Ocean Mixing Barrier Shown: Dye experiment maps slow downward transport; layered structure limits exchange

In a striking ocean experiment, scientists released 75 kilograms of rhodamine dye into the Atlantic Ocean south of Martha’s Vineyard, Massachusetts, to watch how water moves and mixes beneath the surface. The experiment, conducted on August 16–17, 2018, showed that the dye spread readily within the ocean’s upper mixed layer but crossed into the denser water below far more slowly, according to a study published in Continental Shelf Research on ScienceDirect. The findings offer a detailed glimpse into a part of the ocean that is constantly being stirred by winds, waves and currents, and show just how strongly the ocean’s structure can limit movement between its layers.Why release dye into the ocean?The experiment was not intended simply to watch a colourful plume drift through the sea. The researchers were using rhodamine, a neutrally buoyant chemical tracer, as a marker for a parcel of seawater.The release took place about 28 kilometres south of Martha’s Vineyard. Scientists pumped roughly 130 gallons of a rhodamine-ethanol mixture into the water from the research vessel R/V Connecticut, with the mixture designed to have approximately the same density as the surrounding near-surface...