DISSOLVED NUTRIENTS AND ORGANIC CARBON IN THE WATER COLUMN

*CENTRE - NAME: Hellenic National Oceanographic Data Centre (HNODC), National Centre for Marine Research (NCMR)

*TIME - PERIOD: March 1997 - May 1998.

*GEOGRAPHIC - COVERAGE: North and South Aegean Sea.

*PROJECT: MASTIII/MTPII - MATER.

*PARAMETERS: Pressure, Temperature, Salinity, Dissolved Oxygen, Phosphate, Silicate, Ammonium content,Total Nitrogen, Nitrite, Nitrate, Total Organic Carbon.

*INSTRUMENTS: Niskin Bottles.

*SUMMARY: To study the chemical fluxes in the Aegean Sea.
Methodes, for Oxygen: Winkler method on board, for Phosphate: Murphy and Riley method on board, for Nitrate: Strickland and Parsons method, for Nitrite: Strickland and Parsons method, for Silicate: Mullin and Riley method, for Ammonia: Koroleff method on board.

Materials and Methods for Total Organic carbon:
Field sampling
Discrete seawater samples were collected by using a rosette sampler equipped Niskin bottles from the RV Aegaeo at a series of stations. At the beginning of the cruise, Niskin bottles were cleaned with HCl 0.2% and distilled water. Samples were not filtered and were drawn as soon as possible after the rosette sampler was on the deck of the ship (after gas sampling)). The 10 ml samples were collected (without filtration) in duplicate in precombusted (450 C degrees, at least 6 hours) glass vials. All vials were poisoned by addition of HgCl2 (final concentration ~ 10 mg l-1), closed with Teflon lined screw caps and stored in the dark for later analyses at the shore laboratory within 5 months.
HTCO analysis
The Shimadzu instrument used in this study was the commercially available Model TOC-5000 Total Carbon Analyzer with quartz combustion column filled with 1.2% Pt on silica pillows with approximate diameter of 2 mm (Cauwet, 1994). Several aspects of our modified unit have been already described (Yoro et al., 1997; 1999 ; Dafner et al., 1999; 2000). A magnesium perchlorate water trap has been added to the system located before the halogen scrubber, and an in-line membrane filter and the non-dispersive infrared CO2 detector. Prior to analysis, sub samples were acidified with 85% H3PO4 (pH~ 2) sparged for 10 min with CO2-free pure air at a gas flow rate of 40 ml min-1 to remove inorganic carbon as CO2. TOC contamination from the preservation reagent and from H3PO4 was below the detection limit. A hundred micro l injections were repeated 3-4 times for each sample, the analytical precision of the procedure being within 3%, on average. Some variability in values from two different vials gives rise to a lower overall precision (10 %).
To bring the blank down, the catalyst was pre-treated by washing in 1% HCl and gently rinsed with Milli-Q water, and dried in a furnace at a temperature of about 450 C degrees for 10-15 min. Prior to analyses of standards and samples, the catalyst bed was 'conditioned' (during 1- 3 days) by injecting 100 micro l of acidified and sparged Milli-Q water until the lowest stable integrated area was obtained. After two seawater sample injections the column was flushed by three injections of 100 micro l of Milli-Q water. The catalyst was regenerated by using the TC catalyst function of the instrument once a week. Most of the time and after every two weeks of 25 daily samples injections, top of the catalyst (2 cm) was replaced was fresh material. The catalyst being completely renewed every three weeks.)
Calibration of the instrument
Standardisation was carried out every day using potassium hydrogen phthalate (Kanto Chemical Company, Inc.) dissolved in Milli-Q prepared just before sample analyses. The instrument response factor, measured as the slope of the standard addition to DW (r2>0.999 for 19 runs), remained relatively constant and reproducible over the time of analysis ( y = 5997x (+-309) + 764 (+-242)). The accuracy and the system blank of our instrument were determined by analysis of the Deep Atlantic Water (DAW) reference from ampoules provided by J. Sharp. The average DOC concentration in the DAW reference was 45+-3 micro M C (n = 19). Carbon level of LCW ampoules was similar and often higher than DW produced from our laboratory unit. TOC concentration in samples was calculated by averaging all replicate injections of samples, subtracting the average Milli-Q value as the total blank and dividing by the slope of the standardisation curve.

Volume/Number of Profiles: 49 profiles

*REFERENCE:

• Yoro, S. C., Panagiotopoulos, C. and R. Sempere. 1999. Dissolved organic carbon contamination induced by filters and storage bottle. Water Research 33(8), 1956-1959.
• Dafner, E., Sempere, R., N. Gonzales, Gomez, F. and M. Goutx, M. 1999. Cross Slope variations of dissolved organic carbon in the Gulf of Cadiz, NE Atlantic Ocean (February, 1998). Marine Ecology Progress Series, 189 : 301-306.
• Sempere, R., Yoro, S. C. , F. Van Wambeke, and B. Charriere. 2000. Microbial decomposition of arge organic particles in northwestern Mediterranean Sea. Marine Ecology Progress Series, 5. 198 : 61-72.
• Dafner, E., Gonzales-Davila, M., Santana-Casiano, J. M. and R. Sempere. 2000. Total organic and inorganic carbon exchange through the Strait of Gibraltar in September 1997. Deep Sea Research. In Press.

*ORIGINATOR: National Centre for Marine Research, NCMR, Institute of Oceanography, Athens, GREECE.
Laboratoire de Microbiologie Marine (CNRS/INSU, UMR 6117), Universite de la Mediterranee, Centre d'Oceanologie de Marseille, Marseille, FRANCE

*STORAGE MEDIUM: Hard Disk

*AVAILABILITY: subjected to the originator

*CONTACT: National Centre for MArine Research (NCMR), Institute of Oceanography.
Richard SEMPERE, Tel:+33 0-4 91 82 90 50, Fax:+33 0-4 91 82 90 51, Email: sempere@com.univ-mrs.fr

*COMPLETED-BY: Sissy Iona, Tel: +301-9815703, Email: sissy@hnodc.ncmr.gr

*CURRENCY-DATE: 28-02-2001

*REVISION-DATE: 28-02-2001

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