Temperature and salinity of ocean waters

Correct answer: B. Water reduces and salts become concentrated

Explanation: The governing concept is the freshwater budget of the ocean surface. In many subtropical belts, rainfall is relatively limited while strong solar heating and dry descending air promote substantial evaporation. Evaporation removes water molecules as vapour but leaves most dissolved salts behind. If the freshwater loss is not balanced by rainfall, river discharge or ice melt, the remaining seawater contains more salt per unit volume, so salinity rises. Option B correctly expresses this concentration effect. Option A reverses both controlling conditions. Option C is false because seawater naturally contains dissolved salts, and option D is not a general process: rivers usually add freshwater and some dissolved material rather than simply removing ocean salt. Winds and currents can redistribute the salinity, but the local cause remains water loss exceeding freshwater input.

Correct answer: A. High temperature and low salinity

Explanation: The governing concept is the combined control of seawater density by temperature and salinity. Heating causes seawater to expand, so warm water is generally less dense than cold water. Adding freshwater dilutes the dissolved salts and also lowers density. Therefore the combination of high temperature and low salinity in option A gives the strongest tendency toward relatively low-density surface water. Options B and C combine cooling and/or high salinity, both of which generally increase density. Option D is also associated with denser water because freezing rejects salt into the remaining liquid, often raising its salinity; cold conditions additionally increase density. The exact density depends on pressure and composition, but for surface water the temperature-salinity comparison clearly supports A.

Correct answer: B. Receipt of solar energy

Explanation: The governing concept is the latitudinal variation of incoming solar radiation. Toward either pole, the Sun’s rays strike the surface at a more oblique angle. The energy is spread over a larger area, passes through a greater thickness of atmosphere, and is therefore less effective in heating each unit of ocean surface. The receipt of solar energy decreases with increasing latitude, so sea-surface temperature generally also decreases poleward. Option B is correct. River-water supply is not the controlling global pattern, and the quantity of sea salts does not determine the basic poleward temperature gradient. Ocean depth is not what decreases toward the poles; in any case, depth is not the main control of surface heating. Winds, currents, ice and season can modify local values, but reduced insolation explains the broad pattern.

Correct answer: B. High salinity

Explanation: The governing concept is the balance between freshwater input and water loss from the sea. Low river inflow supplies little freshwater to dilute the seawater. At the same time, high evaporation removes water as vapour while leaving most dissolved salts in the basin. If rainfall and other inputs do not compensate for this loss, the salt concentration rises, producing relatively high salinity. Thus option B is correct. Low salinity would require strong freshwater addition, heavy rainfall, melting ice or another effective dilution source. Zero salinity is impossible for an ordinary sea under these conditions, because dissolved salts remain present. “Icy salinity” is not a recognised salinity category. Circulation and exchange with nearby waters may modify the result, but the stated water balance strongly favours high salinity.

Correct answer: A. The surface is directly affected by day-night solar heating

Explanation: The governing concept is the vertical distribution of ocean temperature and the limited penetration of solar energy. Incoming sunlight is absorbed mainly by the upper layer of seawater, so this layer responds relatively quickly to daytime heating and night-time cooling. Waves and surface mixing can spread some heat nearby, but deep water is insulated from rapid daily changes and is influenced more by slow circulation and seasonal processes. Therefore, option A is correct: the sea surface receives direct solar energy and loses heat to the atmosphere, while the other options contradict basic ocean conditions. Option B is wrong because sunlight weakens with depth; option C is physically incorrect, and option D falsely denies the presence of surface water.

Correct answer: B. Rainfall decreases salinity and evaporation increases it

Explanation: The governing concept is the water-balance control of surface salinity. Rainfall adds fresh water to the ocean surface without adding a comparable amount of dissolved salt, so it dilutes seawater and generally lowers salinity. Evaporation removes water vapour but leaves most dissolved salts behind; consequently, the remaining seawater becomes more concentrated and salinity rises. This explains why regions with high evaporation and little rainfall often have relatively high surface salinity, whereas rainy regions tend to have lower values, subject to currents and freshwater inflow. Option B correctly states both opposite effects. Option A reverses them, while C and D ignore the direct influence of the surface water balance.

