Over The Horizon

New Zealand Seafloor on the Map

A new chart of the ocean floor, Undersea New Zealand, has just won major prizes in Europe and United States. Designed and generated by the National Institute of Water and Atmosphere, with production by Terralink NZ Limited, the chart received the prestigious Bartholomew Award from the British Cartographic Society. It also took first prizes at the International Cartographic Association conference in Sweden and the Environmental System Research Institute conference in San Diego.

NIWA applied the latest computer mapping technology to generate detailed images of the ocean floor around New Zealand. Production of the final chart by Terralink also relied upon computer-based techniques.

Dr Lionel Carter, who is part of the NIWA team that developed the chart, says "the almost three-dimensional quality of Undersea New Zealand highlights the marked relief of the seabed. The vast submarine plateaus, trenches, and ridges that surround the landmass are shown with remarkable clarity. The detail is sufficient to highlight the submarine channel systems and numerous volcanoes that dot the ocean floor in water depths down to five kilometres."

Carter points out that some satellite measurements of the planet's surface can also be used to image the shape of the seabed. However, such images rely on approximations of water depth estimated from satellite measurement of the earth's gravity and the height of the sea surface. In contrast, Undersea New Zealand relies on actual water depth measured from ships and is therefore considerably more accurate. The chart is also more detailed and portrays features such as the submarine channels, which are not evident on satellite-derived images.

Publication of the chart is timely. Negotiations over the Law of the Sea Convention are giving maritime nations the opportunity to claim the Legal Continental Shelf where it extends beyond the 200 nautical mile limit of the Exclusive Economic Zone. Undersea New Zealand provides the best overview of the Legal Continental Shelf, and so it is an important planning document.

The wealth of information captured on the chart is a boon for a wide range of groups involved with the marine environment, says Carter. Seafloor features, such as the ridge and trench systems off East Cape and Fiordland, provide an insight into the nature and movement of the boundary between the colliding Pacific and Australian crustal plates -- the main cause of earthquakes in the region. Similarly, the identification of submarine channels indicate the presence of bottom scouring currents that are capable of transporting mud and sand 1000 km from land.

The charting of the undersea volcanoes, many of which were previously unidentified, will be of considerable interest to commercial fisheries. Carter foresees the chart as playing an important role in the understanding and management of our maritime region.

The chart is available from NIWA, PO Box 14-901, Kilbirnie, Wellington.