Northeastern Coast Of Hokkaido Research Articles

The effect of melting treatments on the assessment of biomass and nutrients in sea ice (Saroma-ko lagoon, Hokkaido, Japan)

Melting of sea-ice samples is an inevitable step in obtaining reliable and representative measurements for biogeochemical parameters such as inorganic nutrients and particulate matter. The impact of the sea-ice melting procedure has been previously evaluated for biological parameters such as chlorophyll a and cell abundance. For nutrient and biomass concentrations in sea ice, it is generally considered to be best practice to melt samples fast; however, no systematic evaluation exists in literature. The impact of melting temperature and buffer addition to avoid osmotic shock was tested on ice samples in Saroma-ko Lagoon on the northeastern coast of Hokkaido, Japan. The focus was on inorganic nutrient concentrations (NO3−, NO2−, PO4−, NH4+, Si(OH)4) and particulate organic carbon and nitrogen concentrations and their isotope ratios. Coherent small changes have been observed for the parameter related to nitrogen, suggesting marginal cell lysis of a specific part of the microbial community. When differences are statistically significant, they are close to the uncertainty of the measurements and small in regard to the expected natural variation in sea ice. Our study suggest a minimal effect between melting treatments on biomass (POC, PN, and Chl a) and nutrient measurements in diatom-dominated sea ice and should be repeated where the sympagic community is dominated by flagellates.

Buoyancy shutdown process for the development of the baroclinic jet structure of the Soya Warm Current during summer

The Soya Warm Current (SWC), which is the coastal current along the northeastern part of Hokkaido, Japan, has a notable baroclinic jet structure during summer. This study addresses the formation mechanism of the baroclinic jet by analyzing a realistic numerical model and conducting its sensitivity experiment. The key process is the interaction between the seasonal thermocline and the bottom Ekman layer on the slope off the northeastern coast of Hokkaido; the bottom Ekman transport causes subduction of the warm seasonal thermocline water below the cold lower-layer water, so the bottom mixed layer develops with a remarkable cross-isobath density gradient. Consequently, the buoyancy transport vanishes as a result of the thermal wind balance in the mixed layer. The SWC area is divided into two regions during summer: upstream, the adjustment toward the buoyancy shutdown is in progress; downstream, the buoyancy shutdown occurs. The buoyancy shutdown theory assesses the bottom-mixed-layer thickness to be 50 m, consistent with observations and our numerical results. The seasonal thermocline from June to September is strong enough to establish the dominance of the buoyancy shutdown process over the frictional spindown.

Weaning age in an expanding population: stable carbon and nitrogen isotope analysis of infant feeding practices in the Okhotsk culture (5th-13th centuries AD) in Northern Japan.

The Okhotsk people were sedentary hunter-gatherer-fishers who lived and prospered in Sakhalin, Hokkaido, and the Kurile Islands during the 5th to 13th centuries AD. They expanded rapidly along the northeastern coast of Hokkaido. We reconstructed infant feeding practices of the Moyoro population of the Okhotsk culture in eastern Hokkaido, Japan. Stable isotope ratios in 58 subadult human skeletons were measured. The results suggest that complementary foods with a relatively low carbon isotope ratio were consumed during and after weaning, as observed in ethnographic descriptions of northern human populations such as the Ainu and isotopically suggested in ancient northern hunter-gatherer-fisher populations. Nitrogen isotope ratios of subadults showed that the age at the end of weaning in the Moyoro population was 1.8 (1.4-2.2 in 95% credible interval) years, which is earlier than that in other northern hunter-gatherer-fisher populations. Because weaning age is one of the most important determinants of fertility, a shorter breastfeeding period suggests increased fertility. Furthermore, better nutrition would further promote the population increase, and thus populations of the Okhotsk culture could expand into new regions. These findings are consistent with recent emerging evidence of great contributions of the Okhotsk to the formation of later Ainu populations and culture.

