The underwater world of Wilkes Land
Amazingly, the land beneath our oceans contains over 50% of all microbial life. It provides a continuous record of climate change for millions of years, it can tell us about the evolution of ocean currents and about the processes involved in plate tectonics and continental break-up, yet this marine subsurface remains largely unexplored.
Integrated Ocean Drilling Program
The Integrated Ocean Drilling Program (IODP), made up of an ever-changing cast of international scientists (including Australians and New Zealanders), has spent the last 35 years trying to find out about the world beneath our oceans. Over that time, they have revolutionised the world’s knowledge of plate tectonics, geohazards, historical climate change, marine resources (such as methane gas and minerals) and bizarre life that lives deep beneath the seafloor.
The team of scientists has recently returned from an exciting 2-month voyage of discovery in the Antarctic region of Wilkes Land on-board the Research Vessel JOIDES Resolution. Wilkes Land lies south of Australia and is thought to be a climate-sensitive region of the Antarctic continent. On 28 September 2010, Australian marine geoscientist Dr Neville Exon briefed geologists at GNS Science in Lower Hutt about the expedition. Geologists at GNS Science are analysing some of the 2000m of sediment core that the JOIDES Resolution team managed to return with – despite at times facing near gale-force winds, snow, fog and stray icebergs.
Dr Exon says the cores show that, despite Antarctica’s cold temperatures, some 53 million years ago, the area was once a warm, subtropical environment covered in pine trees and other vegetation. This time was known as the ‘greenhouse’ world and the atmospheric CO2 was at least 10 times greater than it is today.
Then suddenly, in only 400,000 years, this lush subtropical environment was covered in ice and atmospheric CO2 decreased rapidly. Around the world, temperatures dropped, and ice sheets and glaciers developed.
Sediments and microfossils within the cores show that the ice sheet in Antarctica has advanced and retreated several times in the last 50 million years as temperatures have fluctuated. The cores from one drill site resemble tree rings of alternating light and dark sediment that show seasonal variability since the last deglaciation (the retreat of glacial ice) that began some 10,000 years ago.
Dr Exon says that, as well as drilling up a record of greenhouse Antarctica, other cores also show the impact of the first ice in Wilkes Land and the evolution of sea ice in the area.
There was also microbial life in this extreme environment. ‘Extremophile’ microbes were found deep beneath the seafloor. Dr Exon says that around the world these extremophiles have an enormous biomass (there are lots and lots of them), and some may have applications in industrial or medical research. Research on subseafloor extremophiles helps to identify the natural limits to life on Earth, the origins of life and the potential for life on other planets.
Microscopic analyses have also found an unusually well preserved and diverse range of both soft and hard biotic (organisms) remains, including abundant fish, copepods (a tiny free-living or parasitic crustacean) and euphausiids (shrimp-like crustaceans). The team believes that these sediments may well be the most complete record of any ancient ecosystem structure and its variability through the Holocene (the last 12,000 years including present day) recovered from the Southern Ocean.