Andrey G. Kostianoy

Observations of Black Sea mesoscale eddies and associated horizontal mixing

[1]xa0A large (80–90 km in diameter) anticyclonic eddy centered at 43°N, 37–38°E has been the subject of complex investigation in the summer-autumn of 1999 based on measurements carried out during the “Black Sea99” expedition on board of R/V Akvanavt (CTD surveys, deployment of Argos-tracked drifters), analysis of satellite imagery, and using altimetric sea level anomaly maps from merged TOPEX/POSEIDON and ERS-2 satellite data. The eddy was formed as a nearshore anticyclonic eddy (NAE) in the Sochi-Sukhumi region, separated from the coast on 6–9 April 1999, stayed at the center of the eastern basin, which is usually characterized by cyclonic circulation, during about 8 months and decayed near the Turkish coast in December 1999. A compilation of hydrodynamic situations of different years (1993, 1997–1999) suggests that similar open sea anticyclonic eddies are frequently the elements of the circulation in the eastern Black Sea in the warm season (April–December). A positive correlation appears to be between eddies formation and weak macroscale circulation associated with low atmospheric wind forcing. Long lifetime of open sea anticyclones is likely determined by their interaction with neighboring eddies. NAEs separation from the coast and their transformation into open sea eddies provide horizontal mixing of the upper layer waters and results in deflection of the Rim Current offshore, formation of large meanders of the current around the eddies, and its branching when rounding such features. An example of calculation of cross-shelf water transport relating to an offshore Rim Current branch is presented. It is pointed out that an estimation of the shelf/open sea water exchange based on the box balance model does not contradict the assumption that such exchange is considerably determined by NAEs separation from the coast.

The West African coastal upwelling filaments and cross-frontal water exchange conditioned by them

One of the important problems in the oceanography of the wind-driven upwelling regions of the Ocean is the investigation of water exchange processes in the coastal zone. Satellite data (thermal and colour imagery) have changed our view on these processes after the relatively recent discovery of cold, chlorophyll-rich, narrow (< 50 km wide) offshore flowing filaments off the west coasts of North America, North and South Africa. On the basis of satellite IR images and oceanographic original and archive data we investigated systems of filaments in the northwest and southwest African upwelling regions. The spatial distribution of filaments was analyzed. It was found that seasonal variability of the filaments location depends upon the general intensity of upwelling motion along the coast during the year. The main statistical characteristics of filaments were obtained. An example of the three-dimensional velocity structure of the filament was presented. In order to estimate the intensity of cross-frontal exchange process due to filaments, a special procedure was proposed. The values of the velocity of cross-frontal water exchange produced by filaments in these upwelling zones are obtained. It was shown that upwelling filaments play an important role in water exchange between the coastal zone and the open ocean. A non-dimensional parameter which characterizes the permeability of oceanic fronts for water exchange due to mesoscale dynamical structures was introduced and estimated.

Hydrographic survey in the dying Aral Sea

[1]xa0We report the results of a hydrographic survey conducted in November, 2002, in the Uzbekistan part of the western basin of the dying Aral Sea. There were very few hydrographic measurements in this region since at least early 1990s. The salinity in the western deep basin of the Aral Sea varied from about 82 psu at the surface to over 94 psu at the bottom. The absolute lake surface level was about 30.5 m. Hence, the observed salinity values were much higher, and the level much lower, than expected according to earlier predictions. The density in the western basin exhibited an extremely strong stratification of ∼11 kg/m3 per ∼20 m in the bottom layer. The picnocline was accompanied by a temperature inversion whose magnitude was ∼4°C. The observed density stratification effectively isolating the lower part of the water column from surface exchanges may be responsible for the increase of summer SSTs and evaporation rates reported in previous studies. We discovered the hydrogen sulphide contamination in the bottom layer whose upper limit was at the depth of approximately 22 m. Estimates suggest that the western basin salinization occurs not only because of the local evaporation, but also because of the assimilation of the saltier eastern basin water in the course of the interbasin exchange through the connecting channel. The satellite imagery analysis, in particular the Maximum Cross-Correlation method, suggests that the circulation pattern in the Aral Sea in its present limits is cyclonic under the eastern winds that are predominant in the region throughout the year.

