Validating the UK'37-SST relationship in the SW Atlantic Ocean From Core-Top Samples - UK'37; Annual and Seasonal SSTs from Aqua MODIS and Water Column from WOA13 and Coccolithophores Abundance@en

Few studies have evaluated the seasonal and depth distribution of the alkenone unsaturation index (UK'37) signal in sediments in the SW Atlantic Ocean, limiting the understanding of past regional SST estimates from this biomarker proxy. We analyzed 45 core-top sediment samples collected on the continental shelf of the South Brazilian Bight (SBB, 23 °S to 28 °S) to assess the spatial gradient in the UK'37-SST signal and improve future paleoceanographic studies in the region. The proxies were converted to SST using four published paleotemperature equations and then compared to modern observed SST from the World Ocean Atlas (2013) and Aqua MODIS mission data sets. The Bayspline calibration (Tierney and Tingley, 2018, doi:10.1002/2017PA003201) results in the most accurate estimates of modern mean annual SST (p-value 0.99, n = 45, ΔSST of -0.0006°C ± 0.99). We regressed our UK'37 determinations against modern observational SST and found that core-top UK'37 was significantly correlated to mean annual SST, with marginally higher sensitivity to autumn and winter SST patterns. For downcore SST reconstruction in the SBB region, we recommend applying the Bayspline equation for mean annual SST estimates. Standardizing the UK'37-SST equation used in the SBB region will allow for a more meaningful comparison between regional paleoceanographic studies, improving our understanding of past changes in the SW Atlantic.目前针对西南大西洋（Southwest Atlantic, SW Atlantic）沉积物中烯酮不饱和度指数（alkenone unsaturation index, UK'37）信号的季节与深度分布特征的研究较为匮乏，这限制了学界通过该生物标志物代用指标对该区域既往海表温度（Sea Surface Temperature, SST）估算结果的理解。本研究采集并分析了南巴西湾（South Brazilian Bight, SBB，23°S至28°S）大陆架上的45个表层岩心沉积物样品，以评估UK'37-SST信号的空间梯度特征，为该区域未来的古海洋学研究提供支撑。研究团队采用4套已发表的古温度方程将该代用指标转化为SST，并将结果与世界海洋图集（World Ocean Atlas，2013）以及Aqua MODIS卫星任务数据集的现代观测SST数据进行比对。贝叶斯样条（Bayspline）校准（Tierney与Tingley，2018，doi:10.1002/2017PA003201）所得到的现代年平均SST估算结果精度最高（p值=0.99，样本量n=45，SST偏差ΔSST为-0.0006℃±0.99）。研究团队将实测的UK'37数值与现代观测SST进行回归分析，结果表明表层岩心UK'37与年平均SST存在显著相关性，且对秋季与冬季SST分布模式的敏感度略高。针对南巴西湾区域的岩心垂向SST重建工作，我们建议采用贝叶斯样条（Bayspline）方程进行年平均SST估算。统一南巴西湾区域所使用的UK'37-SST方程，将有助于不同区域古海洋学研究之间开展更具科学意义的比对，从而深化我们对西南大西洋既往气候变化的认知。