Investigating decadal and interannual variation in the eastern South Pacific with a numerical model

Repeat hydrographic observations along three sections in the eastern South Pacific (ESP) indicate that substantial changes in the hydrography, and by implication in ocean circulation and water mass formation, have occurred in this region over the last 30 years. In addition, recent current mooring observations off central Chile document strong interannual variability of current and temperature in the ESP. Although several mechanisms have been suggested for the observed changes, including global warming, a weakening of the subtropical gyre in the South Pacific and El Niño-La Niña events, the observational data alone is insufficient to resolve this issue. It is important to understand the nature and causes of ongoing change in the ESP since ocean processes there strongly influence local climate as well as circulation and water mass formation in the global ocean.

As one approach toward this goal, we have developed and applied a three-dimensional numerical ocean model to the ESP. This model extents from the coast of Chile to 105ºW, and from 15ºS to 55ºS and has a resolution of 0.5º by 0.5º. Along the three open boundaries the model is restored to WOCE hydrographic data. With the model we have been able to produce a circulation and tracer distribution in the ESP which is consistent with recent observations. By perturbing this model we are able to investigate mechanisms which have a possible role in driving the observed changes.