The Southern Ocean provides strong contrasts in rates and directions of change in temperature and sea ice between its sectors, but it is unknown how these affect plankton species that are distributed right around Antarctica. Here, we quantify the changing circumpolar distributions of Antarctic krill, based on the CHINARE 2013/14 circum‐Antarctic expedition, plus independent analyses of compiled abundance data (KRILLBASE: 1926–2016). In the 1920s–1930s, average krill densities in the Atlantic‐Bellingshausen sector were eight times those in the other sectors. More recently, however, the concentration factor has dropped to only about twofold. This reflects a rebalancing broadly commensurate with climatic forcing: krill densities declined in the Atlantic‐Bellingshausen sector which has warmed and lost sea ice, densities may have increased in the Ross‐Pacific sector which showed the opposite climatic trend, while densities showed no significant changes in the more stable Lazarev‐Indian sectors. Such changes would impact circumpolar food webs, so to better define these we examined circumpolar trends of isotopic values in krill and other zooplankton based on the CHINARE cruise and a literature meta‐analysis. Krill δ¹⁵N values ranged significantly between sectors from 2.21‰ (Indian) to 3.59‰ (Ross‐Pacific), about half a trophic level lower than another key euphausiid, Thysanoessa macrura. These isoscapes form a baseline for interpreting the reliance of predators on euphausiids, within the varying food webs around the continent. Overall, we suggest that the Indo‐Pacific sector has acted as a refuge for the circumpolar krill stock while conditions for them deteriorated rapidly in the Atlantic sector.

中文翻译：

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改变南极磷虾的周极分布和等值线：印度太平洋生境避难所应对大西洋地区的长期退化

南大洋在其各部门之间温度和海冰变化的速率和方向上形成强烈反差，但尚不清楚它们如何影响南极洲周围分布的浮游生物。在这里，我们基于CHINARE 2013/14环南极考察，加上已编译的丰度数据的独立分析（KRILLBASE：1926-2016），量化了南极磷虾的极地周极分布变化。在1920年代至1930年代，大西洋比林斯豪森地区的平均磷虾密度是其他地区的八倍。然而，最近，集中度仅下降到两倍。这反映了与气候强迫大致相称的再平衡：大西洋-贝林斯豪森地区的磷虾密度下降，该地区的磷肥已经变暖和丢失，在罗斯-太平洋地区，气候趋势相反，密度可能增加，而在较稳定的拉扎列夫-印度地区，密度没有明显变化。这种变化会影响极地食物网，因此，为了更好地定义这些食物网，我们根据CHINARE航行​​和文献荟萃分析了磷虾和其他浮游动物同位素值的极地趋势。磷虾δ¹⁵ N值在2.21‰（印度）至3.59‰（Ross-Pacific）之间显着变化，比另一个关键的植物（Thysanoessa macrura）的营养水平低约一半。这些等值线构成了一个基线，用于解释大陆周围各种食物网中捕食者对虾的捕食依赖。总体而言，我们建议印度太平洋地区作为极地磷虾种群的避难所，而大西洋地区的条件则迅速恶化。