Dissolved Organic Matter Contribution to Seawater Alkalinity and its Molecular Level Information

Abstract

Two species p. minimum (dinoflagellate) and s. costatum (diatom) are studied to evaluate thecontribution of dissolved organic matter to seawater alkalinity. Dissolved organic matter producedfrom dinoflagellate contributes more than that from diatom to seawater alkalinity. Duringphytoplankton incubation, there was ~70μmol/kg ΔAT (measured alkalinity subtract calculatedalkalinity) change due to dissolved organic matter from p. minimum and ~40μmol/kg for s.costatum. The results suggest that dissolved organic matter from different classes of phytoplanktonhave unique capacity of proton acceptance. Electrospray-ionization mass spectrometry (ESI-MS)shows that the major contributors are from low molecular weights less than 600. Dissolved organicmatters with molecular weights at 149, 245, 299, 334 and 413 is the main causes of alkalinityincrease in a dinoflagellate species p. minimum, whereas in diatom species s. costatum they are 157,204 and 281.