Abstract
In order to evaluate suspended particle cleanliness of deep ocean water (DOW), 16 onemonth field samples were collected from DOW pumped from 320m below the surface off the Kochi Prefectural Deep Seawater Research Laboratory from July 2005; surface water (SW) pumped from 5 m below the surface was used as a comparison. Weight of suspended particles filtered onto 0.45 μm Millipore membrane filters was measured. Suspended particles in DOW weighed far less than in SW collected on the same day (14% of those in SW). Weights of suspended particles of DOW were always less than 1 mg/L (0.195-0.993 mg/L, average, 0.550 mg/L). No seasonal patterns were observed in either DOW or SW. Specific filtration speed was 1/3 lower in DOW than SW, and a positive relationship between the amount of suspended particles and the specific filtration speed was only observed for DOW and SW when all the data were analyzed together. Observations of suspended particles collected on Millipore filters by scanning electron microscope revealed that particles found in DOW were small, with few organic aggregates, organic-like films, and planktonic algal cells compared to those of SW. However, trace amounts of chlorophyll α (<4 % of SW) were detected in DOW and other researchers observed planktonic algae (mainly diatoms) when DOW from the present study was cultured under illumination. Consequently, it is important for DOW to be stored under tight darkness to avoid germination of algal seed stock contained in the original DOW.
