Ocean Literacy · Gulf Stream

An Unexpected Gulf Stream: Warm Water on the New England Shelf and in the Arctic

Rob Moir traces the Gulf Stream’s wandering path from a warm-water surprise on the New England shelf to Svalbard’s fjords and the opening of the Arctic sea routes.

By Rob Moir | Ocean River Institute

In the fall of 2011, three offshore lobstermen observed something bizarre about 150 miles south of Point Judith, Rhode Island, far out on the continental shelf and about 25 miles from its outer edge. The seawater was a clearer blue than the familiar gray green. Grabbing the pot buoy, they found the water surprisingly warm. The trap stayed put. The boat drifted. The line angled away from the boat. There was a strong current.

They reported what they had found. Instruments already attached to lobster traps confirmed what the fishermen had sensed. Near-bottom temperatures had risen by more than 10°F.

A large meander of the Gulf Stream with an “unusual tilt in [its] path” was confirmed by scientists at the Woods Hole Oceanographic Institution using sea surface temperature imagery, satellite altimetry, and a surface drifter track. The Gulf Stream was an unprecedented 125 miles north of where it is traditionally. The current was flowing on top of the continental shelf far off Nantucket Shoals and Block Island South.

By the time the Gulf Stream passes south of New England, its upper flow carries roughly 70 million cubic meters of water each second. Depending on how its deep flow and recirculating waters are counted, the full current may exceed 100 Sverdrups. (One Sverdrup is one million cubic meters per second.)

Rather than flowing north in a straight line, the Gulf Stream swings in broad meanders. Some loops pinch off to form warm-core eddies that drift toward the continental shelf off southern New England. Meanwhile, the meanders themselves migrate, shifting position from month to month. The meander motion has been compared to a garden hose wriggling across the grass.

A garden hose lies still when the faucet is barely open. Turn up the flow, and it begins to sweep back and forth in ever-larger arcs. To understand why something meanders so dramatically, we should first look upstream to the faucet. Has the flow become less constrained? Have downstream conditions changed to favor larger-amplitude instabilities? Or is more water being funneled through a narrow passage? The faucet is the Straits of Florida.

To explain why the Gulf Stream might suddenly appear far north on the New England shelf, we look to the other end of its journey.

Warm water at Svalbard

As early as 2006, fishermen and scientists observed warm Gulf Stream water intruding and displacing the “local” cold water far to the north, on the west coast of the Svalbard Archipelago in the Greenland Sea, on the threshold of the Arctic Ocean. The process warmed the local fjords and microclimate. As sea-surface temperatures rose, glaciers on land began to retreat.

The Gulf Stream was first observed off Svalbard in 1810 by Captain William Scoresby. He was surprised to find water six to eight degrees Fahrenheit warmer at depths of 100 to 200 fathoms. Working from his whaling ship while it lay beset in the ice, Scoresby lowered a ten-gallon fir cask fitted with valves at each end that remained open during descent and closed during retrieval, trapping water from depth. Fir was chosen because it was light and a poor conductor of heat. Doubting the accuracy of a thermometer read on deck after the water was brought aboard, Scoresby mounted a recently invented Six’s thermometer, the ancestor of today’s familiar min-max thermometer, inside the cask. The U-shaped instrument recorded the water’s temperature at depth before it could warm on deck.

Scoresby had expected cold water. Instead, he discovered warm Atlantic water beneath the cold Arctic surface.

Two centuries later, Atlantic Water was appearing ever closer to the surface in Svalbard’s fjords. Had more warm Atlantic water begun reaching the Arctic? Had it risen closer to the surface? Or was something else happening?

The Arctic would answer.

Which passage opened first

As the sea ice retreated, a question pursued by generations of explorers became one of commerce: when would ships again be able to pass between the Atlantic and Pacific Oceans?

The Arctic answered sooner than many expected. In the summer of 2008, the Northeast Passage along Siberia became navigable, and 46 ships completed the transit. Two icebreakers had made the passage the previous year.

Which route should have opened first?

The answer seemed straightforward. Earth turns eastward. Water flowing north is deflected to the right by the Coriolis effect. Atlantic water entering the Arctic Ocean follows the coast of Norway and Siberia. NASA satellite imagery showed the retreat beginning along the Eurasian side of the Arctic Ocean. Open water spread across the first half of the counterclockwise Beaufort–Transpolar circulation while thick multiyear ice remained fast against the Canadian Arctic Archipelago.

Confident we understood Arctic Ocean circulation, we were surprised when, in 2008, 18 private yachts and commercial vessels completed the Northwest Passage despite persistent sea ice along Canada’s Arctic coast.

The explanation lay not in the ocean but in the geography.

The Northeast Passage closely follows the Arctic coastline. The Northwest Passage does not. Instead, it threads through the maze of channels carved into the Canadian Shield, crossing some of the oldest rocks on Earth, including nearly four-billion-year-old gneisses and granites. There, solar heating of the narrow waterways accomplished what warm Atlantic water could not. Sunlight finished opening the passage where ocean currents had left off.

Always in motion

The Gulf Stream remains a mystery, not because we know too little, but because it is always in motion. Three Rhode Island lobstermen noticed that change before satellites and drifting buoys explained it. Two centuries earlier, William Scoresby questioned his own measurement and, by improving it, discovered warm Atlantic water in the Greenland Sea. We better understand the Gulf Stream because people have inhabited its waters, questioned what they observed, and shared what they found. Nature continues to surprise us. That is not a failure of science. It is the reason science continues.

The 2011 Gulf Stream diversion is documented in Gawarkiewicz et al., Direct interaction between the Gulf Stream and the shelfbreak south of New England, Scientific Reports, 2012. Scoresby’s fir cask experiments are described at the Ocean River Institute.

About the author

Dr. Rob Moir is a nationally recognized and award-winning environmentalist. He is the president and executive director of the Ocean River Institute, a nonprofit based in Cambridge, MA, that provides expertise, services, resources, and information not readily available locally to support the efforts of environmental organizations.

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