Interannual bottom pressure changes in the Arafura Sea and the remote influence of equatorial Pacific winds

Author: Rui M. Ponte, Christopher Piecuch and Katherine J. Quinn
Date: 
December 6, 2012
Type: 
Presentation
Venue: 
AGU Fall Meeting 2012
Citation: 

Rui M. Ponte; Christopher G. Piecuch; Katherine J. Quinn (2012) Interannual bottom pressure changes in the Arafura Sea and the remote influence of equatorial Pacific winds. AGU Fall Meeting 2012, San Francisco, CA.

Ocean bottom pressure (OBP) is a crucial quantity for understanding changes in ocean circulation and climate, yet general knowledge of its regional variability on climate timescales is lacking. General circulation modeling studies suggest that interannual OBP changes can contribute importantly to low frequency variability in shallow shelf regions, but this suggestion has not been investigated using observations. Taking advantage of recently released ocean mass data from the Gravity Recovery and Climate Experiment (GRACE) as well as an ocean general circulation model, we investigate the nature of interannual OBP variability in the Arafura Sea between Australia and Papua New Guinea. In this region, time series from model and data agree very well (correlation coefficients >0.9), attesting to the presence of OBP variations of order 1 cm sea level equivalent with long periods (>1 yr) over large spatial scales (>750 km). These OBP changes explain most of the interannual sea level variance in this region. Moreover, these interannual OBP time series are significantly correlated with ENSO indices (correlation coefficients >0.8), suggesting ties to broader scale climate variability. Through numerical forcing experiments, we demonstrate explicitly that the OBP changes in the Arafura Sea derive mostly from remote wind forcing over the equatorial Pacific, with local wind driving playing only a minor role. A mixture of equatorially- and coastally-trapped waves is likely involved in what is primarily a baroclinic response to remote winds that leads to a strongly barotropic signal in the shallow Arafura Sea. These results suggest meaningful low frequency signals reside in GRACE data and encourage the further use of GRACE fields for investigations of regional oceanic variability on climate timescales.