceanographic conditions during the month of May in the North Atlantic. Geographical distributions of phytoplankton, zooplankton and limiting nutrient (nitrate) concentration in the surface mixed layer of the ocean are predicted from historical mixed layer depth and the total nutrient made locally available to the plankton ecosystem by convective mixing. The effects of major ocean currents are parameterized in the model through the geographic distribution of nitrate and its vertical gradient. Major upwelling and downwelling circulations control the proximity of high nutrient concentrations to the surface. Model solution of the phytoplankton field with 1° longitude and latitude grid resolution is compared to a recently produced composite of Coastal Zone Color Scanner images of surface chlorophyll in the North Atlantic during May 1979 [W.E. Esaias et al., 1986]. Large-scale chlorophyll patterns seen in the CZCS composite can be explained as transition zones in the supply of plant nutrients to the surface layer by vertical mixing or localities of light limitation of phytoplankton growth by a deep mixed layer.

Investigation of large-scale circulation patterns in the central North Atlantic: the North Atlantic current, the Azores current, and the Mediterranean Water plume in the area of the Mid-Atlantic Ridge

Abstract: Within the framework of the TOPOGULF experiment, five hydrographic boxes were designed to allow a realistic reference level for geostrophic calculations to be identified. By means of both the inverse method of Wunsch (1978, Reviews of Geophysics and Space Physics, 16, 583–620) and the empirical search method of Fiadeiro and Veronis (1982, Journal of Marine Research, 40, 159–192), geostrophic currents and associated transports across the total length of the Mid-Atlantic Ridge between 24° and 53°N were estimated. As a reference level, an intermediate “level of slow motion” was found in terms of σ2 = 36.97–37.035 (1500–2900 dbar) to be in good agreement with hydrographic features. The total transport above this level was calculated as 37 Sv to the east. Much of this transport occurs in two principal currents, the Azores Current (12 Sv) and two branches of the North Atlantic Current (17 Sv). A reversion of the total flow in the layer below the reference level was not observed. The meridional extent of the Mediterranean Water outflow was found to be restricted by the Azores Current in the south, and the southern branch of the North Atlantic Current in the north, and the zonal distribution to be influenced by the Mid-Atlantic Ridge. A schematic circulation picture is attempted as a summarized result deduced from this analysis and selected literature.

The use of anthropogenic tritium and helium-3 to study subtropical gyre ventilation and circulation

Abstract: With tritium and helium-3 ( 3 He) data from the Transient Tracers in the Ocean (tto) expedition and from two other contemporaneous cruises, a synoptic picture of the ventilation and circulation of the subtropical North Atlantic is built. We will see clear evidence of gyre circulation in the tritium- 3 He age distributions on the shallower isopycnals, permitting estimates of the rates of circulation averaged over timescales from months to decades. The entry points of fluid into the main thermocline and the pathways of exchange with the upper ocean on seasonal to decade timescales appear clearly. It is the time-averaged transport processes on those timescales that are important to the uptake of carbon dioxide by the ocean. The overall relation between tritium and 3He within the subtropics exhibits a systematic hook-like pattern that is consistent with ‘strong’ ventilation of the gyre thermocline; a fluid parcel entering the gyre thermocline making only about one circuit around the gyre before being ventilated. Finally, we present a time-series of 3 He measurements made over a period of two years near Bermuda. The mixed layer is demonstrably supersaturated in this isotope throughout a large part of the year, requiring a gas-exchange flux of this isotope to the atmosphere. Model results are presented that permit the calculation of the in situ solubility isotope ratio anomaly for helium (as affected by bubble injection and gas exchange), and that can be used to estimate the upward flux of this isotope. Because only a small fraction of this flux can be produced in the mixed layer, this helium must be ‘mined’ from the main thermocline. The computed flux is consistent with the long-term evolution of the inventories of tritium and 3 He within the main thermocline. This flux has implications regarding the vertical transport of material within and from the permanent thermocline. A single observation of what may be one of the processes responsible for this upward flux is discussed.

