Geoscience Reference
In-Depth Information
Figure 1.3 Left: Henry Bigelow at the wheel of the schooner Grampus in 1912 (courtesy
Bigelow Laboratory). Right: Ken Bowden (courtesy University of Liverpool).
of the biological system developed gradually and only came fully to fruition in the
second half of the twentieth century. A number of pioneering studies were under-
taken before World War II. For example, Knudsen (1907) estimated residual flows
in the North and Irish Seas using a continuity argument for mass and salt applied to
the observed salinity distributions. The results revealed surprisingly small net flows;
for the Irish Sea, Knudsen estimated a net northwards flow of
2cms 1 through the
North Channel. In another important development, G. I. Taylor estimated the level
of tidal energy dissipation in the Irish Sea (Taylor, 1922 ) and showed how it fitted
into the global pattern of energy loss.
By the 1950s, the continuing accumulation of data sets, mainly through the work
of the fisheries agencies, stimulated investigations of the processes controlling the
distribution of water properties. Important contributions in the 1950s and 1960s were
made by Kenneth Bowden ( Fig. 1.3 ), who was amongst the first to investigate the
mechanisms controlling the salt and heat content of the water column. By allowing for
horizontal mixing in the salt balance, he developed an improved model of transport
through the Irish Sea (Bowden, 1950 ) and showed that the net flow is
<
0.5 cm s 1 ,
significantly lower than Knudsen's earlier estimate. This picture of weak residual flows
was further supported by a study of the heat budget for the Irish Sea (Bowden, 1948 ),
from which he concluded (correctly) that the seasonal changes in heat content can
largely be accounted for by the transfer of heat through the sea surface, with the
residual currents playing only a minor role. This understanding of the relative roles
of advection and surface fluxes will be fundamental to our discussion of shelf sea
stratification in Chapter 6 .
Bowden also contributed to the understanding of tidal dynamics in shelf seas by
determining the turbulent stresses in the water column which were bringing about
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