NOAA/WDS Paleoclimatology - Campbell Island, New Zealand 140 Year Temperature Reconstruction

Occupying about 14% of the world's surface, the Southern Ocean plays a fundamental role in ocean and atmosphere circulation, carbon cycling and Antarctic ice-sheet dynamics. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine-atmosphere-ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52-54S). Our annually resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the 1940s, a phenomenon predating the observational record. Climate reanalysis and modelling show a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer. Our results suggest that modern observed high interannual variability was established across the mid-twentieth century, and that the influence of contemporary equatorial Pacific temperatures may now be a permanent feature across the mid- to high latitudes.

南大洋（Southern Ocean）约占全球地表总面积的14%，在海洋与大气环流、碳循环及南极冰盖动力学中扮演着核心角色。然而，其显著的年际变率，加之1950年代前仪器观测记录的匮乏，制约了我们对海-气-冰系统在多年代际时间尺度上的相互作用机制，以及人为强迫所产生影响的认知。为此，我们整合了西南太平洋亚南极岛屿（位于极地与副热带气候交界带，纬度区间为52°S至54°S）上的气候敏感型树木生长数据，与海洋、大气观测资料。本研究重建的年分辨率温度序列捕捉到了1870年代以来的区域气候变化特征，结果显示自1940年代起温度变率显著增强，这一现象早于现代仪器观测记录的起始时段。气候再分析与模式模拟结果表明，热带太平洋海表温度存在同步变化，该变化会激发大气罗斯比波列（Rossby wave train），并在南半球春夏季传播至南半球大部分区域。我们的研究结果显示，当前观测到的高度年际变率已于20世纪中期在南大洋区域确立，且当代赤道太平洋海表温度的影响如今或已成为中高纬度地区的永久性特征。