By Maria Fernanda Ziegler | Agência FAPESP – Brazilian researchers are making preparations to monitor the response of the Atlantic Ocean to climate change. Equipment recently anchored at a depth of almost 4,000 km in the mid-ocean will detect variations in salinity, temperature and maritime current velocity.
The researchers will monitor changes in ocean circulation, which could have consequences for the planet’s climate system. In Brazil, sea levels could rise, and coastal rainfall patterns could be influenced by circulation changes, affecting agricultural production and urban life.
This is the first initiative to study circulation changes in the South Atlantic at strategic points so far from the mainland – in the case of Brazil, these points are 1,950 km from the coast.
The effort is part of the South Atlantic Meridional Overturning Circulation (SAMOC) Initiative, a project that involves researchers and institutions in the European Union, United States, Brazil, South Africa and Argentina. The Brazilian contribution is supported by FAPESP via a Thematic Project that follows studies that began in 2007. The initial stages of the SAMOC Initiative were supported by the US National Oceanic and Atmospheric Administration (NOAA) in cooperation with Argentina and Brazil.
The latest stage is the SAMOC Basinwide Array (SAMBAR), which is also supported by FAPESP under its Research Program on Global Climate Change (RPGCC). SAMBAR will investigate an important southern section of the SAMOC.
“Climate change has been studied largely on the basis of data collected in the atmosphere, but we’ve made far less progress in learning what happens in the oceans, which are the main regulators of Earth’s climate. This is because it is very hard to make measurements in places as remote as the sea bed and the middle of the ocean. The chance to use this equipment for over five years on the bottom of the South Atlantic is a major advancement,” said Edmo Campos, who is affiliated with the University of São Paulo’s Oceanography Institute (IO-USP) and is a principal investigator for the SAMOC Initiative on the Brazilian side.
The equipment for analyzing variations in salinity, temperature and ocean current velocity left Rio de Janeiro on January 15, 2019 on board the Antares, an oceanographic research vessel operated by the Brazilian Navy.
Twenty-two days and 3,105 nautical miles (5,589 km) later, on February 6, the ship docked at the Port of Itajaí in Santa Catarina State, South Brazil.
Equipment was dropped overboard at three remote points of the South Atlantic during the voyage: the Hunter Channel, 900 nautical miles south of Trindade Island; the Meso-Atlantic Ridge, 1,380 nautical miles southeast of the Brazilian coast and 300 nautical miles from Tristan da Cunha; and Vema Channel near the Rio Grande Rise.
Antarctic bottom water
According to Campos, studying the ocean at these points will both extend our knowledge of maritime circulation and climate throughout the planet and help us predict the impact of climate change in Brazil.
“The meridional overturning cell bears the warm surface water of the South Atlantic to the northern hemisphere. On the way back, saltier and hence denser water flows southward at greater depths,” he said.
A key part of this circulation, which the SAMBAR research group will study, is the mass of water coming from Antarctica. Known as Antarctic Bottom Water, this mass forms in the frozen continent and flows to deeper regions of the Atlantic, Pacific and Indian Oceans.
In the Atlantic, the main point of entry for this water mass is the Vema Channel at 30°S latitude. The channel is one of the few places in the South Atlantic with a depth great enough that the freezing and hence denser water coming from Antarctica is not blocked.
“Global warming tends to be slower in the oceans than in the atmosphere. The specific heat of approximately ten meters of water is equivalent to the specific heat of the entire atmosphere. The oceans hold such a vast amount of energy that change has to be slow,” said Mathias Campos van Caspel, a postdoctoral fellow with a scholarship from FAPESP and a chief scientist for the cruise to install the equipment in the ocean.
Any change in the oceans takes a long time to dissipate. “The impact is long-lasting, although recent studies have shown that changes in the oceans are occurring much faster than expected,” Caspel told Agência FAPESP.
Changes occurring in Antarctica can be inferred from analysis of Antarctic Bottom Water, he added.
“Antarctica is one of the first continents to undergo climate change. More directly, with regard to ocean circulation, when this mass meets the deep water of the North Atlantic, it makes the deep water rise in the water column. However, if volume or density changes occur during this interaction, the entire ocean circulation can be disrupted,” he said.
This system can change in various ways. For example, the density of the Antarctic Bottom Water and North Atlantic Deep Water masses may became similar because of glacier melting in Greenland or Antarctica.
“In that case, instead of losing depth, the masses would mix and change the path along which they circulate, with consequences for the deep ocean,” Caspel said. “Any change in this overturning cell may trigger changes in the rest of the system.”
Ocean circulation is not an isolated system. “Everything that happens in the Northern Hemisphere, the North Atlantic and Greenland, including glacier melting, is closely interconnected with what happens in Antarctica. Changes in any of these regions can cause changes along the coast of Brazil,” he said.
Role of the South Atlantic
Understanding what happens in the Atlantic is fundamental to interpreting the Earth’s climate. The Atlantic is the only ocean that transports heat from the southern to the northern hemisphere. In the other oceans, heat is transferred from the equator to the poles.
As Campos explained, the ocean and atmosphere together transfer surplus heat from the equator to higher latitudes, reducing temperature gaps.
“This peculiarity of the Atlantic may have an impact on the climate system, especially if more salt is transported from the South to the North Atlantic,” he said. “This mechanism works like a pump that transports about 1.3 petawatts of heat. Minor changes in heat transport can lead to dramatic climate variations.”
Although the South Atlantic is crucial to the entire Atlantic circulation, most ocean circulation monitoring studies have focused on the North Atlantic.
“To make climate predictions, it’s important to know a lot about what’s happening. There are global models that cover the MOC, but these models will be more trustworthy and complete if they take our measurements into account,” Caspel said.
The three sets of equipment are at more remote locations and are designed to last longer on the sea bed than other devices sunk in the Atlantic prior to the SAMOC Initiative.
“The most costly part of our expeditions is the time spent on the research vessel,” Caspel said. “The equipment has been anchored with a new technology called a Popeye Data Shuttle, which releases a buoy with monitoring data from the sea bed. The data will be transmitted to the researchers by satellite.”
The SAMOC team is one of the first to use this technology for scientific purposes. This means that they will not have to return every year to the sites of the devices in order to collect data. The scientists expect to start working on the first monitoring datasets in 2020.
In addition to the new equipment recently placed on the sea bed by Brazilian researchers, other devices will monitor ocean circulation farther east as part of another SAMBAR campaign involving researchers from South Africa, France, and other EU countries.
“We’re studying variability in the western portion of the South Atlantic with researchers from Argentina and the US. The other countries in the international consortium are focusing on the eastern portion. Each group is responsible for one side of the Atlantic, and we hope to be able to get together to do joint studies and publish collaborative articles,” Campos said.