Three-layer circulation in the world deepest hadal trench.

Area of Science:

• Oceanography
• Deep-sea exploration
• Fluid dynamics

Background:

• The Challenger Deep (CD) is the world's deepest hadal trench.
• Ocean circulation and water mass transport in the CD are poorly understood due to sampling challenges at extreme depths.

Purpose of the Study:

• To investigate the ocean circulation structure and Lower Circumpolar Deep Water (LCDW) transport within the Challenger Deep.
• To elucidate the factors influencing deep-sea hydrodynamics in hadal trenches.

Main Methods:

• Deployment of an extra-deep current meter mooring array in the Challenger Deep.
• Analysis of collected oceanographic data to determine current patterns and water mass movement.

Main Results:

• A distinct three-layer circulation system was identified in the CD.
• The layers consist of a westward LCDW flow, a cyclonic circulation, and an anticyclonic circulation.
• The westward flow exhibits seasonal reversal, indicating bidirectional deep-sea basin connectivity.

Conclusions:

• The three-layer circulation is modulated by LCDW intrusion, local topography, and turbulent mixing.
• Turbulent mixing is a key driver of the anticyclonic circulation.
• Findings enhance understanding of the hydrodynamic environment in Earth's deepest oceanic regions.