南大洋浮游植物和云量

1、海洋生物學(xué)程慧珍22320131151400Phytoplankton and Cloudinessin the Southern Ocean The effect of it is explored over a large phytoplankton bloom in the Southern Ocean with the use of remotely sensed data. over the bloom cloud droplet number concentration (CDNC) was twice and cloud effective radius was reduced

2、by 30%. short-wave radiative flux is comparable to the aerosol indirect effect over highly polluted regions.n ocean biological productivity effect on marine cloudsn We propose that secondary organic aerosol ,formed from the oxidation of phytoplankton produced isoprene can affect chemical composition

3、 of marine cloud condensation nuclei(CCN） and influence cloud droplet number.n Marine aerosols strongly affect properties and lifetime of stratiform clouds, influencing Earths radiation budget and climate.possible mechanisms that phytoplankton modulate properties of marine clouds is:Production of su

4、lfate from the oxidation of dimethyl sulfide (DMS).primary emissions of biogenic organicmatter from wave breaking.n Ideal place :Southern Ocean (SO) near South Georgia Island.Because of its unique spatial location and topography, waters near the island are a natural laboratory for investigating the

5、effects of marine productivity on clouds.Waters in this area can support massive phytoplankton blooms ,with chlorophyll a concentrations (Chl a) more than an order of magnitude higher than the background .Because the surface Chl a in this area can be used as a reliable proxy forthe primary productio

6、n.n Temporal correlation between Chl a andReff. u Data for Chl au MODIS-retrieved cloudeffective radius.Figure 1 Despite its regularity, Fig. 1 shows substantial annual variations in the blooms temporal appearance, spatial extent, and strength, with strong anticorrelation between Chl a and Reff. Phy

7、toplankton productivity and clouds could also be influenced by large scale atmospheric circulationn Effect of phytoplankton on clouds.A rectangular geographical area was selected in the SO from 55W to 21W and 42S to 60S.The background colors in Fig. 2A correspond to the monthly averaged surface Chl

8、a for the year with the largest bloom on record.Figure 2A average Reff for background clouds in this area is 14 mm ,with a sharp decrease (10 mm) in the vicinity of the bloom. water clouds near the bloom region have effective droplet radii 30% smaller than those of background clouds over the SO.Figu

9、re 2B Cloud droplet number concentration(CNDC) can be used as a direct microphysical link between the biology and cloud properties.LWC-cloud liquid water content;rw-density of liquid water; H - the cloud thickness; t - MODIS-observed cloud optical depth ;Reff - effective droplet radius;K-the constan

10、t 0.8uFigure 2B shows that the calculated monthly averaged CDNC outside the bloom area is 55 cm3, whereas in the bloom region, CDNC increases sharply approaching twice the background level.uThis comparison suggests that the magnitude of variation of the SO marine cloud microphysics over the bloom ma

11、y be comparable to anthropogenic indirect aerosol effects.uOther factors may affect CDNCnear the bloom are long-range transported Patagonian dust and sea salt. Figure 2B shows that this is not the case. The enhanced productivity mainly controlled by ocean upwelling, not by dust-Fe fertilization. The

12、refore, dust is not responsible for changes in either ocean productivity or Reff.Submicrometer-sized sea-salt particles can certainly affect CDNC ,but with no accompanied surface wind over the bloom, we can ignore.uAnalysis of Fig. 2 indicates strong coupling between observed changes in marine biolo

13、gical productivity and microphysical properties of warm clouds over the bloomn Role of meteorologyStrong winds -vertical mixing and upwelling.fueling photosynthesis and causing large scale phytoplankton blooms.depression in sea-surface temperatures (SST).Cyclones would therefore generate a correlati

14、on (but no causality) between Chl a and cloud properties.u Quantify the possible influnce of phytoplankton on clouds.Analysis region:inside-enhanced productivity (48S to 56S) near South Georgia Island ;outside-relatively low Chl a (42S to 48S and 56S to 60S).The analysis adresses two main questions:

15、Outside, Reff is mainly controlled by large scale atmospheric parameters and correlation between Reff and Chl a is minor.Inside , the effect of Chl a on Reff has by far the strongest impact of all parameters examineduDo meteorological parameters and Chl a affect Reff differently in the inside and th

16、e outside regions? u Can changes in meteorological parameters affect Reff while changing Chl a?In the outside region, the change in Reff isprimarily associated with variability in meteorological parameters;in the inside region, Chl a is the single most important parameter controlling the Reff.lover

17、the bloom, the relationship between the ocean productivity and Reff of warm clouds is unique to these two variablesn Phytoplankton isoprene SOA and its effect on CCN.Atmospheric oxidation of isoprene may lead to formation of SOA .ocean-emitted isoprene could contribute considerably to the organic fr

18、action of marine CCN. For comparison, SOFeX-N is been done , we include observed Chl a and dissolved isoprene concentrations.The chlorophyll content of seawater, as sensed by the satellite, is related to the rate of isoprene production.Table 2such large discrepancies in dissolved isoprene concentrat

19、ions could arise from the difference in phytoplankton species. Laboratory studies show that isoprene production rates between diatoms, dinoflagellates, and coccolithophores can vary over orders of magnitude.Inside the bloom, diatoms were five times more abundant than the next contributor, dinoflagel

20、lates。Over the blooms in the SO where microphytoplankton typically contributes70% of total cell counts, followed by nano and picophytoplankton.uTo evaluate the role of organic aerosol source on cloud microphysics, we calculated CDNC using a cloud parcel model.The range of SOA concentrations we exami

21、ned is0 to 250 ng m3, addition of SOA corresponds to the condensation growth and aging of marine aerosols.main particulate-phase oxidation products of isoprene SOA are 2-methyltetrols and C5 alkene triols are under low-NOx conditions.Figure 4(A and B)Figure 4 shows that Cloud-base updraft velocity i

22、s constrained by estimated CDNCs outside the bloom region.the excess amount of organic mass increases CDNC; modification of the ambient size and CCN activity of marine aerosols due to addition of organic mass can explain up to 60% of the droplet number concentration over the bloom.Our model results suggest that phytoplankton isoprene emissions could contribute to the orga