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WOS:000660310900002; International audience; Ecosystem models forced by future climate simulations outputs from the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulate a substantial decline of tropical marine animal biomass over the course of the 21st century. Regional projections are however far more uncertain because of well-known biases common to most CMIP5 historical simulations that propagate within the food web. Moreover, the model outputs for high trophic levels marine fauna suffer from lack of validation based on in situ data. In this study, we implement a "bias-mitigation" strategy to reduce the physical oceanography and biogeochemical biases simulated by three CMIP5 models under the future RCP8.5 scenario. We force two very different micronekton models with these "bias-mitigated" outputs to infer the future micronekton changes in the Coral Sea: a 3-D deterministic population dynamics model; and a 3-D statistical model based on in situ hydro-acoustic data. These two models forecast a consistent pattern of micronekton abundance changes in the epipelagic layer (0-150 m) by 2100 for three different climate forcing used, with a marked decrease south of 22 degrees S and a smaller increase further north mostly related to temperature and chlorophyll changes. In contrast, changes in the vertical patterns of micronekton predicted by the two models considerably differ in the upper mesopelagic layers (150-450 m) and lower mesopelagic layer (450-1000 m), highlighting the structural sensitivity in model type. Since micronekton are prey of all larger marine predators, those discrepancies in vertical structures of micronekton may hamper our potential to predict how top predators may evolve in the future.

Fjords along the western Antarctic Peninsula contain rich marine ecosystems and tidewater glaciers potentially sensitive to ocean change, but much is unknown about the physical oceanography of these fjords. This paper presents a comprehensive description of the physical environment of Andvord Bay, a glacial fjord located in the Gerlache Strait on the northern end of the Peninsula. Measurements were collected as part of the FjordEco program between November 2015 and March 2017, including during three research cruises and from a number of fixed installations (sub-surface moorings, time lapse cameras, and automatic weather stations). Andvord Bay is located just north of a sill in the Gerlache Strait. This sill inhibits the direct influence of warm Upper Circumpolar Deep Water from the shelf, and deep waters in the fjord are therefore relatively cold. As a result, glaciers in Andvord Bay are not subject to the substantial ocean-driven retreat observed farther south on the Peninsula. Instead, mass flux from the glaciers occurs mainly through calving. The influence of meltwater in Andvord Bay is small compared to glacial fjords in the Arctic and in the South Shetland Islands, although summer freshening is evident in the fjord near-surface layer, likely as a result of glacial inputs. The combination of surface freshening and the absence of strong mean wind forcing in the fjord results in salinity stratification extending well into the euphotic zone, providing advantageous conditions for phytoplankton blooms. Andvord Bay is generally dynamically quiet compared to the ambient ocean, with the exception of during local katabatic wind events. Exchange with the Gerlache Strait is weak, although the deep waters of the fjord are replenished on an annual scale through slow lateral exchange with the outside. In addition, deep convection may play a role in ventilating subsurface waters in winter.

The Ligurian Sea plays a relevant role in driving both the circulation of the Western Mediterranean Sea and the weather and climate of the area. In order to better understand the peculiarities of this basin, the Oceanographic Data Acquisition System (ODAS) Italia 1 buoy was developed and deployed in the early ‘70s. Throughout the years, the buoy has been fitted with updated measuring and data acquiring systems. Since 2003 the buoy has been part of the Mediterranean Moored Multi-sensor Array network of fixed open ocean observatories with the W1-M3A identifier and presently constitutes one of the Mediterranean sites of the European FixO3 network. Recently, a deep-ocean sub-surface mooring line was, and is, deployed close to it in relation to specific projects. This multidisciplinary observing system is able to perform both long-term operational and ad-hoc monitoring from the lower atmosphere to the deep ocean. It is used for analysis of air–sea interaction processes, study of the physical proprieties of the water column, bio-geo-chemical monitoring of the sea, meteorological and oceanographic model evaluation, calibration of remotely sensed measurements, and development of innovative marine monitoring technologies. After reporting some historical notes and the description of the observing system, this paper summarises and reviews the main oceanographic and atmospheric studies performed during the last 15 years using the data acquired on board.

The Atlantic Water (AW) path suggested by two decades of thermal satellite data observations in the Eastern Mediterranean is similar to the path followed by the AW in the Western Mediterranean but is in contrast with the scheme proposed after the Physical Oceanography of the Eastern Mediterranean (POEM) experiment during the 1990s. Evidence of the AW path along the Libyo-Egyptian coast (Libyo-Egyptian Current; LEC) and around anti-cyclonic eddies of variable size and position (Libyo-Egyptian Eddies; LEEs) is reported in XBT transects, high resolution models and drifter trajectories. In the POEM scheme, the AW was carried eastwards by the Mid-Mediterranean Jet (MMJ) flowing in the middle of the Levantine basin. The MMJ is still noted in recent drifter trajectory analyses, and seasonal surveys and glider missions report that the AW is transferred towards the Levantine basin by the MMJ in subsurface layers. The issue is investigated in this study by considering whether the determination of the AW path and the resolution of the surface circulation are, unlike in the Western Mediterranean, two distinct problems. Historical hydrographic datasets and numerical experiments illustrated in this study demonstrate that satellite observations in the Eastern Mediterranean reveal the path of the surface water of Atlantic origin, which is modified by heating and evaporation into the saltier and warmer Levantine Surface Water (LSW), but do not reveal the path of the submerged AW that maintains the distinctive character of fresh AW in the Levantine basin. Differences between the surface and the submerged circulation in the Mersa-Matruh area explain the reason for the discrepancy. In summer the AW departs from the Sicily Channel at the sea surface and crosses the Ionian Sea in a surface layer 30 m deep. At the entrance to the Levantine basin, part of the AW re-circulates westwards in two separate branches, one directed to the Southern Ionian and the other towards the Central Ionian, causing meanders in the incoming AW. In the Levantine basin, before the Cretan Passage, the AW is close to the Libyan coast with surface layers already modified into LSW and a subsurface fresh AW core centered at 50 m depth. Surface and subsurface flows diverge within the Cretan Passage as they approach the Mersa-Matruh area. According to satellite observations, the LSW flows along the Libyo-Egyptian coast (LEC) and around anti-cyclonic LEEs of variable size and position. In the subsurface layers, the blend and fragmented anti-cyclonic circulation found at the surface is augmented by the AW itself, which becomes saltier and negatively buoyant, and veers offshore joining the MMJ. In summer, the jet assumes the aspect of a submerged injection of fresh AW into the Levantine basin below a depth of 60–70 m. From the Ionian eastwards, the depth of the fresh core of AW sinks by tens of meters from the beginning to the end of summer. In the Sicily Channel, the AW in winter is saltier than in other periods of the year due to evaporation and mixing occurring between the fresh AW and the saltier Ionian Surface Water intruding into the southern side of the Channel in summer.

