The new-submerged Northwest Shelf of Sahul — the combined landmass of Australia and New Guinea at times of lower sea level — was a vast area of land in the Late Pleistocene epoch that connected the Australian regions of the Kimberley and western Arnhem Land during times of lower sea level than today.
Thank you for reading this post, don't forget to subscribe!
Map of Sahul showing the extent of the now-submerged continental shelf (dark gray), with the area of the Northwest Shelf demarcated by a dashed black box, and the present-day distribution of the Köppen climate groups (seasonal precipitation and temperature) showing the extent of modern-day Australia and New Guinea. The tropical distribution of Late Pleistocene sites containing early axe technology are shown as black circles, sites without early axe technology as gray circles, and sites demonstrating Late Pleistocene occupation of the now submerged continental shelves as white circles. Image credit: Peter Hiscock / Norman et al., doi: 10.1016/j.quascirev.2023.108418.
For the majority of the last 65,000 years of human history in Australia, lower sea levels revealed a vast expanse of dry land in the northwest of the continent, connecting the Kimberley and Arnhem Land into a contiguous area.
Through meticulous analysis of high-resolution bathymetric data, Griffith University researcher Kasih Norman and colleagues found that this Northwest Shelf, now submerged, existed as an extensive archipelago during Marine Isotope Stage 4 (71,000-59,000 years ago), which remained stable for 9,000 years.
This transformed into a fully exposed shelf in Marine Isotope Stage 2 (29,000-14,000 years ago), featuring an inland sea adjacent to a sizable freshwater lake, encircled by high escarpments cut by deep gorges.
The team’s demographic modeling indicates that the Northwest Shelf experienced fluctuating potential carrying capacities through Marine Isotope Stages 4-2, potentially supporting populations ranging from 50,000 to 500,000 people at various times.
However, rapid global sea level rises between 14,500-14,100 years ago (during Meltwater Pulse 1A) and between 12,000 and 9,000 years ago resulted in the rapid inundation of approximately 50% of the Northwest Shelf, causing profound changes in the space of human life spans.
These events likely triggered the retreat of human populations ahead of the encroaching coastline, evident in peaks of occupational intensity at archaeological sites across the Kimberley and Arnhem, and the sudden appearance of distinctive new rock art styles in both regions.
“The presence of this extensive archipelago likely facilitated the successful dispersal of the first maritime explorers from Wallacea — the region of modern-day Indonesia — providing a familiar environment for their adaptation to the vast continent of Sahul,” Dr. Norman said.
Furthermore, the study emphasized the critical role that the now-submerged continental margins played in early human expansions.
“The temptation to overlook the continental shelf margins of Late Pleistocene Sahul in discussions of early peopling and expansion risks oversimplification and misunderstanding of this pivotal period in history,” Dr. Norman said.
The implications underscored the need to reevaluate the narrative of early human migration and the impact of climate change on ancient populations.
“Our demographic modeling showed a peak in population size at the height of the latest Ice Age around 20,000 years ago, when the entire extent of the Northwest Shelf was dry land,” Dr. Norman said.
“This finding has now been supported by new genetic research showing very large populations for the Tiwi Islanders — located just to the east of the study region — at the height of the latest glacial period.”
The findings appear in the journal Quaternary Science Reviews.
_____
Kasih Norman et al. 2024. Sea level rise drowned a vast habitable area of north-western Australia driving long-term cultural change. Quaternary Science Reviews 324: 108418; doi: 10.1016/j.quascirev.2023.108418
