Extreme supply of floating ice to the northwestern part of the Pacific Ocean

In January to April, floating ice drifts from the Sea of Okhotsk via the Kuril straits to the northwestern part of the Pacific Ocean. In its turn, ice from the Bering Sea moves southwestward along the eastern coast of the Kamchatka Peninsula. The amount of the ice supplied to the ocean features a significant interannual variability. In this paper, we use the data for the period from 1958 to 2005. During the years with the heaviest ice conditions, floating ice from the Bering Sea moved to the south along Kamchatka Peninsula down the latitude of the Fourth Kuril Strait forming a tongue 30–50 miles wide. The ice drifting from the Sea of Okhotsk to the northwestern part of the Pacific Ocean may move via the passages from the Kunashir to the Kruzenshtern straits and form a band with a width of 30–40 miles depending of the severity of the winter.     

Cold deep water in the South China Sea

Two deep channels that cut through the Luzon Strait facilitate deep (>2000 m) water exchange between the western Pacific Ocean and the South China Sea. Our observations rule out the northern channel as a major exchange conduit. Rather, the southern channel funnels deep water from the western Pacific to the South China Sea at the rate of 1.06 ± 0.44 Sv (1 Sv = 10⁶ m³s⁻¹). The residence time estimated from the observed inflow from the southern channel, about 30 to 71 years, is comparable to previous estimates. The observation-based estimate of upwelling velocity at 2000 m depth is (1.10 ± 0.33) × 10⁻⁶ ms⁻¹, which is of the same order as Ekman pumping plus upwelling induced by the geostrophic current. Historical hydrographic observations suggest that the deep inflow is primarily a mixture of the Circumpolar Deep Water and Pacific Subarctic Intermediate Water. The cold inflow through the southern channel offsets about 40% of the net surface heat gain over the South China Sea. Balancing vertical advection with vertical diffusion, the estimated mean vertical eddy diffusivity of heat is about 1.21 × 10⁻³ m²s⁻¹. The cold water inflow from the southern channel maintains the shallow thermocline, which in turn could breed internal wave activities in the South China Sea.     

Tidal Mixing in the Kuril Straits and Its Impact on Ventilation in the North Pacific Ocean

A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K ₁ tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 10³ cm²s⁻¹. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity (PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the 2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean. This revised version was published online in July 2006 with corrections to the Cover Date.     

Volume transport in the Soya Strait during 2006–2008

Time-series data of the vertical structure of the Soya Warm Current (SWC) were obtained by a bottom-mounted acoustic Doppler current profiler (ADCP) in the middle of the Soya Strait from September 2006 to July 2008. The site of the ADCP measurement was within the coverage of the ocean-radar measurement around the strait. The volume transport of the SWC through the strait is estimated on the basis of both the vertical structure observed by the ADCP and the horizontal structure observed by the radars for the first time. The annual transport estimates are 0.62–0.67 Sv (1 Sv = 10⁶ m³s⁻¹). They are somewhat smaller than the difference between the previous estimates of the inflow and outflow through other straits in the Sea of Japan, and smaller than those obtained in the region downstream of the strait during 2004–05 (0.94–1.04 Sv). The difference in the two periods may be attributed to interannual variability of the SWC and/or the different measurement locations.     

吕宋海峡纬向海流及质量输送

分析和计算了吕宋海峡PR21断面最近海洋调查的部分CTD资料和ADCP资料,再一次证明吕宋海峡常年存在纬向流。但对于天气尺度而言,该流型是多变的。根据高分辨率的海洋环流数值模式4a(1992～1996年)海平面高度(SSH)的输出值,运用地转关系估计了吕宋海峡纬向流的月平均值。研究表明;通过海峡流入、流出南海纬向流的深度一般达到500m左右,200m以上流速较大,平均流速为50cm/s,最大时达80cm/s以上。500m以下的纬向地转流流速较小,通常小于10cm/s.由大洋进入海峡的入流位置位于海峡的中部和南部,月平均入流最大值出现在11月,为50cm/s.位于海峡的北部和南部上层海洋的月平均出流,最大流速亦出现在11月,也为50cm/s,这与秋季北赤道流分叉位置最北(15°N),春季分叉位置最南(14°N)有关。上层流入、流出海峡的流量的月平均值分别约为10×106m3/s和5×106m3/s.当东北季风盛行时(从10月到翌年2月),流入海峡的流量远大于流出海峡的流量,两者的差可达8×106m3/s,而在其他季节两者的差仅为3×106m3/s.这说明东北季风盛行时,会有较多的水从南海南？     

