Regular commenter JohnB pointed me to a new paper on historic sea level changes in Australia: Alan N. Williams, Sean Ulm, Tom Sapienzab, Stephen Lewis and Chris S.M. Turneya,
Sea-level change and demography during the last glacial termination and early Holocene across the Australian continent,
Quaternary Science Reviews Volume 182, 15 February 2018, Pages 144–154, published on line 12 January 2018.
This third note on understanding the impact of sea level change in Aboriginal New England takes this paper as an entry point for a broader discussion focused on the impact of sea level and associated climatic changes on New England Aboriginal life.
Please note that I have not been able to access the full paper at this point for cost reasons. That will have to wait until I can find a library that will give me access. This is an especial problem for their population modelling.
The Williams et al Paper
Map of Australia by Sean Ulm showing sea-level change and archaeological sites for selected periods between 35,000 and 8,000 years ago. PMSL=Present Mean Sea Level. Note the apparently small shifts in Northern NSW relative to some other areas. .
The
on-line abstract of the paper summarises some of the paper in this way:
- Investigation of scale, pace and human impacts of post-glacial sea-level change.
- Presents continental-scale consensus sea-level curve for Sahul between 35-8 ka.
- Demonstrates some 2.12 million km2 (∼21.6%) of land lost, notably during MWP-1a.
- Coastlines changed on average by 139 km, and at a rate of up to ∼23.7 m per year.
- Populations low, but likely severely disrupted, and led to new configurations.
The abstract of the paper reads:
"Future changes in sea-level are projected to have significant environmental and social impacts, but we have limited understanding of comparable rates of change in the past. Using comprehensive palaeoenvironmental and archaeological datasets, we report the first quantitative model of the timing, spatial extent and pace of sea-level change in the Sahul region between 35-8 ka, and explore its effects on hunter-gatherer populations. Results show that the continental landmass (excluding New Guinea) increased to 9.80 million km2 during the Last Glacial Maximum (LGM), before a reduction of 2.12 million km2 (or ∼21.6%) to the early Holocene (8 ka). Almost 90% of this inundation occurs during and immediately following Meltwater Pulse (MWP) 1a between 14.6 and 8 ka. The location of coastlines changed on average by 139 km between the LGM and early Holocene, with some areas >300 km, and at a rate of up to 23.7 m per year (∼0.6 km land lost every 25-year generation). Spatially, inundation was highly variable, with greatest impacts across the northern half of Australia, while large parts of the east, south and west coastal margins were relatively unaffected. Hunter-gatherer populations remained low throughout (<30,000), but following MWP1a, increasing archaeological use of the landscape, comparable to a four-fold increase in populations, and indicative of large-scale migration away from inundated regions (notably the Bass Strait) are evident. Increasing population density resulting from MWP1a (from 1/655 km2 to 1/71 km2) may be implicated in the development of large and complex societies later in the Holocene. Our data support the hypothesis that late Pleistocene coastal populations were low, with use of coastal resources embedded in broad-ranging foraging strategies, and which would have been severely disrupted in some regions and at some time periods by sea-level change outpacing tolerances of mangals and other near-shore ecological communities" .
The authors provided a summary of the paper in
The Conversation,
"Australia’s coastal living is at risk from sea level rise, but it’s happened before", January 16 2018. The map is from this paper.
Some of their key points can be summarised this way:
- The potential impacts of these past sea-level changes on Aboriginal populations and societies have long been a subject of speculation by archaeologists and historians.
- Archaeologists have long recognised that Aboriginal people would have occupied the now-drowned continental shelves surrounding Australia, but opinions have been divided about the nature of occupation and the significance of sea-level rise. Most have suggested that the ancient coasts were little-used or underpopulated in the past.
- Our data show that Aboriginal populations were severely disrupted by sea-level change in many areas. Perhaps surprisingly the initial decrease in sea level prior to the peak of the last ice age resulted in people largely abandoning the coastline, and heading inland, with a number of archaeological sites within the interior becoming established at this time.
- With the onset of the massive inundation after the end of the last ice age people evacuated the coasts causing markedly increased population densities across Australia (from around 1 person for every 355 square km 20,000 years ago, to 1 person every 147 square km 10,000 years ago).
- We argue that this squeezing of people into a landmass 22% smaller – into inland areas that were already occupied – required people to adopt new social, settlement and subsistence strategies. This may have been an important element in the development of the complex geographical and religious landscape that European explorers observed in the 18th and 19th centuries.
- Following the stabilisation of the sea level after 8,000 years ago, we start to see the onset of intensive technological investment and manipulation of the landscape (such as fish traps and landscape burning)
- We also see the formation of territories (evident by marking of place through rock art) that continues to propagate up until the present time. All signs of more people trying to survive in less space.
But what is the evidence for New England?
Shape of the Continental Shelf
The effect of sea level change varies depending on the size of sea level shifts, shifts in land height as the land adjusts to things such as increased or reduced ice weight and the configuration of the land itself.
