Geoscience Australia

Australian Government

Geoscience Australia

Applications of geomorphic mapping

and physical data to bioregionalisation

Alix Post & Phil O’Brien

Geoscience Australia

www.ga.gov.au

Macro-zoobenthos core communitiesGutt (2007)

• Sessile suspension feeder community• Infauna and mobile deposit feeder

community

Primary controls – Phytodetritus flux and sea bed “hardness”

Creating geomorphic map

Input data• GEBCO contours• ETOPO2 satellite bathymetry grid• Seismic lines

Output• Polygons hand digitised

in ArcGIS• 28 categories of geomorphic

features recognised

N

Prydz Bay

Prydz Bay

Shelf depression:< 550 m with closed contours. Typically muddy, biogenic sediments.

Shelf bank:Typically 100-200 m, extending to 500 m. Ice scoured.

Cross shelf valleys:Shelf depression <500 m connected to shelf edge. May be current swept.

Prydz Bay

Upper slope:Mapped from max gradient to lower gradient at ~2500 m. Highly gullied and current swept.

Trough mouth fan:Sediment apron on upper slope.

Lower slope:Extends to lower limit of canyons. Comprises alt. canyons and ridges.

Prydz Bay – Sediments &geomorphology

Phytodetritus-richooze distributioncontrolled by geomorphology

Seamount on seismic line

Height above seabed > 1000 m

Marginal ridge – Outer Adélie Rift BlockMarginal ridge – Outer Adélie Rift Block

D1601Granite, gneiss,

diorite, pelite

7

6

5

S N10 km

George V-Terra Adélie margin – Geomorphic Units

Biogeomorphicunits George V shelfBeaman & Harris,(2005)

Data:MultibeamSingle beamGrab samplesCoresPhotosCTDs

Mertz Drift

Presti et al., Quaternary Science Reviews, 2005

Spearman rank correlation = 0.71

Muddy

Deep/flat

Rocky substrate

Relief

Scours

Coarsesubstrate

Shrimp,infaunal holothurians

Sponges & bryozoa

Bryozoa, sponges, colonial

tunicates

PCA of taxa with correlation to substrate

Bryozoa, sponges, soft

corals

Sponges & solitary tunicates

Post et al., DSR II in press

Hydrocorals and canyon heads, George V continental slope(Post et al., Ant. Sci, 2010)

Conclusions

• Shelf geomorphic units approximate Community-level habitats

• Public bathymetry data sets useful for bioregionalsiation on the scale of around 1: 1 million

Should have value for the slope, rise and deep ocean