Registro continuo de las variaciones de temperatura del agua de fondo en un volcán submarino (Estrecho de Bransfield, Antártida)

• Autores: Antonio Calafat Frau, Miquel Canals Artigas, Xavier Durrieu de Madron
• Localización: Boletín de la Real Sociedad Española de Historia Natural. Sección geológica, ISSN 0583-7510, Tomo 93, Nº 1-4, 1997 (Ejemplar dedicado a: Ciencia antártica: el papel del SCAR), págs. 53-61
• Idioma: español
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• Resumen
  • español

    El fondeo de dos cadenas de termistores y dos transectos de CTD en el volcán submarino E, situado al SE de la Isla Rey Jorge (Estrecho de Bransfield, Antártida), han proporcionado un registro continuo de las variaciones de temperatura del Agua Profunda del Bransfield (BDW). El fondeo 1 (62º 25,98S/ 58º 23,67W, -1030 m) se sitúa en el interior del cráter y el fondeo 2 (62º 26,17S/ 58º 20,77W, -1000 m) se sitúa en el flanco este del mismo. El periodo de medición, con un intervalo de 20 minutos, se prolongó desde el 22/2/95 al 1/12/95. A profundidades de más de 500 m se encuentra el Agua Profunda del Bransfield (BDW) (q -1ºC , S>34,5 y 02 <7.15 mL.L-1), que se forma anualmente por convección de las aguas procedentes del Mar de Weddell durante el invierno.

    Los registros de ambos fondeos muestran un ascenso térmico desde febrero hasta julio, de -1.29ºC a -0.80ºC, seguido de un brusco descenso, hasta -1.6 ºC, de julio a setiembre. A partir de ahí, las temperaturas del agua cerca del fondo se estabilizan en torno al último valor. El estudio espectral de frecuencias demuestra la influencia mareal en dichas oscilaciones. En ambos fondeos la frecuencias más importantes representan las componentes lunar y solar semidiurnas (M2 y S2) seguidas por las componentes diurnas lunisolar y lunar (K1 y O1).

  • English

    Two short thermistor lines were moored in a submarine volcano in the Bransfield Strait, Western Antarctica, SE of King George Island, in order to monitor deep-water temperature variations (Fig. 1). Mooring-1 (62º 25,98S/ 58º 23,67W, -1030 m) was deployed into the crater of the volcano, and Mooring-2 (62º 26,17S/ 58º 20,77W, -1000 m) on its eastern outer flank. Continuous recording was performed during 282 days, from 22/2/95 to 1/12/95, with a sampling interval of 20 minutes.

    Two perpendicular hydrological transects were also done just before the moorings deployment.

    The hydrologic section in Fig. 2 shows the influence of surficial waters from the Bellingshausen Sea (García et al., 1994), forming a 50 m thick layer of warm, fresh waters (q >1ºC, S<34.2 and 02 >7.3 mL.L-1). The temperature decreases down to 200 m depth, where a warmer, saltier and oxygen depleted layer about 200 m thick appears (q >-0.2ºC, S>34.55 and 02 <6.2 mL.L-1). This layer derives from an intrusion of Circumpolar Deep Water (CDW) into the Bransfield Strait across the Boyd Strait, between the Snow and Smith islands. The CDW moves northeastwards along the Shetland Islands continental slope (Capella et al., 1992). Below 500 m depth, the strait is occupied by the Bransfield Deep Water (BDW), with temperature less than -1ºC, salinity about 34.53 and increasing dissolved 02 concentration up to 7.15 mL.L -1. BDW originates from the annual winter convection of waters from the Weddel Sea.

    The temperature variation range measured by the moored thermistors is about 0.8ºC. For both thermistors, the temperature time series show a clear seasonal signal with a continuous increase between February and July, from -1.29ºC to -0.80ºC, followed by a sharp decrease down to -1.6 ºC from July to September. The spectral analysis of the temperature time series (Fig. 4) shows five peaks of high energy. Both time series are dominated by the same tidal harmonic components: lunar (M2) and solar (S2) semidiurnal components, lunisolar (K1) and lunar (O1) diurnal components, and lunar fortnightly (Mf) component. The semidiurnal and diurnal tidal components have higher spectral densities on the outer flank of the volcano, suggesting an attenuation of tidal currents in the crater. Conversely, the lunar fortnightly (Mf) tidal component with a period of 328 h appears with similar amplitude in and outside the volcanic crater.

    Cross-spectra analysis between the two moorings shows highly significant correlation for the different tidal periods. Phase differences for these periods also indicate that the temperature signal in the crater lags the one on the outer flank of the volcano.