Strait Sea Research Articles

A link between Fram Strait sea ice export and atmospheric planetary wave phase

A link is found between the variability of Fram Strait sea ice export and the phase of zonal wave 1 in SLP for the period 1958–1997. Previous studies have found that the link between ice export through Fram Strait and the NAO is inconsistent over time scales longer than the last two decades. Inconsistent and low correlations are also found between Fram Strait ice export and the AO index. The phase of zonal wave 1 explains 60%–70% of the simulated ice export variance after the removal of two anomalous phases in 1966 and 1967. Unlike the NAO and AO links, these high variances are consistent for both the first and second halves of the 40‐year period. This consistency is attributed to the sensitivity of wave‐1 phase to the presence of secondary low pressure systems in the Barents Sea that serve to drive Arctic sea ice southward through Fram Strait.

Prokaryotic plankton biomass and heterotrophic production in western Antarctic waters during the 1995–1996 Austral summer

Abstract We examined prokaryotic biomass (PB) and prokaryotic heterotrophic production (PHP) during spring and summer in three Antarctic areas: Bellingshausen Sea, Bransfield Strait and Gerlache Strait in December 1995 and in January–February 1996. The data gathered allowed comparisons among areas, between seasons, and with the RACER study, carried out 10 years earlier in the same zone (Deep-Sea Res. 38 (1991) 1029). Prokaryotic numbers ranged from 0.67 to 13.3×105 cells ml−1, with a mean of 3.86×105 cells ml−1. In order to obtain accurate estimates of PHP, the effect of temperature on leucine incorporation was studied and conversion factors (CF) were determined empirically. Several experiments were carried out to determine the influence of temperature on leucine incorporation rate. In 5 out of 7 experiments, leucine incorporation increased on increasing temperature from −2 to 4°C, but remained constant at higher temperatures (up to 11°C). In one experiment no response of leucine incorporation rate to temperature was found. CF were determined in filtration-dilution cultures. Parallel cultures from different areas were incubated with different organic matter amendments and at different temperatures. These treatments did not affect the conversion factor except for the incubation at −1.5°C in one experiment. The remaining cultures produced CF that were not significantly different. The average value was 0.81 kgC (mol leucine)−1. The PHP was higher in December (between 25.2 mgC m−2 d−1 in Bransfield Strait and 47.7 mgC m−2 d−1 in Gerlache Strait) than in January (between 8.0 mgC m−2 d−1 in Bransfield Strait and 22.9 mgC m−2 d−1 in Gerlache Strait) in all the areas studied. As a result, doubling times in Bellingshausen Sea and Gerlache Strait increased from 14–17 days in December to 32–75 days in January. In Bransfield Strait doubling times were always around 45 days. In Gerlache Strait this decrease in activity between December and January occurred despite a doubling of the chlorophyll concentration. Prokaryotic abundance was lower than that expected from chlorophyll concentrations and general relationships between chlorophyll and prokaryotic numbers. The prokaryotic plankton was not capable of processing all the organic matter provided by phytoplankton and was, therefore, not limited by resource supply. Lysis due to viruses, on the other hand, was shown to be an important loss factor for prokaryotes (Guixa-Boixereu et al., Deep-Sea Res. II (2002) 827–845). Temperature and predation by viruses might be the two main factors controlling the activity of prokaryotes in these waters.

Numerical study of tidal water mass exchange in an inland sea with archipelago

The tidal water mass exchange in an inland sea with archipelago is numerically studied adopting the control volume based 2-dimensional finite element method to cope with the complex coastline. Yatusiro Sea situated in the south-west of Kyushu, Japan is the model inland sea of our study. Water mass exchange by semi-diurnal (M_2) tidal flow is investigated by the dispersion of Lagrangean particles and by the Eulerean tidal residual flow. Main results are as follows: i) Except the southern part of Ariake Sea and Nagashima Strait, the most part of Lagrangean particles still stay in the areas after 20 periods. ii) The particles in Ariake Sea (Yatusiro Sea) flow into Yatusiro Sea (Ariake Sea) through Yanagi-seto (Misumi-seto). iii) The particles in Hachiman-seto flow into Yatusiro Sea through Oh-seto and Gannojiri-seto. iv) The particles in the south part of Yatusiro Sea flow into Nagashima Strait through Mebuki-seto and Ikara-seto. v) In the Eulerean tidal residual flow, there exists a clock-wise vortex around Shishijima island in Yatusiro Sea.

