副热带东北太平洋混合层深度及潜沉率季节循环对全球变暖的响应

王艺珊; 夏瑞彬

doi:10.12284/hyxb2022202

副热带东北太平洋混合层深度及潜沉率季节循环对全球变暖的响应

doi: 10.12284/hyxb2022202

王艺珊^1,,
夏瑞彬^{1, 2, ,}

1.
南京信息工程大学海洋科学学院，江苏南京 210044
2.
南京信大安全应急管理研究院，江苏南京210044

基金项目: 国家自然科学基金青年科学基金（41606217）；自然资源部海洋环境信息保障技术重点实验室开放基金。

详细信息

作者简介:
王艺珊（2001-），女，山东省威海市人，主要从事物理海洋学方面的研究。E-mail: 201983450039@nuist.edu.cn

通讯作者:
夏瑞彬，主要从事物理海洋学、海气相互作用研究。E-mail: xiarb@nuist.edu.cn

中图分类号: P722；P733.1
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出版历程
- 收稿日期: 2021-12-04
- 修回日期: 2022-07-13
- 网络出版日期: 2022-07-29
- 刊出日期: 2022-10-01

Responses of seasonal cycles of the mixed layer depth and subduction rate to global warming in the subtropical Northeast Pacific

Wang Yishan^1
,,
Xia Ruibin^{1, 2
, ,}

1.
School of Marine Science, Nanjing University of Information Science and Technology, Nanjing 210044, China
2.
Nanjing Xinda Institute of Safety and Emergency Management, Nanjing 210044, China

摘要

摘要: 本文利用第五次国际耦合模式比较计划（CMIP5）中的地球系统模式（ESM2M），结合Argo观测数据和由Ishii等整理的再分析数据集，分析现在气候背景和辐射强迫极端增强下副热带东北太平洋海域（10°～40°N，110°～160°W）混合层深度（MLD）和潜沉率的季节变化特征，研究其对全球变暖的响应。在现在气候背景下，二者最大值均出现在冬季。潜沉率的主要贡献项存在显著的季节变化差异，1−5月主要受侧向潜沉率的变化控制，6−12月则由风应力旋度导致的埃克曼抽吸速度变化主控。全球变暖后，季节循环信号的主控要素不变。但受风应力旋度等要素变化的影响，各季节的MLD减小，大值区范围收缩。由于冬季减小幅度远大于夏季，MLD季节波动幅度（振幅）显著变小。长期看，MLD呈现持续变浅的趋势，其空间不均匀性减弱引起的MLD锋面减弱是控制侧向潜沉率减弱，最终导致总潜沉率减弱的关键。由于埃克曼抽吸速度的季节变化信号对全球变暖的响应较小，因此总潜沉率在冬季受全球变暖的影响最为强烈。上述结果表明，构成潜沉率的两个关键要素对总潜沉率的贡献比例是随着季节变化而改变的：冬季MLD锋面强盛时期，侧向潜沉率的影响将显著增强。全球变暖前后二者截然不同的变化会显著改变潜沉率的季节循环振幅，可能对该区域模态水的形成和输运产生深远的影响。
- 混合层深度 /
- 潜沉率 /
- 副热带东北太平洋 /
- 全球变暖
Abstract: Based on the Earth System Model (ESM2M) of the Coupled Model Intercomparison Project 5 (CMIP5), combined with Argo observation data and the reanalysis dataset compiled by Ishii et al., this paper presents the seasonal variation characteristics of mixed layer depth (MLD) and subduction process in the subtropical Northeast Pacific Ocean (10°−40°N, 110°−160°W) under the present climate background and extreme enhancement of radiative forcing are presented, to study its response to global warming. Under the current climate background, both of MLD and subduction rate reach their maximum values in winter. The main contribution items of subduction rate have significant seasonal variation. From January to May, the subduction rate is mainly controlled by the change of lateral induction rate, while from June to December, the main mechanism is the change of Ekman pumping velocity controlled by wind stress curl. After global warming, the main control elements of seasonal signals remain unchanged. However, under the influences of wind stress curl and other factors, the MLD in each season decreased and the range of the core maximum region shrinks. As the decrease in winter is much larger than that in summer, the seasonal fluctuation range (amplitude) of MLD is significantly smaller. In the long run, MLD shows a trend of continuous shallower, and the weakening of MLD front caused by the weakening of its spatial non-uniformity is the key to control the weakening of lateral induction rate and eventually lead to the weakening of the subduction rate. Since the seasonal variation signal of Ekman pumping velocity has little response to global warming, subduction rate is most strongly affected in winter. The results show that the contribution proportion of the two key factors to the subduction rate changes with the seasons: when the MLD front is strong in winter, the influence of the lateral induction rate will be significantly enhanced. The different variations of the two factors before and after global warming will significantly change the seasonal amplitude of the subduction rate, which may have a profound impact on the formation and transport of mode water in the region.
- mixed layer depth /
- subduction rate /
- subtropical Northeast Pacific /
- global warming

