Hiroo Satoh

Seasonal Variation in Ice Algal Assemblages in the Fast Ice Near Syowa Station in 1983/84

Ice algal assemblages in the fast ice near Syowa Station were investigated from March 1983 to January 1984. Peaks in the standing crop (chlorophyll a) occurred in April–June and October–November; the largest (125 mg chlorophyll a m−2) occurred in mid-November at a site with moderate snow cover. Chlorophyll was most highly concentrated in the bottom of the ice, where the diatoms Amphiprora kufferathii, Berkeleya rutilons, Nitzschia lecointei, N. stellata, N. turgiduloides and Pleurosigma directum were dominant. The chlorophyll concentration within the ice developed mainly in May with little change during the following months at heavily snow-covered sites. Centric diatoms, e.g. Chaetoceros spp., Eucampia antarctica and Rhizosolenia alata were major components in the interior assemblage. The chlorophyll concentration increased in the upper consolidated snow layer during October-January. The dominant species there, Tropidoneis sp., was a minor component of the interior and bottom ice layers. These results suggest that the interior ice algal assemblage was formed by mechanical inclusion of microalgae at the time of sea ice formation, and did not grow in the ice. However, the bottom assemblage grew when irradiance was high enough. The surface assemblage, which was presumed to be inoculated by an interior assemblage through vertical channels, grew in spring.

Primary productivity in the fast ice area near syowa station, Antarctica, during spring and summer 1983/84

In situ measurements of the primary productivity of ice algae and phytoplankton were carried out in the fast ice area near Syowa Station (69°00′S, 39°35′E) during the austral spring and summer of 1983/84. Standing stock of ice algae reached a maximum of 45.1 mg chla m−2 in late October. Phytoplankton standing stock attained a value of 3.57 mg chla m−2 in mid-January. Primary production of ice algae in late October (7.64 mgC m−2 hr−1) was 14 times greater than that in mid-January (0.54 mgC m−2 hr−1). Production in the water column in mid-January (3.46 mgC m−2 hr−1) was 50 times greater than that in late October (0.07 mgC m−2 hr−1). These results indicate a substantial production by ice algae in the spring and by phytoplankton in the summer period.

Seasonal changes of organic carbon and nitrogen production by phytoplankton in the estuary of River Tamagawa

Abstract Seasonal changes of organic carbon and nitrogen production were investigated at a station in the estuary of River Tamagawa in Tokyo Bay. Standing stock of phytoplankton expressed as a concentration of chlorophyll α and their photosynthetic activities fluctuated significantly with sampling periods. Based on the data obtained in 1988 and 1989, the levels of annual production of organic carbon and nitrogen by phytoplankton community in this estuary were estimated to be 1890 gC m −2 yr −1 and 281 gN m −2 yr −1 , respectively.

Bio-Optical Relationship of Case I Waters: The Difference Between the Low- and Mid-Latitude Waters and the Southern Ocean

Both historic and currently operational chlorophyll algorithms of the satellite-borne ocean color sensors, such as SeaWiFS, were evaluated for in situ spectral radiation and chlorophyll data in some Case I waters, including the waters in the Indian Ocean sector of the Southern Ocean. Chlorophyll a concentration of the data set (n = 73) ranged from 0.04 to 1.01 mg m−3. The algorithms had higher accuracy for the low- and mid-latitude waters (RMSE: 0.163–0.253), specifically the most recently developed algorithms of OCTS and Sea WiFS showed 0.163 and 0.170 of Root Mean Square Errors, respectively. However, these algorithms had large errors (0.422–0.621) for the Southern Ocean data set and underestimated the surface chlorophyll by more than a factor of 2.6. The absorption coefficients in the blue spectral region retrieved from remote sensing reflectance varied in a nonlinear manner with chlorophyll a concentration, and the value in the Southern Ocean was significantly lower than that in the low- and mid-latitude waters for each chlorophyll a concentration. The underestimation of chlorophyll a concentration in the Southern Ocean with these algorithms was caused by the lower specific absorption coefficient in the region compared with the low- and mid-latitude waters under the same chlorophyll a concentration.

Optical characteristics of seawater in the North Pacific Ocean

The downward spectral irradiance and upward spectral radiance, and chlorophyll a concentration of surface water were determined in the North Pacific Ocean: Bering Sea, Gulf of Alaska, Central and Equatorial Pacific, Kuroshio region, Yellow Sea, Japan Sea, Tokyo Bay, and Ise Bay. These areas included Case I and Case II water. The optical characteristics in the study area were based on measurements of underwater spectral irradiance. The strong correlation between the attenuation coefficient at 490 nm, K490, and other at wavelengths were observed. The relation between chlorophyll concentration and K490 showed a good correlation at eh coastal and bay areas except a the stations near river mouths. These relations suggested that suspended and dissolved matter were largely of biogenous origin such as fragmented and decomposed phytoplankton. In the clear ocean, at low chlorophyll concentrations, the data points were widely scattered, implying that K490 is sensitive to changes in suspended particles.

Field Obserbation and Satellite Image on Chlorophyll-a Distribution in the Kii Channel, Japan.

Horizontal and vertical chlorophyll-a distributions in the Kii Channel, Japan were revealed using field observational data and the averaged chlorophyll-a concentration in the euphotic layer was estimated. The ocean color image by OCTS taken at nearly the same time reproduces well the surface distirbution of chlorophyll-a concentration in the Kii Channel. Such a fact suggests that we can clarify the temporal and spatial variations in chlorophyll-a distribution in the coastal sea from ocean color images by satellites if we have an empirical relationships between the chllorophyll-a concentration at the sea surface and that in the euphotic layer.

In-water algorithms for estimation of chlorophyll a and primary production in the Arabian Sea and the eastern Indian Ocean

In-water algorithms to estimate the chlorophyll a concentration in the Arabian Sea and the Indian Ocean were set up by computation based on empirical method using subsurface radiance ratio of SeaWiFS bands. A series of investigation for the algorithms was carried out at 16 stations during a cruise in January 1994 from Gulf of Oman to Fremantle, Australia. Photosynthetic productivity of phytoplankton was measured at 12 stations by the stable 13C isotope method. The algorithm of surface chlorophyll a, that the strongest correlation was observed, was Chl.a + Pheo. (mg m-3) equals 0.26 X [Lu(443)/Lu(490)]-3.35 with a coefficient of determination r2 equals 0.93. Most of the standing stock was included in the subsurface chlorophyll maximum (SCM) layer found clearly from 15 to 120 m. Primary production of water column in this area depends on it at the upper layer because of low photosynthetic productivity at SCM. Accordingly a linear relationship with r2 equals 0.90 between the surface chlorophyll a concentration and daily primary production of water column was obtained.