The Puerto Rico Trench is part of a dynamic area, known as the Antilles subduction zone. The oceanic crust of the North American Plate is actively subducting under the Caribbean Plate, resulting in volcanic activity that created many of the islands making up the Caribbean. This North American oceanic crust is formed in the center of the Atlantic Ocean as part of the mid-Atlantic Ridge. In a process known as seafloor spreading, the oceanic crust moves (at a speedy rate of 25 km per million years) from its point of creation outwards. Eventually, the crust ends up close to the Caribbean Plate, where it begins to descend back into the hot mantle. However, during this dual motion of subduction and spreading, the crust gets pulled in two different directions, causing it to tear and reveal interior crustal rock that is rarely exposed.

Frieder Klein, a geochemist at WHOI, is hoping to utilize this exposed rock to answer important questions about long-term oceanic processes. Together with an international team and underwater vehicles like Sentry and Alvin, he hopes to see how oceanic crust is formed at the mid-Atlantic Ridge and how it gets altered by hydrothermal fluids and cooler seawater over millions of years. The chemicals involved in these crustal alterations, including magnesium and calcium ions, have important implications for understanding long-term chemical cycling in the ocean. Other species, such as alkalinity and carbon dioxide, will provide insights into the ocean’s capacity to deal with our current climate crisis.