Copepod community succession during warm season in Lagoon Notoro-ko, northeastern Hokkaido, Japan

Lagoon Notoro-ko, located on the northeastern coast of Hokkaido, Japan, and connected to the Okhotsk Sea by a human-made channel, is strongly influenced by local hydrography, as water masses in the lagoon are seasonally influenced by the Soya Warm Current and the East Sakhalin Current. We here report on the succession of copepod communities during the warm season in relation to water mass exchange. Copepods were categorized into four seasonal communities (spring/early-summer, mid-summer, late-summer/fall, and early-winter) via a cluster analysis based on Bray–Curtis similarities. Spring/early-summer and early-winter communities were characterized by the temperate–boreal calanoid Pseudocalanus newmani, comprising 34.9%–77.6% of the total abundance of copepods during times of low temperature/salinity, as influenced by the prevailing East Sakhalin Current. Late-summer/fall communities were characterized by the neritic warm-water calanoid Paracalanus parvus s.l., comprising 63.9%–96.3% of the total abundance, as influenced by the Soya Warm Current. Mid-summer communities comprised approximately equal abundances of P. parvus, Eurytemora herdmani, Scolecithricella minor, and Centropages abdominalis (12.8%–28.2%); this community is transitional between those of the spring/early-summer and late-summer/fall. Copepod community succession in Lagoon Notoro-ko can be largely explained by seasonal changes in water masses.

Chemical evidence for the origin of the cold water belt along the northeastern coast of Hokkaido

In the southwestern Okhotsk Sea, the cold water belt (CWB) is frequently observed on satellite images offshore of the Soya Warm Current flowing along the northeastern coast of Hokkaido, Japan, during summertime. It has been speculated that the CWB is upwelling cold water that originates from either subsurface water of the Japan Sea off Sakhalin or bottom water of the Okhotsk Sea. Hydrographic and chemical observations (nutrients, humic-type fluorescence intensity, and iron) were conducted in the northern Japan Sea and southwestern Okhotsk Sea in early summer 2011 to clarify the origin of the CWB. Temperature–salinity relationships, vertical distributions of chemical components, profiles of chemical components against density, and the (NO3 + NO2)/PO4 relationship confirm that water in the CWB predominantly originates from Japan Sea subsurface water.

Rotating Stratified Barotropic Flow over Topography: Mechanisms of the Cold Belt Formation off the Soya Warm Current along the Northeastern Coast of Hokkaido

Abstract The Soya “Warm Current” (SWC) flows through a shallow strait between the Japan Sea and the Sea of Okhotsk. The SWC has a jet structure downstream of the strait along the northern coast of Hokkaido with a maximum speed exceeding 1 m s−1 at its axis in summer and fall. A surface cold belt with a subsurface doming structure forms offshore of the SWC axis. Mechanisms of the cold belt formation are discussed from a point of view of resonant interaction between a barotropic stratified flow and a shallow sill and subsequent baroclinic adjustment along the SWC. When a stratified current rides a slope upstream, the thermocline displaces upward greatly and outcrops owing to resonant generation of internal Kelvin waves if the upper layer is thinner than the lower layer. The control section, where a Froude number is unity, occurs “upstream” from the sill crest when the ambient inflow has a barotropic flow component. These upwelling features closely resemble those along the southwestern coast of Sakhalin Island. The SWC then flips from an upwelling-type to a downwelling-type structure; in doing so, it transits from the west coast of Sakhalin to the east coast of Hokkaido. It is this transition that leads to the offshore doming structure, which propagates downstream as a vorticity wave, manifesting the cold belt at the surface.

Effects of snow, snowmelting and refreezing processes on air–sea-ice CO2 flux

AbstractThe air–sea-ice CO2 flux was measured in the ice-covered Saroma-ko, a lagoon on the northeastern coast of Hokkaido, Japan, using a chamber technique. The air–sea-ice CO2 flux ranged from −1.8 to +0.5 mg C m−2 h−1 (where negative values indicate a sink for atmospheric CO2). The partial pressure of CO2 (pCO2) in the brine of sea ice was substantially lower than that of the atmosphere, primarily because of the influence of the under-ice plume from the Saromabetsu river located in the southeastern part of the lagoon. This suggests that the brine had the ability to take up atmospheric CO2 into the sea ice. However, the snow deposited over the sea ice and the superimposed ice that formed from snowmelting and refreezing partially blocked CO2 diffusion, acting as an impermeable medium for CO2 transfer. Our results suggest that the air–sea-ice CO2 flux was dependent not only on the difference in pCO2 between the brine and the overlying air, but also on the status of the ice surface. These results provide the necessary evidence for evaluation of the gas exchange processes in ice-covered seas.

