Climate Regulators: The Role of Boundary Currents

If a large-scale circular gyre is constrained by the presence of a continent, then the flow must follow the edge of that landmass. If the water moves along the margins of the ocean basin, then it is classified as one of the boundary currents.

If the Earth's rotation causes water to pile up on the western side of ocean basins (Western Intensification), then the water must be compressed into a smaller area. If the water is compressed, then it must move with higher velocity and depth to transport the necessary volume.

If the Coriolis parameter increases as water moves toward the poles, then the clockwise or counter-clockwise flow of a gyre is skewed toward the west. This imbalance is what creates the distinct characteristics of western boundary currents.

If western boundary currents are intensified by planetary vorticity, then they are fast, deep, and narrow. If they originate near the equator, then they carry heat toward the poles; however, they are usually nutrient-poor compared to upwelling zones.

If a warm western boundary current moves from the tropics to a colder latitude, then the temperature difference between the water and the air is large. If heat is transferred to the overlying air masses, then those winds carry the warmth to nearby continents.

If equatorward winds move surface water away from the coast due to Ekman transport, then deep water must rise to replace it. Since eastern boundary currents flow toward the equator, they facilitate this upwelling of nutrient-rich water.

If scientists need to quantify the massive flow of currents like the Kuroshio or the Gulf Stream, then they use a standardized unit for volume flux. One Sv represents one million cubic meters of water passing a point every second.

If Western Intensification is caused by the eastward rotation of the Earth, then the eastern side of the basin does not experience the same pressure. If the water is not compressed against the land, then it spreads out and moves at a lower speed.

If a current flows along the eastern margin of an ocean basin (the west coast of a continent) toward the equator, then it is an eastern boundary current. The California, Canary, and Benguela fit this; the Kuroshio and Brazil are western currents.

If a cold current cools the air above it, then the air's ability to hold moisture decreases, causing condensation (fog). If this cool, stable air prevents the rising motion needed for rain, then the adjacent land remains arid.

If the planet's energy balance requires moving excess solar heat away from the tropics, then a physical mechanism is needed. If boundary currents on the western side of basins move poleward, then they serve as that distribution system.

If a fast-moving current like the Gulf Stream develops a meander or curve that pinches off, then it forms an isolated spinning pool of water. If these pools trap warm or cold water inside, then they are known as mesoscale eddies or rings.

If the Earth rotates and the Coriolis effect gets stronger near the poles, then water is forced westward. If wind provides the initial torque for the gyre, then these factors combined create the intensified western flow.

If a single western boundary current can transport over 100 Sverdrups (100 million m³/s) and the total discharge of all global rivers is only about 1.2 Sverdrups, then boundary currents are vastly more powerful.

If an eastern boundary current is driven by the Southeast Trade Winds and causes intense upwelling off the coast of Peru and Chile, then it is the Humboldt (or Peru) Current.

If cold boundary currents sink during thermohaline circulation or if warm currents move to areas where cooling occurs, then the solubility of CO2 changes. If the water sinks, then it carries dissolved carbon into long-term deep-sea storage.

If water piles up in the center of a gyre due to Ekman transport, it creates a pressure gradient. If the Coriolis effect balances the outward push of that pressure, then the resulting geostrophic flow defines the path of the boundary currents.

If the Coriolis effect deflects moving water to the left in the Southern Hemisphere, then the gyres will rotate counter-clockwise. If the rotation is reversed, then the boundary currents follow that reverse direction.

If we identify the poleward-flowing warm current on the western side of the South Atlantic gyre, then it is the Brazil Current.

If the tropics receive a surplus of solar energy and the poles have a deficit, then the planet would have extreme temperature gradients. If boundary currents move that energy from the equator to the poles, then they stabilize the global climate.