Anticyclonic eddies in the northwestern Black Sea

Abstract National Oceanic and Atmospheric Administration (NOAA) Advanced Very-High Resolution Radiometer (AVHRR) imagery (1993, 1998), along with attendant daily meteorological information from seaports and available hydrographic information from different years, was used to investigate the structure and evolution of mesoscale anticyclonic eddies in the northwestern Black Sea, and their role in shelf/deep basin water exchange. In the summer of 1993, two anticyclonic eddies with diameters of 90 and 55 km coexisted without coalescence for 1.5 months over a wide and relatively gentle part of the northwestern continental slope. The directions of the eddies movements inside this zone (speed of movement up to 16 cm/s) were likely determined by the interaction between eddies themselves, and by the Rim Current meandering and forcing. For June–August of 1998, three such eddies have been traced in the sea surface temperature (SST, AVHRR) and chlorophyll a (SeaWiFS) fields. The largest anticyclone with a diameter of 90 km moved during 3 months southwestward from the wide slope region west of Sevastopol to the area of narrower slope southeast of Cape Kaliakra with a mean speed of about 3 cm/s. Together with nonstationary associated elements (cyclones at the eddies peripheries, entrained and ejected jets), anticyclonic eddies determine water exchange processes in a large area of the western Black Sea between 43–45°N and 29–33°E. They transport chlorophyll-rich coastal waters to the deep basin, westerly winds being favorable to the process.

A survey of observations on intrathermocline eddies in the world ocean

A special type of oceanic eddies, intrathermocline eddies (ITE), is studied. A regional survey of ITE observations in the World Ocean is presented. In many cases a new interpretation of observed features is given based on the ITE concept. The main results of Arctic experiments (AIDJEX-1970, 1972, 1975/76; “North Pole” - 2, 8, 12) are reviewed. Special discussion is devoted to the Canary Basin, the Canary upwelling system, the Sargasso Sea, the Pacific, Indian and Southern Oceans. A particular attention is paid to Meddies distribution in the North Atlantic. A southern route of Meddies to the Sargasso Sea through the Kane fracture zone is proposed. A density bimodality of Meddies is observed (σθ = 27.45 to 27.55 and 27.65 to 27.85). The main aspects of ITE generation mechanisms, movements, evolution and geographical distribution are discussed.

Operational satellite monitoring of oil spill pollution in the Southeastern Baltic Sea: 1.5 Years experience

In June 2003 LUKOIL-Kaliningradmorneft initiated a pilot project, aimed to the complex monitoring of the southeastern Baltic Sea, in connection with a beginning of oil production at continental shelf of Russia in March 2004. Operational monitoring was performed in June 2004-November 2005 on the base of daily satellite remote sensing (AVHRR NOAA, MODIS, TOPEX/Poseidon, Jason-1, ENVISAT ASAR and RADARSAT SAR imagery) of sea surface temperature (SST), sea level, chlorophyll concentration, mesoscale dynamics, wind and waves, and oil spills. As a result a complex information on oil pollution of the sea, SST, distribution of suspended matter, chlorophyll concentration, sea currents and meteorological parameters has been received. In total 274 oil spills were detected in 230 ASAR ENVISAT images (400×400 km, 75 m/pixel resolution) and 17 SAR RADARSAT images (300×300 km, 25 m/pixel resolution) received during 18 months. The interactive numerical model Seatrack Web SMHI (The Swedish Meteorological and Hydrological Institute) was used for a forecast of the drift of (1) all large oil spills detected by ASAR ENVISAT in the southeastern Baltic Sea and (2) virtual (simulated) oil spills from the D-6 platform. The latter was done daily for operational correction of the action plan for accident elimination at the D-6 and ecological risk assessment (oil pollution of the sea and the Curonian Spit). Probability of the oil spill drift directed to the Curonian Spit equals to 67%, but only in a half of these cases oil spills could reach the coast during 48 h after an accidental release of 10 m3 of oil.

Patterns of Seasonal and Interannual Changes of Surface Chlorophyll Concentration in the Black Sea Revealed from the Remote Sensed Data

Abstract Several years of CZCS-measured surface pigment’s concentrations in the Black Sea are analyzed to appraise the seasonal and year-to-year fluctuations of phytoplankton biomass and understand the causes of these fluctuations in terms of the Black Sea’s general dynamics. The pattern of seasonal variations is typical for subtropical rather than temperate regions. The range of the absolute value of plant pigment surface concentration measured by remote sensing does not differ greatly from the values measured by direct methods. The pattern of year-to-year variations seems to correlate with cyclic oscillations of winter air temperature. In western shallow regions it is also correlated with the Danube discharge intensity. More intensive winter–spring blooms and a slightly lower level of pigment concentration during warm season are typical for years of with a mild winter. The causes of these regularities seem to be the peculiarities of hydrological and meteorological regimes of the Black Sea. The intensity of winter–spring bloom of phytoplankton appears to depend on hydrological mechanism (i.e., the intensity of water mixing during winter period due to thermic convection and wind mixing) rather than the illumination intensity.

