Mikio NAGANOBU - Academia.edu (original) (raw)
Papers by Mikio NAGANOBU
Proceedings of the NIPR Symposium on Polar Biology, Sep 1, 1989
Memoirs of National Institute of Polar Research. Special issue, Feb 1, 1986
Memoirs of National Institute of Polar Research. Special issue, Feb 1, 1986
Antarctic record, Sep 1, 1981
Proceedings of the NIPR Symposium on Polar Biology, 1995
This paper describes tracks followed by six surface drifting buoys that were deployed in shelf an... more This paper describes tracks followed by six surface drifting buoys that were deployed in shelf and oceanic waters to the north of the South Shetland Islands. Each buoy was deployed with a drogue attached at a depth of 30 m to assess flow patterns at the depth range where krill tended to be most abundant. The buoys were tracked using the ARGOS satellite positioning system. Based on buoy tracks, the surface circulation to the north of the South Shetlands shelf was described as a slow sluggish southwest current with a series of small-scale circular and semi-circular flows in the shelf region, whereas the circulation in the oceanic region was described as the strong northeast current. Between these counter-flowing currents a shear current was found in the slope region. The direct current measurements demonstrated that the oceanographic regime in these waters is not well described by geostrophic calculations. The picture obtained of the surface circulation was considered in conjunction with the distribution of krill catches taken in the area by Japanese vessels during the period from 1981 to 1994. It is suggested that the sluggish and shear currents observed to the north of the islands may have properties which contribute to the formation of stable krill concentrations in the area. The observed long-distance movements of three buoys also suggested that oceanic currents may transport krill from the South Shetland Islands to the South Georgia and South Orkney Islands on a time scale of 110 to 120 and 85 days respectively. Resume islas Shetland del Sus a las islas Georgia del Sur y Orcadas del Sur en una escala temporal de 110 a 120 dias y 85 dias, respectivamente.
Antarctic Science, Feb 27, 2008
The geographical distribution of protozoan parasite Cephaloidophora pacifica Avdeev (Order Eugreg... more The geographical distribution of protozoan parasite Cephaloidophora pacifica Avdeev (Order Eugregarininda) associated with Antarctic krill, Euphausia superba, was examined in samples collected from the vicinity of the Antarctic Peninsula, near Syowa Station, and Pacific and Indian sectors of the Southern Ocean. Cephaloidophora pacifica was found at all stations around the Antarctic, with 96.4% of the euphausiids infected (n ¼ 195). The numbers of C. pacifica per krill ranged from 0 to 8089 krill-1 , and the average was 350.0 AE 787.8 (mean AE SD). The frequency distributions of C. pacifica showed an overdispersed parasite population (i.e. the variance was greater than the mean) at all locations. Statistical analysis showed that whilst the geographical location did not have a significant effect on intensity of C. pacifica the maturity stage of krill did, with an increasing intensity of infection as krill matures. The infestation of E. superba by eugregarinid protozoan is considered to be a circum-Antarctic phenomenon, and it occurs equally throughout the Southern Ocean.
Polar Biology, Jul 23, 1999
Size-fractionated chlorophyll-a concentrations of surface seawater were measured for pico-, nano-... more Size-fractionated chlorophyll-a concentrations of surface seawater were measured for pico-, nano-, and micro-size fractions (<2 lm, 2±10 lm, and >10 lm respectively) during commercial krill ®shery operations in the waters north of the South Shetland Islands. The proportion of green krill (individuals discoloured due to active feeding on phytoplankton) had signi®cant regressions with chlorophyll-a concentrations in microand nano-size fractions. Between these two fractions, chlorophyll-a concentration in the micro-size fraction showed the higher partial regression coecient. This result shows the importance of phytoplankton larger than nano-phytoplankton, especially micro-phytoplankton, in terms of a phytoplanktonic food source for Antarctic krill in the natural environment.
