THEME 2

Nature and Impacts of Southern Ocean Change

The AAPP will determine how and why the physical and biogeochemical environment of the Southern Ocean adjacent to the AAT is changing and assess the impacts of change on climate, sea level, sea ice and marine ecosystems. The Southern Ocean influences climate by taking up and storing more anthropogenic heat and carbon dioxide than any other latitude band of the ocean. The Southern Ocean also influences the stability of the East Antarctic Ice Sheet, through ocean-driven melt of the buttressing ice shelves, and the productivity of marine ecosystems. An assessment of Southern Ocean change and its impacts is essential to deliver on the Antarctic Science Collaboration Initiative (ASCI) objective “to support research that aims to understand the role of the Antarctic region in the global climate system and the implications for marine ecosystems”.

Delivery of this milestone is through an integrated program of physical and biogeochemical observations, modelling and synthesis aimed at understanding the drivers and impacts of change in the Southern Ocean. Knowledge of the impacts of change on interactions between the ocean and the cryosphere, atmosphere and biosphere will underpin research in the other themes.

PROJECT 4: Oceanography PROJECT 5: Biogeochemistry

PROJECT 4: Oceanography

The infrequent ship-board sampling will be complemented by investment in autonomous profiling floats that will provide year-round observations of the East Antarctic sector of the Southern Ocean, including novel biogeochemical sensors and new floats capable of profiling the full ocean depth. The profiling floats provide the only feasible means of tracking changes in the ocean inventory of heat and carbon over broad regions, an essential step to meet the ASCI objective to understand the role of the Antarctic region in the global climate system. Satellite remote sensing will provide additional spatial and temporal context for the less frequent and spatially sparse in situ measurements, including exploitation of the upcoming Surface Water Ocean Topography (SWOT) satellite mission that will provide measurements of sea-surface height across a swath for the first time, and advances in ocean biomass estimates from satellite LIDAR instruments. The observational work will be carried out in close collaboration with IMOS, an AAPP Partner. A hierarchy of numerical models, from ultra-high-resolution process models to global Earth system models, will be used to assess the impacts of Southern Ocean change and the sensitivity of physical and biogeochemical processes to changes in climate.

The key science questions for this project are:

How will changes in ocean circulation and temperature affect East Antarctic ice shelves? The project will determine where and how ocean heat reaches East Antarctic ice shelves and provide improved understanding of the factors that regulate poleward ocean-heat transport across the Southern Ocean to the ice-shelf cavity.
How will Southern Ocean feedbacks (e.g., changes in ocean heat & carbon uptake, sea ice and freshwater) alter the pace of climate change? The project will assess how and why the ocean is changing with time, identify the processes responsible for heat and carbon uptake and their sensitivity to change in ocean circulation/stratification, and work with AAPP Project 6 to assess the contribution of changes in ocean circulation to change in sea ice.
What processes and teleconnections link the climates of Australia and Antarctica, and what do these tell about future change? We will explore the role of teleconnections in driving variations in ocean circulation and water-mass formation and provide measurements of ocean-heat content for assessment of SO influence on Australian climate.
How will the changing physics and chemistry of the Southern Ocean and Antarctica influence marine life? The project will deliver assessments of change in the physical environment (temperature, salinity, currents, stratification, upwelling) of the Southern Ocean, as needed by other AAPP projects.
What is the cause of persistent biases in climate models (e.g., clouds, sea ice) and how can these processes be better represented in climate models? The project will provide better understanding of how the surface ocean influences the lower atmosphere and sea ice.

PROJECT LEADERS

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Benoit

Benoit Legresy

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Annie

Annie Foppert

PROJECT 5: Biogeochemistry

Changes in the physical environment of the Southern Ocean will be assessed by comparing new observations to past measurements. Models will be used to test hypotheses and assess the sensitivity to changes in forcing, as well as to make projections of future change. This effort will use a variety of observational platforms, including the Marine National Facility RV Investigator, the soon-to-be-commissioned Australian icebreaker RSV Nuyina, the Southern Ocean Time Series moored observatory supported by Australia’s Integrated Marine Observing System (IMOS), and autonomous underwater platforms. Measurements will quantify heat and CO₂ uptake, the progress of ocean acidification (contributing to the commitment to UN Sustainable Development Goal 14) and the supply of iron, a key micro-nutrient that regulates the productivity of Southern Ocean ecosystems.

The key science questions for this project are:

What drives the unexpectedly large multi-year and decadal changes in the magnitude of Southern Ocean CO₂ uptake, and how do they affect our understanding of probable future ocean CO₂ uptake?
What is the specific progress of ocean acidification impacts (lowered pH, reduced carbonate saturation, and higher CO₂ availability) and accordingly which regions in the Southern Ocean and Antarctic coastal waters are likely to be more resilient to ocean acidification?
Is iron supply or its bioavailability, as key controllers of Southern Ocean productivity, likely to increase over the coming century, and what processes will control this?
What will be the expected magnitude of change in Southern Ocean primary productivity this century, and what controls this (with Theme 3. Future of Sea Ice, Krill and Ecosystems)?
How will the transfer of energy from phytoplankton to higher levels in the food web be affected by the impact of biogeochemical change on phytoplankton community structure (with Theme 3. Future of Sea Ice, Krill and Ecosystems)?