A box inverse model of the Southern Ocean during the World Ocean Circulation Experiment is constructed to investigate the three-dimensional structure of the regional overturning circulation in that era. The model has many features in common with various preceding inverse studies, but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present. The net overturning circulation of the Southern Ocean is found to consist of two well-defined cells of similar strength. The upper cell consists of a northward transport of 18.8 ± 5.5 Sv of surface, mode and intermediate waters lighter than the 27.5 kg m−3 isoneutral, and an equivalent southward flow in the approximate 27.5–27.9 kg m−3 neutral density range, encompassing the bulk of the Upper Circumpolar Deep Water. The lower cell involves the northward export of 18.6 ± 0.9 Sv of Antarctic Bottom Water and Lower Circumpolar Deep Water denser than 28.08 kg m−3, and an opposing transport in the lighter classes of that water mass. Substantial structural differences between the overturning circulations of the Atlantic, Indian and Pacific basins are indicated by the model’s solution. Overall, the diagnosed Southern Ocean circulation shares many qualitative and some quantitative features with previous inverse estimates, particularly as regards the large-scale, depth-integrated lateral circulation and associated energy fluxes in the subtropics and in the Antarctic Circumpolar Current, and the strength of the upper overturning cell. However, it also suggests several significant adjustments to current views of the regional circulation. Most notable amongst these are: the subpolar circulation of the Southern Ocean is more vigorous and zonally interconnected than generally thought; the associated lower overturning cell is more intense than indicated by most preceding estimates; contrary to common perception, sub-surface mixing processes play a role of comparable importance to air–sea–ice exchanges of buoyancy in underpinning the dianeutral closure of the Southern Ocean overturning, even at shallow (mode and intermediate water) levels; and the connection between North Atlantic deep water formation and Southern Ocean upwelling is fundamentally three-dimensional, such that deep waters from the North Atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans.

New measurements are presented of the currents and hydrography at Jones Bank in the Celtic Sea. These measurements, collected during the summer of 2008, identify a highly energetic internal wavefield generated by the local interaction of seasonally stratified flow with topography. Observations close to the bank crest reveal internal waves of up to 40 m amplitude; approaching 50% of the local water depth. These waves occur during spring periods and are predominantly associated with off-bank tidal flow. We provide evidence that these waves are the result of hydraulic control of the tidal currents which result in supercritical flow in the bottom mixed layer (bml) on the upper slopes of the bank. The waning tide produces a transition from super to subcritical flow, identifiable as a regular hydraulic jump on the bank slope. Microstructure measurements identify a turbulent ‘bore’ associated with such jumps that increases bml turbulence by several orders of magnitude and produces a regular burst of enhanced mixing at the base of the ever-present thermocline. Additional mixing in the surface mixed layer is provided during gale force conditions during the first of the two spring tides observed, occurring at the start of our three-week measurement period. The average thermocline mixing rate during stormy spring tide conditions is 1.9 (±1.0, 95%) × 10 −3 m 2 s −1 , driven by both surface mixing and hydraulic jumps. During the later calm spring period the average thermocline mixing rate is 3.3 (±1.7) × 10 −4 m 2 s −1 , dominated by jump associated events. By comparison, the intervening neap tide period produces no hydraulic jumps and is characterised by relatively calm weather. A strong shear layer is however maintained during this ‘quiet’ period sufficient to enhance thermocline turbulence by a factor 1000 above background levels. A short lived peak in thermocline turbulence during the neap period produces diapycnal mixing as high as 1.6 × 10 −2 m 2 s −1 however a more representative ‘background’ thermocline mixing rate is 2.8 (±0.6) × 10 −5 m 2 s −1 .

