Salinity Minimum Research Articles

An Exchange Window for the Injection of Antarctic Intermediate Water into the South Pacific

Abstract Antarctic Intermediate Water (AAIW) occupies the intermediate horizon of most of the world oceans. Formed in the Southern Ocean, it is characterized by a relative salinity minimum. With a new, denser in situ National Oceanographic Data Center dataset, the authors have reanalyzed the export characteristics of AAIW from the Southern Ocean into the South Pacific Ocean. These new data show that part of the AAIW is exported from the subpolar frontal region by the large-scale circulation through an exchange window of 10° width situated east of 90°W in the southeast corner of the Pacific basin. This suggests the origin of this water to be in the Antarctic Circumpolar Current. A set of numerical modeling experiments has been used to reproduce these observed features and to demonstrate that the dynamics of the exchange window is controlled by the basin-scale meridional pressure gradient. The exchange of AAIW between the Southern and Pacific Oceans must therefore be understood in the context of the large basin-scale dynamical balance rather than simply local effects.

Depth profiles of volatile iodine and bromine-containing halocarbons in coastal Antarctic waters

Measurements of bromoform (CHBr 3), diiodomethane (CH 2I 2), chloroiodomethane (CH 2ICl) and bromoiodomethane (CH 2IBr) were made in the water column (5–100 m depth) of the Southern Ocean within 0–40 km of the Antarctic sea ice during the ANTXX1/2 transect of the German R/V Polarstern, at five locations between 70–72°S and 9–11°W in the Antarctic spring/summer of 2003–2004. Some of the profiles exhibited a very pronounced layer of surface sea-ice meltwater, as evidenced by salinity minima and temperature maxima, along with surface maxima in concentrations of CHBr 3, CH 2I 2, CH 2ICl and CH 2IBr. These results are consistent with in situ surface halocarbon production by ice algae liberated from the sea ice, although production within the sea ice followed by transport cannot be entirely ruled out. Additional sub-surface maxima in halocarbons occurred between 20 and 80 m. At a station further from shore and not affected by surface sea-ice meltwater, surface concentrations of CH 2I 2 were decreased whereas CH 2ICl concentrations were increased compared to the stations influenced by meltwater, consistent with photochemical conversion of CH 2I 2 to CH 2ICl, perhaps during upward mixing from a layer at ∼ 70 m enhanced in iodocarbons. Mean surface (5–10 m) water concentrations of halocarbons in these coastal Antarctic waters were 57 pmol l − 1 CHBr 3 (range 44–78 pmol l − 1 ), 4.2 pmol l − 1 CH 2I 2 (range 1.7–8.2 pmol l − 1 ), 0.8 pmol l − 1 CH 2IBr (range 0.2–1.4 pmol l − 1 ), and 0.7 pmol l − 1 CH 2ICl (range 0.2–2.4 pmol l − 1 ). Concurrent measurements in air suggested a sea-air flux of bromoform near the Antarctic coast of between 1 and 100 (mean 32.3, median 10.4) nmol m − 2 day − 1 and saturation anomalies of 557–1082% (mean 783%, median 733%), similar in magnitude to global shelf values. In surface samples affected by meltwater, CH 2I 2 fluxes ranged from 0.02 to 6.1 nmol m − 2 day − 1 , with mean and median values of 1.9 and 1.1 nmol m − 2 day − 1 , respectively.

