Freshening anomalies in the Indonesian throughflow and impacts on the Leeuwin Current during 2010-2011

Abstract

During the 2010–2011 La Nina and Ningaloo Nino, excessive precipitations in the Maritime Continent and Indonesian-Australian Basin caused surface waters to freshen by 0.3 practical salinity unit in the southeast Indian Ocean. The low-salinity anomalies are observed to be carried westward by the Indonesian throughflow and the South Equatorial Current and transmitted into the poleward flowing eastern boundary current, the Leeuwin Current, along the Western Australian coast. Low-salinity anomalies contribute to about 30% of the anomalous increase of the southward Leeuwin Current transport during the evolution of the 2010–2011 Ningaloo Nino, resulting in unprecedented warming off the coast of Western Australia. Episodical freshening of the Leeuwin Current has been observed at the Rottnest coastal reference station of Western Australia during extended La Nina conditions over the past several decades; low-salinity anomalies at the station during the 2010–2011 Ningaloo Nino are comparable with strong historical events.