Numerical simulation of environmental effect on the transport of Japanese sand eel larvae by the seabed sand picking

The Bisan Strait Sea in The Seto Inland Sea becomes one of the main spawning grounds of the sand eel. The sand eel catch lowers over 80% in spite of the decrease of the direct sand bank area by seabed sand picking in this sea area being about 13% in comparison with 1977 ages in 1998. Then, it was made that the effect of the change of water depth by the seabed sand picking on the transportation to growth field of Japanese sand eel larvae was evaluated according to the numerical model to be a purpose for the Japanese sand eel larvae in the time in which self swimming force in the Bisan Strait sea is scarce. As the result, it was indicated that Japanese sand eel larvae transported to the growth field in the Bisan Strait west sea decreased about 17% according to the numerical model.

Estimation of the transports through the Strait of Gibraltar

An acoustic doppler current profiler (ADCP) is used to measure the currents and estimate the transports over the Camarinal Sill at the Strait of Gibraltar. The deepest measurements of the ADCP compare well with an underlying conventional current meter. The exchange interface between the Atlantic and the Mediterranean water is defined as the depth of the maximum vertical shear. The mean depth of the shear interface is 147 m. The time series of the depth of the interface and the currents are used to estimate the transports across the Strait. The resulting values are 0.78 Sv for the Atlantic inflow and −0.67 Sv for the Mediterranean outflow. The time series of the shear interface include fortnightly oscillations of 19 m. The time series of the transports are compared with the pressure and sea level difference records across the Strait. Linear multiple regression is used to estimate the (statistical) contribution of each parameter on the variation of transports. The cross strait sea level difference is well correlated with the Atlantic inflow and accounts for 57% of the variability of the transport records which improves to 78% when the fortnightly and monthly cycles are included in the linear regression. The Mediterranean outflow is best correlated with the along strait sea level difference which accounts for only 10% of the variability of the transport record. Again the addition of the M sf and the MM cycles improves the percentage of the variance accounted for to 37%. The local, along strait wind component is significantly correlated with, both the Atlantic inflow and the across strait sea level difference.

Anomalous transport of walleye pollock larvae linked to ocean and atmospheric patterns in May 1996

Larvae from a large aggregation of walleye pollock spawning in early spring in Shelikof Strait, Gulf of Alaska, are normally transported to the south-west in the vigorous Alaska Coastal Current. In the spring of 1996, anomalous winds resulted in unusually weak transport in the Shelikof Strait sea valley. The main aggregation of larval pollock in the Shelikof region was surveyed four times in 1996 over a period of about 40 days, including finer-scale sampling of the leading south-western edge of the larval distribution. The south-western edge of the larval distribution showed weak transport up the sea valley for a period of about 10 days, corresponding to the observations of currents, after which many larvae were transported over the shelf region to the west. These observations are unique in over 15 years of monitoring larval transport patterns and demonstrate how anomalous weather, and hence current patterns, influence variability in larval transport.

Estimation of the value of life saving under uncertainty emanating from transport infrastructure investment

In this paper a model for estimating the reduction of the probability of premature death emanating from a transport infrastructure investment is developed. As a starting point a reference probability of premature death is arbitrarily chosen and two measures of estimating the value of life saving are constructed based on the willingness to pay for the reduction in the casualty rate. These two measures are derived from the comparison of the probabilities of premature death before and after the reduction in the casualty rate to the corresponding reference probability. It is then shown that the relationship between the first measure and the reference probability premature death is upward sloping and concave and the relationship between the second measure and the reference probability of premature death is upward sloping and convex. Finally, we empirically tested both measures in the case of the Rion-Antirion suspension bridge which will connect the Western part of Greece through the Rion-Antirion sea strait with the region of Patras and consequently with Athens, providing a faster and more efficient service for the passage of the sea strait than the existing obsolete ferry system. The empirical results show that the theoretical propositions with respect to the concavity and convexity of the functions of each measure with the reference probability are verified.

