Seasonal variability of sea surface chlorophyll-a of waters around Sri Lanka

Abstract

Variability of chlorophyll-a concentration and sea surface temperature (SST) in Natuna waters were analyzed using satellite data Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR). SeaWiFS data with a resolution of 9×9 km 2 and AVHRR with a resolution of 4×4 km 2 were the monthly average data downloaded from NASA website. Chlorophyll-a concentrations and SST were estimated using OC4v4 and MCSST algorithms. In general, the concentration of chlorophyll-a in Natuna waters ranged between 0.11-4.92 mg/m 3 with an average of 0.56 mg/m 3 during the west season and 0.09-2.93 mg/m 3 with an average of 0.66 mg/m 3 during the east season. Chlorophyll-a concentrations were relatively high seen in coastal areas, especially around the mouth of the Kapuas, Musi, and Batang Hari rivers allegedly caused by the high nutrient intake from the mainland. SST variability in Natuna waters ranged from 23.46-30.88 °C during the west season and tended to be lower than that the east season (27.91-31.95 °C). In addition, the SST values tended to be lower in the offshore than that inshore. During the west season (Nov-Feb) and the transitional season (Apr) in the years of Elnino Southern Oscillation (ENSO), the concentration of chlorophyll-a and the SST in Natuna waters was generally higher than that in non-ENSO years. The results of wind analyses showed that ENSO caused the change of direction and speed of wind from its normal conditions. ABSTRAK Variabilitas konsentrasi klorofil-a dan suhu permukaan laut (SPL) di perairan Natuna dianalisis dari data satelit Sea-viewing Wide Field-of-view Sensor (SeaWiFS) dan National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR). Data SeaWiFS dengan resolusi 9×9 km 2 dan AVHRR dengan resolusi 4×4 km 2 merupakan data rata-rata bulanan yang diunduh dari situs NASA. Konsentrasi klorofil-a diestimasi dengan menggunakan algoritma OC4v4 dan nilai SPL diestimasi berdasarkan algoritma MCSST. Secara umum, konsentrasi klorofil-a di Perairan Natuna berkisar antara 0.11-4.92 mg/m 3 dengan rata-rata 0.56 mg/m 3 pada musim barat dan 0.09-2.93 mg/m 3 dengan rata-rata 0.66 mg/m 3 pada musim timur. Konsentrasi klorofil-a relatif tinggi terlihat pada daerah pesisir khususnya di sekitar muara Sungai Kapuas, Sungai Musi, dan Sungai Batanghari yang diduga akibat asupan zat hara yang cukup tinggi dari daratan. Variabilitas SPL di Perairan Natuna berkisar antara 23.46-30.88 °C pada musim barat dan cenderung lebih rendah dibandingkan dengan musim timur yang berkisar antara 27.91-31.95 °C. Selain itu, nilai SPL cenderung lebih rendah pada daerah offshore dan menigkat menuju perairan pantai. Pada musim barat (Nop-Feb) dan musim peralihan (Apr) tahun ElNino Southern Oscillation (ENSO), konsentrasi klorofil-a dan nilai SPL di Perairan Natuna secara umum lebih tinggi dibandingkan pada tahun non-ENSO. Hasil analisis data angin juga menunjukkan bahwa ENSO menyebabkan perobahan pergeraka...

Why do satellite imageries show exceptionally high chlorophyll in the Gulf of Mannar and the Palk Bay during the Norteast Monsoon?

“…However, on an annual scale, the sediment flux in the PB is several orders of magnitude higher than that in the GoM (Sanilkumar et al 2002). Satellite chlorophyll images presented in earlier studies show exceptionally high concentration in the PB during the Northeast Monsoon, which has been a consistent feature in CZCS (Yapa 2000), SeaWIFS (Vinayachandran et al 2004;Rao et al 2011), IRS P4 (Sarangi et al 2008), and Moderate Resolution Imaging Spectroradiometer (MODIS; present study) (Supplementary evidence 1). Although some of the earlier researchers cautioned about the possibility of overestimation of satellite chlorophyll in the PB (Yapa 2000, Vinayachandran et al 2004Sarangi et al 2008), there is no scientific information available so far on the actual causes of this exceptionally high satellite chlorophyll in the PB.…”

Air-Sea Interaction, Coastal Circulation and Primary Production in the Eastern Arabian Sea: A Review

“…With a gradual surface warming and with enhanced stratification, a decrease in the Ch-a concentration to less than 0.2 mg m -3 was inferred during early June. The seasonal Ch-a variability during 1978-86 for the Gulf of Mannar has been described using 1-km spatial resolution Ch-a maps derived from CSCZ (Yapa, 2000). Yapa noted that Ch-a concentrations were higher during the summer monsoon than the winter monsoon.…”

Biological response of the sea around Sri Lanka to summer monsoon

“…Physical processes, however, can lead to high chl a in the western Bay of Bengal [ Gomes et al , 2000]. Elsewhere, a map of chl a distribution around Sri Lanka during the summer monsoon could not be obtained even from composites made using eight years of CZCS images [ Yapa , 2000].…”