- Dona Paula, Goa, India.
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- iiosc2020[at]nio[dot]org
| Abstract Submission No. | ABS-2022-04-0342 |
| Title of Abstract | Meridional variability of subsurface light field from satellite data - Learning from first expedition of IIOE-2 |
| Authors | Aneesh Lotliker*, Alakes Samanta, P. N. Vinayachandran |
| Organisation | Indian National Centre for Ocean Information Services (INCOIS) |
| Address | Indian National Centre for Ocean Information Services (INCOIS) Hyderabad, Telangana, India Pincode: 500090 Mobile: 970369046 E-mail: aneesh@incois.gov.in |
| Country | India |
| Presentation | Oral |
| Abstract | The subsurface radiative transfer has large implication in-terms of energy reservoir within the water column. It also has impact on the ocean thermodynamics from local to regional scale. Thus to account for the energy budget in the upper ocean, it is require to understand underwater radiative transfer. The attenuation coefficient of photosynthetically available radiation (kPAR) defines the subsurface light field, which exhibits linear relationship with downwelling diffuse attenuation coefficient at 490 nm (kd490). The ocean colour remote sensing has the ability to estimate kd490 and thus can be very well utilized to understand subsurface light field at synoptic scale. During the first expedition of second Internal Indian Ocean Expedition (IIOE-2), onboard ORV SN-105, hyperspectral radiometer was operated along 67 E transect, from Goa to Mauritius, measuring surface and subsurface light field. In the present study, two models were evaluated to estimate kPAR from satellite (MODIS-Aqua) derived kd490. Subsequently spatio-temporal variability of kPAR was described using satellite data at monthly climatological scale. The kd490 and kPAR estimated from satellite (MODIS-Aqua) was found in good agreement with in situ data. The satellite-estimated kPAR depicted the water to be oligotrophic and optically clear with maximum euphotic depth reaching up to 80 m. There was no significant variability observed in kPAR, along the cruise transect, at monthly climatological scale. However, at spatial scale, maximum kPAR was observed at 5 N that decreased towards equator and increased further at 10 S. The surface chl-a was very low, along the transect, of the order less than 0.1 mg-m^-3. The deep chl maxima (DCM) was observed at depth 60-70m till 2 S beyond which DCM swallowed till 50m. The average light level at DCM was 11% of the surface. Along the sampling transect, attenuation of light was more sensitive to chlorophyll-a (chl-a) apart from water molecule itself. |