Oceanographic Data of the 28th Japanese Antarctic Research Expedition from November 1986 to April 1987

The results of the oceanographic observations on board icebreaker Shirase and tidal observation at Syowa Station are presented in this report. The oceanographic observations were carried out in the summer mission of the 28th Japanese Antarctic Research Expedition (JARE-28) in 1986-1987. Tidal observation was continued through the winter mission of JARE-27 in 1985-1986

Long-term and seasonal changes of the mean sea level at Syowa Station, Antarctica, from 1981 to 2000

Sea level has been observed since 1966 at Syowa Station, a Japanese Antarctic station located on East Ongul Island(39.6°E , 69.0°S ). An almost continuous record has been obtained from 1981 to 2000 and analyzed to investigate long-term and seasonal changes of mean sea level. After correction of year-to-year variation of the datum, it is found that the annual mean sea level has been falling at a rate of 1.2cm/year. This rate is bigger than previous estimations calculated from shorter records of sea level without appropriate datum adjustment, and also bigger than that expected from geological evidence. Based on discussion of the reasons for the trend, it is suggested that glacial rebound can not be excluded as the cause. The present analysis based on a long record for about 20years also provides the amplitude(2.7cm) and phase of the nodal tide with the period of 18.6years. Characteristics of the seasonal change for the first half of the record(1981-1989) are different from those for the second half(1990-2000), associated with replacement of the observing system in 1990. Comparing with seasonal changes at other Antarctic stations and considering the results of previous studies, it is concluded that the seasonal change observed in the second half is more reliable, and that it reaches its maximum in April and minimum in October with an estimated annual tidal range of about 14cm

A multilevel dataset of microplastic abundance in the world’s upper ocean and the Laurentian Great Lakes

A total of 8218 pelagic microplastic samples from the world’s oceans were synthesized to create a dataset composed of raw, calibrated, processed, and gridded data which are made available to the public. The raw microplastic abundance data were obtained by different research projects using surface net tows or continuous seawater intake. Fibrous microplastics were removed from the calibrated dataset. Microplastic abundance which fluctuates due to vertical mixing under different oceanic conditions was standardized. An optimum interpolation method was used to create the gridded data; in total, there were 24.4 trillion pieces (8.2 × 104 ~ 57.8 × 104 tons) of microplastics in the world’s upper oceans

Seasonal variations of the sea level at Syowa Station,Antarctica

The sea level record at Syowa Station, Antarctica for the period from 1979 to 1988 is analyzed, and the seasonal variation of the sea level is investigated. The level reaches a maximum in early winter and falls to its minimum in mid-summer. The variation shape is very skewed with flat winter peak and sharp summer trough. The ascending speed of the sea-level in fall is much larger than the descending speed in spring. The correlation of the sea level change with several oceanographic and meteorological phenomena are discussed, and several possible mechanisms are reviewed. However, we cannot reach a definitive conclusion yet

Impact of sporadically enhanced river discharge on the climatological distribution of river water in Suruga Bay

In Suruga Bay the river discharge is sporadically enhanced by heavy rainfall, and its daily mean values often exceed by an order of magnitude the seasonal means. We have therefore investigated the impact of the sporadically enhanced river discharge on the climatological distribution of river water in Suruga Bay, performing numerical experiments with an ocean general circulation model. As the river discharge is enhanced, a larger amount of the Coastal Water (defined by salinity less than 33.0) is exported out of shallow areas such as the continental shelf, being less trapped by the bottom topography. Moreover, the high frequency (day-scale) variation in the river discharge causes large temporal variations of the surface salinity distribution in the bay. However, it has only a minor influence in the time-averaged field (under the same condition in terms of the total amount of the discharged river water). It is therefore suggested that in the actual sea, the high frequency (day-scale) variability in the river discharge has only a minor influence on the climatological distribution of river water in the bay

Impact of sporadically enhanced river discharge on the climatological distribution of river water in Suruga Bay

In Suruga Bay the river discharge is sporadically enhanced by heavy rainfall, and its daily mean values often exceed by an order of magnitude the seasonal means. We have therefore investigated the impact of the sporadically enhanced river discharge on the climatological distribution of river water in Suruga Bay, performing numerical experiments with an ocean general circulation model. As the river discharge is enhanced, a larger amount of the Coastal Water (defined by salinity less than 33.0) is exported out of shallow areas such as the continental shelf, being less trapped by the bottom topography. Moreover, the high frequency (day-scale) variation in the river discharge causes large temporal variations of the surface salinity distribution in the bay. However, it has only a minor influence in the time-averaged field (under the same condition in terms of the total amount of the discharged river water). It is therefore suggested that in the actual sea, the high frequency (day-scale) variability in the river discharge has only a minor influence on the climatological distribution of river water in the bay

A numerical experiment on ocean circulations forced by seasonal winds in Suruga Bay

We investigate influence of the seasonal variation in the wind field on water circulation in Suruga Bay by using a wind data set and a numerical ocean model. Counterclockwise vorticity is supplied around the bay mouth from the atmosphere into the ocean in January (winter) and April (spring), whereas clockwise vorticity is supplied in July (summer) and October (autumn). Corresponding to the change in the wind field, a counterclockwise circulation is generated at the sea surface around the bay mouth in January and April, whereas a clockwise circulation in July and October. Moreover, one or two weak circulations are generated to the north of the circulation. These circulations, which are quasi-geostrophic and strongly influenced by land and ocean bottom topography, are generated without effect of the Kuroshio current. Quasi-stagnant and convergent regions tend to appear in the surface layer in the eastern part of the bay, except for autumn. There is a possibility that the wind-driven circulations may play an important role in transport of floating materials, such as seagrass, from in and around the bay to the eastern part of the bay, where a large amount of seagrass has been observed both on the sea surface and floor

A numerical experiment on ocean circulations forced by seasonal winds in Suruga Bay

We investigate influence of the seasonal variation in the wind field on water circulation in Suruga Bay by using a wind data set and a numerical ocean model. Counterclockwise vorticity is supplied around the bay mouth from the atmosphere into the ocean in January (winter) and April (spring), whereas clockwise vorticity is supplied in July (summer) and October (autumn). Corresponding to the change in the wind field, a counterclockwise circulation is generated at the sea surface around the bay mouth in January and April, whereas a clockwise circulation in July and October. Moreover, one or two weak circulations are generated to the north of the circulation. These circulations, which are quasi-geostrophic and strongly influenced by land and ocean bottom topography, are generated without effect of the Kuroshio current. Quasi-stagnant and convergent regions tend to appear in the surface layer in the eastern part of the bay, except for autumn. There is a possibility that the wind-driven circulations may play an important role in transport of floating materials, such as seagrass, from in and around the bay to the eastern part of the bay, where a large amount of seagrass has been observed both on the sea surface and floor