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Long-term variation of surface phytoplankton chlorophyllain the Southern Ocean during 1965–2002

Toru Hirawake
2005 Geophysical Research Letters  
The black bar and white dot indicate no data and location of the sampling station, respectively.L05606 HIRAWAKE ET AL.: CHL A VARIATION IN THE SOUTHERN OCEAN L05606 Figure 3 . 3 Time sequence of (a)  ... 
doi:10.1029/2004gl021394 fatcat:4wvczwjzfbgzla53ut2xlrduly

Estimation of ocean primary production from satellite remote sensing

Toru Hirawake, Shintaro Takao, Koji Suzuki, Jun Nishioka, Yutaka W. Watanabe, Tomonori Isada
2017 Oceanography in Japan  
海の研究 ( ) , ( ) , -, ここ数十年の間に,北極海の急速な海氷後退( et al ; )や南極棚氷の崩壊,熱波や洪 水などの局地的異常気象など,大気・海洋の温暖化の影 響とされる現象が世界各地において頻発している。この 地球温暖化の原因とされる主要な温暖化効果ガスは二酸 化炭素( )である。 年には気候変動に関する政 府間パネル( )が, 放出に関して現状を放置し た場合に人類や生態系は深刻で広範に及ぶ不可逆的な影 響を受ける可能性が高いことを警告し( ) ,途上国や新興国を含む世界各国が放出量削減に 向けて様々な努力を始めている。その削減量の成果を評
doi:10.5928/kaiyou.26.3_65 fatcat:zefwk36gbrehvbi3sceu4he3dy

Ⅰ-2. The outbreak of phytoplankton causing shellfish poisoning induced by the Tsunami

2021 Nippon Suisan Gakkaishi  
NAKANO, 5 TORU HIRAWAKE, 5b KAZUHIKO ICHIMI, 6 KENJI KANEKO 7 AND MOTOYUKI HARA 8 1 Fisheries Technology Institute, National Research and De- velopment Agency, Japan Fisheries Research and Education  ...  The outbreak of phytoplankton causing shellˆsh poisoning induced by the Tsunami YUTAKA OKUMURA, 1a SETSUKO SAKAMOTO, 2 YOSHIO MASUDA, 3 TORU TANABE, 3 SHINNOSUKE KAGA, 4 SHIHO WATANABE, 4 RINAKO  ... 
doi:10.2331/suisan.wa2861-2 fatcat:ze3po4vhxje3bnbbxeaylzohxq

Seasonal Habitat Patterns of Japanese Common Squid (Todarodes Pacificus) Inferred from Satellite-Based Species Distribution Models

Irene Alabia, Mariko Dehara, Sei-Ichi Saitoh, Toru Hirawake
2016 Remote Sensing  
The understanding of the spatio-temporal distributions of the species habitat in the marine environment is central to effectual resource management and conservation. Here, we examined the potential habitat distributions of Japanese common squid (Todarodes pacificus) in the Sea of Japan during a four-year period. The seasonal patterns of preferential habitat were inferred from species distribution models, built using squid occurrences detected from night-time visible images and remotely-sensed
more » ... vironmental factors. The predicted squid habitat (i.e., areas with high habitat suitability) revealed strong seasonal variability, characterized by a reduction of potential habitat, confined off of the southern part of the basin during the winter-spring period (December-May). Apparent expansion of preferential habitat occurred during summer-autumn months (June-November), concurrent with the formation of highly suitable habitat patches in certain regions of the Sea of Japan. These habitat distribution patterns were in response to changes in oceanographic conditions and synchronous with seasonal migration of squid. Moreover, the most important variables regulating the spatio-temporal patterns of suitable habitat were sea surface temperature, depth, sea surface height anomaly, and eddy kinetic energy. These variables could affect the habitat distributions through their impacts on growth and survival of squid, local nutrient transport, and the availability of favorable spawning and feeding grounds.
doi:10.3390/rs8110921 fatcat:wtj6wexrmfgfhcss5nnpbsctdu

Water mass characteristics and their temporal changes in a biological hotspot in the southern Chukchi Sea

