A common misconception of Jules Verne’s landmark novel Twenty Thousand Leagues Under the Sea is that the title refers to the depth of the ocean. The ocean’s average depth is actually about 3.7 kilometers—less than 1 nautical league—but the titular 20,000 leagues is the total distance the crew of the Nautilus traveled horizontally.
More than a century after the book’s publication, scientists are still working to uncover the ocean’s deepest, darkest secrets. In a recent study, Kuwano-Yoshida et al. found that the impact of a certain type of cyclone can be felt at the bottom of the sea.
Cyclones of any sort are sure to make a splash, but those known as explosive, or “bomb,” cyclones are a unique breed. These nontropical cyclones are characterized by a quick drop in sea level pressure—at least 2400 pascals per day—and can produce strong winds, torrential rains, and other oceanic hazards. They seem to form in just a few regions around the globe: the northwest Pacific and northern Atlantic and scattered throughout the Southern Hemisphere.
To find out more about the ocean’s response to explosive cyclones, especially at deep levels, the team of Japanese researchers examined several decades of data from the North Pacific, using models to simulate the circulation of seawater.
To consider the impact of individual cyclones, they zeroed in on one case study: an explosive cyclone that developed over the North Pacific between 15 and 18 January 2011. The wind stress curl (the amount of stress inflicted on the surface of the ocean) strengthened quickly as the cyclone began to develop, and then, as the cyclone reached its peak, water at the bottom of the ocean (at depths of around 5.4 kilometers) began to flow upward. There, water temperature also cooled between the sea surface and about 5 kilometers deep.
These far-reaching (or, rather, deep-reaching) effects confirm our understanding that the ocean’s deepest depths can be affected by activity at the surface. (Geophysical Research Letters, https://doi.org/10.1002/2016GL071367, 2017)
—Sarah Witman, Freelance Writer