Transport of chemical components in sea ice and under-ice water during melting in the seasonally ice-covered Saroma-ko Lagoon, Hokkaido, Japan

Physico-chemical properties in the brine and under-ice water were measured in Saroma-ko Lagoon on the northeastern coast of Hokkaido, Japan, which is connected to the Sea of Okhotsk, during the period from mid-February through mid-March 2006. The brine within brine channels of the sea ice was collected with a new sampling method examined in this study. Salinity, dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (DO), nutrients and oxygen isotopic ratio (δ 18O) contained in the brine within brine channels of the sea ice and in the under-ice water varied largely in both time and space during the ice melt period, when discharge from Saromabetsu River located on the southeast of the lagoon increased markedly due to the onset of snow melting. The under-ice plume expands as far as 4.5 km from the river mouth at mid-March 2006, transporting chemical components supplied from the river into the lagoon. The under-ice river water was likely transported into the sea ice through well-developed brine channels in the sea ice due to upward flushing of water through brine channels occurred by loading of snowfalls deposited over the sea ice. These results suggest that the river water plume plays an important role in supplying chemical components into the sea ice, which may be a key process influencing the biogeochemical cycle in the seasonally ice-covered Saroma-ko Lagoon.

Anticyclonic eddy caused by the Soya Warm Current in an Okhotsk OGCM

An OGCM of the Sea of Okhotsk with a 1/12° horizontal resolution and 45 vertical levels has been constructed, which successfully represents characteristics of its circulations. This article focuses particularly on an anticyclonic eddy forming off Hokkaido in the OGCM. It forms in late summer when the warm and saline Soya Warm Current Water separates from the northeastern coast of Hokkaido. This eddy is identified as the eddy studied by Wakatsuchi and Martin (1991) since its location, evolution and vertical structure are consistent with their description. Numerical experiments with varying transport of the Soya Warm Current (SWC) have been carried out, where the transport of the SWC is changed by applying the Island Rule around Hokkaido. It is shown that the eddy formation depends on the transport of the SWC. When the transport is large, an eddy forms off the Shiretoko Peninsula. When the transport is small, however, the saline Soya Warm Current Water does not reach that area, nor does a distinct eddy form. It is when the inflow transport of the Soya Warm Current is larger than the outflow from the Nemuro Strait and the Kunashiri Channel that the anticyclonic eddy forms.

On the near-bottom pressure variations in the region of the 2003 Tokachi-Oki tsunami source

The Tokachi-Oki earthquake was the strongest seismic event in 2003. The tsunami caused by the earthquake reached a height of four meters at the northeastern coast of Hokkaido. The JAMSTEC successfully recorded the variations of the near-bottom pressure in the region of the tsunami source. An analysis of the data reveals low-frequency (∼ 0.15 Hz) elastic vibrations of the water layer. Estimates of the amplitude, velocity, and duration of the bottom deformation at the tsunami source were obtained.

SHORT REPORT: ECHINOCOCCUS MULTILOCULARIS CONFIRMED ON KUNASHIRI ISLAND, 15 KILOMETERS FROM THE EASTERN PART OF HOKKAIDO, JAPAN

There are two foci of alveolar echinococcosis (AE) caused by Echinococcus multilocularis in Japan. The first focus is on Rebun Island where AE patients were found from 1937, and the second is in eastern Hokkaido where patients have been found since the 1960s. The origin of the second focus is unknown. To further investigate AE in eastern Hokkaido, wild rodents (Muridae) were captured and examined for infection on Kunashiri Island, which is located 15 km off the northeastern coast of Hokkaido. Metacestodes of E. multilocularis were isolated from two of 31 voles, all of which were identified to be Clethrionomys rufocanus. Mitochondrial DNA sequencing data of recovered cestodes showed total identity with the cestode reported from Hokkaido. These results suggest that E. multilocularis may have been introduced to Hokkaido from Kunashiri Island during or after 1965.

