ENSO to multi-decadal time scale changes in East Australian Current transports and Fort Denison sea level: Oceanic Rossby waves as the connecting mechanism Neil J Holbrook a,n , Ian D Goodwin b , Shayne McGregor c , Ernesto Molina d , Scott B Power e a School of Geography and Environmental Studies, University of Tasmania, Hobart, Tasmania, Australia b Department of Environment and Geography, Macquarie University, Sydney, New South Wales, Australia c International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii, USA d Antarctic Climate and Ecosystems CRC, University of Tasmania, Hobart, Tasmania, Australia e Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Victoria, Australia article info Article history: Received 15 June 2010 Accepted 15 June 2010 Available online 1 July 2010 Keywords: East Australian Current El Nin ˜ o – Southern Oscillation Inter-decadal Pacific Oscillation sea level Rossby waves reduced-gravity model abstract The connection between East Australian Current (EAC) transport variability and Australia’s east coast sea level has received little treatment in the literature. This is due in part to the complex interacting physical processes operating in the coastal zone combined with the sparsity of observations available to improve our understanding of these possible connections. This study demonstrates a statistically significant (at the 490% level) relationship between interannual to decadal time scale variations in observed estimates of the EAC transport changes and east coast sea level measured at the high-quality, long record Fort Denison tide-gauge in Sydney Harbour, Australia (33151 0 18 00 S, 151113 0 32 00 E). We further demonstrate, using a linear reduced-gravity ocean model, that ENSO to decadal time-scale variations and the ocean-adjusted multi-decadal trend (approx. 1 cm/decade) in observed sea level at Fort Denison are strongly connected to modulations of EAC transports by incoming westward propagating oceanic Rossby waves. We show that EAC transport and Fort Denison sea level vary in a manner expected from both Tasman Sea generated Rossby waves, which account for the interannual and multi-annual variability, and remotely forced (from east of New Zealand) Rossby wave connections through the mid-latitudes, accounting for the ocean-adjusted multi-decadal trend observed at the New South Wales coast – with the regional-Tasman Sea forcing explaining the greatest overall proportion of EAC transport and sea-level variances. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction The South Pacific poleward-flowing western boundary current – the East Australian Current (EAC) – plays an important role in climate changes in the southwest Pacific. For example, the timing and intensity of EAC changes have been shown to influence both regional climate (e.g., Sprintall et al., 1995) and east coast lows (severe weather events) along the east Australian coast (Hopkins and Holland, 1997). While EAC changes might be expected to affect sea-level changes along the east coast of Australia, the relationship between EAC boundary current dynamics and coastal sea level has received little treatment in the literature. This is due in part to the complex interacting physical processes operating in the coastal zone combined with the sparsity of observations available to examine these connections. At the large scale, there is a clear connection between sea-level gradients (in space and time), upper ocean circulation and large- scale ocean wave dynamics (e.g., Chelton and Schlax, 1996; Qiu and Chen, 2006; Dohan et al., 2009; Send et al., 2009). Identifying the mechanisms that connect sea level with upper ocean dynamics is not only beneficial to our understanding of oceanic changes but also potentially beneficial for ocean forecasting. Nevertheless, quantifying these mechanisms and connections is challenging. For example, the quantification of sea level and heat content variations and trends globally with heterogeneous datasets is an ongoing challenge that demands careful analysis and consideration (e.g., Church and White, 2006; Domingues et al., 2008; Lyman et al., 2010; Trenberth, 2010). Continuous sea- level histories (time series) prior to 1950 are also globally sparse, and are largely based on palaeo-climatic and palaeo-sea-level indicator records and a relatively small number of centennial length tide-gauge records around the world. In Australia, the longest relatively continuous high-quality instrumental sea-level histories are provided by the tide-gauge records at Fort Denison (in Sydney Harbour, on the east coast; Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsr2 Deep-Sea Research II 0967-0645/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr2.2010.06.007 n Corresponding author. Tel.: + 61 0 3 6226 2027; fax: + 61 0 3 6226 628. E-mail address: Neil.Holbrook@utas.edu.au (N.J. Holbrook). Deep-Sea Research II 58 (2011) 547–558