SCIENCE · INVESTIGATE AND EXPLAIN

Follow water and energy without a conveyor shortcut

Combine mechanisms and observations into bounded claims and specify missing transport evidence.

Learning outcome: Distinguish a density tendency from measured velocity, volume transport and heat transport.

Starting recap

Wind, mixing and buoyancy interact; one profile does not trace a permanent global loop.

All lessons are open directly. Your saved experiments remain when you leave and return.

Try

A stipulated uniform normal velocity of 0.10 m/s across 200 m2 carries 20 m3/s.

Open the experiment

Predict

Can identical temperature profiles coexist with different transport directions?

Your prediction and reason

Experiment

Draw paired warm/cool transport arrows, repair an unsupported speed claim and request a matching measurement.

Compare temperature and salinity contributions to density

Illustrative parcel-density comparison · qualitative circulation mechanisms · Original illustrative relation at one common reference pressure: density = 1027 − 0.2(T − 10) + 0.8(S − 35) kg/m³. Lower reference has T=10°C and S=35. S is a dimensionless practical-salinity-like teaching input, not an exact g/kg value. Coefficients are 0.2 kg/m³ per °C and 0.8 kg/m³ per unit of salinity input. Salinity values and coefficients are teaching assumptions, not a validated seawater equation of state or measured profile. Stable/unstable/neutral refers only to this density ordering. No pressure/depth effects, circulation speed, mixing timescale or transport is inferred.

Upper parcel temperature: 10 °C Upper parcel salinity: 35.0 dimensionless teaching salinity

Reset keeps your prediction, captures and practice history.

Separate the effects of temperature and salinity

Start with two hypothetical parcels compared at the same reference pressure. The lower parcel stays at 10°C with salinity input 35 and reference density 1027 kg/m³. Change the upper parcel. Predict which contribution increases its density before inspecting the calculation. The model’s numbers are teaching assumptions, not measured seawater properties or a validated equation of state.

Illustrative upper-parcel calculation, all density terms in kg/m³
Term	Calculation	Value
Reference density	Lower parcel: 10°C, salinity 35	1027.00
Temperature contribution	−0.2 × (10 − 10)	0.00
Salinity contribution	+0.8 × (35 − 35)	0.00
Upper density	1027 + temperature term + salinity term	1027.00
Upper minus lower	1027.00 − 1027.00	0.00

The salinity input is a dimensionless teaching scale resembling practical salinity. It is not an exact grams-per-kilogram conversion. Here −0.2 has units kg/m³ per °C and +0.8 has units kg/m³ per salinity-input unit. Actual seawater density depends nonlinearly on temperature, composition and pressure; this rule is used only for these hypothetical comparisons.

A tendency, not a simulated current

Equal modeled densities give no density contrast in this comparison. Equality is not proof that real seawater is perfectly neutral; the illustrative formula omits additional physics.

Try a competing-effects case and check it

Predict the result at 14°C and salinity 36. Warming contributes −0.80 kg/m³ while the salinity increase contributes +0.80 kg/m³. They cancel in this rule, leaving 1027 kg/m³. At 16°C and the same salinity, the temperature term becomes −1.20, so the net is −0.40: the upper parcel is lighter. “Saltier” alone does not settle the density comparison when temperature also changes.

Try the reverse competition at 6°C and salinity 34. Both contributions again cancel. At 4°C and salinity 34, the cooling term +1.20 exceeds the freshening term −0.80, leaving the upper parcel 0.40 kg/m³ denser. Explain why the word “cold” alone still does not establish a real current’s direction.

Surface transport and deep circulation have different evidence needs

Wind transfers momentum to the sea surface. Rotation deflects moving water; basin boundaries and pressure gradients help shape currents. Wind-driven transport can redistribute heat without requiring every warm parcel to sink. Surface waves and currents are different: a passing wave pattern is not a direct measurement of sustained water transport.

In this idealized Northern Hemisphere example, southward wind along a north–south coast gives depth-integrated Ekman transport to its right, offshore to the west. Deeper water can replace exported near-surface water. The ideal transport direction is not a universal angle for every current or every depth; coasts, duration, friction and stratification matter. Mirror the hemisphere and re-evaluate the direction rather than memorizing this drawing.

Check what the density rule cannot establish

Cooling and increased salinity can favor higher density, but a density contrast alone does not map a global route or supply a flow rate. Deep circulation involves buoyancy changes, winds, mixing, pressure gradients and basin geometry. A conveyor diagram summarizes connected transport; actual parcels do not follow a single closed loop with a universal travel time. To test a transport claim, seek measurements of motion and location over time, not only temperature or salinity.