The Effect of Salinity on Tropical Ocean Models

Abstract: The effect of horizontal salinity gradients on the tropical ocean circulation has not previously been evaluated. It is shown that there are noticeable differences between the dynamic height field calculated with and without the inclusion of salinity variations. Hence salinity has a significant contribution to the geostrophic velocity field. This conclusion is illustrated by running two identical Indian Ocean models:. one initialized using a climatological salinity field while the other has no horizontal salinity gradients. The differences in the temperature and velocity fields after 110 days are of the order of 0.5°C and 10 cm s−1 over some regions of the ocean. Further experiments using the same model for data updating studies showed that the absence of salinity data greatly reduces the usefulness of temperature data. It is concluded that for an accurate simulation of the tropical ocean the salinity field needs to be included.

Scale Upwelling and Primary Production

Abstract: Upwelling due to vortex contraction on the anticyclonic flank of transient mesoscale jets is fast enough and sustained for long enough to effect substantial local increase in primary production. Dynamical constraints limit upwelling to patches with horizontal dimensions of about ten kilometres, similar to those of primary production “hot spots” observed in satellite images. In situ surveys suggest that the distribution of these mesoscale patches of high plankton concentration strongly influences the large scale variation of primary production. The latter can be estimated from the statistics of mesoscale upwelling events. Given the new understanding of mesoscale dynamics, those statistics can be computed using geostrophic turbulence theory, provided the large scale distribution of isopycnic potential vorticity Q is known. (The relevant properties of Q are summarized in an appendix.) The seasonal climatology of Q in the euphotic zone is described, and it is shown how inter-annual variations can be predicted by means of a model of ocean circulation and mixed layer dynamics. A multi-year programme of experiments in the North Atlantic has been undertaken to test the theory. This has involved a series of high resolution sections extending 2,000 km between the Azores and Greenland, and synoptic mapping of mesoscale structure at the inter-gyre front. The phase relationships between distributions of Q, temperature, velocity and concentrations of particles and chlorophyll in the maps are consistent with the theory. The distributions of Q, upwelling and chlorophyll in the sections supports the hypothesis that large scale variation of primary production is best viewed in terms of the statistics of mesoscale events.

Anthropogenic chlorofluoromethanes in newly formed Labrador Sea Water

Abstract: Convection to 2,000 m in the Labrador Sea during severe winters partially renews Labrador Sea Water (LSW)1, a water mass trace-able at intermediate depth throughout the north Atlantic Ocean (north of 40° N)2 and along the western boundary to the Equator3. Anthropogenic chlorofluoromethanes (CFMs) have been used3 to estimate the transit time of LSW from its source region to the Equator, together with its degree of dilution by 'older' waters. CFMs may also be used to constrain 'diagnostic' ocean circulation models4. Such applications depend critically on the concentration and the rate of change of CFMs in newly formed LSW. Here we report the first Labrador Sea CFM data, including measurements from a > 1,500 m deep column of recently renewed water, that suggest that LSW originated at only 60% saturation with respect to contemporary atmospheric concentrations, in contrast to the 100% usually assumed in interpretations of tracer distributions away from source regions. The newly formed water mass was also colder and less saline than any previously measured LSW. Monitoring of CFMs and other tracers in this region will be essential for establishing boundary conditions for models of the North Atlantic tracer distributions.

Climatic Atlas of the Outer Continental Shelf Waters and Coastal Regions of Alaska. Volume 2. Bering Sea. Revision

Abstract: : This project updates the knowledge of climatological conditions presented in the 1977 publication of this atlas. The maps, graphs, and tables in the atlas present a detailed climatic profile of the marine and coastal regions of Alaska. Statistics give the means, extremes, and percent frequency of occurrence of threshold values for these elements: wind, visibility, present weather, sea level pressure, air and sea surface temperature, clouds, waves, and such supplemental information as storm surges, tides, sea ice, cyclone tracks, surface currents, bathymetry, detailed weather, and aviation weather. Data came from 4.5 million surface marine observations and 8.5 million observations for 66 coastal and island stations within the area 40 deg -84 deg N and 110 deg W-160 deg E, and provide the best possible climatologic picture of the outer continental shelf waters and coastal regions of Alaska. Keywords: Marine climatology; Aleutian islands ocean surface; Isopleths; Atmospheric precipitation; Meteorological data tables; Refractive index gradient; Wind velocity.

