Self‐Shading and Meltwater Spreading Control the Transition From Light to Iron Limitation in an Antarctic Coastal Polynya
Self‐Shading and Meltwater Spreading Control the Transition From Light to Iron Limitation in an Antarctic Coastal Polynya
复制标题
自遮蔽和融水扩散控制南极沿海冰间湖从光限制到铁限制的转变
DOI：
10.1029/2020jc016636
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Jones, D. C.
中科院分区：
文献类型：
--
作者：
Twelves, A. G.;Goldberg, D. N.;Henley, S. F.;Mazloff, M. R.;Jones, D. C.
南极西部的多特森冰架(DIS)正在经历快速的基底融化，原因是温暖的、含盐的环极深水(CDW)侵入大陆架。来自DIS的融化水被认为影响邻近的阿蒙森海波利尼亚(ASP)的生物，那里的单位面积净初级生产力(NPP)是南大洋所有沿海波利尼亚中最高的。然而，铁和光在浮游植物春季水华的共生中的相对重要性仍然知之甚少。在这项模拟研究中，我们首先研究了冰架影响NPP的机制，然后绘制了铁光共生的时空格局，最后研究了铁和光供应的环境驱动因素。我们发现，冰架融化导致更高的上层海洋铁浓度，这既是由于从冰川床携带的沉积物释放铁，也间接是通过浮力驱动的倾覆环流将铁从CDW拉到表面。与抑制冰架融化的实验相比，这两种机制都会增加NPP。然后，我们表明，浮游植物的自我遮荫反馈推迟了水华的发生，与光穿透独立于叶绿素的实验相比，峰值NPP降低了80%。与光限制相比，浮游植物吸收造成的铁限制更重要的是a)在季节的后期，b)在水柱中更高，c)离冰架更远。敏感性实验表明，CDW侵入体的变异性通过控制富铁熔体的水平扩散来影响NPP。
Dotson Ice Shelf (DIS) in West Antarctica is undergoing rapid basal melting driven by intrusions of warm, saline Circumpolar Deep Water (CDW) onto the continental shelf. Meltwater from DIS is thought to influence biology in the adjacent Amundsen Sea Polynya (ASP), which exhibits the highest net primary productivity (NPP) per unit area of any coastal polynya in the Southern Ocean. However, the relative importance of iron and light in colimiting the spring phytoplankton bloom in the ASP remains poorly understood. In this modeling study we first investigate the mechanisms by which ice shelves impact NPP, then map spatio‐temporal patterns in iron‐light colimitation, and finally examine the environmental drivers of iron and light supply. We find that ice shelf melting leads to greater upper ocean iron concentrations, both directly due to release of iron from sediments entrained at the glacier bed, and indirectly via a buoyancy‐driven overturning circulation which pulls iron from CDW to the surface. Both of these mechanisms increase NPP compared to experiments where ice shelf melt is suppressed. We then show that the phytoplankton self‐shading feedback delays the bloom and reduces peak NPP by 80% compared to experiments where light penetration is independent of chlorophyll. Compared to light limitation, iron limitation due to phytoplankton uptake is more important a) later in the season, b) higher in the water column, and c) further from the ice shelf. Finally, sensitivity experiments show that variability in CDW intrusion influences NPP by controlling the horizontal spreading of iron‐rich meltwater.
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