Research Topics

Research
Press Release
Topics
Publications
H28-1 Does sea ice supply nutrients to spring phytoplankton bloom in the Sea of Okhotsk?
H25-1 When ocean dynamic drives the land to ocean input of iron
H22-1 Visualization of state transitions uncovered an energy dissipation mechanism in photosynthesis
H19-2 Possible strong annual connection in spring between Asian dust outbreak and stratosphere-troposphere exchange due to annual variations of storm activity
H18-3 Laboratory for Planet Formation: Synergy of Technologies Reveal Origin of Dust Around Nearby Star
H17-4 Boreal forest fire impacts on permafrost disturbance and greenhouse gas emissions
H17-3 Formation and deuterium fractionation of interstellar methanol on ice dusts
H17-2 Monte Carlo Simulation of the Formation of Snowflakes

ILTS Research Topics H28-1

Title

Does sea ice supply nutrients to spring phytoplankton bloom in the Sea of Okhotsk?

Authors

Naoya Kanna1,2, Jun Nishioka1

  1. Pan-Okhotsk Research Center, Institute of Low Temperature Science, Hokkaido University
  2. Graduate School of Environmental Science, Hokkaido University
Abstract

The Sea of Okhotsk, which is a seasonal sea-ice area, is one of the most productive marginal seas and provides a large amount of fishery resources. Generally, it is believed that high productivity in the Sea of Okhotsk depends on the supply of nutrients from sea ice to phytoplankton. Phytoplankton are an important primary producer and they support higher trophic animals within the Sea of Okhotsk. Along with favorable light conditions, phytoplankton requires macronutrients (nitrate and phosphate) and micronutrient (iron) for their growth. Previous studies have revealed that the macronutrient concentrations in sea ice are notably low due to macronutrients discharge from sea ice via salt rejection which occurs during sea ice formation. This means that sea ice does not contribute to macronutrients transport. Although a satellite observation revealed the occurrence of a phytoplankton bloom in the Sea of Okhotsk during sea ice melt, the contribution of sea ice to the spring phytoplankton bloom is not yet fully understood.

In our previous study, we focused on iron measured from sea ice samples collected from the Sea of Okhotsk in winter. We revealed that the concentration of iron is several times greater in sea ice than in the seawater under the ice. As a result, sea ice contributes to iron transport and supplies it to surface waters during sea ice melt. However, iron may not always be readily available to phytoplankton when it is released into the surface water because iron exists mainly in particulate form in the Okhotsk sea ice. In the current study, we conducted a shipboard bottle incubation experiment to assess the biological availability of iron in sea ice from the Sea of Okhotsk. We investigated the response of phytoplankton growth, iron requirements, and the existence form of iron in incubated seawater with the addition of sea ice or inorganic iron. Our results revealed that massive iron in sea ice (mainly existing in particulate form) is available to phytoplankton. Therefore, it is clear that sea ice can support marine ecosystems via iron transport in the Sea of Okhotsk. This provides a new insight to the understanding of iron contribution derived from sea ice to phytoplankton blooms during the spring ice melt in the Sea of Okhotsk.

Figure 1. Photograph of the Sea of Okhotsk in winter. The maximum extent of sea ice usually occurs in late February or early March, when sea ice covers 50-90% of the surface water.

Figure 2. Left panel: Response of phytoplankton growth (as chlorophyll a concentration) during the incubation experiment. Addition of the melted sea ice in seawater stimulated the growth of phytoplankton as compared with the other treatments. Right panel: Net specific growth rate of phytoplankton as a function of enriched dissolved Fe (DFe) concentrations in incubated seawater during the experiment. Abbreviation of PFe indicates particulate Fe. The red symbol () represents the net specific growth rate in the seawater with added melted sea ice.

Figure 3. Schematic of the processes of iron supply and transport by sea ice in the southern Sea of Okhotsk. In spring, iron is supplied from sea ice into surface waters and used by phytoplankton.

Journal
Publication Date

October, 2016

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ILTS Research Topics H25-1

Title

When ocean dynamic drives the land to ocean input of iron

Authors

Jun Nishioka1, Takeshi Nakatsuka2, Yutaka W. Watanabe3, Ichiro Yasuda4, Kenshi Kuma5, Hiroshi Ogawa4, Naoto Ebuchi1, Alexey Scherbinin6, Yuri N. Volkov6, Takayuki Shiraiwa1,7 and Masaaki Wakatsuchi1

  1. Institute of Low Temperature Science, Hokkaido University
  2. Graduate School of Environmental Studies, Nagoya University
  3. Faculty of Earth Environmental Science, Hokkaido University
  4. Atmosphere and Ocean Research Institute, The University of Tokyo
  5. Faculty of Fisheries Science, Hokkaido University
  6. Far Eastern Regional Hydrometeorological Research Institut
  7. Research Institute for Humanity and Nature
Abstract

We demonstrates the pivotal role of tidal mixing in the Kuril Islands chain (KIC) for determining iron (Fe) supply to the euphotic zone of the Western Subartic Pacific. Indeed, Fe derived from sediments in the Sea of Okhotsk is discharged through the KIC into the intermediate water masses (~ 800 m) of the western North Pacific. The redistribution of this Fe-rich intermediate water by intensive mixing as it crosses the KIC is the predominant process determining the ratio of micronutrient (Fe) to macronutrients (e.g., nitrate) in subsurface waters. This process explains the significant phytoplankton growth and great seasonal variability observed in the Western compared to the Eastern Subarctic Pacific.

