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Oxygen Seasonality, Utilization Rate, and Impacts of Vertical Mixing in the Eighteen Degree Water Region of the Sargasso Sea as Observed by Profiling Biogeochemical Floats
Global Biogeochemical Cycles ( IF 5.2 ) Pub Date : 2021-02-17 , DOI: 10.1029/2020gb006824
Samuel Billheimer 1 , Lynne D. Talley 1 , Todd R. Martz 1
Affiliation  

Seasonal oxygen structure and utilization in the Sargasso Sea are characterized using nine profiling floats with oxygen 2021 sensors (years 2005–2008), deployed in an Eighteen Degree Water (EDW) experiment (CLIMODE). During autumn‐winter when the mixed layer is deepening, oxygen increases from the surface to the base of the EDW at 400 m. During spring‐summer, oxygen decreases except between the seasonal pycnocline and compensation depth, creating the seasonal shallow oxygen maximum layer (SOMax) with oxygen production of 0.04 μmol kg−1·day−1. In the underlying seasonal oxygen minimum (SOMin), the oxygen utilization rate (OUR) is 0.10 μmol kg−1·day−1, decreasing with depth to 0.04 μmol kg−1·day−1 in the EDW. Remineralization in May to August is double that of August to November. The Sargasso Sea is a net carbon producer; estimated annual export production from the top 100–250 m is 2.9 mol C m−2 and from the top 400 m is 4.2 mol C m−2. Below the EDW, oxygen decreases seasonally at the same time as in the EDW, indicating remineralization down to 700 m. However, on isopycnals in this deeper layer, oxygen increases during May to September, likely due to lateral advection from nonlocal surface outcrops. Summer shoaling of these isopycnals creates this paradox. The complex vertical oxygen structure in the upper 200 m enables important vertical diffusive flux that modifies the OUR calculated from oxygen change. Ignoring mixing underestimates maximum remineralization by 19% and underestimates maximum net production by 88%. However, vertical mixing is negligible in the deeper layers, so the associated total integrated remineralization error is 5%–9%.

中文翻译:

仿生生物地球化学浮标观测到的藻类海域十八度水域中的氧气季节性,利用率和垂直混合的影响

利用在18度水(EDW)实验(CLIMODE)中部署的9个带有氧气2021传感器(2005年至2008年)的轮廓浮标,对Sargasso海中的季节性氧气结构和利用进行了表征。在秋冬季,当混合层不断加深时,在400 m处氧气从EDW的表面到底部增加。在春季-夏季,除季节性比诺可林和补偿深度之间的氧气减少外,形成了季节性浅层氧气最高层(SOMax),其氧气产量为0.04μmolkg -1 ·天-1。在基本的季节性最低氧气量(SOMin)中,氧气利用率(OUR)为0.10μmolkg -1 ·day -1,随深度降低到0.04μmolkg -1 ·day -1在EDW中。5月至8月的再矿化是8月至11月的再矿化的两倍。萨加索海是一个净碳生产国。最高100-250 m的估计年出口产量为2.9 mol C m -2,最高400 m的估计年出口产量为4.2 mol C m -2。在EDW以下,氧气与EDW同时出现季节性下降,表明再矿化至700 m。然而,在这个较深层的等渗层中,氧气可能在5月至9月期间增加,这可能是由于非局部表面露头引起的横向对流所致。夏季对这些异戊二烯的浅沙化就产生了这种悖论。上部200 m中复杂的垂直氧结构使得重要的垂直扩散通量改变了根据氧变化计算出的OUR。忽略混合会导致最大的再矿化度低估19%,而导致最大净产量低估88%。但是,在较深的层中垂直混合可以忽略不计,因此相关的总综合再矿化误差为5%–9%。
更新日期:2021-03-26
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