August 13, 2021 | Published by | ,

The ocean extremes research program is underway with regular meetings, split between marine heatwaves meetings on the first Friday of the month and ocean biogeochemistry meetings every fortnight.

We have also been engaging externally with industry stakeholders and our peer networks. Pete Strutton met with the Tasmanian Department of Primary Industries, Parks, Water and Environment to develop a student project on aquaculture water quality; Katrin Meissner presented a talk, The climate has always changed – so why are we concerned now? at the joint meeting of mining geologist groups, SMEDG/AIG/GSA; and Denisse Fierro Arcos presented How a marine biologist uses statistics in her work in Spanish at the online conference Women in Data Science (WiDs) Ecuador.

Meanwhile, our researchers have been producing some fascinating results. In an effort to understand future changes they assessed the average state of ocean temperature and trends around the Antarctic margin in a suite of coupled climate models. Ocean warming around the Antarctic coast plays a critical role in melting Antarctic ice shelves, so understanding future changes in Antarctic shelf warming will help determine future changes in both ice shelves and ice sheets. The projections suggest the ocean around Antarctica will warm under future emission scenarios, with the level of warming under the high emission scenario almost double that under the medium-low emission scenario. This warming is due to both wind-driven circulation changes, and to ocean warming to the north of coastal regions.

The oceans team has also found that climate change has already led to profound, previously undetected changes in ocean eddies. They discovered through satellite measurements evidence that ocean eddies are becoming more energetic over large regions of the ocean. Ocean eddies are whirlpools with sizes between 10 and 100 kilometres across, somewhat like cyclones in the atmosphere. They are responsible for the “weather” in the ocean, moving warm and cold water from one location to another. In this way, eddies move and mix heat, carbon, salt, and nutrients and affect everything, from regional processes right up to the global ocean circulation. Ocean eddies play a profound role in both climate and ecosystems, regulating the mixing and transport of heat, carbon, biota, and nutrients, so the findings will have far-reaching implications for climate and fisheries.

Deep below the ocean surface, internal waves also have an impact on oceans, including the meridional overturning circulation which drives the worlds largest global currents. Major gaps exist in our understanding of the pathways between the generation and the breaking of internal waves in the Southern Ocean. This has important implications for the distribution of internal wave-driven turbulent mixing, for the sensitivity of ocean mixing rates, and for the representation of ocean mixing in numerical models. CLEX researchers used observations of internal waves from a turbulent mixing hotspot in the Southern Ocean, identifying and characterising internal waves and the background environment. They found the Antarctic Circumpolar Current strongly influences the life cycle of internal waves and suggest it is important to represent mesoscale flow impacts when parameterizing internal wave-driven mixing in the Southern Ocean.

These changes on the surface and deep below have a direct impact on ocean ecosystems as explored by CLEX researchers with colleagues in the Northern Hemisphere. They explored the main factors influencing zooplankton communities in the high latitudes around the Arctic. The strong seasonality in algal blooms results in a short and pulsed appearance of the large, predominately herbivorous zooplankton in surface waters during the spring.  However, the annual timing of the zooplankton ascent from their winter sleep at depth differs from year to year and among regions. The question was whether changes in the timing of algal blooms due to climate change are leading to a mismatch for seasonal zooplankton ascent and reproduction – an issue that may also impact Antarctic plankton. They found the future prospects of less sea ice and earlier onset of the algal bloom would likely be positive for both Arctic and boreal zooplankton in this region. The deeper zooplankton fauna, below 200m depth, was expected to persist into the future with little change in communities.

Like those zooplankton communities, the future also looks bright for members of the Ocean Extremes program. We were pleased to see Shayne McGregor promoted to Associate Professor by Monash University, and Amelie Meyer joined Fran Kelly on Radio National when it was announced she was a finalist in the Top 5 Science residency with ABC. We will know the result by the next newsletter. Amelie has also been appointed to the advisory committee for the climate science theme of the Environmental Research Conference 2021, where Katrin Meissner is one of the co-chairs for Environmental Research 2021. Congratulations also go to Earl Duran who was awarded a PhD for his thesis that examined the processes controlling mid-latitude ocean circulation and variability around Australia. He now moves to the next part of his career. And at the other end of the PhD journey, we welcome new student Maya Jakes who will be doing a PhD, Production and dissipation of the Thermohaline anomalies in the Antarctic Circumpolar Current using Lagrangian methods, at the University of Tasmania with Helen Phillips, Nathan Bindoff, and Steve Rintoul (CSIRO).