Southern Adriatic Sea, Northern Ionian Sea

Dissolved concentration parameters for other gases in the water column

Gas chromatograph mass spectrometers; spectrophotometers

40 ml water samples are filled into cupper tubes at sea which are pinched off. In the laboratory the gas amount is vacuum extracted from the sample and transferred in a specially designed helium/ neon isotope mass spectrometer. Two helium isotopes 3He, 4He and two Neon iostopes 20Ne, 22Ne are measured. Air aliquots provide the instrument calibration and monitor sensitivity changes. Intercalibration between individual air measurements is achieved by a large reservoir of air which has been kept since the beginning of our measurements. Small air bubbles are sometimes enclosed in the copper tubes during the sampling procedure leading to contamination of the samples. Since neon has no internal sources in the ocean air contamination of the samples can be corrected for using the neon excess in the sample. Samples have been assigned quality flags to identify these corrections. The quality flag is a three digit number, the meaning of the flags is as following: 1 sample taken but not measured; 2 good measurement; 3 questionable measurement, 4 bad measurement (too low); 5 bad measurement (too high); 6 mean of replicate samples; 7 air contamination corrected; 8 helium contamination; 9 sample not drawn. The helium and neon concentrations represent both the sum of the two isotopes. For helium they are nearly identical to 4He which is 106 times more abundant than 3He, for neon the isotope 22Ne makes up 10 % of the sum. delta3He is the deviation of the isotopic ratio R=3He/4He in the water sample compared to that in air Ra=1.384 10-6 . delta3He=((R/Ra)-1)*100 (%). In contrast to neon internal sources of helium in the ocean exist. This is either tritiugenic helium productio or terrigenic release of helium from the ocean floor. These internal additions of helium in the ocean can be used to identify and trace water masses and the combination of helium and tritium measurements allows a dating procedure.

University of Bremen, Department of Tracer-Oceanography
Institute of Environmental Physics NW1 Otto-Hahn-Allee 1
Bremen
Bremen
28359
Germany