Physical Environment of the West Coast Coastal Marine Area
An understanding of the physical setting and processes at work in the West Coast marine and coastal environment is fundamental to any description of its biodiversity, and any ecosystems and habitats which might eventually be protected through the Marine Protected Areas process.
This section of the report describes the physical characteristics of the West Coast within the wider New Zealand marine environment. It then goes on to describe the region in terms of physical attributes like coastal and seafloor geology, underwater and coastal landforms, the impact of tides, waves and weather patterns, and variability in sedimentation and river discharges to the seawater. The physical environment of the West Coast coastal marine area is then characterised in terms of its depth, substrate and exposure.
2.1 New Zealand in the Southern Ocean
New Zealand lies at the boundary between the subtropical waters of the southwest Pacific Ocean and the subantarctic waters in the latitudes of the Southern Ocean known as the ‘Roaring Forties’.
New Zealand’s position in southern temperate latitudes within a largely oceanic hemisphere makes its location unique in many respects and significant for a wide range of marine biodiversity. A comprehensive description of New Zealand’s marine biodiversity is not the intent of this report1 , but several points about New Zealand in the context of the global marine environment are worth noting:
- About 8000 marine species have been described in New Zealand waters, (and there are doubtless many more to be discovered). Marine scientists estimate that perhaps as much as 80 percent of New Zealand’s indigenous biodiversity is found in the sea. While many of our marine species are found in the seas around other countries, some (especially bottom dwelling species) are endemic to New Zealand.2
- The complex topography of New Zealand’s ocean floor includes a great diversity of plateaux, canyons, ocean depths, shelves and seamounts.
- The hydrology of New Zealand’s marine waters produces a complex system of oceanic and coastal currents that affect the distribution and biology of marine species.
The New Zealand land mass lies across one of the most significant ocean boundaries in the southern hemisphere – the Subtropical Convergence3. This circum-global front separates subtropical water in the north from subantarctic water in the south. It is accompanied by strong physical and nutrient gradients which have major implications for the growth of plankton and the richness of the surface waters4. The location of the boundary between the polar and temperate waters varies with the seasons and from year to year, but Figure 2.1 shows the generally accepted ‘average situation’5. Figure 2.1 : New Zealand in the SouthernOcean, showing approximate boundary of subtropical convergence.
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Figure 2.1 New Zealand in the Southern Ocean, showing approximate boundary of subtropical convergence. |
1 E.g., see Morton 2004, Goff et al 2003
2 Dept of Conservation and Ministry for the Envirionment 2000
3 Robertson 1982
4 Vincent et al 191
5 Heath 1985