East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea

Based on the study of 10 sediment cores and 40 core-top samples from the South China Sea (SCS) we obtained proxy records of past changes in East Asian monsoon climate on millennial to bidecadal time scales over the last 220,000 years. Climate proxies such as global sea level, estimates of paleotemperature, salinity, and nutrients in surface water, ventilation of deep water, paleowind strength, freshwater lids, fluvial and/or eolian sediment supply, and sediment winnowing on the sea floor were derived from planktonic and benthic stable-isotope records, the distribution of siliciclastic grain sizes, planktonic foraminifera species, and the U K 37 biomarker index. Four cores were AMS- 14C-dated. Two different regimes of monsoon circulation dominated the SCS over the last two glacial cycles, being linked to the minima and maxima of Northern Hemisphere solar insolation. (1) Glacial stages led to a stable estuarine circulation and a strong O 2-minimum layer via a closure of the Borneo sea strait. Strong northeast monsoon and cool surface water occurred during winter, in part fed by an inflow from the north tip of Luzon. In contrast, summer temperatures were as high as during interglacials, hence the seasonality was strong. Low wetness in subtropical South China was opposed to large river input from the emerged Sunda shelf, serving as glacial refuge for tropical forest. (2) Interglacials were marked by a strong inflow of warm water via the Borneo sea strait, intense upwelling southeast of Vietnam and continental wetness in China during summer, weaker northeast monsoon and high sea-surface temperatures during winter, i.e. low seasonality. On top of the long-term variations we found millennial- to centennial-scale cold and dry, warm and humid spells during the Holocene, glacial Terminations I and II, and Stage 3. The spells were coeval with published variations in the Indian monsoon and probably, with the cold Heinrich and warm Dansgaard–Oeschger events recorded in Greenland ice cores, thus suggesting global climatic teleconnections. Holocene oscillations in the runoff from South China centered around periodicities of 775 years, ascribed to subharmonics of the 1500-year cycle in oceanic thermohaline circulation. 102/84-year cycles are tentatively assigned to the Gleissberg period of solar activity. Phase relationships among various monsoon proxies near the onset of Termination IA suggest that summer-monsoon rains and fluvial runoff from South China had already intensified right after the last glacial maximum (LGM) insolation minimum, coeval with the start of Antarctic ice melt, prior to the δ 18O signals of global sea-level rise. Vice versa, the strength of winter-monsoon winds decreased in short centennial steps only 3000–4000 years later, along with the melt of glacial ice sheets in the Northern Hemisphere.

Tomographic inversion of geoacoustic properties in a range-dependent shallow-water environment.

This paper presents a matched-field tomographic method to estimate the geoacoustic properties of the ocean bottom for a range-dependent medium in shallow water. The inversion method has been developed in order to interpret experimental data from the Haro Strait PRIMER sea trial. This experiment was carried out in June '96 and used low-frequency broadband signals that were received on three vertical line arrays. Inversion of the data is particularly difficult because of the complex bathymetry of the Haro Strait experimental site. For this inversion, a range-dependent ray code was developed to solve the forward problem, allowing an arbitrarily layered bottom environment. The inversion scheme is based on modeling the propagation time and the amplitude of the recorded data, and a simple new cost function is proposed. The signal ray paths are identified automatically using a simple process that compares calculated and measured travel times. Data from multiple source positions are used to invert the range dependence of the geoacoustic model. The environment is separated into segments, and within each segment the inversion is carried out layer by layer for a multilayer geoacoustic model. Starting with the topmost layer, the range-dependent thickness and sound speed are estimated via a Monte Carlo method. Inversion results are presented for synthetic and experimental data from the Haro Strait sea trial.

Recent deeper geophysical results better account for the tectonics in the Italian area

Results from extended DSS profiles (1956-1986) in Italy and surrounding land and sea areas offer good constraints for other geophysical and geological data. Integrated interpretations outline the main tectonic features. Collisional tectonics is predominant in the Alps, for which the Adriatic plate acted as hinterland against the European plate foreland. Main results: W-wards, NW- and N-wards oriented overthrusting on the European crust, bending of the lower European crust, European Moho to 70 km depth with the Adriatic mantle indented above, crustal doubling (Adriatic over the European one). In the Apennines, on the contrary, the Adriatic plate acted as a foreland, against the overthrusts generated by the Tuscanian and Tyrrhenian mantellic bodies, heated, elevated and migrated NE-wards and SE-wards, respectively. Also the Adriatic plate bends under this load-centripetally towards the Tyrrhenian sea, so that the Adriatic Moho from 35 km depth is presumed to descend through a flexure till 40-50 km below the Tuscanian and Tyrrhenian land areas. The external peri-Apenninic area is still in compression and includes thick sedimentary basins, from the Po-plain to Sicily. The internal area is in extension, overlapped by thin, stretched crusts of Ligurian and Tyrrhenian origin, whose remnants occupy most of both seas areas, with two areas of oceanic crust in the SE-Tyrrhenian. Rifting and opening is in action also in the Ligurian Sea and Sicily Strait.