Journal of Geophysical Research, 1994
Hydrographic and drifting buoy data from Japanese cruises show that the Antarctic Divergence in t... more Hydrographic and drifting buoy data from Japanese cruises show that the Antarctic Divergence in the Indian Ocean sector is composed of a street of cyclonic eddies. These eddies measure about 500 km in the zonal direction and 200 km in the meridional. Part of the eastward flowing Antarctic Circumpolar Current (ACC) meanders southward in the regions between the eddies. In the eddy regions, warm, saline Circumpolar Deep Water is upwelled into the shallow layers, while cold, dense coastal water advects into the deep layers; the advection occurs along the isobaths of ridges which extend north from the coast. The combination of the advection with the upwelhng produces a water column denser than the surrounding water and leads to the formation and maintenance of the cyclonic eddies. Presence of the northward extending ridges approximately governs the location of eddy formation. The eddy formation recurs year after year, although eddy locations can vary somewhat. A polynya was observed to persistently occur and corresponded with one of the eddies in location, size, and form. The oceanographic observations also suggest that the primary meridional exchanges of heat and salt in the Antarctic are caused through the eddies and ACC meanders within the Antarctic Divergence. correspondence between the Weddell Polynya and the Atmospheric Circumpolar Trough which coincides with the AD. Therefore the Antarctic climate is significantly
Umi no kenkyū, 1992
Spatial structure of a warm eddy which was located stably above the western side of the Yamato Ri... more Spatial structure of a warm eddy which was located stably above the western side of the Yamato Rise was described in detail by examining hydrographic data, NOAA-infrared image, and current data in summer 1989. The doughnut-like flow structure surrounding a warm-core was found to play a significant role in the northward transport of warm and salin water in summer. However, it was inferred from the analysis of hydrographic data through the year that the above doughnut-like flow disappeared in winter and drastic structural variations of an eddy were brought by wintertime convection. During winter, not only the core-temperature but also the salinity decreased and the shape of an eddy became unclear, suggesting the exchange of a core water with the outer one.
Proceedings of the NIPR Symposium on Polar Biology, 1995
Journal of Oceanography, Mar 7, 2009
We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to th... more We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer
Deep-sea Research Part I-oceanographic Research Papers, Aug 1, 1998
The influences of abiotic and biotic parameters on the occurrence of Antarctic krill (Euphausia s... more The influences of abiotic and biotic parameters on the occurrence of Antarctic krill (Euphausia superba) concentrations were studied in the waters north of the South Shetland Islands, a major krill fishing ground in the Antarctic, during the 1990/1991 austral summer. From early to midsummer krill density increased and showed distinct offshore-inshore differences in abundance and maturity stages. In midsummer , krill density was low in the oceanic zone (8 g m\) and higher in the slope frontal zone (36 g m\), being highest along the shelf break (131 g m\) in the inshore zone. Krill were in the reproductive stage in the oceanic and frontal zones, but non-reproductive in the inshore zone. Water circulation, food and frontal features were considered important environmental factors determining the occurrence of high krill concentrations in these waters. Drifting buoys indicated that the surface water circulation in areas of krill concentrations was characterized by a sluggish current with eddies along the shelf break in the inshore zone and a shear current in the frontal zone, thus enhancing the residence time for krill. Diatom abundance in both the frontal and inshore zones increased from early to midsummer , improving krill feeding conditions. Gravid females were closely associated with the frontal zone, showing that the latter may also be a favored spawning area because of the higher probability of survival for embryos and larvae, in addition to enhanced opportunities for their transport to nursery grounds by prevailing currents. In the waters north of the South Shetland Islands, krill appeared to be highly adapted for exploitation of the rich food resources of the frontal/inshore zone, taking advantage of oceanographic features that led to their retention in these zones.
Japan Geoscience Union, May 1, 2015
Japan Geoscience Union, 2018
The mid-high latitudes of the Southern Hemisphere (SH) are known as the strongest surface-wind ar... more The mid-high latitudes of the Southern Hemisphere (SH) are known as the strongest surface-wind area in the entire oceans. A dominant variability in the SH is characterized by a seesaw pattern between the mid and high latitudes, called the Southern Annular Mode (SAM) (Thompson and Wallace, 2000), which suggests that climate patterns affect the westerly wind, eddy, and sub-Antarctic sea ice (e.g. Hogg et al., 2015; Morioka et al., 2017; Cerrone and Fusco 2018). The relationship between the surface wind stress and sea-surface-temperature (SST) is considered to be a key factor for air-sea interaction over the global ocean. For example, SST perturbations induce perturbations in the surface wind stress, with enhanced stress over warm water and reduced stress over cooler water. Focus in previous studies has been on the Southern Ocean, the Southern Atlantic Ocean, and the Agulhas Return Current (O’Neill et al., 2003; 2005; 2012). However, the detailed relationship between the surface wind s...
