Salinity Minimum Research Articles

Southwest Pacific Ocean Water-Mass Changes between 1968/69 and 1990/91*†

Abstract Water-mass changes are estimated in the southwest Pacific Ocean by comparing a meridional hydrographic section along 170°W between 60°S and the equator occupied in 1968/69 during the Southern Cross cruise and again in 1990 during a NOAA Climate and Global Change cruise. Another comparison is made using a hydrographic section along 35°S between the date line and 169°W occupied in 1969 during USNS Eltanin cruise 40 and again in 1991 during a Mapkiwi cruise. The most robust change consists of cooling (and freshening) on isopycnals, with peak differences exceeding −1.0°C (−0.25 pss) at the base of the subtropical thermocline. The cooling and freshening starts above the stratification minimum of the Subantarctic Mode Water and persists to below the salinity minimum of the Antarctic Intermediate Water. Amplitudes are largest at 48°S, near where these water masses subduct, and decay toward 20°S, near the axis of the Subtropical Gyre. This change is likely the result of surface warming and/or freshening ...

The origin of the North Pacific Intermediate Water

Possible source regions of the North Pacific Intermediate Water (NPIW) were investigated with synoptic conductivity‐temperature‐depth surveys. In the Okhotsk Sea Kuril Basin a pycnostad (referred to as the Okhotsk Sea Mode Water (OSMW)) was found in the density range of 26.6–27 σθ. The pycnostad is not seen in the Western Subarctic Gyre (WSAG); thus it is an indicative water peculiar to the Okhotsk Sea. The maximum thickness is at 26.7–26.9 σθ (centered at 26.8 σθ) which coincides with the NPIW density range in the North Pacific Subtropical Gyre. In the Oyashio area east of the southern Kuril Islands and Hokkaido, waters that have intermediate temperature, salinity, and potential vorticity between the OSMW and the WSAG water were distributed, suggesting a following transport route of the NPIW source water. The thick (thus low‐Q; Q is potential vorticity) and low‐salinity water mass outflowing from the Okhotsk Sea mixes with the relatively warm, saline, and high‐Q WSAG water to form the Oyashio water. A coastal part of the Oyashio water flows southwestward along the east coast of the southern Kuril Islands and Hokkaido, retaining the pycnostad (Q minimum). A large part of the low‐Q Oyashio water flows further southward and merges with the Kuroshio Extension and then flows eastward, forming new NPIW. In this process a salinity minimum develops and the Q minimum disappears because of the mixing with a saline Kuroshio water (old NPIW) without a pycnostad in the NPIW density range. These results suggest that the origin of NPIW is the water mass in the Okhotsk Sea (OSMW) and the density of the water mass primarily determines the NPIW density centered at around 26.8 σθ.

Hydrological and chlorofluoromethane measurements of the Indonesian throughflow entering the Indian Ocean

The Java Australia Dynamic Experiment high‐resolution February–March 1992 conductivity‐temperature‐depth and chlorofluoromethane section obtained between Australia and Bali and on the sills between Flores, Sumba, Sawu, Roti, and the Australian continental shelf allows detailed examination of the water masses distribution and their inferred circulation. A sharp hydrological front between the Indonesian waters and the southern Indian Ocean waters is found between 13°S and 14°S in both seasons (February–March 1992 and August 1989). It separates the high‐salinity surface waters to the south from the lower‐salinity surface waters derived from the Indonesian Seas to the north. It reaches the surface in February 1992, whereas it was capped by a particularly low salinity surface layer in August 1989. Near Bali, the NW monsoon of February–March produces large intrusions of low‐salinity water from the Java Sea, through Lombok Strait in the upper 100 m. At depth, the North Indian Intermediate Water, flowing along the Indonesian coast, brings salty, low‐oxygen and low‐chlorofluorocarbon water. It enters the Sawu Sea through Sumba Strait toward the east, while it undergoes strong mixing with the Indonesian Seas water. The primary pathway of the Indonesian waters is found north of the front and south of the North Indian Intermediate Water, between 13°S and 9°30′S, and the associated salinity minimum can be followed all across the Indian Ocean.

