海水中碳酸根的原位测定方法研究

The carbonate concentration in seawater is one of the most important parameters in the inorganic carbon system. It is also essential to evaluations of the mineralization rates of marine calcifiers and the dissolution rate of calcite and aragonite both on the seafloor and in the water column. For example, the most ecologically significant changes in seawater chemistry that accompany ocean acidification are the decreases in carbonate concentration that have a major impact on calcifying organisms. Thus, highly sensitive and accurate methods are urgently demanded for the determination of carbonate concentration in seawater. However, most of the current available carbonate data is indirect and calculated from other carbon dioxide parameters, which may not be accurate themselves because of the limit of analytical methods. The current direct method for carbonate analysis is based on manual operation, which cannot be applied for field and in situ analysis. Therefore, the aim of this study is to establish the automatic analytical method for the in situ determination of carbonate in seawater and get high resolution carbonate data in the water column for ocean carbon research. The principle chemistry is based on the UV spectrophotometric monitoring of the fast reaction between carbonate and divalent lead. The proposed work will be very essential and supportive for scientific research on marine carbon cycle and ocean acidification. The research contents include: 1) establishment of analytical method--- optimization of reagent consumption, perturbation effect of lead addition, evaluation of in situ parameters on the reaction, correction of salinity, pressure and temperature for the final result, etc; 2) integration of in situ profiler--- design of flow analysis manifold and photometric detection system, manufacture of electronic system for pump and valve control, integration of carbonate profiler, etc; 3) evaluation of profiler and in situ application--- comprehensive evaluation for the accuracy and precision, quality control of the system in real seawater during cruises, comparison of the results using the proposed method and manual method, etc.

海水中碳酸根浓度是计算碳酸钙饱和度、描述海洋钙化生物的矿化速率、方解石/文石的溶解速率和海水碳酸盐体系的重要参数。现有的碳酸根数据大多由间接法、即通过测定CO2系统的其他参数推导获得，因此其他参数测定中存在的问题和误差将进一步放大。而碳酸根的直接测定法的自动化程度低、无法现场原位应用。本项目将针对该领域的薄弱环节，研究二价铅离子和不同浓度碳酸根快速反应时的实时紫外吸收光谱，建立海水中碳酸根测定的原位自动分析方法，现场获取高分辨率的水柱垂直剖面碳酸根浓度数据，为海洋碳循环和海洋酸化研究提供技术支持。研究内容包括：从紫外光谱图上提取碳酸根与铅反应的瞬时信息，用于计算碳酸根浓度；研究试剂、温度、压力等因素对反应的影响，提出优化值和校正方程；采用流动分析和多波长检测等先进技术，设计快速响应、高精度的碳酸根原位剖面仪，现场监测全水柱碳酸根浓度的变化过程等。

海水中碳酸根浓度是计算碳酸钙饱和度、描述海洋钙化生物的矿化速率、方解石/文石的溶解速率和海水碳酸盐体系的重要参数。现有的碳酸根数据大多由间接法、即通过测定CO2系统的其他参数推导获得，因此其他参数测定中存在的问题和误差将进一步放大。而碳酸根的直接测定法的自动化程度低、无法在线分析。本项目针对该领域的薄弱环节，研究二价铅离子和不同浓度碳酸根快速反应时的实时紫外吸收光谱，建立海水中碳酸根测定的自动分析方法和仪器，现场获取高分辨率的碳酸根浓度数据。实验室测试表明，该仪器测定人工海水样品的精密度为1.1%（n=13）。在珊瑚饲养缸的现场观测实验中，仪器测定结果与总碱度和溶解无机碳计算值的偏差为-2.4±15.7 μmol/kg （n=14）。该仪器在南中国海用于近两周的海水表层走航测定及两个剖面离散样品的现场分析，在实验前期测定结果偏差分别为-0.5±5.0 μmol/kg（n=31，走航样品）和2.1±5.7 μmol/kg（n=22，垂直剖面样品），实验后期偏差有增大趋势。航次后针对此现象的可能原因进行了分析，发现通过优化测定程序和仪器现场校正可以提高数据质量。使用改进后的碳酸根自动分析仪在墨西哥湾、美国东岸等海域进行走航观测，走航期间仪器运行状态良好，获得了大量碳酸根的浓度数据，为海洋酸化等的研究提供重要的数据支撑。此外，在本项目的支持下，海水中其他参数自动测定方法也取得较大进展，如pH、磷酸盐、铵氮、硝氮、亚硝氮、六价铬等。这些参数自动测定方法的建立对于海洋碳循环、海洋酸化等的研究具有重要意义，同时这一系统的成功应用，为碳酸根的现场测定打下基础。.在本项目的资助下，申请人已正式发表高水平第一或者通讯作者SCI论文8篇，其中包括JCR 1区论文1篇，2区论文5篇，3区论文2篇。以上论文本基金均有标注。此外，申请人设计组装了6台可应用于现场分析的自动化仪器，授权专利4项，做到创新与实用并重。