The Ultimate Limiting Nutrient for Oceanic Primary Production

为了了解地球气候系统是如何运作的，我们需要了解是什么控制了海洋的初级生产。这在很大程度上决定了大气和海洋之间碳的分配，从而决定了地球温室效应的强度。海洋初级产品还为海洋-大气系统增加氧气，并为其他海洋食物网提供食物供应。浮游植物的数量和更替速度影响着海底白垩等生物成因岩石的形成速度。只有了解对过去海洋初级生产水平的控制，才有可能全面了解地球历史。长期以来，人们一直认为，从基本原理出发，最终限制养分（ULN）是磷，它的供应在很长一段时间内决定了海洋的生产力。其中一个原因是一些固氮生物利用二氮作为氮源的能力，如果硝酸盐耗尽，它们就会大量繁殖。许多模拟研究（例如b[1]）得出结论，ULN是磷。然而，其他研究（例如[2]）表明，铁是代替ULN的，铁是约30%海洋表面初级生产的接近限制养分，其稀缺性经常限制固氮[3]。

In order to know how Earth's climate system works, we need to understand what controls oceanic primary production. This largely determines the partitioning of carbon between the atmosphere and ocean, and hence the strength of Earth's greenhouse effect. Oceanic primary production also adds oxygen to the ocean-atmosphere system as well as providing the food supply for the rest of marine food webs. Phytoplankton populations and rates of turnover affect how quickly biogenic rocks such as chalks are formed at the bottom of the ocean. A full understanding of Earth history is only possible with understanding of controls on past ocean primary production levels.It has long been argued, from first principles, that the ultimate limiting nutrient (ULN), the one whose supply dictates ocean productivion over long timescales, is phosphorus. One reason for this is the ability of some organisms, the nitrogen-fixers, to utilize dinitrogen as their nitrogen source and flourish if nitrate runs out. Many modelling studies (e.g. [1]) have concluded that the ULN is phosphorus. However, other studies (e.g. [2]) suggest that iron, the proximate limiting nutrient for primary production across ~30% of the ocean surface, and whose scarcity often restricts nitrogen fixation [3], is instead the ULN.