The Bounty Trough is a major submerged feature, a
bathymetric depression, of the oceanography of the southwest
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
. It is located off the east coast of
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
's
South Island
The South Island ( , 'the waters of Pounamu, Greenstone') is the largest of the three major islands of New Zealand by surface area, the others being the smaller but more populous North Island and Stewart Island. It is bordered to the north by ...
. It is named after the
Bounty Islands
The Bounty Islands (; "Island of angry wind") are a small group of uninhabited granite islets and numerous rocks, with a combined area of circa in the South Pacific Ocean. Territorially part of New Zealand, they lie about east-south-east o ...
near the Eastern end of the trough. The islands, in turn, are named after .
Extent
The Bounty
Trough
Trough may refer to:
In science
* Trough (geology), a long depression less steep than a trench
* Trough (meteorology), an elongated region of low atmospheric pressure
* Trough (physics), the lowest point on a wave
* Trough level (medicine), the l ...
is located to the South of the
Chatham Rise, and North of the
Campbell Plateau. It runs East-West for a distance of some to the deep ocean between the
Chatham and
Bounty Island groups. The Bounty Trough's western extremity is less than off the South Island's coast.
[Marine Gazetteer Placedetails]
, ''Marine Regions'' Retrieved 10 December 2016. It covers an area of approximately .
[David G. Roberts, A.W. Bally. Regional Geology and Tectonics: Phanerozoic Passive Margins, Cratonic Basins and Global Tectonic Maps, Elsevier, 2012, p517.]
Much of The Bounty Trough lies at depths of , and it marks an indentation in the "coastline" of the largely submerged continent of
Zealandia
Zealandia (pronounced ), also known as (Māori language, Māori) or Tasmantis (from Tasman Sea), is an almost entirely submerged continent, submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83 ...
.
Geology
A curious feature of the Bounty Trough is that it marks the continuation of several main river features in the South Island – the "Otago Fan Complex".
[Carter, L., Carter, R.M. and Davy B. Seismic stratigraphy of the Bounty Trough, south-west Pacific Ocean. Elsevier. Marine and Petroleum Geology, Vol 11, Issue 1. 1994. P79-93.] This is a distinct series of channels existing in the base of the trough which is an extension of the
Clutha and
Waitaki River
The Waitaki River is a large braided river in the South Island of New Zealand. It drains the Mackenzie Basin and runs south-east to enter the Pacific Ocean between Timaru and Oamaru on the east coast. It starts at the confluence of the Ōhau Ri ...
systems.
Both these rivers, especially the Clutha, are noted for their fast flow. This alone would not account for the existence of the channels, though much of their current contours was probably shaped by sediment during the ice ages.
[Sea Floor Geology]
, ''Te Ara Encyclopedia of New Zealand.'' Retrieved 10 December 2014.
The channel system is the remnant of a
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
(failed) rift formed via ocean-floor spreading at the time when Zealandia separated from Antarctica
[Carter, L., and Carter, R.M., (1987)]
The Bounty channel system: A 55-million-year-old sediment conduit to the deep sea, Southwest Pacific Ocean
, ''Geo-Marine Letters'', 7, ''4'', 183–190. between 130 and 85
Mya. The channels provide a major transportation system for sediments from the major rivers in the eastern South Island. At the Eastern end of the rift is the abyssal Bounty Fan.
In July 2012, the
NIWA research ship mapped the area finding a structure of nine canyons ending in "a large deep apron-shaped sediment deposit in the Bounty Trough". The survey considered development of a biodiversity assessment of the area which would then support "potential environmental effects of any oil drilling, and help establish environmental guidelines specific to the area".
[Stuff.co.nz Science]
, ''First map shows canyons, creatures and maybe oil.'' Retrieved 10 December 2016. The mapping also found "pock marks" some deep by in diameter in the margins which may indicate methane seepage. The survey could support petrochemical exploration, though, Roberts et al.
found evidence of "an extensive and effective petroleum system" to be "conjectural".
Both the Otago and abyssal fans, and the rift itself developed from the
Kaikoura Orogeny and were greatly accelerated after about 2.5 Ma, with the onset of global glacial/interglacial climatic cycles and the development of an icecap along the alpine region of South Island. The glacial periods contributed large amounts of sediment to the trough.
Sediment is not being deposited now in the same way as it was during the glacial period.
References
{{Oceanic features of Zealandia, state=collapsed
Geography of the New Zealand seabed
Zealandia