Dynamics of dissolved and particulate organic matter during the spring bloom in the Oyashio region of the western subarctic Pacific Ocean

We evaluated the dynamics of dissolved organic matter (DOM) and particulate organic matter (POM) at various stages of the spring bloom in the Oyashio region of the western subarctic Pacific Ocean by means of samples obtained during 3 cruises in April, May, and June 2003. In April, the average concentration (+/- 1 SD) of nitrate plus nitrite ions was 23.3 +/- 0.39 mu mol 1(-1) in surface waters, and this decreased to below the detection limit (<0.05 mu mol 1(-1)) during the bloom period. About 80% of newly accumulated organic carbon was partitioned into POM. Whereas the C:N ratios of bulk DOM ranged from 13 to 20, the average C:N ratio of newly accumulated DOM was 7.3 +/- 1.5. The lability of DOM was assessed by seawater culture-type incubation experiments on surface seawater samples from each observation site. Although the newly accumulated DOM was relatively rich in nitrogen, most of it escaped rapid (d to wk) bacterial consumption in the seawater culture experiments.