Flow Convergence Caused by a Salinity Minimum in a Tidal Channel

Residence times of dissolved substances and sedimentation rates in tidal channels are affected by residual (tidally averaged) circulation patterns. One influence on these circulation patterns is the longitudinal density gradient. In most estuaries the longitudinal density gradient typically maintains a constant direction. However, a junction of tidal channels can create a local reversal (change in sign) of the density gradient. This can occur due to a difference in the phase of tidal currents in each channel. In San Francisco Bay, the phasing of the currents at the junction of Mare Island Strait and Carquinez Strait produces a local salinity minimum in Mare Island Strait. At the location of a local salinity minimum the longitudinal density gradient reverses direction. This paper presents four numerical models that were used to investigate the circulation caused by the salinity minimum: (1) A simple one-dimensional (1D) finite difference model demonstrates that a local salinity minimum is advected into Mare Island Strait from the junction with Carquinez Strait during flood tide. (2) A three-dimensional (3D) hydrodynamic finite element model is used to compute the tidally averaged circulation in a channel that contains a salinity minimum (a change in the sign of the longitudinal density gradient) and compares that to a channel that contains a longitudinal density gradient in a constant direction. The tidally averaged circulation produced by the salinity minimum is characterized by converging flow at the bed and diverging flow at the surface, whereas the circulation produced by the constant direction gradient is characterized by converging flow at the bed and downstream surface currents. These velocity fields are used to drive both a particle tracking and a sediment transport model. (3) A particle tracking model demonstrates a 30 percent increase in the residence time of neutrally buoyant particles transported through the salinity minimum, as compared to transport through a constant direction density gradient. (4) A sediment transport model demonstrates increased deposition at the near-bed null point of the salinity minimum, as compared to the constant direction gradient null point. These results are corroborated by historically noted large sedimentation rates and a local maximum of selenium accumulation in clams at the null point in Mare Island Strait.

A salinity front in the southern East China Sea separating the Chinese coastal and Taiwan Strait waters from Kuroshio waters

While the current in the entire cross section of Taiwan Strait has been considered for a long time to flow northward in summer, in this paper the observational results are presented to indicate that only the western three-quarters of the northernmost part of the Taiwan Strait is occupied by the Chinese coastal and Taiwan Strait waters, and the remaining part by the lower temperature and higher salinity Kuroshio subsurface waters which have circumvented the northern tip of Taiwan. Chinese coastal and Taiwan Strait waters are separated from Kuroshio waters by a salinity front. In fact, the waters are vertically well-mixed near the front where the surface waters show a clear horizontal salinity maximum but a weak temperature minimum. These surface waters are in sharp contrast to the bottom waters which show a horizontal salinity minimum but a strong temperature maximum. Subsurface waters near the front are distinctively warmer and lighter but less saline and less oxygenated than the waters on either side. The warm, fresh, light, low-oxygen characteristics of these subsurface waters are attributed to the downwelling of waters from the east which have upwelled earlier near the shelf-break northeast of Taiwan. These waters can be traced along the isobath of about 75-m to at least 30°N in the East China Sea (ECS). Similarly, the water column-integrated nutrients, chlorophyll a and primary productivity also show a horizontal minimum near this depth. Such an unusual subsurface warm temperature ridge but low salinity trough correctly delineates the seaward boundaries of the coastal and Taiwan Strait waters in the ECS. The salinity maximum at the surface also seems to define the seaward boundaries of the fresh ( S<33) coastal waters.

The Inflow Path of the East Sea Intermediate Water into the Ulleung Basin in July 2005

To investigate inflow path of the East Sea Intermediate Water (ESIW) into the Ulleung Basin, hydrographic data surveyed in July 2005 were analyzed. The ESIW was characterized by the Salinity Minimum Layer (SML) within a depth range of 100 to 360 meters. Averaged potential temperature and salinity of the SML were 1.835℃ and 34.049 psu, respectively. Mean potential density (σ θ ) of the SML was 27.221 with a standard deviation of 0.0393. On isopycnal surfaces of 27.14 and 27.18 σ θ which correspond to upper layers of the ESIW, the coastal low salinity water was separated from the offshore low salinity water by the relatively warm and saline water which might be affected by the Tsushima Warm Current Water. Relatively cold and fresh water, however, intruded into the Ulleung Basin from the region of Korean coast on isopycnal surfaces of 27.22 and 27.26 which was lower layer of the ESIW. The salinity distribution in the isopycnal layer of 27.14~27.26 with acceleration potential on 27.22 σ θ surface also showed clearly that the low salinity water flowed from the coastal area and intruded into the Ulleung Basin. This implies that the ESIW flows from the north to the south along the east coasts of Korea and spreads into the Ulleung Basin in summer.

