The dataset includes full-depth hydrographic profiles and current data collected by acoustic Doppler current profilers (ADCPs). Water samples were collected and analysed for salinity, inorganic nutrients (nitrogen, phosphorus, silicon), organic nitrogen and phosphorus components, dissolved organic carbon and alkalinity. Measurements of chlorofluorocarbons (CFCs), sulphur hexafluoride (SF6) and helium/tritium tracers were also collected to identify ages of water masses. These core observations were supplemented by measurements made by tied PhD students: measurements of Dissolved Organic Nitrogen (DON) and Dissolved Organic Phosphorus (DOP); isotopic nitrogen signatures; atmospheric deposition of nitrogen and phosphorus; measurements of dissolved organic carbon and dissolved oxygen; and plankton respiration rates. These measurements were taken on the RRS Charles Darwin across the North Atlantic, departing from Bermuda on 1 May 2005 and arriving in Lisbon on 15 June 2005. Data were collected via a number of conductivity-temperature-depth (CTD) casts and continuous underway measurements. The study aimed to examine why ocean temperatures are rising within the tropics and mid-latitudes of the North Atlantic but decreasing at high latitudes. Investigators: National Oceanography Centre, Southampton (NOCS): Elaine McDonagh, Brian King, Harry Bryden, Richard Sanders, Paula Mcleod . University of Liverpool: Ric Williams, George Wolff, Rhiannon Mather, Susan Leadbetter. University of East Anglia: Carol Robinson, Andy Watson, Tim Jickells, Ute Schuster. Proudman Oceanography Laboratory: Clare Postlethwaite.