Primary background: NOAA currents and rotation; NOAA temperature, salinity and deep circulation; NOAA coastal upwelling. The original numerical rule and diagrams above are teaching constructions, separate from measured ocean records.

One observed ocean profile, eight selected levels

This fixed INCOIS Argo record is separate from the illustrative density controls. Float WMO 1900121, cycle 1, ascended in the Indian Ocean at -9.857° latitude, 55.953° longitude. The profile timestamp is 2002-11-11 09:20:28 UTC; it does not mean every level was sampled simultaneously.

Predict before checking: between 96.5 and 206.7 dbar, do temperature and salinity change in the same direction? Use the table to calculate both changes. Then decide whether either change tells you how fast water travels horizontally.

Adjusted values from one ascending profile; original source row indices retained
Source row (zero-based)	Pressure dbar	In-situ temperature °C	Practical salinity	Adjusted QC: pressure / T / S
0	2.6	27.388	35.37806	1 / 1 / 1
9	46.4	27.181	35.37089	1 / 1 / 1
14	96.5	21.169	35.13642	1 / 1 / 1
22	206.7	13.818	35.12019	1 / 1 / 1
29	496.4	8.953	34.78860	1 / 1 / 1
34	996.4	5.864	34.77057	1 / 1 / 1
39	1496.4	3.745	34.74355	1 / 1 / 1
44	1996.0	2.588	34.73743	1 / 1 / 1

The eight selected points omit local structure. Original source row 12, not plotted here, reports 76.3 dbar, 25.461 °C and practical salinity 35.40648—higher than the uppermost selected salinity 35.37806. The complete profile therefore does not show a monotonic salinity decrease. All 45 source rows are retained for audit.

Check the profile comparison and inference

At 96.5→206.7 dbar, temperature changes by 13.818 − 21.169 = −7.351 °C and practical salinity by 35.12019 − 35.13642 = −0.01623. Both decrease between those levels. This is a comparison within an ascending profile, not a climate trend, stationary time series or measured current speed. We selected eight of 45 actual levels; the intervening rows remain in the frozen source record.

The uppermost selected temperature is 27.388 °C, outside the illustrative density lab's range. More fundamentally, these observations occur at unequal pressures. Do not put them into the toy density rule to infer real stability: an appropriate common-reference oceanographic calculation would be needed. A density contrast alone would still not determine current velocity or transport.

Transfer: compare 496.4 and 996.4 dbar using the table. What additional measurement would establish water motion? A suitable displacement/time record with depth context or a direct velocity measurement would help; volume transport also requires a cross-section.

Inspect source fields, quality and missing metadata

The displayed values use PRES_ADJUSTED, TEMP_ADJUSTED and PSAL_ADJUSTED. At source row 0, pressure changes from 5.5 dbar raw to 2.6 dbar adjusted, and salinity from 35.377 to 35.37806. Those are processing versions of one observation, not a measured change through time. Quality flag 1 means good data. The timestamp has QC 1; good quality is not zero uncertainty.

This provider does not expose DATA_MODE, position quality or adjusted-error fields. They remain unavailable, not zero. We do not assert delayed-mode processing or invent error bars. The reported decimal places do not establish accuracy. The source calls practical salinity “PSU”; it is dimensionless and is not directly grams of salt per kilogram. Pressure in dbar is not measured depth in metres.

Exact INCOIS profile query · Provider units and metadata · Argo field and quality guidance · Argo dataset citation.

Data were collected and made freely available by International Argo and contributing national programs, and distributed here by INCOIS. Frozen on 2026-10-26; the local snapshot retains the source's free-use and redistribution terms. This lesson needs no live request. One profile does not describe a permanent global conveyor or the whole Indian Ocean.

Inspect all 45 original source rows

This is the exact frozen CSV response: field names, units row and every original level. Adjusted and raw values are distinct columns.

