Effects Of Mesoscale Eddy On Chlorophyll-a Concentration In The Indo-pacific Warm Pool

As the largest warm pool in the world,Indo-Pacific Warm Pool(IPWP)plays an import role in the processes of mass transport and energy exchange for earth system.For understanding the marine ecological environment and marine bio-physical coupling process more clearly,it is of great significance to study the effects of mesoscale eddies on Chlorophyll-a(Chl-a)concentration in the IPWP.Based on the multi-source data from 1998 to 2018 and combined with Empirical Orthogonal Function(EOF)and Singular Value Decomposition(SVD),this paper firstly makes a statistical analysis of mesoscale eddies,climatological monthly composite averages of Chl-a and then analyses the monthly variation of Chl-a in mesoscale eddies and related main influence mechanisms.The main results are as follow:(1)In the IPWP,a monthly average of 10.2 cyclones and 9.9 anticyclones generate with small monthly difference,and most of these mesoscale eddies generate in the domain of 5° N ? 15° N and 5° S ? 15° S.Compared with anticyclones,more cyclones have larger amplitude and radius in the IPWP.The statistical characteristics of the parameters(like lifetime,amplitude,radius and moving speed etc.)of cyclone and anticyclone are very similar.About 78.8% of mesoscale eddies survive for less than 8weeks,and most of them move westward.(2)The EOF results and climatological monthly composite averages of Chl-a inside mesoscale eddies show that Chl-a is more likely to increase inside cyclones and decrease inside anticyclones and Chl-a inside both cyclones and anticyclones has obvious difference among different months.Inside cyclones,Chl-a increases significantly from February to March and from July to September while slightly from October to January and from April to June.Inside anticyclones,Chl-a decreases significantly from April to November while slightly from December to March.(3)The SVD analysis between Chl-a and related parameters of cyclone shows that the monthly variation of Chl-a is mainly affected by eddy-induced pumping,eddy rotational speed and eddy-induced Ekman pumping.From February to March and from July to September,Chl-a inside cyclones increases significantly as a result of the lager rotational speed which leads to the enhancement of eddy-induced upwelling and the strengthening of eddy-induced Ekman upwelling.From October to January and from April to June,Chl-a in cyclones increases slightly as a result of the smaller rotational speed which leads to the weakening of eddy-induced upwelling and the enhancement of eddy-induced Ekman downwelling.(4)The SVD analysis between Chl-a and related parameters of anticyclone shows that the monthly variation of Chl-a is mainly affected by eddy-induced pumping and eddy-induced Ekman pumping.From January to July,the enhancement of eddyinduced downwelling and the weakening of eddy-induced Ekman upwelling strengthen the inhibition effect of Chl-a,and therefore Chl-a presents a decrease trend.From August to November,the weakening of eddy-induced downwelling and the enhancement of eddy-induced Ekman upwelling weaken inhibition of Chl-a,and therefore Chl-a presents an increase trend.