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    • 　In a class on marine mushrooms-sea chemistry-we explain the distribution of nutrients that limit the primary production of the ocean. The ocean material circulation driven by the primary production is also explained a little. What is important for ocean chemistry is to conduct oceanographic observations at sea sites. A video of oceanographic observation is presented at the bottom of this page.


  • Marine Primary Production and Material Cycle

    • Factors limiting plant photosynthesis (comparing land and oceans)


      　Light, water, carbon dioxide, and nutrients are necessary for plants to photosynthesize and store organic matter (primary production). It is also necessary to have a temperature zone suitable for the plant.

      　Water is the main factor limiting the primary production of terrestrial plants. Plants are not growing very much in deserts where water is scarce, aren't they? Of course, nutrients that are absorbed from roots are essential, but even if plants grow and leaves die down, nutrients are relatively reusable.

      　Marine plants also need light and water, carbon dioxide and nutrients. Primary production in the ocean occurs only on the surface where light reaches. Water and carbon dioxide are enough. When plants grow through photosynthesis, they also take up nutrients. In the ocean, when plants (mainly plankton) die, organic matter is transported from the surface layer to the deep layer. Then, the organic matter decomposes deep, and the nutrients return to the sea water. Therefore, nutrients tend to be depleted at the surface of the ocean. As a result, nutrient components are a major factor limiting the primary production of the oceans.　


      On land, plants and nutrients are easily circulated, and water is the primary factor that rates basic production.

      In the ocean, nutrients are transported to deeper layers and are the main factor that rates basic production.

      　The figure below shows the distribution of the chlorophyll concentration of the photosynthetic pigment by examining the color of the ocean using satellites. There are many phytoplanktons in the green and red areas. In other words, it is a place with a large primary production volume. The most obvious thing is that phytoplankton is remarkable in the subtropics and in the subarctic regions. I wonder why.



      　The distribution of chlorophyll (an indicator of phytoplankton content) is similar to the distribution of phosphate (a type of nutrient) in the surface of the ocean (shown below). It is superficial in the subtropics with low phosphate and many subarctic regions. In other words, there are many (few) phytoplanktons in areas with high (low) nutrients in the surface layer.



      　First of all, know that there is a lot of nutrients in the ocean deep. This is because, as mentioned earlier, organic matter produced in the surface layer settles deeper, and nutrients regenerate into deep seawater.

      　Why, then, is there a small amount of nutrients in the subtropical surface layer and a large amount in the subarctic region? This is because the vertical mixing of water on the surface of the ocean differs between the subtropical and subarctic regions. In the subtropics, solar radiation is strong, and the water on the surface is warmed. Because warm water covers the surface, deep, nutrient-rich water is difficult to bring to the surface. In the subarctic winter, it is cold, remarkable, and water is cooled. Deep, nutrient-rich water is likely to be brought to the surface. Between the subarctic and subtropical regions, the winter cooling is also significant, but in addition, vertical mixing may develop due to vortices that are generated by the collision of water. Therefore, primary productivity increases in subarctic and intermediate regions (mixing regions).



      　In what ocean and when and how much primary production will occur and what factors will limit primary production?　 In addition, along with primary production (organic matter production), various substances move along the ocean with organic matter. This is called the material cycle. It is ocean chemistry that examines primary production and ocean material circulation by following "chemicals".

      　In ocean chemistry, the royal way is to collect, analyze, and analyze seawater. We conduct monthly observations like the video below.




    • 　It does not just collect seawater. Organic particles produced on the surface of the ocean settle and accumulate on the bottom of the sea. It is also important to examine the ocean floor environment. We also collect seabed sediments and conduct chemical analyses. The video below shows an observation on the slope of the Hokkaido coastal shelf, which is highly bioproductive, during the Faculty of Fisheries Sciences Marine Biology three-year on-board training.


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