ROLE OF DISSOLVED ORGANIC-MATTER IN THE MARINE BIOGEOCHEMICAL CYCLE -STUDIES USING AN OCEAN BIOGEOCHEMICAL GENERAL CIRCULATION-MODEL

A biogeochemical general circulation model which includes production a nd consumption processes of dissolved organic matter (DOM) is develope d. The semilabile and the refractory DOM are taken into account. The v ertical distribution of the dissolved organic carbon (DOC) concentrati on and the Delta(14)C value obtained in our model compares well with t he recent observations. It is found that the double DOC maximum zone ( DDMZ) extends in the east-west direction in the equatorial Pacific. Ca se studies, which change the decay time and production ratio constant, show that the horizontal distribution of DOC in the surface layer can be reproduced only when the decay time of the semilabile DOM is about half a year. The semilabile DOM exists only above a depth of 400 m, a nd its vertical and horizontal transport plays an important role in th e marine biogeochemical cycle in the surface layer. However, below tha t depth, only the inert refractory DOM exists, and the role of the ref ractory DOM in the biogeochemical cycle is not important. The global e xport production due to the particulate organic matter (POM) and DOM a t a depth of 100 m is estimated to be about 8 Gt C/yr and about 3 Gt C /yr, respectively. The vertical transport below 400 m is due almost en tirely to POM.