Abstract:We have examined information on the shape and size of Antarctic icebergs as derived from the ship data archive of Arctic and Antarctic Research Institute. The data in the archive cover the period from 1957-2009. For each of five major iceberg shapes we have established their relative frequency of occurrence in the Southern Ocean and the frequency distribution of the iceberg length and freeboard. Weathered and tabular icebergs were observed most often and comprised 66.9% and 22.6% of all reported icebergs respectively. Sloping, pinnacle, and dome icebergs represented correspondingly only 5.6%, 3.2% and 1.7% of the total number of icebergs observed. A distinct maximum was found in frequency distributions of the iceberg length and freeboard for all iceberg shapes. The most frequently observed iceberg lengths (modal length) ranged from 100-200 m for weathered and pinnacled icebergs to 400-600 m for tabular and dome-shaped iceberg. The modal freeboard of icebergs changed from 30-40 m for tabular and weathered icebergs to 50-60 m for domed, pinnacle and sloping icebergs. To calculate the overall mean size parameters of Antarctic icebergs we totalled corresponding mean values for each iceberg shape weighted by the frequency of occurrence of icebergs of each shape. The mean iceberg length and the standard deviation obtained within this approach were correspondingly 381 m and 349 m. The mean iceberg freeboard was equal to 41.2 m with a standard deviation of 12.1 m.

The spatial distribution and multiyear variability of iceberg concentration in the Atlantic and Indian ocean sectors of the Antarctic region have been studied using ship‐borne observations of iceberg occurrence. The collected dataset includes more than 40,000 reports predominantly from Russian and Australian research vessels made over the last 36 years (1970–2005). The analysis of the data has revealed a gradual decrease in the iceberg concentration away from the coast of Antarctica and a substantial variation along the coast line. Large concentration of icebergs was found in the Weddell Sea and north‐east of the Antarctic Peninsula. Several regions in the Atlantic and Indian Ocean sector of Antarctica have been identified where yearly anomalies of the iceberg occurrence exhibit a noticeable correlation with El Niňo/Southern Oscillation (ENSO) events. The strongest ENSO effect was observed in the region east of Drake Passage where the iceberg concentration increased by about 50% during years of the negative Southern Oscillation Index (SOI) phase. The change in the iceberg amount is explained by an increased iceberg drift into this region from the southern part of Weddell Sea and from Pacific Ocean. The latter is caused by anomalous surface pressure High and associated anti‐clockwise circulation around the pressure anomaly developing in the south‐eastern part of Pacific Ocean during the negative phase of ENSO.

ABSTRACT. Information on the occurrence, spatial distribution and morphometric characteristics of Antarctic icebergs is needed in a large number of applications including navigation, heat and freshwater balance calculations, biochemistry of the ocean and climatology. Using over 60 000 ship observations of icebergs in the Southern Ocean collected since the end of the 1940s we have produced a detailed map of the distribution of Antarctic icebergs as well as maps of related statistics including the standard deviation, minimum and maximum values of the iceberg concentration and the probability of iceberg-free observations. The study incorporated small and medium-sized icebergs with a length of <10 nautical miles. Most observations were taken during the warm period of the year, from December to April. It is shown that the iceberg distribution across the Southern Ocean is determined by the location of calving regions and peculiarities of the atmospheric circulation and ocean currents. Iceberg concentration data combined with information on the iceberg size and shape distribution have been used to evaluate the area-integrated characteristics of Antarctic icebergs. The instantaneous number of icebergs in the Southern Ocean was estimated as 132 269 with an uncertainty of 7%. The area and volume of icebergs were equal correspondingly to 55 805 km 2 and 16 893 km 3 with uncertainties of 32-33%.

Earlier studies indicate that during El Niño events the iceberg concentration increases in the east of the Pacific sector and in the west of the Atlantic sector of Southern Ocean, but decreases in the center of the Pacific sector. During La Niña the pattern of the iceberg concentration anomalies in these regions reverses. This iceberg redistribution is explained by anomalous winds and currents around an extensive positive atmospheric pressure anomaly that typically develops in the South-East Pacific during the warm El Niño-Southern Oscillation (ENSO) phase. In this study, the results of iceberg observations during two cruises of the r/v ''Akademik Fedorov'' in Antarctica in January-February 2008 (La Niña) and 2010 (El Niño) have been used to examine the consistency of changes in the iceberg distribution in the Southern Ocean related to El Niño events. The analysis of these observations has shown that in the Pacific Sector of Antarctica changes in the iceberg distribution between 2008 and 2010 followed the scenario outlined above and thus could be associated with the ENSO phase change. Contrary to earlier observations, the iceberg concentration in the Atlantic sector of Antarctica did not increase during 2010 El Niño. The latter is explained by a noncanonical type of 2010 El Niño, El Niño Modoki, and associated atmospheric circulation pattern different from the canonical El Niño. Further analysis has shown that a more frequent occurrence of El Niño Modoki in recent years have resulted in weaker links between El Niño events and the Antarctic iceberg distribution.

Based on meteorological obscrvations from five USSR research ships during Expedition TI10PEX-72 in the Atlantic Ocean for the period from June to August 1972, the relationship between surface winds and pressure gradients near the Equator is analysed. For the narrow Equatorial zone (0-2.5" N) the nearly complete independence of the surface wind speed (rather strong 7-8 m/sec) and direction from the local pressure gradients was found and on this basis the conclusion is drawn concerning the important role of the air stream inertia in this zone. However, the estimates of different terms in the equation of motion for the near-Equatorial latitudes showed that, as in the middle latitudes, the inertia terms of the mean motion are here one order of magnitude smaller than the terms of pressuro gradient. Having this in mind we believe that the only proposition which could be made concerns the important role of the inertia associated with turbulent rather than average motion in the dynamics of the Equatorial atmosphere. It is shown that tho inertia of the air stream near the Equator can account for the asymmetry of the vorticity field around the axis of the Equatorial trough (cyclonic relative vorticity north of the trough axis and the anticyclonic one south of the axis in Northern Hemisphere). It is shown that the wind deflection angles become normal for the usual geostrophio relation over tho sea only north of 11-13" N.