hurricane igor impacts on the stratification and phytoplankton bloom over the grand banks
DESCRIPTION
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) - PowerPoint PPT PresentationTRANSCRIPT
Hurricane Igor Impacts on the Stratification and Phytoplankton Bloom
over the Grand BanksGuoqi Han1, Zhimin Ma2, Nancy Chen1
1Northwest Atlantic Fisheries Centre
Fisheries and Oceans Canada2Memorial University of Newfoundland
(Han et al., 2012)
Supported by Canadian Space Agency GRIP Program
Hurricane Igor Track
Newfoundland
Pasch and Kimberlain,2010
Hurricane Igor
Objectives
• To examine the changes of SST, stratification and phytoplankton concentration
• To examine the linkage between the physical changes and phytoplankton bloom
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.
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
SST Changes
SST decreased by 6 oC (adjustment time 10 h), uniform in space
Chlorophyll Changes
Chlorophyll increased by 0.8 mg/m3
Stratification Changes at Station 27
MLD (the interface depth) deepened from 18 to 60 mDeepening rate: -8.5 x 10-4 m/s (by assuming the SST and the MLD adjustment time the same)
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
Upwelling favorable alongshore wind: 10 m/s
Estimated upwelling speed: 1.4x10-5 m/s (by assuming a horizontal scale of 100 km)
Coastal Upwelling
)(f
curlWw
zE τ
fL
τW
w
aC
Entrainment due to Wind Stirring Ww
at Station 27
A. 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.
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.