Contrastive Analysis Of The Causes Of Phytoplankton Blooms In Tow Upwelling Areas:Vietnam And Somalia

Summer upwelling occurs frequently off the southeast Vietnam coast and northeast Somali,where summer phytoplankton blooms generally prevail during June-August.In the study,we investigate inter-annual variation of Ekman pumping and offshore transport,and their modulation on summer blooms southeast of Vietnam and Somali.Southeast of Vietnam,the results indicate that there are generally low intensities of summer blooms in El Ni?o years,under the background of higher sea surface temperatures(SST)and weaker winds.However,a different pattern of monthly chlorophyll a(Chl-a)blooms occurred in summer of 2007,a transitional stage from El Ni?o to La Ni?a,with weak(strong)wind and high(low)SST before(after)early July.There is a weak phytoplankton bloom before July 2007 and a strong phytoplankton bloom after July 2007.The abrupt change in the wind intensity may enhance the upwelling associated with Ekman pumping and offshore Ekman transport,bringing more high-nutrient water into the upper layer from the subsurface,and thus leading to an evident Chl-a bloom in the region.In the west AS,especially in the region off the Somali coast.The potential mechanisms triggering high Chl-a is speculated by investigating the oceanic conditions including monsoon winds and the derivation parameters(i.e.Ekman transport and Ekman pumping),as well as geostrophic current and aerosol.The summer Chl-a in the region presented strong inter-annual variation,along with Ekman transport and Ekman pumping induced by wind speed and strong wind speed in the southwest AS.The results indicated that there were good correlations between the Ekman transport(ET)and Chl-a,as well as between wind speed and Chl-a,which implied that the wind speed and Ekman transport induced uplift of nutrients into the upper layer of the west AS from the sublayer or coastal regions,inducing phytoplankton blooms off the Somali coasts in summer.Therefore the wind vectors and their derivations play probably important roles in the Chl-a for the AS through wind-induced upwelling and Ekman transport as well as Ekman puming,compared with the aerosol precipitation.