海洋环流与波动重点实验室知识库

印尼贯穿流（Indonesian Throughflow，ITF）是发生在热带海洋的跨洋盆海流，在太平洋和印度洋之间输送着大量的淡水和热量，在全球海洋环流和气候系统中扮演重要角色。风场强迫和浮力强迫是影响ITF多尺度变化的主要机制，但是淡水强迫和盐度效应对ITF多年代变化的影响过程和物理机制却不清楚。本文基于历史水文观测数据、同化数据、再分析数据，以及CMIP6（Coupled Model Intercomparison Project Phase 6）试验等模式数据，研究了不同数据时间窗口内印尼海域内部和海盆尺度的降水和盐度过程在ITF多年代变化中的作用，既对年代际变化特征和多年代长期趋势进行了分析，又对重要季节过程的低频变化进行了讨论，并探讨了未来盐度过程和ITF对全球变暖的响应。

本研究发现，盐度效应是ITF主要分支——望加锡海峡贯穿流（Makassar Strait Throughflow, MST）季节变化的主要控制机制，贡献了MST总季节变化的（69.6±11.7）%。在北半球冬季，经卡里马塔海峡的淡水输运增强，爪哇海局地降水增加，导致爪哇海盐度降低，低盐水北上在望加锡海峡南段形成淡水阻塞，从而激发北向压力梯度异常，引起MST的显著减弱。在北半球夏季，经卡里马塔海峡的淡水输运和爪哇海的局地降水均减少，爪哇海盐度升高，望加锡海峡内出现南向压力梯度异常，导致MST增强。进一步分析发现，经卡里马塔海峡的淡水输运主导了爪哇海淡水收支的季节变化（63.9%），局地降水次之。由于望加锡海峡的淡水阻塞效应与季风有密切关系，其对ITF的影响主要体现在季节时间尺度，在年际和年代际时间尺度上信号较弱。分析发现，在年际和年代际尺度，印尼海域降水和MST体积输运显著负相关（印尼海域降水增加，MST减弱），并分别受厄尔尼诺-南方涛动（El Niño-Southern Oscillation，ENSO）和PDO（Pacific Decadal Oscillation）调控，望加锡海峡内的淡水阻塞效应在ENSO和PDO正位相期间较弱，负位相期间较强。

在多年代时间尺度上，降雨和盐度效应对ITF多年代变化的影响主要受海盆尺度过程的调控。研究发现，在1958–2017年间，盐度效应贡献了ITF体积输运年代际变化的（44.1±15.6）%。在此期间，ITF存在0.11Sv/decade的显著增强趋势，主要是由显著增强的ITF盐容分量（halosteric component）所导致，其热容分量（thermosteric component）呈显著减弱趋势。其中，盐容分量的增强主要是印太降雨的增加引起的：在过去六十年中，印尼海域和赤道西太平洋降水增加，增强了印太海盆上层浮力差，使浮力强迫和盐度效应对印太压力梯度的贡献增加，最终导致ITF盐容分量增强。

降雨和盐度效应对ITF年代际变化的影响与PDO密切相关。PDO正、负位相转换与印尼海域降水与ITF体积输运呈显著负相关：印尼海域降水增加，ITF减弱。尤其显著的是，在1976//77年期间PDO位相由负转正，印尼海域降水和ITF均逆转其长期增强趋势开始减弱；而在90年代中期到大约2013年，PDO位相由正转负，印尼海域降水显著增加，ITF呈现增强趋势。

在更长时间尺度和全球变暖背景下，CMIP6历史模拟（1850–2014年）的ITF未表现出显著长期趋势，但在未来高CO₂排放情景下，随着全球变暖加剧，ssp585试验（2015–2100年）输出的ITF显著减弱，其长期减弱趋势（4.2 Sv/century）由显著减弱的热容ITF分量（8.0 Sv/century）和显著增强的盐容ITF分量（-3.8Sv/century）共同决定。分析表明，在CMIP6历史模拟中，印太海盆降水和海表风应力长期趋势差异较小，导致ITF体积输运的热容和盐容ITF分量长期趋势较弱。而在ssp585试验中，印尼海域和赤道西太平洋降水显著增加，南印度洋降水显著减少，增强的印太海盆间的降水差异增强了ITF上下游区域间的盐度差，增强的浮力强迫强化了盐容压力梯度，最终导致盐度效应增强。ssp585试验中风场的长期趋势则表现为对其平均态的减弱，减弱的赤道太平洋和南印度洋信风导致其对印太压力梯度贡献减小。

