What does the ocean floor look like, and what controls the temperature, salinity and density of seawater?
Describe the features of the ocean floor (continental shelf, slope, abyssal plain, mid-ocean ridge, trench) and explain how temperature and salinity control seawater density (Virginia 2018 Earth Science SOL ES.10).
A SOL-level answer on the ocean for the Virginia Earth Science EOC: the features of the ocean floor and how they relate to plate tectonics, what salinity is and what changes it, how temperature and salinity control seawater density, and why this drives deep circulation, with worked exam questions.
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What this topic is asking
Virginia Earth Science SOL standard ES.10 asks you to describe the ocean floor and the properties of seawater. The EOC tests this with labeled cross sections of the ocean floor (match the feature), with the link between ocean-floor features and plate tectonics, and with reasoning about density from temperature and salinity. The density idea then explains the deep currents covered in the next topic.
Features of the ocean floor
The ocean floor is not flat: it records plate tectonics directly. New crust is made at the ridges and destroyed at the trenches, which is why the youngest seafloor is at the ridge and the oldest near the trenches.
Salinity
So a tropical sea with high evaporation is saltier than the mouth of a large river, where fresh water dilutes the salt.
How temperature and salinity control density
This single rule, cold and salty equals dense and sinks; warm and fresh equals less dense and floats, explains the layering of the ocean and sets up the deep currents in the next topic.
Try this
Q1. Name the deep-ocean feature where new oceanic crust forms. [1]
- Cue. The mid-ocean ridge (a divergent boundary, seafloor spreading).
Q2. Explain how evaporation changes the salinity of seawater. [2]
- Cue. Evaporation removes water as vapor but leaves the dissolved salts behind, so the remaining water has a higher salinity.
Exam-style practice questions
Practice questions written in the style of VDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
VA Earth Science SOL 2023 (style)1 marksWhich ocean-floor feature is the gently sloping, shallow, submerged edge of a continent? (A) the abyssal plain. (B) the continental shelf. (C) the mid-ocean ridge. (D) the trench.Show worked answer →
A 1-point multiple-choice item on ocean-floor features.
The correct answer is B. The continental shelf is the shallow, gently sloping submerged edge of a continent, where the water is relatively shallow and biologically productive. The abyssal plain (A) is the flat deep-ocean floor, the mid-ocean ridge (C) is the underwater mountain chain where new crust forms, and a trench (D) is the deepest part, formed at subduction zones.
The test rewards matching each feature to its position and origin, starting at the shallow shelf near land.
VA Earth Science SOL 2024 (style)2 marksTwo samples of seawater are at the same temperature, but sample X is saltier than sample Y. (a) State which sample is denser and why. (b) Explain what happens when cold, salty water meets warmer, less salty water at the surface.Show worked answer →
A 2-point item on seawater density.
(a) 1 point: sample X (saltier) is denser, because adding dissolved salt increases the mass per unit volume of the water.
(b) 1 point: the colder, saltier (denser) water sinks below the warmer, less salty (less dense) water, which drives vertical (density-driven) circulation in the ocean.
Markers reward identifying the saltier sample as denser in (a) and the sinking of denser water in (b).
Related dot points
- Explain surface currents (driven by wind and deflected by the Coriolis effect into gyres), deep density-driven circulation, and upwelling, and describe how currents transfer heat and affect climate (Virginia 2018 Earth Science SOL ES.10).
A SOL-level answer on ocean currents for the Virginia Earth Science EOC: wind-driven surface currents and gyres, the Coriolis effect, the difference between warm and cold currents, deep density-driven (thermohaline) circulation, upwelling and marine productivity, and how the Gulf Stream affects climate, with worked exam questions.
- Describe how wind generates ocean waves and the parts of a wave, and explain that tides are caused by the gravitational pull of the Moon and Sun, including spring and neap tides (Virginia 2018 Earth Science SOL ES.10 and ES.11).
A SOL-level answer on waves and tides for the Virginia Earth Science EOC: how wind makes waves, the parts of a wave (crest, trough, wavelength, height) and what fetch controls, why tides are caused by the gravity of the Moon (and Sun), the daily pattern of two high and two low tides, and spring versus neap tides, with worked exam questions.
- Explain the processes of the water cycle (evaporation, transpiration, condensation, precipitation, runoff, infiltration) and describe watersheds, groundwater and the water table (Virginia 2018 Earth Science SOL ES.9 and ES.10).
A SOL-level answer on the water cycle for the Virginia Earth Science EOC: the processes that move water (evaporation, transpiration, condensation, precipitation, runoff, infiltration), the energy that drives it, what a watershed and divide are, groundwater and the water table, and porosity and permeability, with worked exam questions.
- Explain plate tectonic theory: the evidence for moving plates, mantle convection as the driving force, the features and motions at divergent, convergent and transform boundaries, and Virginia's geologic provinces (Virginia 2018 Earth Science SOL ES.7).
A SOL-level answer on plate tectonics for the Virginia Earth Science EOC: the evidence from continental fit, fossils and seafloor spreading, mantle convection as the driving force, the features at divergent, convergent and transform boundaries, hot spots, and Virginia's geologic provinces from the Coastal Plain to the Appalachian Plateau, with worked exam questions.
- Describe estuaries and the Chesapeake Bay, including brackish water and its role as a nursery, and explain how watershed land use, runoff and sea-level rise affect coastal Virginia (Virginia 2018 Earth Science SOL ES.10 and human impact).
A SOL-level answer on the Chesapeake Bay for the Virginia Earth Science EOC: what an estuary is and why the Bay's brackish water makes it a nursery, the threats from nutrient runoff and eutrophication, the role of the watershed, sea-level rise and coastal flooding, and conservation, with worked exam questions.
Sources & how we know this
- 2018 Science Standards of Learning (Earth Science) — Virginia Department of Education (2018)
- SOL Practice Items (All Subjects) — Virginia Department of Education (2024)