Large open-ocean polynyas, defined as ice-free areas within the sea ice pack, have only rarely been observed in the Southern Ocean over the past decades. In addition to smaller recent events, an impressive sequence occurred in the Weddell Sea in 1974, 1975 and 1976 with openings of more than 300 000 km² that lasted the full winter. These big events have a huge impact on the sea ice cover, deep-water formation, and, more generally, on the Southern Ocean and the Antarctic climate. However, we have no estimate of the frequency of the occurrence of such large open-ocean polynyas before the 1970s. Our goal here is to test if polynya activity could be reconstructed using continental records and, specifically, observations derived from ice cores. The fingerprint of big open-ocean polynyas is first described in reconstructions based on data from weather stations, in ice cores for the 1970s and in climate models. It shows a signal characterized by a surface air warming and increased precipitation in coastal regions adjacent to the eastern part of the Weddell Sea, where several high-resolution ice cores have been collected. The signal of the isotopic composition of precipitation is more ambiguous; thus, we base our reconstructions on surface mass balance records alone. A first reconstruction is obtained by performing a simple average of standardized records. Given the similarity between the observed signal and the one simulated in models, we also use data assimilation to reconstruct past polynya activity. The impact of open-ocean polynyas on the continent is not large enough, compared with the changes due to factors such as atmospheric variability, to detect the polynya signal without ambiguity, and additional observations would be required to clearly discriminate the years with and without open-ocean polynya. Thus, it is reasonable to consider that, in these preliminary reconstructions, some high snow accumulation events may be wrongly interpreted as the consequence of polynya formation and some years with polynya formation may be missed. Nevertheless, our reconstructions suggest that big open-ocean polynyas, such as those observed in the 1970s, are rare events, occurring at most a few times per century. Century-scale changes in polynya activity are also likely, but our reconstructions are unable to precisely assess this aspect at this stage.

中文翻译：

---

我们是否可以利用冰芯记录来重建南大洋中大洋性多年生polynyas的形成？

在过去的几十年中，在南大洋很少见到大型的洋洋暴风犬，被定义为海冰袋内的无冰区。除了较小的近期事件，1974年，1975年和1976年的韦德尔海发生了一系列令人印象深刻的事件，洞口超过30万公里²持续了整个冬天。这些重大事件对海冰覆盖，深水形成，以及更广泛的说，对南大洋和南极气候具有巨大影响。但是，我们无法估计1970年代之前这种大型的开放海域多角虫的发生频率。我们的目标是检验大陆上的记录，尤其是从冰芯获得的观测资料，是否可以重建多面体活动。首先在基于气象站，1970年代冰芯和气候模型的数据进行的重建中描述了大洋性多面体的指纹。它显示出一个信号，其特征是在邻近韦德海东部的沿海地区，地表空气变暖，降水增加，那里已收集了多个高分辨率冰芯。降水同位素组成的信号更加模糊；因此，我们仅基于表面质量平衡记录进行重建。通过执行标准化记录的简单平均值即可获得第一个重构。考虑到所观察到的信号与模型中模拟信号之间的相似性，我们还使用数据同化来重建过去的polynya活动。与由于大气变化等因素引起的变化相比，开放性海域多面体对非洲大陆的影响还不够大，无法毫无歧义地检测到多面体信号，还需要另外观察才能清楚地区分开放和不开放的年份。海洋波利尼亚。因此，有理由认为，在这些初步重建中，一些高积雪事件可能被错误地解释为polynya形成的结果，而可能会错过一些多年的polynya形成。然而，我们的重建表明，大型的洋洋暴龙，例如1970年代观察到的，是罕见的事件，每个世纪最多发生几次。波利尼娅活动的世纪规模变化也是可能的，但我们的重建工作目前无法精确评估这一方面。