Memoirs of National Institute of Polar Research Special Issue, Dec 1, 1986
Proceedings of the NIPR Symposium on Polar Biology, Sep 1, 1989
Memoirs of National Institute of Polar Research. Special issue, Feb 1, 1986
Memoirs of National Institute of Polar Research. Special issue, Feb 1, 1986
Antarctic record, Sep 1, 1981
Proceedings of the NIPR Symposium on Polar Biology, 1995
This paper describes tracks followed by six surface drifting buoys that were deployed in shelf an... more This paper describes tracks followed by six surface drifting buoys that were deployed in shelf and oceanic waters to the north of the South Shetland Islands. Each buoy was deployed with a drogue attached at a depth of 30 m to assess flow patterns at the depth range where krill tended to be most abundant. The buoys were tracked using the ARGOS satellite positioning system. Based on buoy tracks, the surface circulation to the north of the South Shetlands shelf was described as a slow sluggish southwest current with a series of small-scale circular and semi-circular flows in the shelf region, whereas the circulation in the oceanic region was described as the strong northeast current. Between these counter-flowing currents a shear current was found in the slope region. The direct current measurements demonstrated that the oceanographic regime in these waters is not well described by geostrophic calculations. The picture obtained of the surface circulation was considered in conjunction with the distribution of krill catches taken in the area by Japanese vessels during the period from 1981 to 1994. It is suggested that the sluggish and shear currents observed to the north of the islands may have properties which contribute to the formation of stable krill concentrations in the area. The observed long-distance movements of three buoys also suggested that oceanic currents may transport krill from the South Shetland Islands to the South Georgia and South Orkney Islands on a time scale of 110 to 120 and 85 days respectively. Resume islas Shetland del Sus a las islas Georgia del Sur y Orcadas del Sur en una escala temporal de 110 a 120 dias y 85 dias, respectivamente.
Antarctic Science, Feb 27, 2008
The geographical distribution of protozoan parasite Cephaloidophora pacifica Avdeev (Order Eugreg... more The geographical distribution of protozoan parasite Cephaloidophora pacifica Avdeev (Order Eugregarininda) associated with Antarctic krill, Euphausia superba, was examined in samples collected from the vicinity of the Antarctic Peninsula, near Syowa Station, and Pacific and Indian sectors of the Southern Ocean. Cephaloidophora pacifica was found at all stations around the Antarctic, with 96.4% of the euphausiids infected (n ¼ 195). The numbers of C. pacifica per krill ranged from 0 to 8089 krill-1 , and the average was 350.0 AE 787.8 (mean AE SD). The frequency distributions of C. pacifica showed an overdispersed parasite population (i.e. the variance was greater than the mean) at all locations. Statistical analysis showed that whilst the geographical location did not have a significant effect on intensity of C. pacifica the maturity stage of krill did, with an increasing intensity of infection as krill matures. The infestation of E. superba by eugregarinid protozoan is considered to be a circum-Antarctic phenomenon, and it occurs equally throughout the Southern Ocean.
Polar Biology, Jul 23, 1999
Size-fractionated chlorophyll-a concentrations of surface seawater were measured for pico-, nano-... more Size-fractionated chlorophyll-a concentrations of surface seawater were measured for pico-, nano-, and micro-size fractions (<2 lm, 2±10 lm, and >10 lm respectively) during commercial krill ®shery operations in the waters north of the South Shetland Islands. The proportion of green krill (individuals discoloured due to active feeding on phytoplankton) had signi®cant regressions with chlorophyll-a concentrations in microand nano-size fractions. Between these two fractions, chlorophyll-a concentration in the micro-size fraction showed the higher partial regression coecient. This result shows the importance of phytoplankton larger than nano-phytoplankton, especially micro-phytoplankton, in terms of a phytoplanktonic food source for Antarctic krill in the natural environment.