Figure 1 Illustration of the role of marginal sea and tidal mixing in the oceanic dissolved Fe cycle in the subarctic North Pacific (WSP: western subarctic Pacific, ESP: eastern subarctic Pacific, DSW: dense shelf water, OSIW: Okhotsk Sea intermediate water, OY: Oyashio, NPIW: North Pacific intermediate water)

Journal/Publication Date

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ILTS Research Topics H22-1

Title

Visualization of state transitions uncovered an energy dissipation mechanism in photosynthesis

Authors

Masakazu Iwai1, Makio Yokono1, Noriko Inada2, and Jun Minagawa1

  1. Institute of Low Temperature Science, Hokkaido University
  2. Graduate School of Biological Sciences, Nara Institute of Science and Technology
Abstract

Plants and green algae maintain efficient photosynthesis under changing light environments by adjusting their light-harvesting capacity. It has been suggested that energy redistribution is brought about by shuttling the light-harvesting antenna complex II (LHCII) between photosystem II (PSII) and photosystem I (PSI) (state transitions), but such molecular remodeling has never been demonstrated in vivo. In this study, using chlorophyll Fluorescence Lifetime Imaging Microscopy (FLIM), we visualized phospho-LHCII dissociation from PSII in live cells of the green alga Chlamydomonas reinhardtii.

Induction of energy redistribution upon illumination of the cells by blue light led to an increase in, and spreading of, a 250-ps lifetime chlorophyll fluorescence component (Fig.1). The appearance of the 250-ps component was accompanied by activation of LHCII phosphorylation, supporting the visualization of phospho-LHCII dissociation. The unexpectedly short lifetime of fluorescence (250-ps) from aggregation of the dissociated LHCII suggested a general mechanism for energy dissipation in photosynthesis.

Fig.1. Progress of a state transition in a single cell observed by FLIM. The 170-ps fluorescence lifetime component (blue) was dominant in the cells harboring several LHCII antenna proteins for PSII (0 min). Upon illumination of blue light, the phospho-LHCII started to dissociate from PSII and the 250-ps component (red) became dominant (5 min). The 250-ps lifetime component did not spread over the cell, but formed aggregations. The total fluorescence images were indicated in gray scale (Scale bar, 5 μm).

Journal/Publication Date

This research was described in the following research paper.

The above paper was accompanied by a commentary article.

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ILTS Research Topics H19-2

Title

Possible strong annual connection in spring between Asian dust outbreak and stratosphere-troposphere exchange due to annual variations of storm activity

Authors

Teppei J. Yasunari1, Takayuki Shiraiwa2, Syosaku Kanamori1, Yoshiyuki Fujii3, Makoto Igarashi4, Koji Yamazaki1, Carl S. Benson5, and Takeo Hondoh6

  1. Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
  2. Research Institute for Humanity and Nature, Kyoto, Japan.
  3. National Institute of Polar Research, Tokyo, Japan.
  4. RIKEN Wako Institute, Saitama, Japan.
  5. Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA.
  6. Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan.
Abstract

To assess the material circulations in the North Pacific region, a 50-m ice core was drilled at the summit of Mount Wrangell Volcano, Alaska (62°N; 144°W; 4100 m a.s.l.).

Here we found that the highest annual correlation between seasonal fluxes of fine dust number (0.52-1.00 μm), an indicator of long-range transport, and tritium, a stratospheric tracer, in late spring (Figure 1).

The field observation and ice core data imply that Asian dust strongly polluted Mount Wrangell every spring.

Here we propose that a strong annual relationship between the stratosphere-troposphere exchange (stratospheric material intrusions such as tritium, ozone, and etc. into the troposphere) and Asian dust outbreak are closely connected in springtime due to annual variations of cyclonic activity (Figure 2).

For predicting the future global warming, it is essential to assess the relationship in springtime between them because both the atmospheric dust and one of the stratospheric tracers, ozone, have capabilities changing global radiation budget. Therefore, we should be active for the research focusing on both study fields as soon as possible.

Fig.1. Fine Dust (0.52-1.00 μm), Coarse Dust (1.00-8.00 μm), and tritium fluxes in each seasonal period: (a) early spring to late spring, (b) late spring to summer, (c) summer to fall, (d) fall to winter, and (e) winter to early spring. Asterisks denote the data used for the correlation calculations (sample number n). Also shown are the correlation coefficients between dust and tritium that had a significance level exceeding 90%.

Fig.2. Schematic of the annual relationship between Asian dust storm and the Stratosphere-Troposphere Exchange (STE) in late spring according to our proposal. If the Asian dust increases annually, the amount of STE will also increase.