Saline intrusions in the intermediate waters north of Oahu, Hawaii

The Hawaii Ocean Time-series (HOT) hydrographic observations at station ALOHA (22°45′N, 158°W) reveal that the region is sometimes the site of intrusive interleaving of different water types near the salinity minimum of the North Pacific Intermediate Waters. This interleaving is associated with saline laminae, or lenses, 5–30 km long (submesoscale) and 5–100 m thick (finestructure). The temporal variability of these intermediate waters is investigated statistically, and a background water type is defined against which to measure the strength of intrusions. The salinity minimum shows a relative maximum in variability, caused mainly by the episodic appearance of the saline, finestructure intrusions, which are correlated with low oxygen and silicate concentrations. The intermediate salinity minimum has its southern boundary near the latitude of the Hawaiian Islands, where salinity increases towards the south and oxygen gradually decreases. Thus, stirring processes local to the Hawaiian Ridge may explain the observations. Possible mechanisms are suggested, including fluctuations of the subtropical gyre southern boundary and a hydrodynamically unstable flow at intermediate depths along the ridge. Either process could transport relatively saline water into the ALOHA region, and would lead to interleaving, driven by double diffusion on scales of the order of 10 m in the vertical.

Historical and recent evidence of Scotian Shelf Water on southern Georges Bank

Historical data from 1912–1987 indicate that low salinity (less than 32.0 psu) near-surface water occurs occasionally on southern Georges Bank during May, while none occurs during April. Composite monthly plots of historical near-surface salinity and estimated advection rates show that the southwestern Scotian Shelf is the immediate upstream source of this low salinity water. Optimally interpolated satellite-derived SST and hydrographic data reveal that very cold (less than 2.0°C), low salinity (less than 32.0 psu) Scotian Shelf Water (SSW), initially located south of the 200-m isobath off southern Georges Bank in early March 1992, moved north onto southern Georges Bank during April 1992. SSW was not as extensive during the same period in 1993, as evidence by significantly higher temperatures and salinities. These differences show large interannual variability in the transport and/or properties of SSW flowing onto Georges Bank. Lower (higher) salinities measured during spring 1992 (1993) on southern Georges Bank are consistent with higher (lower) St Lawrence River discharge noted during spring 1991 (1992) and the ∼ nine month lag between annual discharge maxima from rivers located upstream and minimum salinity at Cape Sable in February. However, comparisons between historical occurrences of low salinity (less than 32.0 psu) SSW on southern Georges Bank noted for May 1966, 1971, and 1978, and cumulative St Lawrence River discharge from the spring prior to each occurrence, show no relationship. This suggests that the occurrence of low salinity water on southern Georges Bank is not directly related to variations in upstream river discharge.Although an idealized model of wind forcing on a bank-trapped density front shows that near-surface flow is related to superposition of an Ekman layer and the along-bank gyral circulation, evidence from late winter-spring 1992 and 1993 on Georges Bank shows that except for on-bank movement of the shelf-slope front during late spring 1992, simple Ekman theory does not explain on-bank movement of the SSW plume during 1992 nor the immobile nature of the shelf-slope front during late winter 1992 and late winter-spring 1993. Surface heat flux and satellite-derived SST from Georges Bank and the Scotian Shelf together with a slab mixed-layer model allows estimation of the advective heat flux and transport of SSW flowing onto Georges Bank from the Scotian Shelf during late winter-spring 1992. Mean advective heat flux onto Georges Bank during March–May 1992 is −14.5 mW cm−2 with an estimated error of ∼3.5 mW cm−2, demonstrating that advection of cold SSW onto Georges Bank is required. Mean velocity and transport of SSW flowing onto Georges Bank during March–May 1992 are 13.4 cm s−1 and 0.21 Sv, assuming a SSW depth (width) of 40 m (40 km), demonstrating that flow of SSW onto Georges Bank was robust during the period. At this time, the dynamics that control the flow of SSW across Northeast Channel are unknown.

