The schooner Tara is moored in the harbour in Cape Town on September 3. The French yacht Tara leaves Sunday on the second leg of a three-year voyage across the world's oceans to chart the effects of climate change on micro-organisms which produce half our oxygen.

The French yacht Tara leaves Sunday on the second leg of a three-year voyage across the world's oceans to chart the effects of climate change on micro-organisms which produce half our oxygen.

The 36-metre (118-foot) schooner will depart from Cape Town a year after leaving Lorient in western France to head across the Atlantic and Pacific oceans for New Zealand next August as part of a 150,000-kilometre (93,750-mile) journey.

"Sunday ... will be the birthday of the Tara Oceans project because it's the beginning of the second year of the project," said captain Olivier Marien.

The plankton-studying boat will sail to Ascension Island, the expedition's longest crossing since leaving France, before it heads for Brazil, Argentina and further south to Antarctica.

The crew are collecting samples which are frozen onboard and sent to laboratories every month to map out a baseline for future climate studies.

"We know now that the planet is changing, and the ocean is changing, and we expect much from the ocean to counterbalance what the humans are doing on the planet," Philippe Koubbi, the chief scientist on board told AFP.

"We know that some of the tiny plankton are threatened...and we know that tiny animals or these tiny plants are very very important in controlling the balance in the ocean."

A bio-bank is being created from the research, ranging from viruses and bacteria to fish larvae, and more than 100 scientists are involved in the project.

Plankton ecosystems are little known but the microorganisms absorb half of the world's carbon production and produce as much oxygen as forests.

"This is really what this expedition is really about - is really to look at this planktonic life which is really in the open ocean, really controlling everything," said Koubbi.

A 13-person team will leave Cape Town, where the yacht spent time in dry-dock, with early spring making weather the main challenge and not threats such as sea pirates which were the main concern in the first leg.

The return to ice will be familiar territory for the 1989-built vessel -- now on its eighth scientific voyage -- which was previously named Antarctica and ended a 507-day Arctic trip in 2008.

Next year Tara will also sail via Chile, Easter Island, the Galapagos Islands, the Clipperton Islands, the Marquesas Islands and Papeete.

The first leg crossed the Atlantic, Mediterranean, Red Sea, Arabian Sea and Indian Ocean.

The project's backers include the fashion house Agnes B. and global news agency Agence France-Presse (AFP) is a media partner.

The boat was previously owned by New Zealand yachtsman Sir Peter Blake who was murdered during a scientific expedition in the Amazon river in 2001.

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(c) 2010 AFP