[Aqualist] The Annual A.W. Howitt Lecture. Joint meeting of the GSAV and the Royal Society of Victoria

[Barbara Wagstaff]

The Annual A.W. Howitt Lecture
Joint meeting of the GSAV and the Royal Society of Victoria
Thursday 12th July at 7:00pm
VENUE: The Royal Society of Melbourne Building
9 Victoria Street, Melbourne, 3000 (entrance via LaTrobe Street)
The secret millennial history of Port Phillip Bay
Guy Holdgate
School of Earth Sciences, University of Melbourne
Hidden below 10 metres of water buried in the central muddy basin of Port Phillip is a
secret Holocene story. During recent dredging by the Port of Melbourne Corporation,
three multi-beam surveys over the deeper parts of the sea floor revealed wide, deep
river-channels recessed into the bay floor,  connecting to the Yarra and Werribee rivers.
Twelve new Carbon 14 dates and sub bottom seismic profiling reveal these mud
channels could be as young as 1,000 calendar years BP.
These river features, down to -22 m water depths indicate much of Port Phillip basin
must have been sub-aerially exposed during the late Holocene, (sometime between
1000 and 2800 years BP),  when sea level was similar to the present.  The Bay water
must have evaporated after the separation of ocean water from bay water, possibly
by sand blocking the shallow Nepean Bay Bar channels. During this period bay water
levels fell to -22 metres. Port Phillip became a residual lake, and the Yarra and the
Werribee river channels meandered across a progressively exposed muddy lake floor.
This secret Holocene history of “fluctuating bay levels” has widespread implications
for our understanding of Port Phillip’s history of water balance, salinity, pre-European
climatic events, aboriginal occupation, tribal boundaries and legends about bay
flooding and the Yarra Delta.  What are the future implications?
--
Dr Barbara Wagstaff
Palynologist
School of Earth Sciences
The University of Melbourne
Victoria 3010

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