Simulation studies of the response of deeply towed vehicle to various towing ship maneuvers

The behavior of a long cable towed at slow speeds through the ocean depends in a complex fashion on the path followed by the towing ship relative to the water. A cable simulation program was used to characterize the response of the cable by using idealized towing ship maneuvers as input to the program. The response of the cable was noted and it was found that the behavior of the cable was strongly dependent on the fundamental period of the towing vessel maneuvers. Sinusoidal deviations of the towing ship from a straight towing track resulted in delayed and reduced excursions of the towed vehicle from the tract; the estimated response ratio varied from 0·002 to 0·800, depending both on the period of the deviations (periods ranged from 5·5 to 4·0 hr) and on the towing depth (2 or 6 km). The ship's speed was 3 km/hr. The time lag between ship motion and vehicle response was approximately 0·5 hr for the shallow case and 1·3 hr for the deep case. Simulations runs of a low dragk (faired) cable showed that the behavior of the vehicle when towed at a depth of 6 km was similar to that obtained with a conventional cable at 2 km depth. The response of the towed vehicle to a right-angle turn of the towing ship was investigated and a generalized model of the response developed. The effects of a controllable side force on the towed vehicle were also simulated and it was noted that a deviation (2-hr period) of the towed vehicle from a straight-line track could be reduced from 40 to 2 m by impressing a side force on the vehicle with an average magnitude of 150 newtons (30 lb).     

Hydrographic profiling across the East China sea shelf edge by an underwater sliding vehicle with CTD sensors

Temperature, salinity and density structures were observed on Sept. 23 and 24, 1986 at one vertical section across the East China Sea shelf edge by an advanced type of towed vehicle with CTD sensors which was developed by the Japan Marine Science and Technology Center. The vehicle was towed at a speed of 2.5 m s⁻¹ down to 150 m depth and at intervals of 170–500 m width. The observed profile was 50 km long on Sept. 23 and 70 km long on Sept. 24 along the cross-shelf section. An on-ship acoustic Doppler current profiler was simultaneously used to measure current velocities at depths of 20, 50 and 100 m.Interesting features were noticed. Firstly, there was a vertical displacement of pycnoclines at the lower edge of the surface mixed layer accompanied by vertical inversion of the salinity and temperature in the vicinity of the shelf edge. Pycnoclines were displaced upward by 12 m toward the outer edge on Sept. 23 and by 20 m on Sept. 24. On Sept. 23, the salinity inversion took place in a layer 20 m thick and 8 km wide, whereas the temperature inversion took place in a layer 8 m thick and 1.5 km wide. These vertical inversions were probably generated by vertical shear of tidal currents which was observed by the Doppler current profiler. These results throw light on understanding the vertical mixing process of stratified water on the continental shelf edge. Secondly, an intrusion of the shelf water into the Kuroshio water was observed along pycnoclines below the surface mixed layer 60 to 70 m deep in the Kuroshio region outer break. The measurement was successful in showing a horizontal mixing process of the shelf water and the Kuroshio water which could not be found out by standard CTD observations.     

The optimum dimensions for a long-range, autonomous, deep-diving, underwater vehicle for oceanographic research

From the results of a parameter optimization process based on a “minimum feasible volume” criterion, it is shown that the optimum shape for a transatlantic, deep-diving, autonomous submersible is a “low drag” hull shape with a displaced volume of 4.4 m³, a length of 5.97 m and a maximum diameter of 1.33 m. Calculations show that a vehicle of these dimensions, travelling in a minimum drag “cruise” configuration at a depth of 3000 m, say, and at a velocity of 2.5 m/sec could have a maximum range of 7000 km provided the “hotel” power consumption is kept low.     

