Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA.
Department of Biology, University of Oregon, Eugene, OR, USA.
Geobiology. 2019 Nov;17(6):628-642. doi: 10.1111/gbi.12357. Epub 2019 Sep 8.
Permanently anoxic regions in the ocean are widespread and exhibit unique microbial metabolic activity exerting substantial influence on global elemental cycles and climate. Reconstructing microbial metabolic activity rates in these regions has been challenging, due to the technical difficulty of direct rate measurements. In Cariaco Basin, which is the largest permanently anoxic marine basin and an important model system for geobiology, long-term monitoring has yielded time series for the concentrations of biologically important compounds; however, the underlying metabolite fluxes remain poorly quantified. Here, we present a computational approach for reconstructing vertical fluxes and in situ net production/consumption rates from chemical concentration data, based on a 1-dimensional time-dependent diffusive transport model that includes adaptive penalization of overfitting. We use this approach to estimate spatiotemporally resolved fluxes of oxygen, nitrate, hydrogen sulfide, ammonium, methane, and phosphate within the sub-euphotic Cariaco Basin water column (depths 150-900 m, years 2001-2014) and to identify hotspots of microbial chemolithotrophic activity. Predictions of the fitted models are in excellent agreement with the data and substantially expand our knowledge of the geobiology in Cariaco Basin. In particular, we find that the diffusivity, and consequently fluxes of major reductants such as hydrogen sulfide, and methane, is about two orders of magnitude greater than previously estimated, thus resolving a long-standing apparent conundrum between electron donor fluxes and measured dark carbon assimilation rates.
海洋中的永久性缺氧区域广泛存在，并表现出独特的微生物代谢活性，对全球元素循环和气候产生重大影响。由于直接测量速率的技术难度，这些区域的微生物代谢活性速率的重建一直具有挑战性。在卡里亚科盆地（Cariaco Basin），它是最大的永久性缺氧海洋盆地，也是地球生物学的重要模型系统，长期监测已经产生了生物重要化合物浓度的时间序列；然而，潜在的代谢物通量仍然难以量化。在这里，我们提出了一种基于一维时变扩散传输模型的计算方法，该模型包括对过拟合的自适应惩罚，用于根据化学浓度数据重建垂直通量和原地净生产/消耗速率。我们使用这种方法来估计卡里亚科盆地次透光带水柱（深度 150-900 m，2001-2014 年）内的氧、硝酸盐、硫化氢、铵、甲烷和磷酸盐的时空分辨通量，并确定微生物化学生产活动的热点。拟合模型的预测与数据非常吻合，大大扩展了我们对卡里亚科盆地地球生物学的认识。特别是，我们发现扩散系数，以及主要还原剂（如硫化氢和甲烷）的通量，比以前估计的要大两个数量级，从而解决了电子供体通量和测量的暗碳同化率之间长期存在的明显难题。