PLATFORM_NUMBER,CYCLE_NUMBER,DIRECTION,time,JULD_QC,latitude,longitude,PRES,PRES_QC,PRES_ADJUSTED,PRES_ADJUSTED_QC,TEMP,TEMP_QC,TEMP_ADJUSTED,TEMP_ADJUSTED_QC,PSAL,PSAL_QC,PSAL_ADJUSTED,PSAL_ADJUSTED_QC
,,,UTC,,degrees_north,degrees_east,decibar,,decibar,,degree_Celsius,,degree_Celsius,,PSU,,PSU,
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,5.5,1,2.6,1,27.388,1,27.388,1,35.377,1,35.37806,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,9.4,1,6.5,1,27.375,1,27.375,1,35.377,1,35.37834,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,14.3,1,11.4,1,27.302,1,27.302,1,35.376,1,35.37714,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,18.9,1,16.0,1,27.268,1,27.268,1,35.374,1,35.37504,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,23.9,1,21.0,1,27.247,1,27.247,1,35.373,1,35.37396,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,29.0,1,26.1,1,27.243,1,27.243,1,35.374,1,35.37495,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,34.4,1,31.5,1,27.239,1,27.239,1,35.375,1,35.37597,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,39.2,1,36.3,1,27.231,1,27.231,1,35.374,1,35.37496,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,43.9,1,41.0,1,27.227,1,27.227,1,35.372,1,35.37321,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,49.3,1,46.4,1,27.181,1,27.181,1,35.369,1,35.37089,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,59.4,1,56.5,1,26.874,1,26.874,1,35.401,1,35.40385,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,69.6,1,66.7,1,26.231,1,26.231,1,35.401,1,35.40441,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,79.2,1,76.3,1,25.461,1,25.461,1,35.401,1,35.40648,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,89.7,1,86.8,1,23.931,1,23.931,1,35.304,1,35.31376,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,99.4,1,96.5,1,21.169,1,21.169,1,35.131,1,35.13642,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,109.3,1,106.4,1,19.968,1,19.968,1,35.104,1,35.10599,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,119.6,1,116.7,1,19.708,1,19.708,1,35.101,1,35.10602,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,129.3,1,126.4,1,18.546,1,18.546,1,35.108,1,35.11077,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,138.9,1,136.0,1,18.069,1,18.069,1,35.102,1,35.10677,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,149.4,1,146.5,1,16.922,1,16.922,1,35.084,1,35.0865,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,168.9,1,166.0,1,16.142,1,16.142,1,35.094,1,35.09767,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,189.2,1,186.3,1,14.663,1,14.663,1,35.085,1,35.08771,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,209.6,1,206.7,1,13.818,1,13.818,1,35.118,1,35.12019,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,229.5,1,226.6,1,13.267,1,13.267,1,35.103,1,35.10528,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,248.8,1,245.9,1,12.71,1,12.71,1,35.092,1,35.09405,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,299.0,1,296.1,1,11.565,1,11.565,1,34.981,1,34.9829,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,349.4,1,346.5,1,10.741,1,10.741,1,34.915,1,34.91695,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,399.2,1,396.3,1,9.875,1,9.875,1,34.836,1,34.83772,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,449.4,1,446.5,1,9.376,1,9.376,1,34.799,1,34.80067,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,499.3,1,496.4,1,8.953,1,8.953,1,34.787,1,34.7886,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,599.1,1,596.2,1,8.293,1,8.293,1,34.767,1,34.76867,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,699.5,1,696.6,1,7.497,1,7.497,1,34.774,1,34.77563,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,799.6,1,796.7,1,6.846,1,6.846,1,34.774,1,34.77559,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,898.8,1,895.9,1,6.345,1,6.345,1,34.77,1,34.77159,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,999.3,1,996.4,1,5.864,1,5.864,1,34.769,1,34.77057,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1099.4,1,1096.5,1,5.476,1,5.476,1,34.769,1,34.77061,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1199.4,1,1196.5,1,4.971,1,4.971,1,34.765,1,34.76662,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1299.1,1,1296.2,1,4.48,1,4.48,1,34.76,1,34.76163,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1399.6,1,1396.7,1,3.991,1,3.991,1,34.746,1,34.74754,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1499.3,1,1496.4,1,3.745,1,3.745,1,34.742,1,34.74355,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1599.1,1,1596.2,1,3.476,1,3.476,1,34.739,1,34.74052,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1698.9,1,1696.0,1,3.264,1,3.264,1,34.74,1,34.74154,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1799.5,1,1796.6,1,3.017,1,3.017,1,34.738,1,34.73951,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1899.0,1,1896.1,1,2.832,1,2.832,1,34.737,1,34.73853,1
1900121,1,A,2002-11-11T09:20:28Z,1,-9.857,55.953,1998.9,1,1996.0,1,2.588,1,2.588,1,34.736,1,34.73743,1

Upper illustrative density 1027.00 kg/m³; lower 1027.00 kg/m³; upper minus lower 0.00 kg/m³. neutral density ordering.