Hydrothermal plumes in the eastern Manus Basin, Bismarck Sea: CH4, Mn, Al and pH anomalies

We present evidence for strong hydrothermal activity in the eastern Manus Basin (depth: 1700–2100 m), the existence of large scale triple-layered buoyant plumes at depths of 1100 m (“shallow plume”), 1700 m (“deep plume”), and 1400 m (“middle plume” with less extent than the other two plumes) that were revealed from water column anomalies of CH₄, Mn, Al and pH observed in November to December 1990. Judging from the horizontal distribution of these parameters, the deep plume seems to originate from two distinct hydrothermal sites (eastern and western sites) in the research area, the eastern site being visually ascertained with deep-tow observations at the same time. The CH₄/Mn ratio (mol mol⁻¹) of the deep plume (0.02–0.05) is the lowest yet observed in hydrothermal plumes. The order of magnitude difference of CH₄/Mn ratios between the shallow plume and the deep plume suggests that different kinds of fluid-rock interaction occurred to make the hydrothermal end members for the deep and shallow plumes. The shallow plume, which had an areal extent of more than 50 km, may be an episodic “megaplume”, because it was not recognized in the previous CH₄ profiles in 1986, and because it has a similar CH₄/Mn ratio as the megaplume observed in the North Fiji Basin. We found that the eastern deep plume is characterized by enormously high aluminium concentrations (0.6– 1.5 μmol kg⁻¹), pH anomalies (0.1) and high Al/Mn ratios (10–17). The endmember fluid for the eastern deep plume may have an unusually low pH value to dissolve this much aluminum during fluid-rock interaction, or this plume may originate from an eruption-influenced fluid.     

An improved “benchmark” method for estimating particle settling velocities from time-series sediment trap fluxes

A new method, based on fitting Fourier series to time-series (TS) data from sediment traps, was developed to estimate the settling velocities (SVs) of sinking particles in the open ocean. This new method was applied to data from MedFlux, as well as from the US JGOFS NABE, EqPac, and ASPS studies. Fluxes of mass and of four chemical tracers, as well as the molar ratios of the latter, were plotted on logarithmic scales; Fourier series were then fit to these data. In each case we determined the most likely settling velocity using a likelihood-based nonlinear fitting algorithm. Variation among estimates using single tracers was significantly less than variation using tracer ratios; we therefore concluded that estimates based on single tracers are to be preferred to estimates based on tracer ratios. Our results also showed no obvious differences among SVs estimated using different single tracers. The best estimate of settling velocity using single-tracer fluxes with good temporal resolution (i.e. for sites with cup rotation times 8.5 days) is 205 m/d, with standard deviation 74 m/d. For MedFlux data alone (which have a resolution of 4–6 days), the estimate is 220±65 m/d. This latter value is within 10% of the estimate of average settling velocity (242±31 m/d) made using MedFlux IRS traps in “settling velocity” mode.     

A deep towed explosive source for seismic experiments on the ocean floor

A new seismic source for carrying out high resolution measurements of deep ocean crustal structure has been constructed and successfully used in a number of ocean bottom refraction experiments on the Mid Atlantic Ridge near 23° N. The source is towed within 100 m of the ocean floor on a conventional 0.68 coaxial cable and is capable of firing, upon command from the research vessel, up to 48 individual 2.3 kg explosive charges. The explosive used was commercially available Penta-Erythritol-Tetra Nitrate (PETN) that was activated by 14.9 gm m^–1 Primacord and DuPont E-97 electrical detonators. For safety reasons each detonator was fitted with a pressure switch that maintained a short until the source was at depth in excess of approximately 300 m. In addition, a mechanical protector isolated the detonator from the main charge and was only removed by the physical release of the explosive from the source package. These and other safety precautions resulted in several misfires but three experiments were successfully completed during the summer of 1985 at source depths of 3000–4000 m.     

Depositional environments of the Mediterranean “Lower Evaporites” of the Messinian salinity crisis: Constraints from quantitative analyses

We use simple quantitative analyses to evaluate controversial water level scenarios for the Mediterranean “Lower Evaporites” of the Messinian salinity crisis. Our results indicate that a shallow-water scenario for the Lower Gypsum units – with Mediterranean water level lower than the sill at Gibraltar – would imply unrealistic salt thicknesses on the order of 3 km. Some outflow to the open ocean must have persisted, implying that the Mediterranean was a deep-water basin during Lower Gypsum formation. Since glacio-eustatic fluctuations do not seem to have had a major influence on Lower Gypsum deposits, Mediterranean water level was even substantially higher than the Gibraltar sill. Our analyses furthermore show that precessional changes in the freshwater budget may explain the observed cyclic lithological changes of gypsum and non-evaporitic sediments. Potential precipitation of gypsum in the deep Mediterranean basins would have critically depended on the availability of oxygen and thus on the stratification of the water column. Finally, our results indicate that the deep Mediterranean halite units could have been deposited under shallow conditions, assuming that they correspond to the ~ 70 kyr time interval between glacials TG12 and TG14, when Mediterranean outflow to the Atlantic was blocked.     

