Short Note Determination of the mean sea level at Deception and Livingston islands, Antarctica BISMARCK JIGENA 1 , JUAN VIDAL 1 and MANUEL BERROCOSO 2 1 Department of Applied Physics, University of Cádiz, CP 11510, Puerto Real, Cádiz, Spain 2 Department of Mathematics, University of Cádiz, CP 11510, Puerto Real, Cádiz, Spain bismarck.jigena@gm.uca.es Received 5 March 2014, accepted 16 June 2014, first published online 5 September 2014 Introduction According to Dragani et al. (2004), the first observations of the sea levels at Deception Island were made in 1991. Tidal data were obtained over four days in summer by a visual tide staff located near the Decepción Station (Argentina) geodetic benchmark (BARG). This geodetic benchmark, belonging to the Deception Island geodetic network (REGID), was used as the vertical and horizontal datum. Based on these tidal data, an orthometric height value of 2.547 m for the BARG was calculated. This orthometric level was translated by geometric levelling to the point LN00, the fundamental point of the levelling network of Deception Island (RENID); the mean sea level obtained relative to LN00 was 5.430 m. Later, Vidal et al. (2012) calculated mean sea levels (MSLs) with respect to vertices of the REGID corresponding to tidal data registered during three months in the 2007–08 Antarctic campaign at DECMAR (Deception Island) and LIVMAR (Livingston Island) stations. The results of new tidal observations for two years on Deception and Livingston islands are presented here. Instrumentation and data Data were obtained using two moorings, each with a SAIV TD304 bottom pressure sensor at points near the coast, obtaining average local values of depth of the tide gauge of 3.147 m at Deception Island and 7.475 m at Livingston Island. The tidal observations at DECMAR and LIVMAR stations were made between February 2011 and April 2013. Pressure (P), temperature (T) and conductivity (C) data were recorded at the stations with a CTD SAIV SD 204 sensor that has an accuracy of ± 0.02 ppt for salinity, S, (derived from P, T and C) and ± 0.01ºC for T. Additionally, AQUAlogger 520 PT were used. These sensors have an accuracy of ± 0.05°C for T and 0.005% of full scale (10 m) for P. The geometric levelling was made using a Leica model NA2 optical level with an accuracy of ± 0.7 mm for one kilometre double run levelling. The GPS data for positioning of benchmarks and stations were taken from Vidal et al. (2012). The gravimetric observations were made with a LaCoste & Romberg model D-203 relative gravimeter. Methodology To convert hydrostatic pressure into a sea level equivalent height P = P a + ρgh was used, where P is the pressure registered by the sensor of the tide gauge, P a is the atmospheric pressure, g is the acceleration due to gravity (average value calculated for Deception Island is 9.822083 m s -2 ) and ρ the density of the water in the study area, calculated using the records of T and S. Vidal et al. (2012) used a constant reference value of 990.8 mb (hPa) as P a which corresponds to the average value of P a in the region during the period 1978–89 (Rakusa-Suszczewski et al. 1992). The sea level for any particular time can be corrected by adding or subtracting the changes caused by P a changes on the reference values: at low enough frequency the correction is c. -1 cm of sea surface height for every +1 mb (hPa) of P a (Chelton & Enfield 1986). For this study, records of P a were taken concurrently with the tidal measurements, obtaining average values of 988.39 mb at Deception Island and 987.27 mb at Livingston Island. Fig. 1a. Location of tidal station. b. Detailed map of Livingston Island showing the location of LIVMAR and BEJ1. c. Detailed map of Deception Island showing the location of DECMAR, COLA, LN00 and BARG. Antarctic Science 27(1), 101–102 (2015) © Antarctic Science Ltd 2014 doi:10.1017/S0954102014000595 101 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102014000595 Downloaded from https://www.cambridge.org/core. IP address: 207.241.231.80, on 30 Oct 2018 at 08:28:11, subject to the Cambridge Core terms of use, available at