Rumi Sohrin

Water Column Profiles of Dissolved Inorganic Radiocarbon for the Kuroshio Region, Offshore of the Southern Japanese Coast

We present the water column profiles (surface to 2000 m depth) for dissolved inorganic radiocarbon (14CDIC) from 2 stations in the Kuroshio region including the Kuroshio large meander (LM) of 2004–2005. Surprisingly, the Δ 14CDIC value varied up to 125‰ in the intermediate layer, especially near 600 m depth. In addition, the Δ 14CDIC value was approximately –150‰ at 200 m depth at the northern station of Kuroshio in August 2005. This value is ~100‰ less than other Δ 14CDIC values for the same depth. In comparison, the Δ 14CDIC water column profiles for the southern station of Kuroshio and GEOSECS station 224 decrease down to 600 m depth and were similar below 600 m depth. Our results suggest that strong upwelling associated with the Kuroshio LM has a powerful influence on the Δ 14CDIC water column profiles in the study region.

Response of Subtropical Coastal Sediment Systems of Okinawa, Japan, to Experimental Warming and High pCO2

Increasing seawater temperatures and CO2 levels associated with climate change affect the shallow marine ecosystem function. In this study, the effects of elevated seawater temperature and partial pressure of CO2 (pCO2) on subtropical sediment systems of mangrove, seagrass, and coral reef lagoon habitats of Okinawa, Japan, were examined. Sediment and seawater from each habitat were exposed to four pCO2-temperature treatments, including ambient pCO2- ambient temperature, ambient pCO2-high temperature (ambient temperature + 4°C), high pCO2 (936 ppm)-ambient temperature, and high pCO2-high temperature. Parameters including primary production, nutrient flux, pigment content, photosynthetic community composition, and bacterial abundance were examined. Neither high temperature nor high pCO2 alone impacted mangrove and seagrass sediment primary production significantly (Tukey’s test, P > 0.05). However, the combined stress significantly (Tukey’s test, P 0.05) under the combined stress, suggesting that heterotrophic processes were less affected by the combined stress than autotrophic processes. In summary, mangrove and seagrass sediments minimize the negative impacts of elevated temperature and pCO2 via increased primary production and carbon storage. Lagoonal sediments also act as a carbon sink under temperature and ocean acidification stress.

Microbes in Groundwater of a Volcanic Mountain, Mt. Fuji; 16S rDNA Phylogenetic Analysis as a Possible Indicator for the Transport Routes of Groundwater

Huge groundwater reserves are under the foot of Mt. Fuji, the tallest volcanic mountain in Japan, and the residence time of the groundwater as estimated from the 36Cl/Cl isotope ratio is in the range of 20–35 years. All springwater samples contain nearly saturated concentrations of oxygen. The groundwater field was separated into four areas based on regional slopes of the groundwater table and estimated groundwater flow directions. Springwater samples showed that physicochemical characteristics of the groundwater in the region are relatively constant; Ion concentrations were characterized as the Ca-HCO3 type, irrespective of location at the foot of the mountain. The density of prokaryotes in the springwater, which was in the range of 102–104 cells mL−1, was low compared with any other groundwater so far reported. Although the density of prokaryotes was low, retrieved clones show that the prokaryotes belonged to eight bacterial and two archaeal phyla, and included both aerobic and obligate anaerobic prokaryotes. Some retrieved clones were related to thermophilic prokaryotes, which are optimally adapted to temperatures greater than 40°C. This finding suggests that at least some of the source of the groundwater was located at a depth of 600 m or greater, based on a temperature gradient of 4°C/100 m. This depth is far below the lava layer which was taken to be a substantial pool of groundwater. Microbiological information may provide insight into the transport route of groundwater until it emerges.