Analysis of velocity field in the eastern Black Sea from satellite data during the Black Sea '99 experiment

[1]xa0Maximum cross correlation (MCC) analysis of National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) imagery of the eastern Black Sea in late September 1999 has been used to reconstruct the velocity and vorticity fields of the upper layer of the sea. Analysis revealed the large-scale dynamic features characteristic of the Black Sea, namely the Rim Current, as well as the detailed pattern of mesoscale vortical activity including meanders, eddies, and dipoles, which are often observed on satellite visible, infrared, or sea color imagery. The dynamical character of the pronounced dipole structure in the northeastern part of the Black Sea was determined by comparison with satellite IR images, geostrophic velocities calculated on the basis of conductivity-temperature-depth (CTD) casts performed and trajectories of six Argos-tracked surface velocity program (SVP) drifters deployed during the Black Sea 99 expedition onboard R/V Akvanavt on 25–30 September 1999.

Chapter 15 Remotely sensed coastal/deep-basin water exchange processes in the Black Sea surface layer

The role of mesoscale structures (eddies, dipoles, jets) in horizontal mixing and coastalJdeep-basin water exchange in the Black Sea was investigated with National Oceanic and Atmospheric Administration (NOAA) Advanced Very-High Resolution Radiometer (AVHRR) imagery during 1993 and 1996-1998, together with relevant meandaily meteorological data from seaports and available hydrographic data of different years. In summer 1993 two anticyclones with diameters of about 90 and 55 km co-existed without coalescence over the northwestern continental slope. Cyclones at the eddies peripheries, entrained and ejected jets, filaments, and a pinched-off cyclone near Cape Hersones (44°35N, 33°22E) associated with wind-driven coastal upwelling contributed to the water exchange in the region. Four anticyclones about 50 km in diameter and associated cyclones at their peripheries were observed in the southeastern region in November 1996. Surface circulation in the region was considerably changed over several days because of the anticyclones movements, and formations and disruptions of short-lived dipoles of anticyclones and associated cyclones at their peripheries. Near-shore anticyclonic eddies with diameters of 40-80 km and lifetimes up to one month, which form along the Caucasian coast and propagate with velocities up to 17 cm s-1 in the general direction of the Rim Current, can evolve into deep-sea eddies southwest of Novorossiisk. Offshore jets, up to about 200 km in length and associated with the anticyclones, are an effective mechanism of coastalJdeep-basin water exchange in the northeastern region.

Mesoscale eddies and related processes in the northeastern Black Sea

Abstract Mesoscale dynamics in the northeastern Black Sea in Autumn 1993 and 1997 is considered on the basis of analysis of the NOAA AVHRR imagery together with relevant hydrographic measurements and meteorological information. Over the course from 6 September to 8 October 1997, five near-shore anticyclonic eddies (NAEs) about 40 km in diameter were observed within the region between Tuapse and the Kerch Strait, their movement speed reaching about 15 cm/s at separate parts of their trajectories. Separation of an NAE (NAE-1) from the coast in the region of a widening shelf/slope west of Novorossiysk and its transformation into deep-sea eddy was traced. Lifetime of the anticyclone was no less than 1 month, its mean offshore speed was about 4.3 cm/s. According to the SeaWiFS data, the increased chlorophyll a concentration (compared with the mean concentration at the center of the eastern part of the sea) was observed on 8 October 1997 in four “young” NAEs after an intense precipitation, the decreased one at the same time occurred in NAE-1, which was depleted of supply by shelf waters. In Summer 1993, a large NAE (about 95 km in diameter) was observed in the region between Tuapse and Gelendzhik. Evolution of the eddy from 3 June to 8 November 1993 was traced. Lifetime of the eddy exceeded 5 months. Its mean offshore speed to the southwest since its separation from the coast (around 17 August) in the Novorossiysk region was about 1.2 cm/s. The difference between dynamic situations in the same season (autumn) of 2 years, 1997 and 1993, was likely associated with peculiarities of atmospheric circulation and related intensity of cyclonic circulation in the Black Sea.