Changes in the Gulf Stream
Crossing the Gulf Stream is a rite of passage for many East Coast offshore sailors. I’ll never forget my first time. The Stream seems to generate its own weather, and the precipitous clouds on the horizon ahead were the initial clue that we were approaching. Then there was the sudden spike in the temperature of the ocean, up into the high 70s, as confirmed by the boat’s seawater thermometer. The water itself shifted to a darker shade of blue, flecked with yellow patches of sargassum. And with a slight northerly breeze (thank God it was slight) leaning into the northward flowing current, the waves stood up into a progression of steep but reasonable, negotiable hills, the boat rising and falling with their flow. It was all very memorable. The Gulf Stream, the so-called “river in the sea” that trucks along in places at a good 4 to 5 knots, is truly a force of nature.
And, remarkably, it is also slowing down.
Such was the conclusion of a pair of recent scientific studies focused on the Atlantic meridional overturning circulation (AMOC) — an ocean circulation system that includes the Gulf Stream — recently published in the journal Nature. Simply put, a section of the warm, salty surface waters of the Stream eventually peel off to form the North Atlantic Current which ascends into the high, chilled Nordic latitudes, heating the atmosphere on the way. There, the water cools and the weight of its salinity causes it to plunge into the depths, where it begins a return journey down the coasts of North and South America. The entire cycle has been likened to an “ocean conveyer belt” that plays a key role in Earth’s climate by exchanging warm water from the equator with cold water from the Arctic.
And the conveyer belt, so crucial to distributing heat across the planet, is not as quick as it used to be.
According to the Nature report, the two studies that issued this finding used vastly different methodologies: “classic examples of ‘top-down’ and ‘bottom-up’ approaches.” The former based its report on direct measurements of sea-surface temperatures; the latter relied on measuring deep-sea sediment cores that reflect the speeds of the bottom waters on their