The Norwegian Component of the Ecosystem Studies of Sub-Arctic Seas (NESSAS) was funded by the Research Council of Norway from 2005 to 2008. Its aim was to quantify the impact of climate variability on the structure and function of the marine ecosystem of the Barents Sea and adjacent waters in order to predict the ecosystem responses to possible future climate change and their possible economic impact. This paper reviews research highlights dealing with climate forcing and its influence. New insights were provided on the role of large-scale atmospheric forcing on the physical oceanography including the effect of Arctic and Atlantic cyclones on the variability of the ice extent in the Barents Sea and the non-linear response of the sub-polar gyre to North Atlantic Oscillation (NAO) forcing. In addition, the NAO was also shown to influence the biology, for example shrimp recruitment in the Barents Sea and primary production in the Nordic Seas, with the strength and sign of the correlations being spatially dependent. The importance of longer term climate variability in the form of the Atlantic Multidecadal Oscillation (60–80 years period) was stressed, as it leads to significant changes in fish production, shifts in distribution and changes in spawning sites in the Barents Sea as well as other northern Atlantic ecosystems. Results from comparative studies between several US ecosystems and those of the Norwegian and Barents Seas are presented, including evidence of increased primary productivity in the Barents Sea in recent years and the poleward movement of zooplankton and fish. In addition recruitment patterns of major demersal and pelagic species in the Barents Sea generally show synchrony with those in the Gulf of Maine indicating a common external forcing. Possible ecosystem scenarios for the Barents Sea under anthropogenic-induced future climate change were developed including expectations of structural and functional changes due to distributional changes of many species. Of particular note is the likelihood of increases in the productivity of several fish species, including cod and herring, which potentially could result in higher fisheries yields.

The distribution of 239Pu in Atlantic and Indian Ocean waters about four decades after their main injection from atmospheric nuclear weapons tests is discussed. Recent data obtained in the framework of the SHOTS (Southern Hemisphere Ocean Tracer Studies) projects are evaluated and compared with previous investigations. Seawater samples were collected during the round the globe BEAGLE2003 (Blue Ocean Global Expedition) along the 30°S transect in the Atlantic and the 20°S transect in the Indian Ocean. The results indicate transport of surface waters labelled with 239Pu from the western North Pacific via the Indonesian Seas to the South Indian Ocean and then to the South Atlantic Ocean. Along the whole BEAGLE2003 sampling route, the Atlantic Ocean has the lowest 239Pu content due to its particle scavenging on the long way from the western North Pacific. On the other hand, concentrations of the conservative 137Cs tracer are in all three oceanic basins comparable. The primary productivity reflected by the chlorophyll content in surface waters has similar longitudinal distribution as 239Pu. Radioactive and chlorophyll tracers revealed that the most important current system in each southern oceanic basin is represented by the Subtropical gyre. While the main streams of the gyres maintain high concentrations of tracers, inside the loops the tracer concentrations are the lowest.

137Cs originating from global fallout is transported into the ocean interior by advection and diffusion, and the 137Cs concentration is reduced by radioactive decay. 137Cs concentrations in the global ocean can be simulated by global integration of the coarse-resolution Parallel Ocean Program to understand the mechanism of material transport in the ocean. We investigated the transport mechanism of 137Cs to the Southern Hemisphere using an ocean general circulation model (OGCM) and compared the simulated results with observations of 137Cs concentrations in the Southern Hemisphere. 137Cs was deposited on the ocean surface mainly as global fallout originating from atmospheric nuclear weapons testing since 1945, and the global distribution of cumulative 137Cs deposition has been reconstructed from global measurements of 137Cs in rain, seawater, and soil. We estimated the global distribution of 137Cs deposition from 1945 to 2003 using these distribution data, 137Cs deposition data observed at the Meteorological Research Institute, Tsukuba, Japan, from 1958 to 2003, and 137Cs deposition data for 1945–1957 estimated from ice-core data. We compared the simulated results with 137Cs sections from the South Pacific, Indian, and South Atlantic Oceans obtained during the BEAGLE2003 cruise in 2003. The simulated 137Cs sections were in good agreement with the observations, except for the effects of mesoscale eddies, which not be simulated by the model because of its coarse resolution. OGCMs can simulate the general pattern of 137Cs distribution in the world’s oceans and improve our understanding of the transport mechanism leading to those 137Cs distributions on a time scale of several decades. The model simulation results suggest that the 137Cs deposited in the North Pacific advected to the South Pacific and Indian Ocean, and then to the South Atlantic over about four decades. The North Pacific is thus an important source area of 137Cs to the Southern Hemisphere.

During the reoccupation of the WOCE transect A10 at 30°S by the BEAGLE2003 cruise, the SHOTS project partners collected a large number of samples for the analysis of isotopic tracers. 137Cs was mostly deposited on the oceans surface during the late 1950s and early 1960s, after the atmospheric detonation of large nuclear devices, which mostly occurred in the Northern Hemisphere. The development of advanced radioanalytical and counting techniques allowed to obtain, for the first time in this region, a zonal section of 137Cs water concentrations, where little information existed before, thus constituting an important benchmark for further studies. 137Cs concentrations in the upper waters (0–1000 m) of the south-eastern Atlantic Ocean are similar to those observed in the south-western Indian Ocean, suggesting transport of 137Cs labeled waters by the Agulhas current to the Benguela Current region. In contrast, bomb radiocarbon data do not show this feature, indicating the usefulness of 137Cs as a radiotracer of water mass transport from the Indian to the South Atlantic Ocean.

Oceanic fronts shape marine ecosystems; therefore front mapping and characterization are among the most important aspects of physical oceanography. Here we report on the first global remote sensing survey of fronts in the Large Marine Ecosystems (LME). This survey is based on a unique frontal data archive assembled at the University of Rhode Island. Thermal fronts were automatically derived with the edge detection algorithm of Cayula and Cornillon, 1992 , Cayula and Cornillon, 1995 , Cayula and Cornillon, 1996 from 12 years of twice-daily, global, 9-km resolution satellite sea surface temperature (SST) fields to produce synoptic (nearly instantaneous) frontal maps, and to compute the long-term mean frequency of occurrence of SST fronts and their gradients. These synoptic and long-term maps were used to identify major quasi-stationary fronts and to derive provisional frontal distribution maps for all LMEs. Since SST fronts are typically collocated with fronts in other water properties such as salinity, density and chlorophyll, digital frontal paths from SST frontal maps can be used in studies of physical–biological correlations at fronts. Frontal patterns in several exemplary LMEs are described and compared, including those for: the East and West Bering Sea LMEs, Sea of Okhotsk LME, East China Sea LME, Yellow Sea LME, North Sea LME, East and West Greenland Shelf LMEs, Newfoundland–Labrador Shelf LME, Northeast and Southeast US Continental Shelf LMEs, Gulf of Mexico LME, and Patagonian Shelf LME. Seasonal evolution of frontal patterns in major upwelling zones reveals an order-of-magnitude growth of frontal scales from summer to winter. A classification of LMEs with regard to the origin and physics of their respective dominant fronts is presented. The proposed classification lends itself to comparative studies of frontal ecosystems.

