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A-level · 15 minutes · no login

Thermohaline conveyor

All teacher notes · Open the lab · 2058 words · ·

Field photograph or official scientific figure for teaching thermohaline. A second photograph for the projector script — not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.Wikimedia Commons / NASA / USGS / NOAA, public domain or CC

Why this lesson, and why the 3D

Thermohaline conveyor is a fifteen-minute projector lesson, not a homework packet and not a film with a quiz bolted on. Put this hook on the board before you dim the lights: Density is colour. Cold salty water sinks. The conveyor is slow and global. By the end of the slot a pupil should be able to follow the school conveyor, read density as colour, and flag that this is a schematic — not a pipe you can visit, not a Tuesday switch. Curriculum tags in the header (A-level; APES; NGSS HS-ESS2) are filters, not a flag. The room is worldwide; SI first; International English. Ages on the card (A-level, APES, HS Earth Sci) are a suggested band, not a gate.

Iceland sits near a famous sink region in the school story of North Atlantic Deep Water. Cold, often salty water can become dense enough to dive; that dive is one engine of a slow global loop. A UK A-level class that treats the conveyor as a pipe under the Atlantic will misread both a Met Office ocean brief and a US east-coast headline. Mississippi-scale freshwater at high latitude is a density caution, not a countdown clock. Holderness waves and the Gulf Stream ribbon are surface machines; this lab is density in the deep. The timescale is centuries, not a day. Nuclear-test tracers and ocean arrays read this loop; a classroom globe cannot. The skill is to follow the school conveyor, name temperature and salinity as the density pair, and refuse cinema that switches it off next Tuesday.

The 3D is a named, inspectable object. Click the part, not a caption. If the model will not spin, the Why panel still carries the mechanism, the two photographs, and the film. Do not apologise for the model. Drive it. A silent spin teaches a screensaver. A named mesh that changes under a slider teaches the process.

Fifteen minutes on the projector

Read density as colour. Dark: cold dense. Warm: light. Thermohaline means temperature and salinity control density. Play the loop: surface, sink, deep return, upwell. Deep water forms in cold, often salty high-latitude seas, not in equatorial shallows. Iceland sits near a famous sink region in the school story. This is a school conveyor, not a pipe you can visit. Flag the simplification. It will not switch off next Tuesday. Headlines are not a lab. It can change. That is not the same sentence as cinema. Freshwater input is a caution, not a countdown. Mississippi belongs here as density, not prophecy. Finish in Check.

Open the lab full screen (F). Labels on (L). Speak the first step before you touch a slider: Read density as colour. Blue-dark: cold dense. Red-warm: light. Swatches sit on the floor. Then the second: Play the loop: surface, NADW sink, deep return, Indo-Pacific upwell. Then the third: School conveyor — not a pipe you can visit. Centuries, not a day. Headlines are not a lab.

Time, labels, and T (true scale) are the whole desk. Play walks the process; T removes the vertical lie where one was drawn. Space plays; arrows nudge time; R resets. Parameters the URL can remember: t, labels, true scale. If you only have eight minutes, skip the last step and finish in Check. Projector layout (P) is for the back row: one idea, large type, the model still live.

Read the swatches first: warm/light versus cold-saline. Then play the loop. Point at the NADW sink, the deep return, the Indo-Pacific upwell. Hide labels (L) and ask which limb is sinking. Orbit so the globe and the schematic tubes both read. A dark sphere marks the North Atlantic dive near Iceland’s story. Keyboard: space play, L labels, R reset. Particles are tracers on a cartoon, centuries sped into a lesson. Flag the schematic out loud before you leave. Finish in Check.

The in-site film is “How Do Oceans Circulate? Crash Course Geography #9” (Crash Course Geography, about 11 min, Crash Course / Complexly on YouTube. Standard YouTube licence. Educational embed, autoplay off.). Autoplay is off. Play one minute if you need a second voice; do not let the film eat the slot. The 3D still has to move under your hand.

What the third row will get wrong

You will hear the misconception before you have finished the first sentence. Write the false claim on the board and leave it there until the model has contradicted it. Do not skip this. A fluent pupil can recite the hook and still believe the false sentence.

“It will switch off next Tuesday.” — no. It can change; headlines are not a lab.

“The conveyor is a pipe you could visit in a submarine.” — no. It is a school cartoon of a slow, messy, global density circulation. Flag the simplification.

“Deep water forms in the warm equatorial shallows because the Sun is strongest there.” — no. Sinking wants density. Cold, often salty high-latitude seas, not the equator.

Pitfalls to keep in your pocket: Day-after-tomorrow cinema as fact. Teaching the conveyor as a pipe under the Atlantic. Putting deep-water formation on the equator because the Sun is ‘stronger’ there. Do not let a pupil leave thinking the 3D is a photograph. It is a teaching model. Where vertical exaggeration exists, T collapses it and the caption says so. A labelled lie of scale is honest. An unlabelled one is a cartoon.

