Ocean Color Satellite Imagery and Shipboard Measurements of Chlorophyll a and Suspended Particulate Matter Distribution in the East China Sea

Satellite-derived ocean color data of Coastal Zone Color Scanner (CZCS) on board the Nimbus-7 and Ocean Color and Temperature Scanner (OCTS) on board the Advanced Earth Observing Satellite (ADEOS) are jointly used with historical in situ data to examine seasonal and spatial distributions of chlorophyll a (Chl-a) and suspended particulate matter (SPM) concentrations in the East China Sea. Ocean color imagery showed that Chl-a concentrations on the continental shelf were higher than those of the Kuroshio area throughout the year. Satellite-derived Chl-a concentrations are generally in good accordance with historical in situ values during spring through autumn (although no shipboard in situ measurement was conducted at nearshore areas). In contrast, ocean color imagery in winter indicated high Chl-a concentrations (4–10 mg m^–3) on the continental shelf where bottom depth was less than 50 m when surface water was turbid (2–72 g m^–3 of SPM at surface), while historical in situ values were usually less than 1 mg m^–3. This suggests that resuspended bottom sediment due to wind-driven mixing and winter cooling is responsible for the noticeable overestimation of satellite-derived Chl-a concentrations. The algorithm for ocean color needs to be improved urgently for turbid water.     

Convection induced by cooling at one side wall in two-dimensional non-rotating fluid —applicability to the deep Pacific circulation—

In recognition that similarity in the density balance leads to resemblance in circulation between the two-dimensional non-rotating and three-dimensional rotating systems which have similar density stratification, we investigate convection induced by cooling at one side wall and heating at the sea surface by using a two-dimensional non-rotating model as idealized representation for the deep Pacific circulation. In the model, various vertical profiles are taken for the side wall cooling, which are assumed to correspond to the density structure of the Anatarctic Circumpolar Current. In a small diffusivity range, two important features are found to be robust against change in the vertical profile of the side wall cooling. One is that the density stratification is horizontally almost uniform. The other is that the balance in the density equation between the vertical advection and the vertical diffusion holds in the interior. Consequently, the vertical density balance, together with the equation of continuity, determines the circulation pattern for the prescribed vertical profile of the side wall cooling. The multi-layered meridional flow, which is expected to exist in the deep Pacific, is shown to form for certain vertical profiles of the side wall cooling.     

Lower Cd/P ratio in settling particles than in surface seawater in the Okinawa Trough

The characteristics of the ratios between cadmium (Cd) and phosphorus (P) in settling particles collected from the Okinawa Trough in the East China Sea were examined using a sediment trap, moored at a depth of 811 m for one year. The Cd/P ratios varied within a narrow range throughout the year, in spite of the large seasonal change in the total dry mass, Cd, and P fluxes. The average Cd/P ratio of settling particles was 0.062 (nmol/μmol), which was obviously lower than that of surface seawater around the study site (0.16). This lower ratio in the Okinawa Trough particles collected using the 811 m-moored trap certainly reflected the mixture of biologically produced organic matter around the study site and other components that were mainly transported as lateral flux from the shelf edge and slope area of the East China Sea.     

Controlled experiment in the ionosphere with a rocket-borne plasma gun

A controlled active experiment was performed by a plasma gun on-board a rocket to study the plasma stream across the magnetic field in space. A mother and daughter system was employed. An 8 kV 0.8 μF (25 J) capacitor bank on the daughter rocket was discharged every 12 s and about 10¹⁶ ion and electron pairs were ejected. A plasma signal was detected on the electron temperature probe. The propagation speed of the plasma stream is estimated to be 10⁶ cm/s, considerably lower than that obtained in the prelaunch test. The amplitude of the plasma signal decays as the inverse square of the mutual distance between the mother and daughter rockets and this decay is much slower than the free streaming. The importance of the geomagnetic field on the plasma propagation in space is discussed.     

Internal deformation of Sikhote Alin volcanic belt, far eastern Russia: Paleocene paleomagnetic results

We present paleomagnetic results of Paleocene welded tuffs of the 53–50 Ma Bogopol Group from the northern region (46°N, 137°E) of the Sikhote Alin volcanic belt. Characteristic paleomagnetic directions with high unblocking temperature components above 560 °C were isolated from all the sites. A tilt-corrected mean paleomagnetic direction from the northern region is D=345.8°, I=49.9°, α₉₅=14.6° (N=9). The reliability of the magnetization is ascertained through the presence of normal and reversed polarities. The mean paleomagnetic direction from the northern region of the Sikhote Alin volcanic belt reflects a counterclockwise rotation of 29° from the Paleocene mean paleomagnetic direction expected from its southern region. The counterclockwise rotation of 25° is suggested from the paleomagnetic data of the Kisin Group that underlies the Bogopol Group. These results establish that internal tectonic deformation occurred within the Sikhote Alin volcanic belt over the past 50 Ma. The northern region from 44.6° to 46.0°N in the Sikhote Alin volcanic belt was subjected to counterclockwise rotational motion through 29±17° with respect to the southern region. The tectonic rotation of the northern region is ascribable to relative motion between the Zhuravlevka terrane and the Olginsk–Taukhinsk terranes that compose the basements of the Sikhote Alin volcanic belt.     

