Long-term variations of surface and intermediate waters in the southern Indian Ocean along 32°S     

Taiyo Kobayashi  Keisuke Mizuno  Toshio Suga 《Journal of Oceanography》2012,68(2):243-265

Variations of water properties in surface and intermediate layers along 32°S in the southern Indian Ocean were examined using a 50-year (1960–2010) time series reproduced from historical hydrographic and Argo data by using optimum interpolation. Salinity in the 26.7–27.3σ_θ density layer decreased significantly over the whole section, at a maximum rate of 0.02 decade⁻¹ at 26.8–26.9σ_θ, for the 50-year average. Three deoxygenating cores were identified east of 75°E, and the increasing rate of apparent oxygen utilization in the most prominent core (26.9–27.0σ_θ) exceeded 0.05 ml l⁻¹ decade⁻¹. The pycnostad core of Subantarctic Mode Water (SAMW) and the salinity minimum of Antarctic Intermediate Water shifted slightly toward the lighter layers. Comparisons with trans-Indian Ocean survey data from 1936 suggest that the tendencies found in the time series began before 1960. Interestingly, cores of many prominent trends were located just offshore of Australia at 26.7–27.0σ_θ, which is in the SAMW density range. Spectrum analysis revealed that two oscillation components with time scales of about 40 and 10 years were dominant in the subsurface layers. Our results are fairly consistent with, and thus support, the oceanic responses in the southern Indian Ocean to anthropogenic climate change predicted by model studies.  相似文献   

Effects of cyclonic mesoscale eddies on the marine ecosystem in the Kuroshio Extension region using an eddy-resolving coupled physical-biological model   总被引：2，自引：0，他引：2  

Yoshikazu Sasai  Kelvin J. Richards  Akio Ishida  Hideharu Sasaki 《Ocean Dynamics》2010,60(3):693-704

Effects of mesoscale eddies on the marine ecosystem in the Kuroshio Extension (KE) region are investigated using an eddy-resolving coupled physical-biological model. The model captures the seasonal and intra-seasonal variability of chlorophyll distribution associated with the mesoscale eddies, front variability, Kuroshio meanders, and upwelling. The model also reproduces the observed interannual variability of sea surface height anomaly (SSHA) in the KE region along a zonal band of 32–34°N from 2002 to 2006. The distribution of high surface chlorophyll corresponds to low SSHA. Cyclonic eddies are found to detach from the KE jet near 150°E and 158°E and propagate westward. The westward propagating cyclonic eddies lift the nutrient-rich thermocline into the euphotic zone and maintain high levels of chlorophyll in summer. In the subsurface layer, the pattern in chlorophyll is influenced by both lateral and vertical advection. In winter, convection inside the eddy entrains high levels of nutrients into the mixed layer, increasing production, and resulting in high chlorophyll concentration throughout the surface mixed layer. There is significant interannual variability in both the cyclonic eddy activity and the surface phytoplankton bloom south of the KE jet, although whether or not there is a causal link is unclear.  相似文献   

Coastal upwelling along the north coast of Papua New Guinea and El Niño events during 1981–2005     

Takuya Hasegawa  Kentaro Ando  Keisuke Mizuno  Roger Lukas  Bunmei Taguchi  Hideharu Sasaki 《Ocean Dynamics》2010,60(5):1255-1269

We investigate the relationship between sea surface temperature (SST) cooling and upwelling along Papua New Guinea’s (PNG) north coast before the onset of El Niño events using a hindcast experiment with a high-resolution ocean general circulation model. Coastal upwelling and related SST cooling appear along PNG north coast during the boreal winter before the onsets of six El Niño events occurring during 1981–2005. Relatively cool SSTs appear along PNG north coast during that time, when anomalous northwesterly surface wind stress, which can cause coastal upwelling by offshore Ekman transport appearing over the region. In addition, anomalous cooling tendencies of SST are observed, accompanying anomalous upward velocities at the base of the mixed layer and shallow anomalies of 27°C isotherm depth. It is also shown that entrainment cooling plays an important role in the cooling of the mixed layer temperature in this region.  相似文献   

Preliminary results of in-situ XCTD/CTD comparison test   总被引：4，自引：0，他引：4  

Keisuke Mizuno  Tomowo Watanabe 《Journal of Oceanography》1998,54(4):373-380

The current status of XCTD manufactured by the Tsurumi Seiki Co. is described based on XCTD/CTD comparison tests conducted in the Pacific and Indian Ocean in November 1996 and January 1997 respectively. The falling rates of used probes are generally consistent and differences between individual probes stay within a small range of +/−5 m through the full depth range (0–1000 m), although the rate is slightly different from the depth-time equation provided by the manufacturer. Temperature and salinity accuracy is estimated to be better than 0.05°C and 0.05 psu respectively. Comparison of vertical temperature/salinity sections of XCTD/CTD constructed separately along a line on which XCTD stations locate midway of CTD stations. The hydrographic structures obtained are generally consistent, and the difference of surface dynamic height (referred to 1000 db) is 0.03 dyn m in RMS.  相似文献   

