Detection of Pacific tropical water variability by taut-line moorings in the western equatorial Pacific

This study uses temperature and salinity time series acquired with taut-line moorings in the western equatorial Pacific to investigate water mass behavior on the thermocline layer. Basically, it is insufficient to trace water mass variation by the original discrete depth coordinate data because of relatively high variability of density at fixed depth near the thermocline. A reconstruction method based on the density surface motion caused by tidal forcing was used to derive continuous profiles of temperature and salinity from vertically discrete measurements at fixed depths. This method can represent detailed vertical salinity structures and their variation, especially along the potential density surface of 24.8σ_θ, where the salinity maximum of South Pacific tropical water (SPTW) appeared. Variability around the 24.8σ_θ surface at each site was as large as that observed at the surface, which suggests a strong influence of SPTW behavior. High salinity along the 24.8σ_θ surface within the equatorial band of the western Pacific appeared during boreal fall-winter at sites far from New Guinea. In contrast, high salinity appeared near New Guinea during the boreal spring-summer. These features suggest the influence of the New Guinea Coastal Undercurrent. Over longer time scales, several higher salinity events were observed. The most pronounced salinity event occurred during 2007–2008. Interannual variation of the salinity anomaly along the 24.8σ_θ surface was negatively correlated with the Niño 3.4 sea surface temperature anomaly. A long-term salinity anomaly shift from negative to positive occurred around the end of 2002. The relationship with decadal variation in subtropical cell transport is also discussed.     

西太平洋副热带高压变化与赤道太平洋海温场的联系

通过对西太平洋副热带高压变化的多年统计分析,发现其具有明显的年际和年代际变化特征,副高面积和强度均存在3~4 a和11~14 a显著周期,副高西伸脊点存在3~5 a和准13 a显著周期。副高面积和强度变化基本一致,与赤道中东太平洋海表温度（SST）存在显著的正相关关系,西伸脊点与中东太平洋海表温度变化则存在负的相关关系。赤道太平洋不同经度的SST与副高变化存在明显的差异,赤道中太平洋SST异常与副高变化的关系最为密切,东太平洋相对偏弱,而西太平洋呈现相反的相关关系。由此可以认为,赤道中太平洋异常SST变化是影响副高变化的关键区域。根据它们之间存在的密切关系,通过回归分析,建立了它们二者之间的回归方程,对2013年春夏季副高的强度和西伸脊点位置变化进行了预测,为2013年我国汛期降水预测提供一定的参考。     

Effects of interannual salinity variability on the dynamic height in the western equatorial Pacific as diagnosed by Argo

In this paper, interannual variations of the ocean dynamic height over the tropical Pacific are diagnosed using three-dimensional temperature and salinity fields from Argo profiles, with a focus on the...     

热带太平洋西部及赤道暖水区的初级生产力

描述了对热带太平洋西部(1991年11月WOCE调查)及赤道暖水区(1992年11月至1993年2月的TOGA-COARE调查)的叶绿素a分布和初级生产力(C),及其与理化环境的关系.西部海域叶绿素a平均总量达19.79mg/m2,暖水区为2.168mg/m2;暖水区的潜在初级生产量高于西部海域,量值分别为228mg/(m2·d)和171mg/(m2·d),次表层最大值成为调查海域水体叶绿素a分布的一个明显特点.叶绿素a总量平面分布趋向表明:高生物量主要位于巴士海峡邻近、菲律宾以及伊里安岛的近岸站位,此外,在2°～4°N之间的观测区.低生物量主要位于外洋海域.生物量的分布与不同海域的物理过程变化有关,而海水涌升可能是导致温度、盐度和营养盐分布产生变化,并因而导致高生物量的一个重要的物理过程.     

Primary productivity in the western tropical Pacific and equatorial warm waters

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中太平洋西部赤道潜流的水文分析

本文利用我国1979年1～2月和4～6月在中太平洋西部的考察资料,分析了赤道潜流区的温、盐分布及赤道潜流的流系特征,并给出了潜流区及其周围海区的流场结构。     

Dispersion relation of internal waves in the western equatorial Pacific Ocean

Based mainly on TOGA COARE data, that is, the CI''D data from R/V Xiangyanghong No.5 (Pu et al.,1993),the temperature and current data from the Woods Hole mooring and other deep current data, the layered numerical profiles of buoyancy frequency and mean current components are figured out.A numerical method calculating internal wave dispersion relation without background shear current, used by Fliegel and Hunkins (1975),is improved to be fit for the internal wave equation with mean currents and their second derivatives.The dispersion relations and wave functions of the long crested internal wave progressing in any direction can be calculated inveniently by using the improved method.A comparison between the calculated dispersion relation in the paper and the dispersion relation in GM spectral model of ocean internal waves (Garret and Munk, 1972) is performed.It shows that the mean currents are important to the dispersion relation of internal waves in the western equatorial Pacific Ocean and that the currents make the wave progressing co-directional with (against) the currents stretched (shrink).The influence of the mean currents on dispersion relation is much stronger than that of their second derivatives, but that on wave function is less than that of their second derivatives.The influences on wave functions result in the change of vertical wavenumber, that is, making the wave function stretch or shrink.There exists obvious turning depth but no significant critical layer absorption is found.     

