Sea level rise in Southwest Pacific dropped by factor of 6 during latter half of 20th century

According to a paper published last week in the journal Earth and Planetary Science Letters, the rate of sea level rise in the Southwest Pacific region (Tasmania & New Zealand) dropped by a factor of 6 from 4.2 mm/yr between 1900-1950 to only 0.7 mm/yr between 1951-2000.

Nineteenth and twentieth century sea-level changes in Tasmania and New Zealand

W. Roland Gehrels^a, , , S. Louise Callard^b, Patrick T. Moss^c, William A. Marshall^a, Maarten Blaauw^d, John Hunter^e, J. Andrew Milton^f, Mark H. Garnett^g

Abstract

Positive deviations from linear sea-level trends represent important climate signals if they are persistent and geographically widespread. This paper documents rapid sea-level rise reconstructed from sedimentary records obtained from salt marshes in the Southwest Pacific region (Tasmania and New Zealand). A new late Holocene relative sea-level record from eastern Tasmania was dated by AMS¹⁴C (conventional, high precision and bomb-spike), ¹³⁷Cs, ²¹⁰Pb, stable Pb isotopic ratios, trace metals, pollen and charcoal analyses. Palaeosea-level positions were determined by foraminiferal analyses. Relative sea level in Tasmania was within half a metre of present sea level for much of the last 6000 yr. Between 1900 and 1950 relative sea level rose at an average rate of 4.2 ± 0.1 mm/yr. During the latter half of the 20th century the reconstructed rate of relative sea-level rise was 0.7 ± 0.6 mm/yr. Our study is consistent with a similar pattern of relative sea-level change recently reconstructed for southern New Zealand. The change in the rate of sea-level rise in the SW Pacific during the early 20th century was larger than in the North Atlantic and could suggest that northern hemisphere land-based ice was the most significant melt source for global sea-level rise.

Highlights

► Salt marshes in Tasmania and New Zealand record rapid recent sea-level rise. ► Throughout the last 6000 yr sea levels were relatively stable. ► Sea level started rising substantially between 1880 and 1900. ► The rate of sea-level rise in Tasmania between 1900 and 1950 was 4.2 ± 0.1 mm/yr. ► Early 20th century sea-level rise may be attributed to Northern Hemisphere ice melt.