Historical sea-level changes in Australia: Testing the Arctic ice melt hypothesis

Rates of regional and global sea-level rise during the 20th century were faster than in any
century over the last 3000 years. Sea-level rise accelerated between ~1850 and ~1950, before
greenhouse gases became the dominant forcing agent, which suggests, in part, a natural
origin. The acceleration appears to have been more rapid in the Southern Hemisphere, which,
according to geophysical theory, could point at a contribution from Northern Hemisphere
land-based ice melt. More high-resolution relative sea level (RSL) reconstructions from the
Southern Hemisphere are needed to test this hypothesis, and to complement a limited dataset
of proxy and tide-gauge records. This study establishes three new RSL records for
southeastern Australia (covering ~1830 – 2018) from analyses of salt-marsh sediments. New
training sets of contemporary salt-marsh foraminifera were used for transfer-function
analyses to derive palaeo sea-level estimates. High-resolution chronologies were established
via Accelerator Mass Spectrometry radiocarbon, radiogenic lead, stable lead isotope ratios
and pollen analyses. The new records demonstrate that, when corrected for glacio-isostatic
adjustment, sea level has risen by ~0.2 – 0.3 m since ~1830 in southeastern Australia. Rates of
sea-level rise were especially high over the first half of the 20th century, with maximum
average rates of 4.0 (-0.4 – 7.1 95 % confidence range) mm yr-1, but there is regional variability
between sites. A modelled sea-level budget indicates that the acceleration was initially driven
by the barystatic component (including gravity, rotation and deformation), but subsequently
amplified and driven by sterodynamic sea-level change. An analysis of the sea-level
fingerprints of the barystatic component to 20th century global sea-level rise points at a
significant input from the Greenland (17 %) and Antarctic Ice Sheets (11 %) as well as glaciers
in Alaska (14 %), the Russian Arctic (10 %), western Canada and the US (9 %), south Asia and
southern Andes (8 % each).