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Toda M.J.,Institute of Low Temperature Science | Toda M.J.,Hokkaido University | Lakim M.B.,Sabah Parks
Entomological Science | Year: 2011

A total of 21 Colocasiomyia species, including 17 undescribed species, are reported from Sabah (Mt. Kinabalu and neighboring areas), Malaysia, based on samples collected from inflorescences of 14 or 15 Araceae species. This number of species is the largest as a local fauna of this genus in the world. The high species diversity is attributed to 12 undescribed species belonging to the Colocasiomyia baechlii species group. A particular breeding habit of Colocasiomyia is sharing of the same inflorescence by a pair of species, with partial niche separation between them: one species uses exclusively the pistillate (lower female-flower) section of the spadix for oviposition and larval development, whereas the other mostly uses the staminate (upper male-flower) section. However, the baechlii group species show quite different patterns of host plant use: many (up to eight) species cohabit on the same inflorescence. It is unlikely that they separate their breeding niches micro-allopatrically within an inflorescence. Instead, species composition and their proportions of individual numbers vary among different localities, seasons and host plants, with partial overlap among them. Such partial separations in local distribution, phenology and host selection would in combination contribute to their coexistence and promote the species diversity of this group. © 2011 The Entomological Society of Japan.

Ohshima K.I.,Institute of Low Temperature Science | Kimura N.,National Institute of Polar ResearchTachikawa Japan | Tamura T.,Japan National Institute of Polar Research
Journal of Geophysical Research C: Oceans | Year: 2015

We examined to what degree a simplified polynya model can explain a real polynya based on satellite-derived sea-ice data. In the model, the polynya area, defined as the frazil ice production region, is determined by a balance between the offshore consolidated ice drift and frazil ice production. We used daily polynya area, ice production, and ice drift data derived from AMSR-E. The study area is the Ross Ice Shelf Polynya (RISP), which has the highest sea-ice production in the Southern Ocean. As a modification of the original model to apply the available satellite data set, we introduced the lag time by which produced frazil ice is transported and accumulated at the polynya edge. The model represents a half (48-60%) of the polynya variability when using a lag time of 1.5 days. The frazil ice collection depth at the polynya edge, a key parameter in the model, is estimated to be ∼16 cm. The expansion of the RISP is achieved by ice divergence, and the contraction is achieved mostly by ice production. Both the wind and the remaining components (mainly regarded as the ocean current component) in the ice divergence are larger in the western part of the RISP, which explains the larger extent there. In the one-dimensional frame, assuming that the frazil ice produced within the RISP transforms into consolidated ice with a thickness of 16 cm, the frazil ice production (∼1.7 × 103 m2 d-1) within the RISP approximately balances the export (∼1.6 × 103 m2 d-1) of consolidated thin ice from the RISP edge. © 2015. American Geophysical Union.

Hirano D.,National Institute of Polar ResearchTachikawa Japan | Fukamachi Y.,Institute of Low Temperature Science | Watanabe E.,Japan Agency for Marine - Earth Science and Technology | Ohshima K.I.,Institute of Low Temperature Science | And 4 more authors.
Journal of Geophysical Research: Oceans | Year: 2016

The nature of the Barrow Coastal Polynya (BCP), which forms episodically off the Alaska coast in winter, is examined using mooring data, atmospheric reanalysis data, and satellite-derived sea-ice concentration and production data. We focus on oceanographic conditions such as water mass distribution and ocean current structure beneath the BCP. Two moorings were deployed off Barrow, Alaska in the northeastern Chukchi Sea from August 2009 to July 2010. For sea-ice season from December to May, a characteristic sequence of five events associated with the BCP has been identified; (1) dominant northeasterly wind parallel to the Barrow Canyon, with an offshore component off Barrow, (2) high sea-ice production, (3) upwelling of warm and saline Atlantic Water beneath the BCP, (4) strong up-canyon shear flow associated with displaced density surfaces due to the upwelling, and (5) sudden suppression of ice growth. A baroclinic current structure, established after the upwelling, caused enhanced vertical shear and corresponding vertical mixing. The mixing event and open water formation occurred simultaneously, once sea-ice production had stopped. Thus, mixing events accompanied by ocean heat flux from the upwelled warm water into the surface layer played an important role in formation/maintenance of the open water area (i.e., sensible heat polynya). The transition from a latent to a sensible heat polynya is well reproduced by a high-resolution pan-Arctic ice-ocean model. We propose that the BCP, previously considered to be a latent heat polynya, is a wind-driven hybrid latent and sensible heat polynya, with both features caused by the same northeasterly wind. © 2016. American Geophysical Union.

Mitsudera H.,Institute of Low Temperature Science | Nakamura T.,Institute of Low Temperature Science | Sasajima Y.,Atmosphere and Ocean Research Institute | Hasumi H.,Atmosphere and Ocean Research Institute | Wakatsuchi M.,Institute of Low Temperature Science
Journal of Geophysical Research C: Oceans | Year: 2015

Dense Shelf Water (DSW) formation in the northwestern continental shelf of the Sea of Okhotsk is the beginning of the lower limb of the overturning circulation that ventilates the intermediate layer of the North Pacific Ocean. The upper limb consisting of surface currents in the Okhotsk Sea and the subarctic gyre has not been clarified. Using a high-resolution North Pacific Ocean model with a curvilinear grid as fine as 3 km × 3 km in the Sea of Okhotsk, we succeeded in representing the three-dimensional structure of the overturning circulation including the narrow boundary currents and flows through straits that constitute the upper limb, as well as the lower limb consisting of DSW formation and ventilation. In particular, pathways and time scales from the Bering Sea to the intermediate layer via the ventilation in the Sea of Okhotsk were examined in detail using tracer experiments. Further, we found that the overturning circulation that connects the surface and intermediate layer is sensitive to wind stress. In the case of strong winds, the coastal current under polynyas where DSW forms is intensified, and consequently diapycnal transport from the surface layer to the intermediate layer increases. Strong winds also induce a positive sea surface salinity anomaly in the subarctic region, causing a significant decrease in the density stratification and increase in the DSW salinity (i.e., density). These processes act together to produce intense overturning circulation and deep ventilation, which may subduct even to the bottom of the Sea of Okhotsk if the wind is strong. © 2015. American Geophysical Union. All Rights Reserved.

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