The parcels have equal illustrative density within arithmetic tolerance: neutral density ordering in this restricted comparison. Temperature contributes 0.00 and salinity 0.00 kg/m³ relative to the reference. These assumed coefficients are not a validated seawater equation of state; no observed profile, current speed or transport is calculated.

Observation to attach to a capture

Captures preserve the hypothetical upper parcel temperature and salinity. Replay recalculates the illustrative density ordering; it does not measure seawater, calculate current speed or change recorded ocean observations.

Understand

Build an argument with different kinds of evidence

Place three headings on paper: mechanism, controlled comparison and observation. Under mechanism, draw wind transferring momentum to water in a rotating basin with boundaries. Under controlled comparison, record one temperature/salinity pair and the illustrative density ordering. Under observation, identify the fixed INCOIS Argo profile and a numerical property difference. Each contributes something useful, but none can silently replace the others.

Your task is to decide which claim this collection supports and which additional measurement would answer a different question. A strong argument need not promise an exact current speed. It can explain a physical tendency, report measured properties and explicitly identify the missing movement evidence.

Follow water across a section

For a paper example only, suppose an independently measured current carries warmer water northward across a chosen section, while an equal volume of cooler water returns southward. With similar density and heat capacity, this exchange can carry thermal energy northward overall. The temperature contrast matters together with transport direction and amount. Temperature alone supplies neither direction nor volume flow.

Sketch both arrows and label this a stipulated example, not a finding from the Argo profile. If the warmer branch instead travels south and the cooler branch north, the implied net heat transport reverses under the same assumptions. A map of temperatures without motion information would not select between these two cases.

A numerical refresher makes the missing quantities concrete. Assume uniform velocity perpendicular to a section is 0.10 m/s and section area is 200 m². Multiplying gives volume transport 20 m³/s: meters per second times square meters leaves cubic meters per second. Doubling the area doubles transport at that stipulated velocity. Real sections generally require combining velocities across varying depths and positions; one temperature/salinity profile supplies none of those velocity samples.

Repair the conveyor shortcut

NOAA’s ocean-current explanation connects circulation to multiple influences. Its global-conveyor overview also discusses mixing and wind-driven upwelling. Use the broad connection between surface and deeper waters without turning the picture into one permanent closed pipeline followed by every parcel.

Winds, buoyancy changes, rotation, boundaries and mixing interact. Water can branch, recirculate and exchange properties along its route. A density difference is not an engine that supplies a perpetual flow without energy transfers. The two-layer lab computes a static ordering under explicit assumptions; it does not calculate those pathways, a sinking speed or an overturning time.

Now repair this statement: “The upper model layer is heavier, so the float must travel south at a known speed.” Retain the valid part: the modeled ordering is susceptible to overturning in the simple no-forcing setup. Remove the direction and speed, which do not follow. The actual profile’s geography does not restore those missing measurements.

Choose evidence that matches the claim

For a local movement question, request direct water-velocity observations with depth and time context, or suitable displacement/time evidence with its sampling limits. For volume transport, request a defined cross-section and velocities across it. For a long-term change, request repeated, comparable observations over a justified period. These requests are different because their target quantities differ.

Keep the source’s good-data flags and unavailable error fields in the argument. Quality flags do not supply unreported velocities. Nor does adding more decimal places to the toy density result make it a validated calculation for the observed profile. Cite the INCOIS source for the actual record and identify your paper examples separately.

Transfer: change the coast and the ordering

Consider a fictional Southern Hemisphere coast with ocean to its west and land to its east. Assume idealized depth-integrated wind-driven transport is left of a northward wind. Is that transport offshore? Separately place water of density 1028 above water of density 1027 kg/m³ at common reference pressure. Explain the ordering without claiming either example determines an actual sinking rate.

Check the ocean-claims transfer

Left of north is west, so the stipulated transport is offshore for this coast; continuity can require replacement from below. The heavier upper layer is unstable in the simple density comparison. These are separate bounded arguments. Neither gives an actual vertical speed, and the transport assumption is not a universal surface-current direction or an equatorial rule. The disclosed solution is public practice, not independent mastery evidence.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Separate a fictional transport calculation, a controlled density comparison and the authentic profile.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Read a recorded ocean profile Next: Earth and space science and next units

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