We find that STMW extends across the entire width of the Tasman Sea in a very broad swath between the Tropical Convergence in the north (just to the south of New Caledonia), the southeast Australian coast in the west to as far south as 39°S (likely due to the southward extension of the EAC), and eastwards along the Southern STMW boundary in a meandering pathway that broadly follows the Tasman Front. The total STMW volume across the region (i.e., west of 180°) varies seasonally by a factor of more than three between the estimated maximum of 6.6 (±0.5) × 1014 m3 in October and minimum of 1.9 (±0.4) × 1014 m3 in May. Interannual variations O (±0.5 × 1014 m3) are also observed in the spatial extent of the thick mode water and its total volume. El Nino composite maps show an anomalous thickening of the STMW during the El Nino year with October positive thickness anomalies in excess of +20 m (total volume anomaly of +0.6 × 1014 m3) manifested throughout the subtropical gyre interior as far north as New Caledonia. Total volume anomalies tend to be positive from January of the El Nino year through to the July following (18 months). The maximum correlation coefficient r = −0.3 between 3-monthly STMW volume anomalies and the Southern Oscillation index is statistically significant at the 95% confidence level. We conclude that during the anomalous cooling of the upper Southwest Pacific Ocean in the El Nino year, winter-time convection and STMW formation is enhanced across the region resulting in an El Nino – Southern Oscillation climate signal that is identifiable below the mixed layer by the increased STMW volume which persists through to the following winter. Finally, some evidence for the possible decadal modulation of the STMW variability is also discussed.

The first global ocean reanalysis with focus on the Asian–Australian region was performed for the period October 1992 to June 2006. The 14-year experiment assimilated available observations of altimetric sea-level anomaly, satellite SST and quality-controlled in situ temperature and salinity profiles from a range of sources, including field surveys and the Argo float array. This study focuses on dominant circulation patterns in the South-East Asian/Australian region as simulated by an eddy-resolving and data-assimilating ocean general circulation model. New estimates of the ocean circulation are provided which are largely in agreement with the limited number of observations. Transports of key currents in the region are as follows: The total (top-to-bottom) annual mean Indonesian Throughflow transport and its standard deviation are 9.7 ± 4.4 Sv from the Pacific to the Indian Ocean with a minimum in January (6.6 Sv) and a maximum in April (12.3 Sv). The Leeuwin Current along the west coast of Australia is dominated by eddy structures with a mean southward transport of 4.1 ± 2.0 Sv at 34°S. Along the southern coast of Australia a narrow shelf edge current known as the South Australian Current advects 4.5 ± 2.6 Sv eastward at 130°E. The South Australian Current converges east of Tasmania with the eddy-rich extension of East Australian Current. At 32°S this current transports 36.8 ± 18.5 Sv southward. A dominating feature of the circulation between north-eastern Australia and Papua–New Guinea is the strong and quasi-permanent Coral Sea Gyre. This gyre is associated with the highly variable Hiri Current which runs along the south coast of Papua–New Guinea and advects 8.2 ± 19.1 Sv into the Western Pacific Ocean. All of these transport estimates are subject to strong eddy variability.

Recent global warming caused by humans and the prediction of a reduced Atlantic Ocean meridional overturning circulation in the future has increased interest in the role of the overturning circulation in climate change. A schematic diagram of the overturning circulation called the “Great Ocean Conveyor Belt,” published by Wallace Broecker in 1987, has become a popular image that emphasizes the inter-connected ocean circulation and the northward flux of heat in the Atlantic. This seems a good time to review the development of the conveyor belt concept and summarize the history of overturning circulation schematics. In the 19th century it was thought that symmetric overturning circulation cells were located on either side of the equator in the Atlantic. As new hydrographic measurements were obtained, circulation schematics in the early 20th century began to show the inter-hemispheric overturning circulation in the Atlantic. In the second half of the 20th century schematics showed the global ocean overturning circulation including connections between the Atlantic and the Pacific and Indian Oceans. Some recent schematics of the overturning circulation show its complexities, but as more information is included these schematics have also become complex and not as easy to understand as the simple Broecker 1987 version. However, these complex schematics, especially the quantitative ones, represent valuable syntheses of our developing knowledge of the overturning circulation.

According to the current paradigm of modern climatology and oceanography, the global ocean thermohaline circulation works as the so-called “global ocean salinity conveyor belt” – a system of currents connecting different ocean basins and most notably – the northern North Atlantic and northern North Pacific Oceans – the most distant regions of the world ocean. It is shown here that a slight disparity in freshwater redistribution between the Atlantic and Pacific oceans can be sufficient for building up and maintaining a global conveyor-type ocean thermohaline circulation. On the other hand, relatively small changes in this disparity leading to change in sea surface salinity contrasts between and in the north-south within the northern parts of these two oceans can easily change the conveyor.

