Observed deep anticyclonic cap and its geological effects over Caiwei Guyot

Caiwei Guyot (1308~5600 m) in the Northwest Pacific is one of the most watched Co-rich crust contract areas nowadays. Based on 3-year in-situ data during 2012-2015, the detailed structure of a deep anticyclonic cap and its geological effects were observed over Caiwei Guyot. With depth-dependent physical settings, the deep anticyclonic cap comprised an anticyclonic circulation (with time-averaged current reaching 2.5 cm/s) varying significantly with episodic cap shedding at the summit, a cyclonic circulation (0.7 cm/s) situated above an anticyclonic circulation (0.9 cm/s) at the slope, and a stable but highly asymmetric anticyclonic circulation (4.9 cm/s) at the foot. This anticyclonic cap extended from 900-m depth to 5588-m depth. In contrast to a classic anticyclonic cap where the cold-core occurred above the summit center, an anomalously colder ring above the summit rim was observed, which was associated with anticyclonic cap shaped by guyot terrain. The Taylor cap dynamics can explain much of three-layer structure of the anticyclonic cap. Moreover, apparent correlation of M₄ tide and time-averaged current indicated that rectification of M₂ tide also played an important role in cap generation at the summit. Finally, inside the anticyclonic cap, the combination of enhanced flow with scalar-averaged speed reaching 10.1 cm/s at the summit rim, on-slope flow, and secondary vertical circulation was verified to induce thicker sediments (~100 m) at the summit center as well as abundant Co-rich crusts and sediment ripples along the rim. It revealed that dynamics of the anticyclonic cap can significantly modulate Co-rich crusts distribution.