Cobalt is an essential micronutrient in seawater. In the marine environment, it is present in the dissolved fraction at very low concentrations, < 10-9 mol dm-3. Bound to organic ligands, it forms stable complexes in the dissolved fraction of seawater, which have been poorly investigated. Adsorption cathodic stripping voltammetry was used to characterise cobalt complexes with organic ligands under seawater conditions. The method is based on the adsorption of formed complexes with selected organic ligands present in the sea (catechols, humic acid, phospholipids) on the surface of the mercury drop electrode and their reduction. In addition to the electrochemical studies, the complexes were also investigated by the spectrophotometry method. Since some of the ligands used (phospholipids) are amphiphilic molecules, cobalt complexation was also monitored at the water/air phase boundary using the Langmuir-Blodgett method and Atomic force microscopy. Cobalt formed stable complexes with the ligands with high conditional stability constants log KCo(II)-4NC2 = 21.86 (pH = 8.2) and log KCo(II)-4NC2 = 21.11 (pH = 6.5), and log KCo(II)HA2 = 11.32, log KCo(II)Phen2PC = 23.02, and log KCo(II)Phen2PC2 = 29.31 (pH = 8.2) formed at a hydrophobic mercury drop electrode in a model seawater solution (NaCl, pH = 8.2, Ic = 0.55 mol dm-3). Cobalt complexes soluble in aqueous solution were detected spectrophotometrically as well, and the equilibrium stability constants of the complex log KCo(II)-4NC = 5.76±0.40 (pH = 6.5), log KCo(II)-4NC = 3.98 ± 0.17 were calculated. (pH = 8.2) and log KCo(II)- HA = 3.80±0.29 (pH = 8.2). The Langmuir-Blodgett method shows the binding of 1,10-phenanthroline and cobalt to the PC monolayer. The determined layer stability constant is extremely low and amounts to K1 = 2.4 x 10-2 m3 mol-1 , while the addition of 1,10-phenanthroline leads to the formation of a layer of high stability with constant K2 = 4.86 x 1010 m2 mol-1. Atomic force microscopy showed that the mixture of phenanthroline and phospholipids of both standard and real samples, shows the formation of vesicles, while the addition of cobalt to the mixture leads to the formation of "terraces" due to the connection of molecules. The studies carried out in this dissertation have shown the importance of knowing the speciation of cobalt and understanding the biogeochemical processes in which it is involved in the marine environment.