SCIENCE · INVESTIGATE AND EXPLAIN

Connect winds, boundaries and surface currents

Separate moving water from wind and wave-pattern motion while tracing momentum transfer.

Learning outcome: Explain why a wind arrow alone does not determine an ocean current.

Starting recap

Wind stress, rotation, pressure and basin boundaries influence motion; the density lab supplies no current velocity.

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

Try

A stipulated uniform 0.20 m/s water velocity for 30 minutes gives 360 m displacement.

Open the experiment

Predict

Must a wave crest, air and a floating marker move in the same direction?

Your prediction and reason

Experiment

Draw separate wind, wave and water arrows; compare hemisphere/coastline sketches and identify unmeasured current quantities.

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

Follow the water rather than a passing crest

Imagine watching a wave crest travel across the sea while also tracking a floating marker. Those are different observations. A current is directed movement of water; a propagating surface-wave pattern is not itself a map of the water’s net transport. Water particles can move back and forth or in orbits as waves pass, while currents and wave-related drift can also contribute to their net motion.

Draw three arrows on paper: wind in the air, movement of a wave pattern, and transport of water. Label each before comparing their directions. Neither a wave photograph nor a wind arrow alone determines the complete current. A real floating marker may also be pushed directly by wind, so it is not automatically a perfect water-following instrument.

Transfer momentum across the surface

Wind exerts stress on the ocean surface and transfers momentum to the water. Stress means force per area. The resulting motion depends on more than the instantaneous direction of the wind: rotation, pressure differences, friction, changing conditions and boundaries all matter.

NOAA Ocean Exploration’s current explanation identifies wind, density differences and other influences, including the effects of landforms. Our mechanism sketch is original and qualitative. It is not an observed current map or a solver for a particular wind event.

Use an ideal map with a straight coastline. Draw an alongshore wind, then a separate water-transport arrow with its assumptions labeled. Moving surface water away from a coast can be associated with replacement from below; moving it toward a coast can produce a different adjustment. These are continuity arguments in a bounded setting, not a guarantee that every shore has the same current pattern.

Include rotation and the basin boundary

In the rotating frame, Coriolis deflects moving water to its right in the Northern Hemisphere and left in the Southern Hemisphere. The direction is relative to motion. Pressure gradients and boundaries help organize currents into basin-scale patterns, while the coastline and seafloor constrain possible pathways.

Do not replace this explanation with “water always travels directly with the wind.” Nor should a simplified arrow angle be treated as a universal observed angle. Different depths and changing conditions can have different velocities. The current’s speed and direction are physical quantities that need observations or a suitable dynamical model.

For a paper calculation, prescribe a uniform eastward water velocity of 0.20 m/s for 30 minutes. Convert 30 minutes to 1800 seconds; displacement is 0.20 × 1800 = 360 m east. This is conditional constant-velocity arithmetic, not a forecast produced by the lab. Reversing the velocity reverses displacement; doubling duration doubles it only if the prescribed velocity persists.

Connect surface transport with density processes

The shared lab addresses a different but related question: whether one illustrative water layer is lighter or heavier than another at a common reference pressure. It does not calculate wind stress, current velocity, transport volume or a trajectory. Changing a temperature or salinity control should not be interpreted as directly commanding a surface current.

Heat exchange and freshwater changes can alter density contrasts. Winds and mixing also matter to deeper circulation and to the return of water toward the surface. NOAA’s conveyor overview includes wind-driven upwelling and mixing alongside density-linked motion. Treat the conveyor image as an organizing metaphor, not a single closed perpetual pipe with every parcel following the same route.

Make a two-column ledger: mechanism illustrated here and quantity still unmeasured. Put wind stress and rotation in the first, and the actual local velocity field in the second. For density, put relative layering tendency in the first and overturning time or global circulation strength in the second.

Transfer: distinguish three reported motions

An unfamiliar report observes eastward-moving wave crests, a wind from the west and a marker displaced 100 m north. It concludes that the marker measurement must be wrong. Explain why the observations need not identify the same motion and name an additional useful measurement.

Check the ocean-surface transfer

Wave-pattern propagation, air motion and net marker transport are different quantities. Currents, wave-related drift and direct wind effects on the marker can contribute differently. A suitable water-velocity measurement at stated depth, together with marker and wind context, could test the interpretation. The qualitative sketch alone cannot reject the displacement or supply a complete current field.

Apply

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

Distinguish a mechanism sketch from a measured current field or a perpetual conveyor.

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: Defend limits and transfer Next: Compare temperature and salinity contributions

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