Extending instrumental sea-level records with coral microatolls

Relative sea level (RSL) records are crucial for constraining future sea level projections. Currently the two main data sources of these records are tide gauges and satellite altimetry, however both of these are limited temporally. In the case of tide gauge records, the chronologically longer data set, an additional problem is their uneven spatial distribution, with low latitudes severely underrepresented. This is much the case in Southeast Asia where reliable tide gauge records only begin in the 1970s. Rather fortuitously however, coral microatolls, abundant on many reefs in the low latitudes including Southeast Asia, can be used as proxy sea-level records. These vertically constrained coral colonies can record relative sea level with vertical resolution potentially on the order of ~3 cm, and annual temporal resolution.

Here we present RSL reconstructions based on a combination of tide gauges from the Malacca straits region and three coral microatolls sampled on Mapur Island, approximately 100 km to the south east of Singapore. We reconstructed 8 sea-level index points for the period between 1915 and 2016, with the sea level trend over this period equal to 0.43 ± 0.41 mm/yr. (1s). The tide gauge records for the same period produce a faster rate of sea level rise at 1.16 ± 0.35 mm/yr. (1s). When the two records are combined the trend is 0.83 ± 0.28 mm/yr. (1s). The combined record is characterised by lower uncertainties than either of its components and provides a better informed, and regionally specific, RSL record. Coral microatolls can be found in many coastal reefs around the region and could be used to supplement tide gauge series in many key regions of demographic or economic importance.