High potential activity of extracellular alkaline phosphatase in deep waters of the central Pacific

We found high potential activities of alkaline phosphatase associated with particles (0.2 μm or greater size fraction) in deep waters (1000–4000 m) of the central Pacific Ocean. The potential enzyme activity at depth (0.03 – 0.3 nM h⁻¹) was up to 50% of that at the surface (0–125 m). In contrast, activities of α- and β-d-glucosidase in the deep layer were low (generally less than 1 % of those in the upper layer), yielding up to two orders of magnitude difference in the ratio of alkaline phosphatase and α- and β-d-glucosidase activities with depth. It is unlikely that the phosphatase is actively produced by microorganisms inhabiting the deep-sea environment, where labile organic carbon supply is limited and phosphate concentration is high (2.4 – 3.0 AM). Instead, deep-water phosphatase is probably supplied by rapidly sinking particles and their subsequent fragmentation and dissolution. Different distributions of phosphatase and glucosidase indicate that sinking particles of phytoplankton origin are an important source of alkaline phosphatase enzymes in the deep sea.     

Silicate to Nitrate Ratio of the Upper Sub-Arctic Pacific and the Bering Sea Basin in Summer: Its Implication for Phytoplankton Dynamics

Consumption of silicate and nitrate (Si:N molar ratio) in the upper layer of the pelagic subarctic Pacific in summer was evaluated by a regression analysis of silicate vs. nitrate concentrations at the upper 100 m depth. Based on data of three cruises, the pelagic subarctic Pacific can be classified into two groups. First group is characterized by roughly 1:1 consumption of silicate and nitrate, and occupies rather larger area of subarcfic Pacific, i.e., the Gulf of Alaska and the Western Subarctic gyre (averaged slope of Si:N linear regression: 1.21, n = 10 and 1.45, n = 9, respectively). Second group is the regions of the Bering Sea basin and the Oyashio region, and showed higher silicate consumption compared to that of nitrate (averaged slope of Si:N linear regression: 2.14, n = 9 and 2.36, n = 3, respectively). The Si:N difference observed is possibly attributed to relative contribution of diatoms production among the phytoplankton assemblages in the regions, i.e., dominance of diatoms production in the regions of the second group. Higher accumulation of ammonium at the bottom of euphotic layer in the summer Bering Sea basin would also contribute to increase consumption ratio of Si:N amounts.     

Southward intrusion of the intermediate Oyashio water along the east coast of the Boso Peninsula,Japan II. Intrusion events into Sagami Bay

In the previous paper (Yanget al., 1993), it was shown that there always exists the coastal salinity-minimum-layer (SML) water just off the Boso Peninsula. The coastal SML water is bounded by the current zone of the Kuroshio, and a relatively high salinity domain separates it from the offshore SML water which would be a continum of the North Pacific Intermediate Water. We suggested that the coastal SML water region indicates the pathway along which the Intermediate Oyashio Water intrudes into Sagami Bay. In this paper, by selecting seven cases where we found the coastal SML water having abnormally high oxygen content and low salinity, we try to follow the intrusion manner of the Intermediate Oyashio Water into Sagami Bay by using available hydrographic data taken routinely by various organizations in the period from 1973 to 1986. Some of these water can be traced from the observation line near the cape of Inubo to the central part of Sagami Bay, and its propagation speed along the coast is shown to be of order of 1 cm/s. The intruding intermediate Oyashio water usually has a complicated layered structure in it, and its time scale of persistence is shown to be only a few months.     

Seasonal variation of the current in the Tsushima Strait deduced from ADCP data of ship-of-opportunity

The ADCP data obtained in the Tsushima Strait in the period from February 1987 to November 1990 on board twelve patrol vessels and one research vessel belonging to Maritime Safety Agency was analyzed. Total amount of the data is 200,053, but after quality check, we used 158,401 data for the analysis of the current field and its variability in the strait. The seasonal variation of the currents had been believed to be large. However, no direct current observation throughout the season had been made, and the knowledge on the seasonal variation was derived indirectly from the data of the sea level difference across the strait and of the density field given by hydrographic observations. ADCP data indicates that the seasonal variation of the current field is considerably small in all sub-regions. In the relatively strong current region to the west of the Tsushima Island, the northeast current component has maximum value in the early winter season.     