Journal of Geophysical Research, 1994
Hydrographic and drifting buoy data from Japanese cruises show that the Antarctic Divergence in t... more Hydrographic and drifting buoy data from Japanese cruises show that the Antarctic Divergence in the Indian Ocean sector is composed of a street of cyclonic eddies. These eddies measure about 500 km in the zonal direction and 200 km in the meridional. Part of the eastward flowing Antarctic Circumpolar Current (ACC) meanders southward in the regions between the eddies. In the eddy regions, warm, saline Circumpolar Deep Water is upwelled into the shallow layers, while cold, dense coastal water advects into the deep layers; the advection occurs along the isobaths of ridges which extend north from the coast. The combination of the advection with the upwelhng produces a water column denser than the surrounding water and leads to the formation and maintenance of the cyclonic eddies. Presence of the northward extending ridges approximately governs the location of eddy formation. The eddy formation recurs year after year, although eddy locations can vary somewhat. A polynya was observed to persistently occur and corresponded with one of the eddies in location, size, and form. The oceanographic observations also suggest that the primary meridional exchanges of heat and salt in the Antarctic are caused through the eddies and ACC meanders within the Antarctic Divergence. correspondence between the Weddell Polynya and the Atmospheric Circumpolar Trough which coincides with the AD. Therefore the Antarctic climate is significantly
Umi no kenkyū, 1992
Spatial structure of a warm eddy which was located stably above the western side of the Yamato Ri... more Spatial structure of a warm eddy which was located stably above the western side of the Yamato Rise was described in detail by examining hydrographic data, NOAA-infrared image, and current data in summer 1989. The doughnut-like flow structure surrounding a warm-core was found to play a significant role in the northward transport of warm and salin water in summer. However, it was inferred from the analysis of hydrographic data through the year that the above doughnut-like flow disappeared in winter and drastic structural variations of an eddy were brought by wintertime convection. During winter, not only the core-temperature but also the salinity decreased and the shape of an eddy became unclear, suggesting the exchange of a core water with the outer one.
Proceedings of the NIPR Symposium on Polar Biology, 1995
Journal of Oceanography, Mar 7, 2009
We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to th... more We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer
Deep-sea Research Part I-oceanographic Research Papers, Aug 1, 1998
The influences of abiotic and biotic parameters on the occurrence of Antarctic krill (Euphausia s... more The influences of abiotic and biotic parameters on the occurrence of Antarctic krill (Euphausia superba) concentrations were studied in the waters north of the South Shetland Islands, a major krill fishing ground in the Antarctic, during the 1990/1991 austral summer. From early to midsummer krill density increased and showed distinct offshore-inshore differences in abundance and maturity stages. In midsummer , krill density was low in the oceanic zone (8 g m\) and higher in the slope frontal zone (36 g m\), being highest along the shelf break (131 g m\) in the inshore zone. Krill were in the reproductive stage in the oceanic and frontal zones, but non-reproductive in the inshore zone. Water circulation, food and frontal features were considered important environmental factors determining the occurrence of high krill concentrations in these waters. Drifting buoys indicated that the surface water circulation in areas of krill concentrations was characterized by a sluggish current with eddies along the shelf break in the inshore zone and a shear current in the frontal zone, thus enhancing the residence time for krill. Diatom abundance in both the frontal and inshore zones increased from early to midsummer , improving krill feeding conditions. Gravid females were closely associated with the frontal zone, showing that the latter may also be a favored spawning area because of the higher probability of survival for embryos and larvae, in addition to enhanced opportunities for their transport to nursery grounds by prevailing currents. In the waters north of the South Shetland Islands, krill appeared to be highly adapted for exploitation of the rich food resources of the frontal/inshore zone, taking advantage of oceanographic features that led to their retention in these zones.
Japan Geoscience Union, May 1, 2015
Japan Geoscience Union, 2018
The mid-high latitudes of the Southern Hemisphere (SH) are known as the strongest surface-wind ar... more The mid-high latitudes of the Southern Hemisphere (SH) are known as the strongest surface-wind area in the entire oceans. A dominant variability in the SH is characterized by a seesaw pattern between the mid and high latitudes, called the Southern Annular Mode (SAM) (Thompson and Wallace, 2000), which suggests that climate patterns affect the westerly wind, eddy, and sub-Antarctic sea ice (e.g. Hogg et al., 2015; Morioka et al., 2017; Cerrone and Fusco 2018). The relationship between the surface wind stress and sea-surface-temperature (SST) is considered to be a key factor for air-sea interaction over the global ocean. For example, SST perturbations induce perturbations in the surface wind stress, with enhanced stress over warm water and reduced stress over cooler water. Focus in previous studies has been on the Southern Ocean, the Southern Atlantic Ocean, and the Agulhas Return Current (O’Neill et al., 2003; 2005; 2012). However, the detailed relationship between the surface wind s...
Memoirs of National Institute of Polar Research Special Issue, Dec 1, 1986