Seasonal cycles of temperature, salinity and dissolved oxygen observed in the Hawaii Ocean Time-series

Profiles of temperature, salinity and dissolved oxygen observed during the first 5 years of the Hawaii Ocean Time-series (HOT) were fit with annual and semi-annual harmonics to describe the annual variation of water mass properties in the North Pacific subtropical gyre. The fit was made to data on pressure and density surfaces. Generally, there are three areas in the water column where the fit is best, one near the surface, another near 500 m/26.6 σ φ and a third at about 800 m/27.2 σ φ . For temperature, the fit is best within 120 m of the surface, as the surface layer warms and cools with the local seasonal forcing. Minimum surface temperature is in mid-March, while minimum temperature at 100 m is in mid-May. For salinity, the most significant seasonal cycle is found in the core of the North Pacific Intermediate Water near 500 m. This seasonal cycle is associated with oscillations in the salinity of the main salinity minimum of 50 mpsu, with vertical displacements of the salinity minimum of 40 m. For oxygen, the most significant fits are at the surface and in the Antarctic Intermediate Water oxygen minimum near 800 m, where vertical displacements of the oxygen minimum of 25 m and variations of 2 μM kg −1 were observed. Examination of the residuals left after removing the annual cycle indicates that the remaining variability generally has timescales of less than 6 months with little interannual variability. The exception to this is in the near-surface waters, where larger interannual variability is observed. Residuals show strong vertical coherence as non-seasonal variation tend to extend throughout a large portion of the water column.

Marine mollescan proxy data applied to Scottish late glacial and Flandrian sites: strengths and limitations

Abstract Knowledge of modern benthonic marine molluscs found in shallow water enables their distribution to be correlated with hydrographic conditions and the derived proxy data applied to late Quaternary assemblages. The application of such data for bottom temperature, minimum sea surface temperature and minimum salinity to four Flandrian and Late glacial sites shows that it is possible to follow changes in these parameters with time, in some cases in considerable detail. The chief limitations are that faunas from some boreholes and sections are sparse and of low diversity and that few taxa are restricted to narrow ranges of temperature and/or salinity. Where fossils of stenothermal and stenohaline species are absent from a profile, faunal analysis inevitably yields a less than precise picture of conditions. It is possible to give only generalized constraints on water depth because this is not a prime factor controlling the distribution of molluscs on the seafloor today. The palaeoenvironmental analysis of the four sites is briefly discussed in a wider context.

The distribution of intermediate water in the western equatorial Pacific during January–February 1986

The distribution of intermediate water in the western equatorial Pacific (WEP) for the two month period January–February, 1986, is examined with hydrographic data collected by researchers on six different ships from five different countries. The WEP contains intermediate waters derived from the poleward reaches of both the North and South Pacific, and the mixing of these waters creates a complex and interleaving pattern of fronts. Antarctic Intermediate Water (AAIW) enters the WEP via the Vitiaz Strait in the New Guinea Coastal Undercurrent with a characteristic salinity minimum of about 34.55 at a density of approximately 27.2 σ φ). The salinity minimum is seen as far north as 10°N; however, distributions of oxygen indicate that newer AAI W from the South Pacific spreads only as far as 2°S to the east of 143°E and possibly further north to the west of 143°E. North Pacific Intermediate Water (NPIW) has a salinity minimum of less than 34.5. It enters the WEP via the Mindanao Current at 26.5–26.6 σ φ and spreads eastward in the North Equatorial Countercurrent (NECC) as a thin filament at about 2–3.5°N. This filament is visible as far east as 150°E. An intermediate water mass named North Pacific Tropical Intermediate Water (NPTI W) is found between two fronts at approximately 4.5 and 10°N between 26 and 27 σ φ. NPTIW is associated with a core salinity maximum and oxygen minimum at 26.8 ay and may be part of a “shadow zone”, an area of weak flow isolated from surface forcing. A companion to NPTIW. South Pacific Tropical Intermediate Water (SPTIW), spreads into the western equatorial Pacific in the Equatorial Intermediate Current along the Equator centred at 27.1 σ φ. It is identified by a lateral oxygen minimum between 2°N and 2°S as far west as 143°E.

