本月晚些时候，NOAA将宣布其对墨西哥湾缺氧的“死区”将有多大的预测。今年的预测将基于一个合奏，该合奏结合了四个不同的计算机模型的结果。但是什么是死区？研究人员如何预测它的规模？
海湾中的低氧区或死区是氧气水平极低的区域。之所以称为死区，是因为氧气很少，以至于鱼类和贝类（包括经济重要的物种，例如虾）无法在那里生存。
“低氧区可能会导致居住在海湾地板上的生物，例如螃蟹，但许多鱼能够避免它。”丹·奥贝诺（Dan Obenour），北卡罗来纳州的环境工程师一个新模型这将是NOAA合奏缺氧预测的一部分。“无论如何，该区域大大降低了许多鱼类的栖息地，威胁渔业。”
创建一个死区
缺氧是由因素汇合而引起的，但是两个最重要的变量是密西西比河倾倒在海湾和海湾水域的分层的营养。
Each year the Mississippi dumps a massive load of nutrients into the Gulf, largely stemming from agricultural runoff across the Mississippi River Basin. These nutrients serve as fertilizer for aquatic plant life, resulting in algal blooms. As the algae decomposes, or is eaten and excreted by animals, it creates enormous amounts of organic matter that sink to the bottom of the Gulf.
有机物的这种增加为吞噬它的细菌提供了一种smorgasbord。但是那些细菌消耗的氧气 - 随着细菌在新发现的餐票上蓬勃发展，它们会消耗越来越多的水中的氧气。
Obenour说：“简而言之，养分是推动低氧区域创造的燃料。”但是水的分层使该区域持续并生长。
有争议的是所谓的“ pycnocline”，它是海湾表面温暖，更新鲜的水，在海湾深处遇到更冷，更咸的水。寒冷的咸水比温暖的淡水要密集得多，在两层之间形成了明显的区别。
两个水层密度的差异很重要，因为密度的差异越大，在整个pycnocline上的混合越少。这意味着表面层中的氧气更少进入更深的水域 - 无法补充藻类饮食细菌所用的氧气。
这也是为什么你们每一个死区消失ar. Each autumn, when surface temperatures cool and winds increase, surface waters are able to mix with deeper waters again – and the oxygen levels return to normal.
预测缺氧
为了帮助渔业经理和其他公职人员做出计划决策，NOAA每年都会进行预测，以预测低氧区的规模。
今年标志着NOAA预测将首次由多种模型的结果组成，这些模型结合了密西西比州，天气和海洋状况的养分负荷数据。
每个模型都采用略有不同的方法来计算驱动低氧区域的动态 - 这是一件好事。
Obenour说：“通过结合多个模型，我们希望创建一个更强大的预测，以解决不确定性的能力，” Obenour说。
“例如，”奥伯努尔说，“我开发了海湾相关部分的平均风速的原因。风会影响到缺氧形成的海湾浅层部分的营养和淡水流量。其他模型在制定季节性预测时并未明确考虑风，但是它们可能比我的模型更详细地考虑其他过程。”
Other research institutions that contributed to the hypoxia forecast modeling effort include the University of Michigan, Louisiana State University, the Louisiana Universities Marine Consortium, the College of William & Mary’s Virginia Institute of Marine Science, Texas A&M University, and the U.S. Geological Survey.
It’s not yet clear what NOAA’s forecast for the 2015 dead zone will look like. But at least now you’ll have a good idea of what went into it.
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鲍勃（Bob）有几个想法：
1) As the article notes, the nitrate and phosphorous of importance is the outflow from the river. This rapid influx of nutrients is what drives the sudden increase in bacterial populations. Regular supplies from the ocean aren’t enough to fuel such growth.
2) I’ll conjecture that there are two factors involved for the main channel (mississippi) versus the atchafalaya and sabine pass. One side is, the main channel carries much more water than the others. That leads to larger bacterial blooms, and to a stronger stable lid over the warmer, saltier water below. Second side is, the mississippi outlet is near deep water, while the other two are shallow water. Waves breaking in shore have much more chance to mix in the nutrients from below in the extensive shallow water zones. Deeper water means less wave mixing.
Why don’t they measure nitrate and phosphorus during the spring in the Gulf of Mexico at the areas where hypoxia tends to occur? Wouldn’t this show a true relation between the nutrients and the algal growth? Also why does the hypoxia happen around the Atchafalaya and Sabine outlets and not the Mississippi outlet?