Melting of the Greenland ice sheet, formation of sea ice and flow of the Gulf Stream
Hammered by rising sea levels, extreme weather events and increasing ocean acidity, headlines talk about climate change giving the ocean another punch. “Crucial ocean current system weakens” or “Critical ocean system could be on the verge of collapse due to climate change” or “Climate crisis: Scientists spot warning signs of Gulf Stream collapse Are just a few of these titles. Yet as sure as the sun rises in the east, the world turns. At the equator, the planetary rotation is 1,000 miles per hour, resulting in a flow of westerly winds and ocean currents across the Atlantic from the Azores to Brazil. The current extends to the Gulf of Mexico in the northern hemisphere.
The body of water moves clockwise around the gulf. At the Florida Keys, the current enters the Florida Strait. A strait is a narrow channel of water that connects two large bodies of water. Seawater first races between Florida and Cuba, then between Florida and the Bahamas. Much of the water in the Gulf of Mexico, water native to Africa in a worldwide circulation, is thrown through the 59-mile-wide narrows and into the Atlantic Ocean. To dissipate some of the excess energy, the Gulf Stream behaves a bit like when a mountain river hits a plain or when a train crashes sending wagons zigzagging in all directions. The Gulf Stream winds, forming large east and west loops on its winding northward journey.
After Newfoundland, part of the Gulf Stream diverges north to the Arctic Ocean to cause a gyre rotating counterclockwise. Part of the Gulf Stream tilts southeast to become the Azores Current, completing the North Atlantic gyre known as the Atlantic Meridional Turning Circulation (AMOC).
The Atlantic circulation has been well known for centuries. Columbus sailed the Azores Current to the equatorial drift towards the New World. Benjamin Franklin described the Gulf Stream. So, it comes as no surprise to most when the United Nations Intergovernmental Panel on Climate Change concluded in its 2019 report that while AMOC will “very likely” weaken later this year. century, the collapse is “very unlikely”.
Recent headlines from The Flickering and Stopping Gulf Stream were based on two articles in Nature. A report looked for fingerprints in the massive amount of data coming from buoys, drones, dinghies and satellites. Through model simulations, a spatial and seasonal ‘fingerprint’ characteristic of sea surface temperature ‘was calibrated. Evidence has been found of seawater temperature changes suggesting cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region. Therefore, they conclude that their results are consistent (although not necessarily causal) with the southern Atlantic overturning circulation having record values over the past 150 years out of 1600.
The other study looked at water temperatures and mapped thermoclines in the Labrador Sea. The researchers also examined the size of sortable silt grains in two sediment cores under seawater flowing to the southern Labrador Sea off Cape Hatteras. Evidence has been found indicating that the Labrador Current has weakened over the past 150 years. Modeling studies have shown that increasing freshwater flows over a few decades could weaken the current. Further examination revealed discrepancies between model data and high variability with an unknown number of factors at play in the Labrador Sea, where the West Greenland Current becomes the Labrador Current. More research is needed to improve the accuracy of the projected changes.
Greenland meltwater is feared to be a massive volume of fresh water inhibiting the flow of the Gulf Stream. Extreme warming in Greenland reached a new high on August 14, 2021, when it rained over the highest point of the Greenland ice sheet and air temperatures remained above zero for about nine time. Such hot and humid weather set in Greenland in 2019, 2012, 1995 and once in the late 1800s.
The meltwater sparkles an azure blue spread over the white glacial ice. Widespread surface melt is easily mapped and measured from satellites. It is not known how much of this puddle of fresh water on the ice will freeze when the weather cools. Probably less than 50% flows. If the drainage was more efficient, the meltwater would not collect on the surface. The ice cap recedes as it melts, exposing land that becomes lush with vegetation. Melt water seeps into the soil and is returned to the atmosphere.
It is possible that modelers overestimate the volume of freshwater entering Greenland and underestimate the strength of this global current called ‘flow’. The Gulf Stream is stronger than the Mississippi, Nile, Danube, Amazon, and all the other freshwater rivers in the world combined. The Gulf Stream moves nearly four billion cubic feet of water per second, nearly 300 times faster than the typical flow of the Amazon River.
