SEAFRAME time series from the Southern Shelf reveal a neglected major upwelling mechanism

ABSTRACT

In this era of climate change, it is important to have a reference state. For this purpose, an array of 12 port-based SEAFRAME gauges was established by Professor Geoffrey Lennon, through the Flinders University of South Australia, around the Australian coastline between 1991 and 1993. In addition to changes in sea level, they also record air and water temperature and wind velocity. We provide a method to extract the daily temperature anomaly between atmospheric and oceanic temperature recorded in the SEAFRAME gauge system. Thus, a fine-resolution record of the coastal ocean temperature structure can be obtained, which is a direct index of the vertical coastal heat flux that characterises both downwelling and upwelling. Results are presented for four gauges on the Southern Shelf for 2005, and for the ocean temperature anomaly time series during 2001–2010 at Portland, which monitors the structure of the Bonney Coast upwelling. This time series is also compared with that from an ECMWF model, and with that at Esperance which monitors an upwelling of similar strength on a wider shelf. The analysis reveals a second upwelling process in addition to the Ekman upwelling, which we have called the Flinders upwelling. The Ekman upwelling is due to a vertical velocity at the base of the mixed layer. The Flinders upwelling is due to a vertical velocity at the top of the mixed layer, which has been previously ignored. Along the Southern Shelf, the SEAFRAME data suggest that the Flinders upwelling is the dominant process.

KEYWORDS:

• Ocean temperature
• SEAFRAME tide gauges
• heat flux
• Flinders Current
• Southern Australian upwelling

Acknowledgments

We would like to thank Ann Gargett, David Bowers, John Church and Hugo de Oliveira for interactive discussions during the preparation of this paper, and also two reviewers for several encouraging and useful critical comments. This paper is dedicated to Geoff Lennon whose untiring efforts were responsible for the establishment and maintenance of the SEAFRAME array.

Disclosure statement

No potential conflict of interest was reported by the author(s).