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Hiroshi Ishida Yutaka W. Watanabe Joji Ishizaka Toshiya Nakano Naoki Nagai Yuji Watanabe Akifumi Shimamoto Nobuhiro Maeda Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186
Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a
(Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season,
as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4
and 2.3% year−1 in the subtropical area along 137°E (STA137) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA175) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year−1 in STA137 and KEA175; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year−1 in STA137 and KEA175, respectively. Water density (σ
θ
) at 75 m depth had also decreased by 0.006 and 0.05 year−1 in STA137 and KEA175, respectively. The ratio of biogenic opal to biogenic CaCO3 in the sinking flux decreased by 0.015 year−1 in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening
and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density
of surface water caused by warming in the western North Pacific, especially in the summer. 相似文献
2.
Osamu Shida Tomonori Hamatsu Akira Nishimura Akifumi Suzaki Jun Yamamoto Kazushi Miyashita Yasunori Sakurai 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2822
The Japanese Pacific walleye pollock (Theragra chalcogramma) stock is the largest stock of this species in Japanese waters. It is a key component of the Oyashio ecosystem. In southern Hokkaido waters, these fish spawn mainly during January and February near the mouth of Funka Bay (FB), and most eggs and larvae are transported into FB. During midsummer juvenile pollock migrate along the southern coast of Hokkaido to a nursery ground on the continental shelf off eastern Hokkaido (Doto area). However, some eggs and larvae are transported southward to the Tohoku region (TR). Transport depends largely on the Oyashio, which generally flows southward along the eastern coasts of Hokkaido and Tohoku. Thus, this stock has two different recruitment routes: FB–Doto and FB–TR. In the 1980s, when the southward flow of the Oyashio was strong, the number of age-2 pollock estimated from a virtual population analysis (VPA) indicated that recruitment to the entire stock remained at a medium level. In the 1990s, when the Oyashio weakened, strong year-classes occurred in 1991, 1994, and 1995, but not in the latter half of the 1990s. Juvenile catches in the TR by commercial fisheries, which can be taken as indices of recruitment level via FB–TR, were high during the 1980s and decreased in the 1990s. Although there was no significant difference in the average number of recruits between the 1980s and the 1990s as estimated from a VPA, the recruitment patterns differed between the two decades. Here, we propose that recruitment routes of this stock shifted in response to environmental changes. 相似文献
3.
Daisuke Tsumune Jun Nishioka Akifumi Shimamoto Shigenobu Takeda Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):111
The first iron (Fe) – fertilization experiment in the western North Pacific was carried out using SF6 to trace the Fe-fertilized water mass. A solution in 10,800 liters of seawater of 350 kg of Fe and 0.48 M of SF6 tracer was released into the mixed layer over a 8 × 10 km area. On the first underway transects through the patch after the Fe release, we observed a significant increase of dissolved Fe (ave. 2.89 nM). The fertilized patch was traced for 14 days by on-board SF6 analysis. A Lagrangian frame of reference was maintained by the use of a drogued GPS buoy released at the center of the patch. The patch moved westward at a rate of 6.8 km d−1. Mixed layer depth increased from 8.5 to 15 m during the experiment. Horizontal diffusivity was determined by the change of SF6 concentration in the patch. The horizontal diffusivity increased during the experiment. We evaluate here the fate of Fe in a Fe-fertilized patch using the dilution rate determined from sulphur hexafluoride (SF6) concentration. Dissolved Fe concentrations subsequently decreased rapidly to 0.15 nM on Day 13. However, the dissolved Fe half-life of 43 h was relatively longer than in previous Fe-enrichment studies, and we observed a larger increase of the centric diatom standing stock and corresponding drawdown of macro-nutrients and carbon dioxide than in the previous studies. The most important reason for the larger response was the phytoplankton species in the western North Pacific. In addition, the smaller diffusivity and shallower mixed layer were effective to sustain the higher dissolved Fe concentration compared to previous experiments. This might be one reason for the larger response of diatoms in SEEDS. 相似文献
4.
