Diurnal and annual variations of temperature and salinity of interstitial water in sandy beaches

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Abstract
The dynamics of temperature and salinity was studied at four beaches situated along the Swedish East and West Coast, representing salinities from 7 to 22 ‰. Diurnal and seasonal temperature variations were registered at various depths in the beach. The maximum diurnal amplitude was measured in May and amounted to 37.2°C with a maximum temperature at the dry sand surface of 43° C. In winter the sand is frozen often down to 60–70 cm depth, but in spite of low air temperatures the values below a few cm depth will not fall below —2 to —3°C. The greatest diurnal amplitudes and vertical gradients are attained in spring. The pronounced horizontal and vertical gradients in summer decrease towards autumn when, however, during a short period with night frost, great diurnal amplitudes again occur. Changes in salinity chiefly take place along a horizontal gradient at right angles to the water's edge. Inside a sea of 7‰. S freshwater could sometimes be encountered at 0.8 m distance from the water-line. The vertical gradient is less pronounced. The greatest difference between the salinity of the upper 5 mm of sand and the layers 2.5 cm further down amounted to 140 ‰. The influence of waves, evaporation, rain, beach slope and water-level upon the salinity conditions of the sandy beach is discussed.