1. Alix Post & Phil O’Brien
Australian Government
Geoscience Australia
Applications of geomorphic mapping
and physical data to bioregionalisation
Alix Post & Phil O’Brien
Geoscience Australia

2. Macro-zoobenthos core communities Gutt (2007)
Sessile suspension feeder community
Infauna and mobile deposit feeder community
Primary controls – Phytodetritus flux and sea bed “hardness”

3. 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

4. Prydz Bay

5. Prydz Bay Shelf depression:
< 550 m with closed contours. Typically muddy, biogenic sediments.
Cross shelf valleys:
Shelf depression <500 m connected to shelf edge. May be current swept.
Shelf bank:
Typically m, extending to 500 m. Ice scoured.

6. Prydz Bay
Upper slope:
Mapped from max gradient to lower gradient at ~2500 m. Highly gullied and current swept.
Lower slope:
Extends to lower limit of canyons. Comprises alt. canyons and ridges.
Trough mouth fan:
Sediment apron on upper slope.

7. Prydz Bay –
Sediments &
geomorphology
Phytodetritus-rich
ooze distribution
controlled by geomorphology

8. Seamount on seismic line
Height above seabed > 1000 m

9. Granite, gneiss, diorite, pelite
Marginal ridge – Outer Adélie Rift Block
D1601
Granite, gneiss, diorite, pelite 7 6 5 S N
10 km
In places, underlying structures in the continental margin produce topographic features that extend beyond the lower slope unit. One such area is off Terra Adelié where a region of undulating sea floor culminates in a ridge of basement about 150 km north of the slope. The structural slope extension is of low relief and unlikely to support different types of substrate or experience different processes to the surrounding abyssal sediment plain however the marginal ridge protrudes hundreds of meters above the sediment plain. Dredging and seismic lines indicate that it is outcropping rocky material (Sato et al. 1984). An attempt at coring these sediments produced sand to gravel sized manganese nodule (Howard pers. Comm. 2003). These observations suggest the ridge is current swept. Other prominent structural margin ridges are present in the Antarctic Peninsula and Scotia Sea.
The Gunnerus Ridge and Astrid Ridge are prominent marginal ridges that jut from the East Antarctic Margin between 010oE and 040oE. They are shallow enough to suggest that they may significantly modify the flow of the East Wind Drift, possibly producing upwelling and hence having a significant influence on local primary productivity and ecosystems.

10. George V-Terra Adélie margin – Geomorphic Units

11. Biogeomorphic units George V shelf Beaman & Harris, (2005) Data:
Multibeam
Single beam
Grab samples
Cores
Photos
CTDs

12. Presti et al., Quaternary Science Reviews, 2005
Mertz
Drift
Presti et al., Quaternary Science Reviews, 2005

13. PCA of taxa with correlation to substrate
Sponges & bryozoa
Sponges &
solitary tunicates
Muddy
Deep/
flat
Rocky substrate
Relief
Scours
Coarse
substrate
Bryozoa, sponges, colonial tunicates
Shrimp,
infaunal holothurians
Bryozoa, sponges, soft corals
Spearman rank correlation = 0.71
Post et al., DSR II in press

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

16. 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