With the increase in greenhouse gases from human activity as well as the thinning of the ozone layer over Antarctica, winds over the Southern Ocean are increasing in strength. As they travel across the ocean surface they cause turbulence leading to mixing that penetrates to the mid-depths of the water column. Warmer surface water penetrates deeper into the ocean’s mid-depths and mixes with the colder dense water found near the sea floor. This means the entire water column is warming and that leads to thermal expansion which has only one way to go, and that is up. Hence sea level rise.
It is an autonomous underwater vehicle that is 3.62 meters (11.8 feet) in length, weighs 700 kilograms (over 1,500 pounds), can dive to 6,000 meters, (almost 19,700 feet) and has a mission range of 2,000 kilometers (approximately 1,200 miles). The mission it undertook is part of a joint project with the University of Southampton, Woods Hole Oceanographic Institute, British National Oceanography Centre, British Antarctic Survey, and Princeton University.
What Boaty is telling us is that climate models looking at ocean impacts need revision.
States Dr. Elenor Frajka-Williams, from the National Oceanography Centre in a news release this week, “The data from Boaty McBoatface gave us a completely new way of looking at the deep ocean—the path taken by Boaty created a spatial view of the turbulence near the seafloor.”
Professor Alberto Naveira Garabato, University of Southampton’s project leader, is quoted stating “Our study is an important step in understanding how the climate change happening in the remote and inhospitable Antarctic waters will impact the warming of the oceans as a whole and future sea level rise.”
The results of the mission are described in the June 17, 2019 issue of the journal, Proceedings of the National Academy of Sciences (PNAS). In the article entitled, “Rapid mixing and exchange of deep-ocean waters in an abyssal boundary current,“ it describes this previously undocumented mixing mechanism and the boundary currents that transfer heat from above into the deep ocean. These abyssal currents convey warmer surface water below ocean mid-depths. Boaty observed them as it descended into the ocean depths and cruised along for more than 180 kilometers (112 miles), a mere 90 meters (295 feet) above the ocean floor.
When you heat freshwater from room temperature to the boiling point it undergoes thermal expansion, increasing in volume by 4%. This is the same phenomena that occurs in a mercury thermometer when you have a fever and take your temperature. The heat from your mouth or other orifices causes the mercury in the tube to expand and rise.
Freshwater has a lower specific gravity than seawater. So thermal expansion in it increases even more than the 4% described above.
Then there is the consideration of how warmer water impacts surface ice and the continental ice shelves of Antarctica which lie partially over the Southern Ocean. In the past decade we have observed several large ice shelves in Antarctica fracture and break up because of warming ocean water undermining and eroding the ice shelves lying above.
Boaty’s first mission will prove to fill a critical knowledge gap in our understanding of the heating of the global ocean and will alter the modeling we currently use to forecast the impact of atmospheric warming and increased winds on the world’s oceans.
When you look at the picture below it is hard to imagine that in this environment anything could change. But the tens of thousands of years of accumulation of snow and ice that created Larsen C may be coming to an end.
The latest research done by the British Antarctic Survey combines satellite and radar telemetry from multiple installations on the ice surface and indicates Larsen C has lost 4 meters (over 13 feet) of ice thickness and seen its surface sink by one meter (39 plus inches) between 1998 and 2012. The erosion of the ice is not just happening because of a warming atmosphere which has increased 2.8 Celsius (5 Fahrenheit) degrees over the last five decades, but also from a warming ocean invading beneath the ice shelf.
Larsen C covers 48,600 square kilometers (18,765 square miles) and reaches a thickness of 350 meters (approximately 1,150 feet) on average. it is bigger than the states of Connecticut and Rhode Island combined, and yet as Antarctic ice shelves go (based on what you see on the map below), is far from being the biggest.
The British study entitled, Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning, which appears in the science journal, The Cryosphere, indicates a growing crack through the entire shelf. Combined with the undermining by a warmer ocean and thinning of the ice volume the shelf may soon float above a subsea ridge that currently acts as a dam to hold it in place. When that happens and not if, researchers forecast a significant calving event with as much as 12% of the shelf plunging into the ocean. That will be far more spectacular than what was witnessed with the earlier collapses of Larsen A and B. And if the entire ice shelf collapses within the next few decades estimates are that it will add about 10 centimeters (3.93 inches) to global ocean sea levels. Although that may not sound like much, for low lying coastal communities it could be the difference between staying dry or being inundated. Combined with accelerated melting from Greenland and other Antarctic ice sheets and describing it as “the tip of the ice berg” seems apt.
For those who are climate change skeptics, weather stations in March of this year reported the highest daytime temperature ever recorded on the Antarctic Peninsula. The site – Argentina’s Marambio Base, an islet off the coast. The reading – 17.5 Celsius (63.5 Fahrenheit) degrees. That temperature was recorded at the end of the Antarctic summer and surpassed the previous record dating back to 1961. Yes, it’s only weather and weather is not the same as climate change, but when you combine it with the evidence of ice shelf thinning on the Peninsula’s largest remaining ice shelf, it is not hard to connect the dots.