The Response of a Coupled Ocean-Atmosphere General Circulation Model to Wind Bursts

Abstract: A coupled ocean-atmosphere general circulation model has been developed for TOGA related problems. The coupled model consists of an ocean model of the tropical Pacific and a global low-order spectral atmosphere model. The two models interact via wind stress and sea surface temperature. In order to avoid a climate drift within the coupled model, a flux correction method is applied.Experiments were performed by introducing a westerly wind stress burst over the western equatorial Pacific for one month. Thereafter, the wind burst is turned off and the response of the coupled model to the initial disturbance is investigated. The results are compared with the response of the ocean model run with the same disturbance in an uncoupled mode.It is shown that the coupling leads to a significant increase of the duration of anomalous conditions in the ocean. SST anomalies persist for about 12 months in the coupled run, while they have already disappeared after 4 months in the uncoupled case. The increase in persistence is due to the feedback of the atmosphere, which responds with an eastward shift of the ascending branch of the Walker Circulation.In a second experiment with the coupled model the initial disturbance was introduced within another season. The results show no basic differences to the results of the first experiment.An interesting result of the coupled model runs is the occurrence of spontaneous westerly wind bursts over the western Pacific, which developed by internal dynamics. Location and duration of these spontaneous wind bursts show some correspondence with the time-space structure of observed westerly wind stress episodes over the western Pacific.

The Use of Cs and Sr Isotopes as Tracers in the Arctic Mediterranean Seas

Abstract: The Arctic Mediterranean Seas constitute an oceanic region in which the thermohaline circulation has a strong advective component and deep ventilation processes are very active relative to other oceanic areas. Details of the nature of these circulation and ventilation processes have been revealed through use of Cs and Sr isotopes from bomb-fallout and nuclear-waste sources as ocean tracers. In both cases, their regional input is dominated by advective supply in the Norwegian Atlantic Current and Norwegian Coastal Current, respectively. The different temporal, spatial, and compositional input patterns of these tracers have been used to study different facets of the regional circulation. These input differences and some representative applications of the use of these tracers are reviewed. The data discussed derive from samples collected both from research vessels and from Arctic ice camps. The topics addressed include: ( a ) the role of Arctic Intermediate Water as source, supplying recent surface water to North Atlantic Deep Water via the Denmark Strait overflow; ( b ) deep convective mixing in the Greenland Sea; ( c ) circulation or recirculation of Atlantic water in the Arctic basins; and ( d ) the role of Arctic shelfwaters in the ventilation of intermediate and deep water in the Eurasian and Canadian basins.

Ocean current and temperature structures in Algoa Bay and beyond in November 1986

Abstract: Data on ocean temperature, currents, salinity and nutrients were obtained in an area off Algoa Bay on the south-east coast of South Africa during a ship's cruise in early November 1986. Satellite imagery provided information on the position of the Agulhas Current during the cruise period, while wind data were available from weather stations on the eastern and western sides of Algoa Bay. It is surmised that wind-forcing plays a major role in water circulation in the Bay and over the inshore continental shelf remote from the influence of the open ocean. The predominantly barotropic current flow, of the order of 0,5 m·s−1, was downwind and influenced by topographic features and coastline shape. The Agulhas Current influences the ocean structures by long-term (large episodic meanders) and short-term (upwelling forced by the Current, core upwelling in frontal eddies and warm frontal plumes at the surface) fluctuations. Temperature structures showed well mixed water in Algoa Bay and a strong thermocline over th...

Mathematical Modelling of Ocean Circulation

Abstract: The problems of ocean dynamics present more and more com plex tasks for investigators, based on the continuously sophisti cation of theoretical models, which are applied with the help of universal and efficient algorithms of numerical mathematics. The present level of our knowledge in the field of mathemat ical physics and numerical mathematics allows one to give rather complete theoretical analysis of basic statements of problems as well as numerical algorithms. Our task is to perform such analy sis and also to analyze the results of calculations in order to improve our knowledge of the mechanism of large-scale hy drological processes occurring in the World Ocean. The new level of numerical mathematics has essentially influenced, the formation of new solution methods of ocean dynamics prob lems, among which an important one is the splitting method, which has been already widely practised in various fields of science and engineering. A number of monographs by N. N. Yanenko, A. A. Samarsky, G.!. Marchuk (Rozhdestvensky and Yanenko 1968; Samarsky and Andreyev 1976; Marchuk 1970, 1980b) and others are devoted to the description of this methods. But the methods of the splitting theory require extensive creative work for their application to concrete problems, which are peculiar, as a rule, in problem formulation. The success of the application of these methods is related to the deep understanding of the essence of the described processes. In the last decades fundamental works of Arakawa, K."