Journal
Publication Date

2007 May 19

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ILTS Research Topics H18-3

Title

Laboratory for Planet Formation: Synergy of Technologies Reveal Origin of Dust Around Nearby Star

Authors

H. Kimura, T. Yamamoto (ILTS), M. Tamura, K. Sudo, L. Abe (National Astronomical Observatory, Japan), M. Fukagawa (Nagoya University, California Institute of Technology)

Abstract

A combination of observing strategy and advanced technology has produced the most detailed picture yet of a dust disk surrounding a nearby star. Observations of the disk surrounding the star Beta Pictoris by a team of researchers from the National Astronomical Observatory of Japan, Nagoya University and Hokkaido University suggest that asteroid and comet-like objects are colliding to produce fluffy icy dust-balls the size of bacteria.

This research was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan through a Grant-in-Aid for Scientific Research on Priority Areas for the "Development of Extra-solar Planetary Science." For more, see "Subaru Topics | Subaru Telescope, NAOJ".

Fig.1. Polarization vectors superimposed among the image of the Beta Pictoris disk showing the direction of the light's polarization. Most of the vectors are perpendicular to the direction towards the central star,indicating that the light originated from the star and then reflected off particles in the disk. The light is polarized by about 10%.

Fig.2. The degree of polarization of the light as a function of distance to the central star for both the upper left and lower right portions of the disk. There is a dip at a distance of 100 astronomical units at both sides. Since this dip corresponds to a decrease in brightness as well, it probably corresponds to a region where there are fewer planetesimals and therefore less dust.

Journal
Publication Date

April 20, 2006

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ILTS Research Topics H17-4

Title

Boreal forest fire impacts on permafrost disturbance and greenhouse gas emissions

Authors

Masami FUKUDA et al.

Abstract

We obtained knowledge that appeared to be new about permafrost disturbance and greenhouse gas emissions caused by forest fire in Siberia based on field observation in CREST project of Japan Science and Technology Agency (Principal Investigator: Masami FUKUDA, Institute of Low Temperature Science), and we updated conventional concepts. 1) We observed greenhouse gas emissions caused by fire and their elementary processes in east Siberian taiga near Yakutsk. 2) We investigated permafrost degradation process and according methane emission in fire-disturbed scars. 3) We carried out monitoring of direct CO2 emission during combustion and long-term monitoring of CO2 emission in the process of organic-matter decay. As for forest CO2 absorption, we confirmed temporal change of carbon budget by tower meteorological observation before and after an artificial forest disturbance. These observation results indicate that forest fire in the permafrost zone can destroy mutual relationships between taiga forest and underlying permafrost, and cause irreversible change of the forest into continuous emission of greenhouse gases such as CO2 and methane. Further clarification of the phenomena and rapid countermeasures for them are necessary.

Please refer to the following homepage for the contribution of the members in Institute of Low Temperature Science. http://frost2.lowtem.hokudai.ac.jp/lab_guide.html

Journal
Publication Date

2004

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ILTS Research Topics H17-3

Title

Formation and deuterium fractionation of interstellar methanol on ice dusts

Authors

Naoki Watanabe & Akira Kouchi

Abstract

Recent astronomical observations found abundant solid methanol on ice dusts and the deuterium fractionation of methanol molecule. Methanol is one of most primordial organic molecule and thus very important. The processes of formation and deuterium fractionation were one of the mystery in astronomy. Our experiments revealed for the first time that methanol molecule can be produced efficiently by the successive hydrogenation of CO on dust surfaces via tunneling reactions in space and the surface reactions play an important role in the deuterium fractionation.

Journal
Publication Date

1. 2005 March 28
2. 2004 November 20

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ILTS Research Topics H17-2

Title

Monte Carlo Simulation of the Formation of Snowflakes

Authors

Ken-ichi Maruyama & Yasushi Fujiyoshi

Abstract

If "the snow crystal is a hieroglyph from the heavens" (Nakaya 1938), then the snowflake is a scroll from the heavens. A snowflake contains much information within its fractal geometry. Conventionally, the change in the size distribution of snowflakes by collision and coalescence is calculated by solving the stochastic equation, assuming the snowflake shape is a sphere or an oblate spheroid. However, the shape should also be taken into account carefully, because it can have big effects on the fall velocity and growth of snowflakes. In this paper, we developed a stochastic microphysical model of snow aggregation by combining a simple aggregation model with a Monte Carlo method. This kind of model has been developed in cosmic dust or aerosol formation studies, but, strangely, has never been applied to the formation of snowflakes. By using this model, we are able to investigate both the change in the size distribution and the shape of individual snowflakes at the same time. Explicit treatment of the shape of individual snowflakes in the new model facilitates examination of the structure of snowflakes and the relationships between the physical parameters of the generated snowflakes consistent with those of observed snowflakes. As shown in the figure, complexities in the shapes of snowflakes are successfully simulated. The growth rates of the aggregate model of snowflakes are also calculated and compared with those of the conventional model. Our model could improve the parameterizations of cloud microphysical processes, although we still need to consider the effects of vapor deposition, riming, breakup, melting, and breakup during melting, and also make numerous comparisons with observations.

Fig. For comparison: The image of a generated snowflake and the picture of a snowflake.

Journal
Publication Date

2005 May

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