Between September 25 and October 25 there were a total of 69 CTD casts with the NBP’s 24 bottle rosette system deployed from ship’s Baltic room (‘Baltic CTD’) and 14 casts with a sensor-only CTD package deployed from the stern A-frame (‘Stern CTD’) when conditions or work on the ice did not allow starboard-side access to the water. The Baltic room system includes a 24-place rosette frame with ... bullister-type rosette bottles of slightly less than 10 liter capacity each. Data acquisition for these two CTD systems as well as the Trace Metal Clean (TMC) CTD took place on an NBP Windows XP computer running Sea-Bird’s Seasave software. Electronics problems and computer software freeze-ups required repeated re-terminations of the CTD cables and at least one change of CTD computer during the course of NBP07-09. All three CTD packages included dual temperature, salinity, and oxygen sensors, while the Baltic and TMC packages additionally carried transmissometers, fluorometers, and PAR sensors (the latter being depth-rated to 1000m, it was removed from the Baltic CTD frame for deep casts). Additionally, dissolved oxygen (winkler method) and salinity values determined via laboratory analysis of water collected from rosette bottles following the Baltic and TMC casts were used to correct for any drift that may be detected in the cast data. Other laboratory analyses of water samples collected from rosette bottles included DMS, pH, total pH, DIC, total alkalinity, nutrients, and chlorophyll. Depending on water column characteristics such as temperature, salinity, and (later in the cruise / season), fluorescence, niskin bottles were triggered at various (between two and 23) depths during the CTD up-cast. Additional water sampling was conducted from the NBP’s uncontaminated seawater line, both for salinity analyses and for total CO2, which will be analyzed at the Lamont-Doherty Earth Observatory in conjunction with the ongoing Takahashi pCO2 surface observation project.
Our first three Baltic CTD casts to 500-550m were acquired over a north-south transect from southeast of Peter 1 Island (7016S), to the most southerly CTD location of the cruise (70 38 S). All three CTD casts showed characteristic winter profiles with a cold (-1.8C), fresh (33.96-34.02ppt) surface mixed layer down to 90m, 120m and 150m (from north to south), overlying warm (1.4-1.9C), salty (34.68-34.72ppt) Upper Circumpolar Deep Waters.