Protists in marine ice

Marine ice cores drilled from deep within the Amery Ice Shelf in East Antarctica have been found to contain some 30 species of protists — microscopic marine plants and animals.

The protists were identified at four core depths — 277, 290, 360 and 390m — in a band of thick marine ice about 90km from the calving front of the ice shelf.

The discovery has enabled scientists from the Australian Government Antarctic Division, the Antarctic Climate and Ecosystems Cooperative Research Centre and the Polar Research Institute of China, to identify the parent water from which the marine ice formed, providing an insight into the ocean currents in the region and the movement of warm and cold water beneath the 550km-long floating ice shelf.

Marine ice forms when ice at the deep base of the ice shelf, near the grounding zone, melts and ascends the sloping underside of the shelf. As the less salty, cold water rises, the pressure decreases and the water begins to freeze again. The ice crystals adhere to the underside of the ice shelf and, as they do so, may scavenge marine organisms or detritus in the water column and incorporate this material into the marine ice.

These electron micrographs show two of the four taxonomic groups of protists found trapped in the marine ice cores — diatoms, chrysophytes, silicoflagellates and dinoflagellates.

As different protists are found in different environments (open water or sea ice-dominated regions, for example), the presence, distribution and abundance of individual taxa enable scientists to infer the origin of parent water masses from which the marine ice is formed, and to gain an insight into water temperature, salinity and sea ice proximity.

As sea ice diatoms and cold, open water diatoms dominated the marine ice of the Amery Ice Shelf, scientists concluded that the ice was seeded from melting pack and/or fast ice protist communities in the highly productive waters of Prydz Bay to the north of the shelf.

More information

  • D Roberts et al (2006). Protists in the marine ice of the Amery Ice Shelf, East Antarctica. Polar Biology. DOI 10.1007/s00300-006–0169-7.