What drives surface and deep ocean currents, and how do they affect climate?
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.
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What this topic is asking
Virginia Earth Science SOL standard ES.10 asks you to explain ocean currents: the surface currents driven by wind, the deep currents driven by density, upwelling, and how currents move heat and shape climate. The EOC tests this with cause items (what drives surface versus deep currents), the Coriolis effect, warm-versus-cold current effects on climate, and the role of the Gulf Stream off Virginia. It builds directly on the density rule from the previous topic.
Surface currents, wind and the Coriolis effect
Warm and cold currents
Surface currents are classed by the water they carry. A warm current moves water away from the equator toward the poles (warmer than the surrounding water); a cold current moves water toward the equator from higher latitudes (cooler than its surroundings). The Gulf Stream is a famous warm current that flows north along the eastern United States, past Virginia, and across the Atlantic, carrying tropical heat toward Europe.
Deep (density-driven) circulation
The contrast to remember: wind drives the surface currents; density drives the deep currents.
Upwelling
Upwelling is the rising of cold, nutrient-rich water from the deep ocean to the surface, usually where winds push surface water away from a coast and deep water rises to replace it. Because it brings up nutrients, upwelling supports abundant marine life and some of the world's most productive fisheries.
Currents and climate
Ocean currents move enormous amounts of heat around the planet, so they strongly influence climate. A warm current offshore makes a coastal climate milder and wetter (the Gulf Stream helps keep western Europe warmer than its latitude would suggest); a cold current makes a coast cooler and often drier. This is one reason coastal and inland places at the same latitude can have very different climates.
Try this
Q1. State what drives surface currents and what drives deep currents. [2]
- Cue. Surface currents are driven by wind (and deflected by the Coriolis effect); deep currents are driven by density differences (temperature and salinity).
Q2. Explain why upwelling areas support rich fisheries. [2]
- Cue. Upwelling brings cold, nutrient-rich deep water to the surface; the nutrients support large populations of plankton and the fish that feed on them.
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 marksWhat is the main force that drives surface ocean currents? (A) the Moon's gravity. (B) wind. (C) earthquakes. (D) the salinity of the water.Show worked answer →
A 1-point multiple-choice item on surface currents.
The correct answer is B. Surface ocean currents are driven mainly by the prevailing winds dragging on the water surface, then deflected by the Coriolis effect into looping gyres. The Moon's gravity (A) causes tides, earthquakes (C) can cause tsunamis but not steady currents, and salinity (D) drives the deep (density) circulation, not the wind-driven surface currents.
The test rewards knowing that wind drives surface currents while density differences drive deep currents.
VA Earth Science SOL 2024 (style)2 marksThe Gulf Stream is a warm surface current that flows north along the eastern United States, past Virginia, toward Europe. (a) Explain how this current affects the climate of the regions it passes. (b) State what generally happens to deep ocean water at the poles and why.Show worked answer →
A 2-point item on currents and climate.
(a) 1 point: the warm Gulf Stream carries heat from the tropics toward higher latitudes, warming the coastal climate and the air over and downwind of it (it helps keep western Europe milder than its latitude would suggest).
(b) 1 point: at the poles the surface water is cold and salty, making it dense, so it sinks and flows along the ocean floor, driving the deep (thermohaline) circulation.
Markers reward linking the warm current to a warmer climate in (a) and the sinking of cold, salty (dense) polar water in (b).
Related dot points
- 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.
- 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 how temperature affects air pressure and density, how wind blows from high to low pressure, the Coriolis effect, and local winds such as land and sea breezes (Virginia 2018 Earth Science SOL ES.8).
A SOL-level answer on air pressure and wind for the Virginia Earth Science EOC: how temperature controls air density and pressure, why wind blows from high to low pressure, the difference between rising low-pressure systems (stormy) and sinking high-pressure systems (fair), the Coriolis effect, and land and sea breezes, with worked exam questions.
- Distinguish weather from climate, explain the factors that control climate (latitude, elevation, water, ocean currents, prevailing winds), and describe the evidence for climate change and the enhanced greenhouse effect (Virginia 2018 Earth Science SOL ES.9).
A SOL-level answer on climate for the Virginia Earth Science EOC: the difference between weather and climate, the factors that control climate (latitude, elevation, proximity to water, ocean currents, prevailing winds), the evidence for climate change, the enhanced greenhouse effect, and its impacts on Virginia, with worked exam questions.
- Describe the composition and layers of the atmosphere and explain how energy is transferred by radiation, conduction and convection, including the greenhouse effect (Virginia 2018 Earth Science SOL ES.8).
A SOL-level answer on the atmosphere for the Virginia Earth Science EOC: the composition (mostly nitrogen and oxygen), the layers (troposphere, stratosphere with the ozone layer, mesosphere, thermosphere), and the three ways energy moves (radiation, conduction, convection) plus the greenhouse effect, 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)