1. Dissolved Free Amino Acids along the 40°S Atlantic Ocean transect – JC068 Amandine Sabadel 1,2 Malcolm Woodward 2 1 University of Otago, Dunedin, NZ 2 PML, Plymouth, UK

2. Nitrogen in DFAAs Why study DFAAs? – To assess their role in the marine food web as potential source of N for phytoplankton – AAs’ N isotopic ratios is a key element to food web studies How ? – Developing an analytical technique using HPLC for separating 18 amino acids – Fluorescence detection for AAs speciation … method inspired by Kuznetsova et al. (2004) (used as base for method development)

3. HPLC analytical method (hardware) Use of a solution gradient between: – Sodium acetate buffer/THF – Methanol Mixing compartment absolutely necessary Use of a « simple » C18 column Detection with a fluorimeter Fig. 01 – HPLC system at PML Prior to analysis, samples were filtered at sea during JC068 through 0.2 µm filters and frozen until required for analysis

4. HPLC analytical method (chemical) OPA reacts with AAs in presence of a thiol  We used 2-mercaptoethanol Reaction possible only on primary amines  Therefore, does not detect AAs like: Proline What can be detected: – Small (Simple): Alanine, Glycine, Taurine – Nucleophilic AAs : Serine, Threonine – Hydrophobic: Valine, Leucine, Isoleucine, Methionine – Aromatic: Phenylalanine, Tyrosine – Acidic: Aspartic acid, Glutamic acid – Amide: Aspargine, Glutamine – Basic: Argine, Lysine, Histidine … 18 Amino acids! Fig. 02 – OPA reaction on primary amine. Condensation of the amine group with the dicarboxyl compound in presence of a thiol.

5. Chromatograms  15 standards AAs, 5 nmol/l each Seawater sample  Station 01, CTD 01, 400 m Detection limit was different for each amino acids, but was down to ~ 10 pmol/l

6. The UK-Geotraces JC068 cruise A few numbers… 313 Seawater samples taken from CTD rosette along the 40°S transect + 5 Standards to run every day New OPA reagent solution made up every day Each sample takes 1 hour run therefore: 1 ½ months to analyze them all!

7. Preliminary results Fig. 03 – Variation in concentration of glutamic acid along the water column. Data from Station 8, station 13 and Station 19 Little is known about the DFAAs in open oceans… However the work on the 40°S South Atlantic transect has shown similar behaviour with the work of Lee and Bada (1977) in the North Atlantic Ocean

8. Preliminary results Even though they are found in different concentration, each amino acids appears to have a similar behaviour along the watercolumn. Their concentrations are elevated at the surface and suddenly decrease passed 400 m.

9. Alanine, Aspartic acid, Glutamic acid and Histidine – 400 m

10. Future work Publication of the DFAAs analytical method Completion of each amino acids’ concentrations depth profile N isotopic ratio from particulates samples taken along the 40°S transect Work on an analytical method to extract DFAAs from seawater and get to their N isotopic ratios

11. Merci ! A big thank you to: -Gideon Henderson -Malcolm Woodward -PML -All the people from the JC068 Cruise