Submarine frontier

The New Zealand Continental Shelf Project

Written by       Photographed by NIWA

New Zealand is undergoing a renaissance in how it views the oceans that surround it. While early Maori navigators and European whalers appreciated the sea’s importance, 20th-century New Zealanders came to see its encompassing vastness as something that isolated them from the rest of the world. In the last 30 years, however, that view has changed remarkably, such that the oceans are now seen as a vast resource of enormous economic and conservation value.

In part, this change in perception reflects the increasing diversity of New Zealand’s economy and the growing understanding that the country isn’t just a collection of “shaky islands”, but the emergent peaks of a vast underwater continent. This continent has the fifth-largest Exclusive Economic Zone (EEZ) in the world, covering some 4 million km2, slightly more than half the size of the land area of Australia. Compare that with New Zealand’s land area of 268,680 km2—and consider, too, its coastline length of some 15,100 km (equivalent to the straight-line distance between Wellington and Tehran)—and it becomes clear why New Zealanders now view their surrounding oceans and seafloor as important.

The inclusion of the sea in New Zealand’s perception of its geography has occurred during a time of profound change in its economy. From the 1970s, the country has moved from an economy based almost entirely on agriculture (with coastal fisheries bringing in a comparatively small revenue of less than $50 million), to one that is vastly more diverse and now includes a significant marine sector. Today there is a multibillion dollar fishing and aquaculture industry, a marine-engineering and boat-building industry and a $25 million marine-ecotourism industry; the vast majority of goods continue to be exported via the country’s ports and seaways; and offshore hydrocarbon reserves form a critical aspect of New Zealand’s energy supply.

With exploitation of the ocean has come increasing awareness of the need to protect the marine environment, both along the coast and within the EEZ and surrounding seas, including the Southern Ocean. Since New Zealand’s first marine reserve—at Goat Island, near Leigh, north of Auckland—was gazetted in 1975, more than 35 further areas of the seafloor and coastline have acquired protection under various pieces of legislation, with further areas proposed for like treatment.

In addition, New Zealanders continue to learn (and, some might say, relearn) ways in which the marine environment can have a direct impact on their lives. For example, it is now widely understood that large changes in sea surface temperatures in the equatorial Pacific—a phenomenon known as El Niño produce droughts in New Zealand that periodically cause a $1billion reduction in GDP. There is a growing appreciation of the fact that the sea-floor around New Zealand is dynamic, being strewn with submarine volcanoes, riven by faults, cut by submarine canyons and swept by avalanches— all of which present potential hazards to coastal communities.

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But what of the future? Where Bare New Zealand’s new submarine frontiers? These questions are directly tied to the 1982 United Nation’s Convention on the Law of the Sea (UNCLOS). UNCLOS, though not that well known, is arguably one of the more successful international conventions, com­prising a range of articles covering issues such as: unhindered interna­tional shipping; innocent passage within territorial seas; sea access to landlocked states; setting rules for marine research; providing for the development of mineral resources beyond national shelf boundaries; and conservation and management of high seas fisheries.

The best-known articles are prob­ably numbers 55–75, which allow coastal states, such as New Zealand, to declare an EEZ extending 200 nautical miles (nm) from the coast­line, including that of any offshore islands. New Zealand’s EEZ gives it certain sovereign economic rights over living and non-living resources both in the water column (such as the hoki and orange roughy fisher­ies) and on and beneath the seafloor (such as oil and gas reserves).

A depiction of NIWA's research vessel Tangaroa engaged in multibeam mapping. An array of 135 separate sonar beams are directed at the seafloor as the vessel motors above, and reflected signals are used to construct a detailed surface topography of the seabed. The mapped swathe is 2-5 km wide depending on water depth. Deeper water allows more beam spreading, producing a wider, but slightly less detailed image.
A depiction of NIWA’s research vessel Tangaroa engaged in multibeam mapping. An array of 135 separate sonar beams are directed at the seafloor as the vessel motors above, and reflected signals are used to construct a detailed surface topography of the seabed. The mapped swathe is 2-5 km wide depending on water depth. Deeper water allows more beam spreading, producing a wider, but slightly less detailed image.

Equally as important, though less well-known, is article 76, which al­lows a coastal state to define an ex­tended continental shelf beyond the 200 nm EEZ if it can demonstrate that the seafloor in question is linked to, or is an extension of, its landmass. The article broadly recognises that the sea-floor of the world’s oceans falls into two categories: deep ocean, formed along mid-ocean ridges (part of the great tectonic conveyor system) and generally, though not exclusively, deeper than 4000 m; and various elevated features, including ridges, plateaux and rises, that are linked by other geological processes to an emergent land mass, whether this be a large continent or a small uninhabited island. Under article 76, seafloor in the latter category qualifies for exten­sion of the continental shelf.