Paleo sea surface salinities in the low‐latitude Atlantic: The δ18O record of Globigerinoides ruber (white)

On the basis of the comparison of δ18O values of Globigerinoides ruber (white) (δ18OG. ruber) from modern sediments and measured sea surface temperatures (SST) and salinity (SSS), δ18OG. ruber values most clearly record summer SST and SSS of the uppermost 50 m of water in the low‐latitude Atlantic. A new transfer equation is presented for estimating local summer paleo SSS at 0–50 m depth using δ18OG. ruber, paleo SST, and the global δ18O ice effect of sea water, with the standard error reaching ±0.72 ‐ ±0.77‰ SSS. The equation was applied to a 35 kyr long δ18OG. ruber record and paleo SST estimates based on planktonic foraminiferal assemblages to reconstruct the paleo SSS changes along the east Atlantic margin off the northwest Sahara. The resulting local SSS show a general increase by 0.3–1.4‰ during the last glacial maximum (LGM) and large parts of glacial Termination I, suggesting a general increase in the upwelling of the highly saline North Atlantic Central Water and/or a reduced lateral advection of less saline Canary Current water. Two short salinity lows (up to 0.35‰ less than today) during and after the LGM are coeval with the Heinrich meltwater events 1 and 2 in the North Atlantic, indicating the breakdown of coastal upwelling and meltwater advection from the north. Both events are followed by an extreme SSS maximum (38.15‰) along with the restoration of the salinity conveyor belt. At 9.0–5.5 ka the salinity minimum (up to 0.65‰ less than today) reflects the continental runoff linked to the phase of strong North Saharan humidity during the early Holocene climatic optimum.

North Pacific Intermediate Water in the Kuroshio/Oyashio Mixed Water Region

Abstract The North Pacific Intermediate Water (NPIW) originates as a vertical salinity minimum in the mixed water region (MWR) between the Kuroshio and Oyashio, just east of Japan. Salinity minima in this region are examined and related to the water man structures, dynamical features, and winter mixed layer density of waters of Oyashio origin. Stations in the MWR are divided into five regimes, of which three represent source waters (from the Kuroshio, Oyashio, and Tsugaru Current) and two are mixed waters formed from these three inputs. Examination of NPIW at stations just east of the MWR indicates that the mixed waters in the MWR are the origin of the newest NPIW. Multiple salinity minima with much finestructure are seen throughout the MWR in spring 1989, with the most fragmented occurring around the large warm core ring centered at 37°N, 144°E, suggesting that this is a dominant site for salinity minimum formation. The density of the NPIW in the MWR is slightly higher than the apparent late winter surfa...

Exchange of water masses between the East China Sea and the Kuroshio off northeastern Taiwan

At least six water masses take part in the mixing processes between the East China Sea and the Kuroshio off northeastern Taiwan: the Kuroshio Surface Water (SW), Kuroshio Tropical Water (TW), Kuroshio Intermediate Water (IW), East China Sea Water (ECSW), Coastal Water (CW) and the Taiwan Strait Water (TSW). SW is depleted in nutrients and normalized alkalinity but has the highest temperature and pH of all these waters. TW has relatively high temperature, and the highest salinity of all waters. The salinity maximum in the Kuroshio is usually between 100 and 300 m deep, with large interannual and seasonal variability. IW is characterized by a salinity minimum, high nutrient content and alkalinity, but low pH and oxygen. ECSW is low in salinity, temperature and nutrients, but high in oxygen and normalized calcium and alkalinity. CW has low salinity and nutrient content but is high in normalized alkalinity. TSW is generally depleted in nutrients. The characteristics of the above mentioned waters are discussed. The mixing percentages of SW, TW, IW, and the composite Shelf Surface Water (composed of ECSW, CW and TSW) off the northeast corner of Taiwan in September 1988 and December 1989 are calculated.

Reactive silicate in shelf waters near Otago Peninsula, New Zealand

Reactive Si data from 19 monthly occupations of two transects near Otago Peninsula in 1986-87 showed low surface values (≤1 μM) during spring and summer, and high values (>4 μM) in winter. Concentrations were greatest after flooding in the Clutha River, 100 km south of the study area. In spring and early summer, concentrations were lowest inshore at the surface. At other times of the year, concentrations were highest in inshore surface waters, and usually coincided with the salinity minimum. Vertical gradients across the Southland Front, a near-horizontal thermal front outcropping near the shelf break, were calculated and compared with phosphorus gradients from the same samples. Nine of 21 Si gradients were negative (i.e. concentrations decreased with depth), whereas only 1 of 24 phosphorus gradients was negative. This implies that riverine Si flux is important in establishing Si gradients across the Southland Front. The results are a further indication of the importance of the Clutha River to the Otago shelf system.

