Carbon and nutrient enrichment potential of South Java upwelling area as detected using hindcast biogeochemistry variables

Abstract

Biogeochemical cycles and ecosystems in the South Java upwelling area respond to physical conditions, the diurnal cycle, intraseasonal variability, and climate variations. Whilst carbon and nutrient enrichment occur annually in response to monsoon driven upwelling, the spatiotemporal trends in chlorophyll-a (Chl-a), nutrient and particulate carbon in response to that upwelling are less well understood. Furthermore, the presence of Indonesian throughflow (ITF) may enhance the biogeochemical dynamics in the area. Our study aimed to assess the carbon and nutrient enrichment in the South Java upwelling area. We evaluated satellite derived and hindcast modeled datasets of biogeochemistry variables such as nutrients, Chl-a, particulate organic carbon (POC), particulate inorganic carbon (PIC), net primary production (NPP), dissolved oxygen (DO), and sea surface temperature. The temporal trends and spatial distributions were assessed to detect potential enrichment that affects the direct or indirect responses. The concentration Chl-a, NPP, POC, nitrate, and phosphate intensified during the July–October period in this region. Silicate showed a different pattern, i.e., the highest concentration occurred from March to May which likely correlated to the ITF. Annually, the highest peak of POC concentration was detected earlier (in September) than that of PIC (in October–November). The spatial distribution of POC on surface waters is also likely to be affected by input from the Java Sea or ITF. The intensified concentration of POC from September to November occurred at the Sunda, Bali, and Lombok Strait outlets. The record shows that the highest POC concentration occurred throughout the year in the coastal area. Carbon and nutrient enrichment occurs from July to November during the upwelling period. This paper discusses the highest positive peaks of biogeochemical parameters during September 2011, 2015, and 2019, which co-occurred with El Niño-Southern Oscillation and Indian Ocean Dipole events. This paper also discusses the potential effect of ITF on the upwelling area and the direct or indirect biological responses of the nutrient enrichment.