Juan Vidal

Study of tides and sea levels at Deception and Livingston islands, Antarctica

Abstract During the 2007–08 Spanish Antarctic campaign, two moorings of bottom pressure sensors were carried out over a ten week period. This paper presents the results of the tidal analysis from sea level records obtained at Deception and Livingston islands (South Shetland Islands, Antarctica). The main objective of this paper is to present a detailed study of the tidal characteristics at these two islands, for which statistical and harmonic analysis techniques are applied to the tidal records. A geodetic network was used to reference the pressure sensors. Geometric levelling, with an accuracy of 1 mm, allowed us to link the tidal marks with geodetic vertices located on Livingston and Deception islands. The amplitudes and phase lags obtained by harmonic analysis are compared to the harmonic constants of several coastal stations and co-tidal and co-range charts. Results show an evident influence of tides in the sea level signal, with a clear mixed semi-diurnal behaviour and a daily inequality between high and low waters. Measurements of salinity and temperature were made using electronic sensors. Results from this study showed that salinity and temperature were strongly influenced by tides. Seawater temperature varied in a manner that was consistent with the time series of residual bottom pressure.

Hydrodynamic Modeling of Port Foster, Deception Island (Antarctica)

A numerical, non-linear, barotropic, two-dimensional tidal model is implemented and used to simulate the M2,S2, O1 and K1 constituents in Port Foster (Deception Island, Antarctica). The model is validated by comparing the simulation results against measured water levels data collected in several stations inside the domain. Once the model has been validated, the total volume of Port Foster is exchanged with Bransfield Strait during the flood and the ebb tide have been estimated.

Precise determination of HPGe detector efficiency for gamma spectrometry measurements of environmental samples with variable geometry and density

Abstract A methodology to determine the full energy peak efficiency (FEPE) for precise gamma spectrometry measurements of environmental samples with high-purity germanium (HPGe) detector, valid when this efficiency depends on the energy of the radiation E, the height of the cylindrical sample H, and its density ρ, is introduced. The methodology consists of an initial calibration as a function of E and H and the application of a self-attenuation factor, depending on the density of the sample ρ, in order to correct for the different attenuation of the generic sample in relation to the measured standard. The obtained efficiency can be used in the whole range of interest studied, E = 120–2000 keV, H = 1–5 cm, and ρ = 0.8–1.7 g/cm3, being its uncertainty below 5%. The efficiency has been checked by the measurement of standards, resulting in a good agreement between experimental and expected activities. The described methodology can be extended to similar situations when samples show geometric and compaction differences.

Determination of the mean sea level at Deception and Livingston islands, Antarctica

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 2.547m 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 5.430m. 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.

Determination of an experimental geoid at Deception Island, South Shetland Islands, Antarctica

Abstract Deception Island is an active volcano located in Bransfield Strait. Its volcanic activity is linked to the presence of gravity anomalies that influence the definition of the geoid. In this paper, a precise undulation geoid model (GeoiDEC14) has been computed from GPS, gravimetric and levelling measurements. GeoiDEC14 highlights local anomalies of the island that match with hot spots, such as the minimum values shown in Fumarole Bay and Whalers Bay (fumarole areas), or the maximum values found in the remains of lava at Colatinas, Black Glacier and Murature Point. Comparison of GeoiDEC14 with global models always shows negative values due to an average of 18.80 m for our model compared to 19.80–20.60 m for models such as ITSG-Grace2014s, EGM08, AIUG-Grace03s or EGM96. This difference is due to the lack of resolution of global models and to the volcanic activity on the island. To confirm the results, the same measurements were taken on nearby Livingston Island. The values of geoid undulation on this island reaffirm the lack of detail in the global geoid in the area, presenting an average of 18.90 m, similar to the average value of GeoiDEC14.