Tidal-induced pulses in the flow through the Strait of Gibraltar

Abstract: Ship data collected in the 1960s and recent data from ship, aircraft and satellites indicate that the flow in the Strait of Gibraltar does not move in the form of continuous currents but as tidal-induced pulses. A descriptive model based on these data is presented. The model indicates that the pulses are a result of increases in the speed of the tidal streams as they encounter the constrictions of the regional bathymetry (especially the Camarinal Sill and between the Camarinal Sill and Tarifa). Periodic increases modify the regional flow so that during each tidal cycle, the eastward-flowing surface Atlantic water and westward-flowing deep Mediterranean water are alternately emitted as large pulses into the Mediterranean Sea (Atlantic water) and Atlantic Ocean (Mediterranean water).

Surface Energy Fluxes of the South Atlantic Ocean

Abstract: Fluxes of sensible, latent and radiational energy and momentum across the surface of the South Atlantic Ocean have been calculated by substituting ship meteorological observations into bulk aerodynamic and empirical radiation equations. Upper-air measurements of humidity and temperature have been used to supplement the surface empirical infrared radiation formula. North Atlantic fluxes have been updated using upper-air humidities and the same technique. Charts of annual fluxes and meteorological variable averages are presented and discussed in terms of meteorological conditions, oceanic heat advection, upwelling, and horizontal mixing of water in the various regimes of the South Atlantic. Comparisons between meteorological conditions, oceanic currents, and fluxes over the North and South Atlantic have been made. Summations of total heat flux show that the cold South Atlantic gains 4.7 × 1014 W, while the warm North Atlantic loses 6.6 × 1014 W. Oceanographic calculations based on currents and temp...

Mass, heat and nutrient fluxes in the Atlantic Ocean determined by inverse methods

Abstract: Inverse methods are applied to historical hydrographic data to address two aspects of the general circulation of the Atlantic Ocean. The method allows conservation statements for mass and other properties, along with a variety of other constraints, to be combined in a dynamically consistent way to estimate the absolute velocity field and associated property transports. The method was first used to examine the exchange of mass and heat between the South Atlantic and the neighboring ocean basins. The second problem addressed concerns the circulation and property fluxes across the 24 and 36 deg N in the subtropical North Atlantic. Conservation statements are considered for the nutrients as well as mass, and the nutrients are found to contribute significant information independent of temperature and salinity.

Controls of CO2 sources and sinks in the Earth scale surface ocean: Temperature and nutrients

Abstract: Several regions in the ocean in which disequilibrium persists on an annual avarage between CO2 in the surface water and the overlying atmosphere were examined using various models in which CO2 does cycle in a steady state at which sources (ocean outgassing) and sinks (ingassing) are in balance. The relative values of the surface temperature and surface nutrients, the two major contributors to the CO2 source and/or sink properties, are determined. Results from models with two ocean surfaces indicate that the sink in the north Atlantic and the sources in the equatorial Atlantic and Pacific are all dominated by the global temperature patterns. Results from ocean models with three surface zones show that, in the equatorial Pacific, the temperature control is responsible for over 50 percent (and, possibly, for almost 70 percent) of the CO2 outgassing, with the balance coming from the earth scale surface nutrient structure.