Volume transport of the Soya Warm Current revealed by bottom-mounted ADCP and ocean-radar measurement

The vertical structure of the Soya Warm Current (SWC) was observed by a bottom-mounted acoustic Doppler current profiler (ADCP) in the region of the SWC axis near the Soya Strait during a 1-year period from May 2004. The ADCP data revealed a marked seasonal variability in the vertical structure, with positive (negative) vertical shear in summer and fall (winter and spring). The volume transport of the SWC is estimated on the basis of both the vertical structure observed by the ADCP and horizontal structure observed by the ocean radars near the strait. The transport estimates have a minimum in winter and a maximum in fall, with the yearly-averaged values in the range of 0.94–1.04 Sv (1 Sv = 10⁶ m³ s⁻¹). These lie within a reasonable range in comparison to those through other straits in the Japan Sea.     

Velocity Field of the Oyashio Region Observed with Satellite-Tracked Surface Drifters during 1999–2000

Based on the surface drifters that moved out from the Sea of Okhotsk to the Pacific, the surface velocity fields of mean, eddy, and tidal components in the Oyashio region are examined for the period September 1999 to August 2000. Along the southern Kuril Island Chain, the Oyashio Current, having a width of ∼100 km, exists with velocities of 0.2–0.4 m s⁻¹. From 40°N to 43°N, the Subarctic Current flows east- or northeastward with velocities of 0.1–0.3 m s⁻¹, accompanied by a meandering Oyashio or Subarctic front. Between the Oyashio and Subarctic current regions, an eddy-dominant region exists with both cyclonic and anticyclonic eddies. The existence of an eastward flow just south of Bussol' Strait is suggested. The 2000 anticyclonic warmcore ring located south of Hokkaido was found to have a nearly symmetric velocity structure with a maximum velocity of ∼0.7 m s⁻¹ at 70 km from the eddy center. Diurnal tidal currents with a clockwise tidal ellipse are amplified over the shelf and slope off Urup and Iturup Islands, suggesting the presence of diurnal shelf waves. From Lagrangian statistics, the single-particle diffusivity is estimated to be ∼10 × 10⁷ cm²s⁻¹.     

Oceanic Odyssey of a satellite-tracked drifter: North Pacific variability delineated by a single drifter trajectory

A near-surface satellite-tracked drifter launched off the east coast of the Kuril Islands on September 4,1993 began a 2.5-year Odyssey across the North Pacific Ocean. During its travels, the drifter encountered numerous energetic oceanographic regimes as it moved from the region of the Kuril-Kamchatka Trench to the continental margin of the Kuril Islands, through Friza Strait into the Sea of Okhotsk, seaward again through Bussol’ Strait, and then eastward across the North Pacific. Oceanic features detected along the basin-wide trajectory include a quasi-permanent anticyclonic eddy over the Kuril-Kamchatka Trench, open-ocean wind-driven inertial oscillations, coastal-trapped diurnal shelf waves, semidiurnal tidal currents, transient cyclonic and anticyclonic eddies, through-strait flows, and wave-like mesoscale meanders. The single drifter track delineates the dynamically-rich variability of upper ocean currents, emphasizes the marked difference in flow dynamics between boundary and open ocean regions, and provides a time-scale for the movement of surface waters across the entire North Pacific.     

