『Abstract
The aim of this study is to assess the global occurrence of large
submarine canyons to provide context and guidance for discussions
regarding canyon occurrence, distribution, geological and oceanographic
significance and conservation. Based on an analysis of the ETOPO1
data, this study has compiled the first inventory of 5849 separate
large submarine canyons in the world ocean. Active continental
margins contain 15% more canyons (2586, equal to 44.2% of all
canyons) passive margins (2244, equal to 38.4%) and the canyons
are steeper, shorter, more dendritic and more closely spaced on
active than on passive continental margins. This study confirms
observations of earlier workers that a relationship exists between
canyon slope and canyon spacing (increased canyon slope correlates
with closer canyon spacing). The greatest canyon spacing occurs
in the Arctic and the antarctic whereas canyons are more closely
spaced in the Mediterranean than in other areas.
River-associated, shelf-incising canyons are more numerous on
active continental margins (n = 119) than on massive margins (n
= 34). They are most common on the western margins of South and
North America where they comprise 11.7% and 8.6% of canyons respectively,
but are absent from the margins of Australia and Antarctica. Geographic
areas having relatively high rates of sediment export to continental
margins, from either glacial or fluvial sources operating over
geologic timescales, have greater numbers of shelf-incising canyons
than geographic areas having relatively low rates sediment export
to continental margins. This observation is consistent with the
origins of some canyons being related to erosive turbidity flows
derived from fluvial and shelf sediment sources.
Other workers have shown that benthic ecosystems in shelf-incising
canyons contain greater diversity and biomass than non-incising
canyons, and that ecosystems located above 1500 m water depth
are more vulnerable to destructive fishing practices (bottom trawling)
and ocean acidification caused by anthropogenic climate change.
The present study provides the means to assess the relative significance
of canyons located in different geographic regions. On this basis,
the importance of conservation for submarine canyon ecosystems
is greater for Australia, islands and northeast Asia than for
other regions.
Keywords: Submarine canyons; Geomorphology; Global; Active continental
margin; Passive continental margin; Benthic ecology; Conservation』
1. Introduction
1.1. The origins of submarine canyons
1.2. Continental margin type and submarine canyon morphology
1.3. Significance of submarine canyons
1.4. Vulnerable marine ecosystems
1.5. Aims and objectives of this study
2. Methods
3. Results
3.1. Canyon identification in relation to resolution of data
3.2. Canyon spacing
3.3. Occurrence and morphology of shelf-incising and blind canyon
types
3.4. Canyon length
3.5. Canyon slope
3.6. Occurrence of dendritic canyon limbs (canyon dendricity)
3.7. Depth range
3.8. Canyon sinuosity
4. Discussion
4.1. Canyons incising active versus passive margins
4.2. Mediterranean canyons
4.3. models of canyon evolution
4.4. Where do the VME-associated canyons occur?
5. Conclusions
Acknowledgements
Appendix A. Supplementary data
References
Fig. 8. Generalised, schematic 3D diagram contrasting the geomorphic attributes characteristic of submarine canyons occurring on passive and active continental margin types. The mean values with standard deviations listed are from Table 1, with values that are significantly different between active and passive margins (at 95% confidence intervals) highlighted in yellow. Harris and Whiteway(2011)による『Global distribution of large submarine canyons: Geomorphic differences between active and passive continental margins』から |