A new dataset that highlights the dependence of algae on Antarctic sea ice will help scientists predict future food security for Southern Ocean herbivores such as krill. 

Scientists at the Antarctic Climate and Ecosystems Cooperative Research Centre led an international effort to compile a circum-Antarctic biomass database drawn from 32 international research voyages between 1983 and 2008. 

The data provides important information on the large-scale spatial and temporal characteristics of Antarctic sea ice algal distribution. Sea ice algal communities provide an important early-season food source for Southern Ocean herbivores, such as Antarctic krill, which in turn provide food for penguins, seals and whales.

Dr Klaus Meiners, a sea-ice ecologist with ACE CRC and the Australian Antarctic Division, led the international effort to compile the database, which involved researchers from Australia, France, Germany, Belgium, UK, USA and Russia. The data base consists of 1300 sea ice cores, comprising 8247 individual core segments sampled in the frozen zone of the Southern Ocean.

Dr Meiners said the database would help scientists to identify the key physical drivers of the annual ice algal growth cycle, as well as supporting the testing and validation of ice algal production and ecosystem models currently being developed.

“This study highlights that the vertical distribution of ice algae is critically dependent on sea ce thickness,” Dr Meiners said. “We know that 0.4 — 1 metre thick sea ice, which is the current mean Antarctic sea ice thickness, harbours communities that provide a readily accessible food source for ocean herbivores such as Antarctic krill.

“The study therefore suggests that predicted changes in ice thickness will impact on the vertical distribution of ice algae, with possible flow-on effects on Antarctic krill and Southern Ocean food webs.”

In contrast to phytoplankton (microscopic plants growing in the open ocean), ice algae cannot be observed from space and thus its temporal and spatial distribution is poorly understood. Classical sampling methods like ice coring are still the standard technique to quantify the amount of ice algae in sea ice. The researchers also used the observations to describe the seasonal development of ice algae on a circum-Antarctic scale for the first time.

Sea ice plays a key role in Earth’s climate system and is a structuring element of Antarctic marine ecosystems. It serves as a floating carrier of the microscopic algae that grow within the ice surface, interior and bottom layers. Climate models predict that both Antarctic ice extent and ice volume/thickness will strongly decrease by the end of the century.

The research has been published in Geophysical Research Letters.