East Australian Current velocity, temperature and salinity data products.

The East Australian Current (EAC) is the complex, highly energetic western boundary current that flows along the east coast of Australia. The EAC and its associated turbulent eddies dominate the marine climate of the Coral and Tasman Seas and the eastern Australian continental shelf. Here we present a series of consistent EAC data products that combines in situ temperature, salinity and velocity observations from the Australian Integrated Marine Observing System (IMOS) and Commonwealth Scientific and Industrial Research Organisation (CSIRO) EAC mooring array and North Stradbroke Island reference site. The EAC data products are produced from over 1000 individual instrument files collected during six 18-month deployments in the East Australian Current (EAC) off Brisbane, Australia at 27 °S between 2012-2022. The mooring individual instrument files are combined, interpolated onto a common vertical, temporal (hourly and daily) and spatial grid. The ITCOMPSOM method is used to fill missing data in the time series. These data product can be used to investigate intra- and interannual EAC variability and boundary current dynamics.

Isotopic evidence for an intensified hydrological cycle in the Indian sector of the Southern Ocean.

The hydrological cycle is expected to intensify in a warming climate. However, observational evidence of such changes in the Southern Ocean is difficult to obtain due to sparse measurements and a complex superposition of changes in precipitation, sea ice, and glacial meltwater. Here we disentangle these signals using a dataset of salinity and seawater oxygen isotope observations collected in the Indian sector of the Southern Ocean. Our results show that the atmospheric water cycle has intensified in this region between 1993 and 2021, increasing the salinity in subtropical surface waters by 0.06 ± 0.07 g kg-1 per decade, and decreasing the salinity in subpolar surface waters by -0.02 ± 0.01 g kg-1 per decade. The oxygen isotope data allow to discriminate the different freshwater processes showing that in the subpolar region, the freshening is largely driven by the increase in net precipitation (by a factor two) while the decrease in sea ice melt is largely balanced by the contribution of glacial meltwater at these latitudes. These changes extend the growing evidence for an acceleration of the hydrological cycle and a melting cryosphere that can be expected from global warming.

A large-scale view of marine heatwaves revealed by archetype analysis.

Marine heatwaves can have disastrous impacts on ecosystems and marine industries. Given their potential consequences, it is important to understand how broad-scale climate variability influences the probability of localised extreme events. Here, we employ an advanced data-mining methodology, archetype analysis, to identify large scale patterns and teleconnections that lead to marine extremes in certain regions. This methodology is applied to the Australasian region, where it identifies instances of anomalous sea-surface temperatures, frequently associated with marine heatwaves, as well as the broadscale oceanic and atmospheric conditions associated with those extreme events. Additionally, we use archetype analysis to assess the ability of a low-resolution climate model to accurately represent the teleconnection patterns associated with extreme climate variability, and discuss the implications for the predictability of these impactful events.

Observational Needs for Improving Ocean and Coupled Reanalysis, S2S Prediction, and Decadal Prediction.

Developments in observing system technologies and ocean data assimilation (DA) are symbiotic. New observation types lead to new DA methods and new DA methods, such as coupled DA, can change the value of existing observations or indicate where new observations can have greater utility for monitoring and prediction. Practitioners of DA are encouraged to make better use of observations that are already available, for example, taking advantage of strongly coupled DA so that ocean observations can be used to improve atmospheric analyses and vice versa. Ocean reanalyses are useful for the analysis of climate as well as the initialization of operational long-range prediction models. There are many remaining challenges for ocean reanalyses due to biases and abrupt changes in the ocean-observing system throughout its history, the presence of biases and drifts in models, and the simplifying assumptions made in DA solution methods. From a governance point of view, more support is needed to bring the ocean-observing and DA communities together. For prediction applications, there is wide agreement that protocols are needed for rapid communication of ocean-observing data on numerical weather prediction (NWP) timescales. There is potential for new observation types to enhance the observing system by supporting prediction on multiple timescales, ranging from the typical timescale of NWP, covering hours to weeks, out to multiple decades. Better communication between DA and observation communities is encouraged in order to allow operational prediction centers the ability to provide guidance for the design of a sustained and adaptive observing network.

The southern ocean meridional overturning in the sea-ice sector is driven by freshwater fluxes.

The oceans are traversed by a large-scale overturning circulation, essential for the climate system as it sets the rate at which the deep ocean interacts with the atmosphere. The main region where deep waters reach the surface is in the Southern Ocean, where they are transformed by interactions with the atmosphere and sea-ice. Here, we present an observation-based estimate of the rate of overturning sustained by surface buoyancy fluxes in the Southern Ocean sea-ice sector. In this region, the seasonal growth and melt of sea-ice dominate water-mass transformations. Both sea-ice freezing and melting act as a pump, removing freshwater from high latitudes and transporting it to lower latitudes, driving a large-scale circulation that upwells 27 ± 7 Sv of deep water to the surface. The upwelled water is then transformed into 22 ± 4 Sv of lighter water and 5 ± 5 Sv into denser layers that feed an upper and lower overturning cell, respectively.

Use of a blocking primer allows selective amplification of bacterial DNA from microalgae cultures.

The production of algae is a crucial component of many aquaculture systems and the role of bacteria in this process is an important although complex one. We report the development of a new blocking primer that allowed PCR amplification of bacterial DNA in the presence of algal chloroplast DNA.