To investigate characteristics of biogeochemical environment of the Korea Deep Ocean Study(KODOS) area in the northeast Pacific Ocean, we preferentially measured inorganic nutrients and fluorescent organic matters. Typically, the permanent thermocline was well developed at the depth of 200∼1000m in the study area. Nitrate, phosphate and silicate were low in the surface mixed layer and increased with depth. N/P and N/Si showed 15 and 0.2 respectively in the deeper layer. Two fluorophores, biomacromolecule(protein-like) and geomacromolecule (humic-like), were observed by three dimensional fluorescence excitation/emission spectra matrix. Biomacromolecule(maximum fluorescence at Ex_280nm/Em_330nm) ranged from 41.9 to 147.0 TU with its maximum in the surface mixed layer and minimum in deeper water. This is a same trend that has been reported for DOC in the equatorial Pacific. This suggests that biomacromolecule might be labile and converted to refractory humic substance after bacterial degradation in the deeper layer. On the contrary, geomacromolecule(maximum fluorescence at Ex_330nm/Em_430), ranged from 7.6 to 46.5 QSU, showed minimum in the surface mixed layer(euphotic zone) implying photodegradation and then increased with depth at all stations. In the characteristics of vertical profiles, the relationship between biomacromolecule and geomacromolecule showed negative correlation. Such trend can be attributed to biochemical regeneration or formation of fluorescent materials accompanying oxidation and remineralization of settling organic matter.

Distribution patterns of the chemical species, contained or dissolved in the sediments and porewater, were studied from the submarine environments around Deok-Jeok Island, Yellow Sea. The sediments in the study area are predominantly composed of medium to coarse sands, and consequently of very low organic carbon (0.003% - 0.26% dry weight sediments). As opposed to the strong enrichment of porewater with nutrients and heavy metals in the ordinarily muddy, organic-rich sediments, the porewater enrichment is not intense in this sandy, organic-poor sediments; porewater phosphate is enriched to the maximum of only seven (average two) times over that in the bottom water. Concentrations of the heavy metals dissolved in porewater show a bit greater enrichment than the nutrient: Zn shows the lowest enrichment (7 times that of the bottom water) and Mn the highest (450 times that of tie bottom water). However, these enrichments of the chemical species in porewater arc the natural consequences of decomposition of the organic matter in sediments, and still fall short in the magnitude of those in the muddy, organic-rich sediments. Mining of the sands in the study area may pose a threat to the seawater quality as it causes a large scale porewater discharge to the bottom water. The additional supply of the nutrients by this discharge may develop an eutrophic state and, in consequence, an excessive nutrification of the water column. Since the residence times of the nutrients are much longer than those of the heavy metals, a long-term monitoring of the concentration changes in the porewater nutrients is very important to assess the potential deterioration of the seawater associated with the sand mining in the study area.