DOI: 10.1594/pangaea.820322
title: Chlorofluorocarbons and noble gas measured on water bottle samples during POLARSTERN cruise ANT-XXVII/2

description: Noble gases (3He, 4He, 20Ne):480 samples on 46 stations were drawn from the CTD/rosette for stable helium isotopes (3He, 4He) and neon along the Prime Meridian and the Weddell Section. On all of these stations we sampled on the fully available vertical resolution in the upper 300 meters for estimating upwelling velocities and on some stations on the Weddell section full vertical profiles for additional analysis of water mass composition.In the IUP Bremen noble gas lab the samples are processed in a first step with a UHV (ultra high vacuum) gas extraction system. The required vacuum conditions are achieved by a rotary pump and an oil diffusion pump. To maintain contamination-free samples, the extraction system is checked for leaks on each sample separately. Sample gases are transferred via water vapour into a glass ampoule kept at liquid nitrogen temperature. Quality checks of this sample preparation line are done on a routine basis. This includes special vacuum checks and preparing accurately defined samples for internal control measurement.For analysis of the noble gas isotopes the glass ampoules are connected to a fully automated UHV mass spectrometric system equipped with a two stage cryo system. Every 2 to 4 samples the system is calibrated with atmospheric air standards (reproducibility &lt;0.2%). Also measurement of line blanks and linearity are done. The performance of the Bremen facility is described in Sültenfuß et al. (2009, doi:10.1080/10256010902871929).Error estimate for absolute noble gases concentrations:Delta(4He) &lt; 1.0 %Delta(Ne) &lt; 1.0 %Delta(delta3He) &lt; 0.3 %Chlorofluorocarbons (CFC-12, SF6):During this cruise we used an analytical technique for the simultaneous measurements of the trace gases sulphur hexafluoride (SF6) and the chlorofluorocarbon CFC-12 in water and air. The determination of the two compounds was performed by analysis with gas chromatography with electron capture detection.We analyzed 1400 water samples from 98 stations as profiles for CFC-12 and SF6 along the Prime Meridian and the Weddell Section.Water-samples were collected in 200 ml glass ampoules from 10 l Niskin bottles. 150 ml of this water are transferred to a water purge chamber. After purge of the water, the compounds are trapped on a 1/16" trap, packed with Carboxen 1000 and Porapak-Q. Thermal desorption of the sample gases, held in the trap are flushed onto a Porasil-C and MS5A pre-columns, where SF6 and CFC-12 are separated from nitrous oxide, and any other late eluting compounds. SF6 and CFC-12 are refocused then on a 1/16" Porapak-Q packed trap, to narrow their chromatographic peaks and enhance their detection. After thermal desorption the released gases are separated on a GS Gaspro capillary column (0.32 mm ID x 30 m). SF6 and CFC-12 are then detected by Agilent 6890 N micro-ECD.Concentrations of SF6 and CFC-12 reported on SIO 98 scale (Prinn et al., 2000, doi:10.1029/2000JD900141; Vollmer and Weiss, 2002, doi:10.1016/S0304-4203(02)00015-4). Based on the analysis of replicate water samples, we estimate precisions of 0.4% for SF6 and 0.5% for CFC-12. Overall accuracy, including that off the calibration scale is estimated to be 2% or 0.020 fmol/kg for SF6 and 1.6% or 0.005 pmol/kg for CFC-12 (whichever is greater). The accuracy accounts for uncertainties of calibrated sample volume, calibration curve, extraction efficiency, standard and working gas, water blank, etc. The limit of detection is estimated to be 0.020 fmol/kg for SF6 and 0.003 pmol/kg for CFC-12 for all four expeditions.Tracer measurement were funded by the Deutsche Forschungsgemeinschaft within the SPP 1158 "Antarktisforschung", grant RH 25/38-1. We thank Eberhard Fahrbach, Gerd Rohardt and the scientific party to participate in the ANT XXVII/2 expedition and for the excellent assistance and cooperation on board. We thank also master and crew of RV Polarstern.Noble gas measurements: Jürgen Sültenfuß; CFC measurements: Klaus BulsiewiczThe tracer data set was carefully checked for accurate measurements and outliers. Quality flags: ? = doubtful; / = bad; # = mean of replicates.