Variability of water properties in late spring in the northern Great South Channel

Regional CTDIADCP surveys made in the northern Great South Channel (GSC) in late spring of 1988 and 1989 show different patterns of surface salinity in the extent of the freshwater plume east of Cape Cod. In April 1988, the surface plume was just beginning to form along the outer coast of Cape Cod, while 6 weeks later in the season in 1989, the minimum salinity was about 1.5 less, and a large pool of water fresher than 31.6 had pushed eastward over much of the northern GSC region. The difference in the amount of freshening between these two years is due primarily to the 6-week difference in the seasonal cycle and increased river discharge in 1989. The offshore spreading of the low-salinity plume was driven by the deeper circulation and upwelling-favorable winds. The distribution of Maine Intermediate Water (MIW) also significantly differed between April 1988 and June 1989. In April 1988, the seasonal thermocline was just beginning to form, and the spatial structure of MIW was relatively uniform. In June 1989, a narrow core of temperature minimum water (with T min in a range of 3.2–4.4°C) was found along the western flank of the northern GSC between 40 m and 120 m. This colder and fresher water spread to mix with the interior MIW as the core flowed southward into the central GSC. Hydrographic data plus satellite sea-surface temperature images showed a relatively permanent continuous thermal front (with a 10-km cross-isobath variation) along the eastern flank of Nantucket Shoals, across the northern shallow region of the GSC and along the northwestern flank of Georges Bank, which separated the well-mixed water over the shallow region of the GSC from stratified water in the center of the northern GSC. Comparison of the location of this front with theoretical predictions by LODER and GREENBERG [(1986) Continental Shelf Research, 6, 397–414] suggests that enhanced tidal mixing due to the spring-neap cycle is important in determining the relative balance between buoyancy import and tidal mixing in the GSC region.

On the southerly extent of the Antarctic Circumpolar Current in the southeast Pacific

A front at 67°S in the Bellingshausen Sea at 85°W is shown to be part of the Antarctic Circumpolar Current (ACC) and the southernmost zone of concentrated eastward transport at that longitude. The front lies 6° south of the Polar Front at 88°W and 3° north of the Continental Water Boundary. The front is continuous to the east through Drake Passage where it forms a southern branch of the Polar Front, for which reason we have named it the Southern Polar Front. Data from a towed profiling CTD were able to distinguish the Polar Front from the Southern Polar Front, even though they were only 0.5° apart. Thus the width of the ACC south of the Polar Front varied considerably. About a third of the transport of the ACC also lay south of the Polar Front, with 15 Sv carried by the Southern Polar Front alone at 85°W. Distinguishing features of the Southern Polar Front were a water mass boundary associated with a zone of concentrated baroclinic flow and a surface salinity minimum. These features also have been found at the Greenwich Meridian at 53°S, so the Southern Polar Front can be traced round at least a quarter of the globe. To the west of the Bellingshausen Sea both Eltanin data and the Fine Resolution Antarctic Model show that the AAC is at its narrowest at 145°W, where its southern boundaries lie as far north as 56°S. At this longitude the ACC meets the topographic barrier of the Pacific-Antarctic Ridge. To conserve potential vorticity the current is forced to make a southward loop as it crosses the ridge and the current broadens dramatically. The flow remains broad until forced to sharpen by the constriction of Drake Passage. A similar broadening of the ACC is seen where it crosses the Southwest Indian Ridge south of Africa at 30°E. Here it remains broad until it encounters the Kerguelen Plateau. Thus the eastern boundaries of both the Weddell and Ross Gyres are determined by where the ACC crosses midocean ridges.

