The Indian Ocean has the ability to absorb three times as much atmospheric nitrogen as the Atlantic Ocean does and, as a result, can play a crucial climate role as a huge, offshore carbon sink.
That's one of the findings of scientists who have just arrived in Fremantle having sailed across the Indian Ocean conducting experiments on global change and deep-water biodiversity.
The scientists arrived in Australia yesterday on board the Spanish Navy research vessel Hesperides after a month-long voyage from Cape Town.
The scientists are part of a $23 million (€17 million) world-wide ocean research project - the Malaspina Circumnavigation Expedition - which involves more than 400 scientists from 10 countries, including researchers from UWA Oceans Institute and the CSIRO.
The scientists collected around 4,000 ocean samples in the Indian Ocean, from as deep as 4,000 metres. Their work involved:
The nitrogen supply from the atmosphere plays an important role in regulating climate because it helps plankton to grow and capture carbon dioxide from the atmosphere.
"Nitrogen is a key nutrient for phytoplankton to grow, perform photosynthesis and capture atmospheric carbon dioxide," said Professor Carlos M. Duarte, the Coordinator of the Malaspina expedition.
Prof. Duarte is a research scientist with the Spanish National Research Council (CSIC), which is leading the Malaspina expedition. He is also the newly appointed Director of the Oceans Institute at The University of Western Australia.
"The microorganisms that make up the phytoplankton community, remove more CO2 from the atmosphere than land plants do, and therefore play a critical role in climate regulation," he said.
The researchers on board Hesperides found high concentrations of silicate in water samples collected in the Indian Ocean from the surface down to 4,000 metres deep.
"We have found silicate concentrations three times higher than those in the Atlantic Ocean," said fellow CSIC researcher Dr Jordi Dachs, who was the Chief Scientist on board Hesperides for the Cape Town-Perth voyage, the fourth leg of the circumnavigation.
"This is significant because silica is an essential element for diatoms to grow, and these diatoms, which contain symbionts able to fix atmospheric nitrogen play a particularly important role in carbon cycling in the ocean."
The Malaspina scientists found numerous Rhizosolenia diatoms in the water column extending from the surface down to 100 metres deep. This genus tends to be associated with a nitrogen-fixing cyanobacteria to produce organic matter with which to build their cells.
"The fact that the concentration of silicate in the Indian Ocean exceeds that of other nutrients such as nitrate and phosphate favours diatom associations with nitrogen fixing bacteria," says Dr Dachs.
During the voyage from Cape Town to Perth, the Malaspina scientists investigated the Indian Ocean ecosystem down to 4,000 metres with nets, sampling bottles and other instruments in a total of 24 sampling stations.
A total of 4,000 samples have been collected to examine the concentration of greenhouse gases in the water and analyse the isotopic composition of atmospheric water vapour, thereby helping resolve water cycling in the atmosphere over the Indian Ocean.
The scientists also conducted a detailed study of persistent organic pollutants in the Indian Ocean. Such a detailed investigation of pollutant fluxes and cycling on the Indian Ocean has never been conducted before.
In addition, Malaspina researchers also observed that the Indian Ocean is particularly rich in zooplankton. The researchers have collected gelatinous organisms from the Salp family and jellyfish of the genus Physalia and Velilla. They have also obtained information on the microbial proteins present in surface waters.
The scientists also released five SMOS buoys to improve global observing data from the ocean. These buoys are designed to measure the salinity at 0.5m below the surface, and will serve to validate and calibrate satellite information from the Space Mission of the European Space Agency, the first mission to derive ocean salinity from space.
A fraction of the samples collected on the voyage will go into the Malaspina Collection, a time capsule that will remain locked for 30 years. These specimens will be investigated by future scientists using, in all likelihood, research tools not yet available and posing new research questions.
Setting sail for Sydney - CSRIO involvement
The Hesperides will be in Fremantle until 17 March and then continue its circumnavigation, working in the Southern Ocean and sailing on to Sydney and Auckland.
As part of this next leg, scientists will undertake research in conjunction with the CSIRO and the UWA's Oceans Institute.
This will include towing a plankton recorder to provide a continuous inventory of the abundance and diversity of plankton organisms in Australian waters.
"The ocean south of Australia is a particularly interesting region where three oceans - the Indian, Pacific and Southern - converge. Exploring the biodiversity of these waters will surely reveal surprises," said Professor Susana Agustí, the Chief Scientist on the Perth-Sydney leg of the voyage, and a Research Professor with UWA Oceans Institute.
Tony Malkovic (on behalf of UWA Oceans Institute) (+61 4) 11 103 398
Janine MacDonald (UWA Public Affairs) (+61 8) 6488 5563 / (+61 4) 32 637 716
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