9:00 AM - 9:15 AM
[ACG42-01] Toward a macroscale perspective to study the land-to-ocean influence
★Invited Papers
The ocean receives freshwater mainly from precipitation and land water discharge, and their ratio is about 10:1 on the global average. This supply of freshwater, together with the loss of freshwater due to evaporation, acts as the boundary conditions for the sea level and salinity and controls the physical phenomena in the ocean. Land water discharge also provides the ocean with various dissolved and suspended materials. The principal origins of the nutrients, which contain the elements essential to the oceanic primary production, are upwelling of deep water and land water discharge. Their ratio is about 10:1 for the case of nitrogen and phosphorus which are supplied as the dissolved form, while the contribution from land water discharge surpasses that from deep water upwelling for the case of iron whose origin in land water is suspended solids. From the viewpoint of supply, therefore, land water discharge must non-negligibly affect the ocean globally, but its reality has not been sufficiently studied. On the other hand, the coastal seas must be under a stronger influence of land water, but the relative importance compared with the open ocean has not been clarified.
Furthermore, human activities have been affecting land water discharge and thus significantly changing how land water discharge influences the ocean. The amount of nitrogen and phosphorus supplied to the ocean by land water discharge was estimated to be doubled during the 20th century due to the increased use of artificial fertilizers. On the other hand, upwelling of deep water, which provides the open ocean with nutrients, is being weakened due to global warming. Global warming also affects the supply of materials to the ocean through changes in rivers. For example, the frequency and intensity of heavy river discharge have been increasing in Japan due to more frequent torrential rainfalls and strong typhoons. On such events, muddy streams which contain large amounts of various materials reach offshore.
The influence of land water discharge on the ocean has long been studied from a local perspective in coastal zones. Considering the above-mentioned background and ongoing changes, however, what is needed now is studies from a global perspective. In this presentation, I would like to discuss the future direction of studies on the land-to-ocean influence by introducing the newly launched research project “Macro Coastal Oceanography”.
Furthermore, human activities have been affecting land water discharge and thus significantly changing how land water discharge influences the ocean. The amount of nitrogen and phosphorus supplied to the ocean by land water discharge was estimated to be doubled during the 20th century due to the increased use of artificial fertilizers. On the other hand, upwelling of deep water, which provides the open ocean with nutrients, is being weakened due to global warming. Global warming also affects the supply of materials to the ocean through changes in rivers. For example, the frequency and intensity of heavy river discharge have been increasing in Japan due to more frequent torrential rainfalls and strong typhoons. On such events, muddy streams which contain large amounts of various materials reach offshore.
The influence of land water discharge on the ocean has long been studied from a local perspective in coastal zones. Considering the above-mentioned background and ongoing changes, however, what is needed now is studies from a global perspective. In this presentation, I would like to discuss the future direction of studies on the land-to-ocean influence by introducing the newly launched research project “Macro Coastal Oceanography”.