Variation of the sea surface temperature distribution across the Kuroshio in the Tokara Strait

Distribution of the sea surface temperature (SST) across the Kuroshio has been measured in the Tokara Strait by the Kagoshima Prefectural Experimental Fishery Station, using a thermometer installed on boardEmerald-Amami, a ferry that operates regularly between Kagoshima and Naha. The data from 1 October 1978 to 30 September 1981 were analyzed in this paper.A sharp temperature front is usually formed at the northern edge of the current zone of the Kuroshio, and its position is very variable and moves north and south between Satamisaki and Nakanoshima. The northward migration of the front can easily be traced, but the southward migration is obscure in many cases. Some of the southward migrations seem to be understood as arising from the alternate appearance of two different fronts, namely a weakening of the northern front and a strengthening of the southern front, which are associated with the double structure of the Kuroshio front. The temperature contrast across the Kuroshio front is very weak in August through October, and the phase of its seasonal variation lags a few months behind that of temperature itself. Transitions between the states with and without temperature contrast occur suddenly, though the transition times differ year by year. Periodical fluctuations with a period of several tens of days are often observed in the migration region of the Kuroshio front. The fluctuations sometimes look very periodical within limited time periods, but the fluctuations are very changeable in nature from year to year.The results show that continuous observation of the SST distribution across the Tokara Strait yields a good tool for monitoring fluctuations of the Kuroshio path and the occurrence of the Ohsumi Branch Current, at least in the season when a large horizontal temperature contrast exists.     

Experimental degradation of crude oil by marine bacteria

The ability of biodegradation for crude oil was examined for ten strains of marine bacteria. With regard to their degradation ability forn-alkanes the microorganisms tested could be divided into four groups, although the same result was not observed for microbial degradation of aromatic hydrocarbons obtained by the UV measurements.     

Seasonal Variations in the Sea off Sanriku Coast, Japan

The temperature and salinity data obtained by the Iwate Fisheries Technology Center for the 25-year period from 1971 to 1995 were analyzed to clarify the seasonal variations in the sea off Sanriku, Japan. The variations of three typical waters found in this region, the Tsugaru Current water, the Oyashio water, and the Kuroshio water are discussed in terms, of a T-S scatter diagram referring to the water mass classification proposed by Hanawa and Mitsudera (1986). The mean temperature and salinity fields averaged for each month show clear seasonal variation. Distributions of the Tsugaru Current water and the Oyashio water can barely be distinguished in the fields deeper than 200 m since the Tsugaru Current has a shallow structure; however, the fields at 100 m depth indicate remarkable seasonal variation in the area of the Tsugaru Current. At 100 m depth, the temperature and salinity fronts between the Tsugaru Current water and the Oyashio water gradually disappear in January through April, appear again in May, then become clearest in September. This revised version was published online in July 2006 with corrections to the Cover Date.     

Shallow temperature inversions in the Pacific Ocean near Japan

The statistical properties of shallow temperature inversions in the Pacific Ocean near Japan were investigated using data obtained from. BT observations. In the sea east of Honshu, the Kuroshio front forms the southern boundary of the area where temperature inversions are abundant. Though the occurrence frequency of the temperature inversion layers is very low in the sea south of Honshu, the path of the Kuroshio influences its regional distribution in this region also, and the high occurrence area shifts offshore when the large cold water mass is present off Enshu-nada. The magnitude of the inversion temperature differences in the sea south of Honshu is considerably smaller than that in the sea east of Honshu. The magnitude of inversion thickness has a clear tendency to increase from south to north in the sea east of Honshu, reflecting the higher occurrence frequency of large-scale thick inversion layers in the northern part under the influence of the sub-arctic water mass. The frequency distribution of the inversion thickness in each sub-region (1° square area) in the sea south of Honshu is very similar to that in the region just south of the Kuroshio front in the sea east of Honshu, suggesting that the inversion layers may be generated by similar mechanisms in the sea south of the Kuroshio front.     

Large-scale landslides in Toyama Prefecture,central Japan,and their probable relationship with earthquakes

Large-scale landslides along the Kubusu and Besso rivers in Toyama Prefecture are developed in the Miocene Iwaine Formation, which is composed of andesitic lava, tuff, and tuff breccia. In the middle member of this formation, the tuff is easily altered to montmorillonite-bearing rock, and subsequently plays an important role in the development of landslides events, which tend to be large-scale events, as the massive lava of the upper member forms a cap rock over the tuff. The Kiritani and Koinami basins, which are flat intermontane basins located along the Kubusu and Besso rivers, respectively, are interpreted as landslide-dammed lakes, later filled with sediment. Accelerator mass spectrometry ¹⁴C ages show that the landslides forming each dam occurred simultaneously, at approximately 2500 BP. These ages were measured from wood fragments embedded in the landslide material of Kiritani, and from an in situ stump drowned during the impoundment of Koinami. If the trigger of these landslides was an earthquake, it is most likely to have been the penultimate event along the Atotsugawa fault zone.