HEOBI: Heard-Earth-Ocean-Biosphere Interactions

Voyage Number

IN2016_V01

Voyage Dates

06 Jan, 2016 to 28 Feb, 2016

Voyage Location

Fremantle to Hobart

Chief Scientist

Prof Mike Coffin

Institution

Institute for Marine and Antarctic Studies (IMAS)

View the full voyage

Voyage summary

Research voyage to the sub-Antarctic territories of Heard and McDonald Islands to explore the role of underwater volcanoes in nourishing an iron-deficient Southern Ocean.

Situated entirely within the Indian Ocean sector of the Southern Ocean, Australia’s only active volcanoes - Heard and McDonald Islands on the Kerguelen Plateau - are among the world’s most active hotspot volcanoes. Existing data suggests that Heard and McDonald Islands are surrounded by fields of undersea volcanoes for several hundred kilometres.

The main objective of this voyage is to test the hypothesis that hydrothermal systems associated with active underwater hotspot volcanoes supply iron to the Southern Ocean which in turn nourishes phytoplankton blooms. Iron promotes the growth of phytoplankton, which are a crucial source of oxygen to Earth’s atmosphere and the base of the oceanic food chain. Much of the knowledge around sources, mechanisms, and processes that supply iron to the Southern Ocean remain a mystery.

The hypothesis will be tested by producing high resolution, three-dimensional maps of the seafloor around the islands. From this mapping, together with deep tow camera imaging and TRIAXUS sensor data, researchers will identify potential active submarine volcanoes and hydrothermal systems, and sample these volcanoes and their surrounding shallow sediments. They will also look for evidence of phytoplankton blooms.

Voyage impact

As a result of this voyage, researchers for the first time documented the role of active Heard and McDonald Islands, and nearby submarine volcanoes in supplying iron to the Southern Ocean. They found that nearshore waters had elevated dissolved iron levels. Although biomass was not correspondingly elevated, fluorescence induction data indicated highly productive resident phytoplankton.

Researchers discovered >300 acoustic plumes emanating from the seafloor and ascending up to tens of metres into the water column near Heard and McDonald Islands. Deep tow camera footage showed bubbles rising from the seafloor in an acoustic plume field north of Heard Island.

They also mapped ~1,000 km of uncharted seafloor around Heard and McDonald Islands. Submarine volcanoes punctuate the adjacent seafloor, and yielded iron-rich rocks similar to those found on Heard and McDonald Islands. Acoustic plumes emanating from some submarine volcanoes suggest active seafloor hydrothermal systems.

Finally, researchers commenced a multidisciplinary research effort to identify the sources, mechanisms, and processes in the Heard and McDonald Islands area that supply iron to the Southern Ocean. This research will advance geoscientific, biogeochemical and physical understanding of the region and Southern Ocean beyond.