PLEA Network

6 June 2018, Climate Central, Global Conveyer Belt: Ocean Current Slowing. June 8 is World Oceans Day, a time to raise awareness about the importance of the oceans to our planet. Ocean currents and broader circulations move vast amounts of water around the world, redistributing heat and energy, and helping regulate the global climate. Wind-driven currents like the cold California Current and the warm Gulf Stream are drivers of local climates. But a larger ocean circulation caused by differences in temperature and salinity drives even greater amounts of water around the world. This thermohaline circulation, also known as the global ocean conveyor belt, involves both surface and deep water throughout the global ocean. But the conveyor appears to be slowing down. Fresh water from the melting Greenland ice sheet is running into the North Atlantic, decreasing the salinity of the ocean there so the water does not sink as much. Reconstructions from corals in combination with global simulations indicate the conveyor is slowing, with one estimate indicating a 15 percent slowing of the conveyor since the middle 20th century. This slowing circulation means less heat is transported into the North Atlantic, so the water there is colder, and this leaves the warmer water to dwell longer in the western Atlantic. The warming water can add additional fuel to coastal storms along the East Coast of the U.S., and its slower movement means higher sea levels there, as the slower speed effectively piles up water along the coastline. The conveyor also brings nutrient-rich water into the Atlantic from the deeper waters of the Southern Ocean, so the slowdown diminishes the supply of these nutrients that aid the growth of seaweed and algae, which are among the components at the base of the ocean food web. Read more here