Shigeto Nishino, Takashi Kikuchi, Amane Fujiwara, Toru Hirawake, Michio Aoyama
2016 Biogeosciences  
<p><strong>Abstract.</strong> We analysed mooring and ship-based hydrographic and biogeochemical data obtained from a Hope Valley biological hotspot in the southern Chukchi Sea. The moorings were deployed from 16 July 2012 to 19 July 2014, and data were captured during spring and autumn blooms with high chlorophyll <i>a</i> concentrations. Turbidity increased and dissolved oxygen decreased in the bottom water at the mooring site before the autumn bloom, suggesting an accumulation of particulate
more » ... organic matter and its decomposition (nutrient regeneration) at the bottom. This event may have been a trigger for the autumn bloom at this site. The bloom was maintained for 1 month in 2012 and for 2 months in 2013. The maintenance mechanism for the autumn bloom was also studied by hydrographic and biogeochemical surveys in late summer to autumn 2012 and 2013. Nutrient-rich water from the Bering Sea supplied nutrients to Hope Valley, although a reduction in nutrients occurred in 2012 by the influence of lower-nutrient water that would have remained on the Chukchi Sea shelf. In addition, nutrient regeneration at the bottom of Hope Valley could have increased nutrient concentrations and explained 60<span class="thinspace"></span>% of its nutrient content in the bottom water in the autumn of 2012. The high nutrient content with the dome-like structure of the bottom water may have maintained the high primary productivity via the vertical nutrient supply from the bottom water, which was likely caused by wind-induced mixing during the autumn bloom. Primary productivity was 0.3<span class="thinspace"></span>g<span class="thinspace"></span>C<span class="thinspace"></span>m<sup>−2</sup><span class="thinspace"></span>d<sup>−1</sup> in September 2012 and 1.6<span class="thinspace"></span>g<span class="thinspace"></span>C<span class="thinspace"></span>m<sup>−2</sup><span class="thinspace"></span>d<sup>−1</sup> in September 2013. The lower productivity in 2012 was related to strong stratification caused by the high fraction of surface sea ice meltwater.</p>
doi:10.5194/bg-13-2563-2016 fatcat:ba7jz7gubrfbdne32l3hx2ydsm

Variability in spring phytoplankton blooms associated with ice retreat timing in the Pacific Arctic from 2003–2019

Hisatomo Waga, Hajo Eicken, Toru Hirawake, Yasushi Fukamachi, João Canário
2021 PLoS ONE  
Furthermore, Waga and Hirawake [22] explored interannual variations in occurrences of evident fall blooms in the Pacific Arctic.  ...  Writing -review & editing: Hisatomo Waga, Hajo Eicken, Toru Hirawake, Yasushi Fukamachi.  ...  Funding acquisition: Hisatomo Waga, Toru Hirawake, Yasushi Fukamachi. Methodology: Hisatomo Waga, Hajo Eicken. Visualization: Hisatomo Waga. Writing -original draft: Hisatomo Waga.  ... 
doi:10.1371/journal.pone.0261418 pmid:34914776 pmcid:PMC8675671 fatcat:yxpnon37bndx5nki6qk45i47qq

Predicting potential fishing zones for Pacific saury (Cololabis saira) with maximum entropy models and remotely sensed data

Achmad F. Syah, Sei-Ichi Saitoh, Irene D. Alabia, Toru Hirawake
2016 Fishery Bulletin  
Fishing locations for Pacific saury (Cololabis saira) obtained from images of the Operational Linescan System (OLS) of the U.S. Defense Meteorological Satellite Program, together with maximum entropy models and satellite-based oceanographic data of chlorophylla concentration (chl-a), sea-surface temperature (SST), eddy kinetic energy (EKE), and sea-surface height anomaly (SSHA), were used to evaluate the effects of oceanographic conditions on the formation of potential fishing zones (PFZ) for
more » ... cific saury and to explore the spatial variability of these features in the western North Pacific. Actual fishing regions were identified as the bright areas created by a 2-level slicing method for OLS images collected August-December during 2005-2013. The results from a Maxent model revealed its potential for predicting the spatial distribution of Pacific saury and highlight the use of multispectral satellite images for describing PFZs. In all monthly models, the spatial PFZ patterns were explained predominantly by SST (14-16°C) and indicated that SST is the most influential factor in the geographic distribution of Pacific saury. Also related to PFZ formation were EKE and SSHA, possibly through their effects on the feeding grounds conditions. Concentration of chl-a had the least effect among other environmental factors in defining PFZs, especially during the end of the fishing season.
doi:10.7755/fb.114.3.6 fatcat:ddxsgpnehrf6dkfrwkmdu7v7ti

