(Table 1) Comparison between bulk ICP-OES measurements and LA-ICP-MS analyses for Mg/Ca and Sr/Ca ratios of Globigerinoides sacculifer from ODP Hole 165-1000A

We constructed a high-resolution Mg/Ca record on the planktonic foraminifer Globigerinoides sacculifer in order to explore the change in sea surface temperature (SST) due to the shoaling of the Isthmus of Panama as well as the impact of secondary factors like diagenesis and large salinity fluctuations. The study covers the latest Miocene and the early Pliocene (5.6-3.9 Ma) and was combined with d18O to isolate changes in sea surface salinity (SSS). Before 4.5 Ma, SSTMg/Ca and SSS show moderate fluctuations, indicating a free exchange of surface ocean water masses between the Pacific and the Atlantic. The increase in d18O after 4.5 Ma represents increasing salinities in the Caribbean due to the progressive closure of the Panamanian Gateway. The increase in Mg/Ca toward values of maximum 7 mmol/mol suggests that secondary influences have played a significant role. Evidence of crystalline overgrowths on the foraminiferal tests in correlation with aragonite, Sr/Ca, and productivity cyclicities indicates a diagenetic overprint on the foraminiferal tests. Laser ablation inductively coupled plasma-mass spectrometry analyses, however, do not show significantly increased Mg/Ca ratios in the crystalline overgrowths, and neither do calculations based on pore water data conclusively result in significantly elevated Mg/Ca ratios in the crystalline overgrowths. Alternatively, the elevated Mg/Ca ratios might have been caused by salinity as the d18O record of Site 1000 has been interpreted to represent large fluctuations in SSS, and cultivating experiments have shown an increase in Mg/Ca with increasing salinity. We conclude that the Mg/Ca record <4.5 Ma can only reliably be considered for paleoceanographical purposes when the minimum values, not showing any evidence of secondary influences, are used, resulting in a warming of central Caribbean surface water masses after 4.5 Ma of ~2°C.本研究以浮游有孔虫（planktonic foraminifer）Globigerinoides sacculifer为研究对象，构建了高分辨率镁钙比（Mg/Ca）记录，旨在探究巴拿马地峡（Isthmus of Panama）抬升引发的海面温度（Sea Surface Temperature, SST）变化，以及成岩作用（diagenesis）、剧烈盐度波动等次要因素的影响。本研究覆盖晚中新世至上新世早期（5.6~3.9 Ma），并结合氧同位素18（d18O）数据分离出海面盐度（Sea Surface Salinity, SSS）的变化。 在4.5 Ma之前，基于Mg/Ca比值反演的SST与SSS呈现中等幅度波动，表明太平洋与大西洋之间存在表层水团的自由交换。4.5 Ma之后，d18O的升高代表加勒比海海域盐度随巴拿马地峡通道（Panamanian Gateway）的逐步闭合而不断升高。Mg/Ca比值升高至最高7 mmol/mol的现象，暗示次要因素已产生显著影响。与文石（aragonite）、锶钙比（Sr/Ca）及生产力周期（productivity cyclicities）相关的有孔虫壳体表面晶体增生层证据，表明有孔虫壳体受到成岩叠加改造。 然而，激光剥蚀电感耦合等离子体质谱法（Laser ablation inductively coupled plasma-mass spectrometry）分析并未显示晶体增生层中的Mg/Ca比值显著升高，基于孔隙水数据的计算也未得出晶体增生层Mg/Ca比值显著升高的确定性结果。另一种可能是，Mg/Ca比值升高由盐度变化导致：1000站位（Site 1000）的d18O记录被解读为代表SSS的剧烈波动，且培养实验已证实Mg/Ca比值随盐度升高而增加。 本研究认为，4.5 Ma之前的Mg/Ca记录仅在使用未显示任何次要影响迹象的最小值时，才可可靠用于古海洋学（paleoceanographical）研究；据此得出，4.5 Ma之后加勒比海中部表层水团升温约2℃。