Two places, not a slogan

Thermohaline means temperature and salinity control density. Cold water is denser; salty water is denser; the combination can sink. Deep water forms in cold, often salty high-latitude seas — North Atlantic and Southern Ocean in the school map — not in equatorial shallows. Iceland sits near a famous North Atlantic sink region. Play the loop: warm, lighter water at the surface, a dive where it is cold-saline, a deep return, then upwelling in the Indo-Pacific story. Colour is density: darker cold-saline, warmer light. Swatches on the floor are the key: warm/light versus cold-saline. NADW is the school name for the North Atlantic dive. This is a school conveyor, not a pipe you can visit, not a single ribbon in the real ocean, not the AMOC in a research paper. Flag the simplification out loud. It can change. That is not the same sentence as cinema. Freshwater input — a big river, ice melt — can lower density and argue with sinking. Mississippi as a freshwater caution belongs here as a mechanism, not a prophecy. Gyres are wind-driven surface loops; this is the density machine underneath, slower by orders of magnitude. Centuries, not a day.

The first place to land is North Atlantic. The second is Freshwater input caution. Same process, different rock or climate. If a pupil can only name one place, they have a postcard, not a mechanism. Atlas entries for those names are a click from the case list; send them back to the lab with one sentence they can say in Check.

Do not flatten the comparison into “this country versus that country.” Name the landform. Holderness is till, not chalk. Hawaii is a hotspot, not an island arc. Yosemite is a glacial trough, not a river canyon. The 3D is allowed to be schematic; the place names are not allowed to be sloppy.

Figures and the film

Field photograph: Ice and dense water at a polar sinking region. Density as a driver. Credit: NASA, public domain.

Mechanism photograph: Field photograph or official scientific figure for teaching thermohaline. Field photograph or official scientific figure for teaching thermohaline. A second photograph for the projector script — not the lab cover. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC. Credit: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.

Two photographs, two jobs. The field picture is the place. The mechanism picture is the process. Do not run the lesson on a single Apollo Earth disc. A carbon-cycle class is a forest and a seam, not a blue marble. An ENSO class is a Pacific temperature map, not Africa from Apollo 17.

Words they must be able to say

Say these out loud once while you click the matching mesh. If a word has no mesh, it still has a photograph in Terms.

Thermohaline: Density-driven ocean circulation from heat (thermo) and salt (haline). Density: Mass per volume. Cold and salty both raise seawater density. NADW: Cold, often salty water that can sink in the North Atlantic school story. Exam language also accepts “North Atlantic Deep Water”. Deep water formation: Sinking where the surface becomes dense enough. High-latitude seas, not equatorial shallows. Upwelling: Return of deeper water toward the surface. Indo-Pacific in this schematic. Conveyor: School cartoon of a global density loop. Not a pipe. Not a GCM. Salinity: Salt content. More salt, higher density, all else equal.

Exam-language toggle (the Teacher tab) swaps UK/US pairs where they exist — levée/levee, arête/arete — so a mixed room is not punished for spelling.

Close the slot

Without the 3D view: cold salty water sinks; warm light water stays up. Temperature and salinity set density. Deep water forms in high-latitude seas, not on the equator. Iceland sits near a famous sink in the school story. The conveyor is a slow global schematic — centuries, not a day, not a pipe, not a Tuesday switch. Freshwater can change density; that is a caution, not a countdown. Gyres are a different lab. Colour is density, not a travel poster.

Finish in Check — ten questions, not a mood. The bank mixes definition, process, the misconception you just killed, a named place, and a read-the-model item (click the part; T). If a pupil can only recite the hook, they have not used the geometry. Wrong answers still show the one-line explain. Do not skip the explain.

Sources on the Teacher tab are the trail, not a bibliography to copy. NOAA AMOC; UK Met Office ocean.

Link back to the live lab and keep the same slug. Do not invent a parallel worksheet that contradicts T, SI, or the named parts.

This note is worldwide. Curriculum tags (A-level; APES; NGSS HS-ESS2) are filters, not a flag. A class in Nairobi, London, or Shanghai can use the same 3D. Ages (A-level, APES, HS Earth Sci) are a suggested band. If a sentence only works in one exam board, rewrite it before you project it.

Write these three lines on the board before you dim the lights. One: Density is colour. Cold salty water sinks. The conveyor is slow and global. Two: the misconception “It will switch off next Tuesday.”. Three: the named parts they must click. Then drive the model. Check is ten questions covering definition, process, the misconception, a place, and a read-the-model item. Do not skip the explain on a wrong answer.

Board, units, and what not to say

SI first. Metres, kilometres, degrees Celsius, metres per second. A conversion in brackets is courtesy, not a second system. Do not let a pupil leave thinking the 3D is a photograph. It is a teaching model. Where vertical exaggeration exists, T collapses it and the caption says so.

Do not say “teaching mesh”, “sprinkle”, or “thin free surface not a fat pipe” out loud. Say the landform. Seasons are ~23.44° of axial tilt, not Earth–Sun distance. The outer core is liquid; S-waves do not pass. Yosemite is a glacial U-trough. San Andreas is a transform. Hawaiʻi and Yellowstone are hotspots. Florida is not a glacial trough.

If the room is noisy, projector layout (P) is the back-row setting: one idea, large type, the model still live. Full screen (F). Labels (L). Space plays. Arrows nudge time. R resets. The URL can remember t, labels, true scale. Send them home with the same link; there is no login.

In-site film

How Do Oceans Circulate? Crash Course Geography #9. Crash Course Geography. Crash Course / Complexly on YouTube. Standard YouTube licence. Educational embed, autoplay off. Autoplay off.