Analysis of salinity measurements near islands on the French continental shelf of the Bay of Biscay

The Bay of Biscay is characterised by large fresh water inputs from two major rivers, the Loire and the Gironde, with a mean discharge of about 900 m3/s. To describe the spatial and temporal variability of the Loire and Gironde plumes, continuous salinity measurements were made at 4 locations on French coastal islands over periods lasting at least two years. These islands are located at a distance from the large local gradients linked to local inputs. Whereas sea surface salinity in the centre of the Bay of Biscay is 35.6, salinities at the coast vary between about 35 in summer to occasionally less than 30 in late winter or in spring. Minimum salinities do not occur at the same time along the coast, indicating a strong spatial gradient. Near the Loire and Gironde estuaries, a strong temporal correlation between discharges and salinity variation appears. Far from the estuaries, some drops in salinity seem to be correlated with a change of wind regime. In summer, a general decrease from north to south is found along the coast and may be linked to northwesterly wind conditions, which drive surface water to SW of the bay. These data constitute the first set of time series of salinity. They will be pursued to assess the interannual variability which is presumed to be high because of the large variability in river discharges and wind regimes.

Low salinity intrusions in the western English Channel

Low salinity (<35) surface waters (LSSW) at the southern entrance to the western English Channel (48.5°N, 5.1°W, near Ushant) were observed in late winter (March–April) in three successive years (2002–04) during near continuous ship of opportunity operations. The source of the LSSW is the northward spreading plumes from the Loire (47.5°N, 2.5°W) and Gironde (45.6°N, 1.2°W) along the French Atlantic coast. Fastest plume travel times were associated with northeasterly winds, consistent with Ekman theory. Differences between years in the mean winter (January–March) combined river discharges ( D) was consistent with the minimum salinities ( S min) of the LSSW (2004: D=4211 m 3 s −1, S min=33.68; 2003: D=3630 m 3 s −1, S min=33.90; 2002: D=1579 m 3 s −1, S min=34.53). Winter mean (1905–74) salinity is otherwise 35.33 near Ushant. The LSSW intruded into the western English Channel in each year, suggesting a common phenomenon. The low salinity intrusion was freshest (mean=35.11±0.21) and most penetrative (reaching 50.7°N, 1.0°W by the end of the year) in 2003 on account of (1) entering on a spring tide giving greater tidal excursion into the western English Channel and (2) intrusion favourable winds (southwesterly/southeasterly) acting on the longer term residual flow. Less penetration occurred in 2004 when the arrival of the LSSW coincided with a neap tide followed by intrusion-resistant northwesterly winds, resulting in a less saline (mean=35.20±0.23) intrusion. In 2004, transport tended to be offshore to at least 100 km from the French Atlantic coast (47°N, 4.8°W–48°N, 4.7°W). In 2002, the lower volume of plume water relative to the other years produced a more saline intrusion (mean=35.25±0.12). Prevailing westerly winds may have pushed this intrusion northwards beyond the route of the ferry, making it difficult to assess the true extent of the intrusion in 2002. A link of the LSSW to phases of the winter North Atlantic Oscillation index from a literature search of the last 84 years was inconclusive.