We present the results of six dye tracer experiments that measured the mixing and circulation at the shelfbreak front on the New England Shelf. The last three were conducted during the New England Shelfbreak Productivity Experiment (NESPEX) with concurrent isopycnal float deployments. The results are consistent with the Chapman and Lentz [Chapman, D.C., and Lentz, S.J. (1994). Trapping of a coastal density front by the bottom boundary layer. Journal of Physical Oceanography, 24, 1465–1479.] model prediction of the separation and upwelling along the shelfbreak front of bottom boundary layer (BBL) water forced by an Ekman buoyancy flux, but show considerable variability. Cross-shelf velocities at the detachment point are 2–3 × 10−2 m/s. But seaward, over the slope region, dye tagged water was sheared from the main patch into small filaments that upwelled along the front with cross-shelf speeds up to 0.1 m/s. Cross-shelf diffusion was of order 10 m2/s in the mixed bottom layer and 1 m2/s in the interior along the front. Within the stratified front, the mean vertical diffusivity was Kz ∼ 4 × 10−6 m2/s. The dispersion of shelfwater in the slope region is effected by turbulent flow with advective speeds exceeding the small scale diffusive mixing. The mean flux of the detached BBL water is sufficient to account for the net loss of shelf water during its transit from Cape Cod to Cape Hatteras.

During the 1950s and 1960s, an extensive field study and interpretive effort was made by researchers, primarily at the Scripps Institution of Oceanography, to sample and understand the physical oceanography of the eastern tropical Pacific. That work was inspired by the valuable fisheries of the region, the recent discovery of the equatorial undercurrent, and the growing realization of the importance of the El Nino phenomenon. Here we review what was learned in that effort, and integrate those findings with work published since then as well as additional diagnoses based on modern data sets. Unlike the central Pacific, where the winds are nearly zonal and the ocean properties and circulation are nearly independent of longitude, the eastern tropical Pacific is distinguished by wind forcing that is strongly influenced by the topography of the American continent. Its circulation is characterized by short zonal scales, permanent eddies and significant off-equatorial upwelling. Notably, the Costa Rica Dome and a thermocline bowl to its northwest are due to winds blowing through gaps in the Central American cordillera, which imprint their signatures on the ocean through linear Sverdrup dynamics. Strong annual modulation of the gap winds and the meridional oscillation of the Intertropical Convergence Zone generates a Rossby wave, superimposed on the direct forcing, that results in a southwestward-propagating annual thermocline signal accounting for major features of observed thermocline depth variations, including that of the Costa Rica Dome, the Tehuantepec bowl, and the ridge–trough system of the North Equatorial Countercurrent (NECC). Interannual variability of sea surface temperature (SST) and altimetric sea surface height signals suggests that the strengthening of the NECC observed in the central Pacific during El Nino events continues all the way to the coast, warming SST (by zonal advection) in a wider meridional band than the equatorially trapped thermocline anomalies, and pumping equatorial water poleward along the coast. The South Equatorial Current originates as a combination of equatorial upwelling, mixing and advection from the NECC, and Peru coastal upwelling, but its sources and their variability remain unresolved. Similarly, while much of the Equatorial Undercurrent flows southeast into the Peru Undercurrent and supplies the coastal upwelling, a quantitative assessment is lacking. We are still unable to put together the eastern interconnections among the long zonal currents of the central Pacific.

Upper ocean (above 750 m) temperature structure of the northwestern subtropical Atlantic, including the Gulf Stream and a recirculation gyre south of the Stream, is characterized using primarily bathythermograph (BT) data collected between 1950 and 2003. Geostrophic calculations, using mean temperature–salinity relationships to compute dynamic height, are used to estimate velocities and transports. The mean annual Gulf Stream transport at 72° W relative to 750 m, 36.1 Sv, is approximately equal to the sum of the transport of the Florida Current, 32.0 Sv, and a shallow recirculation gyre described by Wang and Koblinsky [Journal of Physical Oceanography 26 (1996) 2462–2479], 5.5 Sv. The annual cycle of geostrophic transport relative to 750 m at 72° W is in phase with both an earlier published annual cycle of transport relative to 2000 m derived from hydrographic observations and the annual cycle of Florida Current transport measured indirectly by a submarine cable (i.e., maximum transports are observed in the summer and minimum in the fall, early winter). However, simple Sverdrup dynamics are inadequate to explain these cycles as maximum Sverdrup transports extend from winter to summer, while observed transports are minimum (maximum) in fall/winter (summer). The annual cycles derived from the BT data of the size of the shallow southern recirculation gyre, Gulf Stream position and upper layer transport (relative to 300 m) are in phase (maximum size, northern position and transport in fall) and consistent with the WK results derived from altimetry. However, the shallower annual cycles are out of phase with the deeper signals (i.e., maximum for the former (latter) are observed in fall (summer)). Decadal signals after 1965 in Gulf Stream position, geostrophic transport relative to 450 m, and the size of a recirculation gyre south of the Stream are approximately in phase as observed for the annual signal. This gyre and the shallow WK gyre exhibit the same horizontal structure, however, the decadal signal propagates deeper into the water column (at least to 700 m). The eastern expansion and contraction of the gyre on decadal time-scales is correlated with propagating SST signals. The sampling implications of these findings are addressed.

This paper provides a retrospective analysis of the relationship of physical oceanography and biology and recruitment of three Eastern Bering Sea flatfish stocks: flathead sole (Hippoglossoides elassodon), northern rock sole (Lepidopsetta polyxystra), and arrowtooth flounder (Atheresthes stomias) for the period 1978–1996. Temporal trends in flatfish production in the Eastern Bering Sea are consistent with the hypothesis that decadal scale climate variability influences marine survival during the early life history period. Density-dependence (spawning stock size) is statistically significant in a Ricker model of flatfish recruitment, which includes environmental terms. Wind-driven advection of flatfish larvae to favorable nursery grounds was also found to coincide with years of above-average recruitment through the use of an ocean surface current simulation model (OSCURS). Ocean forcing of Bristol Bay surface waters during springtime was mostly shoreward (eastward) during the 1980s and seaward (westerly) during the 1990s, corresponding with periods of good and poor recruitment. Distance from shore and water depth at the endpoint of 90-day drift periods (estimated time of settlement) were also found to correspond with flatfish productivity.

