Comparison of sinking particles in the upper 200 m between subarctic station K2 and subtropical station S1 based on drifting sediment trap experiments

Drifting sediment trap experiments were conducted during various seasons to elucidate the characteristics of particles sinking through the upper 200 m of the water column in the western Pacific at subarctic station K2 and subtropical station S1. The sinking particle flux increased when primary productivity was high at each station, during June–July at K2 and during February at S1. Biogenic opal (Opal) and CaCO₃ were the major components of the fluxes at K2 and S1, respectively. Contrary to the expectation of a high flux at the eutrophic station K2 and low flux at the oligotrophic station S1, the annual average organic carbon fluxes at 100 m were comparable at both stations: 62.7 mg C m^?2 day^?1 at K2 and 56.1 mg C m^?2 day^?1 at S1. The similarity of the fluxes was perhaps a reflection of the unexpectedly high primary production at S1. At K2, the organic carbon export ratio (organic carbon flux/primary productivity) was significantly and negatively correlated with primary production and tended to decrease with depth. The magnitude of the rate of attenuation of the organic carbon flux with depth was larger at S1 than at K2. This rate of attenuation tended to decrease and increase with primary production at K2 and S1, respectively. The explanation for these patterns may be that the flux of labile organic carbon at relatively shallow depths decreased with increasing primary production at K2, and zooplankton grazing pressure increased with increasing primary productivity at S1.     

Polychlorinated biphenyl (PCB) concentrations and congener composition in masu salmon from Japan: A study of all 209 PCB congeners by high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS)

We collected two subspecies of masu salmon: Oncorhynchus masou masou from four localities (southern Sea of Japan northward to Hokkaido) and O. masou ishikawae from upstream from Ise Bay close to a heavy industrial area. All 209 PCB congeners were analyzed using HRGC/HRMS. PCA ordination of congener concentrations divided data into three groups: (i) ssp. masou from Hokkaido, (ii) ssp. masou from the other regions and (iii) ssp. ishikawae. The highest ∑ PCB concentration (40.39 ng/wet wt) was in ssp. ishikawae followed by ssp. masou from southern waters; however the TEQ_{dioxin-like PCBs} was highest in ssp. masou from southern water (1.96 pg-TEQ_{dioxin-like PCBs}/g wet wt.) due to the high proportion of congener #126 in its complement (#126 has the highest toxic equivalency factor among congeners). There is likely a contamination source offshore in the southern Sea of Japan and/or along the migratory route of ssp. masou.     

Stable isotope-guided analysis of congener-specific PCB concentrations in a Japanese coastal food web

Organisms collected from a coastal ecosystem in Japan were analyzed for concentrations of 205 polychlorinated biphenyls (PCBs) congeners; analyses were guided by δ¹³C and δ¹⁵N measurements. The regression slopes of log PCB concentration on δ¹⁵N value are regarded as indices of biomagnification in food webs. The slope (wet weight basis) of ΣPCBs was +0.104; the slope (lipid weight basis) was close to zero. Lipid content increased from 0.06% in a primary producer to 8.32% in the highest trophic level consumer. Hence, biomagnification of ΣPCBs (wet weight basis) can be attributed to increase of lipid content through the food web. For most of the congeners, the slopes (wet weight basis) exceeded those (lipid weight basis) by ca. 0.10. Slopes increased with increasing PCB chlorination levels between chlorine numbers 1–6; slopes decreased at higher chlorination levels. This decrease is likely caused by a decrease in membrane permeability with increasing molecular weight.     

Upper ocean warming pattern in the past 50 years

A long-term warming pattern of global subsurface ocean was detected separately from other natural variations. Three dominant modes were extracted: a long-term warming mode, a mode related to the El Niño/Southern Oscillation, and a mode related to the Atlantic Multidecadal Oscillation. The long-term warming mode explained 78 % of the global mean temperature variance from the surface to a depth of 300 m, and the other two modes could explain most of the residual variance. Subsurface warming associated with the long-term warming mode was strong in the subtropics. In contrast, there was a local minimum of warming in the northern hemisphere subarctic ocean, and warming was suppressed in subsurface waters south of the equator. Atmospheric changes associated with the long-term warming mode showed negative (positive) sea level pressure anomalies at high (middle) latitudes in both hemispheres, and an intensification and/or a poleward expansion of mid-latitude westerlies. Wind stress curl changes were negative in the subtropics and positive in the subarctic of the northern hemisphere; changes that were consistent with the strong warming in the subtropics and the local minimum of warming in the subarctic. Warming of Southern Ocean subsurface waters coincided with southward migration and intensification of westerly winds, whereas surface warming to the south of 50°S was suppressed, probably by strengthened northward Ekman transport. Positive wind stress curl off the equator with weakening of the tropical easterly winds in the Pacific and Indian Oceans was consistent with the subsurface negative temperature anomaly there.     

Distribution and photo-physiological condition of phytoplankton in the tropical and subtropical North Pacific

To better understand the vertical distribution of phytoplankton in the tropical and subtropical North Pacific, we used fast repetition rate fluorometry to investigate the photo-physiological condition of the phytoplankton assemblage in this region between February and March 2007. Along 155°E, between the equator and 24°N, the peak of fluorescence (F _m), an indication of the deep chlorophyll maximum (DCM), was deeper than the top of the nitracline and occurred at the 2.4 ± 1.3 % (mean ± SD) light depth (relative to 0 m). The photochemical efficiency (F _v/F _m) and effective absorption cross-section of photosystem II (σ_PSII) were low at the surface but increased rapidly at depths between the top of the nitracline (40–138 m) and the DCM (70–158 m), an indication that the photo-physiological condition of the phytoplankton improved below the top of the nitracline. The depth of the maximal F _v/F _m [Z(F _v/F _{m max})] was 18–32 m deeper than the DCM and corresponded to the 0.8 ± 0.2 % light depth. The values of F _v/F _m at the Z(F _v/F _{m max}) were 20 % higher than those at the DCM and averaged 0.48 ± 0.01. These results suggest that the phytoplankton assemblage beneath the DCM had a high potential photosynthetic performance capacity and was growing by using the very low ambient light in this region.     

Characteristic seasonal variation of vertical air temperature profile in urban areas of Japan

The seasonality of the vertical air temperature profile in an urban area in the vicinity of the coast was studied. The vertical air temperature profile showed the characteristic seasonality. In the summer, the atmosphere was thermally stratified in the 60–100 m layer, while the 20–60 m layer was unstable or weakly stable throughout the day due to the strong solar radiation. On the other hand, no temperature inversion layer was observed in the winter presumably due to the heat supply from the sea as well as the strong wind speed in the vicinity of the coast. The vertical air temperature profiles at nighttime in the spring and autumn were transitional between the summer and the winter. In contrast, the vertical air temperature profile in the daytime in the spring was similar to that in the summer, while that in the autumn was comparable to that in the winter. Characteristic findings in the study due to the site location, i.e., in the vicinity of the coast, can be summarized as follows: (1) the elevated temperature inversion layer at noon was observed in the summer, and (2) no temperature inversion layer was observed in the winter.