Light absorption and scattering by particles and CDOM at the New England shelfbreak front

A fine‐scale survey of physical, chemical, and optical properties was done across the shelfbreak front in the Middle Atlantic Bight region south of Martha's Vineyard, Cape Cod (70.5°W) during late summer 2002. The front displayed physical and biological structure typical for this region and season: a density‐compensating front with strong horizontal T and S and optical gradients, and a chlorophyll maximum layer that deepened in the seaward direction across the front, became detached beneath the shelfbreak jet, reappeared on a deeper and greater density surface on the seaward side of the shelfbreak front, and then shoaled again in the seaward direction. At times the shoreward leading edge of the chlorophyll maximum layer seaward of the front was situated beneath the chlorophyll maximum layer shoreward of the front. Hydrography on the shoreward side of the front was dominated by a bolus of cold pool water of shelf origin with minimum salinity and temperature of 33 and 10°C, respectively. The cold pool was also a pool of high CDOM absorption whose distribution coincided with the temperature and salinity across the front. The persistence of sharp horizontal T, S, and CDOM gradients indicated that advective processes exceed diffusive mixing processes at the front. CDOM in the euphotic zone showed a strong inverse relationship to temperature and, below the euphotic zone, a strong inverse relationship to salinity, indicating a terrestrial CDOM source within the cold pool and a photodegradation sink at the surface. Cross‐frontal exchange of shelf CDOM and upper slope waters is inferred from the T‐S properties of the CDOM pool and previously reported measurements of the mixing and circulation at this site. The chlorophyll specific absorption coefficients of discrete samples collected within the chlorophyll maximum layers, along with LPS surveys of dissolved and particulate absorption and scattering, indicate that the variability of optics at the shelfbreak front is influenced mostly by particle optics. Due to the presence of the cold pool with its high CDOM signature, the waters masses across the shelfbreak front can be considered as case 1 for particles but case 2 for dissolved materials.

Possible Density Change of the Origin of North Pacific Intermediate Water Due to Double Diffusion in the Mixed Water Region

In this study we test Talley's hypothesis that Oyashio winter mixed-layer water (26.5–26.6σ θ) increases its density to produce the North Pacific Intermediate Water (NPIW) salinity minimum (26.7– 26.8σθ) in the Mixed Water Region, assuming a combination of cabbeling and double diffusion. The possible density change of Oyashio winter mixed-layer water is discussed using an instantaneous ratio of the change of temperature and salinity along any particular intrusion (R l ). We estimate the range of R required to convert Oyashio winter mixed-layer water to the NPIW salinity minimum due to double diffusion, and then assume double-diffusive intrusions as this conversion mechanism. A double-diffusive intrusion model is used to estimate R in a situation where salt fingering dominates vertical mixing, as well as to determine whether Oyashio winter mixed-layer water can become the NPIW salinity minimum. Possible density changes are estimated from the model R by assuming the amount of density change due to cabbeling. From these results, we conclude that Oyashio winter mixed-layer water contributes to a freshening of the lighter layer of the NPIW salinity minimum (around 26.70σθ) in the MWR.

Hydrography of the eastern Arabian Sea during summer monsoon 2002

Hydrographic observations in the eastern Arabian Sea (EAS) during summer monsoon 2002 (during the first phase of the Arabian Sea Monsoon Experiment (ARMEX)) include two approximately fortnight-long CTD time series. A barrier layer was observed occasionally during the two time series. These ephemeral barrier layers were caused byin situ rainfall, and by advection of low-salinity (high-salinity) waters at the surface (below the surface mixed layer). These barrier layers were advected away from the source region by the West India Coastal Current and had no discernible effect on the sea surface temperature. The three high-salinity water masses, the Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), and Red Sea Water (RSW), and the Arabian Sea Salinity Minimum also exhibited intermittency: they appeared and disappeared during the time series. The concentration of the ASHSW, PGW, and RSW decreased equatorward, and that of the RSW also decreased offshore. The observations suggest that the RSW is advected equatorward along the continental slope off the Indian west coast.