在历史模拟（1850–2014年）和ssp585试验（2015–2100年）中，盐度效应在ITF年际变化中的贡献分别为37.6%和39.7%，在ITF年代际变化中的贡献分别为42.9%和44.7%，不同试验中盐度效应对ITF多年代变化的贡献随全球变暖增加。这表明，随着全球变暖加剧，盐度效应在ITF年际和年代际变化中或许将发挥更为重要的作用。

The Indonesian Throughflow (ITF) is the unique gateway connecting the tropical Pacific and Indian Oceans, with strong transports of freshwater and heat content from the Pafic to the Indian Ocean, and plays an important role in the global ocean circulation and climate system. Previous studies suggested that wind and buoyancy forcing play important roles in the ITF variability on multipe time scales, however, the multi-decadal dynamic process and mechanism of precipitation and salinity effect that modulate the ITF are uncertain. In this research, we have used data products based on observation, assimilation, reanalysis, numerical models, and the historical run and ssp585 experiments (following approximately RCP8.5 global forcing pathway but with new forcing based on SSP5) from the CMIP6 (Coupled Model Intercomparison Project Phase 6). We have investigated the roles of salinity associated with precipitation in the Indonesian seas in multi time scales focusing on processes within the Indonesian seas and the basin-scale Pacific-Indian Oceans processes, and the responses of ITF to the global warming as a result of global warming in the future.

The salinity effect is the main controlling mechanism of the seasonal variability of the Makassar Strait Throughflow (MST), the main branch of ITF, and contributes (69.6±11.7) % of the total seasonal variability of MST. In boreal winter, the intensified freshwater transport from the Karimata Strait and precipitation within the Java sea leads to strong freshening in the Java Sea, and strong northward pressure gradient due to buoyancy forcing occurs in the Makassar Strait and leads to a weakened MST. The MST reverses to be intensified in boreal summer due to weakened freshwater transport from the Karimata Strait and precipitation within the Java sea, which leads to increasing salinity in the Java Sea and southward pressure gradient in the Makassar Strait that intensifies the MST. The freshwater transport from the Karimata Strait plays a dominant role in the seasonality of the freshwater flux in the Java Sea, and regional precipitation plays a secondary role. The important role of seasonal freshwater plug in the Makassar Strait closely associated to the monsoon in the MST variability is mainly on the seasonal time scale, with weak influence on the interannual and interdecadal time scales. On the interannual and multi-decadal time scales, the MST transport is negatively correlated to the precipitation in the Indonesian seas, significantly, and is modulated by ENSO (El Niño-Southern Oscillation) and PDO (Pacific Decadal Oscillation) modes, respectively, which leads to stronger MST and seasonality of which over negative pahses of ENSO and PDO, and weaker over positive phases.

On the multi-decadal time scale, the role of precipitation and salinity effect is mainly regulated by basin-scale dynamic processes. Over 1958–2017, the salinity effect contributes (44.1±15.6) % of the total ITF multi-decadal variability, and the significantly intensified halosteric ITF determined the long-term intensified ITF trend of -0.11 Sv/decade, with a long-term weakened thermosteric ITF component. The increasing precipitation in the western tropical Pacific Ocean and the Indonesian seas and decreasing precipitation in the southern Indian Ocean enhance the basin-scale salinity difference in the upper layers, and lead to stronger buoyancy forcing that intensified the Indo-Pacific pressure gradient, which intensifies the salinity effect.

Precipitation in the Indonesian seas that modulated by PDO (Pacific Decadal Oscillation) is negatively correlated to the ITF transport (positive precipitation and negative ITF transport as increase). During the “regime shift” in 1976/77 when the PDO phase turns to be positive, the long-term increasing precipitation in the Indonesian seas and ITF transport reverse to be weakened until the mid-1990s, when PDO turns to be negative, the precipitation and ITF turn to be intensified and reach the maximums around 2013.

