HR: 0800h
AN: OS41B-0533    [Abstracts]
TI: Southwest Pacific Subtropical Mode Water: a Climatology
AU: * Holbrook, N J
EM: neil.holbrook@mq.edu.au
AF: Division of Environmental and Life Sciences, Macquarie University, Sydney, NSW 2109, Australia
AU: Maharaj, A M
EM: angela.maharaj@mq.edu.au
AF: Division of Environmental and Life Sciences, Macquarie University, Sydney, NSW 2109, Australia
AB: The large scale distribution and changes in southwest Pacific Subtropical Mode Water (STMW) are investigated and discussed. The paper presents geographic maps showing the spatial distribution of STMW thicknesses, with a vertical temperature gradient <2.0°C/100m occupying the 14°-20°C range below the mixed layer depth, across the entire southwest Pacific region. STMW changes in areal thickness extent, vertical cross-sectional area along selected transects, and total volume, are examined on seasonal and interannual time scales between 1973 and 1988. We find that STMW extends across the entire width of the Tasman Sea in a very broad swath between the Tropical Convergence in the north (just to the south of New Caledonia), the southeast Australian coast in the west to as far south as 39°S (likely due to the southward extension of the EAC), and eastwards along the southern STMW boundary in a meandering pathway that broadly follows the Tasman Front. The total STMW volume across the region (i.e., west of 180°) varies seasonally by a factor of more than three between the estimated maximum of 6.6 \( ± 0.5 \) × 10¹⁴ m³ in October and minimum of 1.9 \( ± 0.4 \) × 10¹⁴ m³ in May. Interannual variations O(± 0.5 × 10¹⁴ m³) are also observed in the spatial extent of the thick Mode Water and its total volume. El Niño composite maps show an anomalous thickening of the STMW during the El Niño year with October positive thickness anomalies in excess of +20m (total volume anomaly of +0.6 × 10¹⁴ m³) manifested throughout the subtropical gyre interior as far north as New Caledonia. Total volume anomalies tend to be positive from January of the El Niño year through to the July following (18 months). The maximum correlation coefficient r = -0.3 between three-monthly STMW volume anomalies and the Southern Oscillation index is statistically significant at the 95% confidence level. We conclude that during the anomalous cooling of the upper southwest Pacific Ocean in the El Niño year, winter-time convection and STMW formation is enhanced across the region resulting in an El Niño - Southern Oscillation climate signal that is identifiable below the mixed layer by the increased STMW volume which persists through to the following winter.
DE: 4215 Climate and interannual variability (1616, 1635, 3305, 3309, 4513)
DE: 4223 Descriptive and regional oceanography
DE: 4283 Water masses
DE: 4522 ENSO (4922)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting