Department of Earth System Science, University of California at Irvine, Irvine, CA, 92617, USA.
Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, 04544, USA.
Nat Commun. 2018 Nov 19;9(1):4868. doi: 10.1038/s41467-018-06892-w.
Variation in ocean C:N:P of particulate organic matter (POM) has led to competing hypotheses for the underlying drivers. Each hypothesis predicts C:N:P equally well due to regional co-variance in environmental conditions and biodiversity. The Indian Ocean offers a unique positive temperature and nutrient supply relationship to test these hypotheses. Here we show how elemental concentrations and ratios vary over daily and regional scales. POM concentrations were lowest in the southern gyre, elevated across the equator, and peaked in the Bay of Bengal. Elemental ratios were highest in the gyre, but approached Redfield proportions northwards. As Prochlorococcus dominated the phytoplankton community, biodiversity changes could not explain the elemental variation. Instead, our data supports the nutrient supply hypothesis. Finally, gyre dissolved iron concentrations suggest extensive iron stress, leading to depressed ratios compared to other gyres. We propose a model whereby differences in iron supply and N-fixation influence C:N:P levels across ocean gyres.
海洋颗粒有机物质（POM）的 C:N:P 变化导致了对潜在驱动因素的竞争性假说。由于环境条件和生物多样性的区域共变，每个假说都能很好地预测 C:N:P。印度洋提供了一个独特的正温度和养分供应关系来检验这些假说。在这里，我们展示了元素浓度和比率如何在日变化和区域尺度上变化。POM 浓度在南部回旋流中最低，在赤道上升，在孟加拉湾达到峰值。元素比率在回旋流中最高，但向北接近 Redfield 比例。由于原绿球藻主导着浮游植物群落，生物多样性的变化不能解释元素的变化。相反，我们的数据支持养分供应假说。最后，回旋流溶解铁浓度表明存在广泛的铁胁迫，导致与其他回旋流相比，比率下降。我们提出了一个模型，即铁供应和固氮的差异影响整个海洋回旋流的 C:N:P 水平。
