Assessing the Reliability of Planktic Foraminifera Ba/Ca as a Proxy for Salinity off the Sunda Strait

The Ba/Ca ratio of planktic foraminifera carbonate serves as a new geochemical proxy for seawater Ba/Ca and thus providing information on modern and past salinity and freshwater discharge. In this study the applicabili ty of Ba/Ca ratio of core-top Globigerinoides sacculifer collected off the eastern tropical Indian Ocean (ETIO) for paleoceanographic reconstructions was investigated. In doing so, we conducted a series of cleaning experiments for Ba/Ca extraction by using different reductive solutions. Our new results suggest that the Ba/Ca ratio of G. sacculifer cannot be utilized as a tracer for modern and past salinity changes in the ETIO region off the Sunda Strait. We suggest that the existence of seasonal upwelling adds an addi tional signal to the seawater Ba/Ca in the ETIO, and thus complicates the interpretation of G. sacculifer Ba/Ca as a freshwater tracer. Moreover, our cleaning experiment results show that the cleaning protocol of Mg/Ca, DTPA, and hydroxylamine can be used to extract valuable Ba/Ca ratios from planktic foraminifera tests

The role of the Sunda Strait in the glacial to Holocene development of the eastern tropical Indian Ocean hydrography

The eastern tropical Indian Ocean (ETIO) off southern Indonesia is a very important region for the global thermohaline circulation as it hosts the exit pathway of the Indonesian Throughflow (ITF). From this region cool and fresh ITF waters are advected by the South Equatorial Current (SEC) to the Indian Ocean. Consequently, the ITF water freshens the Indian Ocean. Nevertheless, the hydrology condition was different during the Last Glacial Maximum (LGM). During this period the sea level was low and the Sunda Shelf was an exposed land. Marine records and simulation study suggest that the exposure of the Sunda Shelf caused a significant reduction in convection over the Indonesian region, resulting arid condition and saltier sea surface condition off south Java. Armed with two sedimentary archives collected from the ETIO off the Sunda Strait, this dissertation investigates the evolution of hydrological changes in the ETIO during the past ~40 kyr B.P. with respect to the flooding of the Sunda Shelf. Furthermore, this dissertation examines the applicability of planktic foraminifera Ba/Ca ratio as a tracer for freshwater discharge. New results of Mg/Ca-based sea surface temperature (SST), seawater à ´18O (à ´18Osw), and XRF-Ti/Ca ratio of GeoB 10042-1 and GeoB 10043-3 collected from off the Sunda Strait revealed that the region has experienced prominent hydrological changes during the past ~40 kyr B.P. The results show that sea surface conditions off the Sunda Strait were cooler and saltier conditions during the last glacial compared to the Holocene, and support previous finding that suggests slowdowns of the Atlantic meridional overturning circulation (AMOC) during the Heinrich stadials 1-3 and the Younger Dryas have caused dry conditions in the ETIO region. Whereas during the Holocene sea surface conditions off the Sunda Strait exhibit warmer and fresher conditions, particularly after the opening of the Sunda Strait at ~10 kyr B.P. This fresher sea surface condition is maintained until today as a consequence of persistent transport of low salinity Java Sea water into the ETIO via the Sunda Strait. Novel millennial-scale reconstruction of past bottom water conditions (foraminifera à µNd) show distinct modifications of the bottom water (2171 m) off the Sunda Strait during the past 19 kyr. Modifications of the bottom water during the last deglaciation and the Holocene correspond to a strong- and a weak thermocline ITF flow, respectively. Furthermore, the results imply that the variability of the detrital à µNd data off the Sunda Strait is susceptible to the ITF flow and large terrigenous material supply from the Sunda Strait. Planktic foraminifera Ba/Ca ratio has been recently used to reconstruct modern and past freshwater discharge. The application of this proxy is based on the observation that suggests that the Ba/Ca ratio of seawater is directly incorporated into foraminifera calcite, and river water has a distinctly higher Ba/Ca ratio than seawater. However, cleaning experiments results on planktic foraminifera G. sacculifer collected from the ETIO revealed that the Ba/Ca ratio of G. sacculifer cannot be used as a tracer for modern and past salinity changes due to the appearance of seasonal upwelling complicates the interpretation of the proxy

The Effect of ENSO on the Variability of Chlorophyll-a and Sea Surface Temperature in the Maluku Sea

The Maluku Sea features strong Chlorophyll-a (Chl-a) bloom and sea surface temperature (SST) cooling during the Southeast Monsoon season. Using high-resolution Chl-a and SST satellite observations over a long time window, this study aims to investigate the effect of El Nino Southern Oscillation (ENSO) on the seasonal variability of Chl-a and SST in the Maluku Sea. During the El Nino and La Nina, the maximum Chl-a concentration (greater than 0.5 mg/m3) and minimum SST (less than 27.5 °C) are observed in August. This finding is in line with prior investigation. Moreover, we reveal that the ENSO does not alter the seasonal variability of Chl-a and SST in the region, but the magnitudes of summertime Chl-a bloom and SST cooling are enhanced (reduced) by about 0.1 mg/m3 and 0.5 °C during the El Nino (La Nina). This is caused by an increase (decrease) in the sea level pressure gradients, which possibly enhanced (reduced) wind-driven mixing in the Maluku Sea

Phytoplankton chlorophyll-a biomass and the relationship with water quality in barrang caddi, spermonde, indonesia

The investigation of spatial changes in phytoplankton biomass and turbidity provide essential information for the survival of the coral reef ecosystem. The phytoplankton biomass variations are driven by many factors, such as nutrient inputs from anthropogenic and natural. In turn, turbidity is determined by sediment resuspension or transport from terrestrial systems. The estimation of phytoplankton biomass is represented by the chlorophyll-a concentration. This study aimed to analyze the chlorophyll-a dynamics to water quality parameters, such as turbidity, suspended solids, dissolved oxygen, pH, salinity and temperature. The in-situ data gathered at 26 stations in the waters of the Barrang Caddi Island in August 2020. The results show that chlorophyll-a and turbidity have a negative correlation in the western and eastern regions, since turbidity inhibits the rate of photosynthesis and causes the decreasing of phytoplankton biomass. Nevertheless, the highest concentration of chlorophyll-a was found in the southern location, in small spots around islands and reefs, including near Barrang Caddi Island. Total Suspended Solid has more significant effect on chlorophyll-a than other water parameters, such as turbidity, temperature, salinity in the study area. © 2022, Polskie Towarzystwo Inzynierii Ekologicznej (PTIE). All rights reserved