Thermocline of the Flores and Banda seas

In December 1991, 30 conductivity‐temperature‐depth (CTD) stations to 1000 dbar were obtained from the R/V Baruna Jaya I in the Flores Sea, Banda Sea, and Alor‐Wetar passage of the Indonesian sea. A salinity maximum within the interval 100–150 dbar and a salinity minimum within the interval 300–350 dbar mark water mass core layers derived from the North Pacific. They are drawn into the Flores Sea from the Makassar Strait, with subsequent flow into the Banda Sea, and are weakened en route by strong vertical mixing characteristic of the Indonesian seas. In the Flores Sea, water below 300 dbar becomes saltier with increased distance from the Makassar Strait, suggesting that an advective process may be drawing relatively salty water into the Flores Sea lower thermocline from the Banda Sea. The Banda‐to‐Flores Sea flow may be a consequence of vertical transfer of horizontal momentum produced by the same turbulent processes that are responsible for enhanced vertical mixing. The interocean transport profile may not correspond exactly with the Pacific‐to‐Indian Ocean pressure gradient profile, as deeper water is carried along with the through flow by the effects of eddy viscosity. The 550‐m sill at the southern end of the Makassar Strait creates a situation where downward flux of momentum entrains deeper water that must be compensated by lower thermocline water drawn from the Banda Sea. Geostrophic transport relative to 1000 dbar in the Banda Sea shows not only a strong through flow transport in the upper 300 dbar (6.3×106 m3 s−1) but also a deeper flow toward the Flores Sea (1.5×106 m3 s−1 from 300 to 500 dbar and an additional 2.4×106 m3 s−1 from 500 to 1000 dbar). A simple model suggests that the magnitude of the deeper westward flow is proportional to the vertical eddy viscosity coefficient. Water mass analysis shows that either the South Pacific or Indian Ocean can provide the lower thermocline Banda Sea water.

Diagnosing Climate Change and Ocean Ventilation Using Hydrographic Data

Changes in atmospheric forcing can affect the subsurface water column of the ocean by three different mechanisms. First, warmed mixed-layer water that is subducted into the ocean interior will cause subsurface warming; second, the subducted surface water can be freshened through changes in evaporation and precipitation; and third, the properties at a given depth may be changed by the vertical displacement of isotherms and isohalines without changes of water masses. These vertical displacements of the water column can be caused either by changes in the rates of renewal of water masses or by dynamical changes (such as changes in wind stress). A method for analysing the subsurface temporal changes in hydrographic data is described in terms of these three processes: “pure warming,” “pure freshening,” and “pure heave.” Linear relations are derived for the relative strength of each process in terms of the observed changes of potential temperature and salinity in two different coordinate frames: (i) constant density surfaces, and (ii) isobaric surfaces. Inverse methods are applied to three realizations of the SCORPIO section at 43°S in the Tasman Sea. These sections were obtained in 1967, and in the austral winter and summer of 1989 and 1990, respectively. This data is used to explore the relative strengths of surface warming, surface freshening, and heave of the water column. The six-month differences for this region show small changes in Sub-Antarctic mode water (SAMW) and are not characterized by any one process, whereas below the mode waters the observed differences are well described by the heave process. In contrast, the 23-year differences show significant changes in the properties of the water that flows into the Tasman Sea: SAMW (300-700 db) is well described by pure warming of near- surface waters, while the changes observed at the depth of the salinity minimum are consistent with pure freshening. The observed changes in the interior of the ocean between adjacent seasons do not exhibit significant changes of water masses, consistent with the distance of this section from the outcrop region of the density surfaces of interest. For the 23-year differences, changed surface waters subducted into the ocean interior have sufficient time to influence the temperature-salinity correlations. The skill of our approach in discriminating between short-term changes (almost exclusively heave) and long-term changes associated with the subduction of changed surface waters is particularly encouraging. Although the observed changes could equally well be natural variability, they are qualitatively consistent with coupled numerical models of climate change in which surface waters are warmed and increased precipitation occurs south of the Sub-Antarctic Front.

Thermohaline structure and geostrophic flow in the gulf of California, during 1992

Hydrographic data from two cruises, taken in February and August 1992, were used to describe the vertical thermohaline structure, the presence of water masses in the region of the mouth and central part of the Gulf of California, and meridional and zonal flows, respectively. The observations presented here show a marked thermal change between both seasons, with surface temperatures of about 19.00ºC in February and 32.00ºC in August. Thermal maxima (32.75ºC) and salinity minima (33.00) define a significant presence of Tropical water in the interior of the gulf in 1992, which suggests the occurrence of the El Niño phenomenon. This condition increased the intensity of the geostrophic flow and, in the central part of the gulf, velocities of 95 cm s–1 were recorded in February and of ll5 cm s–1 in August.

