Currents

Measurements Impacts Beyond the Gulf References

What are currents?

Ocean currents are the continuous flow of water along a path. Flow direction and intensity depend on: (1) wind speed and direction, (2) the spinning of Earth, (3) landmasses (e.g., continents, islands, undersea ridges) that are "in the way" of current flow, and (4) the density of the water mass. Together with atmospheric flow, ocean currents regulate Earth's temperature: cooler water flows towards the equator and warmer water flows towards the poles.

Gulf of Maine currents

The current patterns in the Gulf of Maine are greatly affected by the physical characteristics of the gulf and its coastline. Although currents change seasonally, here's how they generally flow:

currents
  1. Cold water enters the gulf over the Scotian Shelf, Browns Bank and through the Northeast Channel.
  2. Once in the gulf, water flows around Nova Scotia and into the Bay of Fundy.
  3. The coast then deflects currents southwestward...
  4. ...forming the Gulf of Maine Gyre, which rotates counterclockwise, moving surface waters about 7 nautical miles per day.
  5. Tidal fluctuations and shallow water over Georges Bank form a secondary, clockwise-spinning gyre.
  6. Water leaves the gulf through the Great South Channel and over the eastern portion of Georges Bank.

It takes about three months for surface water to completely circle the Gulf of Maine. Deep waters also circulate, but much more slowly, taking about a year to complete the circuit. Freshwater river input from more than 60 rivers along the coastline contributes to circulation in the gulf.

What does GoMOOS measure?

GoMOOS instruments measure surface current speed and direction at a depth of 2 meters. On most buoys, currents are measured through the whole water column at 4 meter intervals. Current speed (expressed in knots, miles per hour, and kilometers per hour) and current direction (expressed in compass degrees) are measured for 1 minute. These speeds and directions are then averaged to obtain that hour's readings.

Impacts of currents

East CoastCurrents affect the marine environment by moving bodies of water with different temperatures, salinities, or nutrient levels to new areas. The Gulf Stream is a good example: this mighty current moves warmer, more saline water from the equator up the east coast of the United States. In the satellite image at right, the Gulf Stream is clearly visible as a band of warmer water (red colors) that flows into the cooler northern Atlantic Ocean (green colors).

Given that currents affect temperature, salinity, and nutrients, they are key to the growth and survival of marine organisms. Moreover, many organisms depend on currents for locomotion. For example, planktonic organisms go wherever currents take them. On the other hand, strong swimmers may use currents to their advantage, "riding" them to conserve energy.

Beyond the Gulf: Global currents

global currentsSurface currents generally move warm water from the equator toward the poles and cool water from the poles toward the equator. Their paths are deflected by continents and the Coriolis force which contribute to the formation of large mid-ocean gyres. In the Northern Hemisphere these gyres rotate clockwise; in the Southern Hemisphere they rotate counterclockwise. Deep water currents also help regulate Earth's climate; however, their movement is driven by density which is controlled by temperature and salinity.

References