ENCurrents off the coast of northern Brazil can be used to study changes in the larger oceanic circulation pattern in the Atlantic, when variable winds in the regions are properly accounted for.
A sketch of the circulation pattern in the Atlantic Ocean. Credit: Böning/Scheinert (GEOMAR). Used with permission.
In the Atlantic Ocean, water circulates like a kinked conveyer belt through a mechanism called the Atlantic Meridional Overturning Circulation (AMOC), transporting heat and salt from the south to the north. Warm and salty water rushes into the Atlantic from around the tip of South Africa. Together with water that enters the Atlantic through the passage between Antarctica and South America, it travels across the hemisphere toward the Caribbean. In so doing, it concentrates along the northern coast of South America and follows the natural contour of the continents northward. It eventually reaches the northern North Atlantic, where it releases its heat into the air and sinks to the depths. From there, the water roughly retraces its path in the reverse direction along the ocean floor.
Scientists believe this movement of heat and salt through the Atlantic is a major controller of climate on Earth and thus are highly interested in forecasting changes in the circulation pattern. Off the northern shores of Brazil, the circulation is propelled by the aptly named North Brazil Current (NBC), which flows northwest along the country’s coastline. Here Rühs et al. investigate whether changes in the NBC can be linked to changes in the overall AMOC and thus perhaps climate as a whole.
Using a collection of computer models configured to recreate real-world conditions from the past 50 years, the researchers analyzed whether or not changes in the AMOC would manifest in the NBC as well. Their simulations show that perturbations to the AMOC are captured in the NBC but that much of the signal is masked by highly variable winds in the region that greatly influence the North Brazil Current.
Surface currents in the Atlantic Ocean—like those off the northern shores of Brazil—are heavily influenced by wind. For the most part, winds drive the formation of large-scale ocean gyres that govern the overall horizontal movement of ocean water on Earth, but they’re variable on various time scales The authors conclude that using the NBC as a proxy for understanding changes in Atlantic Ocean circulation will first require a way to remove wind-driven gyre variability from the equation. (Geophysical Research Letters, doi:10.1002/2015GL065695, 2015)
—David Shultz, Freelance Writer
