Rapid Chlorophyll-a Increase Events With Sea Surface Cooling in the Northwestern Pacific Ocean Detected From Satellite Data
Abstract
Some previous studies indicated that single tropical cyclone can have a significant impact on primary production by lifting nutrient-rich water through strong vertical mixing and upwelling. In this study we aimed at comprehensively detecting rapid large Chl-a increase events with large sea surface temperature (SST) drops, which suggest the quick upwelling of nutrient-rich water below the thermocline. Such events will need strong atmospheric disturbances. We picked up all the events that Chl-a increases within 10 days exceeded monthly standard deviations by analyzing satellite Chl-a and SST data in the northwestern Pacific Ocean during August 2002 - July 2007. This analysis can detect cases that Chl-a increased and SST decreased rapidly after passages of typhoons and extratropical depressions. The events with large SST drops often happen south off Japan, in the Sea of Okhotsk and in the regions between 35°N and 45°N, especially in the Kuroshio-Oyashio Extension region. They occur most frequently in the late summer and autumn, and less frequently in spring. This suggests that SST easily decreases greatly in a short period when there is mature seasonal thermocline. However, near SST fronts the detected events may have been caused by the horizontal migration of the SST fronts as well as the vertical mixing. The events south off Japan result from passages of tropical cyclones, and very strong typhoons tend to cause the Chl-a increase southeast off the Ryukyu Islands. Typhoons have a stronger effect in the regions west off the Izu Islands and southeast off the Ryukyu Islands. On the other hand, most of the events north of 35°N are caused by extratropical depressions. The increase of Chl-a tends to become larger as the corresponding SST decrease gets larger in oligotrophic regions. However, such relation can not be seen when Chl-a is larger than about 0.4 mg m-3. The reason for it will be that the injection of nutrient-rich water below the thermocline into the surface layer is not necessary so much for the increase of Chl-a when nutrients still remain near the surface even in summer.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMOS43C1299K
- Keywords:
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- 0480 Remote sensing;
- 4247 Marine meteorology;
- 4273 Physical and biogeochemical interactions;
- 4572 Upper ocean and mixed layer processes;
- 4855 Phytoplankton