Deep-Sea Eukaryote Ecology of the Semi-Isolated Basins Off Japan

The Japanese archipelago is surrounded by the Pacific to the east, the Okhotsk Sea to the north, the Sea of Japan to the west and the Okinawa Trough to the south. The last three seas form semi-isolated deep basins, all with potentially tectonic origin but a different primary energy source as well as hydrographic and faunistic history. The Okhotsk Sea is connected to the Pacific through the deep straits between the Kurile Islands. As a result much of the fauna has links with that fauna found at similar depths in the Pacific. By contrast, the Sea of Japan was isolated from the main Pacific during the last ice age and became anoxic. Even today the link is only through narrow shallow straits. As a result the fauna is impoverished and is believed to be composed of cold-adapted eurybathic species rather than true deep-sea species. The deep-water fauna of both these seas derive their energy from sinking surface primary production. The Okinawa Trough has a much younger tectonic history than the Okhotsk Sea or the Sea of Japan. In the Okinawa Trough the most noticeable fauna is associated with hydrothermal activity and chemosynthesis forms the base of the food chain for the bathyal community. The variable nature of these three basins offers excellent opportunities for comparative studies of species diversity, biomass and production in relation to their ambient environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Absorption of Atmospheric CO2 and Its Transport to the Intermediate Layer in the Okhotsk Sea

In the southwestern Okhotsk Sea off Hokkaido we observed chemical components related to the carbonate system for 1 year from August 1997 to June 1998. Using the conservative components salinity and water temperature, we confirmed the existence of two water masses flowing into the intermediate layer of the Okhotsk Sea, the East Sakhalin Current Water (ESCW) which becomes denser by mixing of brine water, and the Forerunner of Soya Warm Current Water (FSWW) which becomes denser due to cooling of the saline Kuroshio water. The ΔNTC_x values were calculated by comparing the ESCW and the FSWW with the Pacific Deep Water (PDW). The ΔNTC_x values obtained are 100–110 μmol/kg and 70–100 μmol/kg for the ESCW and the FSWW off Hokkaido, respectively, which are considerably larger than that of the Kuroshio water. These large ΔNTC_x values may be due to both low DIC concentration in the surface water and intense gas exchange under the cold and stormy winter conditions for the ESCW and the cooling of the FSWW as it flows northward. Since the flow rates of dense waters concerned with the ESCW and the FSWW have previously been estimated as 0.9 Sv and 0.2 Sv, respectively, the amount of atmospheric CO₂ absorbed and transported to the intermediate layer turns out to be 3.9−4.1 × 10¹³ gC/yr. This flux is small on a global scale, but the flux divided by the surface layer of the Okhotsk Sea is 30 gC/m²/yr, which is 5 times greater than the mean absorption flux of anthropogenic CO₂ in the world's oceans. It is thus considered that atmospheric CO₂ is efficiently absorbed in the Okhotsk Sea. This revised version was published online in July 2006 with corrections to the Cover Date.     

The South China Sea,a <Emphasis Type="Italic">cul-de-sac</Emphasis> of North Pacific Intermediate Water

This study discusses branching of the Kuroshio Current including North Pacific Intermediate Water (NPIW) into the South China Sea (SCS). The spreading path of the subtropical salinity minimum of NPIW is southwestward pointing to the Luzon Strait between Taiwan and Luzon islands. Using a large collection of updated hydrography, results show that the SCS is a cul-de-sac for the subtropical NPIW because even the NPIW’s upper boundary neutral density surface σ _N = 26.5 is completely blocked by the Palawan sill and partly blocked by the southern Mindoro Strait. In autumn, NPIW is driven out of the Luzon Strait by the preceding anticyclonic summer monsoon due to an intraseasonal variation and seasonal phase lag response to the weaker summer monsoon. Stronger inflow under winter monsoon than outflow under summer monsoon results in a net annual transport of NPIW of about 1.1 ± 0.2 Sv (1 Sv = 10⁶ m³s⁻¹) into the SCS. This net transport accounts for the anomaly in NPIW transport across the World Ocean Circulation Experiment section P8 (130° E). An earlier study estimated a large westward NPIW transport of about 3.9 ± 0.2 Sv, resulting in a difference of 1.2 ± 0.2 Sv from the basin-wide mean of 2.7 ± 0.2 Sv. Observations are generally in agreement with numerical results although the intraseasonal signal seems to cause a slight bias and remains to be simulated by future model experiments.     

Simulated Pathways of the Northwestern Pacific Water in the Okhotsk Sea

Izvestiya, Atmospheric and Oceanic Physics - Water exchange between the Pacific Ocean and the Okhotsk Sea through the Kuril Straits and transport of Pacific waters into and from the Okhotsk Sea are...     