The evolution and decay of El Nino 1997–8 was observed in coastal waters off Oregon in a sequence of cruises along 44.6°N from the coast to more than 150 km offshore. Hydrographic observations were made during eleven cruises between July 1997 and April 1999 at stations on the Newport Hydrographic Line, which had been occupied regularly from 1961 to 1971. The data from the earlier decade provide a basis for defining ‘normal’ conditions and allow comparisons with the recent El Nino in terms of T, S, spiciness and geostrophic velocity. Independent of El Nino, the ocean in July 1997 was already anomalously warm offshore of 50 km and above 100 m. By September 1997 there were unambiguous indications of El Nino: isotherms and isohalines sloped down toward the coast indicating poleward flow over shelf and slope, and anomalously spicy water was present at the shelf-break. In November 1997 and February 1998 shelf-break waters were even warmer, and there was strong poleward flow inshore of 100 km, extending to depths greater than 200 m. The April 1998 section closely resembled that of April 1983 (another El Nino year) but by June 1998 the anomalies were mostly gone. November 1998 was near normal and the sections from subsequent cruises resemble the mean sections from 1961–1971. Four cruises between November 1997 and November 1998 included sampling at several latitudes between 38° and 45°N. As expected, these sections show significant alongshore gradients, but also a surprising degree of homogeneity in the anomalous features associated with El Nino (in the temperature, salinity, spiciness and geostrophic velocity fields). The anomalous signature of El Nino was stronger at its winter peak in 1998 than in 1983, but the signature in the temperature and spiciness fields, and in coastal sea level, did not persist as long as in 1983. By April 1999, the coastal ocean from 38°N to 45°N was significantly colder than it had been in April 1984.

A peculiar aspect of western marginal seas is that some of them accommodate large transports whereas others, apparently similar seas, accommodate relatively small transports. For instance, about 30–40 Sv of Atlantic upper water passes through the Caribbean and yet only 2 Sv or so passes through the Sea of Japan. The passages connecting the Caribbean to the Atlantic are somewhat larger than their Sea of Japan counterparts, but the dimensions of the gaps are too similar to each other to account for the large difference in the transports. Four different baroclinic models are used to investigate the problem. First, we used a wind-driven, layer-and-a-half isopycnal model with an idealized basin and an adjacent marginal sea separated from the main basin by a thin and long island. In this scenario, thermocline water enters the marginal sea via a gap to the south of the island and exits the sea via a gap to the north of the island. The mean latitudinal position of the marginal sea is gradually increased and the numerical transport across the sea is measured. We then compared the transport determined this way to that computed using three analytical baroclinic models: Godfrey's island rule (Godfrey, J. S. (1989). A Sverdrup model of the depth-integrated flow for the world ocean allowing for island circulations. Geophysical and Astrophysical Fluid Dynamics, 45, 89–112.), the ‘β-controlled’ transport formula (Nof, D. (1993). The penetration of Kuroshio water into the Sea of Japan. Journal of Physical Oceanography, 23, 797–807), and the general gap transport formula (Nof, D., (1995). Choked flows and wind-driven interbasin exchange. Journal of Marine Research, 53, 23–48). The results were also compared to Minato and Kimura's (Minato, S., & Kimura, R. (1980). Volume transport of the western boundary current penetrating into a marginal sea. Journal of the Oceanographic Society of Japan, 36, 185–195) barotropic calculations. All four baroclinic models show that, when the marginal sea is situated in low and mid latitude, the penetration of thermocline water into the marginal sea decreases rapidly with increased latitude. By contrast, in equatorial marginal seas, the penetration of thermocline water increases with increasing latitude. Minato and Kimura's (1980) barotropic model shows a similar behavior except that the maximum transport occurs at a much higher latitude. Excellent agreement between the numerics and Godfrey's island rule formula is found in equatorial seas. As the latitude of the marginal sea increases to low and mid latitudes, the deviations from the numerics increase dramatically though the agreement is still very reasonable. Both the β-controlled formula and the gap formula are relatively accurate in mid latitudes when the sea is close to the separation latitude. The importance of frictional forces within the western boundary current results in the β-controlled formula failing for marginal seas situated far away from the separation latitude. Similarly, the general gap formula fails in equatorial latitudes where there is no western boundary current south of the island. On the basis of all four baroclinic models, it is suggested that the reason for the small transport within the Sea of Japan (relative to the Caribbean) is its relatively high latitude and not the size of the gaps connecting it to the Pacific Ocean (or frictional effects).

The Mediterranean Sea has been investigated intensively since the early nineties, using modern techniques and collaborative approaches. This overview summarizes some of the resulting advances that were made concerning the physical oceanography of the western Mediterranean. The water mass formation processes are now much better understood and have been quantified to a large extent. The boundary conditions of the system in terms of surface fluxes and strait transports can be determined with improved accuracy, thus enabling future investigation of interannual variability. The dynamics of the surface and intermediate layers have revealed a variety of eddy and mesoscale processes that are important for the circulation and spreading of water masses. The deep circulation is being investigated with Lagrangian techniques (tracers and floats). First results show a large component of the deep water originating from the Tyrrhenian Sea and intense cyclonic and anticyclonic eddy flows.

