Periodicities in sediment temperature time-series at a marine shallow water hydrothermal vent in Milos Island (Aegean Volcanic arc, Eastern Mediterranean) Stefano Aliani a, * , Roberto Meloni a , Paul R. Dando b a CNR Institute Marine Science Forte S.Teresa, Pozzuolo di Lerici I-19036, La Spezia, Italy b School of Ocean Sciences, University of Wales-Bangor, Menai Bridge, Anglesey LL59 5AB, UK Received 23 June 2003; accepted 26 November 2003 Abstract Time-series data sets of total bottom pressure (tidal plus atmospheric), seawater temperature and sediment temperature from a marine shallow hydrothermal vent (Milos, Hellenic Volcanic Arc, Aegean Sea) were studied to determine factors influencing periodicity at the vents. Bottom pressure and vent temperature were mainly opposite in phase, with the main fluctuations of vent temperature occurring at tidal frequencies. Although the fluctuations in atmospheric pressure were of the same order as those due to tidal pressure, the contribution of atmospheric pressure was considerably weaker at diurnal frequencies. Some sudden discontinuities in sediment temperature were recorded, at least one of these may have been caused by seismic events. Seawater temperature changes were not reflected in the sediment temperature record. Transient loadings, such as tidal loadings, barometric pressure and earth tides, may affect the pore pressure in sediments, influencing fluid expulsion and sediment temperature as a consequence. Most of the contribution to the fluctuations in sediment temperature depends on tidal loadings. Gravitational forces, in the form of earth tides, can also be involved and barometric pressure is probably responsible for long period temperature oscillations. D 2004 Elsevier B.V. All rights reserved. Keywords: Hydrothermal vents; Sediment temperature; Tide; Milos Island; Aegean Sea 1. Introduction Temperature is one of the most commonly mea- sured variables in long-term observations on hydro- thermal vents, due to the ease of measurement and to the stability of the sensor in corrosive environments. The temperature of fluid from submarine hydrother- mal vents changes over time according to the activity of the vent system (Foucher et al., 1992; Kinoshita et al., 1996; Schultz et al., 1996) and is important both in determining the distribution and behavior of vent biota (Hessler et al., 1988; Dando et al., 1995c; Chevaldonne ´ et al., 1991; Fujiwara et al., 1998; Momma et al., 1998) and in following the mixing of hydrothermal fluids with seawater (Chevaldonne ´ et al., 1991; Stu ¨ben et al., 1996). The deep sea sedimented vent field in the Guaymas Basin (Little et al., 1988) showed evidence of fluid 0924-7963/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2003.11.015 * Corresponding author. Tel.: +39-01-8797-8311; fax: +39-01- 8797-0585. E-mail address: stefano.aliani@ismar.cnr.it (S. Aliani). www.elsevier.com/locate/jmarsys Journal of Marine Systems 46 (2004) 109 – 119