Northwestern Weddell Sea deep outflow into the Scotia Sea during the austral summers of 2000 and 2001 estimated by inverse methods

The northward outflow of cold, dense water from the Weddell Sea into the world ocean basins plays a key role in balancing the global heat budget. We estimate the geostrophic flow patterns in the northwestern Weddell Sea using box inverse methods applied to quasi-synoptic hydrographic data collected during the Brazilian DOVETAIL 2000 and 2001 austral summer cruises. The analysis is focused on the variations of the deep Weddell Sea outflow into the Scotia Sea within boxes that bound the main deep gaps over the South Scotia Ridge. To determine the geostrophic volume transports in each box, mass, salt, and heat are conserved within neutral density layers that are not in contact with the atmosphere. Implementing the inverse model and using property anomaly equations weighted by the flow estimate uncertainty our results are consistent with those reported in the literature. A bottom triangle extrapolation method is introduced, which improves the estimated property fluxes through hydrographic sections. In the austral summer of 2000 the transports of Weddell Sea Deep Water (WSDW) through the Philip Passage, Orkney Passage, and southwestern Bruce Passage are 0.01±0.01, 1.15±0.33, and 1.03±0.23 Sv (1 Sv=10⁶ m³ s⁻¹, >0 is northward), respectively. After extrapolation within bottom triangles these transports increase to 0.12±0.03, 3.48±1.81, and 1.20±2.16 Sv. Analysis of the hydrographic data reveal distinct oceanographic conditions over the Philip Passage region, with evidence of mesoscale meanders, warmer and saltier Warm Deep Water (WDW) and colder WSDW observed in 2001 than in 2000. Despite these differences the WSDW transport does not present a significant variation between 2000 and 2001. The WSDW transports through the Philip Passage in 2001 are 0.012±0.001 and 0.113±0.001 Sv after extrapolation within bottom triangles. The circulation derived from the inversion in the austral summer of 2001 suggests a sharp weakening of the barotropic cyclonic flow in the Powell Basin, which may be due to northerly and northeasterly winds associated with an atmospheric low-pressure center located west of the Antarctic Peninsula. We suggest that similar variations in atmospheric forcing may explain changes in the intensity of the cyclonic flow observed in the northwestern Weddell Sea and Powell Basin.     

Formation and transport of intermediate water masses in a model of the Pacific Ocean

A basin-wide ocean general circulation model of the Pacific Ocean was used to investigate how the interior restoration in the Okhotsk Sea and the isopycnal diffusion affect the circulation and intermediate water masses. Four numerical experiments were conducted, including a run with the same isopycnal and thickness diffusivity of 1.0×103 m2/s, a run employing the interior restoration of temperature and salinity in the Okhotsk Sea with a time scale of 3 months, a run that is the same as the first run except for the enhanced isopycnal mixing, and a final run with the combination of the restoration in the Okhotsk Sea and large isopycnal diffusivity. Simulated results show that the intermediate water masses reproduced in the first run are relatively weak. An increase in isopycnal diffusivity can improve the simulation of both Antarctic and North Pacific intermediate waters, mainly increasing the transport in the interior ocean, but inhibiting the outflow from the Okhotsk Sea. The interior restoration generates the reverse current from the observation in the Okhotsk Sea, whereas the simulation of the temperature and salinity is improved in the high latitude region of the Northern Hemisphere because of the reasonable source of the North Pacific Intermediate Water. A comparison of vertical profiles of temperature and salinity along 50°N between the simulation and observations demonstrates that the vertical mixing in the source region of intermediate water masses is very important.     