There are perhaps fewer than 30 countries realistically able to claim there is seafloor beyond their respec­tive 200 nm boundaries that can be considered other than deep ocean, or that doesn’t abut the EEZ of a neigh­bouring state. A casual inspection of the central Pacific highlights the scarcity of qualifying countries. Here, many island nations sit atop steep-sided volcanoes surrounded by deep ocean, with few associated submarine ridges or plateaux outside their 200 nm boundaries. In contrast, New Zealand can define a considerable extended continental shelf, which will last in perpetuity. Its geographical isolation and complex geology work to its advantage.

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Is an extended continental shelf important, or is it just about national pride? In New Zealand’s case, the answer is that it is extremely important. An extended continental shelf bestows the same sovereign eco­nomic rights over living and non-liv­ing resources of the seabed as a nation enjoys in its EEZ. What it doesn’t bestow is rights over resources in the water column, hence no new fisheries are in the offing. But this still leaves hydrocarbons and minerals, as well as sedentary species that live on the seafloor.

It might seem a bit fanciful to think that organisms living at depths of up to 2000 m and more than 200 nm from land have an economic value. But many compounds currently being tested by the pharmaceutical and nutraceutical industries come from bottom-dwelling marine organ­isms found in remote areas of the ocean. Such “bio-prospecting” and screening for bio-medicinal com­pounds is the focus of many inter­national research groups, including groups in New Zealand.

In many cases, the animals and compounds concerned are now pro­duced, respectively, in aquaculture farms and laboratories. For instance, the active enzyme in cold-water wash­ing powder was discovered in whale carcasses decaying on the seafloor, but is now mass-produced by fermen­tation in a laboratory.

As important as the finds them­selves is the fact that an extended continental shelf allows coastal states like New Zealand to manage such exploitation and to ensure that they are conducted in an environmentally sustainable way.

What has New Zealand been doing to define the limits of its continental shelf? When New Zealand ratified UNCLOS in 1996, it had a statutory ten years in which to acquire and compile sufficient information to sub­stantiate which areas beyond the 200 nm EEZ were linked to its landmass, and submit these to the UN-appoint­ed Commission on the Limits of the Continental Shelf (CLCS). The 21­ member commission comprises vari­ous experts in hydrographic mapping, marine geophysics and marine and geodesic surveying, and previously in­cluded a New Zealander, Iain Lamont (formerly of the Hydrographic Office of the Royal New Zealand Navy).

In determining which areas of the sea-floor are linked to New Zealand in the manner defined by UNCLOS, bathymetrical, marine-geological and geophysical data are crucial, the first to ascertain the depth and shape of the sea-floor, the latter its structure and composition, and the third its physical properties and the processes acting upon it. Such information is necessary to demonstrate the validity of a claim.

Vent organisms litter a patch of seafloor on the Rumble 5 volcano, north of the Bay of Plenty. The starfish predate the abundant clams, which are brown on the outside and white within the shell.
Vent organisms litter a patch of seafloor on the Rumble 5 volcano, north of the Bay of Plenty. The starfish predate the abundant clams, which are brown on the outside and white within the shell.

Article 76 defines “continental shelf” using two key criteria: the max­imum change in gradient at the base of the continental slope, and—rel­evant in some cases only—sediment thickness. These were established as a result of research during the 1950s, 60s and 70s into so-called Atlantic-style passive margins. Typified by the continental shelves of Africa and South America where those landmass­es border the Atlantic Ocean, these are of a relatively simple configura­tion: a more-or-less even slope down to a low-angle sediment wedge at the base. They are not near the edge of a tectonic plate, so there are no earth­quakes or volcanoes to disturb their arrangement.

In contrast, New Zealand, in com­mon with many countries bordering the western Pacific, has been astrad­dle, or near, an active plate boundary for tens (if not hundreds) of millions of years. Consequently, its continen­tal margin is a confusion of ridges, plateaux and seamounts thrown up by the powerful forces at work where plates collide. Some of these features, although formed apart from the continental mass, have, as a result of plate movement, been driven into it and are now “welded”, or embed­ded, there. Conversely, in some places continental blocks have been torn free and retain only a tenuous connection to their former home. In such a setting, the application of the article 76 criteria is far from straight­forward

Furthermore, the technical prescription for iden­tifying the base of a continental slope, formulated over 20 years ago, is equivocal—an inconvenience of no small moment, as how steep the sea-floor should be in order to be considered part of the continental slope rather than the abyssal sea-floor can have a pro­found affect on the final position of the shelf bound­ary. Similarly, questions arise over what geophysical techniques can be used to determine sound velocities within sea-floor sediments for conversion into meas­urements of thickness.

In addition to the two key criteria, there is provi­sion for “evidence to the contrary” to support a link between what is unambiguously continental and a sea-floor feature separate from it. Take the example of a granite-cored seamount. Granite intrusions rich in silica are only ever associated with continental rocks, never with the seafloor formed along mid-ocean ridges.

