Coral-based reconstruction of salinity and temperature variability in the southern Makassar Strait and its Influence on the Indonesian Throughflow

印度尼西亚洋流是赤道西太平洋表层和上层温跃层水向印度洋输送的主要通道。由于在北方冬季风期间，华南海和爪哇海的低盐度表层水会季节性地流入马卡萨尔海峡，因此ITF的水量和温度会随季节而变化。 这种低盐度的“栓塞”在马卡萨尔海峡产生了一个向北的压力梯度，季节性地抑制了远西太平洋温暖的表层水向南自由流入印度洋。最终的结果是印度洋温跃层的冷却和清新。尽管在ITF上马卡萨尔海峡的季节性淡化具有海洋学意义，但人们对马卡萨尔海峡盐度的世纪至十年尺度变化知之甚少。以前基于马卡萨尔海峡沉积物岩心的低分辨率研究表明，在小冰期（约公元1600-1850年），海峡的盐度和海表温度都降低了。 本研究利用滨珊瑚属种。从Kapoposang在南部马卡萨尔海峡附近的西南苏拉威西岛和吉利梅诺在龙目岛海峡附近的巴厘岛开发部分复制，近每月的分辨率，微量元素（Sr/Ca）和稳定同位素（d18 Osw）记录跨越过去250年。结果表明，珊瑚Sr/Ca的变化准确地跟踪年度双峰海表温度循环。这项研究将加强对这一关键海峡的盐度和SST变化的了解，以限制ITF在过去250年的变化。 预计马卡萨尔海峡南部淡水收支的变化将改变“淡水栓”的强度，马卡萨尔海峡表层的盐度较低，导致ITF较冷。资金支持博士后助理和本科生的研究经验。

The Indonesian Throughflow (ITF) is the main conduit for transporting surface and upper thermocline water from the western equatorial Pacific into the Indian Ocean. The volume and temperature of the ITF varies seasonally due to the seasonal influx of low salinity surface water from the South China and Java Seas into the Makassar Strait during the northern winter monsoon. This low salinity "plug" generates a northward pressure gradient in the Makassar Strait that seasonally inhibits the flow of warm surface water in the far western Pacific Ocean from freely flowing southward into the Indian Ocean. The net result is a cooling and freshening of the Indian Ocean thermocline. Despite the oceanographic significance of this seasonal freshening of the Makassar Strait on the ITF, little is known about century to decadal-scale variability of salinity in the Makassar Strait. Previous low-resolution studies based on sediment cores in the Makassar Strait indicate that during the Little Ice Age (~1600-1850 AD), salinity and sea surface temperature in the strait were both reduced. This research utilizes Porites sp. coral cores from Kapoposang in the southern Makassar Strait near S.W. Sulawesi and from Gili Meno in the Lombok Strait near Bali to develop partially replicated, near-monthly resolution, trace element (Sr/Ca) and stable isotope (d18Osw) records spanning the last 250 years. Results show that coral Sr/Ca variability accurately tracks the annual bi-modal sea surface temperature cycle. The research will enhance understanding of salinity and SST variability in this critical strait in order to constrain ITF variability over the last 250 years. Changes in the freshwater budget of the southern Makassar Strait are expected to alter the intensity of the "freshwater plug", with lower salinity in the Makassar Strait surface layer leading to a cooler ITF. Funding supports a postdoctoral associate and research experiences for undergraduates.