ul 2004 
Observation of biological manifestation of physical forces with synergistic use of IRS P4 
OCM & MSMR 
R.M. Dwivedi“ , S.K. Singh“ , Mini Raman* , S.R. Nayak* , Sushma Parab® and Prabhu Matondkar^ 
“Space Applications Centre, Ahmedabad 380 015, India - rmdwivedi@rediffmail.com 
? Natoinal Institute of Oceanography, Goa (India) 
KEY WORDS: Remote sensing, Ocean colour, Ocean Color Monitor, Chlorophyll, Primary Productivity, wind, Winter bloom, 
Convection, Northern Arabian Sea 
ABSTRACT: 
Primary productivity of the ocean is basically governed by two limiting factors; light and nutrients. In tropical waters where 
generally light is not a limiting factor, nutrients play an important role in causing changes in productivity of the region. Availability 
of nutrients is strongly influenced by turbulence of water. Wind induced turbulence is one of the causes for transport of nutrients to 
euphotic zone that gives rise to high productivity. Multi-date primary productivity images were generated for the period February- 
march, 2000-2001 in the northeastern Arabian Sea to verify this hypothesis. This is the period when winter bloom occurs in the 
Northern Arabian Sea (NAS). Species identification through water samples collected from the ship indicated that this bloom is 
dominated by noctiluca millaris of dianofleggelete class. Literature describes this bloom to be result of winter cooling and increased 
density of surface waters due to evaporation by prevailing northeasterly winds. An attempt was made to relate observed variability in 
productivity with magnitude of wind forces. 
Primary Productivity images were generated with OCM (Ocean Colour Monitor)/Oceansat I and wind fields using MSMR (multi 
frequency scanning microwave radiometer)/Oceansat | data. Northeastern Arabian Sea (Gujarat coast) was selected as the study area. 
A common grid of 1°x1° was selected for the synergistic study of OCM and MSMR. Analytical model based on photosynthesis- 
Light relation was used to compute mixed layer primary productivity of the Arabian Sea. P-I parameters were measured for the 
Northeastern Arabian Sea from the ship. These inputs along with the OCM derived chlorophyll and diffuse attenuation coefficient 
were used to compute mixed layer primary production of area for middle of February to March for the years 2000 and 2001. Mixed 
layer primary production images were generated for the northeastern Arabian Sea and weekly MSMR winds were processed for the 
February and March months respectively for both the years. It was observed that primary productivity varies in concert with 
magnitude of wind speed. This shows that productivity in the Arabian Sea is coupled with physical forcing action. The synergistic 
analysis of OCM and MSMR showed that a variation in the wind speed has influence on primary productivity of the study area. This 
complies with the expected physical-biological coupling. 
1. INTRODUCTION i Influence of wind on spatial pattern of primary 
productivity 
Time series observations of chlorophyll pattern from Oceansat I il. Study of temporal variations in productivity due 
/ OCM earlier in February-March, 2000 had shown large scale to temporal variations in wind force using time 
increase in abundance of phytoplankton in the open ocean series chlorophylVOCM and wind . seped 
waters at depths greater than two thousand meters in NAS. /Quickscat. 
Banse and McClain, 1986, Banse, 1987 and Prasanna Kumar et 
al., 2000 have reported this event to be winter bloom of Spatial variations in productivity levels revealed overall 
phytoplankton. Time series chlorophyll images generated from correspondence between Primary Productivity and magnitude 
OCM demonstrate that this bloom occurs every year in NAS of wind whereas study of seasonal pattern of the two 
during specific time slot from January end to middle of March parameters indicated time lag in chlorophyll of about four days 
and extends over almost entire Northern Arabian Sea from typically in most cases. 
northern most up to 15?N latitude. It develops as a result of 
enrichment of nutrients, which is created by vertical mixing in 2. METHODOLOGY 
winter. Cooling of surface waters due to seasonal effect as well 
as due to evaporation caused by northeasterly winds generates 2.1 Mixed Layer Primary Production 
convection and it causes vertical mixing of water mass. Asa 
result, nutrients can cross thermocline and enter shallower In the present work, non-spectral analytical model of platt et al. 
waters in euphotic zone giving rise to high productivity of (1990) was implemented in the Arabian Sea. It makes use of 
phytoplankton. This forcing mechanism is required to activate photosynthesis-light relationship | to compute the mixed layer 
photosynthesis in tropical waters where growth of primary production. It. requires chlorophyll, diffuse attenuation 
phytoplankton is controlled by availability of nutrient. Pattern coefficient, P-I (photosynthesis-light) parameter and day length 
of chlorophyll, SST and wind was studied for the period of as its inputs. The mixed layer column production is given by an 
winter bloom using OCM, AVHRR, MSMR, Quickscat and expression with depth and time integrals, 
ship data. It was observed that the three parameters co-vary, 
Which confirms that wind generated physical forcing controls D Zm 
productivity in NAS during the season of winter bloom. Por = bh bh Bzbp’(zb) dzdt. 
Biological influence of physical forces on water mass was 
studied from two angles. Non-spectral approach used to compute the mixed layer 
primary production for the study area uses solution of the above 
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