Collaborative research: Sediment geochemical control on ocean acidification and carbon budget in a river dominated shelf system

在许多沿海地区，化肥冲入河流导致藻类大量繁殖。在较深的水域或沉积物中消耗藻类产生的有机物质会消耗氧气，导致许多地方（如墨西哥湾北部）出现低氧“死区”。这种营养输入、藻类生长和氧气损失的过程被称为富营养化。有机物质的消耗也会将溶解的二氧化碳释放到水中，并直接或间接地促进海洋酸化。为了理解和预测这种对酸化的影响，重要的是要了解水柱中有机物质的降解与沉积物中的降解有多少，它在季节和年份之间的变化有多大，以及它是如何受到风暴等过程的影响的。在这个项目中，来自三个机构的调查人员及其研究生和本科生将在墨西哥湾北部进行实地观察和计算机建模的结合，以解决这些问题。他们将通过当地的推广活动与公众分享他们的成果，并通过与当地教师的伙伴关系和课程开发与路易斯安那州的中学生分享他们的成果。该研究将采用观测和数值模拟相结合的方法，以更好地了解陆架沉积物在季节尺度上驱动底水溶解无机碳（DIC）和pH动态和酸化中的作用。过去和现在的研究都没有解决这一机制。由于目前缺乏知识，很难为该地区建立一个全面的碳预算。拟议的研究将(i)量化底栖生物通量在导致底水酸化的DIC生产中的作用；（ii）确定底栖生物DIC随季节变化通量对酸化底水的重要性；（iii）探讨偶发性再悬浮事件在调节DIC底栖生物通量中的重要性。利用最先进的底栖着陆器平台，将在路易斯安那大陆架进行季节性采样，记录原位沉积物和底水耗氧率、有机物再矿化率、沉积物氧渗透深度、底栖生物DIC通量和伴随的pH值下降。海底流速和浊度也将与沉积物孔隙水和水柱采样一起记录。作为这些详细的近床和海底观测的补充，我们将利用最近开发的流体动力学、沉积物输运和生物地球化学耦合模型（HydroBioSed），将观测到的底栖生物通量估计扩大到年尺度。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In many coastal regions fertilizer washed down rivers leads to high production of algae. Consumption of organic material produced by the algae in deeper waters or in sediments consumes oxygen, leading to low-oxygen "dead zones" in many places like the northern Gulf of Mexico. This process of nutrient input, algal growth, and loss of oxygen is called eutrophication. Consumption of the organic matter also releases dissolved carbon dioxide into the water, and contributes directly and indirectly to ocean acidification. In order to understand and predict this impact on acidification, it is important to understand how much of the organic matter degradation occurs in the water column versus in the sediments, how variable it is between seasons and years, and how it is affected by processes such as storms that disturb the bottom sediments. In this project, investigators from three institutions along with their graduate and undergraduate students will conduct a combination of field observations and computer modeling to address these questions in the northern Gulf of Mexico. They will share their results with the public through local outreach activities, and with secondary school students in Louisiana through partnerships and curriculum development with local teachers.The proposed research will use a combined observational and numerical modeling approach to better understand the role of shelf sediment in driving bottom water dissolved inorganic carbon (DIC) and pH dynamics and acidification at seasonal scales. Past and current studies have not addressed this mechanism. This current lack of knowledge makes it difficult to construct a comprehensive carbon budget for this region. The proposed research will (i) quantify the role of benthic fluxes in DIC production leading to acidification in the bottom water; (ii) determine the importance of the seasonally changing benthic DIC flux in acidifying the bottom water; and (iii) explore the importance of episodic resuspension events in modulating benthic fluxes of DIC. Seasonal sampling will be carried out in Louisiana shelf using state of the art benthic lander platform to record in situ sediment and bottom water oxygen consumption rates, organic matter remineralization rates, sediment oxygen penetration depths, benthic fluxes of DIC and accompanying pH drop. Bottom current velocities and turbidity will also be recorded in conjunction with sediment porewater and water column sampling. Complementing these detailed near-bed and seabed observations, we will utilize a recently developed coupled hydrodynamics, sediment transport and biogeochemistry model (HydroBioSed) to scale up observed estimates of benthic fluxes to an annual scale.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.