In this paper we revisit, with a thorough in-depth analysis, the dataset collected in the hydrographic surveys of the international collaborative programme POEM (Physical Oceanography of the Eastern Mediterranean) in the period 1986–1987. The work has two major objectives. The first is to refine the dynamic picture of the Ionian upper thermocline sub-basin scale circulation, rather less definitive than the dynamic picture of the Levantine Sea circulation. The second is to identify the pathways of the major water masses of the basin not only in the near-surface, but also in the intermediate and deep layers. To our knowledge, this is the first work defining the pathways of the Levantine Intermediate Water (LIW) and of the Adriatic Deep Water (ADW)/Eastern Mediterranean Deep Water (EMDW) that characterize the intermediate and deep circulations. The major novel results can be summarized as follows. In the upper thermocline: (1) The Atlantic Ionian Stream (AIS) jet entering the Sicily Straits bifurcates into two main branches at 37°N, ∼ 17°E. It advects the Modified Atlantic Water (MAW) into the Ionian Sea interior. The first branch turning directly southward encloses an overall anticyclonic area comprising multiple centers around which the MAW is advected. (2) The second AIS branch extends further into the northeastern Ionian, where it too turns southward before crossing the entire Ionian Sea meridionally, advecting MAW on its left side and Ionian Surface Water (ISW) on its right. This branch of the jet is confined to the Ionian margin and does not pass around the Pelops gyre. (3) A new water mass, the LSW, is formed in the Levantine basin and enters the Cretan passage, then is first veered cyclonically south of Crete by the Cretan gyre and successively is entrained anticyclonically around the Pelops gyre, and then enters the Aegean Sea. (4) A permanent cyclone located in the northeastern Ionian determines the pathway of mixed Adriatic Surface Water/Ionian Surface Water (ASW/ISW). (5) A permanent cyclone is found in all the surveys near the tip of the Italian boot. This novel analysis of the LIW pathways shows that: (1) The major source of intermediate LIW during the period 1986–1987 was actually in the Levantine Sea. LIW formed there entered the Cretan passage, was veered cyclonically by the Cretan gyre south of Crete and then entered the southern Ionian Sea. The major LIW pathway was westward directly to the Sicilian Straits. (2) Secondary important LIW pathways were determined by the interior structures. The strong Pelops anticyclone was entraining LIW around its periphery and was determining the LIW northward pathway that closely followed the eastern Greek coastline. It was along this pathway that LIW entered the Otranto Strait. A further branch of LIW was entrained and recirculated around the multiple Ionian Anticyclones (IA) of the western Ionian Sea. (3) The Cretan cyclone is a feature confined to the upper thermocline-intermediate layer. It disappears at ∼ 400 dbar while the Pelops anticyclone is strongly barotropic below the upper 100 dbar and penetrates quite intense down to 800 dbar. (4) A further completely novel result concerns the new water mass found in the deep layer that spreads on the 29.15 kg/m3 isopycnal surface. This water mass, characterized by high salinity and high oxygen content, is formed inside the Aegean Sea and is observed to spread out all around the Cretan Arc Straits. The final fully novel result is the demonstration of a second pathway for the ADW exiting from the Otranto Strait that is transformed into EMDW and occupies the abyssal layers of the Ionian Sea interior. The traditional pathway for EMDW is along the isobaths along the western side of Italy but ADW was observed to be exiting from the Otranto Strait in the eastern Hellenic trench at 39.5°N, both during POEM-ON86 and POEM-AS87. This second pathway for EMDW follows isobath contours along the western side of Greece. The two EMDW routes converge and merge between 36°N and 35°N, so producing a deep layer of EMDW that occupies uniformly the abyssal plain of the interior of the Ionian Sea.

The aim of this paper is to present a detailed energy budget of the M2 ocean tides over the world ocean, based on the hydrodynamic tidal solution FES94.1 which includes not only the characteristics of the sea surface tidal elevations, but also of the tidal currents. Global and regional budgets are given. The global energy input by astronomical forcing, deduced from the (2,2) spherical harmonic development of the M2 sea surface elevation solution, is 2.35 TW (lower by 0.1 TW than for the new altimetric solutions produced recently directly from satellite observations). One major feature emerging from the present analysis is that a quarter of this energy input takes place over the South Atlantic Ocean. On the other hand, ocean tides work against astronomical forcing over three areas: Eastern Indian Ocean, southwest of the South American Continent, and around New Zealand. This energy is dissipated (in FES94.1) by bottom friction over the main continental shelves, but the outstanding feature is that 40% of the tidal energy is dissipated over the North Atlantic Ocean. Energy is thus redistributed from the areas of energy input to feed the areas of dissipation. The Pacific Ocean, the Indian Ocean and the South Atlantic Ocean receive more energy in total than they dissipate, in contrast with the Atlantic Ocean and the Arctic Ocean, where a large deficit must be compensated by a net influx of energy from the other basins. One third of the total M2 energy input by astronomical forcing over the world ocean flows northwards through the Equatorial Atlantic. Detailed energy dissipation estimates are computed over the different areas of energy dissipation and compared to the previous estimates published in the literature.