Potential for autumn aeration of stored rough rice and the potential number of generations of Sitophilus zeamais Motschulsky in milled rice in Japan

Historical weather data from 84 sites in Japan were used to estimate the number of hours ⩽15°C from 1 September to 31 October, based on the individual years from 1994 to1999, to evaluate the potential for using aeration at a threshold level of 15°C to cool rough rice stored during autumn. The number of hours ⩽15°C in September and October ranged from 68±21 in Kyushu to 1067±27 h in northern Hokkaido. At an airflow rate of 0.0013 m 3/s/m 3, the time required to cool a storage silo containing rough rice to 15°C ranged from 85 days in southern Japan to 5 days in northern Japan. Weather data for the same sites were also used to estimate the number of hours below 15°C from 1 May to 30 September, to evaluate the potential of Sitophilus zeamais Motschulsky, the maize weevil, to infest bagged milled rice at ambient or uncontrolled temperatures. The number of hours ⩽15°C from 1 May to 30 September ranged from 33±15 h in Kyushu to 2392±130 h on the northeastern coast of Hokkaido. As temperature decreased, there was a predicted increase in the number of days required to complete a generation, and as relative humidity increased, a predicted increase in the number of generations that could be produced. These simulation studies show how historical weather data can be used to develop risk management models for storage of bulk rough rice and bagged milled rice in Japan. Aeration during autumn could be used to cool large-bulk storage silos containing rough rice, while the simulations for development of Sitophilus zeamais populations on bagged milled rice emphasize the importance of insect management strategies for value-added products.

Moscow-Tokyo and the Northern Territories Dispute

The most serious barrier today to a major improvement in relations between Tokyo and Moscow is the long-standing and bitter dispute over a number of small islands lying between the northern Japanese island of Hokkaido and the USSR's Kamchatka Peninsula. The territories in question-Etorofu, Kunashiri, Shikotan and the Habomai Islands-are claimed by both the Japanese and the Soviets, but have been occupied by the latter since the end of World War II. The first two are the most southerly of the Kuriles, a chain of islands that stretches for around a thousand kilometres between Hokkaido and the Kamchatka Peninsula, and are sometimes known as the southern Kuriles. Shikotan and a cluster of small islands known as the Habomais lie off the northeastern coast of Hokkaido (see Map 1). Japan refers to these islands as the Northern Territories and asserts that their return is the sine qua non for the negotiation of a peace treaty with the USSR to end the formal state of war between the two countries and for the development of good relations with Moscow. The Northern Territories comprise about 5,000 square kilometers, with the southern Kuriles making up 90% of the total land area. No Japanese citizens currently reside in the Kuriles, some 16,000 having been repatriated after the Soviet occupation at the end of World War II. The former Japanese inhabitants had worked on the islands as fishermen, hunters, and agricultural workers, and the abundance of fish in the area also attracted many seasonal workers from Hokkaido during the summer fishing season. With the exception of access to fisheries, the Northern Territories are not, however, of great economic importance to either Japan or the Soviet Union. Their real significance lies in the realms of politics and strategy.

A Prehistoric Maritime Culture of the Okhotsk Sea

AbstractThis paper analyzes the culture history of the little-known Okhotsk culture and makes suggestions about its relationships with neighboring cultures. The Okhotsk culture is important in understanding the cultural history of the northern Pacific because it shows no affinities with the Ainu and Japanese cultures and has an economy remarkably like that of the more distant Aleut and Eskimo. The Okhotsk culture appears to have historical relationships with cultures in Siberia and Manchuria. The maritime hunting economy of this culture was probably derived from the Eskimo via Bering Sea and the Siberian coast. Other cultural elements, the most noticeable being ceramics, were of mainland origin and served as an influential force in forming Okhotsk culture. Once established on Sakhalin, this culture moved southward along the northeastern coast of Hokkaido, where a secondary and later cultural center developed. Migrations up the Kuriles occurred shortly thereafter. This culture probably flourished for at least a thousand years, beginning in Sakhalin several centuries before Christ and persisting until sometime after A.D. 1000 and possibly until the 17th century in the Kuriles. Several unsolved problems concerning the Okhotsk culture are presented.

Derivation of Einstein Effect from Eclipse Observations of 1936

THE total solar eclipse of June 19, 1936, gave Japanese astronomers an excellent opportunity for solar research. The central line ran just parallel to the north-eastern coast of Hokkaido, facing Okhotsk Sea. More than twenty sites were occupied by Japanese and visiting observing parties. Our party, being the expedition from the Tohoku Imperial University at Sendai, decided to make observations at Kosimizu, the co-ordinates of which are: astronomical longitude: 144° 28′ 3″ E. = 9h. 37m. 52˙2s. E. astronomical latitude: 43° 51′ 21″ N.