Monthly Bonaire coral d18O and d18Oseawater from the last interglacial, 120.5 -129.7 ka ago

The seasonality of hydroclimate during past periods of warmer than modern global temperatures is a critical component for understanding future climate change scenarios. Although partially analogous to these scenarios, the last interglacial (LIG, Marine Isotope Stage 5e, ~127-117 ka) is a popular test-bed. We present coral d18O monthly resolved records from multiple Bonaire (southern Caribbean) fossil corals (Diploria strigosa) that date to between 130 and 118 ka. These records represent up to 37 years and cover a total of 105 years, offering insights into the seasonality and characteristics of LIG tropical Atlantic hydroclimate. Our coral d18O records and available coral Sr/Ca- sea surface temperature (SST) records reveal new insights into the variable relationship between the seasonality of tropical Atlantic seawater d18O (d18Oseawater) and SST. Coral d18O seasonality is found to coevolve with SST and insolation seasonality throughout the LIG, culminating in significantly higher than modern values at 124 and 126 ka. At 124 ka, we reconstruct a 2-month lead of the coral d18O vs. the Sr/Ca-SST annual cycle and increased d18Oseawater seasonality. A fully-coupled climate model simulates a concomitant increase of southern Caribbean Sea summer precipitation and depletion of summer d18Oseawater. LIG regional hydroclimate differed from today's semiarid climate with a minor rainy season during winter. Cumulatively our coral d18O, d18Oseawater and model findings indicate a mid-LIG northward expansion of the South American Intertropical Convergence Zone into the southern Caribbean Sea, highlighting the importance of regional aspects within reconstructions of LIG hydroclimate seasonality.

全球暖于现代的古气候时期的水文气候季节变化，是理解未来气候变化情景的关键组成部分。尽管与未来气候变化情景存在部分相似性，但末次间冰期（Last Interglacial，简称LIG，海洋同位素阶段5e，约127~117 ka）是广受青睐的试验研究平台。本研究报道了来自加勒比海南部博奈尔岛的多件年代介于130~118 ka的化石对称脑珊瑚（*Diploria strigosa*）的月分辨率珊瑚δ¹⁸O记录。这些单条记录最长覆盖37年，总累计时长达105年，为解析热带大西洋末次间冰期水文气候的季节变化与特征提供了新认知。
我们的珊瑚δ¹⁸O记录与已发表的珊瑚Sr/Ca-海表温度（Sea Surface Temperature，简称SST）记录，揭示了热带大西洋海水δ¹⁸O（δ¹⁸O_seawater）季节变化与SST之间的可变关系。研究发现，末次间冰期内珊瑚δ¹⁸O的季节变化与SST及日照季节变化协同演化，并在124 ka与126 ka时达到显著高于现代的峰值。在124 ka时，我们重建得到珊瑚δ¹⁸O较Sr/Ca-SST年周期提前2个月的相位，且海水δ¹⁸O的季节变化幅度增强。
全耦合气候模型模拟显示，加勒比海南部夏季降水同步增加，且夏季海水δ¹⁸O出现贫化。末次间冰期区域水文气候与现今的半干旱气候存在差异：彼时冬季存在小幅雨季。
综合我们的珊瑚δ¹⁸O、海水δ¹⁸O及模型结果，表明末次间冰期中期南美热带辐合带（South American Intertropical Convergence Zone）向北扩张至加勒比海南部区域。这一结果凸显了在末次间冰期水文气候季节变化重建中区域特征研究的重要性。