Lightning Lecture AMOS Annual Meeting and International Conference on Tropical Meteorology and Oceanography

Extreme temperatures in the Tasman Sea interior (#1002)

Gabriela G Pilo 1 , Neil N Holbrook 1
  1. University of Tasmania, Hobart, TASMANIA, Australia

Extreme temperatures can be defined as those exceeding the 90thpercentile threshold relative to climatology. In the Tasman Sea, between Tasmania and New Zealand, extreme sea surface temperatures were observed for ~250 subsequent days from September 2015 to May 2016. Regional surface waters during this ‘marine heatwave’ event reached up to 3oC above climatology, impacting local biological communities, fishing and harvesting practices, and marine aquaculture. While several studies characterise extreme temperatures in the ocean surface, extreme temperatures at subsurface are poorly understood. This knowledge gap is due, in large part, to limited subsurface observations. Here, we aim to characterise extreme temperature events in the Tasman Sea interior. We use output from the Ocean Forecasting Australia Model version 3 to identify and characterise temperature extremes between the surface and 2000 m depths. We show that extreme subsurface temperatures are characterised by different intensities, durations, and depth penetration. These differences might be linked to different drivers. We found that eddy and current-driven extreme temperatures tend to occur off Australia’s east coast, extending from the surface to 1500 m depth, are up to 3oC warmer than climatology at mid-depth (100-500 m), and typically last for up to 60 days. Atmospheric-driven extreme temperatures tend to occur over the entire Tasman sea. These extremes may extend from the surface to 150 m depth, are up to 3oC warmer than climatology, and typically last for 30 days. Extreme temperatures are also evident between 500 and 2000 m depths, in the centre of the Tasman Sea. At these depths, extreme temperatures are ~0.2oC warmer than climatology and can persist for over 400 days. The causes for these deep extreme temperatures are being explored. Characterising deep extreme temperatures is the first step to understand their drivers and potential impacts.