Marine Atlas: Maximizing Benefits for Solomon Islands

VOYAGE TO THE BOTTOM OF THE SEA: GEOMORPHOLOGY

Solomon Island’s sea floor is rich in physical features that affect the distribution of biodiversity, fishing grounds and deep-sea minerals.

Submarine Canyon

The nation’s seascape is as diverse under- water as its landscape above, including towering underwater mountains (seamounts) that attract migratory species from hundreds of kilometres away, and deep-sea canyons that carry nutrient-rich water from the deep ocean to the shallow areas. Geomorphology (the study and classification of these phys- ical features) reveals both the geological origin of the features as well their shape (morphology), size, location and slope. The geomorphology of the sea floor influ- ences the way the ocean moves (see also chapter “Go with the flow”), wind direction and the distribution of water temperature and salinity (see also chapter “Hotter and higher”). These factors affect the distribution of biological communities, resulting in differ- ent biological communities being associated with different types of sea-floor geomor- phology. For example, seamounts generally have higher biodiversity and a very different suite of species to the adjacent, deeper abyssal areas. Similarly, different economic resources are often associated with different features. Many fisheries operate on certain features, such as the shelf, slope or over seamounts, based on where their target species occur. In Solomon Islands, important deep-sea snapper is mostly found on outer reef slopes and around seamounts (mainly in depths from 100 to 400 metres; see chapter “Fish- ing in the dark”). Furthermore, different types of deep-sea mineral deposits are also associated with different features, such as the sea-floor massive sulfide deposits found along mid-ocean ridges (see chapter “Un- derwater Wild West”). Solomon Islands’ waters harbour 18 differ- ent geomorphic features, which are present- ed in this map and associated figures. The distribution of geomorphology reflects many

food. They also act as a conduit between the deep-sea floor and the shallow shelf areas. On all these features, areas of steep sea floor (escarpments) are likely to con- tain hard substrate which, coupled with increased current flow, create ideal habitats for filter-feeding organisms such as sponges and cold-water corals. The trench and trough systems to the north and south of the main islands have some of the deepest waters in the Pacific Ocean, with depths over 9,000 metres in Solomon Islands’ waters. The area also has many small- to medium-sized basins. Deeper areas can act as sinks, accumulating ma- terials that have sunk in the water column, including pollution from human activities. The numerous plateaus in this region are also likely to interact with currents, creating further unique habitats.

0 km

100

200

Shelf

0

Shelf break

Terrace Escarpment

2

Slope

Foot of slope

Slope

km depth

Rise

Continental Crust - Granite

4

Fan

Sediments

Sediment Drifts

0 km

200

400

Ridge

2

Pinnacles

Guyot

Seamounts

Abyssal Hills

Trough

4

km depth

Seamount

Continental Crust - Granite

6

Sediment

Ocean Crust - basalt

Subduction Zone

Sediment Drifts

Upwelling lava

of the patterns observed in the bathyme- try map, as geomorphology is primarily a classification of the shape of the sea-floor features. Some notable features in Solomon Islands’ waters include 52 seamounts and seven guyots. Seamounts are large—at least 1,000 metres high—conical mountains of volcanic origin, while guyots are seamounts with flattened tops (see chapter “Underwa- ter mountains”). In addition to seamounts, there are numerous large ridges throughout Solomon Islands’ western and southern waters. These ridges rise more than 1,000

metres from the surrounding sea floor and their steep sides interact with currents, cre- ating important habitats for many species. Solomon Islands has narrow continental shelfs which are characteristic of Pacific Islands. The adjacent sloping areas are incised with numerous large submarine canyons, of which there are 135 in Solomon Islands’ waters. These canyons are char- acterized as areas of high biodiversity due to their steep sides featuring rocky slopes, strong currents and enhanced access to

MAXIMIZING BENEFITS FOR SOLOMON ISLANDS

SUPPORTING VALUES

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