Coastal oceanographic regimes of the Northern Argentine Continental Shelf (34–43°S)

The oceanographic regimes of the Northern Argentine Continental Shelf (NACS, 34°–43°S) are derived from advected waters of subantarctic origin, local sources of continental run-off, and a locally generated salinity maximum. Based on 3690 CTD profiles, monthly mean wind fields at coastal stations, and river discharge data, we define the oceanographic regimes over the shelf by analyzing salinity characteristics and spatial distribution: (1) a maximum in salinity (33.7–34.2) originating from the Gulf of San Matías; (2) a relative salinity minimum (30.0–33.3) of the El Rincón estuarine system; (3) a salinity minimum (0–33.0) originating in the Río de la Plata; and (4) waters of the continental shelf (33.5 and 33.7). Temperature over the shelf is controlled by sea–air heat exchange coupled with bathymetry. An analysis of the Simpson parameter of stability ( ϕ) provided an objective definition of a vertically homogenous coastal zone separated from seasonally stratified shelf waters south of 37°S. Bottom temperature gradients and synoptic sections in the winter and spring indicate the presence of a shallow sea front at the 40–50-m isobaths south of 37°S, persistent throughout the year. We define two seasonal periods, autumn–winter and spring–summer, based on seasonality in monthly mean winds fields, continental run-off, fresh water balance and the spatial distribution of salinity signals. Maximum seasonal variation in the extent and location of the oceanographic regimes occurs within the coastal zone. In the autumn–winter period, we observe a northward extension of the Río de la Plata and Gulf of San Matías waters, as well as a reduction of the El Rincón and Continental Shelf waters near the coast. The spring–summer period is characterized by Río de la Plata waters flowing to the south and east, a reduction of Gulf of San Matías waters and an invasion of El Rincón and Continental Shelf waters into the coastal areas. In a general sense, waters across the NACS undergo a seasonal oscillation in distribution and extension that implies a spring–summer reversal of the characteristic shelf-wide north–northeastward direction of flow within the coastal zone.

Effect of salinity on the distribution, growth, and toxicity of Karenia spp.

The first recorded bloom of Karenia spp., resulting in brevetoxin in oysters, in the low salinity waters of the Northern Gulf of Mexico (NGOMEX) occurred in November 1996. It raised questions about the salinity tolerance of Karenia spp., previously considered unlikely to occur at salinities <24 psu, and the likelihood that the bloom would reoccur in the NGOMEX. Salinity was investigated as a factor controlling Karenia spp. abundance in the field, using data from the NGOMEX 1996 bloom and Florida coastal waters from 1954 to 2004, and growth and toxin production in cultures of Karenia brevis (Davis) G. Hansen and Moestrup. During the NGOMEX bloom, Karenia spp. occurred much more frequently at low salinities than in Florida coastal waters over the last 50 years. The data suggest that the NGOMEX bloom started on the NW Florida Shelf, an area with a higher frequency of Karenia spp. at low salinities than the rest of Florida, and was transported by an unusual westward surface current caused by Tropical Storm Josephine. The minimum salinity at which growth occurred in culture ranged between 17.5 and 20 psu, but the optimal salinity ranged between low values of 20 or 25 and high values of 37.5–45 psu, depending on the clone. The effect of salinity on toxin production in one clone of K. brevis was complex, but at all salinities brevetoxin levels were highest during the stationary growth phase, suggesting that aging, high density blooms may pose the greatest public health threat. The results demonstrate that Karenia spp. can be a public health threat in low salinity areas, but the risk in the NGOMEX is relatively low. No bloom has occurred since the 1996 event, which was probably associated with a special set of conditions: a bloom along the Florida Panhandle and a tropical storm with a track that set up a westward current.

Interannual and Decadal Variabilities of NPIW Salinity Minimum Core Observed along JMA’s Hydrographic Repeat Sections

