Winter Ice Study on Key Species

Six Australian Antarctic Division personnel have recently returned from a 60-day voyage to the Weddell Sea, where they joined the international Winter Ice Study on Key Species.

This German-led multi-disciplinary project onboard the icebreaker Polarstern brought together a team of 47 scientists and support engineers from eight countries.

The goal of the voyage was to learn more about sea ice and the key species associated with it. Antarctic krill were the main focus because this is the most abundant animal species in the sea ice zone and they play a central role in Antarctic marine food webs.

Much of the work of the Antarctic Division team built on research conducted during the Australian-led Sea Ice Physics and Ecosystem eXperiment-II (SIPEX-II) in 2012 and reported in Issue 23 of Australian Antarctic Magazine.

The Antarctic Division team was led by sea ice ecologist Dr Klaus Meiners, whose main aim was to measure physical and biological sea ice properties using an instrumented Remotely Operated Vehicle (ROV). The ROV was first used successfully for this purpose during SIPEX-II.

Assisting Klaus were electrical engineers Peter Mantel and Mark Milnes, who were primarily responsible for maintaining and operating the ROV, as well as its instrument payload, consisting of a sonar, accurate depth sensor and a spectral radiometer. These instruments were fitted to the vehicle before the voyage, by the Antarctic Division’s Science Technical Support team. The combination of these sensors allows the determination of ice thickness and ice algal biomass simultaneously.

Ice algae are a critical food supply for krill and other organisms living under the ice. Using video and a newly developed upward-looking stills camera, the ROV was also used to determine the number of krill larvae living under the ice. ROV measurements were conducted in tandem with the collection of live krill larvae by a German dive team. The data will be compared to independently determined measurements of ice and snow thickness collected from the ice surface by a German sea ice physics team. Together, this information will provide insights into the relationship of sea ice thickness, snow thickness, ice algal biomass and krill larval density.

Mr Rob King also collected krill using nets and a modified fish pump, which proved to be a key tool to catch krill for various physiological measurements carried out by the Antarctic Division and other groups. Rob also deployed deep sea light traps and cameras (with critical engineering support from Mark and Peter) to determine if krill were feeding at the sea floor, up to 5800m below, and to bring a sample of live krill to the surface. However, preliminary data from these deployments suggest that feeding at the sea floor might not be a key strategy for krill during this period, at least around the locations where the camera was deployed.

Also onboard was Dr Simon Jarman, who is leading the molecular genetics work that will be performed at the Antarctic Division after the voyage. This work is part of a newly established European-Australian effort to investigate the role of so-called ‘clock genes’ in polar zooplankton species (Australian Antarctic Magazine 23: 10–11, 2012).

Antarctic zooplankton are attuned to the daily and seasonal cycles of their environment. The new project attempts to identify internal molecular clocks that help the organisms to synchronise their physiology and life cycle to the changes in their environment on daily and seasonal time scales. Molecular genetic analysis of DNA in krill stomachs will also be used to identify the food that krill consume from the underside of the ice and from the open sea.

University of Tasmania and Quantitative Antarctic Program student Roland Proud completed the six- member team. Roland calibrated and operated the ship’s echosounders to improve acoustic methods to determine krill biomass. Echolocation of krill targets allowed efficient and effective trawl deployment, providing samples for biological analysis. The acoustic data recorded on the voyage will enable the team to estimate the density of krill along the ship’s path and will be key to understanding the temporal and spatial variability in krill distribution on large scales.

The Australian team will now spend months collating, analysing, and interpreting all their data and samples in order to better understand the dynamics of the under-ice habitat. Initial results indicate a high spatial patchiness in sea ice thickness, algal biomass and krill larval distribution, with the latter also strongly influenced by daily migration patterns.

Rob King1, Simon Jarman1 and Klaus Meiners1,2

1. Australian Antarctic Division
2. Antarctic Climate and Ecosystems Cooperative Research Centre