Abstract

<p>Mean sea levels are changing worldwide, and local tidal changes have been widely reported. Knowledge of regional changes in mean sea level, and local changes in tides are crucial to inform effective climate adaptation. An essential element of this is the availability of accurate observations of sea level. Sea level data in the Republic of Ireland, prior to the establishment of the National Tide Gauge Network in the mid-2000s, is very limited but belies a wealth of historical data available in archival form. In this study, we digitize records located in Cork Harbour, Ireland from 1842 and show how short duration (6 weeks), high quality data, with a large interval (177 years) to the present, can accurately inform tidal and mean sea level changes. We consider error sources in detail and estimate that for M2 the accuracy of these historical measurements is 1% and 2 minutes for amplitude and timing respectively; and our mean sea level estimates are accurate to the centimetre level. Our results show remarkable tidal stability with a 2% change in the amplitude of the M2 component and 4 minute change in the phase over a period of 177 years; and a mean sea level rise of 41 cm in the Cork Harbour area since 1842, approximately in line with global mean sea level trends plus local glacial isostatic adjustment. More broadly, we show that with careful seasonal, nodal, and atmospheric corrections, together with good knowledge of benchmark provenance, these historic, survey-oriented data can accurately inform of sea level changes.</p>

Highlights

  • Sea level is a combination of mean sea level (MSL), tide, and a non-tidal residual due to weather and other causes (Pugh and Woodworth, 2014)

  • Haughton (1856) made a nationwide survey of high and low waters for a period of a year in 1850–1851 at 12 sites, 6 of which coincide with the Airy sites. Surveys such as those of Airy and Haughton are limited in time – 8 weeks of continuous measurements in 1842 and upwards of 1 year of high and low waters in 1850–1851, respectively – the long interval of over 150 years between these measurements and modern measurements indicates that long-term MSL and tidal changes may be detected against natural year-on-year sea level variations

  • Airy and most 19th-century sea level analysts computed mean tide levels (MTLs), the average of paired high and low water levels, whereas TASK analyses provide an estimate of Z0, which is the mean sea level (MSL), the arithmetic average of all data

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Summary

Introduction

Sea level is a combination of mean sea level (MSL), tide, and a non-tidal residual due to weather and other causes (Pugh and Woodworth, 2014). Long-period mean sea level data prior to the establishment of the National Tide Gauge Network in the mid-2000s in the Republic of Ireland are limited to observations in Dublin (1938–2009) and Malin Head (1958–2002) (Holgate et al, 2013). Surveys such as those of Airy and Haughton are limited in time – 8 weeks of continuous measurements in 1842 and upwards of 1 year of high and low waters in 1850–1851, respectively – the long interval of over 150 years between these measurements and modern measurements indicates that long-term MSL and tidal changes may be detected against natural year-on-year sea level variations To this end we have initiated a full study of these historical data, especially at the 22 Airy sites and the 12 Haughton sites. In order to determine the tidal constituent changes, we obtained a 6-week record of sea level at Airy’s exact location in Passage West in June–July 2019

Case study location
Data collection
Adjustments and confidence limits
Seasonal variations
Nodal adjustments
Uncertainties
Adjustments to mean sea level
Weather effects
Datums
Results
Mean sea level
Discussion
Conclusions and future work
Full Text
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