Correct answer: A. A large river delta and heavy-rainfall region

Explanation: The governing concept is the balance between freshwater input and water loss at the sea surface. A large river delta receives substantial river discharge, which contains very little salt compared with seawater. Heavy rainfall adds another source of fresh water and dilutes the surface layer. Together, these processes can make salinity relatively low, especially near the coast, although currents and mixing may modify the exact value. Thus option A is correct. A dry enclosed sea generally loses water through strong evaporation and may become saltier; a warm subtropical sea with high evaporation also tends to have elevated salinity. Option D combines heat and limited river inflow, conditions that usually favour concentration rather than dilution.

Correct answer: A. About 35 parts of dissolved salts in one thousand parts of seawater

Explanation: The governing concept is salinity expressed in parts per thousand, commonly written as ‰ or ppt. A value of 35 ppt means that approximately 35 parts by mass of dissolved salts are present in 1,000 parts by mass of seawater, with the remaining mass consisting mostly of water and a small proportion of other dissolved substances. It is a concentration measure, not a statement about depth, time, sand, or drying. Therefore option A is correct, although the wording is most precise when it says 35 parts of salts in 1,000 parts of seawater rather than in pure water. Option B confuses salts with sediment, while C and D attach the number to unrelated measurements or events.

Correct answer: B. A sequence showing temperature change with depth

Explanation: The governing concept is the ocean’s vertical thermal structure. The surface layer is directly exposed to solar heating and atmospheric exchange and may therefore be relatively warm. Beneath it, the thermocline is the zone in which temperature decreases comparatively rapidly with increasing depth. Below the thermocline, deep water is generally colder and its temperature changes slowly because sunlight does not reach it effectively and mixing is limited. The exact strength and depth of these layers vary with latitude, season and circulation, but the profile still represents temperature change through depth. Hence option B is correct. Option A wrongly suggests uniform temperature, while C concerns salinity and D describes river water rather than a marine thermal profile.

Correct answer: A. Difference in density

Explanation: The governing concept is density stratification. Heating usually makes water expand slightly, so warm water becomes less dense and tends to remain above cooler, denser water. Cooling generally increases density, allowing cold water to sink when it is denser than the water below or around it. Salinity also affects density, so the actual layering of seawater reflects both temperature and salt content. This difference in density can produce stable layers, vertical mixing, and, under suitable conditions, sinking and rising motions. Option A is therefore correct. Coast length does not directly determine whether a parcel sinks, sea colour is only a visual property, and rainfall sound has no physical role in water density or layering.

Correct answer: A. Deep-water movement and ocean circulation

Explanation: The governing concept is thermohaline circulation, in which ‘thermo’ refers to temperature and ‘haline’ to salinity. Cooling generally makes seawater denser, while increased salinity also raises density. Where surface water becomes sufficiently cold and saline, it can sink, and this sinking is balanced by movement and mixing elsewhere, helping drive deep and broad ocean circulation. Winds and tides also influence ocean movement, but density differences are an important cause of deep-water formation and circulation. Thus option A is correct. Coastal road construction and soil farming are human activities unrelated to density-driven ocean motion. Mountain building is mainly associated with tectonic forces and cannot be described as the process produced by these seawater density differences.

Correct answer: A. Low solar heating and increased salinity when ice forms

Explanation: The governing concept is the combined effect of latitude, temperature, salinity and density. High latitudes receive less solar energy at a lower angle, so the sea surface can remain cold. When seawater freezes, the ice is made mostly of freshwater and excludes much of the salt; the remaining liquid water becomes saltier and therefore denser. Cold temperature itself also generally increases seawater density. If the resulting water is dense enough, it can sink and contribute to deep-water formation. Therefore option A correctly gives both relevant mechanisms. More sunshine would favour warming, while heavy rainfall and river discharge generally dilute seawater and lower salinity. The disappearance of the surface is not a geographical or physical explanation.

