Intermediate and deep water formation in the Okinawa trough
Document Type
Article
Date of Original Version
1-1-2013
Abstract
Water mass formation in the intermediate and deep layers of the Okinawa Trough is investigated using two distinct data sets: a quasi-climatological data set of the water properties of the minimum salinity surface produced from Argo float profiles and historical CTD data, and a velocity data set in the Kerama Gap measured by moored current meters during June 2009 to June 2011. The formation process of Okinawa Trough Intermediate Water is explained on the basis of horizontal advection and mixing of North Pacific Intermediate Water (NPIW) and South China Sea Intermediate Water (SCSIW). The salinity-minimum water intruding into the Okinawa Trough through the channel east of Taiwan is approximately composed of 45% NPIW and 55% SCSIW, while that through the Kerama Gap is 75% NPIW and 25% SCSIW. Salinities of these water masses increase in the Okinawa Trough due to strong diapycnal diffusion; its coefficient is estimated as 6.8-21.5 × 10-4 m2 s-1 based on a simple advection-diffusion equation. On the other hand, deep water in the Okinawa Trough, below the sill depth of the Kerama Gap (∼1100 m), is ventilated by overflow in the bottom layer of the Kerama Gap down to the deepest layer (∼2000 m) in the southern Okinawa Trough. A simple box model predicts that this bottom overflow (0.18-0.35 Sv) causes strong upwelling (3.8-7.6 × 10-6 m s-1) in the southern Okinawa Trough, which must be maintained by buoyancy gain of the deep water due to strong diapycnal diffusion (4.8-9.5 × 10-4 m2 s-1). Key Points The Kerama Gap bottom overflow causes the deep ventilation in Okinawa Trough Salinity minima are attenuated by strong diapycnal mixing in Okinawa Trough Okinawa Trough is an upwelling area of North Pacific Intermediate Water © 2013. American Geophysical Union. All Rights Reserved.
Publication Title, e.g., Journal
Journal of Geophysical Research: Oceans
Volume
118
Issue
12
Citation/Publisher Attribution
Nakamura, Hirohiko, Ayako Nishina, Zhaojun Liu, Fumiyo Tanaka, Mark Wimbush, and Jae Hun Park. "Intermediate and deep water formation in the Okinawa trough." Journal of Geophysical Research: Oceans 118, 12 (2013). doi: 10.1002/2013JC009326.