In my
first note on the impact of sea level changes, I mentioned that I had only just found a 2010 paper: Alan Jordan, Peter Davies, Tim Ingleton, Edwina Foulsham, Joe Neilson and Tim Pritchard,
Seabed habitat mapping of the continental shelf of NSW, Department of Environment, Climate Change and Water NSW, Sydney 2010. This focuses on the current seabed habitat along the NSW, but it contains some of the best local descriptions that I have seen of the shape of the continental shelf itself in Northern NSW.
I am still working my way through this
paper, but I would summarise some of the conclusions in this way. In
considering them, remember that we are dealing with variations in sea levels
over my study period from perhaps 50-60m below current levels to 120-130m below
to perhaps 2m above and then a fall back to current levels. In combination with
associated climatic changes, this would have had significant habitat changes
for local Aboriginal populations as land was revealed and then submerged.
It will be clear from the Sean Ulm map
reproduced above, that the effects of sea level changes along the NSW coast
were smaller than in other parts of Sahul, but that doesn’t really provide much
local information.
To further out thinking here, the overall
width of the continental shelf is defined as the distance to the shelf break.
From this point, the seabed falls away quickly. The shelf break occurs at
varying heights, leading to variations in depth below current sea levels. The
continental shelf slopes down from the current shoreline at varying angles.
Higher land on the shelf may appear as reefs or islands.
The NSW study shows considerable regional
variations in the depth of the shelf break and the certainty with which it can
be defined. The shelf break between Cape
Howe in the far south of
NSW to Forster on the Mid North Coast varied predominantly between depths of
130–170m and gradually decreased in areas further north to depths of
approximately 80–110m off the Northern Rivers.
During the LGM, sea levels dropped to 120-130m
below current levels. In Southern New England
up to Forster, the shelf break with its sharp decline in height would have
remained largely below sea level, although it might have been quite close to
the shore. Further north, the shelf break would have been marked by a line of
cliffs or at least precipitous decline 15-50m above then sea level.
The study did not report on the 130m
contour, focusing instead on the 200m contour deep zone. The distance to the
outer edge of the 200-metre contour deep zone revealed the smallest zone widths
of 13.4 kilometres and 13.9 kilometres were off Hat Head and Sawtell
respectively. The broadest areas occurred off the Stockton Bight with a zone
width of up to 46.7 kilometres.
The authors also looked at the extent of the
intermediate-depth zone, 25–60m. This is significant because 60m below current
is around the sea level when the Aborigines spread across Sahul. This ranged
from 1.5 kilometres off Botany Bay, 1.6
kilometres off Shellharbour to 17.5 kilometres just north of Yamba.
The majority of wide (greater than 8
kilometres) intermediate-depth areas were located north of Hat Head, reflecting
the overall shallower slope of the shelf in that region. The small number of
wide intermediate areas south of Port Jackson mostly reflected the presence of
shallow embayments and/or offshore reefs.
Some information was also provided on the
shallow-depth zone boundary defined as 25m This was universally narrow along
the NSW coast, varying between 0.3 kilometres off Sydney
Harbour and Botany
Bay to 3.5 kilometres off the Shoalhaven Bight south of Nowra. The
width of the immediate-depth zones was more variable than the shallow-depth
zones: 70 per cent of the widths of shallow-depth zones were between 0.8 and
1.8 kilometres whereas 70 per cent of widths for intermediate-depth zones were
between 5 and 15 kilometres.
In considering this information, we need to
remember that the coastal land as we know it today did not exist in the past,
but has been formed in part by a constant battle between land and sea, the
rivers and creeks depositing silt, the sea eroding the shore. Accepting this
and very roughly :
·
We have a fall in height of 25m
in the first 0.3-3.5 kilometres.
·
Followed by a further fall of
up to 35m in the next 3.5-16 kilometres
·
With a further fall of 60-60m
in the remaining distance to the LGM sea line.
If we take the period to the LGM, the
additional land at then sea levels was most extensive in the Northern Rivers,
narrowed south of Nambucca Heads before widening again. The delta-estuarine-lake
formations that we know today and which were such rich environment in
Aboriginal times did not exist. Lacking the accumulated sand and silt, land
levels along much of the existing coastline would have been lower. The path of
the rivers and streams would have been different, less meandering. They are
likely to have been faster flowing given the slope of the continental shelf.
The pre-LGM coastline was established for a considerable period. I do not know
to what extent the rivers were able to create estuarine conditions, given the
geography that I have described.
The land areas revealed by the LGM drops in
sea levels were greatest in the north and south broken by the strip in the
middle where the continental shelf is particularly narrow. With steeper slopes
and colder temperatures it seems likely if not certain that the land, as
suggested by Sandra Bowdler, became relatively inhospitable.[1] I say
likely but not certain because of the degree of local variation, the
possibility of micro-environments.
