Science for Brazil (Reino Unido)

Oceanographers probe climate secrets of South Atlantic

Publicado em 05 fevereiro 2014

Data gathered during the maiden international voyage of Brazil’s newest oceanographic research ship Alpha Crucis is helping unravel the secrets of the South Atlantic, and in future will perhaps explain this ocean’s role in global climate change.

A recent study published online in the Journal of Geophysical Research: Oceans (JGR) includes data gathered during the December 2012 cruise of Alpha Crucis along 35°S, a scientifically-significant line of latitude running between southern Africa and Latin America.

The study shows that the southern half of the Atlantic Ocean is receiving increasing volumes of water from the Indian Ocean, whose waters are not only warmer but also saltier than the waters from sub-Antarctic regions.

As the waters of the South Atlantic flow toward the north, they transport and release heat into the atmosphere at higher latitudes. As they become saltier and, consequently, heavier, they will tend to sink more rapidly before reaching the North Atlantic.

The resulting changes to the waters of the South Atlantic Ocean – which flow northward to the North Atlantic – could affect both the sub-Arctic regions and the waters of the North Atlantic.

This new research is part of a large-scale international project involving institutions from the United States, France, Brazil, South Africa, Argentina, Russia and Germany. The object is to study heat circulation in the area – South Atlantic Meridional Overturning Circulation (SAMOC).

The objective of SAMOC is to monitor the meridional flows and thermodynamic properties of bodies of water along latitude 35°S, which begins at the Chuí region in South America and extends to South Africa. According to Brazilian project coordinator Edmo Campos of São Paulo University’s Oceanographic Institute, researchers have christened the 35°S line “SAMBA [SAMOC Basin-wide Array.”

SAMBA is the southern gateway to a region through which the mixture of waters from the Indian and Pacific Oceans enters the subtropical region of the South Atlantic. To the north, a significant portion flows on to the North Atlantic as part of the Meridional Overturning Circulation (MOC).

Brazilian, Argentine and North American researchers assumed responsibility for monitoring the western part of the SAMBA line. Researchers in South Africa and France are studying the eastern region. A collaboration of the United States with other countries, including Brazil, is currently planning the implementation of the monitoring system for the central part of the line.

The participation of Brazilian researchers is funded by the São Paulo Research Foundation (FAPESP). Financing was agreed for a Thematic Research Project conducted under the auspices of the FAPESP Research Program on Global Climate Change and an agreement forged between the Pernambuco Research Foundation and the French National Research Agency (ANR).

In fact, Brazil is stepping up its aspirations in the sphere of oceanography. According to Edmo Campos, the objective is to take cover the entire extension of the SAMBA line and contribute data to international partners studying variations in the heat transportation system between the oceans, that can eventually have impacts on a regional and global scale.

The first experiments involving Brazilian participation in the project were conducted in late 2009 using the Brazilian navy’s oceanographic vessel Cruzeiro do Sul. However most field research at the Oceanography Institute had been at a standstill since 2008 when its Professor W. Besnard oceanographic vessel was destroyed by a fire.

Since then, however, there has been a significant upgrade with the acquisition of Alpha Crucis in 2012. The ship belongs to the Oceanography Institute at the University of São Paulo (IO – USP) and received the bulk of its funding from FAPESP. In addition, USP in September 2013 took delivery of the Alpha Delphini, a R$6 million purpose-built small survey vessel suitable for coastal waters that was also funded by FAPESP.

The 970 tonne, 64 metre Alpha Crucis was built for the US Navy and previously owned by the University of Hawaii, having been launched in 1974. The ship cost around US$7 million, before refitting. She can cruise for 40 days, making studies on the open ocean possible and broadening the geographical limits of research.

Furthermore, she has the most modern equipment, including multi-beam sonar capable of producing a three-dimensional map of the sea floor. She also has a dynamic positioning system, which allows the ship to maintain its position on oceanographic stations, an underwater profiler, two current profilers, winches and cranes that are suitable for several different tasks and more than 100 square metres of laboratory space, sufficient for the 20 scientific crew.

During its SAMBA cruise, Alpha Crucis laid a string of echo-sounders on the sea floor along the western end of the line. Called Current, Pressure Inverted Echo-Sounders (CPIES), the echo-sounders emit a sound signal in the direction of the ocean’s surface. Using the time the signal takes to reach the surface and return to the sea floor, researchers can infer the density and temperature of marine currents and, therefore, estimate the speed with which they transport heat.

In a separate project, since April 2013 Brazil has also shown its increased capacity to undertake remote monitoring of the ocean using automated buoys anchored in waters of the South Atlantic over 3,000 deep.

Designed and built in Brazil, the Atlas-B Guariroba is taking its place in another international project comparable to SAMOC. The equipment was built by a group of researchers at the USP’s Oceanography Institute (IO-USP). The buoy development project was led by Edmo Campos.

In the equatorial and tropical portions of the Atlantic Ocean between Brazil and Africa, this type of monitoring has been conducted using a series of North American-made buoys belonging to Projeto Pirata, a joint programme between France, Germany, and the United States. The subtropical portion, however, still needs attention—a gap that the buoy in question, the Atlas-B Guariroba, was developed to help fill.

For the layman, one of the most notable findings from the Alpha Crucis cruise and resulting JGR article is the truly massive scale of heat transfer taking place at the point where the world’s oceans mingle. The South Atlantic transports heat to the North Atlantic at a rate of 1.3 petawatts, which represents a quantity of energy equivalent to that produced by more than 200,000 large-scale hydroelectric dams.

No wonder, then, it can be hypothesized that any small change in this process of transporting heat could set off a series of consequences for the planet’s climate.

Click here to access JGR article. Temporal variability of the Meridional Overturning Circulation at 34.5°S: Results from two pilot boundary arrays in the South Atlantic. By E Campos and others.

Click here to read a complete article by Brazilian journalist Elton Alisson.