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In-Depth Information
Harmer realised that in the present period Atlantic depressions which approach
Western Europe mostly travel east over the North Sea between eastern England
and Holland. As a result, strong westerly winds and rough seas which generally
prevail in the southern sector of these low pressure systems would frequently affect
the Dutch coast.
The climate of the Pliocene appears to have undergone gradual refrigeration, as
indicated by changes in the molluscan fauna of the Crag Sea. Harmer noted that
although species were characteristically southern during the early Pliocene
(resembling those of the Mediterranean in the present period) the sea was gradually
invaded by boreal mollusca which eventually completely supplanted the southern
fauna in the Red Crag as the climate became cooler on the approach of the Pleis-
tocene glaciation. He found, for instance, that species now only found north of the
Arctic Circle, became established in the Crag Sea as far south as 52 N.
Harmer suggested that the climate of regions lying to the north of the British Isles
during the late Pliocene probably became considerably colder than today as ice
sheets and snowfields were established over Scandinavia, leading to the formation
of permanent anticyclones. He proposed that these high pressure patterns which
later extended across the British Isles and northern Europe during the Pleistocene
may be compared, but on a different time-scale, with the semi-permanent anticy-
clones which form in winter during the present period over the continental regions
of northern Eurasia and North America. Under such so-called blocking high con-
ditions travelling depressions approaching the British Isles from the North Atlantic
take a more southerly track than usual with stormy weather and strong easterly
winds frequently occurring over eastern England and the southern North Sea.
Harmer described how such conditions in the Pliocene epoch might have affected
northeast Essex where he had spent several years carrying out field studies of the
Red Crag.
It is not difficult to understand, when standing on the cliff at Dovercourt, looking out to sea
over the bay formed by the projecting headlands of Walton-on-the-Naze on one side, and
of Felixstowe on the other, that it would need only the prevalence of strong easterly winds
to reproduce there the conditions of the Red Crag period. Were the direction of the winter
gales which now drive vast quantities of sand and dead shells on to the shores of Holland,
turned towards Essex, the mud flats of Dovercourt Bay would soon become silted up with
shelly sand, as was that of the Waltonian region at a former period (Harmer
1902
).
4.3 Weather and Climate in the Pliocene and Pleistocene
Epochs
In 1901, Harmer published a landmark article on palaeometeorology in the
Quarterly Journal of the Geological Society, 'The influence of the winds upon
climate during the Pleistocene Epoch: A palaeometeorological explanation of
some geological problems'. This paper (read on 8 May 1901 at the Proceedings of
