============================== Originally posted 2011-8-4 ================================== North Pole Environmental Observatory 2011 Aerial CTD Survey NSF Grants OPP-9910305, OPP-0352754, and ARC-0856330 CTD Station Position Latitude _ Longitude Cast Date / Time Cast 1 Barneo 89 deg 28.293 min North _ 134 deg 01.954 min East 2011-4-16 / 1801 UTC Cast 2 86N90E 86 deg 03.954 min North _ 089 deg 39.967 min East 2011-4-17 / 1317 UTC Cast 3 88N90E 87 deg 57.735 min North _ 089 deg 42.9 min East 2011-4-17 / 1805 UTC Cast 4 87N90E 86 deg 59.142 min North _ 090 deg 29.739 min East 2011-4-18 / 1233 UTC Cast 5 89N90E 88 deg 56.768 min North _ 089 deg 34.707 min East 2011-4-18 / 1658 UTC Cast 6 87N180 87 deg 02.029 min North _ 179 deg 52.794 min East 2011-4-19 / 1154 UTC Cast 7 90N 89 deg 57.741 min North _ 033 deg 34.757 min West 2011-4-19 / 1802 UTC Cast 8 85N170W 85 deg 06.811 min North _ 170 deg 43.215 min West 2011-4-20 / 1454 UTC Cast 9 86N170W 86 deg 03.252 min North _ 173 deg 56.703 min West 2011-4-20 / 1901 UTC Cast 10 88N180 88 deg 14.11 min North _ 173 deg 51.69 min West 2011-4-21 / 1438 UTC Each cast is an ASCII file of eleven numerical columns with a short header- _ Depth (m) _ Pressure (dbar) _ Temperature in situ (deg C) _ Potential Temperature (deg C) _ Conductivity (S/m) _ Salinity (psu) _ Density (sigma-theta) _ Dissolved Oxygen (ml/l) _ Dissolved Oxygen (mg/l) _ Dissolved Oxygen (%sat) _ Dissolved Oxygen (Mmol/Kg) Part of the observational program of the North Pole Environmental Observatory, these CTD-chemistry stations were obtained using a Twin Otter skiplane operating out of the Russian Ice Station Barneo to record ocean sections from the North Pole along 180 degrees and 90 degrees East longitudes. The measurements were made with a Seabird SBE-19plus Seacat (s/n 5076) following a landing at these positions on the Arctic sea ice. Mounted on and plumbed together with the CTD was SBE-43 Dissolved Oxygen Sensor s/n 229. Suspended on the line above the CTD and plumbed to its pump outflow was an ISUS V2 Nitrate Sensor. Using a winch installed in the aft door of the airplane also allowed Niskin Bottles to be mounted and tripped at chosen depths on the line, and water samples from these were drawn inside the heated fuselage. Concentrations of various chemical tracers were obtained, and these and the Nitrate data are archived in a different submission. Data processing followed a modified SEASOFT recipe with certain constants determined by empirical trial. Temperature and conductivity were low-pass filtered with a time constant of 0.5 seconds, the dissolved oxygen voltage was filtered with a time constant of 1.0 seconds, and pressure was filtered with a time constant of 1.0 seconds. Alignment is the step that compensates for separate sensors with differing time constants and located at different points in the CTD plumbing by shifting individual data channels in time. Temperature was advanced relative to pressure by 0.55 seconds, a value determined by varying the temperature advance to select the value that did the best job of minimizing salinity spiking. The dissolved oxygen voltage was advanced by 5.0 seconds, selected as the value that best balances bringing the downcast and upcast traces together on a temperature-oxygen plot with matching down and up oxygen minima and maxima on a profile plots against pressure. An oxygen advance of 5 seconds turns out to be right in the middle of Sea-Bird's expected range of 2-to-7 seconds. Finally a cell thermal mass correction was applied to conductivity, choosing parameters Alpha = 0.025 and Tau = 9.0 from the theoretical equations offered in Morison, et al (1994). Only then were the derived variables salinity, density, and dissolved oxygen concentration calculated. Oxygen is offered in four different units for the user's convenience. In spring Arctic conditions with cold air temperatures, a frequent problem has been seawater freezing in the plumbing the instant it enters the water and not dissipating before reaching a substantial depth, despite efforts to keep the instrument warm and even after a long period with the instrument soaking in the Mixed Layer. This can result in contamination of the top of the downcast. In 2011, we were able to compensate for this problem, allowing us to report all of the downcasts here, since they are freer of instrument wake effects and show the best resolution and detail of small features. Measurements by the Switchyard Project (http://psc.apl.washington.edu/switchyard) taken during May 2011 provide CTD and ocean chemistry coverage of the Lincoln Sea region, and are archived in submissions by Lamont-Doherty Earth Observatory and the University of Washington. Separately archived are other components of the North Pole Environmental Observatory including drifting buoys and bottom-anchored moorings. Profile plots and other analysis using these data may be viewed at the NPEO website (http://psc.apl.washington.edu/northpole). Reference: Morison, J., R. Andersen, N. Larson, E. D'Asaro, and T. Boyd, 1994: The Correction for Thermal-Lag Effects in Sea-Bird CTD Data. J. Atmos. Oceanic Technol., 11, 1151-1164. Sea-Bird Electronics, Inc., 2011: "SEASOFT V2: SBE Data Processing UserŐs Manual". For further information, please contact Dr. James Morison morison@apl.washington.edu (206) 543-1394 Dr. Michael Steele mas@apl.washington.edu (206) 543-6586 Dr. Matt Alkire malkire@apl.washington.edu (206) 897-1623 Roger Andersen roger@apl.washington.edu (206) 543-1258 at Polar Science Center, Applied Physics Lab, University of Washington 1013 NE 40th, Seattle, WA 98105-6698 USA FAX (206) 616-3142