Quantitative reconstruction of the lake water paleotemperature of Daihai Lake, Inner Mongolia, China and its significance in paleoclimate

By measuring Sr/Ca ratios of the ostracod shells (Limnocthere cf. inopinata) in sediments of the Daihai Lake, and combined with Sr²⁺/Ca²⁺ ratios of the lake water, this paper obtained paleosalinity of the lake water. Vaporizing experiment of the lake water in laboratory showed that there was a quantitative relationship between salinity and oxygen isotope. Using this relationship, oxygen isotope values of the paleo-lake water were calculated. By measuring the oxygen isotope of the authigenic carbonate in the lake’s sediments, and in combination with the oxygen isotope values of the paleo-lake water, the paleotemperature of the lake water was calculated. Finally, based on these proxies, the paleoclimate in the lake basin was explored.     

Assessment of carbon- and fluorescence-based primary productivity in Ariake Bay,southwestern Japan

A comparative account of primary productivity (PP), in the characteristically turbid and highly dynamic waters of Ariake Bay, measured by ¹³C uptake and fast repetition rate fluorometer (FRRF) was conducted to ensure compatibility between the two methods. Estimates from both methods depicted strong linearity for both short-term (r² > 0.90) and daily (r² = 0.42–0.93) measurements, except in the near-surface (∼0 m) layer. ¹³C-based short-term (1 h; in situ) PP estimates showed similar magnitudes and trend with the instantaneous PP measured by FRRF concurrently. Whereas, unlike short-term measurements, the daily PP estimates from both methods showed large difference, with FRRF-based time integrated daily PP resulting in 1.09–1.82 times higher than the carbon-based daily (24 h; simulated in situ) PP. This difference between daily PP estimates was mainly due to: (1) the temporal variation of water column chlorophyll a (Chl a) because of frequent moving of water mass, and (2) the dissimilarity in ambient light field conditions between the two methods. Results revealed that considering the above two environmental factors invariable over a daylength, fairly close approximation of daily PP, compared to ¹³C-based daily PP, could be obtained from FRRF. Hence, FRRF-based daily PP can be considered as more realistic in this highly dynamic water body like Ariake Bay where water column parameters are subjected to strong temporal variation. The relationship between Chl a-specific photosynthetic rate (P^B) and the corresponding photosynthetically active radiation (PAR) in the water column (PAR–P^B relationship) was found to be linear for FRRF and curvilinear for ¹³C-based measurements in the near-surface layer, for the same intensities of incident PAR, and this is thought to be the primary basis for the higher difference in PP estimates at the near-surface layer. Considering the minor variations in FRRF-based time series of PAR–P^B relationships, a combined and/or instantaneous PAR–P^B relationship in combination with incubation Chl a and light field condition was used to obtain fairly close estimates of daily water column integrated PP from FRRF.     

Subducting seamounts and deformation of overriding forearc wedges around Japan

Two subducting seamounts under inner trench slopes have been identified around Japan on the basis of magnetic anomalies, morphology and geological structure. The first one is located under the foot of the inner trench slope at the junction between the Japan Trench and the Kuril Trench. Another one occurs beneath the slope slightly seaward of the Tosabae (the basement high at the trench slope break along the Nankai Trough off Shikoku). The magnetic anomalies of seamount origin are accompanied by the characteristic morphology of a forearc wedge i.e., a swell landward and a depression seaward. The seamounts beneath the inner trench slopes have preserved magnetization showing reasonably consistent directions, which suggests that the subducting seamounts have kept roughly their original shapes. The morphology of the forearc wedge can be explained by a subducting seamount on the oceanic crust pushing the forearc material forward and upward. Deformation of the forearc wedge by the subducting seamount extends to the forearc basin. The seamounts are stronger and less deformable than the inner slope material and are not offscraped onto inner trench slopes.

Two other examples of deformed inner trench slopes around Japan which can be explained by subduction of topographic highs are presented. One example is a depression on the foot of the inner trench slope northeast of the junction between the Kyushu-Palau Ridge and the Nankai Trough. Another one is an area of complex morphology of the inner trench slope along the Japan Trench around the Daiichi-Kashima Seamount.     

Persistent organochlorine residues in sediments from the Chukchi Sea, Bering Sea and Gulf of Alaska

Three surface sediments and two sediment cores were collected from the Gulf of Alaska, Bering Sea and Chukchi Sea, and analysed for persistent organochlorines (OCs). The geographical distributions of OCs showed different patterns according to their physicochemical properties. The concentrations of HCHs and HCB revealed rather uniform distribution, suggesting their more transportable nature in long-range atmospheric transport. On the other hand, DDTs and PCBs were predicted to be less transportable via the atmosphere due to the decreasing trends of residue levels in sediments from south to north. The OC profiles in the sediment core from the Gulf of Alaska which seemed to be preserved without turbation revealed the elevated residue levels from bottom to surface layers. This implies that the aerial inputs of OCs in the cold ocean are still continuing significantly. The accumulation rates of OCs into sediments were rather smaller than the atmospheric inputs, indicating that the residue levels in water bodies are unlikely to decrease rapidly in the near future.