Modelling the choice of mode and estimation of the value of travel time savings for the case of the Rion-Antirion suspension bridge in Greece

In this paper we estimate value of time savings specifically applied to the case of the Rion-Antirion suspension bridge which will connect the Western part of Greece through the Rion-Antirion sea strait with the region of Patras and consequently with Athens providing a faster and more efficient service for the passage of the sea strait than the existing obsolete ferry system. Value of time savings are important in determining that the correct level of tolls are based not only on market-oriented values but that they also ensure revenue maximization and user acceptance. Estimation of a multinomial logit model is done for the value of time savings for business and non-business categories of travellers who can only choose between private cars and buses. Our results show that for the case of non-business the value of time is about 60% of the wage rate, for the case of business, it is 85% of the wage rate.

Springtime microprotozoan abundance and biomass in the southeastern Bering Sea and Shelik of Strait, Alaska

We surveyed springtime biomass and abundance of the >20 nm microprotozoa in surface waters of the SE Bering Sea and Shelikof Strait, Alaska. This study was part of the Fisheries Ocean- ography Coordinated Investigations (FOCI) program examining processes which affect the recruit- ment variability of walleye pollock (Theragra chalcogramma). Microprotozoa are a potential prey resource for larval pollock which has not been previously examined. In both areas, the >20 (im micro- protozoa were predominantly dinoflagellates and ciliates. At the time of sampling (May 1990 in Sheli- kof Strait and April 1992 in the SE Bering Sea), the spring diatom bloom was under way in Shelikof Strait, but not in the SE Bering Sea. Heterotrophic dinoflagellates dominated the microprotozoan assemblage in Shelikof Strait, but not in the SE Bering Sea. In the SE Bering Sea. total microprotozoan abundances ranged from 300 to 6233 organisms 1 ' and biomass from 0.58 to 9.73 jig C I1. In Shelikof Strait, abundance and biomass were higher, ranging from 850 to 14 960 organisms 1' and from 1.29 to 70.73 jig C I ', respectively. These biomass levels are comparable to those reported from other coastal and oceanic regions. Microprotozoan biomass levels were sufficient to support the estimated metabolic needs of first-feeding larval walleye pollock. It remains to be shown whether larval pollock use this resource.

Actual flux of the Huanghe (yellow river) sediment to the Western Pacific ocean

More than 90% of the Huanghe sediment load is deposited in the lower reaches of the river and within the shallow estuarine area. Additional sedimentation occurs in the southern part of Bohai so that the actual flux of sediment to the Yellow Sea (Huanghai) is very limited. We show that this flux takes place via a nepheloid layer across the Bohai Sea strait, transporting ∼ 6·10 9 kg·y −1, i.e. less than 1% of the Huanghe sediment discharge.

An Association of Marine Tractive and Gravity Flow Sandy Deposits in the Eocene of the NW Part of the Island of Pag (Outer Dinarides, Croatia)

The Eocene clastics of the NW part of the island of Pag overlie carbonate platform deposits and are dominantly sandy. Besides minor components, they include cross-laminated and cross-bedded sandstones produced by marine tractive flows, mostly directed toward E, and ESE, and dominantly massive sandstones probably deposited by gravity flows. The area was situated close to sand-rich sources and river mouth(s). Possible settings include a delta-related shallow-marine area, and a sea strait. Structural deformation intervened very early in the history of a complex outer dinaric foreland realm and governed its subsequent evolution, in contrast to a simple foreland trough envisaged before.

Geostrophic adjustment in a channel: nonlinear and dispersive effects

We consider the general problem of geostrophic adjustment in a channel in the weakly nonlinear and dispersive (non-hydrostatic) limit. Governing equations of Boussinesq-type are derived, based on the assumption of weak nonlinear, dispersive and rotational effects, both for surface waves on a homogeneous fluid and internal waves in a two-layer system. Numerical solutions of the Boussinesq equations are presented, giving examples of the geostrophic adjustment in a channel for two different kinds of initial disturbances, both with non-zero perturbation potential vorticity. The timescales of rotational separation (that is, the separation of the Kelvin and Poincaré waves due to their dispersive properties) and that of nonlinear evolution are considered, with particular concern for the resonant interactions of nonlinear Kelvin waves and linear Poincaré waves described by Melville, Tomasson & Renouard (1989). A parameter measuring the ratio of the two timescales is used to predict when the free and forced Poincaré waves may be separated in the solution. It also distinguishes the cases in which the linear solutions are valid for the rotational separation from those requiring the full Boussinesq equations. Finally, solutions for the evolution of nonlinear internal waves in a sea strait are presented, and the effects of friction on the wavefront curvature of the nonlinear Kelvin waves are briefly considered.