Spatiotemporal variations in suitable areas for Japanese scallop aquaculture in the Dalian coastal area from 2003 to 2012

Yang Liu, Sei-Ichi Saitoh, I. Nyoman Radiarta, Hiromichi Igarashi, Toru Hirawake
2014 Aquaculture  
36 The Japanese scallop (Mizuhopecten yessoensis) is an important commercial species in 37 the Dalian coastal area. The present study employed a suitable aquaculture site-selection 38 model (SASSM) and used satellite remote-sensing data to analyze the spatiotemporal 39 distribution of suitable areas for Japanese scallop aquaculture in the Dalian coastal area 40 from 2003 to 2012. The study area was divided into four marine zones. The results 41 demonstrated that the suitability scores of
more » ... aquaculture areas were high in May 42 and low in February. The Changhai County (Zone II) and Lushunkou areas (Zone III) 43 exhibited high potential for Japanese scallop aquaculture development. The results of 44 the suitability models were consistent with the existing scallop aquaculture in the study 45 area. These zones, combined with climatic events [the winter East Asian Monsoon 46 (EAM) and El Niño/La Niña-Southern Oscillation (ENSO) events], were used to 47 examine the impact of climate variability on scallop aquaculture. Results suggest that 48 the suitability scores in Zone III were more sensitive to changes in environmental 49 factors (e.g., sea surface temperature, chlorophyll-a, and suspended sediment) and 50 climate changes, whereas the correlations among these factors were not significant in 51 Zone II. Adaptation to these changes should be considered when developing plans and 52 management strategies for scallop aquaculture. 53 54
doi:10.1016/j.aquaculture.2013.11.033 fatcat:c7pkk5vq2rdhtgkr7lanjf6br4

Influences of size structure and post-bloom supply of phytoplankton on body size variations in a common Pacific Arctic bivalve (Macoma calcarea)

Hisatomo Waga, Toru Hirawake, Masahiro Nakaoka
2020 Polar Science  
The post-bloom period was defined as the period from the end of the spring bloom period to the date of sea-ice freeze-up (Waga and Hirawake, 2020) .  ... 
doi:10.1016/j.polar.2020.100554 fatcat:j5hjjrm2lnchlelqolrntefa6m

Differences in Rate and Direction of Shifts between Phytoplankton Size Structure and Sea Surface Temperature

Hisatomo Waga, Toru Hirawake, Amane Fujiwara, Takashi Kikuchi, Shigeto Nishino, Koji Suzuki, Shintaro Takao, Sei-Ichi Saitoh
2017 Remote Sensing  
Species distributions are changing with various rates and directions in response to recent global warming. The velocity of sea surface temperature (SST) has been used to predict species migration and persistence as an expectation of how species track their thermal niches; however, several studies have found that evidence for species shifts has deviated from the velocity of SST. This study investigated whether estimation of the velocity of shifts in phytoplankton size structure using remote
more » ... ng data could contribute to better prediction of species shifts. A chlorophyll-a (Chla) size distribution (CSD) model was developed by quantifying the relationships between the size structure of the phytoplankton community and the spectral features of the phytoplankton absorption coefficient (a ph (λ)), based on the principal component analysis approach. Model validation demonstrated that the exponent of CSD (hereafter, CSD slope), which can describe the synoptic size structure of a phytoplankton community, was derived successfully with a relative root mean square error of 18.5%. The median velocity of CSD slope across the ocean was 485.2 km·decade −1 , broadly similar to Chla (531.5 km·decade −1 ). These values were twice the velocity of SST, and the directions of shifts in CSD slope and Chla were quite different from that of SST. Because Chla is generally covariant with the size structure of a phytoplankton community, we believe that spatiotemporal changes in Chla can explain the variations of phytoplankton size structure. Obvious differences in both rate and direction of shifts were found between the phytoplankton size structure and SST, implying that shifts of phytoplankton size structure could be a powerful tool for assessing the distributional shifts of marine species. Our results will contribute to generate global and regional maps of expected species shifts in response to environmental forcing.
doi:10.3390/rs9030222 fatcat:wsu25oarsvhkjaovifehow4cli

