Dataset for the paper: Factors influencing sea-ice algae abundance, community composition, and distribution in the marginal ice zone of the Southern Ocean during winter.

Microalgae and bacteria living in Antarctic sea-ice play a fundamental role in polar-ocean biogeochemistry, accounting for ∼25% of primary production in sea-ice-covered regions of the Southern Ocean. However, a paucity of measurements in the marginal ice zone (MIZ), particularly during winter, means that sea-ice algal dynamics are poorly understood, resulting in uncertainties in the drivers of Antarctic food-web and carbon-cycle variability. We investigated the relationships among biogeochemical parameters and sea-ice algae in the MIZ of the Indian Southern Ocean in winter 2017 through measurements of sea-ice algae functional groups, chlorophyll, and nutrient concentrations, in the sea-ice and the underlying surface seawater. We observed an abundant, active algal community within the sea-ice, which we attribute to passing cyclones that kept the ice permeable, along with biogeochemical and irradiance conditions that allowed for algal growth. The sea-ice conditions facilitated the proliferation of sea-ice diatoms, to chlorophyll concentrations >5 μg/L (versus 1.5 μg/L in the underlying seawater). The dominant taxa were of the generaFragilariopsis, Pseudo-nitzschia, Coscinodiscus, andChaetocerosspp., similar to those observed previously near east Antarctica. While sea-ice algae growth should have caused significant nutrient drawdown, nitrate concentrations were higher in the ice than in the underlying seawater. Since silicate was strongly drawn down, presumably by sympagic diatoms, we attribute the elevated nitrate concentrations to an active microbial loop (i.e., regeneration and nitrification). Our study highlights the ecological significance of the Southern Ocean MIZ in winter, providing a vital environment for overwintering sea-ice algae and bacteria that remain active despite the harsh conditions.

栖息于南极海冰中的微藻与细菌，在极地海洋生物地球化学循环中发挥着核心作用，其贡献约占南大洋海冰覆盖区域初级生产力的25%。然而，边缘冰区（Marginal Ice Zone, MIZ）的观测数据极度匮乏，尤其在冬季，这导致我们对海冰藻类的动态变化认知不足，进而使得南极食物网与碳循环波动的驱动机制存在诸多不确定性。本研究于2017年冬季，针对南大洋印度洋扇区的边缘冰区（MIZ）展开调研，通过测定海冰及其下覆表层海水中的海冰藻类功能群、叶绿素与营养盐浓度，探究了生物地球化学参数与海冰藻类之间的关联。研究团队在海冰内部观测到了丰富且具有活性的藻类群落，我们将其归因于过境气旋维持了海冰的渗透性，辅以适宜藻类生长的生物地球化学与光照条件。海冰环境促进了海冰硅藻的大量繁殖，其叶绿素浓度可达5μg/L以上（下覆海水中的叶绿素浓度仅为1.5μg/L）。优势类群隶属于脆杆藻属（Fragilariopsis）、拟菱形藻属（Pseudo-nitzschia）、圆筛藻属（Coscinodiscus）以及角毛藻属（Chaetoceros spp.），与此前在东南极附近观测到的类群特征相似。尽管海冰藻类的生长本应造成营养盐的显著消耗，但海冰内的硝酸盐浓度反而高于下覆表层海水。由于硅酸盐被大量消耗（推测为冰栖硅藻所为），我们将硝酸盐浓度升高的现象归因于活跃的微生物环（即营养再生与硝化作用）。本研究凸显了冬季南大洋边缘冰区（MIZ）的生态重要性——尽管环境条件严苛，该区域仍为越冬海冰藻类与细菌提供了维持活性的关键生境。