Deep hydrographic structure along 12°N and 13°N in the Philippine Sea     

Katsuto Uehara  Keisuke Taira 《Journal of Oceanography》1990,46(4):167-176

Hydrographic casts down to the bottom along two zonal sections at 12°N and 13°N (from 144°E to 127°E) were made with a CTD. Their analysis verified the existence of cold and saline abyssal water between the Mariana Ridge and the Kyushu-Palau Ridge. This result provides evidence of flow into the Philippine Sea through the deep gap called the Yap-Mariana Junction. The properties of deep water are variable in the West Mariana basin but quite homogeneous in the Philippine Basin, indicating the transitional nature in the West Mariana Basin and the existence of older bottom water in the Philippine Basin. A close examination suggests that the bottom water is slightly colder in the western part of the Philippine Basin than in the eastern part of the basin. This slightly colder deep water with a hundred kilometer scale in the western Philippine Basin might be related to a broad western boundary current flowing equatorward along the eastern rise of the Philippine Trench.  相似文献   

Occurrence of PSP-producing dinoflagellate Alexandrium tamiyavanichii in Bingo-Nada, the central coastal water of the Seto Inland Sea, Hiroshima Prefecture, Japan     

Beppu R  Nojima K  Tsuruda S  Gomez-Delan G  Barte-Quilantang M  Taniyama S  Sagara T  Nishio S  Takayama H  Miyazawa K  Asakawa M 《Marine pollution bulletin》2008,56(4):758-763

During surveillance of the distribution of the paralytic shellfish poison (PSP)-producing dinoflagellate in 2003, 2004 and 2005 along the coastlines of the Seto Inland Sea, Hiroshima Prefecture, Japan, some species of toxic phytoplankton were isolated from the eastern coasts, Bingo-Nada, the central regions of the Seto Inland Sea. It was rather unexpectedly revealed from the basis of the morphological characteristics that they were unambiguously identified as Alexandrium tamiyavanichii and Alexandrium catenella. Two strains (ATY041106, ATY051018) of A. tamiyavanichii showed a specific toxicity of 38.7 x 10(-6) and 111.5 x 10(-6)MU/cell, respectively. These values seemed to be several times or much higher than that of A. catenella (AC030816, AC040614), having a specific toxicity of 4.5 x 10(-6) and 4.1 x 10(-6)MU/cell, respectively, isolated in the same area. From the results of HPLC-furuorometric analysis, it revealed that the toxins in ATY041106 exist almost exclusively as beta-epimers (C2, GTX3, GTX4), which accounted for 72.7 mol%. The toxin profiles of this strain are featured by the presence of a large amount of GTX3 (59.1 mol%) and a small amount (20.6%) of C1 and 2 in comparison with the PSP compositions of A. tamarense, which is isolated as the main responsible species in Hiroshima Bay, a western part of coastal sea in Hiroshima Prefecture. On the other hand, it revealed that the toxin profiles of two strains (AC030816, AC040614) of A. catenella exist almost exclusively as beta-epimers (C2, GTX3, GTX4), which accounted for 81.8 and 56.5 mol%, as the same manner. The toxin profiles of these two strains are featured by the presence of a large amount of C2 (80.5 and 46.3 mol%) in comparison with the PSP compositions of A. tamiyavanichii. To our knowledge, this is the first record to show the distribution and harmful influence of A. tamiyavanichii and A. catenella in Bingo-Nada in Hiroshima Prefecture. Though contamination of bivalves with these PSP-producing planktons in this area has not occurred yet so far, attention should be paid to this species as well as the other causative dinoflagellate from the stand point of public health and food hygiene.  相似文献   

Detectability analysis of interplate fault slips in the Nankai subduction thrust using seafloor observation instruments     

Agata  Ryoichiro  Hori  Takane  Ariyoshi  Keisuke  Ichimura  Tsuyoshi 《Marine Geophysical Researches》2019,40(4):453-466

To help the decision making regarding where to locate new observation instruments on the seafloor, we examined the detectability of interplate earthquakes and slow slips in the Nankai subduction thrust in Japan using seafloor observation instruments. Here, the detectability is defined as the smallest magnitude of the interplate fault slip detected by the assumed observation points based on crustal deformation simulation. In the detectability analyses, we considered the effect of sensor drifts that are particularly associated with seafloor observations. In addition, we introduced high-resolution three-dimensional (3D) finite element modeling of crustal deformation to consider the effect of the topography and 3D heterogeneous crustal structure around the Nankai Trough. The results of the detectability analyses show that introducing new seafloor stations for tilt observation in the Nankai region should increase the detectability of small- or medium-sized interplate earthquakes and slow slips significantly. Based on the obtained results, we also discuss the advantage of both the existing and the new observation instruments in detecting interplate fault slips.

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