Winter atmospheric circulation in the Arctic Basin and possible relationships to the great salinity anomaly in the northern North Atlantic

Variations in synoptic activity are assessed in terms of potential influences on ice transport and indicators of shifts in the Arctic atmospheric circulation related to the “Great Salinity Anomaly” of the northern North Atlantic. Winter pressure anomalies suggest an increased contribution to the Fram Strait sea ice flux by multiyear ice from along the northern coasts of Greenland and Ellesmere Island. This may be related to a teleconnection involving changes in anticyclonicity over the central Arctic Ocean and Canadian Arctic Archipelago.

Lagrangian tidal stress and basin-wide residual eddy dynamics in wide coastal sea straits

Abstract The tidal stress formulation is used to investigate the dynamics generating and governing tidally induced meso-scale recirculations in wide coastal sea straits for an idealized barotropic tidal wave. Particular attention is paid to the Lagrangian aspects of the residual dynamics and we present a first-order estimate of the Lagrangian tidal stress field in terms of a quasi-Eulerian field. The strength of the Lagrangian tidal stress may be related in a simple expression to the gradient of the bottom friction strength and the area swept out by the principal tidal current ellipse. We apply the analysis to the rectification processes active over a strongly sloping escarpment within an idealized representation of a wide coastal sea strait. It is demonstrated that the residual circulation for each of the Eulerian, Stokes’and Lagrangian cases is essentially governed by forced quasigeostrophic dynamics with source term being the curl of the relevant tidal stress. When the spatial dimension of the source term approaches the dimension of the basin, coastal boundary conditions become important. Finally, it is shown that the generation of an observed cyclonic basin-wide eddy in eastern Dixon Entrance, British Columbia, Canada is consistent with a tidal rectification process active over the strongly sloping escarpment connecting Dixon Entrance and Hecate Strait. It is concluded that a sufficiently strong rectification process active over a limited sector of the eddy circumference may substantially influence the circulation within adjacent bodies of water where no significant tidal nonlinearities are present.

A variational inverse method for the reconstruction of general circulation fields in the northern Bering Sea

The knowledge of the dynamical structures associated with the general circulation in the Northern Bering Sea and Bering Strait is improving as numerical models together with in situ observing systems become more and more sophisticated. The ultimate objective being the design of a realistic model, it is fundamental to confront the results stemming from numerical simulations with the extensive set of hydrographic data collected since the beginning of the century. A variational inverse model has been developed for the study of continental seas with the aim of reconstructing, on the basis of local measurements (such as CTD profiles carried out at isolated hydrographic stations), continuous fields of the state variables representative of the general circulation. A numerical inverse methodology based on a variational principle and a finite element discretization has been designed to generate dynamically consistent patterns, providing a practical tool for the visualization and the mathematical interpretation of observations. Horizontal distributions of temperature, salinity, nutrients, chlorophyll and other chemical tracers, as well as the horizontal transport of water are reconstructed by using synoptic data collected from the ISHTAR NSF Research Project. Among the three water masses that can be distinguished in the region, the Anadyr Stream is obviously the main source of nutrients for the whole basin. The trace of a permanent upwelling located close to the Siberian coast can be detected on a series of general circulation patterns representative of various tracers. The strong vertical motions resulting from this upwelling allow an intensive primary productivity and determine the particularly fertile conditions for the development of the ecosystem in the Chukchi Sea.

On the behaviour of outflows with low potential vorticity from a sea strait

On the behaviour of outflows with low potential vorticity from a sea strait

On the behavior of outflows with low potential vorticity from a sea strait

Behaviour of outflows from a sea strait contained in a shallow upper layer is investigated by using a simple quasigeostrophic model. The outflow is assumed to have two piecewise-uniform potential vorticities and the higher one to be the same value as that in the open ocean. It is shown that this simple model can reproduce both the gyre mode and the coastal mode similar to those observed near the Tsugaru Strait, which connects the Sea of Japan with the North Pacific, and in laboratory experiments. In addition to these two modes, a coastal mode in which the current at the downstream temporally widens can also occur in the present model. The existence of these three modes can be attributed to the limited capacity of the downstream coastal current to advect the low potential vorticity fluid and the characteristics of frontal waves. The responses of the flow pattern to the changes in the outflow conditions are also briefly examined. DOI: 10.1034/j.1600-0870.1991.t01-1-00007.x