The motto of oceanography should be: “It’s not that simple.”
Dallas Murphy wrote that in a book containing his reflections from numerous voyages with ocean scientists, entitled Follow the Water: Exploring the Sea to Discover Climate. The author goes on to say:
“One reason why the ocean has been left out of the climate-change discussion is that its internal mechanisms and its interactions with the atmosphere are stunningly complex. That the ocean has been left out has helped pitch the discussion toward unproductive, distracting extremes–either global warming is bunk or sea levels are about to rise twenty feet–and to frame the issue as a matter of opinion, like the place of prayer in public schools.”
He also quotes respected Oceanographer Carl Wunsch: “One of the reasons oceanography has a flavor all it’s own lies in the brute difficulty of observing the Ocean.”
A previous post on the Climate Water Wheel referred to the metaphor of the ocean serving as a thermal flywheel in our planetary climate due to the massive storage of solar energy in bodies of water. Another post provided some basics on the dynamics of sea ice.
Now, in keeping with the motto above, we shall see that indeed, it is not that simple when we look more closely inside the Arctic Ocean. For example, consider this map from Woods Hole Oceanographic Institution (WHOI):
“Follow the water: Cold, relatively fresh water from the Pacific Ocean enters the Arctic Ocean through the Bering Strait. It is swept into the Beaufort Gyre and exits into the North Atlantic Ocean through three gateways (Fram, Davis, and Hudson Straits). Warmer, denser waters from the Atlantic penetrate the Arctic Ocean beneath colder water layers, which lie atop the warmer waters and act as a barrier preventing them from melting sea ice.
Once in the Arctic Ocean basin, the water is swept into a mammoth circular current—driven by strong winds—called the Beaufort Gyre (BG). Mighty Siberian and Canadian rivers also drain into the gyre to create a great reservoir of relatively fresh water. Winds trap this water in a clockwise flow, but periodically, the winds shift and the gyre weakens, allowing large volumes of fresh water to leak out. This is “the flywheel,” said WHOI physical oceanographer Andrey Proshutinksy, and when it turns off, fresh water flows toward the North Atlantic.
The water exits the Arctic Ocean via several “gateways.” It can flow through the Fram Strait, between northeast Greenland and Svalbard Island, and then branch around either side of Iceland. It can flow around the west side of Greenland through Baffin Bay and out Davis Strait. It may also flow through a maze of Canadian islands and out Hudson Strait.
These gateways are two-way: They also let in the warmer Atlantic waters that—if not for the halocline—could melt Arctic sea ice.”
The BG Flywheel System
The research indicates that the complexity can be imagined as a series of flywheels, interacting and combining to moderate the short term effects of weather and changes in circulations of water and winds. Note that this conception shows the ocean flywheel as having four components or layers that operate in their own patterns while being interconnected.
And, as the flywheel system depicts, the ocean components are stratified by both temperature and salinity (saltiness). When sea ice forms, it releases salt into surface waters. These waters become denser and sink to form the Arctic halocline, a layer of cold water that acts as barrier between sea ice and deeper warmer water that could melt the ice. (Illustration by Jayne Doucette, WHOI)
More from WHOI:
Summarizing several hypotheses introduced recently in the publications mentioned above we conclude that the oceanic BG is a major part of the Arctic climate system and is responsible for:
a) Stabilization of the anticyclonic circulation of sea ice and upper ocean layers
b) Accumulation and release of liquid fresh water and sea ice from the BG
c) Ventilation of the ocean in coastal polynyas and openings along shelf-break
d) Regulation of the circulation and fractional redistribution of the summer and winter Pacific waters in the Arctic Ocean
e) Regulation of pathways of the freshwater from the Arctic to the North Atlantic
The sea ice flywheel is an intermediate link between the atmosphere and ocean. Also, sea ice is a product of the atmosphere and ocean interactions. It transfers momentum from the atmosphere to the ocean modifying it depending on sea ice concentration, thickness and its surface and bottom roughness and regulates heat and mass exchange between the atmosphere and ocean. Sea ice flywheel of the system is responsible for:
a) Regulation of momentum and heat transfer between the atmosphere and ocean
b) Accumulation and release of fresh water or salt during melting-freezing cycle
c) Redistribution of fresh water sources through involvement of the first year ice from the marginal seas into the BG circulation and keeping it there for years and transforming it into highly ridged and thick multi-year ice under converging conditions of the BG ice motion.
d) Memorizing of the previous years conditions and slowing down variations in order to avoid abrupt changes
e) Protection of ocean from overcooling or overheating (the latter is extremely important for polar biology)
Our planet’s climate has changed so little over thousands of years that alarms have been sounded over less than 1 degree celsius of estimated average warming since the Little Ice Age ended 150 years ago. But actually, our Modern Warming period was preceded by the Medieval Warm period, the Roman, and the Minoan Warm periods. Each of them was slightly cooler than the previous, and all of them warmer than now.
If you are looking for explanations why our moderate climate persists over millennia and varies only within a tight range of temperatures, give a thought to the role of the Arctic flywheel system.
Of course, even this is far from the whole story. As the map above shows, there’s lots more than the Beaufort Gyre going on. For example, the Transpolar Current drives flows of ice and water on the European side, in addition to the Beaufort Gyre acting on the North American side.
And despite the emphasis above on the Pacific water, the Atlantic Gulf stream supplies most of the water entering the Arctic.
“The Arctic Ocean is permanently supplied with new water from the Gulf Current, which enters the sea close at the surface near Spitsbergen. This current is called the West Spitsbergen current. The arriving water is relatively warm (6 to 8°C) and salty (35.1 to 35.3%) and has a mean speed of ca. 30 cm/sec-1. The warm Atlantic water represents almost 90% of all water masses the Arctic receives. The other ~10% comes via the Bering Strait or rivers. Due to the fact that the warm Atlantic water reaches usually the edge of the Arctic Ocean at Spitsbergen in open water, the cooling process starts well before entering the Polar Sea.”