============================= Originally posted 2010-7-16 ================================== ======================== Slight position corrections 2010-8-16 ============================= North Pole Environmental Observatory 2010 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 03.423 min North _ 070 deg 56.277 min East 2010-4-21 / 2007 UTC Cast 2 NP85E90 84 deg 59.500 min North _ 089 deg 59.120 min East 2010-4-22 / 1236 UTC Cast 3 NP86E90 85 deg 59.100 min North _ 089 deg 34.400 min East 2010-4-22 / 1658 UTC Cast 4 NP90 89 deg 59.500 min North _ 007 deg 04.000 min West 2010-4-23 / 1019 UTC Cast 5 NP88E90 87 deg 57.380 min North _ 089 deg 15.410 min East 2010-4-23 / 1359 UTC Cast 6 NP87_180 86 deg 58.260 min North _ 179 deg 50.270 min East 2010-4-24 / 1645 UTC Cast 7 NP86W173 86 deg 00.230 min North _ 173 deg 17.200 min West 2010-4-24 / 2049 UTC Cast 8 NP89_180 89 deg 01.100 min North _ 178 deg 39.900 min West 2010-4-25 / 1342 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) except that the dissolved oxygen columns are not present in Casts 2 and 3. 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 an SBE-43 Dissolved Oxygen Sensor, initially s/n 229. Following the first station, this oxygen sensor was found to have sustained damage from exposure to freezing temperatures, and beginning with Cast 4, it was replaced with s/n 938. Consequently, oxygen profiles were not obtained from Casts 2 and 3. Suspended on the line above the CTD and plumbed to its pump outflow was an ISUS V2 Nitrate Sensor provided by our chemical colleagues at Oregon State University. 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 by OSU. 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 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 2.80 seconds for s/n 229 used during Cast 1 and by 2.40 seconds for s/n 938 used during Casts 4 through 8, selected as the values that best brought the downcast and upcast traces together on a temperature-oxygen plot. 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 2010, we were mostly 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. Casts 1 and 2 began with substantial periods of soaking and exercising the winch, but were not brought closer to the surface than 12 meters before the profile downcast was begun. Those two profiles begin at 12 meters; the remaining six began within three meters of the surface. A caution is justified for the very top of oxygen profiles 4 through 8 in the Mixed Layer, each measured by SBE-43 s/n 938, where a certain instability in oxygen concentration may be instrumental, but which also shows a curious qualitative similarity among all five. Measurements by the Switchyard Project (http://psc.apl.washington.edu/switchyard) taken during May 2010 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., 2010: "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 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