Tuesday, 17 July 2012

Extending the record - Nauru, west-central Pacific

Nauru is a small rocky island just 0.5° south of the equator. I have a slight connection with Nauru in that I was tasked with analysing rock samples from Nauru for phosphate content, many (many!) moons ago. Nauru has a SEAFRAME tide-gauge (and meteorological) installation on the west of the island, maintained by the South Pacific Sea Level and Climate Monitoring Program run by the Australian National Tidal Centre (BOM). A chart for Nauru (1993-2011) is included on the  South Pacific Sea Level reference page (sidebar top). PSMSL has data from an earlier gauge which I will refer to as Nauro-A, and the 1993 installation as Nauro-B. The overlap between the two records spans just 18 months, but the difference (due to different benchmarks used) varied little over that period, averaging 267mm.

With the data from Nauro-A reduced by 267mm until the date of the 1993 installation a reconstruction from mid-1974 to end 2011 is possible.

Note that while the overall rate is just 0.59 mm/year, the trend line is below the 13-month moving-average line on the left.

A plot of the annual rate from 1974 to the year on the lower axis confirms that the long-term rate has stabilised at just over 0.5 mm/year. Is Nauru rising from the waves, cancelling out the effect of much of the sea-surface rise?

The GPS plot from the station on Nauru seems to contradict that idea, at least between 2003 and 2009 (latest available on the 'net). If anything, the station dropped a little over that period, which would have increased the gauge readings. With this reconstruction, and the convincing data from Hawaii in my last post (amongst many other instances), I'm beginning to doubt the veracity of the claimed 3.2 mm/year "accelerated" rate post-1993 (satellite era for sea-level measurements).

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