Background to the voyage
Background to the voyage
New Zealand bathymetry (courtesy NIWA)
Macquarie Ridge sample sites.
The Macquarie Ridge (see right. Star denotes Nelson College for Girls and the square is Wellington, the start and return point of the voyage) extends southwest of New Zealand and then curves southeast before ending at around 58 degrees south. If we look in the Northern Hemisphere this is almost equivalent to Inverness, in the north of Scotland. The Ridge is almost 1400 km long and if you look closely is infact a series of smaller peaks, rising around 2000 – 3000 m. The Ridge was created between 12.5 and 52 million years ago – just over 10 million years after the dinosaurs went extinct.
Marine Physics
The main oceanographic aim of the voyage is to determine how the Antarctic Circumpolar Current (ACC) interacts with the Macquarie Ridge. The ACC is the world’s largest current and transports about 135 x 106 m3 s-1, or 135 times the water in all the world's rivers. When it comes into contact with the Macquarie Ridge (or any of the other ridge systems in the Southern Ocean) it is funneled in to the gaps within the ridge. These provide us with an opportunity to accurately measure how much water is in the different branches, or fronts, of the ACC, and how they vary over time.
For the last year we have had nine oceanographic moorings across two gaps in the ridge. On the moorings current meters are mounted to measure the speed and direction of the flow through the two gaps. As well as speed we also measure the temperature and salinity of the ocean along the ridge and in the gaps where the moorings are. The temperature and salinity of a parcel of water provide a signature identifying where the water came from. Thus along the ridge we hope to use these signatures to identify where the waters have come from.
Marine Geology
We also aim to collect a transect of sedimentary cores along the Macquarie Ridge to understand changes in the ocean currents and climate in the past. Using sedimentary characteristics, microfossils, and various geochemical analyses we will study changes in the water masses over the last couple of glacial/interglacial cycles for approximately the last 500,000 years. How did these changes in ocean circulation affect New Zealand's climate over this time period?
Marine Biology
Ridges and seamounts (undersea mountains) are prominent features found in all oceans of the world. They are thought to be very important as they can support high levels of biodiversity and unique communities of animals. They can often be highly productive ecosystems, and may act as feeding grounds for fishes, marine mammals, and seabirds. They may be targeted for fishing and mining (as some seamounts can contain valuable metal deposits) and as such may be vulnerable. Yet despite their potential importance we do not know much about these systems – during this voyage we will visit some seamounts that have never been studied to learn what lives on them, and how one seamount might differ from another.