We investigated the variation of the North Pacific Intermediate Water (NPIW) distribution in the western North Pacific, focusing on the intermediate salinity minimum (S < 34.2) core observed along the meridional hydrographic sections including the 137°E repeat section by the Japan Meteorological Agency. This core is a cross-section of a low salinity tongue extending westward along the recirculation in the subtropical gyre. The core size shows remarkable variabilities in interannual and decadal time scales. The salinity change in the density layer during the period of core expansion (shrinking) represents the spatial salinity change in the tongue toward the west (east). Thus, we conclude that the core size variation is associated with the zonal wobble of the tongue having thicker distribution to the east, rather than temporal changes of the water mass itself. The core size at 137°E is well correlated with the meridional gradient of the depth in the isopycnal surface at the salinity minimum representing the recirculation intensity, suggesting a relation with the intensity of the subtropical gyre. A significant lag-correlation between the gradient and the wind forcing over the North Pacific suggests that the first mode baroclinic Rossby waves excited in the central North Pacific propagated westward to change the intensity of the recirculation in interannual time scales. In decadal time scales, it is found that the wind stress curl and heat flux fields in the North Pacific precede the recirculation by about 11 years.

Observation of frontal waves and associated salinity minimum formation along the Kuroshio Extension

High‐resolution observations with a towed–conductivity‐temperature‐depth system were conducted along the Kuroshio Extension, where the Kuroshio and the Oyashio merge and new North Pacific Intermediate Water (NPIW) is formed. Large‐amplitude frontal waves at an intermediate depth corresponding to a density range of NPIW (26.6–26.9σθ) were discovered here along the main stream of the Kuroshio Extension. A remarkable salinity minimum due to the intense intrusions of Oyashio water was observed near the trough of the frontal wave with an apparent wavelength of ∼100 km. Around the troughs (crests) of the frontal waves, the horizontal velocity in the intermediate layer was directed to the southern Kuroshio water side (northern Oyashio water side) relative to the upper layer. Horizontal velocity fields converged (diverged) around the wave trough (crest), indicating downwelling (upwelling). The amplitude of the frontal waves was observed to grow in the downstream direction, where isolated eddies were observed. This suggests that the development of frontal waves and wave breaking enhance isopycnal mixing and cross‐frontal exchange across the main stream of the Kuroshio Extension.

Salinity Variations in the Southern California Current*

Abstract Hydrographic observations southwestward of the Southern California Bight in the period 1937–99 show that temperature and salinity variations have very different interannual variability. Temperature varies within and above the thermocline and is correlated with climate indices of El Niño, the Pacific decadal oscillation, and local upwelling. Salinity variability is largest in the surface layers of the offshore salinity minimum and is characterized by decadal-time-scale changes. The salinity anomalies are independent of temperature, of heave of the pycnocline, and of the climate indices. Calculations demonstrate that long-shore anomalous geostrophic advection of the mean salinity gradient accumulates along the mean southward trajectory along the California Current and produces the observed salinity variations. The flow anomalies for this advective process are independent of large-scale climate indices. It is hypothesized that low-frequency variability of the California Current system results from unresolved, small-scale atmospheric forcing or from the ocean mesoscale upstream of the Southern California Bight.

Characteristics and Trends of River Discharge into Hudson, James, and Ungava Bays, 1964–2000

Abstract The characteristics and trends of observed river discharge into the Hudson, James, and Ungava Bays (HJUBs) for the period 1964–2000 are investigated. Forty-two rivers with outlets into these bays contribute on average 714 km3 yr−1 [= 0.023 Sv (1 Sv ≡ 106 m3 s−1)] of freshwater to high-latitude oceans. For the system as a whole, discharge attains an annual peak of 4.2 km3 day−1 on average in mid-June, whereas the minimum of 0.68 km3 day−1 occurs on average during the last week of March. The Nelson River contributes as much as 34% of the daily discharge for the entire system during winter but diminishes in relative importance during spring and summer. Runoff rates per contributing area are highest (lowest) on the eastern (western) shores of the Hudson and James Bays. Linear trend analyses reveal decreasing discharge over the 37-yr period in 36 out of the 42 rivers. By 2000, the total annual freshwater discharge into HJUBs diminished by 96 km3 (−13%) from its value in 1964, equivalent to a reduction of 0.003 Sv. The annual peak discharge rate associated with snowmelt has advanced by 8 days between 1964 and 2000 and has diminished by 0.036 km3 day−1 in intensity. There is a direct correlation between the timing of peak spring discharge rates and the latitude of a river’s mouth; the spring freshet varies by 5 days for each degree of latitude. Continental snowmelt induces a seasonal pulse of freshwater from HJUBs that is tracked along its path into the Labrador Current. It is suggested that the annual upper-ocean salinity minimum observed on the inner Newfoundland Shelf can be explained by freshwater pulses composed of meltwater from three successive winter seasons in the river basins draining into HJUBs. A gradual salinization of the upper ocean during summer over the period 1966–94 on the inner Newfoundland Shelf is in accord with a decadal trend of a diminishing intensity in the continental meltwater pulses.

