The Characteristics of Physical Oceanographic Environments and Bottom Currents in the KODOS Study Area of the Northeastern Tropical Pacific

Abstract : Hyrdography and deep currents were measured from 1997 to 1999 to investigate deep-seaenvironments in the KODOS (Korea Deep Ocean Study) area of the northeastern tropical Pacific. KODOSarea is located meridionally from the North Equatorial Current to the boundary between the NorthEquatorial Current and the Equatorial Counter Current. Strong thermocline exists between 10 m and 120 mdepths at the study area. Since that strong thermocline does hardly allow vertical mixing between surfaceand lower layer waters, vertical distributions of temperature, salinity, dissolved oxygen and nutrientsdrastically change near the thermocline. Salinity-minimum layer, which indicate the North PacificIntermediate Water (NPIW) and the Antartic Intermediate Water (AAIW), vertically occupies vertically atthe depths from 500 m down to 1400 m. The NPIW and the AAIW horizontally occur to the north and tothe south of 7 o N, respectively. The near-bottom water shows the physical characteristics of 1.05C and34.70 psu at the depths of 10 m to 110 m above the bottom (approximately 4000-5000 m), which wasoriginated from the Antarctic Circumpolar Water. It flows northeastwards for 2 to 4 months at the studyarea, and its mean velocity was 3.1-3.7 cm/s. Meanwhile, reverse (southwestward) currents appear for about15 days with the average of 1.0-6.1 cm/s every 1 to 6 months. Dominant direction of the bottom currentsobtained from the data for more than 6 months is northeastward with the average speeds of 1.7-2.1 cm/s.Therefore, it seems that deep waters from the Antarctica flow northwards passing through the KODOS areain the northeastern tropical Pacific.Key words : (KODOS), (the North Equatorial Current), (the EquatorialCounter Current), (thermocline), (deep waters), (the Antarctic CircumpolarWater)*Corresponding author. E-mail : hrshin@kongju.ac.kr