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Hurricane Igor Impacts on the Stratification and Phytoplankton Bloom over the Grand Banks

Hurricane Igor Impacts on the Stratification and Phytoplankton Bloom over the Grand Banks. Guoqi Han 1 , Zhimin Ma 2 , Nancy Chen 1 1 Northwest Atlantic Fisheries Centre Fisheries and Oceans Canada 2 Memorial University of Newfoundland (Han et al., 2012)

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Hurricane Igor Impacts on the Stratification and Phytoplankton Bloom over the Grand Banks

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  1. Hurricane Igor Impacts on the Stratification and Phytoplankton Bloom over the Grand Banks Guoqi Han1, Zhimin Ma2, Nancy Chen1 1Northwest Atlantic Fisheries Centre Fisheries and Oceans Canada 2Memorial University of Newfoundland (Han et al., 2012) Supported by Canadian Space Agency GRIP Program

  2. Hurricane Igor Track Newfoundland Pasch and Kimberlain,2010

  3. Hurricane Igor

  4. Objectives • To examine the changes of SST, stratification and phytoplankton concentration • To examine the linkage between the physical changes and phytoplankton bloom

  5. Satellite SST and Chlorophyll Data • AVHRR 8-d 4-km SST from NOAA. • Merged MERIS and MODIS 8-d 4-km Chlorophyll from the ACRI-ST GlobColour Service.

  6. Other Data • Buoy SST at B1 (inshore) and B2 (continental slope) from EC • T/S profiles at Station 27 off St. John’s from DFO AZMP Program

  7. SST Changes SST decreased by 6 oC (adjustment time 10 h), uniform in space

  8. Chlorophyll Changes Chlorophyll increased by 0.8 mg/m3

  9. Stratification Changes at Station 27 MLD (the interface depth) deepened from 18 to 60 m Deepening rate: -8.5 x 10-4 m/s (by assuming the SST and the MLD adjustment time the same)

  10. Upwelling due to Wind Stress Curl Translation speed: 60 km/h Maximum sustained wind: 35 m/s Diameter of the maximum wind: 180 km Estimated upwelling speed: 3.4x10-4 m/s Coastal Upwelling Upwelling favorable alongshore wind: 10 m/s Estimated upwelling speed: 1.4x10-5 m/s (by assuming a horizontal scale of 100 km)

  11. Entrainment due to Wind Stirring Wwat Station 27 • MLD deepening: -8.5 x 10-4 m/s • B. Ekman pumping (WE): 3.4x10-4 m/s • C. Coastal upwelling (WC): 1.4 x10-5 m/s Ww=A-B-C = -12 x 10-4 m/s Wind stirring effect is predominant.

  12. Conclusions Hurricane Igor caused an SST decrease of 6 oC over the Grand Banks. The storm triggered an increase of 0.8 mg/m3 in the phytoplankton concentration. In situ measurements show a deepening of the mixed–layer depth from 18 to 60 m. The bloom was triggered mainly by the vertical mixing due to the wind stirring effect.

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