DRIVERS OF ELEVATED CHLOROPHYLL-A IN LUMAJANG WATERS: A COMPARATIVE ANALYSIS OF UPWELLING AND TERRESTRIAL RUNOFF MECHANISMS

Bayu MUNANDAR , Adzkia Noerma ARIFA , Annisa Aulia LUKMAN , Anindya WIRASATRIYA , Yusuf Jati WIJAYA

DOI: 10.21163/GT_2026.211.14

ABSTRACT: The Lumajang Waters (LW) is located in South Java and is one of the waters with outstanding primary productivity. The variation in primary productivity in a water body serves as an indicator of its aquatic fertility. Many seasonal parameters and physical oceanographic phenomena (currents, upwelling, nutrients, wind and waves) can influence the variability of chl-a in the ocean. In the current study, we conducted a comprehensive analysis of chl-a variability using both horizontal and vertical data. We found the highest chl-a in Lumajang waters occurred from July to October, and the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) events make higher chl-a. The peak chl-a concentration in 2019 was 2.03 mg/m³ in July, whereas in 2023 it reached 3.01 mg/m³ in October. However, we found the value of correlation between wind (Ekman Mass Transport (EMT)) and Chl-a was stronger in 2019 than in 2023. The coastal upwelling that increases in chl-a concentration in 2019 and 2023 is observable as a lifted water mass with a density of 23 kg/m³ from 100 meters depth to the surface. Despite lower intensity of coastal upwelling, chl-a concentration in 2023 was higher than in 2019. On the other hand, Rrs 555 in 2023 which represents Total Suspended Solids (TSS) exhibited a 2-times higher than the other years, particularly from August to October. The high Rrs 555 may be associated with the increase of TSS brought by river runoff, considering that many rivers flow from the upper land and fertilize the waters of Lumajang. These characteristics make Lumajang waters very unique, as two mechanisms run together influencing the chl-a variation.

Keywords: Rrs 555; Upwelling; Chlorophyll-a; Density; Lumajang Waters.

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