Species Assemblages in Saltmarsh Ponds in Western Iceland in Relation to Environmental Variables

The fauna and flora of 63 saltmarsh ponds in western Iceland were investigated. Forty-five taxa were identified. A DECORANA analysis of presence/absence of species showed salinities to be the chief determinants of species composition. Salinities were highly variable, but minimum salinities appeared to be most critical, although maximum salinities as well as elevation of ponds had additional significant effects. The majority of the species are marine species, most of which are commonly found under fully marine conditions. Minimum salinities experienced can therefore be expected to be particularly critical for such species. Some species were shown to have a distinct modal abundance pattern with the mode at intermediate salinities. Species richness was positively related to salinities. A shift in composition of dominant angiosperms indicating a reduction in salinities had taken place between 1977-78 and 1991. The species composition of the ponds shows similarities to that of estuaries although significant differences can be seen. The species composition also shows similarities to that recorded from saltmarsh ponds in Britain, Netherlands and Germany

Lead and aluminum in Atlantic surface waters (50°N to 50°S) reflecting anthropogenic and natural sources in the Eolian transport

Lead and aluminum were measured with a 40–100 km resolution in surface water on two transects across the Atlantic Ocean, one in May 1990 from Cape Town to the North Sea, the other in November 1990 from the North Sea to the Strait of Magellan. Samples were drawn 14 m below surface at normal speed from a 2‐m‐long snorkel system mounted on the bottom of the ship directly into a clean‐room area. In the tropics, both Pb and Al show maximum concentrations in the Intertropical Convergence Zone (ITCZ) correlated with each other and with minimum salinities, indicating wet deposition as their common source. Even in this area characterized by large inputs of mineral aerosols, the Pb/Al ratio shows that the major source of soluble lead (>95%) is anthropogenic. At higher latitudes, Al is low throughout (10–20 nmol/kg), whereas enhanced Pb values show the anthropogenic inputs off south Africa, northern Argentina and especially western Europe. Very low Pb and especially Al concentrations in the upwelling areas associated with the Canary and Benguela currents show that the enhanced biogenic particle fluxes cause an efficient scavenging of both lithogenic particles known to arrive here by dry deposition, and of the adhering reactive trace metals.

An Arctic source for the great salinity anomaly: A simulation of the Arctic ice‐ocean system for 1955–1975

A fully prognostic Arctic ice‐ocean model is used to study the interannual variability of the sea ice during the period 1955–1975 and to explain the large variability of the ice extent in the Greenland and Iceland seas during the late 1960's. In particular, the model is used to test the conjecture of Aagaard and Carmack (1989) that the Great Salinity Anomaly (GSA) was a consequence of the anomalously large ice export in 1968. The objective here is to explore the high‐latitude ice‐ocean circulation changes due to wind field changes. In the simulations the ice extent in the Greenland Sea increased during the 1960's, reaching a maximum in 1968, as observed, and maxima in ice extent were always preceded by large pulses of ice export through the Fram Strait. The ice export event of 1968 was the largest in the simulation, being about twice as large as the average and corresponding to 1600 km3 of excess fresh water. The simulated upper water column in the Greenland Sea has a salinity minimum in the fall of 1968, followed by very low winter salinities. The simulations suggest that, besides the above average ice export to the Greenland Sea, there was also fresh water export to support the larger than average ice cover. Three low‐salinity anomalies, which are created by the variability in ice production/melt, exited through the Fram Strait in 1963–1965, 1966, and 1967–1969, the later two events being associated with a net freshwater export of about 900 km3.The total simulated freshwater input of 2500 km3 to the Greenland Sea compares well with the estimated total freshwater excess of the GSA of about 2200 km3 as it passed through the Labrador Sea (Dickson et al., 1988). Considering the uncertainties in the model, it is possible that the ice export could account for even larger portion of the freshwater excess. However, the main conclusion is that these model results show the origin of the GSA to be in the Arctic, as suggested by Aagaard and Carmack (1989) and support the view that the Arctic may play an active role in climate change.