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图 1 Argo观测数据混合层深度的季节变化

Fig. 1 The seasonal variation of mixed layer depth from the Argo dataset

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图 2 2月份Argo数据空间平均的温度、盐度和密度垂直廓线与混合层深度

选取混合层深度大值范围为27.5°～29.5°N，137.5°～139°W；自定义混合层深度为水平实线，数据集自带混合层深度为水平虚线

Fig. 2 Vertical profile of thermohaline, density and mixed layer depth from Argo dataset in February

The range of the maximum mixed layer depth is 27.5°−29.5°N，137.5°−139°W; the solid horizontal line is the customized mixed layer depth, the dashed horizontal line is the built-in mixed layer depth of the dataset

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图 3 副热带东北太平洋海域混合层深度

Fig. 3 Mixed layer depth in the subtropical Northeast Pacific area

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图 4 混合层深度的季节变化

取值范围为25°～35°N，120°～150°W；图例中数字表示该数据或模式结果的年平均混合层深度

Fig. 4 Seasonal variation of the mixed layer depth

The range is 25°−35°N，120°−150°W; the numbers in the legend represent the annual mean mixed layer depth in the observation data or model simulation

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图 5 辐射强迫极端增强前后潜沉率（左）、侧向潜沉率（中）、埃克曼抽吸速度（右）对比图

a−c. 2月历史实验；d−f. 2月辐散强迫极端增强情景实验（RCP 8.5）；g−i. 7月历史实验；j−l. 7月辐散强迫极端增强情景实验（RCP 8.5）；等值线为混合层深度，单位：m

Fig. 5 Subduction rate (left), lateral induction rate (center) and Ekman pumping velocity (right) before and after the enhancement of radiative forcing

a−c. The historical experiments in February; d−f. the representative concentration pathway climate forcing scenarios experiments (RCP 8.5) in February; g−i. the historical experiments in July; j-l. the representative concentration pathway climate forcing scenarios experiments (RCP 8.5) in July; the contour is mixed layer depth, unit: m

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图 6 潜沉率（SR）、侧向潜沉率（LD）与埃克曼抽吸速度（WE）季节变化

潜沉率大值区范围为21.5°～23.5°N，135°～145°W

Fig. 6 Seasonal variation of subduction rate (SR), lateral induction rate (LD) and Ekman pumping velocity (WE)

The range of large subduction region is 21.5°−23.5°N, 135°−145°W

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图 7 风应力旋度在辐射强迫增强前后空间差值

差值为辐散强迫极端增强情景实验（RCP 8.5）值减历史实验值；正（负）值代表向下的风应力旋度增强（减弱）

Fig. 7 Spatial difference of wind stress curl before and after the enhancement of radiative forcing

The difference is the value of representative concentration pathway climate forcing scenarios experiment (RCP 8.5) minus the value of historical experiment; positive (negative) value represents downward wind stress curl enhancement (weakening)

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图 8 混合层深度年平均（a）及季节循环振幅（b）长期变化

Fig. 8 Long-term variation of annual average mixed layer depth (a) and seasonal cycle amplitude (b)

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图 9 2月侧向潜沉率（a）、埃克曼抽吸速度（b）、潜沉率（c）及对应的季节循环振幅（d−f）长期变化

潜沉率大值区范围为21.5°～23.5°N，135°～145°W

Fig. 9 Long-term variation of lateral induction rate (a), Ekman pumping velocity (b), subduction rate (c) in February and corresponding seasonal amplitude (d−f)

The range of large subduction region is 21.5°−23.5°N，135°−145°W

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