Recent developments in “added-mass” planing theory

The results of several recent isolated investigations in planing theory are consolidated in this paper, together with new insights generated by a recent numerical solution of the vertically impacting wedge problem by Zhao and Faltinsen [(1992), Water entry of two-dimensional bodies. J. Fluid Mech. 246, 593–612]. As a result, in contrast to some earlier studies, it is found that the “wetted width” associated with the added mass is not that of the intersection of the wedge with the undisturbed water surface, but the wetted width of the splashed-up water, as originally proposed by Wagner [(1932), Uber Stoss-und Gleitvorgange an der Oberflache von Flussig-Keiten, Zeitschrift für Angewandte Mathematik und Mechanik, Band 12, Heft 4 (August)]. However, the splash-up ratio is not the value of (π/2–1) which he proposed, but a value which decreases with increasing deadrise, originally proposed in the late-1940s by Pierson (“Pierson's hypothesis” in the paper). For 30° deadrise, for example, Pierson's splash-up ratio is two-thirds that of Wagner's.The new equations are employed to determine the increase in the “added mass” of prismatic hull sections due to chine immersion, using experimental data. If m_o^′ is the added amss of the hull section whose chines are just wetted, Payne [(1988), Design of High-speed Boats. Volume 1: Planing. Fishergate, Inc., Annapolis, Maryland, U.S.A.] postulated that the increase in added mass due to a chine submergence (z_c) would be

where b is the chine beam and k is a constant which Payne [(1988), Design of High-speed Boats. Volume 1: Planing. Fishergate, Inc., Annapolis, Maryland, U.S.A.] gave as .The present analysis includes the “one-sided flow” correction introduced in Payne [(1990), Planing and impacting forces at large trim angels. Ocean Engng 17, 201–234]. Partly for that reason and partly because of the more precise analysis of the experimental data, the present paper revises the value to k = 2 for wetted length to beam ratios normally employed. For deadrise angles in excess of 40° and wetted keel to beam ratios in excess of 2.0, there is some evidence that k < 2.0.The revised theoretical formulation is compared with eight different sets of experimental data for flat plate and prismatic hull forms and is found to be in excellent agreement when the speed is high enough for “dynamic suction” (a loss of buoyancy at low speeds and low wetted lenghts) to be unimportant. This is true for “chines-dry” operation with deadrise angles up to 50° and chines-wet operation at length to beam ratios far in excess of the most extreme conventional practice.The research involved in performing this analysis led to the realization that different towing tanks measure different wetted chine lengths for the same hulls and test conditions. Some consistently measure more splash-up than “theory” (based on Pierson's splash-up hypothesis) predicts and others measure somewhat less than the theory. Some examples are given in Appendix B. The reason for this is not understood.     

High concentrations of marine snow and diatom algal mats in the North Pacific Subtropical Gyre: Implications for carbon and nitrogen cycles in the oligotrophic ocean

A video plankton recorder (VPR) and a remotely operated vehicle (ROV) were utilized on three cruises in the oligotrophic North Pacific Subtropical Gyre (NPSG) between 1995 and 2002 to quantify the size and abundance of marine snow and Rhizosolenia diatom mats within the upper 305 m of the water column. Quantitative image analysis of video collected by the VPR and an ROV-mounted particle imaging system provides the first transect of marine snow size and abundance across the central North Pacific Gyre extending from 920 km NW of Oahu to 555 km off Southern California. Snow abundance in the upper 55 m was surprisingly high for this oligotrophic region, with peak values of 6.0–13.0×10³ aggregates m⁻³ at the western- and easternmost stations. At stations located in the middle of the transect (farthest from HI and CA), upper water column snow abundance displayed values of 0.5–1.0×10³ aggregates m⁻³. VPR and ROV imagery also provided in situ documentation of the presence of nitrogen-transporting, vertically migrating Rhizosolenia mats from the surface to >300 m with mat abundances ranging from 0 to 10 mats m⁻³. There was clear evidence that Rhizosolenia mats commonly reach sub-nutricline depths. The mats were noted to be a common feature in the North Pacific Gyre, with the lower salinity edge of the California Current appearing to be the easternmost extent of their oceanic distribution. Based on ROV observations at depth, flux by large (1.5 cm) mats is revised upward 4.5-fold, yielding an average value of 40 μmol N m⁻² d⁻¹, a value equaling previous estimates that included much smaller mats visible only to towed optical systems. Our results suggest that the occurrence across a broad region of the NPSG of particulate organic matter production events represented by high concentrations of Rhizosolenia mats, associated mesozooplankton, and abundant detrital marine aggregates may represent significant stochastic components in the overall carbon, nitrogen, and silica budgets of the oligotrophic subtropical gyre. Likewise, their presence has important implications for the proposed climate-driven, ecosystem reorganization or domain shift occurring in the NPSG.     

