Strong seasonality is a key feature of high-latitude systems like the Barents Sea. While the interannual variability and long-term changes of the Barents Sea are well-documented, the seasonal progression of the physical and biological systems is less known, mainly due to poor accessibility of the seasonally ice-covered area in winter and spring. Here, we use an extensive set of physical and biological in situ observations from four scientific expeditions covering the seasonal progression from late winter to late summer 2021 in the northwestern Barents Sea, from fully ice-covered to ice-free conditions. We found that sea ice meltwater and the timing of ice-free conditions in summer shape the environment, controlling heat accumulation, light and nutrient availability, and biological activity vertically, seasonally, and meridionally. In March and May, the ocean north of the Polar Front was ice-covered and featured a deep mixed layer. Chlorophyll-a concentrations increased strongly from March to May along with greater euphotic depth, indicating the beginning of the spring bloom despite the absence of surface layer stratification. By July and in September, sea ice meltwater created a shallow low-density surface layer that strengthened stratification. In open water, chlorophyll-a maxima were found at the base of this layer as surface nutrients were depleted, while in the presence of ice, maxima were closer to the surface. Solar heating and the thickness of the surface layer increased with the number of ice-free days. The summer data showed a prime example of an Arctic-like space-for-time seasonal variability in the key physical and biological patterns, with the summer situation progressing northwards following sea ice retreat. The amount of sea ice melt (local or imported) has a strong control on the conditions in the northwestern Barents Sea, and the conditions in late 2021 resembled pre-2010 Arctic-like conditions with high freshwater content and lower ocean heat content.

强烈的季节性是巴伦支海等高纬度系统的一个关键特征。虽然巴伦支海的年际变化和长期变化已有详细记录，但物理和生物系统的季节性进展却鲜为人知，这主要是由于冬季和春季季节性冰覆盖区域的交通不便。在这里，我们使用了四次科学考察的大量物理和生物现场观测数据，涵盖了巴伦支海西北部从冬末到夏末的季节演变，从完全冰覆盖到无冰条件。我们发现海冰融水和夏季无冰条件的时间塑造了环境，控制热量积累、光和养分可用性以及垂直、季节性和经向的生物活动。3月和5月，极锋以北的海洋被冰覆盖，并具有深层混合层。从 3 月到 5 月，叶绿素a浓度随着透光深度的增加而急剧增加，这表明尽管没有表层分层，但春季开花的开始。到了七月和九月，海冰融水形成了浅层低密度表层，从而加强了分层。在开放水域中，由于表面营养物质耗尽，叶绿素最大值出现在该层的底部，而在存在冰的情况下，最大值更接近表面。太阳加热和表层厚度随着无冰天数的增加而增加。夏季数据显示了关键物理和生物模式中类似北极的时空季节性变化的典型例子，夏季情况在海冰消退后向北发展。海冰融化量（本地或进口）对巴伦支海西北部的状况有很强的控制作用，2021 年末的状况类似于 2010 年之前的北极状况，淡水含量高，海洋热量含量低。