RRS Discovery Cruise 230, 07 Aug-17 Sep 1997. Two hydrographic sections across the boundaries of the subpolar gyre: FOUREX

This report describes RRS Discovery Cruise 230, designed as a repeat of the International Geophysical Year (IGY) survey section 4, roughly from Cape Finisterre (Spain) to Cape Farewell (Greenland). IGY 4 was first surveyed in 1957, so this repeat gives a 40–year look at decadal variability in the North Atlantic from the eastern boundary regime via the junction of subtropical and subpolar gyres to the western boundary regime. Additional short sections were measured (a) midway between Cape Farewell and Denmark Strait, (b) across Denmark Strait and (c) from Iceland to Scotland in order (i) to assess the spatial variability of the western boundary regime up the east Greenland coast to Denmark Strait, (ii) to assess the exchange between the northern North Atlantic and the Nordic Seas, (iii) to create a large scale North Atlantic closed box for evaluation of the circulation, and (iv) to continue the long time series of Rockall Trough sections. Sections were measured with stations for CTD, LADCP and tracer chemistry (CFCs, oxygen, nutrients, CO2). Continuous measurements of high precision position and heading navigation data were made; also of VM–ADCP, depth and TSG. Continuous high–quality meteorological measurements were made, with a view to assessing Ekman fluxes, and comparing with fluxes inferred from Irminger Basin float data. This cruise is a UK contribution to the World Ocean Circulation Experiment.