Spatio-temporal variability of Asian dust and its impact on biological productivity in the East/Japan Sea
Abstract:
Asian dust (the second largest dust source globally), originating in Taklimakan and Gobi deserts, is transported rapidly from northeastern Asia to North America by westerly winds. It is believed that during this period of transportation, as the dust travels eastward, it temporarily relieves the iron-limitation that may be responsible for suppressing primary productivity in the ocean environment. However, until now the relationship between these short-lived dust events and ocean primary productivity has not been confirmed. Located downwind from the source regions of Asian dust, the East/Japan Sea (EJS) is an ideal location to examine this relationship. Here, we present the results from an investigation into the spatial and temporal variation of chlorophyll-a before and after dust events in the EJS, using satellite data (chlorophyll-a and aerosol index) observed between 1998‒2014. The aerosol index (AI) is an indicator used to specify both the magnitude of a dust event, and its range. The mean AI for ocean generally lies between 0.2 and 1.2. In the EJS, between 1998 and 2014, the mean AI was ~0.8‒1.2. The maxima in AI occurred in April (e.g., ~1.6 in 2001), while the minima appeared primarily in September (e.g., ~0.7 in 2005). There was the tendency for Asian dust to pass over the northern EJS (> 40°N) during the winter and spring seasons, and to move along the Russian coasts during summer season. This temporally varying spatial pattern indicates that Asian dust more directly influences the northern EJS (> 40°N) than the southern EJS (< 40°N). Further, it was found that the concentration of chlorophyll-a in the northern EJS increased from a pre-dust event magnitude of 0.5 to a post-dust event value of 5.8 mg m-3 in response to the strong April 2006 Asian dust event. This increase was nearly three times higher than the climatological chlorophyll-a value averaged for the period of 1998‒2014 (2.1 mg m-3). Finally, it should be noted that the response to Asian dust events was not immediate as a time lag of anywhere between 7 and 20 days was seen. These results are consistent with artificial iron fertilization experiments conducted in open oceans.