With the arrival of the warm Holocene, the
seas rushed back, penetrating deep inland in some spots. You can get a feel for
this is you remove all the present sand dunes, all the now accumulated silt and
sand in the estuaries and flood plains, with a water level 1-2m higher than
present sea levels. Now the streams and rivers carrying higher water volumes in
the wetter climate began to push back against the seas, progressively creating
the coastline we know today.
Archaeological
Dates
We do not know when the Aborigines first
settled the area that would later be called Northern NSW, the broader New England.
We know from dating at Warren Cave
in Tasmania that the Aborigines had reached Tasmania around 35,000 years ago [2]while
dates from Willandra
Lakes in South West New
South Wales suggest occupation as early as 40 to 41,000 years ago, perhaps even
later[3]. The
dates we have for New England are more recent.
The Cuddie Springs site near Brewarrina
suggests occupation as long ago as 35,000 years BP.[4] However,
dates here have been subject to considerable dispute and there presently
appears to be no agreement on the issue.[5]
Excluding Cuddie Springs, we have a date of greater than 20,200 years BP from a
hearth at Glennies Creek 35 kilometres north of Branxton in the Hunter, while a
site on a former terrace of Wollombi Brook near Singleton suggested a date
range of 18,000-30,000 years BP. At Moffats
Swamp near Raymond
Terrace, a date of 17,000 years BP was obtained. On the Liverpool Plains,
Aboriginal occupation has been dated to at least 19,000 years BP[6]. Further
north in South-East Queensland, the Wallen
Wallen Creek site shows continuous occupation from about 20,000 years ago.[7]
I note that there are some problems with
these dates that I have not yet resolved. However, for present purposes it is
the broad pattern that I am interested in.
Note, first, that the dates are late
Pleistocene dates from the LGM period. However, there are no coastal zone dates
from the Hunter to Wallen Wallen Creek. The entire Tablelands and much of the
coast is presently an archaeological blank.
Wallen Wallen Creek lies on North Stradbroke
Island, then part of the
mainland some distance from the coast. The suggestion is that it was a transit
camp for people moving to the coast. Something of the same may be true for Moffats Swamp which lies not far from the
present coastline but would then have been some distance from the sea.
The two other Hunter sites are further
inland and could have been refuge areas with access to water and game. Richard
Wright suggests that the Liverpool Plains was a relatively fertile area even
during the harsh climatic conditions of the LGM, although he notes that there
were periods when the climate did deteriorate significantly.[8]
Dates then seem to vanish. Then we have a
first date of 9,320+/-160 from Stuart’s Point in the Macleay Valley
as the coastal zone begins to stabilise.[9]. From
around 4,000 years ago a rush of dates begins. Intensification had begun.
Discussion
Recognising that the continental shelf in New England is far narrower and therefore the scale
effects of sea level change are less, my preliminary analysis does seem broadly
supportive of the new paper, recognising that I have only read the summary.
However, I do have some questions in my mind.:
To begin with, I am reluctant to accept
that there were no Aboriginal people on the humid coastal strip between the
Hunter and Southern Queensland. I think that
we need a lot more micro or local level information on the changing environment
including sea levels.
Then we have the language patterns. As best
I understand it, the differences between the northern and southern coastal
languages could support re-occupation from north and south. But then we have
the problem of the length of time required for the languages to differentiate
into the pattern that existed at the time of European occupation. I don’t have
an answer for this.
[1] Sandra Bowdler, “The empty coast: Conditions for human occupation
in southeast Australia
during the late Pleistocene”. In O'Connor S, editor, Altered ecologies: fire, climate and human influence on terrestrial
landscapes. Vol. Terra Australis; 32.
http://epress.anu.edu.au: ANU E Press. 2010. p. 177-186.
[2] John Mulvaney & Johan Kamminga, Prehistory
of Australia,
Allen & Unwin, Crows Nest, 1999. P186.
[3] Munvaney & Kamminga, op cit, p197.
There is debate about the Wilandra
Lakes dates, with some
arguing for older dates. Josephine Flood, Archaeology of the Dreamtime, J.B. Publishing, Marleston, revised
edition, 2004, p1.
[4] Josephine Flood, Archaeology
of the Dreamtime, p189.
[5] The Wikipedia article, Cuddie Springs, provides
an interesting discussion on this issue. Accessed 15 April 2009.
[6] Dates drawn from Dominic Steele Consulting Archaeology, Preliminary
Aboriginal Archaeological Survey & Assessment, Proposed Upgrade of State Highway SH23,
Shortland to Sandgate New South Wales,
December 2005, p17
[7] Ian Walters, Antiquity of Marine
Fishing in South-East Queensland, QAR, Vol 9, 1992, pp35-39. P35.
Accessed on
line 4 April 2009.
[8] Richard Wright, The Future of
Australia's Prehistoric Past,
Arts: The Journal of the Sydney University
Arts Association, Vol 12 (1984). pp 22-34
[9] Graham Knuckey, A shell
midden at Clybucca, near Kempsey, New South Wales, Journal, Australian
Archaeology Volume 48, 1999 - Issue 1, pp1-11