A review: iron and nutrient supply in the subarctic Pacific and its impact on phytoplankton production

Jun Nishioka, Hajime Obata, Toru Hirawake, Yoshiko Kondo, Youhei Yamashita, Kazuhiro Misumi, Ichiro Yasuda
2021 Journal of Oceanography  
AbstractOne of the most important breakthroughs in oceanography in the last 30 years was the discovery that iron (Fe) controls biological production as a micronutrient, and our understanding of Fe and nutrient biogeochemical dynamics in the ocean has significantly advanced. In this review, we looked back both previous and updated knowledge of the natural Fe supply processes and nutrient dynamics in the subarctic Pacific and its impact on biological production. Although atmospheric dust has been
more » ... considered to be the most important source of Fe affecting biological production in the subarctic Pacific, other oceanic sources of Fe have been discovered. We propose a coherent explanation for the biological response in subarctic Pacific high nutrient low chlorophyll (HNLC) waters that incorporates knowledge of both the atmospheric Fe supplies and the oceanic Fe supplies. Finally, we extract future directions for Fe oceanographic research in the subarctic Pacific and summarize the uncertain issues identified thus far.
doi:10.1007/s10872-021-00606-5 fatcat:kuu6nbjtgrc67neinqgui4pepy

Behaviors of the Yukon River Sediment Plume in the Bering Sea: Relations to Glacier-Melt Discharge and Sediment Load

Kazuhisa A. Chikita, Tomoyuki Wada, Isao Kudo, Sei-Ichi Saitoh, Toru Hirawake, Mitsuhiro Toratani
2021 Water  
Sediment plumes, released to the Bering Sea from the delta front of the Yukon River, Alaska, are initiated mainly by glacier-melt sediment runoffs in the glacierized regions of the Yukon River drainage basin. The surface sediment plumes are extended around the fan-shaped Yukon River delta, which is followed by the northwestward dispersion. During continuous measurements of the Yukon River discharge and sediment load, behaviors of the sediment plumes were explored by shipboard and coastal
more » ... tions in the Bering Sea. At the high river sediment load of ca. 2500 kg/s, the plume partially plunged into the sea bottom layer. The plunging probably originated in the nepheloid-layer formation from the flocculation of river-suspended sediment, of which more than 90% wt. is silt and clay (grain size d < 63 μm). In order to numerically obtain the area of the surface sediment plumes, a satellite image analysis was performed by using three near-infrared bands in MODIS/Aqua or MODIS/Terra. The plume area was significantly correlated (R2 = 0.735, p < 0.01) to the sediment load averaged for the two days with time lags of 20 days and 21 days to the date of a certain satellite image. Hence, the dispersion of plume-suspended sediment appears to be controlled by the sediment runoff events in the Yukon River rather than the northward "Alaskan Coastal Water".
doi:10.3390/w13192646 fatcat:st2oszrswnek7bxmq7m7jdly3q

Sediment-Associated Phytoplankton Release From the Seafloor in Response to Wind-Induced Barotropic Currents in the Bering Strait

Hiroto Abe, Makoto Sampei, Toru Hirawake, Hisatomo Waga, Shigeto Nishino, Atsushi Ooki
2019 Frontiers in Marine Science  
Bering Strait is the single gateway between the Arctic and Pacific Oceans, and has localized strong currents, which can exceed 100 cm s −1 . Although massive spring phytoplankton blooms and the subsequent production of particulate organic matter that sinks to the seafloor are observed in the surrounding regions of the Bering Strait, the impact of the locally strong current on the horizontal and vertical transport of the particles remains unclear. Therefore, we conducted year-round mooring
more » ... ements from 2016 to 2017 by focusing on near-bottom processes associated with ocean currents. Our time-series analysis showed that high-turbidity events, triggered by strong barotropic currents, occurred near the seafloor in all seasons. Consequently, the fluorescence sensor detected highly concentrated chlorophyll a in the resuspended sediment; however, the amount of chlorophyll a release was seasonal, with large and small amounts being released during the warm and cold seasons, respectively. The small amounts of chlorophyll a may be attributed to small amounts of phytoplankton in the sediment owing to less input of fresh phytoplankton from the overlaying water column and organic matter decomposition in the sediments under no-light conditions. The barotropic currents were modulated by surface winds associated with an intercontinental atmospheric pattern having a 5000-km spatial scale on a timescale of 6 days. The locally strong ocean current in the Bering Strait, driving the upward transport of sediment and the subsequent horizontal transport, may play a vital role in supplying particulate organic matter/phytoplankton/nutrients to the downstream region of the southern Chukchi Sea where the formation of biological hotspots is reported.
doi:10.3389/fmars.2019.00097 fatcat:mjvom3dpazf7rnjx6yuaaxka7y

