The roles of mixed layer depth in affecting chemical and biological characteristics of Makassar straits, Indonesia

Abstract

Mixed Layer Depth (MLD) is able to determine the amount of light and nutrients abundance for the growth of phytoplankton, its known that phytoplakton pigments are the main absorbers and light scatterers in the ocean. Location wich has deeper MLD and large seasonal variations are the most productive areas, also could have blooming or the maximum growth of large phytoplankton occurring in the existence of a limited number nutrients for several days. The aims of this study are to understand the characteristics of the MLD and it roles to the abundance of Chlorophyll and nutrient in Indonesia Through-Flow/ITF (Indonesia: “ARLINDO”), specifically the area along Makassar Strait. The Chlorophyll and oceanographic parameters were obtained based on measuring by CTD in TIMIT 2016 expedition. The MLD was deep (~43 m) in the northern part of the transect (around Central Sulawesi Island) and shoaled progressively until about 13 m in the southern transect (the Southern Makassar Strait). The Chlorophyll-a (Chl-a) concentration show a decline pattern from the north to the south transects with the maximal Chl-a is 0.37 mg/m3. Nutrient parameters in southern Makassar Strait studied were NODC (National Oceanographic Data Center) data from WOA (World Ocean Atlas), it can indicated a correlation between nutrient (Nitrate) with Chlorophyll. The mean correlation in mixing layer for whole area is 0.78, showing that Nitrate concentration is highly related proportional to Chlorophyll abundance, while below the mixing layer, correlation value is -0.52, indicating the inverse relation between Chlorophyll and nutrient. Based on those correlation, and assumption that the source of Chlorophyll is from phytoplankton, it can be concluded that phytoplankton needs Nitrate in its metabolism process as well as other productivities reason in mixing layer, while in depth below the mixing layer, growth of phytoplankton is no longer depends on concentration of Nitrate nutrient.