To verify the actual usefulness of time-dependent tracer dating techniques in the ocean, we simultaneously obtained two cross
sections of sulfur hexafluoride (SF6) and chlrofluoromethanes (CFC-11, trichlorofluoromethane; CFC-12, dichloro-difluromethane; CFC-113, trichlorotrifluoroethane)
in the western North Pacific in 1998. The vertical distribution patterns of SF6 and CFC-113 were similar in shape to those of CFC-11 and CFC-12. Maximum penetration depths of SF6 and CFC-113 remained around 800 m in the subpolar region and 400 m in the tropical region, while the maximum penetration
depths of CFC-11 and CFC-12 were still found below 1000 m depth. We also found all maximum contents of these tracers around
26.6−26.8σθ with a gradual decrease southward. This suggested that a new subsurface water mass in the subpolar region spread out over
the entire North Pacific, which agrees closely with previous studies based on the salinity minimum. Moreover, we compared
the tracer ages (the elapsed period of a water mass from when the water mass left from the ocean surface) using ten time-dependent
tracer dating techniques, CFC-11, CFC-12, CFC-113, SF6, CFC-11/CFC-12, CFC-113/CFC-11, CFC-113/CFC-12, SF6/CFC-11, SF6/CFC-12 and SF6/CFC-113. This quantitative evaluation of multiple tracer dating techniques in the ocean was the first confirmation of its
usefulness based on the observational data on the ocean basin-wide scale. We conclude that SF6/CFC-11, SF6/CFC-12, SF6/CFC-113 and SF6 dating techniques would be the most promising tools for determining the age of water mass not only just for the past several
decades but for the future, too.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Tomoo Katsura Sho Yokoshi Kazuyuki Kawabe Anton Shatskiy Maki Okube Hiroshi Fukui Eiji Ito Akifumi Nozawa Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2007,34(4):249-255
The electrical conductivity of (Mg0.93Fe0.07)SiO3 ilmenite was measured at temperatures of 500–1,200 K and pressures of 25–35 GPa in a Kawai-type multi-anvil apparatus equipped
with sintered diamond anvils. In order to verify the reliability of this study, the electrical conductivity of (Mg0.93Fe0.07)SiO3 perovskite was also measured at temperatures of 500–1,400 K and pressures of 30–35 GPa. The pressure calibration was carried
out using in situ X-ray diffraction of MgO as pressure marker. The oxidation conditions of the samples were controlled by
the Fe disk. The activation energy at zero pressure and activation volume for ilmenite are 0.82(6) eV and −1.5(2) cm3/mol, respectively. Those for perovskite were 0.5(1) eV and −0.4(4) cm3/mol, respectively, which are in agreement with the experimental results reported previously. It is concluded that ilmenite
conductivity has a large pressure dependence in the investigated P–T range. 相似文献
6.
Takashi Kudo Minoru Sasaki Yoshihiro Uchiyama Akifumi Nozawa Hisashi Sasaki Takeshi Tokizawa Shinji Takarada 《Island Arc》2007,16(1):133-155
Abstract The Hakkoda‐Towada caldera cluster (HTCC) is a typical Late Cenozoic caldera cluster located in the northern part of the Northeast Japan Arc. The HTCC consists of five caldera volcanoes, active between 3.5 Ma and present time. The felsic magmas can be classified into high‐K (HK‐) type and medium‐ to low‐K (MLK‐) type based on their whole‐rock chemistry. The HK‐type magmas are characterized by higher K2O and Rb contents and higher 87Sr/86Sr ratios than MLK‐type magmas. Both magmas cannot be derived from fractional crystallization of any basaltic magma in the HTCC. Assimilation‐fractional crystallization model calculations show that crustal assimilation is necessary for producing the felsic magmas, and HK‐type magmas are produced by higher degree of crustal assimilation with fractional crystallization than MLK‐type magmas. Although MLK‐type magmas were erupted throughout HTCC activity, HK‐type magmas were erupted only during the initial stage. The temporal variations of magma types suggest the large contribution of crustal components in the initial stage. A major volcanic hiatus of 3 my before the HTCC activity suggests a relatively cold crust in the initial stage. The cold crust probably promoted crustal assimilation and fractional crystallization, and caused the initial generation of HK‐type magmas. Subsequently, the repeated supply of mantle‐derived magmas raised temperature in the crust and formed relatively stable magma pathways. Such a later system produced MLK‐type magmas with lesser crustal components. The MLK‐type magmas are common and HK‐type magmas are exceptional during the Pliocene–Quaternary volcanism in the Northeast Japan Arc. This fact suggests that exceptional conditions are necessary for the production of HK‐type magmas. A relatively cold crust caused by a long volcanic hiatus (several million years) is considered as one of the probable conditions. Intensive crustal assimilation and fractional crystallization promoted by the cold crust may be necessary for the generation of highly evolved HK‐type felsic magmas. 相似文献
7.
Tomohiro Deguchi Yutaka Watanuki Yasuaki Niizuma Akifumi Nakata 《Progress in Oceanography》2004,61(2-4):267
The diets of breeding seabirds can be a good monitor of marine environmental changes. From 1984 to 2001 we monitored the diets of black-tailed gulls (Larus crassirostris) (“surface foragers”), rhinoceros auklets (Cerorhinca monocerata) (“epipelagic divers”), and Japanese cormorants (Phalacrocorax filamentotus) (“bottom divers”) that breed on Teuri Island at the northern boundary of the Tsushima Warm current in the Sea of Japan/East Sea. Between 1984 and 1987, both the gulls and the auklets foraged on the sardine (Sardinops melanostictus), but after 1992, they switched to the anchovy (Engraulis japonica). This change might reflect the collapse of the sardine stock in the late 1980s. In the 1990s, the year-to-year variations of the percentage of anchovy in the diets of the three seabird species showed similar trends: High in 1994 and 1998–2001; and low in 1992–1993 and 1995–1997. The estimated stock size of the anchovy population in the Tsushima Current area was positively correlated with the percentage of mass of anchovy in the seabirds’ diets. Thus, the short-term annual changes of the total anchovy availability, which might reflect SST or the volume transport of Tsushima Current, possibly affected the seabirds diets on this island. 相似文献
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