Water properties and transports of abyssal water through the Wake Island Passage

Water mass characteristics and volume transports of northward flowing abyssal water into the Wake Island Passage in the North Pacific Ocean were examined by carrying out high quality hydrographic surveys in May 2003, October 2004 and December 2005 along with mooring observations from May 2003 to December 2005. A fairly tight and linear relation between potential temperature (θ) and properties (salinity, dissolved oxygen and silicate) is seen below θ ~ 1.1°C (~ 4000 m), meanwhile the relationship above θ ~ 1.1°C is scattered and can be divided into relatively salty, oxygen-rich and silicate-poor south part and the opposite north part. The results suggest that a boundary of water masses lies at θ ~ 1.1°C in the deep passage and the abyssal water below the boundary flows northward. In addition to the three hydrographic sections, two hydrographic sections previously conducted in the deep passage in 1975 and 1999 are reexamined for transport estimates. Geostrophic calculations relative to θ = 1.1°C surface indicate northward transports of the abyssal water from 0.5 to 2.2 Sv. The abyssal water temperature colder than 1.1°C is found to be increased by 0.012°C on the average between 1975 and 2005. The warming is greater than double standard deviation from the temporal mean temperature profile obtained from mooring observation from May 2003 to October 2004.