Spatial and Temporal Variability of the Volume Transport across the Indonesian Straits and Connections with the Indian Ocean Circulation

Author(s)

Bruno Castaldi

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto Oceanográfico (IO/DIDC)
• Defense date: 2018-09-21

Examining board members

Edmo Jose Dias Campos; Tercio Ambrizzi; Olga Tiemi Sato

• Advisor: Edmo Jose Dias Campos

Abstract

The global Meridional Overturning Circulation (MOC) plays a significant role in the Earth\'s climate system by redistributing all over the world the excess heat gained by Earth in low latitudes. In its superficial branch, warm waters are exchanged throughout the world\'s ocean basins. The Indonesian Throughflow (ITF) and the Agulhas Leakage (AL) are the main processes responsible, respectively, for importing Pacific Ocean waters into the Indian Ocean, and for exporting Indian Ocean waters into the Atlantic Ocean. Recently, changes in both systems have been reported and can be related to global warming consequences, processes of air-sea interactions and variabilities in the ocean circulation and wind patterns. In the present work, output of a high-resolution, global implementation of HYCOM (Hybrid Coordinate Ocean Model) from different runs were used, aiming at a study of the structure and variability of the ITF, and to evaluate the use of a numerical tool for tracking virtual Lagrangian particles to correlate circulation patterns of the ITF and the AL. For the ITF, analysis of the models\' output provided a mean volume transport in the upper 700 m depth of about 13 Sv, what is in the range of values reported by observations and other numerical simulations in the region. The seasonal variability was found to be related to the monsoons wind regimes, and the ITF\'s response to the El Niño-Southern Oscillation (ENSO) was evaluated. During five La Niña events, the mean volume transport was of approximately 16 Sv, and for also five El Niño events, of approximately 12 Sv. Results show an abrupt increase in the heat transport between 2002 and 2012, what could be related to changes in the heat content within the Indian Ocean for the same period. Heat transport anomalies were analyzed in the last years of the time series and present a clear correlation with Nino3.4 index, denoting a strong response of the ITF to the 2014/16 El Niño. Numerical test-experiments simulating Lagrangian particles have been performed, to identify and quantify water masses\' origins compounding the ITF and to correlate variabilities signals of ITF in the Indian Ocean\'s basin circulation and in the Agulhas Leakage. (AU)

• FAPESP's process: 14/02225-2 - Connections between Agulhas Leakage and the South America's Climate - a study using a Coupled Ocean-Atmosphere Model
• Grantee: Bruno Castaldi
• Support Opportunities: Scholarships in Brazil - Doctorate