Quantifying post Little-Ice-Age freshwater influences and ocean dynamics in the Central American Sea using a novel tracer combination: 234U/238U– (P)SST – 14C

在热带美洲，未来的气候情景预测低纬度地区也将升温，这也将对区域海表温度、降水（包括热带气旋）产生重大影响。在过去的几个世纪里，中美洲海的SST变化得到了充分的研究，并显示出从季节到数十年尺度的变化。强迫包括海洋环流强度、大气相互作用、太阳辐照度、淡水排放和火山气溶胶的变化。然而，海洋表面运动和SST变率的较小尺度变化的影响，例如区域淡水排放的影响，或者垂直混合和亚中尺度涡旋对这些时间尺度的影响，很难评估，因此在很大程度上是未知的。我们建议在这里研究热带珊瑚中的U同位素（即海水234 U/238 U比值）与代用品衍生的SST（（P）SST）和放射性碳相结合，以揭示淡水流量变化，海洋平流和混合以及表面热量在亚年度到数十年的时间尺度上。为了证明这一概念，我们选择了研究小冰河时代以来的时间。250年），因为丰富的SST重建存在中美洲海和仪器数据可用于过去c。40年。因此，我们将能够量化所有三个代理的同步变化，以推断淡水释放到墨西哥湾流前体水团中的影响。该项目可从该地区的几个地点获得长珊瑚岩心，包括加勒比海（波多黎各、尤卡坦半岛）、佛罗里达海峡（古巴）和热带大西洋西部（马提尼克岛）。我们还计划对博内尔岛和委内瑞拉附近的加勒比海南部的珊瑚进行间断分析。汇编这一前所未有的数据不仅可以复制海洋-大气相互作用的区域信号，而且还可以评估所研究的代用时间序列中的时间和空间梯度。与区域降水量估计和热带气旋重建的比较将允许评估对所有代理的影响，特别是评估海水过量234 U是否可以作为研究档案和其他地方的淡水排放的代理。这将为今后利用热带珊瑚研究气候变异性提供宝贵的修正。

In the tropical Americas, future climate scenarios predict increased warming also in the lower latitudes, which will have significant implications also on regional sea surface temperature (SST), precipitation including tropical cyclones. Over the past centuries, SST changes in the Central American Seas have been well-studied and were shown to exhibit variability from the seasonal to multi-decadal scale. The forcing includes variations in the strength of ocean circulation, atmospheric interactions, solar irradiance, freshwater discharge and volcanic aerosols. However, the impact of variations on the smaller scale of surface ocean motion and SST variability, such as from regional freshwater discharge, or the influence of vertical mixing and sub-mesoscale eddies on these timescales is difficult to assess and therefore largely unknown. We propose here to study U-isotopes (i.e. the seawater 234U/238U ratio) in tropical corals in combination with proxy derived SST ((P)SST) and radiocarbon, to reveal freshwater discharge changes, ocean advection and mixing and surface heat on sub-annual to multi-decadal timescales. To prove the concept, we have chosen to study the time since the Little Ice Age (c. 250 years) since a wealth of SST reconstructions exist for the Central American Sea and instrumental data is available for the past c. 40 decades. Therefore, we will be able to quantify synchronous changes of all three proxies to infer the influence of freshwater release into the precursor water masses of the Gulf Stream. Long coral drill cores are available to the project from several sites across the region including the Caribbean Sea (Puerto Rico, Yucatán peninsula), as well as from the Florida Strait (Cuba), and the western tropical Atlantic (Martinique). We further plan on punctuated analysis of corals from the southern Caribbean Sea off Bonaire and Venezuela. The compilation of this unprecedented data will not only allow to replicate regional signals of ocean – atmosphere interactions, but also to assess temporal and spatial gradients in the studied proxy time series. The comparison with regional precipitation estimates and tropical cyclone reconstructions will allow to assess the impact on all proxies, and in particular to assess if the seawater excess 234U can be applied as a proxy for freshwater discharge in the studied archives and elsewhere. This will constitute a valuable amendment for future studies of climate variability using tropical corals.