On longer time scales and under the background of global warming in the future, the ITF transport from the CMIP6 historical run (1850–2014) indicates no significant trends, however, the ITF transport in the ssp585 experiments indicates a significant decreasing trend of ~4.2Sv/century determined by the intensified halosteric ITF (~-3.8Sv/century) and the weakened thermosteric ITF components (8.0Sv/century) with the global warming. During the historical run, basin-scale differences of precipitation and sea surface wind stress trends between the Pacific and the Indian Oceans are quite weak, which leads to weak and cancelling trends of halosteric and thermosteric ITF components that present an ITF with no significant trend. In the ssp585 experiments, the long-term trends of precipitation have intensified the climatological mean pattern, which has enhanced the salinity difference between the Pacific and the Indian Oceans and intensified the salinity effect. On the other hand, the long-term trends of large-scale wind stress have weakened the climatological mean, which has weakened the Indo-Pacific pressure gradient and led to a weakened ITF.

As global warming intensifies, the roles of salinity effect in the interannual and multi-decadal scales might be more important. The contributions of salinity effect in the inter-annual and multi-decadal variability of the ITF transport are 37.6% and 42.9% in the historical run, and 39.7% and 44.7% in the ssp585 experiments, and the multi-decadal contributions are notably stronger than the inter-annual, with stronger contributions in the ssp585 experiments than that in the historical run.

第1章 绪论                                                                                                      1

1.1 引言                                                                                                          1

1.2 研究现状                                                                                                   2

1.2.1 ITF的观测历史                                                                                        3

1.2.2 ITF的形成和多尺度变化机制                                                                    4

1.2.3 ITF体积输运的长期趋势                                                                         10

1.3 科学问题的提出                                                                                       13

1.4 主要内容和章节安排                                                                                14

第2章 数据和方法                                                                                          15

2.1 研究数据                                                                                                 15

2.1.1 观测数据                                                                                              15

2.1.2 同化、再分析和模式数据                                                                      16

2.1.3 CMIP6数据                                                                                          18

2.2 研究方法                                                                                                 19

2.2.1 114°E经向断面体积输运计算                                                               19

2.2.2 ITF体积输运变化中的温、盐贡献分离                                                    19

2.2.3 热输运和淡水输运计算                                                                          22

第3章 印尼海域内部盐度过程对ITF的影响                                                       23

3.1 MST的季节变化特征                                                                                24

3.2 量化盐度效应在MST季节变化中的贡献                                                     29

3.3 盐度效应影响MST季节变化的机制分析                                                     32

3.4 印尼海域盐度过程在MST年际和年代际变化中的作用                                39

3.5 小结                                                                                                        45

第4章 海盆尺度的盐度过程对ITF年代际变化的影响                                         47

4.1 ITF的年代际变化和长期趋势                                                                     47

4.2 多年代增强的盐度效应                                                                             56

4.3 印太海盆盐度和降水变化对ITF的影响                                                       60

4.4 PDO对ITF年代际变化的影响                                                                    71

4.5 小结                                                                                                        76

第5章 基于CMIP6探究盐度效应对ITF的影响                                                   78

5.1 历史模拟试验                                                                                          78

5.2 未来ssp585试验中的ITF                                                                          84

5.3 未来全球变暖背景下盐度效应的增强                                                        90

5.4 小结                                                                                                      100

第6章 结论和展望                                                                                        102

6.1 主要结论和创新点                                                                                  102

6.1.1 印尼海域内部盐度过程对MST的影响                                                   102

6.1.2 海盆尺度盐度过程在ITF年代际变化中的作用                                        103

6.1.3 更长时间尺度和未来全球变暖背景下的盐度效应                                   105

6.2 创新点                                                                                                   106

6.3 展望                                                                                                      106

参考文献                                                                                                     109

致  谢                                                                                                          119

作者简历及攻读学位期间发表的学术论文与其他相关学术成果                       121