DOI: 10.1594/pangaea.787499
title: Chlorofluorocarbons and noble gas measured on water bottle samples during POLARSTERN cruise ANT-XXIV/3

description: During the cruise a total of 1620 samples on 97 CTD/water bottle stations were collected for chlorofluorocarbons (CFC-11 and CFC-12); 32 stations were occupied along the Greenwich Meridian section, 37 stations along the Weddell Sea section, and 28 stations across the Drake Passage. The water samples from the CTD/rosette system were collected into 100 ml glass ampoules and sealed off after a CFC free headspace of pure nitrogen had been applied. The CFC samples will be analysed in the CFC-laboratory at the IUP in Bremen. The determination of CFC concentration will be accomplished by purge and trap sample pre-treatment followed by gas chromatographic (GC) separation on a capillary column and electron capture detection (ECD). The amount of CFC degassing into the headspace will be accounted for during the measurement procedure in the lab. The system will be calibrated by analyzing several different volumes of a known standard gas. Additionally the blank of the system is analyzed regularly.Furthermore, 480 samples from 41 stations were collected for helium isotopes (3He, 4He) and neon (Ne); 10 stations along the Greenwich Meridian section, 14 stations along the Weddell Sea section, and 17 stations across the Drake Passage. The water samples from the water bottles were stored in clamped off copper tubes. They will be analysed with the IUP-Bremen noble gas mass spectrometer (combined quadrupole and sector field mass spectrometer), after the gases were extracted from the sea water samples and separated from other gaseous components by several cooling traps.The water samples for helium isotopes and neon from the CTD-bottle-system are tapped in copper tubes, preventing air contamination and bubbles during the filling of the tubes and squeezed at both ends to keep them gas tight during transportation and storage.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:D(4He) &lt; 1.0 %D(Ne) &lt; 1.0 %D(d3He) &lt; 0.5 %The Chlorofluorocarbon (CFC-11 and CFC-12) water samples from the CTD-bottle-system are stored in glass ampoules without contact to the atmosphere during the tapping. Immediately after sampling the ampoules are flame sealed after a CFC free headspace of pure nitrogen had been applied.The loss of CFCs into the headspace is considered by a careful equilibration between liquid and gas phase under controlled conditions before the sealed ampoules are opened and a precise measurement of the volume of the headspace. The determination of CFC concentrations in the IUP Bremen gas chromatography lab is accomplished by purge and trap sample pre-treatment followed by gas chromatographic (GC) separation on a capillary column and electron capture detection (ECD). The system is calibrated by analyzing several different volumes of a known standard gas. CFC concentrations are calibrated on SIO98 scale (Prinn et al., 2000, doi:10.1029/2000JD900141). A more detailed description of the measurement system is given by Bulsiewicz et at. (1998, doi:10.1029/98JC00140). Accuracy (i.e. uncertainties of calibrated sample volume, calibration curve, extraction efficiency, standard and working gas, water blank, etc.):CFC-12 &lt; 1.8 %CFC-11 &lt; 2.8 %Precision (i.e. mean error from 19 replicate samples):CFC-12 &lt; 0.007 pmol/kg or &lt; 0.9% (which ever is greater) (n=6)We do not give a value for the precision of CFC-11. Offline sample chromatograms regularly show a negative peak in the vicinity of the CFC-11 peak, which decreases the accuracy of CFC-11 in comparison to CFC-12, and which does not allow giving an objective estimate of a precision for CFC-11.CFC-11 data between stations 140 and 193 (south of 61°S on the Prime Meridian and east of 28°W on the Weddell Sea section) are not reliable due to a possible hidden peak below the CFC-11 peak and possible problems with the measurement unit during that time (K. Bulsiewicz, personal communication, 2010). We flag these CFC-11 data as doubtful.Sampling on board and measurement of CFCs and noble gases at the IUP Bremen was funded by the Deutsche Forschungsgemeinschaft within the SPP 1158 "Antarktisforschung", grant RH 25/32. We thank Eberhard Fahrbach, Gerd Rohard and the scientific party to participate in the ANT-XXIV/3 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.