Coastal Zone Color Scanner

Abstract: The Coastal Zone Color Scanner (CZCS) spacecraft ocean color instrument is capable of measuring and mapping global ocean surface chlorophyll concentration It is a scanning radiometer with multiband capability With new electronics and some mechanical, and optical re-work, it probably can be made flight worthy Some additional components of a second flight model are also available An engineering study and further tests are necessary to determine exactly what effort is required to properly prepare the instrument for spaceflight and the nature of interfaces to prospective spacecraft The CZCS provides operational instrument capability for monitoring of ocean productivity and currents It could be a simple, low cost alternative to developing new instruments for ocean color imaging Researchers have determined that with global ocean color data they can: specify quantitatively the role of oceans in the global carbon cycle and other major biogeochemical cycles; determine the magnitude and variability of annual primary production by marine phytoplankton on a global scale; understand the fate of fluvial nutrients and their possible affect on carbon budgets; elucidate the coupling mechanism between upwelling and large scale patterns in ocean basins; answer questions concerning the large scale distribution and timing of spring blooms in the global ocean; acquire a better understanding of the processes associated with mixing along the edge of eddies, coastal currents, western boundary currents, etc, and acquire global data on marine optical properties

Remote sensing of shelf sea currents using a high‐frequency ocean surface current radar system

Abstract: In a deployment of an ocean surface current radar system made during May 1985, currents were measured in a region of sea to the northeast of Anglesey, Wales, and compared with data obtained from three current meters. The uppermost current meter was fixed at 5 m from the surface, in a water column of 40-m depth with tidal range of 9 m. In the east–west direction, close to the orientation of the major axis of the tidal ellipse, the radar and top current meter show good agreement to within an rms value of 0.16 m s−1, consistent with earlier comparative studies. For the weaker north–south components of the flow, however, differences between the radar results and those from the current meters are apparent. A larger-amplitude north-south signal is recorded by the radar. In terms of the M2 rotary (clockwise and anticlockwise) components of the flow, the radar data contain amplitude and phase anomalies with respect to a predicted surface behavior deduced from the current meter records and theory. In particular, anticlockwise phase at the surface is advanced considerably (by ≃ 20°). Further analysis shows that the flow field recorded by the radar has two components: the predicted tidal response, and an additional elliptical term of lower eccentricity than the main east–west tidal signal and with major axis directed close to north. Hourly synoptic maps of tidal circulation patterns derived from the radar show a smooth transition from near-westward flows on the ebb to near-eastward flows on the flood. The variation of north–south residual currents with height can be interpreted in terms of a “mean state” consistent with geostrophic shear and associated with the roughly east–west density gradient.

Transports of water masses through the Faroese Channels determined by an inverse method

Abstract: The transport of water between the Atlantic Ocean and the Norwegian Sea through the Faroese Channels is studied by means of geostrophic calculations and use of an inverse method. The inverse method is used to evade the arbitrary character of a priori choice for a level of no motion. The resulting transport of Atlantic water into the Norwegian Sea (≈8 × 106 m3 s−1) agrees with existing estimates based on water and heat budgets of the Norwegian Sea, but the horizontal structure of the flow differs from literature. The flow of intermediate and deep water from the Norwegian Sea towards the Atlantic Ocean (≈106 r3 s−1) agrees with reported values.

Climatic Atlas of the Outer Continental Shelf Waters and Coastal Regions of Alaska. Volume 1. Gulf of Alaska, Revision

Abstract: : This project updates the knowledge of climatological conditions presented in the 1977 publication of this three-volume atlas. Such environmental information for the three Alaskan marine and near-coastal areas is important for resource development of the outer continental shelf-The Gulf of Alaska (Volume I), the Bering Sea (Volume II), and The Chukchi and Beaufort Seas (Volume III) as shown on the map below. The maps, graphs and tables in the atlas present a detailed climatic profile of the marine and coastal regions of Alaska. Statistics give the means, extremes, and percent frequency of concurrence of threshold values for these elements: Wind, visibility, present weather, sea level pressure, air and sea surface temperature, clouds, waves, and such supplemental information as storm surges, tides, sea ice, cyclone tracks, surface currents, bathymetry, detailed weather, and aviation weather. Data came from 4.5 million surface marine observations and 8.5 million observations for 66 coastal and island stations within the area 40 deg -84 deg N and 110 deg W -160 deg E, and provide the best possible climatological picture of the outer continental shelf waters and coastal regions of Alaska.