Water fluxes through the Cretan Arc Straits, Eastern Mediterranean Sea: March 1994 to June 1995

Five research cruises were undertaken incorporating ADCP sections along the Cretan Arc Straits and CTD surveys covering the entire area of the Straits and the Cretan Sea. In addition, six moorings (with 15 current meters) were deployed within the Straits, which monitored flows in the surface (50 m), intermediate (250 m), and deep (50 m from the bottom) layers. The ADCP, CM, and CTD datasets enable the derivation of water transports through the Cretan Arc Straits to be assessed. Flow structure through the Cretan Arc Straits is not the typical flow regime with a surface inflow and deep outflow, instead there is a persistent deep outflow of Cretan Deep Water (CDW) (σ_θ>29.2) with an annual mean of ˜0.6 Sv, through the Antikithira and Kassos Straits at depths below 400 m and 500 m, respectively. CDW outflowing transports are higher (˜0.8 Sv) in April–June, and lower (˜0.3 Sv) in October–December. Within the upper water layer (0–˜400 m), the transport and the water exchanges through the Straits are controlled by local circulation features, which weaken substantially below 200 m. The Asia Minor Current (AMC) influences the Rhodes and the Karpathos Straits, resulting in a net inflow of water. In contrast, the Mirtoan/West Cretan Cyclone influences the Antikithira and Kithira Straits, where there is a net outflow. In the Kassos Strait, there is a complex interaction between the East Cretan Cyclone, the Ierapetra Anticyclone and the westward extension of the Rhodes Gyre, which results in a variable flow regime. There is a net inflow in autumn and early winter, and a switch to a net outflow in early spring and summer. The total inflow and outflow, throughout all of the Straits, ranged from ˜2 to ˜3.5 Sv, with higher values in autumn and early winter and lower in summer. The AMC carries ˜2 Sv of inflow through the Rhodes and Karpathos Straits, and this accounts for 60–80% of the total inflow. About 10–15% of the total outflow is of CDW, and a further 45–70% occurs through the upper 400 m of the Kithira and Antikithira Straits. The Kassos Strait exhibits a net inflow of ˜0.7 Sv in autumn and early winter, with a net outflow of ˜0.5 Sv in early spring and summer.     

Velocity structures and transports of the Kuroshio and the Ryukyu current during fall of 2000 estimated by an inverse technique

An inverse calculation using hydrographic section data collected from October to December 2000 yields velocity structure and transports of the Kuroshio in the Okinawa Trough region of the East China Sea (ECS) and south of central Japan, and of the Ryukyu Current (RC) southeast of the Ryukyu Islands. The results show the Kuroshio flowing from the ECS, through the Tokara Strait (TK), with a subsurface maximum velocity of 89 cm s⁻¹ at 460 dbar. In a section (TI) southeast of Kyushu, a subsurface maximum velocity of 92 cm s⁻¹ at 250 dbar is found. The results also show the RC flowing over the continental slope from the region southeast of Okinawa (OS) to the region east of Amami-Ohshima (AE) with a subsurface maximum velocity of 67 cm s⁻¹ at 400 dbar, before joining the Kuroshio southeast of Kyushu (TI). The volume transport around the subsurface velocity maximum southeast of Kyushu (TI) balances well with the sum of those in TK and AE. The temperature-salinity relationships found around these velocity cores are very similar, indicating that the same water mass is involved. These results help demonstrate the joining of the RC with the Kuroshio southeast of Kyushu. The net volume transport of the Kuroshio south of central Japan is estimated to be 64∼79 Sv (1 Sv ≡ 10⁶ m³s⁻¹), of which 27 Sv are supplied by the Kuroshio from the ECS and 13 Sv are supplied by the RC from OS. The balance (about 24∼39 Sv) is presumably supplied by the Kuroshio recirculation south of Shikoku, Japan.     

Isotopic tracers for water masses in the coastal region of eastern Hokkaido

In this study we used two stable isotopes, δ¹³C and δ¹⁸O, for water mass classification in the coastal region off eastern Hokkaido. δ¹³C* values, which were corrected for the biological effect, and δ ¹⁸O values up to 300 m depth suggested that the isotopic character of the onshore and offshore water in the southern Okhotsk Sea, the Nemuro Strait and the western North Pacific could be explained by the mixing of three source waters: the Oyashio water (OYW), Soya Warm Current water (SWCW) and East Sakhalin Current water (ESCW). In summer, δ ¹³C*-δ ¹⁸O plots indicated mixing between SWCW from the southern Okhotsk Sea and OYW in the Pacific coast of southeastern Hokkaido, while temperature-salinity plots of the onshore water showed minimal difference from the offshore OYW. In winter, on the other hand, the mixed water of ESCW and OYW (or SWCW) appeared in the Pacific coastal region, distributed as cold, low salinity onshore water. Finally, we estimated mixing ratios of OYW, SWCW and ESCW in the coastal region of western North Pacific using their mean values of δ ¹³C* and δ ¹⁸O as endmembers. These results suggest seasonal and yearly changes of water mass combination en route from the southern Okhotsk Sea to the western North Pacific.     

