In deep water

Scientists are learning more about the sea floor around New Zealand

A 

While we know that the sea is a big place, few of us realise just how big it really is. More than 66% of the world’s surface is covered by ocean, and the sea makes up 97% of the environments on Earth that can support living things. The vast majority of this area – and New Zealand’s seas are no exception – remains unexplored. In fact, the deepest parts of the ocean are so poorly known that nearly every submarine dive or research trawl (pulling up specimens from the seabed) brings new knowledge of genuine significance to oceanographers. Our present knowledge of land biodiversity (all animal and plant life) compared with ocean biodiversity is one measure of how early we are in the task of researching the deep sea. A good example is the New Zealand takahe bird. In 1948, a small population of takahe, a flightless bird which at that time was thought to be extinct, was found living in New Zealand’s mountains. The rediscovery of this one species created a sensation among bird lovers. In dramatic contrast, new species from New Zealand’s deep sea are today being discovered at a rate of about one every two weeks.

B 

What’s more, catching, examining and naming a new species is only the first step in the learning process. Just because an animal has been given a scientific name and shelf space in a museum doesn’t necessarily mean that we know anything at all about its lifestyle and ecology. Most deep-sea animals have never been seen alive, and the few that have were almost certainly acting unnaturally in the glare of lights from the submarine camera with which they were observed. For this reason, our understanding of life in the deep sea relies heavily on conjecture: fierce debate continues among scientists over such details as how fast a giant squid can swim, and why lantern fish flash their little lights. In some respects, deep-sea biology parallels the way that detectives hunt for criminals, requiring comparable problem-solving and clue-finding skills.

C 

The sea floor around New Zealand has a wide range of seabed features. One of the most important are seamounts, which are underwater volcanoes. Most of the world’s charted seamounts were discovered in the past 40 years, although the exact number around New Zealand is not known. One of the most conspicuous is the Bollons Seamount, which among others was visited by a scientific expedition in 2002. It rises more than three kilometres above the surrounding seabed, and measures two hundred kilometres across, making it a remarkable size, and therefore of particular interest.

D 

Research has shown that these mountains of the deep are home to many species, although it is not clear why. One theory is that the ocean currents cause plankton, which is an important source of food, to thrive on their upper surfaces. Another factor is that they are not completely draped with the fine mud that covers just about everything else in the deep sea. Instead, their rocky surfaces provide attachment points for animals like sponges and anemones. Many seamounts are found on the Chatham Rise, which is a huge platform in a remote part of the ocean. The top of the rise is covered with small seamounts, many of which have been named by the inhabitants of the nearby Chatham Islands. They come fishing here because a valuable species called orange roughy seasonally migrates to these shallow waters to spawn.

E 

Canyons are another of New Zealand’s underwater features. These trenches cut deeply into the sea floor and come unusually close to land. At Goose Bay, the squid that live in the canyon attract sperm whales, and every year thousands of people come to see the whales just off the coast, helping local tourism. Further south, near the city of Dunedin, several canyons are found. Since the 1960s, the University of Otago’s ship Munida has conducted research in this area, leading to many unusual discoveries. Among these was a population of button-sized coral, whose remains had originally been mistaken by early fossil collectors for small dinosaur bones.

F 

Scientists believe that canyons were created when powerful underwater currents cut into the seabed. Nearly all submarine canyons are located offshore from a large river, as it is the force of this flowing from the land into the sea that set the underwater current in motion. However, there are other explanations for canyons in other parts of the world, and a spectacular example took place in November 1929, when a significant earthquake in Canadian waters triggered an underwater current that travelled more than 720 kilometres, creating a canyon and cutting an undersea communication cable in the process.

G 

Research in the seas around New Zealand has resulted in a far better understanding of the seamounts, canyons and other underwater features that stand out from the otherwise flat sea floor. Indeed, the seabed generally is very flat compared to the land. To deal with this, oceanographers use a technique called ‘vertical exaggeration’ in their maps, to make changes in ocean depth more apparent. Unfortunately, this has resulted in many people believing that the seabed is much steeper than it really is. But this misunderstanding aside, we know much more about the deep ocean today than we did even 20 years ago, and the speed of scientists’ discoveries is only likely to increase.