Origin of “paired” aseismic rises: Ceará and Sierra Leone rises in the equatorial, and the Rio Grande Rise and Walvis Ridge in the South Atlantic

In the equatorial Atlantic the Ceará and Sierra Leone rises lie on opposing sides of the mid-ocean ridge and are equidistant from its axis. The northern and southern boundaries respectively, of the two rises are formed by the same fracture zones. The area of shallowest acoustic basement under the Ceará Rise coincides with the presence of a 1–2 km thick seismic layer (velocity: 3.5 km/sec) lying over the oceanic layer 2. This 3.5 km/sec layer is interpreted as a sequence of volcanics which began erupting about 80 m.y. ago when the sites of the two rises lay at the ridge axis. As the “abnormal” volcanic activity ceased, the breakup of this volcanic pile into two pieces has formed the Ceará and Sierra Leone rises.

In the South Atlantic, the northern and southern boundaries of the Rio Grande Rise are also formed by fracture zones and an approximately 1 km thick layer with a velocity of 3.5 km/sec exists also under this rise. The same fracture zones appear to bound the Walvis Ridge. Drilling data suggests that both the Rio Grande Rise and Walvis Ridge have subsided continuously since their creation. The igneous rocks recovered from both rises consist of alkalic basaltic suites typical of oceanic volcanic islands. The existing data favor a model in which “excessive” volcanism along the same segment of the Mid-Atlantic Ridge created both the South Atlantic aseismic rises between 100 and 80 m.y. ago. In both the examples, the northern and southern boundaries of the rises are formed by the same fracture zones which originally bounded the abnormally active segment of the ridge axis.     

Overrunning of shelf water in the southern Mid-Atlantic Bight

Analyses of two years (1992 and 1993) of high-resolution sea surface temperature satellite images of the southern Mid Atlantic Bight (MAB), showed that unusually extensive overhang of shelf water occurs episodically, and coherently over along shelf distances of several 100 km. These episodes are dubbed overrunning of the Slope Sea by shelf water. The overrunning volume has a “face” and a “back” (southern and northern limit). It transports substantial quantities of shelf water southward, and does not retreat onto the shelf, but eventually joins the western edge of the Gulf Stream in the vicinity of Chesapeake Bay. The combined analyses of satellite imagery and various in situ data further demonstrated that the shelf waters overrunning the Slope Sea were not mere surface features but reached depths between 40 and 60 m. Results confirm previous concepts on shelf circulation, shelf–slope exchange and fate of shelf water. They also shed new light on shelf water budget: overrunning of the Slope Sea and southwest transport by upper slope current constitutes an important conduit for shelf water transport. Winter storms move the shelf–slope front, and with it shelf water, offshore to distances 10–40 km. The offshore displacement of shelf water can be related to the onshore veering of the Gulf Stream near Cape Hatteras, producing a blocking effect on the shelf circulation. Such a blocking effect of the southwestward flow of shelf water in the MAB appeared to be the reason for the overrunning of shelf water off New Jersey. In addition, the excess fresh water discharge from the St. Lawerence was also observed to be related to the overflow of shelf water off New Jersey.     

