海水硝酸盐跃层深度计算方法研究  

Quantification of nitracline depth in seawater

作　　者：孟宇 陈双玲 MENG Yu;CHEN Shuangling(Second Institute of Oceanography,MNR,Hangzhou 310012,China;State Key Laboratory of Satellite Ocean Environmental Dynamics,Hangzhou 310012,China)

机构地区：[1]自然资源部第二海洋研究所,浙江杭州310012 [2]卫星海洋环境动力学国家重点实验室,浙江杭州310012

出　　处：《海洋学研究》2023年第3期1-13,共13页Journal of Marine Sciences

基　　金：国家自然科学基金项目(42030708,42276184,41906159)。

摘　　要：硝酸盐是海洋中浮游植物生命活动可利用的主要氮形态,其跃层深度(Z_(N))会直接影响硝酸盐垂向输送、海洋初级生产力以及海洋碳循环。随着海洋观测技术的不断发展,硝酸盐剖面数据的采集呈现多样化,包括船基CTD观测和生物地球化学浮标BGC-Argo自动观测等,且垂向采样分辨率差异较大(CTD较低,BGC-Argo较高)。针对不同采样数据,亟需对硝酸盐跃层深度计算方法进行系统且定量化的对比分析研究。本文利用西北太平洋历史船测CTD数据和BGC-Argo浮标数据,采用差值法、梯度法和阈值法分别计算对应硝酸盐跃层深度。研究结果表明:就单一硝酸盐剖面,基于BGC-Argo数据,差值法计算的Z_(N)与目视解译的Z_(N)相差仅为0.2 m,阈值法次之为20.0 m,梯度法相差最大为202.8 m;基于CTD数据,差值法计算的Z_(N)与目视解译的Z_(N)相差2.0 m,阈值法相差49.0 m,梯度法相差155.0 m。相较于梯度法和阈值法,差值法计算的Z_(N)与目视解译的Z_(N)相差最小。根据误差统计分析结果发现,基于BGC-Argo数据,三种方法计算得到的Z_(N)与目视解译的Z_(N)均呈现良好相关性,其中差值法计算结果误差最小(R^(2)为0.77,RMSE为28.48 m),阈值法的R^(2)为0.64,RMSE为34.85 m,梯度法的R^(2)为0.52,RMSE为53.80 m;对于CTD数据,由于其垂向采样分辨率较低,三种方法计算得到的Z_(N)与目视解译的Z_(N)相差较大,但相比于梯度法和阈值法,差值法的误差仍最小(R^(2)为0.81,RMSE为16.13 m),阈值法的R^(2)为0.47,RMSE为27.65 m,梯度法的R^(2)为0.42,RMSE为36.41 m。通过对比分析各方法的特点和差异性,初步探究了各方法的适用性,可为深入研究硝酸盐垂向分布特征和向上输运过程提供科学参考。Nitrate is the main nitrogen form available for phytoplankton life activities in the ocean,and its nitracline depth(Z_(N))directly affects the vertical transport of nitrate and the ocean primary productivity,and then further influences the carbon cycle.With the advancement of ocean observation technologies,the profile data of nitrate have been collected in diversified ways,such as ship-based CTD observations and BGC-Argo automatic observations.The vertical sampling resolution of these techniques varies significantly(the vertical sampling resolution of CTD is lower than that of BGC-Argo).In view of different sampling data,it is urgent to conduct systematic and quantitative comparative analysis and study on the computing methods of Z_(N).In this study,three different methods:difference method,gradient method and threshold method,are adopted to compute the corresponding Z_(N)by using the historical ship-based CTD data and BGC-Argo buoy data in the Northwest Pacific Ocean.The results show that in the case of single nitrate profile,based on BGC-Argo data,the difference between observed Z_(N)and the Z_(N)calculated by difference method is only 0.2 m,followed by threshold method is 20.0 m and gradient method is 202.8 m at most.Based on CTD data,the difference between observed Z_(N)and Z_(N)calculated by difference method is 2.0 m,the threshold method is 49.0 m,and the gradient method is 155.0 m.Compared with the gradient method and threshold method,the difference between the Z_(N)calculated by the difference method and the observed Z_(N)is the smallest.According to the results of statistical error analysis,it is found that the Z_(N)calculated by the three methods based on BGC-Argo data show a good correlation with the observed Z_(N).Among them,the error of difference method is the smallest(R^(2)=0.77,RMSE=28.48 m).The R^(2)and RMSE of threshold method are 0.64 and 34.85 m,and the R^(2)and RMSE of gradient method are 0.52 and 53.80 m.For CTD data,due to its low vertical sampling resolution,the Z_(N)calculated by the thre

关 键 词：硝酸盐跃层深度 梯度法 差值法 阈值法 西北太平洋 BGC-Argo CTD 

分 类 号：P734.4[天文地球—海洋化学]