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is subject to secular and periodic fluctuations as well as irregular or random variations.

These variations have been shown to be tightly correlated with the dynamics of the

Atmospheric Circulation Index (ACI) or the ‘Vangengeim-Girs’ Index (Girs, 1974),

which characterises a dominant direction of air mass transport within Atlantic-Eurasian

region. Global climate changes, such as variations in atmospheric circulation and wind

stress, would affect the LOD (Klyashtorin, 1998). The LOD index is measured as the

difference between the actual (astronomical) length of the day and the standard day of

86400 SI seconds (Stephenson and Morrison, 1984). The longest available LOD time

series covers more than 350 years (McCarthy and Badcoc, 1986, Figure 3), but the time

series appears inconsistent (data prior to 1800 displayed little variation in comparison to

the 1800-1984 period, Figure 3). The International Time Bureau in Paris carries out

continuous registration of the LOD since 1800. These records corroborate the above

LOD index over the 1800-1984 period.

Air temperature has been recorded in Europe since centuries and has been

therefore widely used to assess environmental changes on animal populations over a

long-term period (e.g. Gian-Reto et al., 2002). There is, however, no consistent time

series of sea surface temperature (SST) for the Mediterranean before the most recent

period. Some studies, however, showed that air temperature correlates quite well with

inshore sea temperature, so that we used air temperature as a proxy of SST (e.g.

Fromentin and Planque, 1996; Fromentin et al., 1998; Southward et al., 1988;

Beaugrand et al., 2002). We firstly focused on two time series of temperature of the

Northern Hemisphere (NH), because they were the longest ones available: (i) the annual

average of the NH air temperature estimated over the past 150 years from a grid box of

time series of land and ocean surface air temperature (Jones et al., 1997; 1999; 2001;

Parker et al., 1994, Figure 3) and (ii) an annual time series of NH temperature

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