Mariners off Brazil have been surprised to find fresh water in the ocean more than 40 miles from the coast. The less dense water of the Amazon River gushes over the salt water. The researchers hypothesize that fresh meltwater covers the Arctic Ocean and Greenland Sea and that this will slow down the thermohaline circulation of water masses with different temperature and salinity profiles.
In June 2019, I empirically verified the hypothesis by going for a swim to taste the surface water in southeast Greenland next to the world’s largest waterfall. Between Iceland and Greenland, in the Demark Strait, jets of cold, nutrient-rich arctic water flow through the straits. Here it collides with warm, nutrient-poor Atlantic water. The denser arctic water plunges to 11,500 feet to form the East Greenland Current.
Tasiilaq, Greenland is surrounded by rugged mountains. Through the vertical rocky cut, house-sized icebergs drift, circle the bay and drift. The watershed that flows into Tasiilaq is large and includes the Greenland ice cap behind other mountains. In the large crucible, I climbed down the ship’s ladder with strict instructions from the captain to keep my head above the water. Throwing into the cold water in the company of icebergs, I fired three shots and three shots back. The taste sparked memories of swallowing unwelcome mouthfuls of seawater in Nantucket Sound. The familiar salty taste was that of the Atlantic Ocean, 36 parts per thousand salt. Clearly, not the Mediterranean Sea which contains 40 parts per thousand of salt, nor the brackish waters of estuaries. Definitely not fresh. Despite the proximity of melting ice and icebergs, there was no freshwater lens over this part of the Greenland Ocean.
Locked in our technologies, it is nearly impossible to understand the enormity of the ocean, the landmass of Greenland (ten times the size of Britain), the workings of colossal ecosystems and the interlocking complexity of ocean kingdoms. In the past, only about a third of the Arctic Ocean was free of sea ice at the end of summer.
Currently, sea ice is melting, revealing more than two-thirds of the Arctic Ocean. When winter returns in October, there is now twice as much frost in open water. When sea ice forms, it is fresh water. When water freezes, it becomes a more ordered state and releases energy in the form of latent heat. The salt is concentrated in the cold water of the cradle. It becomes the densest seawater in the world and sinks. It is this process, in the Arctic and around Antarctica, that drives the thermohaline circulation of the global ocean. A drifting buoy submerged in the Gulf Stream will travel around the world in about 1,000 years.
In 2011, the Gulf Stream meandered far across the continental shelf, closer to Rhode Island than ever before, indicating more energy to dissipate.
In 2007, the Gulf Stream surfaced in Svalbard, a Norwegian archipelago on the threshold between the Atlantic and Arctic Oceans. The heat of the Gulf Stream is now melting the glaciers of Svalbard. The warmer Atlantic water flows into the Arctic Ocean as an intermediate current. This is a positive feedback loop that accelerates the melting of sea ice in the surface waters of the Arctic Ocean.
Global warming is the process by which greenhouse gases retain the energy of the planet. The reflected heat returns to the blue planet. As the water heats up, it expands and the sea level rises. Of all the water in the world, less than 2% is ice. Melt water will be responsible for less than 1% of sea level rise over the next hundred years.
Locally, when we increase soil depth, increase the amount of vegetation and reduce storm runoff, reduce the volume of wastewater discharged into the ocean, researchers have found indications that the rise in the level of the sea. sea can be reduced by up to 25%. Water vapor is the biggest greenhouse gas. Better we manage water cycles will have profound benefits in locally protecting homes against extreme weather events and significant effects globally reducing the harmful effects of greenhouse gases.
Climate change has increased thermal energy to the ocean. This manifests as more intense storms with record amounts of precipitation. Hurricanes passing over ocean waters, in just 24 hours, amplify from Category 4 to Category 5 (with four times the storm power). The increase in energy in the ocean by climate change also strengthens the Gulf Stream.
Dr. Rob Moir is a nationally recognized and award-winning environmentalist. He is President and Executive Director of the Ocean River Institute, a non-profit organization that provides expertise, services, resources and information not available locally to support the efforts of environmental organizations. Please visit www.oceanriver.org for more information.