Ocean currents and cetacean migrations

Natural motorways of the ocean

The SOFAR channel carries blue whale song over 1,600 km. The Humboldt Current feeds the cetaceans of Peru. This database lists the major oceanographic phenomena directly linked to the distribution of cetaceans.

To go further

Oceanography structures the lives of cetaceans: annual migrations, thermal preferences, acoustic propagation (SOFAR) and climate change.

Ocean currents: the motorways of cetaceans

Cetaceans make use of the major ocean currents as so many biological motorways. The Gulf Stream and the Kuroshio border productive thermal fronts where fin whales gather. The Humboldt Current (Peru, Chile) sustains the upwelling that feeds the krill and concentrates blue whales and sperm whales.

At depth, the SOFAR channel (Sound Fixing And Ranging), the layer of minimum sound speed between 600 and 1,200 m, allows the songs of blue whales and fin whales to carry over hundreds and even thousands of kilometres. It was in this channel that the mysterious 52 Hz whale was first detected, in 1989, by the hydrophones of the United States Navy.

Map of ocean currents worldwide: speed, seasons and years

The currents named above are not abstractions: they can be measured. The map below draws on the Global Drifter Program, that is, thousands of drifting buoys tracked by satellite since 1979. These are not model outputs but trajectories actually travelled. Three entry points are offered: the 46-year mean, the seasons, and ocean currents year by year from 1995 to 2025.

128,437cells measured

0.09 m/smedian ocean speed

1.50 m/smaximum : Gulf Stream

1.4 %of the ocean above 0.5 m/s

Speed and streamlines: two readings of the ocean currents

Two readings of the same velocity field. Speed shows where the ocean really moves: the scale is a square root, without which 99% of the surface would have the same tint. Streamlines traces the path that a float released at sea would follow, which matches the idea of an ocean highway.

Period

Moyenne annuelle. Grille au demi-degré, 46 ans de bouées moyennés. Les saisons sont données dans leur sens boréal : dans l'hémisphère sud, elles sont inversées.

Mean speed:0.05 m/s0.15 m/s0.30 m/s0.60 m/s1.20 m/sArrows above 0.30 m/s

The map zooms with the scroll wheel and pans by dragging.

Ocean currents season by season: the monsoon reverses the Somali Current

La plupart des grands courants marins changent peu au fil de l'année. Le Kuroshio, south of Japan, goes from 0.66 m/s in boreal summer to 0.54 m/s in winter: the circulation is there all year round. The Gulf Stream behaves in the same way.

The Indian Ocean is the exception, and it is the most spectacular reversal on the map. Off Somalia, around 52 degrees east and 7 degrees north, the current sets vers l'est à 0,54 m/s en été boréal, driven by the south-west monsoon, and vers l'ouest à 0,35 m/s en hiver, under the north-east monsoon. It is also there that the highest speed in the whole ocean in summer is found, at 2.15 m/s, whereas in the annual mean that maximum belongs to the Straits of Florida. This reversal drives the Somali upwelling, one of the most productive in the world, and hence the seasonal presence of the baleines bleues of the north Indian Ocean population.

Take care when reading the selector: the seasons are named there in their boreal sense. In the southern hemisphere, “summer” means the months of June to August, which are winter there.

Ocean currents year by year, from 1995 to 2025

The selector offers two things of different kinds. The climatologie moyenne 46 ans de bouées sur une grille au demi-degré : elle est pleine, lisse, et montre la circulation permanente. Une year is reconstructed from the trajectories of that year alone, aggregated to 2 degrees. It is full of holes, faster in appearance because the eddies have not had time to cancel out, and that is precisely why it is interesting: it keeps what the mean erases.

Un exemple. Dans le Pacifique équatorial central, entre 170 et 120 degrés ouest, le courant porte vers l'ouest presque toutes les années, de 20 à 40 cm/s. Deux années s'inversent nettement et portent vers l'est : 1997, at 27 cm/s, and 2015, at 6 cm/s. These are the two major El Niño events of the series. The trade winds weaken, the warm water piled up in the west flows back towards South America, and the upwelling of cold water that feeds the whole food chain of the eastern Pacific stops. A third year, 2021, also stands out towards the east, but on 349 records against 5,706 in 1997: that is sampling noise, and that is the honest limit of the exercise. The coverage rate shown opposite each year serves exactly that: knowing what we are looking at.

Speed of the great ocean currents: Gulf Stream, Kuroshio, Agulhas

Courant	Position	Speed
Straits of Florida, Gulf Stream	26°N 80°O	1,50 m/s
Agulhas Current	35°S 25°E	1,34 m/s
Gulf Stream, Cape Hatteras	36°N 73°O	0,83 m/s
Kuroshio, south of Japan	34°N 140°E	0,74 m/s
Equatorial Counter Current	6°N 150°O	0,32 m/s
South Equatorial Current	3°S 25°O	0,30 m/s
Median of the whole ocean	toutes zones	0,09 m/s

These are measurements, not a model. Elles viennent du Global Drifter Program : des milliers de bouées dérivantes suivies par satellite depuis 1979, moyennées par la NOAA et l'université de Miami sur une grille au quart de degré. Les zones sans couleur sont celles où aucune bouée n'est passée. Les cartes année par année ne viennent pas de cette climatologie, qui n'a pas d'axe de temps : elles sont reconstruites à partir des trajectoires brutes au pas de six heures, du même programme et sous la même licence. Données sous licence Creative Commons Attribution 4.0, via le serveur ERDDAP de l'AOML. Fond de carte Natural Earth, domaine public.

What the map teaches, and what it corrects

The first lesson is an order of magnitude. The median speed of the surface ocean is 0.09 metres per second, a third of a kilometre per hour. Only 1.4% of the surface exceeds 0.5 m/s. The image of an ocean crossed by powerful rivers is therefore misleading: most of it moves very slowly, and the great currents are narrow exceptions.

The second is that these exceptions are concentrated along the western boundaries of the oceans. The Florida Strait reaches 1.50 m/s and the Agulhas Current 1.34 m/s, the two highest values in the dataset. This western intensification is a consequence of the Earth’s rotation, and it explains why the fin whale and the other large cetaceans gather along these fronts, where the meeting of waters of different temperatures concentrates the prey.

The third concerns the areas left without colour. They do not mean that the water there is motionless, but that no buoy has passed through. That is the honest limit of observational data, and it echoes what our map of sightings at sea already says: a map of measurements shows the sampling effort as much as the phenomenon.

To take this further, the page on Crozet and Kerguelen details the Antarctic Circumpolar Current and its fronts, and the one on thermal and bathymetric preferences links these structures to the distribution of species.