The custom-designed sub-ice platelet sampling system in action. Photo: Vanessa Wells/Elanti Media
Sea ice extent, and the exchange of carbon dioxide (CO2) and other gases between the atmosphere and ocean, varies from year to year, influenced by changes in atmospheric and open-ocean conditions. Understanding the difference between seasonal variability and long-term change is key to predicting Antarctica’s influence on the future global climate system.
Researchers in the Sea Ice and Carbon Cycle Feedbacks project are analysing variability in sea ice and the carbon cycles in the Ross Sea region and on larger scales, including connections to atmospheric circulation and climate processes across the Southern Ocean, and much of the Southern Hemisphere.
Collecting an air sample aboard a Heritage Expeditions cruise, 2017 Photo: Sherry Ott
Some research highlights from the past year:
Radiocarbon transport between ocean and atmosphere
We have evaluated the radiocarbon content of atmospheric CO2 over the Southern Ocean between 2016 and the present. Observations and models exhibit a decrease in atmospheric ∆14CO2 (the measure of radiocarbon content) in the 50-70° southern latitudes, relative to lower and higher latitudes. This is consistent with our broad understanding that upwelling of deep waters will decrease ∆14CO2 in this region, however the models consistently underestimate the magnitude of the decrease. We are working on testing different model parameterisations to accurately reflecting the full behaviour of carbon cycle dynamics in the Southern Ocean.
More ships of opportunity
Our ships of opportunity research programme, in which volunteers collect air samples on ships crossing the Southern Ocean, has been extended to include Heritage Expeditions, Sanford fishing vessels, the Royal New Zealand Navy and NIWA. This support is critical to measure the radiocarbon content of the CO2 in the air samples, giving us a snapshot over a period of a few days as the ships are at sea.
Microplastics, sea ice & marine ecosystems
Biogeochemical modelling was used to investigate the long-term effects of microplastic contamination on marine ecosystems. Results found that regional recovery from microplastic-induced changes could take hundreds of years for certain areas, such as coastal upwelling zones, the North Pacific, and the Southern Ocean. The recovery process is hindered by factors like surface stratification and reduced sea ice cover. The study also identified the importance of sea ice in trapping biogenic oxygen as the main oxygen recharge mechanism for the global deep ocean. The schematic below (Kvale & Oschlies, 2023) shows the slow recovery of the microplastic-induced oxygen deficit in the basin.
Detecting polynya from space
Detailed analysis on satellite data, with spatial scales ranging from 25 km to less than 1 km, means we can identify polynya in the Ross Sea region right through the winter months. This published work is the first to develop objective techniques for identification of polynya morphologies. Our efforts are now on understanding linkages between wintertime polynya variability and large-scale climate patterns.
Improving the snow radar system
We are developing and testing new techniques to determine sea-ice thickness, with a focus on accurately measuring snow depth. This year, with collaborators from the Alfred Wegener Institute AWI), we have developed a new snow radar system suitable for use with the AWI ‘mini-bird’ (which measures the total thickness of snow and ice above the water’s surface). This airborne instrument combination was successfully tested in alpine regions of New Zealand, and will be deployed for large-scale surveys in the Western Ross Sea - including Terra Nova Bay and the Ross Sea Polynya - in the coming 2023/24 Antarctic field season.
Sampling platelet ice & sympagic community
The custom-built sampling system (pictured at top) was successfully used to collect twelve contiguous sea ice and sub-ice platelet layer (SIPL) cores during the 2022/23 Antarctic field season. The cores were collected from sites evenly distributed between ‘mature’ and ‘immature’ platelet layer habitats - an unexpected opportunity afforded by the unprecedented sea ice growth conditions of winter 2022.
Supplementary data collected included: