Abstract

Sea-surface films and the corresponding 10-cm subsurface waters were sampled on three cruises to the eutrophic and oligotrophic waters in the Gulf of California and off the west coast of Baja California. The following constituents and properties were measured: NH ₄ ⁺, NO ₂ ^-, NO ₃ ^-, PO ₄ ^3-, SiO ₃ ^2-, urea, ATP and Chl- a; dissolved and particulate organic carbon and nitrogen; lipid, protein and carbohydrate; total viable and nitrifying bacteria; simulated in situ bacterial heterotrophy; microplankton and simulated in situ primary productivity; surface potential and film pressures; ultraviolet absorption; and film-formation rates using surface potential and chemical methods.

Mean enrichment factors (film concentration/10-cm concentration) for the three cruises were: 1.1-2.4 for the soluble inorganic nutrients, dissolved organic carbon, nitrogen, urea, carbohydrate, and lipid; 1.3-2.0 for ATP, Chl- a, microplankton and bacteria; and 1.1-3.7 for particulate carbon and nitrogen and both dissolved and particulate protein. Particulate and dissolved carbon and nitrogen were the only constituents never depleted in the films relative to the subsurface waters. Systematic, significant correlations between the various chemical and biological parameters measured were few, reflecting the complexity of processes which form and maintain surface films.

Protein, carbohydrate and lipid carbon accounted for 15-114% (mean = 50%) of the total particulate organic carbon and 14-42% (mean = 28%) of the total dissolved organic carbon in both the films and 10-cm waters. Lipid was not the major identified constituent of films, averaging 18% of the particulate organic carbon and 2.5% of the dissolved organic carbon. There was more protein relative to carbohydrate in film samples compared to 10-cm water; there was also more protein relative to carbohydrate in particulate compared to dissolved mater. Microplankton plus bacterial carbon averaged 16% of the particulate organic carbon in films and 19% in 10-cm waters.