Do Winds Control the Confluence of Subtropical and Subantarctic Surface Waters East of New Zealand?

• Main Author: Fernandez, Denise
• Format: Thesis
• Language: unknown
• Published: 2012
• Subjects: Physical Geography and Environmental Geoscience not elsewhere classified; Fronts; Eddies; Subtropical-subantarctic confluence; School: School of Geography; Environment and Earth Sciences; 040699 Physical Geography and Environmental Geoscience not elsewhere classified; Marsden: 260403 Physical Oceanography; Degree Discipline: Geophysics; Degree Level: Masters; Degree Name: Master of Science; Antarctic; Curl; Marsden; New Zealand; Pacific; Soi; The Antarctic; Antarc*
• Online Access: https://doi.org/10.26686/wgtn.16998688.v1; https://figshare.com/articles/thesis/Do_Winds_Control_the_Confluence_of_Subtropical_and_Subantarctic_Surface_Waters_East_of_New_Zealand_/16998688

The confluence region east of New Zealand is one of only a few places in the world where the Antarctic Circumpolar Current meets the strong southwardflowing boundary current of a subtropical gyre. The convergence of subtropical and subantarctic water creates strong fronts. The fronts have clear signatures in height and temperature that make them appropriate places to investigate ocean/climate variability. The location and extent of the New Zealand confluence should respond to changes in large-scale wind patterns, as changes in South Pacific currents have been linked to wind shifts. However, recent studies have shown that highly energetic eddies, local winds, and the bathymetry may be significant controls of currents and associated fronts. This thesis investigates the temporal and spatial variability of the confluence and evaluates its response to variability in South Pacific winds. Analysis of the 18-year time series, from January 1993 to December 2010, of sea surface height mapped from satellite altimetry was used to investigate the location and extent of fronts and the eddy activity and relate these to the wind forcing. Wind stress data were used with the Island Rule to estimate the winddriven transport of the western boundary currents that feed the confluence. In addition, the climate modes Southern Annular Mode (SAM) and Southern Oscillation Index (SOI) were used to examine the influence of the principal modes of atmospheric variability. Time series of the local wind stress curl and local climate indices were calculated and compared to the intensity of the confluence to test any influence of local forcing. In addition, bathymetric effects were investigated by evaluating evidence for preferred front locations near topographic features. Sea level anomalies in the confluence region are increasing at 3.4 cm decade⁻¹. The sea surface height gradients and the eddy kinetic energy are also increasing at a rate of 0.01 cm km⁻¹ and 23 cm² s⁻² per decade respectively, indicating an intensification of the fronts and ...