Correct answer: A. It affects the exchange of heat and moisture

Explanation: The governing concept is the ocean–atmosphere interaction. Sea-surface temperature controls how much sensible heat and water vapour are exchanged between the ocean and the atmosphere. A warmer surface can transfer more heat and moisture upward, supporting convection, cloud formation and precipitation under suitable atmospheric conditions. A cooler surface generally supplies less heat and evaporation, although winds, currents and atmospheric circulation also affect the final climate outcome. Because oceans store and redistribute heat, sea-surface temperature can influence coastal climates and larger weather patterns. Option A is correct. Sea sand formation, mountain erosion and river length are not the direct climatic effects described by surface temperature, so options B, C and D are unsuitable.

Correct answer: A. It contains more dissolved salts

Explanation: The governing concept is salinity and the effect of dissolved salts on water use. Highly saline seawater contains a large concentration of dissolved salts, especially sodium chloride along with other minerals. Drinking it directly gives the body more salt than the kidneys can efficiently remove using the available water. This can increase the body’s need for water and may cause dehydration rather than hydration. Desalination can remove much of the dissolved salt and make seawater usable, but untreated seawater is not normally suitable for drinking. Therefore option A is correct. Option B is false because seawater is mostly water; C is false because it is usually liquid; and D is false because salinity does not mean that water is always cold.

Correct answer: C. By comparing both effects in the water balance

Explanation: The governing concept is the water balance of the sea surface. Rainfall adds freshwater and normally dilutes seawater, tending to reduce salinity, whereas evaporation removes water and leaves most dissolved salts behind, tending to increase salinity. When both processes are strong, their relative amounts, along with river input, freezing or melting of ice, and exchange with nearby waters, must be considered. If evaporation exceeds freshwater gain, salinity may rise; if rainfall is greater, it may fall. Therefore, option C is correct because it compares both opposing effects rather than treating either one as decisive. Option A and option B ignore an important process, while option D has no scientific basis.

Correct answer: A. Because latitude affects solar heating and currents transfer water

Explanation: Ocean temperature has a broad latitudinal pattern because the angle of incoming sunlight and the length of day vary from the equator towards the poles. Lower latitudes generally receive more direct solar energy, while higher latitudes receive more oblique rays. Ocean currents then redistribute heat: warm currents carry tropical water towards cooler regions, and cold currents bring cooler water towards lower latitudes. Coastlines, winds, seasonal changes, and mixing can further modify the pattern. Thus option A is correct because it includes both the basic control, latitude, and the important modifying process, currents. Options B, C, and D either describe unrelated effects or deny an established relationship.

Correct answer: A. Pycnocline

Explanation: A pycnocline is the ocean layer in which water density changes rapidly with depth. Density is affected mainly by temperature and salinity: colder water is generally denser, and saltier water is also generally denser. Therefore, sharp vertical changes in either or both properties can produce a pronounced pycnocline. Option A is correct because “pycno” refers to density. A thermocline specifically describes a rapid temperature change, while a halocline describes a rapid salinity change. These layers can occur together or overlap, but their definitions are different. “Coastal layer” is not the standard term for a rapid vertical density gradient, so option D is unsuitable.

Correct answer: A. Open oceans have greater water exchange

Explanation: Salinity reflects the balance between salt input, freshwater addition, evaporation, and removal or dilution through water exchange. A dry enclosed sea may lose much water through intense evaporation while receiving limited freshwater and having restricted circulation with the open ocean. Salts then become concentrated, so its average salinity can be unusually high. The open ocean has broader circulation and greater exchange with other basins, allowing water and dissolved substances to be redistributed and reducing persistent local concentration. Rainfall and river input may also dilute some areas. Option A is correct because stronger exchange helps regulate salinity. Options B, C, and D are false: oceans do receive rain, enclosed seas can evaporate strongly, and open-ocean water contains dissolved salts.

Correct answer: A. The amount of solar radiation changes with the season

Explanation: Seasonal sea-surface temperature changes are governed chiefly by the seasonal variation in incoming solar radiation. Earth’s axial tilt and its revolution around the Sun change the Sun’s angle, day length, and the amount of energy received at a location during the year. The surface ocean absorbs, stores, and redistributes this heat, so its temperature usually changes more slowly than land temperature. Winds, cloud cover, currents, mixing, evaporation, and freshwater input can strengthen or moderate the seasonal signal. Option A is correct because it identifies the basic energy source and seasonal control. The sea does not dry up, salinity does not become zero, and river flow is not the primary explanation, so B, C, and D are incorrect.

Correct answer: A. Warm region with heavy rainfall

Explanation: Sea-surface temperature and salinity are controlled by partly different processes. Strong solar heating can make the surface water warm, while heavy rainfall adds fresh water and dilutes the dissolved salts, lowering salinity. Therefore, a warm region that also receives abundant rain can show both high temperature and low salinity, so option A is correct. A dry region generally promotes evaporation and can raise salinity; extensive ice formation is associated with cold conditions and may increase nearby salinity when ice rejects salt; and an enclosed dry sea commonly loses water through evaporation, producing high rather than low salinity. Ocean currents and river discharge may also modify the local result.

Correct answer: A. High evaporation in a hot, dry region

Explanation: A hot, dry climate supplies strong heating and favours rapid evaporation from the sea surface. Evaporation removes water vapour but leaves most dissolved salts behind, so the remaining seawater becomes more saline. Solar heating also keeps the surface relatively warm; consequently, option A gives the most suitable combination. Near a large river mouth, freshwater dilution usually lowers salinity. Melting ice adds freshwater and tends to cool the nearby water, while heavy rainfall both cools or moderates the surface and dilutes its salts. Local currents and mixing can alter the exact value, but the general geographical relationship clearly supports high evaporation in a warm, dry region.

Correct answer: A. Different organisms are adapted to different temperature conditions

Explanation: Temperature is a major environmental control on marine life. Each species has a tolerance range within which its enzymes, metabolism, growth, reproduction and feeding work effectively. Warm-water, temperate and cold-water organisms therefore tend to occupy different regions, although currents, oxygen, food supply and salinity also matter. Thus option A is correct because organisms are adapted to particular thermal conditions. Option B is wrong because temperature creates ecological differences rather than making organisms identical. Options C and D deny basic physical and biological relationships: temperature does not turn the sea into land, and it clearly affects survival, activity and geographical distribution.

Correct answer: A. It affects the water conditions in which they live

Explanation: Salinity is the concentration of dissolved salts in water, and it affects the osmotic balance of marine organisms. Cells must regulate the movement of water and salts across their membranes; a sudden or unsuitable salinity change can cause water loss, excessive water uptake, physiological stress or even death. Species therefore have different salinity tolerances, and estuarine organisms often adapt to changing values while many open-ocean organisms prefer a narrower range. Option A is correct because salinity is a basic habitat condition. The other options are biologically or physically false: salinity does not turn organisms into stone, create only sound, or transform liquid water into air.

Correct answer: A. A density difference can create stratification

Explanation: Heating makes surface seawater expand slightly and become less dense, whereas colder deep water is generally denser. Gravity allows the denser water to remain below the lighter water, producing vertical stratification. This stable layering resists ordinary vertical mixing unless strong winds, waves, convection or currents supply enough energy to break it down. Therefore option A is correct. Option B is false because temperature and salinity differences commonly produce different densities. Options C and D are nonsensical: deep water is still liquid water within the ocean, and surface water obviously contains water. Salinity can strengthen or weaken the temperature-created density contrast, so both properties are relevant.

Correct answer: A. It helps identify regional differences and water masses

Explanation: Ocean maps showing temperature and salinity reveal how water properties vary from place to place and with depth. Similar combinations of temperature and salinity can identify a water mass formed in a particular source region, while sharp contrasts may indicate fronts, boundaries or current-related mixing. These patterns help geographers interpret density, circulation, climate influence, nutrient movement and habitats. Thus option A is correct. The measurements do not describe a coastal language, transform seawater into soil or remove rivers from the landscape. A map is useful precisely because it displays the spatial distribution of these physical properties and permits comparison between oceanic regions.