28 páginas, 22 figuras, blooms (HABs) because they are highly productive, nutrient-rich environments, prone to high-biomass blooms. This review identifies those aspects of the physical environment important in the development of HABs in upwelling systems through description and comparison of bloom events in the Benguela, California and Iberia systems. HAB development is dictated by the influence of wind stress on the surface boundary layer through a combination of its influence on surface mixed-layer characteristics and shelf circulation patterns. The timing of HABs is controlled by windstress fluctuations and buoyancy inputs at the seasonal, event and interannual scales. Within this temporal framework, various mesoscale features that interrupt typical upwelling circulation patterns, determine the spatial distribution of HABs. The inner shelf in particular provides a mosaic of shifting habitats, some of which favour HABs. Changes in coastline configuration and orientation, and bottom topography are important in determining the distribution of HABs through their influence on water stratification and retention. A spectrum of coastline configurations, including headlands, capes, peninsulas, Rías, bays and estuaries, representing systems of increasing isolation from the open coast and consequent increasing retention times, are assessed in terms of their vulnerability to HABs., Support was provided to B.M.H. from the Ecology and Oceanography of HABs Pacific Northwest Program (publication #27 for ECOHAB PNW and #328 for the National ECOHAB program) by Grants from the NOAA Coastal Ocean Program (NA170P2789), the National Science Foundation (NSF) (OCE-0234587), and by NOAA support through the Olympic Region HAB Program (NA07OA0310). This publication was also supported by Grant P50 ES012762 from the National Institute of Environmental Health Sciences (NIEHS), NIH and OCE-0434087 from the NSF.

Autocorrelation functions of sea surface temperature (SST) and depth of the 20°C isotherm (D 20 ) are estimated at 95 locations along the tropical Pacific expendable bathythermograph (XBT) ship-of-opportunity tracks, and used to determine statistical parameters required for optimal interpolation. The parameters are variances for signal and noise, and spatial/temporal decorrelation scales. Estimates were made for two periods of time: June 1979 to May 1982 proceding the 1982/83 El Nino, and June 1979 to May 1983 including it. Parameters for the first period indicate smaller scales and weaker signals than the ones for the second. The difference results from El Nino, whose large temperature signal dominates the statistical structure. Understanding the dynamics of the smaller interannual signals and in particular the precursors to El Nino is as important as understanding El Nino. The smaller scales are therefore recommended for optimal interpolation and design of the XBT network. Three summaries of the scales are presented: 1) averages in three degree latitude bands; 2) values in dynamic regions representing the major zonal currents; and 3) median values for 95 estimates in the tropical Pacific 18°N to 18°S. The median values are recommended for design of the tropical XBT network. The median scales for the depth of the 20°C isotherm are: 3° latitude, 15° longitude and 2 months; and the median signal-to-noise (amplitude) ratio is 0.75. Scales for SST are greater than or equal to scales for D 20 , thus subsurface temperature is the limiting factor in designing the network. Analysis of mapping errors suggests that optimal sampling requires two to three samples per decorrelation scale. Two modes of XBT sampling are recommended for TOGA. Broadscale sampling for horizontal mapping of the temperature field is recommended at a density of two samples per scale, which requires an XBT station every 1.5° latitude and 7.5° longitude, monthly. The broadscale mode should be implemented in as large an area as possible with available shipping. Sampling on repeated transequatorial sections for time series studies is recommended at a density of three samples per scale, which requires 18 sections per year, with stations every 1° latitude. The time series mode is useful for more accurate studies of thermal structure and currents, and should be implemented on a few routes in each ocean which transect major thermal features.

Introducción de los editores a este número de la revista dedicado a "Mediterranean physical oceanography and biogeochemical cycles: Mediterranean general circulation and climate variability"

THE TASK of unravelling the factors governing the circulation of the oceans is one of the foremost in physical oceanography, yet the origin of the idea of the internal circulation of the ocean is obscure. Only since the time of the Challenger expedition, which sailed in 1872, has it been generally accepted that density differences within the ocean, due to variations in salinity and temperature, can set great water masses in motion. It was W. B. Carpenter's conviction, based on the earlier work of H.M.S's Lightning and Porcupine between 1868 and 1870, that cold dense water flowed from polar regions towards the equator in the ocean depths while a return flow of warmer lighter water took place at the surface, which led him to promote the expedition (DEACON, 1971). PRESTWlCH (1875) traced back similar ideas to the early 1800s. In the intervening years they had fallen out of favour when confusion arose over results obtained with Six self-registering thermometers, insufficiently protected against the effects of pressure (McCONNELL, 1978) and the widespread belief that sea water's maximum density occurred at the same temperature as in fresh water. Temperature differences were generally held to be responsible for circulation but some writers, such as MAURY (1855) in The Physical Geography of the Sea, thought that salinity was more important. Before the end of the 18th century it would not have been at all obvious from studying observations of subsurface temperature that such a situation existed. Measurements in the Mediterranean, such as those made by MARSIGLI (1725), indicated a mean temperature below the level affected by seasonal changes. There was no reason to think of this as exceptional and it fitted in well with the ideas of those who believed the centre of the earth to be warm, and its heat to be transmitted through the sea floor. If it were not for this and the vertical mixing which ensued, said DORTOUS DE MAIRAN (1749), the water in the depths of the sea would turn to ice. Measurements in the Southern Ocean, made on Captain Cook's second voyage, appeared to confirm this view by showing the existence of warmer water beneath the cold surface layer (DEACON, 1971). Proof of the presence of polar water in the depths of tropical seas was not obtained until after 1800 but THOMPSON (1798) had already explained examples of deep-sea temperature, below the atmospheric mean prevailing in the latitudes where they were taken, by the spread of cold water, due to its greater density. However, his was not the first attempt to outline a theory of ocean circulation. A similar idea, but relying on salinity instead of temperature differences, had been put forward in a remarkable paper nearly half a century earlier. In 1755 the Royal Swedish Academy of Sciences published in its Transactions a paper by a German author, HerrWAITZ, Privy Councillor to the Landgrave of Hesse-Cassel. It was entitled: 'An investigation into the reasons why the water of the Atlantic Ocean always flows into the Mediterranean Sea through the Straits of Gibraltar.' WAITZ (1755) argued that the difference