Thermal structures in the Kuroshio extension measured with a towed thermistor chain

Two-dimensional temperature data observed by use of a 275 meter towed thermistor chain deployed from an oceanographic research vessel USS MARYSVILLE, which cruised with a speed of 6.2 knots in July 1966 across the Kuroshio Extension in the North Pacific, are investigated. Two-dimensional variations of the distribution of the isotherms along the ship's track are analyzed with special reference to their slope, wavelength and wave height. The results show that the slope and wave height of isotherms have a tendency to increase as the temperature decreases. Even if the contribution of wave heights smaller than 1.5 m is neglected, i.e., contribution of large scale slope with a horizontal scale of 5–30 km is subtracted, this tendency is still detected. In contrast to this, the wavelength evaluated by the crest to crest method has no dependency on the temperature. Power spectrum of the isotherm depth is proportional tok ^–1.87 for 13°C andk ^–2.13 for 27°C, wherek is the wave number. It is shown that the spectra of warmer isotherms are relatively well approximated by –2 power law (Garrett and Munk spectrum) for internal waves rather than the –5/3 power law (Kolmogorov spectrum) for three dimensional isotropic turbulence.     

Magnetic basement in the central Bay of Bengal

Analyses of about 6000 km of processed magnetic data in the central Bay of Bengal using Analytical Signal Processing and Werner Deconvolution techniques revealed that the depth to top of the magnetic basement varies between 5 and 12 km from the sea surface, where the water column thickness is about 3.4 km. These inferred depths are comparable to the reported acoustic basement depths. The basement map derived from magnetic interpretation defines the general configuration of the central Bay of Bengal. The N10–12° W trending subsurface 85° E Ridge buried under 2 to 3 km thick sediments is a prominent tectonic feature. Offshore basins characterised by deeper magnetic basement (9 km) and 100–200 km wide are present on either sides of the ridge. These basins were filled with 6–8 km thick lower Cretaceous to recent sediments. Integrated geophysical study depicts that the magnetic basement is characterised by NW-SE, NE-SW, NNE-SSW, N10-12° W and E-W trending structural features that are associated with the lower Cretaceous ocean floor. The Analytical Signal Processing and Werner Deconvolution techniques proved to be effective in determining the depth to the basement in areas covered by thick sediment overburden and characterized by a complex geologic/tectonic framework.     

Heated diver decompression shelter: The “womb concept”

A hybrid thermal protection method using waste heat from a surface-mounted outboard motor is shown to create a warm “micro-climate” environment for divers. The effects of surface heater capacities, water flow rates, shelter volume and shelter insulation on micro-climate temperatures are characterized. During long, cold-water decompression stops this method offers a reliable, low-cost alternative to surface-supplied hot water suits or diver-carried heating systems. An added bonus for divers using closed-circuit breathing apparatus is prolonged durations of their carbon dioxide scrubbers when surrounded by the warm water “micro-climate”. Closed-circuit and open-circuit options of this diver decompression shelter concept are evaluated.     

MOS-1/1b MESSR Observations of the Antarctic Sea Ice: Ice Bands and Ice Streamers

Meso- or submeso-scale features of the Antarctic sea ice are investigated using the MOS-1/1b MESSR Images (spatial resolution of approximately 50 m) received at Syowa Station. Particular attention is paid to the ice bands and ice streamers in coastal polynyas. In the Antarctic Ocean, ice bands can be often seen not only at the ice edge but also in the ice interior zone throughout the year and they extend for hundreds of kilometers in the latitudinal direction. It is found that the width and spacing of ice bands tend to decrease from winter to summer. The width of ice band is about 2–6 km in August and September, and 0.1–0.7 km in December. The spacing of ice bands is about 3–10 km in August and September, and 0.1–2 km in December. In coastal polynyas, ice streamers, which are composed of new ice, are sometimes observed. In general, the row of the streamers is spaced at 0.5–2 km with a width of 0.1–1.0 km.     

Nocdap results: On the relationship of extreme waves and currents for design of offshore structures

Simultaneous wind, wave, and current data during 21 storms spanning four winters at Tromsøflaket (230 m depth) were analysed to determine joint probabilities of occurrence. Waves were measured with a Waverider Buoy, winds with a recording anemometer onboard a vessel and currents at up to five depths with Aandera RCM-4 current meters. Measured currents were filtered to separate tidal currents from residual currents. In most of the statistical analyses, the actual current profiles were replaced with a simplified “equivalent” profile (constant above 50 m depth) whose magnitude was chosen to give the same drag load on a single pile as the actual profile when both profiles were combined with wave orbital velocities. The data suggest that the equivalent current is weakly correlated with the wave height. Within the range of the data analysed, an in-line equivalent residual current of 30 cm sec⁻¹ is adequate for design drag force calculations.The data presented here are used to illustrate a procedure for data analysis and are not suitable for use as design criteria.     