An anticyclonic eddy in the intermediate layer of the Luzon Strait in Autumn 2005

The complicated flow pattern in the intermediate layer of the Luzon Strait could directly affect the efficiency of the water and energy exchange between the South China Sea (SCS) and the North Pacific. Here we present a subsurface anticyclonic eddy in the Luzon Strait deduced using observations conducted in October 2005. On the basis of the hydrographic and current measurements, an anticyclonic eddy was found in the intermediate layer, i.e., about 26.8–27.3σ_θ, 500–900 m. It captures part of the SCS Intermediate Water outflow in the northern Luzon Strait, and carries it to flow southward and then westward back into the SCS in the southern Luzon Strait, with volume transport of about 1.9 × 10⁶ m³ s⁻¹. The simulated results from Hybrid Coordinate Ocean Model also suggest the existence of this anticyclonic eddy that develops and lingers for a month long.     

Nutrient budgets for the South China Sea basin

Varying atmospheric forcing and an elaborate geography make for a complex flow in the South China Sea (SCS). Throughout the year, the surface waters of the Kuroshio flow into the SCS, while the surface waters of the SCS flow out through the Bashi Channel. Cumulatively, there is a small (1 Sv) net outflow of surface water (0–350-m depth) from the SCS in the wet season, but a net inflow (3 Sv) in the dry season through the Bashi Channel. The differences are mainly made up by inflow and outflow of Sunda Shelf Water in the wet and dry seasons, respectively.Seawater, phosphorus, nitrogen and silicate budgets were calculated based on a box model. The results point out an intermediate water outflow (350–1350-m depth) into the West Philippine Sea (WPS) through the Bashi Channel in both the wet and dry seasons, though this, along with the nutrients it carries, is slightly larger in the dry season (2 Sv) than in the wet (1.8 Sv). More importantly, the export of nutrient-laden SCS intermediate water through the Bashi Channel subsequently upwells onto the East China Sea (ECS) shelf. The denitrification rate for shelves in the SCS is 0.11 mol N m⁻² year⁻¹, calculated by balancing the nitrogen budget. The oxygen consumption and the nutrient regeneration rates, based on the mass-balance and the one-dimensional advection–diffusion models, stand between those for the Bering Sea and the Sea of Japan.     

The Increase of Biogenic Sulfate Aerosol and Particle Number in Marine Atmosphere over the Northwestern North Pacific

During a cruise aboard the R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998 the particle number concentrations and the major ionic components of size fractionated aerosols were measured to investigate the aerosol produced by marine biological activity. Continuous low concentrations of nitrate (<1.8 nmol m⁻³), similar to the marine air background level, were found over the northwestern North Pacific (40–45°N) and the Sea of Okhotsk (44–45°N). Over the Sea of Okhotsk, a high concentration of chlorophyll-a (5.4 mg m⁻³) in seawater was observed, and atmospheric concentrations of non sea-salt (nss-) sulfate (44 nmol m⁻³), methane sulfonic acid (MSA) (1.8 nmol m⁻³) and particle number in the size range of 0.1 < D < 0.5 μm (199 cm⁻³) were found to be 9, 7, and 2 times, respectively, higher than those in the background marine air. The increase in particle number concentrations mainly in the size range of 0.2 < D < 0.3 μm was likely caused by the increase of biogenic sulfate over the high productive region of the Sea of Okhotsk. In humid air conditions (R.H. > 96%), the increased biogenic sulfate that condensed the large amount of water vapor would not have sufficient solute mass to activate as cloud condensation nuclei (CNN) and would remain as aerosol particles in the marine air with frequent sea-fogs over the high productive region. Biogenic sulfate originating from dimethyl sulfide (DMS) would gradually grow into the CCN size and continuously supply a great number of CCN to the marine air in the northwestern North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.