Principal Investigators: Kerrie Swaddling, Patti Virtue, Iain Suthers, and Jason Everett
Onboard: Patti Virture, Hugh Jones, and Pearse Buchanan
The Southern Ocean sea ice zone supports rich and diverse invertebrate communities. Larval krill depend on the sea ice habitat for refuge and sustenance in late winter/early spring. The sea ice community is particularly vulnerable to impacts of ocean warming and acidification. Our project focuses on the structure and biomass of the zooplankton community in the sea ice, directly under the sea ice and in the water column.
This research will increase understanding of the contribution of ice associated fauna to the larval krill diet and the vulnerabilities of this ecosystem in a changing ocean. Outcomes from our project will include enhanced understanding of where biomass is concentrated in the sea ice zone during the transition time in late winter/early spring, before the onset of the phytoplankton bloom.
Coupled to this will be a rare opportunity to develop a picture of the food resources available to larval krill during winter, a season of importance to the successful recruitment and growth of this species. Lower trophic level invertebrates (e.g. copepods, krill, and pteropods) are crucial components of the Southern Ocean ecosystem and responsible for much of the energy transfer from primary producers to higher order consumers.
One novel aspect of our project will be the first deployment of a Laser Optical Plankton Counter (L-OPC) to describe Biomass Size Spectra (BSS) for the Southern Ocean sea ice habitat. The L-OPC represents advanced technology that can resolve particles down to 100 μm and up to 20 cm in size.
We will deploy the L-OPC to derive empirical relationships between plankton size structure and taxonomic composition in the sea ice zone, as determined from net catches and sea ice cores. We will be able to determine directly the depth distribution of larval krill relative to that of their food sources.
Further, by deploying this instrument for the first time in the sea ice zone we will add to the growing database of plankton size observations from different water masses (either in-situ or from plankton samples), allowing us to estimate the biological effect of interannual oceanographic variation as harbingers of climate change.
The L-OPC will be deployed at every major sea ice location, where the ship is stopped for at least half a day. The instrument will be docked to a data logger and lowered on a wire at the approximate speed of 1 m s-1. The L-OPC will be mounted on a frame set up on the sea ice, and deployed at sea ice stations. Particle abundance will be recorded from depths under the sea ice down to 200 meters.
In addition, at each sampling location 4 cores will be collected with a SIPRE ice corer that will be operated manually by the field personnel. Immediately after collection, the cores will be sectioned into 10 cm long segments and each segment melted in filtered seawater, maintained at temperatures of less than 4ºC.
For half of the cores collected from a location the melted core water will be filtered through a 53 um mesh sieve and the contents of the sieve preserved in borax-buffered formaldehyde. These samples will be used for identification and enumeration of the sea ice assemblage, and for later measurements of length. For the remaining cores the animals will be filtered from the core water and stored frozen for elemental (CHN) isotopic (del 15 N, del 13C) analysis.
This project is a joint collaboration between Kerrie Swadling and Patti Virtue (IMAS), and Iain Suthers and Jason Everett of UNSW. Hugh Jones and Pearse Buchanan will be heading south with Patti and taking care of the field sampling.