Article 76 also limits the distance to which a country can extend its continental shelf. In water deeper than 2500 m, the limit is 350 nm from the coastline; in shal­lower areas, it is 100 nm from the 2500 m isobath, or contour line. These limits are intended to prevent land­locked nations and those with a narrow continental shelf—the majority—being unduly disadvantaged.

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In 1996, with so much at stake, New Zealand began a decade-long, multi-million-dollar project to acquire the bathymetrical, marine-geological and geophysical data necessary to determine the outer edge of its continental shelf.

The first step in the appropriately titled New Zea­land Continental Shelf Project (NZCSP) was to review existing data to ascertain where the edge of the conti­nental shelf might be, and to assess whether they were of sufficient quality and quantity to build a convincing case for a submission to the CLCS. Various agencies­ principally the Royal New Zealand Navy, GNS Science (formerly the Institute of Geological and Nuclear Sci­ences) and the National Institute of Water and Atmos­pheric Research (NIWA)—held relevant data, some dating back more than 40 years. Digital bathymetry records, paper sounding charts, satellite altimetry data, ship-borne gravity and magnetic data, marine seismic-reflection data, offshore drill-hole cores, rock dredge samples—all were reviewed in the first 18 months of the project. This analysis used knowledge from New Zealand’s ongoing marine-geological and geophysical research efforts.

In some regions, data—principally ships’ echo-sounding tracks—are suf­ficiently dense to define the outer lim­it of the continental shelf. The south-eastern edge of the Campbell Plateau is a good example; many research vessels that have passed through the area en route between New Zealand and the Southern Ocean or Antarc­tica having recorded numerous tracks. In other places data are very few, and individual ships’ tracks are hundreds of kilometres apart. In some areas, the continental margin is clearly complex, warranting closer study. This is the case to the north of New Zealand, where ridges formed by coalescing submarine volcanoes and volcanic sediments form prominent ridge spurs that extend great distances from the margin.

With such reliance on ships’ echo-sounding tracks, it is hardly surpris­ing that the question of data quality has focused on the vintage, and hence accuracy, of ship navigation. Forty years ago all latitudinal fixes were made using a sextant, their accuracy being dependent on the skill of the operator, and inaccuracies of 3–4 nm were common. From 1967 to 1988, position at sea was determined using a mix of transit-satellite measurements and dead reckoning, which had an uncertainty of 0.25–0.5 nm (possibly more early in the period on account of incomplete satellite coverage, es­pecially in the Southern hemisphere). From 1988 to 1996, the satellite-based global positioning system (GPS) gave an uncertainty of 30–100 m, while the introduction of differential GPS in 1996 cut the margin of error to 1–10 m. In a few areas, recent, more accu­rate ship-track data have superseded older, less accurate data.

Following the data review in 1996–98, a comprehensive UNCLOS survey programme was proposed and funded. The programme, using New Zealand’s own deepwater research vessel, Tangaroa, and specialist ships from overseas, was completed in 2002. Amounting to more than 350 days of at-sea data collection, this represented a significant achievement in logistical planning and manage­ment. The programme had three main parts: fine-scale mapping of the sea-floor with multi-beam sonar to identify links with the New Zealand landmass in critical areas; shallow and deep seismic-reflection geophysics to determine sediment thickness and the nature of deep crustal rocks; and sea-floor sampling to test (sometimes confirming, sometimes disproving) earlier geological interpretations by comparing the sea-floor with onshore rocks.

Since 2002 the NZCSP has con­centrated on data analysis and the writing of its submission. Broadly speaking, New Zealand has five separate contiguous areas beyond the 200 nm boundary that include submarine features such as the Lord Howe Rise, the Three Kings Ridge, the Hikurangi Plateau, the eastern and south-eastern Chatham Rise and the southern Campbell Plateau. The submission will soon be complete and lodged with the United Nations, with initial reviewing by the CLCS expected to start in August this year. To date, only four coastal states (Rus­sia, Brazil, Australia and Ireland) have lodged submissions, all of which remain under consideration by the commission.

At the same time as it has been analysing data, New Zealand has had to negotiate boundary restrictions where it shares extended continental shelf with another country, first and foremost with Australia. Negotiations with Australia commenced in 2002, and after an extensive process of ex­changing data, comparing interpreta­tions of international law and sharing marine–geological knowledge, a mar­itime treaty was signed in July 2004. The treaty demarcates the common extended continental shelf, and be­came law in both countries in January 2006. New Zealand is currently ne­gotiating with both Fiji and Tonga to fix a boundary across the continental shelf to the north of New Zealand.

What will be the outcome of all these efforts? Though nothing can be certain until the CLCS makes its rec­ommendations, it is hoped that New Zealand’s extended continental shelf will encompass somewhere between one and two million km2 beyond its 200 nm EEZ. This will be New Zealand’s new frontier. The chal­lenge will then be to understand, use, manage and protect that part of the world’s oceans, for which New Zea­land will be directly responsible.

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