We incubated Fe-limited seawater with sea-ice sections to evaluate which forms of iron (Fe) released from melting sea ice can favor phytoplankton growth. Biological availability (bioavailability) was approximated by fractionating Fe into soluble (<1000 kDa), colloidal (1000 kDa–0.2 μm), and labile particulate (>0.2 μm) sizes. Results show that phytoplankton thrived after the addition of sea ice. While the labile particulate fraction dominated the total Fe pool in sea ice, the concentration of dissolved Fe (<0.2 μm) was likely not enough to support phytoplankton growth in seawater over time. The concentrations and molar ratios of Fe, Mn and Al in acid-digested particles indicate that particulate Fe in sea ice were derived from multiple origins. Specifically, the Fe to Al ratio in sea ice was higher than in lithogenic material, suggesting that the sea ice were enriched with biogenic material. Our study suggests that particulate Fe from sea ice should be considered an important source of biologically available Fe in ice-covered marginal seas.

我们用海冰切片孵育了有限铁含量的海水，以评估从融化的海冰中释放出的哪些形式的铁（Fe）有利于浮游植物的生长。通过将铁分为可溶的（<1000 kDa），胶体的（1000 kDa–0.2μm）和不稳定的颗粒（> 0.2μm）大小，可以估算出生物的可利用性（生物利用度）。结果表明，添加海冰后浮游植物蓬勃发展。尽管不稳定的颗粒部分占了海冰中总Fe的主要部分，但随着时间的推移，溶解的Fe（<0.2μm）的浓度可能不足以支持海水中浮游植物的生长。酸消化颗粒中Fe，Mn和Al的浓度和摩尔比表明，海冰中的Fe颗粒来自多个来源。具体来说，海冰中的铁铝比高于成岩材料中的铁铝比，这表明海冰中富含生物物质。我们的研究表明，海冰中的颗粒状铁应被认为是冰覆盖边缘海中可生物利用的铁的重要来源。