Estimating ocean mixing from widely available temperature and salinity data (Argo floats)

What is it about?

Ocean ventilation is vital in the climate system, transferring fluid and properties from the surface to the ocean interior. Yet, the ways in which stirring and mixing modulate ventilation are poorly understood, due to the sparseness of small-scale ocean observations. By applying a novel approach to the widely available Argo floats, the global network of autonomous profiling instruments, we diagnose stirring and mixing processes in the subtropical North Atlantic over a recent decade. Our results reveal a shift after 2018, with mesoscale stirring becoming more dominant in response to a major cooling and freshening event. The enhanced stirring dampens temperature and salinity contrasts, thus distributing the effects of externally forced, large-scale changes across the North Atlantic.

Featured Image

Photo by Irene Demetri on Unsplash

Photo by Irene Demetri on Unsplash

Why is it important?

Our results show that ocean mixing and stirring play a critical role in spreading and dampening large-scale climate signals across the North Atlantic. Direct measurements of ocean mixing are scarce, which has long limited our understanding of these processes. We present and ground-truth a method that overcomes this gap: using temperature and salinity observations that are already widely available, it estimates how much irreversible mixing occurs along density surfaces (isopycnal, driven by stirring) and across them (diapycnal). The approach we present here can be applied directly to globally available finescale ocean data, offering a powerful tool for characterizing how stirring and mixing vary in space and time, and for assessing their impact on the distribution of temperature, salinity and other tracers throughout the global ocean.

Perspectives