Year-to-year changes of the mesozooplankton community in the Chukchi Sea during summers of 1991, 1992 and 2007, 2008

Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Ichiro Imai
2011 Polar Biology  
A recent drastic decrease in sea ice cover area was observed in the western Arctic Ocean during summer, yet little information is available for its effect on zooplankton community. To evaluate the effect of sea ice reduction on zooplankton, we studied year-to-year changes of zooplankton community structure in the Chukchi Sea during summers of 1991, 1992 (when sea ice extended), 2007 and 2008 (when sea ice reduced). Zooplankton abundance ranged from 4,000 to 316,000 ind. m −2 (mean: 70,000), and
more » ... was greater north of Lisburne Peninsula in 2008. Zooplankton biomass ranged from 0.07 to 286 g wet mass m −2 (mean: 36), and was greater south of Lisburne Peninsula in 2007. Cluster analysis based on zooplankton abundance showed a division of the zooplankton community into four groups. Occurrence of each group was separated geographically and interannually, and geographic distributions of each group in 1991 and 1992 were similar but those in 2007 and 2008 were shifted northward. Abundance and biomass in 2007/08 were higher than in 1991/92, indicating that further sea ice reduction would have a positive effect on zooplankton production (e.g. invasion of large Pacific species and temperature effects on their growth rate). The northern shift in geographic distribution of the zooplankton community in 2007/08 indicates that sea ice reduction would have a negative effect on the zooplankton community (loss of characteristic Arctic species) in part of the Chukchi Sea. These apparently contradictory effects of sea ice reduction on zooplankton community emphasize the critical need for continued monitoring in this area.
doi:10.1007/s00300-011-0988-z fatcat:rknenkeehvfw5d6fi4qlc6ehda

Changes in phytoplankton community structure during wind-induced fall bloom on the central Chukchi shelf

Amane Fujiwara, Shigeto Nishino, Kohei Matsuno, Jonaotaro Onodera, Yusuke Kawaguchi, Toru Hirawake, Koji Suzuki, Jun Inoue, Takashi Kikuchi
2018 Polar Biology  
The recent increasing of atmospheric turbulence has had considerable impact on the oceanic environment and ecosystems of the Arctic. To understand its effect on phytoplankton community structure, a Eulerian fixed-point observation (FPO) was conducted on the Chukchi shelf in fall 2013. Temporal and vertical distributions of the phytoplankton community were inferred from algal pigment signatures. A strong wind event (SWE) occurred during the observation term, and significant convection supplied
more » ... trients from the bottom layer to the surface. Before the SWE, pigment composition in the warmer, less saline, and nutrient-poor surface waters was diverse with low concentration of chlorophyll-a (chla). Vertical mixing induced by the SWE weakened the stratification and brought sufficient nutrients to enhance diatom-derived pigment concentrations (e.g., fucoxanthin and chlc3), suggesting increases in diatoms. We also developed a model to predict the distribution of major phytoplankton pigment/chla ratios using a profiling multi-wavelength fluorometer (Multi-Exciter) with higher spatio-temporal resolution. The Multi-Exciter also captured changes in pigment composition with environmental changes at the FPO site and at four observation sites 16 km from the location of the FPO. Furthermore, we investigated the change in grazing rates of the major Arctic copepod Calanus glacialis copepodid stage five to assess the interaction between primary and secondary producers during the fall bloom. Increased diatom biomass caused a significant increase in the grazing rate on microphytoplankton (> 20 µm) and a decrease on nanophytoplankton (2-20 µm), indicative of a strong cascade effect because of the reduction of microzooplankton due to the grazing from C. glacialis. We conclude that SWEs during fall might affect food webs via the alternation of seasonal succession of phytoplankton community structure.
doi:10.1007/s00300-018-2284-7 fatcat:zqo667fnmjeh7igx5up2u2kpri
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