The South China Sea, a cul-de-sac 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.

A tracer study of ventilation in the Japan/East Sea

During the Circulation Research in East Asian Marginal Seas (CREAMS) summer cruises in 1999, a suite of samples was collected for tracer analysis. Oxygen isotopes combined with tritium-helium ventilation timescales and noble gas measurements give unique insights into the ventilation of water masses in the Japan/East Sea (JES). In particular, noble gases and oxygen isotopes are indicators of brine rejection, which may assist in explaining the recent changes observed in the ventilation of the JES. Oxygen isotope data presented here indicate that both thermally driven convection and brine rejection have played significant roles in deep-water formation but that brine rejection is unlikely to be a significant contributor at the moment. A 6-box ventilation model of the JES, calibrated with tritium and helium-3 measurements, performed better when a significant decrease of dense-water formation rates in the mid-1960s was incorporated. However, the model calculations suggest that Japan Sea Intermediate Water formation is still occurring. Subduction of sea–ice melt water may be a significant ventilation mechanism for this water mass, based on an argon saturation minimum at the recently ventilated salinity minimum in the northwestern sector of the JES. The salinity and oxygen isotope budgets imply a potential bottom-water formation rate of 3.97±0.89×1012 m3 yr−1 due to brine rejection, which could account for a time averaged fraction of between 25% and 35% of the ventilation of subsurface water formation in the JES.

Tracing tropical and intermediate waters from the South China Sea to the Okinawa Trough and beyond

Intermediate waters with a salinity minimum from 350 to 1350 m depths have been reported to flow out of the South China Sea (SCS) through the Luzon Strait. This eastward flowing SCS Intermediate Water (SCSIW) is blocked by the northward flowing Black Stream (Kuroshio) southeast of Taiwan and is forced to turn to the north. The SCSIW subsequently enters and occupies the western half of the Okinawa Trough. Because of strong upwelling in the SCS basin, the SCSIW contains more nutrients than does the Kuroshio Intermediate Water in the Philippine Sea. One of the major purposes of this note is to reconfirm that the SCSIW actually does upwell onto the East China Sea (ECS) shelf and to show that the South China Sea Tropical Water (SCSTW), with a salinity maximum of 50–150 m in depth, follows the same pathway as the SCSIW and similarly occupies the western half of the Okinawa Trough. Part of these relatively nutrient‐rich subsurface waters upwell, thereby supplying nutrients to the ECS shelves. The remaining SCSIW and SCSTW flow along with the Kuroshio and can be traced as far east as 140°E, south of Japan. This is just around the region where the Oyashio joins the Kuroshio to form the North Pacific Intermediate Water.

Prediction of water salinity in the Yumaguzinskoe Reservoir under construction

Factors responsible for the formation of water salinity in the Yumaguzinskoe Reservoir, which is under construction in the upper reaches of the Belaya River, are analyzed. Based on the prediction experience and a sufficient amount of initial data on water quality of the Belaya River, the universally accepted algorithm of prediction for years of different water supply levels using the calculation method of “running-out” has been modified. As revealed, the minimum water salinity at the reservoir spillway is observed in May–August, the maximum water salinity being in January–March. The regularities of a general nature have been found.