16 
Sy, A. et al. (2002): Upper Ocean Climate Ship-of-Opportunity Programme of BSH - A Status Report 
3. BSH contribution to the climate module of GOOS in the North Atlantic Ocean 
(GOOS A-2 corridor) 
3.1 Scientific background 
As a contribution to CLIVAR and GOOS, BSH combined the AX-3 XBT programme with 
occasional XCTD sections and with repeats of research vessel based full-depth CTD 
measurements along the extended WOCE hydrographic section A-2/AR19 between English 
Channel and Grand Banks (Fig. 10). The scientific rationale of this BSH funded programme is to 
monitor ocean climate variability and change in this North Atlantic key region (BSH, 1999). This 
ocean area is characterized by extremely high variability of the North Atlantic Current (NAC) 
(e.g. Krauss, 1986; Sy, 1988; Sy et al., 1992; Lozier et al., 1995; Schmitz, 1996) (Figs. 5, 11 
and 15). Changes in its path and intensity, and hence the space-time variability of its heat 
transport, have an obvious impact on European climate. Furthermore, this corridor represents 
the division line of subpolar-subtropical exchange, and anomaly patterns suggest a north-south 
heat storage anomaly dipole across this latitude. Long-term observations in such a priority 
region thus are indispensable contributions to European climate prediction efforts. 
Fig. 10:The BSH network of ocean climate investigation in the central North Atlantic 
(GOOS A-2 corridor). It consists of bi-monthly XBT sections (red) 
supplemented by CTD sections every 2-3 years (black dots). The locations 
of hydrographic stations have been designed to form closed boxes in order 
to improve geostrophic current estimates by application of the box inverse 
theory (Wunsch, 1978; Sy, 1988). 
It is believed that the THC of the North Atlantic underlies a natural and recurrent mode of 
variability of the atmosphere known as the North Atlantic Oscillation (NAO), i.e. the northern 
North Atlantic responds by significant adjustments of its stratification to changes in the strength 
and location of the sea level pressure dipole between the Icelandic low and Azores high on 
interannual to interdecadal time scales (Dickson et al.,1996; Sy et al.,1997a; Bersch et al., 1999;