Seasonal and interannual variability of surface Chlorophyll-a off the Halmahera Island
Riza Yuliratno Setiawan (a*), Anindya Wirasatriya (b), Iskhaq Iskandar (c)
a) Department of Fisheries, Faculty of Agriculture, Universitas Gadjah Mada, Jl. Flora Gd. A4, Bulaksumur, Yogyakarta 55281, Indonesia
*riza.y.setiawan[at]ugm.ac.id
b) Department of Oceanography, Faculty of Fisheries and Marine Sciences, Diponegoro University, Jl. Prof. Soedarto, S.H., Tembalang, Semarang 50275, Indonesia
c) Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Sriwijaya. Jl. Palembang - Prabumulih, Km. 32, Inderalaya, OI, Sumatra Selatan, 30662, Indonesia
Abstract
Long-term satellite data (2003-2017) are analyzed to investigate the variability of ocean surface chlorophyll-a (Chl-a) concentration off the Halmahera Island under influence of the Indonesian Australian Monsoon and the El Niño-Southern Oscillation (ENSO). In this study, we first analyzed the seasonal variability of Chl-a, and then describe the relationship between sea surface Chl-a, sea surface temperature (SST), and sea surface wind stress in the region. Our results demonstrate that prevailing northerly and southeasterly wind stresses play a pivotal role in generating Chl-a maxima off the Halmahera Island. On seasonal time scale, the strengthening of northerly and southeasterly wind stresses (up to ~0.01 N m-2) during the Northwest and Southeast Monsoon seasons produce enhanced phytoplankton blooms associated with sea surface cooling (~28.8 °C) in the area of study. On interannual time scale, the largest positive Chl-a and wind stress anomalies and the coolest SST anomaly are observed in 2006 during El Niño event. Meanwhile, the greatest negative Chl-a anomaly is prevailed during the 2016 negative IOD event. This study demonstrates that wind variability is the essential factor in determining the magnitude of Chl-a maxima off the Halmahera Island.
Keywords: Chlorophyll-a; ENSO; Halmahera Island
Topic: Coastal and Ocean Dynamics