The is the lowest point in any ocean, eleven kilometers of water above a narrow trench floor, and the intuition is that water down there barely moves. Almost nobody has measured it, because the instruments that go that deep are rare. Jiang and colleagues sent two super-deep gliders down in September and October of two thousand eighteen and read the water properties on the way. What is the water doing?
Flowing west, and faster than expected. A westward dominates the deep layer, carrying about one and three tenths of volume transport and weakening gradually with depth. That is roughly twice what previous work estimated. The horizontal distribution of water properties forms three layers, turning from a northeast-southwest pattern to north-south and then to east-west as depth increases from three thousand to seven thousand meters.
Ocean circulation in the Challenger Deep is rarely investigated, for the obvious reason. Getting an instrument to the bottom of the deepest trench on earth and bringing data back is hard, so observations are sparse and the picture rests on very little.
Jiang and colleagues worked from hydrographic data collected by two super-deep Chinese Sea-Wing gliders during September and October of two thousand eighteen, analyzing water properties and circulation structure through the trench.
The horizontal distribution of water properties came out as roughly three layers, with the orientation of the pattern rotating as depth increases from three thousand to seven thousand meters. It runs northeast-southwest at the top of the range, then north-south, then east-west. That structure is a joint result of water uplift, advection and diffusion inside the trench.
The deep layer is dominated by a westward geostrophic flow, weakening gradually with depth and carrying about one and three tenths sverdrups of volume transport. That is twice the figure from previous studies. The authors suggest two reasons: temporal variation in how much intrudes from the Southern Ocean, and a different choice of reference level.
wat. Eleven kilometers down, the water is not sitting there. It is moving west, twice as hard as anyone had it.
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A trench is usually treated as a sink where water settles. A current twice the expected size makes it part of the circulation, which changes what reaches the bottom and how fast.
How do we know?
Jiang and colleagues analyzed hydrographic data collected by two super-deep Sea-Wing gliders in the Challenger Deep during September and October of two thousand eighteen.
What is still unknown
Two gliders over two months in one trench. The authors attribute the unexpectedly large transport partly to temporal variation and partly to using a different reference level, so the figure is not directly comparable with earlier ones.
Learn something?
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