Crustal structure of the South Florida Platform,eastern Gulf of Mexico: An ocean-bottom seismograph refraction study

Five seismic refraction lines, 70–90 km long, were shot in the South Florida Platform region of the Gulf of Mexico using digital ocean-bottom seismographs. Apparent velocities and depths were calculated from the refracted arrivals using a flat-layer model for the region. The two dominant refractors have apparent compressional-wave velocity ranges of 5.6 to 5.9 km s^–1 and 6.2 to 6.7 km s^–1. On the Sarasota Arch, the depth to the top of a 5.8–5.9km/s layer is 3–4 km below sea level. This depth corresponds to the depth to the crystalline basement. The basement dips to the north and to the south from the arch, with velocity of the upper crust increasing from 5.8–5.9 km s^–1 to a maximum of 6.7 km s^–1 at a depth of 6.3 km. Under the continental slope, the crust has presumably been thinned and extended. The deepest refractor has an apparent velocity of about 7.5 km s^–1 at a depth of 25 km. The thickness of the crustal section and the absence of any mantle arrivals in these long refraction profiles on the platform suggest that thick continental crust underlies the South Florida Platform. A north-south cross-section through the platform suggests the presence of two structural highs separated by a portion of the South Florida Basin, which contains at least 5 km of sediment.     

Estimation of sea-bed conductivity and its influence upon velocity measurements with towed electrodes

A formula to determine an effective electric conductivity of channel-bed from measurements of water velocity, cross-channel potential difference and electric current-density is presented. The effective conductivity defined in this paper is the conductivity averaged over depth from channel-bed surface to a depth of the order comparable to a breadth of the channel. Effective conductivities for the Izu Island region and the Straits of Tsugaru are estimated as 2.2×10^–2 mhos/m and 6.0×10^–2 mhos/m, which are considerably large and very large, respectively, in comparison to most of those determined for several regions near England. High conductivities for these regions are consistent with the distribution of underground conductivity anomaly deduced from that of geomagnetic field anomaly observed at the earth's surface in Japan. An influence of underground conductivity upon measurements of sea surface water velocity with towed electrodes is estimated for the regions.     

First measurements from a deep-tow transient electromagnetic sounding system

An electromagnetic sounding system has been developed to map the shallow electrical conductivity structure of the deep sea floor. The instrument consists of a magnetic source and several colinear magnetic receivers forming an array which is towed along the seafloor. The source generates a time varying magnetic field; the shape of the resulting magnetic field waveform at the receivers depends on the electrical conductivity below the seafloor between the receivers and the source. The instrument can be towed systematically over a study area under acoustic transponder or GPS navigation to construct a map of the electrical conductivity. Towing speeds of greater than 1 m s^–1 (2 knots) can be achieved without adversely effecting data quality. The instrument is sufficiently robust to survive continual contact with thinly sedimented, abrasive basalt. We present the first results from a deployment in August, 1990 near the Cleft Segment of the Juan de Fuca Ridge along an 8 km track to the west of the spreading center. Unforeseen problems with the instrument restricted the utility of the measurements for constructing detailed vertical conductivity profiles, but the measurements were adequate to determine an average conductivity in the upper 25 m, at more than 70 stations. The conductivity was found to vary from 0.1 to 0.4 S/m along the track.     

Large scale flow separation and mesoscale eddy formation in the Algerian Basin

During the ELISA/MATER experiment floats released at about 600 m depth in the Levantine Intermediate Water layer south of Sardinia in July 1997 have revealed the existence of a coherent eddy, approximately 50 km in diameter and lasting for several months. This anticyclonic eddy was first observed south-west of Sardinia in November 1997 and drifted inside the Algerian Basin during the following months until April 1998. This eddy contained Levantine Intermediate Water at intermediate level and seemed to be related to 2 main large scale features: (a) a cyclonic gyre (250 km in diameter and 3–4 months period) located in the Algerian Basin and (b) a boundary current located along the continental slope south and west of Sardinia and originating from the Sardinia–Tunisia channel. We will first describe the “Sardinian” eddy, from a kinematical point of view, and the Algerian Gyre and second, give some insights about the eddy origin and its importance for LIW large scale spreading in the Western Mediterranean Sea.