Long-term variation in seawater composition at the base of the thermocline

Abstract: Measurements of the chemical composition of seawater over a time scale of years at a fixed point in the ocean below the main thermocline have not been previously reported because of navigational limitations, ship and hydrowire instability, and, to a large extent, cost. The deep-water pipeline at the Natural Energy Laboratory of Hawaii at Keahole Point (Fig. 1a) provides a unique opportunity to address the question of time-varying water composition at a fixed site in the ocean below the mixed layer. In this study we examine the composition of sub-thermocline seawater through weekly sampling (surface-water data are also available, but are not discussed here). The mean deep-water composition obtained over about five years is representative of regional mean-water composition, and significant variation in water composition is observed on time scales exceeding one year. This unexpected long-term variation probably represents cyclic displacement of deep water masses in response to variation in the regional ocean circulation.

A Study of Geostrophy in Tropical Pacific Ocean Currents during the NORPAX Tahiti Shuttle using a Shipboard Doppler Acoustic Current Profiler

Abstract: Continuous velocity measurements from a shipboard Doppler acoustic long on the NORPAX shuttle experiment in the central equatorial Pacific are presented. The time mean of these velocities shows the classical zonal equatorial currents as well as their meridional circulation. The velocities are used with concurrent CTD data to examine the geostrophic balance of zonal currents in the upper 117 m. Estimates of the errors of the acoustic data are produced from a comparison between that data and concurrent profiling current-meter data, and are used to establish the reliability of the balances observed. Both the time mean and the time varying balances are investigated, as well as the departures from geostrophic balance. The mean zonal velocities between 4°S and 10°N are found to be in approximate geostrophic balance. Departures from geostrophy in the mean are observed near the surface at the equator. The meridional advection of meridional momentum appears to be only partly responsible for this departure...

Ocean Currents Over the Continental Slope

Abstract: Publisher Summary This chapter discusses the different aspects of ocean currents over the continental slope. Continental slopes underlie some 12% of the world ocean's surface area. Their importance to ocean circulation is out of proportion, since most of the major ocean currents flow over them and are in various ways affected by their topography. Superimposed on the typical upwelling regime are variations in the strength of the alongshore flow in response to changes of the wind stress. Coastal currents driven by density differences due to river runoff are common on continental shelves but reach to the upper slope only in a few places. Strong surface cooling, in the absence of significant salinity contrasts, produces cold and heavy coastal waters, the opposite of the coastal freshening case. Shallow water cools off rapidly, as its temperature also becomes uniform due to thermal convection, and tends to underflow less completely cooled deeper water. It is found that the fundamental slope effect examined above turns up in a different guise if the angular momentum balance of a fluid column fixed in space is considered instead of vorticity, allowing for external torques as well as the torque due to momentum advection.

Gulf Stream velocity structure through inversion of hydrographic and acoustic Doppler data

Abstract: Near-surface velocities from an acoustic Doppler instrument are used in conjunction with CTD/O2 data to produce estimates of the absolute flow field off Cape Hatteras. The data set consists of two transects across the Gulf Stream made by the R/V Endeavor cruise EN88 in August 1982. An inverse procedure is applied which makes use of both the acoustic Doppler data and property conservation constraints. Velocity sections at approximately 73 deg. W and 71 deg. W are presented with formal errors of 1-2 cm/s. The net Gulf Stream transports are estimated to be 116 + or - 2 Sv across the south leg and 161 + or - 4 Sv across the north. A Deep Western Boundary Current transport of 4 + or - 1 Sv is also estimated. While these values do not necessarily represent the mean, they are accurate estimates of the synoptic flow field in the region.

Wind-Driven Cross-Equatorial Flow in the Pacific Ocean

Abstract: A scheme for calculation of cross-equatorial flow is presented which permits an estimation of meridional velocity at the equator from hydrographic station data and surface wind stress. It is offered to rationalize the observations that surface winds are neither zonal nor spatially uniform at the equator and that large-scale patterns exist in the meridional slope of the dynamic height field at the equator. Using historical data in the equatorial Pacific for surface wind stress and dynamic height, a large-scale estimate of meridional velocity is presented for the upper 2000 m with a zonal resolution of 10° of longitude. The flow across much of the central equatorial Pacific is northward in the upper 200 m and southward at greater depth. Southward near-surface currents are estimated east of 120°W, in agreement with direct current measurements at 110°W. The frictional component to the flow, although determined only in the vertically integrated sense, is included assuming an exponential decay from the...