N2 fixation variability in the oligotrophic Sulu Sea, western equatorial Pacific region over the past 83 kyr

N₂ fixation is an important biological process that adds new nitrogen to oceans and plays a key role in modulating the oceanic nitrate inventory. However, it is not known how, when, and where N₂ fixation rates have varied in response to past climate changes. This study presents a new record of nitrogen isotopic composition (δ¹⁵N) over the last 83 kyr from a sediment core (KH02-4 SUP8) taken in the Sulu Sea in the western equatorial Pacific region; data allow the N₂ fixation variability in the sea to be reconstructed. Sediments, sinking, and suspended particulate organic matter (POM) all have lighter isotopic values compared to the δ¹⁵N values of substrate nitrate (av. 5.8‰) in North Pacific Intermediate Water. These lighter δ¹⁵N values are regarded as reflecting N₂ fixation in the Sulu Sea surface water. A δ¹⁵N mass balance model shows that N₂ fixation rates were significantly enhanced during 54–34 kyr in MIS-3 and MIS-2. It has been speculated that higher interglacial denitrification rates in the Arabian Sea and the eastern tropical Pacific would have markedly decreased the global oceanic N inventory and contributed to the increase in N₂ fixation in oligotrophic regions, but such a model was not revealed by our study. It is possible that changes in N₂ fixation rates in the Sulu Sea were regional response, and accumulation of phosphate in the surface waters due to enhanced monsoon-driven mixing is thought to have stimulated enhancements of N₂ fixation during MIS-3 and MIS-2.     

赤道太平洋次表层海温距平的EEOF分析及与厄尔尼诺的关系

通常气候变量场在时间上存在着显著的自相关及交叉相关,扩展的经验正交函数(ExtendedEOF,以下记作EEOF)分析是在经典的EOF基础上发展而来的,它同时考虑了要素的空间和时间相关性,可以得到变量场的移动性分布结构。本文通过对赤道太平洋次表层海温距平(SOTA)场的EEOF分解,发现第一特征向量是关于ElNino的模态,它反映了ElNino的发生持续消亡的整个过程,对应的时间系数(第一主分量)与Nino3指数有很好的同时相关。第二特征向量是关于西太平洋暖池的模态,它反映了西太平洋暖池从暖位相到冷位相(同时东太平洋从冷位相到暖位相)的过程,第二主分量与滞后6～10个月的Nino3指数有很好的相关性。这两个主分量不但有助于了解赤道太平洋海温异常的过程,而且为厄尔尼诺的预报提供了重要线索。     

Influence of ENSO variability on sinking-particle fluxes in the northeastern equatorial Pacific

A time-series sediment trap was operated from July 2003 to July 2008 at a station located in the 10°N thermocline ridge of the northeastern equatorial Pacific (10°30′N, 131°20′W), with the aim of understanding variations in natural background sinking-particle flux and the influence on such fluxes of ENSO (El Niño-Southern Oscillation). Each one of weak El Niño, moderate El Niño and moderate La Niña were observed during the monitoring period. During non-ENSO periods, total mass fluxes varied from 4.1 to 36.9 mg m⁻² d⁻¹, with a distinct seasonal variation, ranging from an average flux of 14.0 mg m⁻² d⁻¹ in the warm season (June-November) to 25.3 mg m⁻² d⁻¹ in the cold season (December-May). This seasonal fluctuation was characterized by a distinct difference in CaCO₃ flux between the two seasons. The enhanced particle fluxes during the cold season are attributed to the supply of nutrient-enriched subsurface water by wind-driven vertical mixing, supported by a simultaneous reduction in sea surface temperature and enhanced trade winds. The weak El Niño event occurred in the monitoring period had no recognizable effect on particle fluxes in the study area, but the moderate El Niño event was accompanied by a significant reduction in particle fluxes to 60% of the average background value in the warm season. In contrast, particle fluxes during the moderate La Niña increased to a maximum value of 129.9 mg m⁻² d⁻¹, almost three times the average background value. Organic carbon and biogenic silica fluxes were most sensitive to the El Niño and La Niña conditions. The observed variations of particle fluxes are synchronized with those of chlorophyll-a, suggesting primary productivity for the main cause of flux change. The present data indicate that marked seasonal variability in background fluxes commonly exceeds the variability associated with ENSO and post-ENSO signals, which should be taken into account when evaluating the influence of ENSO on sinking particle fluxes in the 10°N thermocline ridge area.     

西赤道太平洋暖池区光合色素分布及其对浮游植物群落的指示作用

利用光合色素的生物标志性可以在"纲"水平上表征浮游植物群落结构。依托大洋科学考察第20航次和21航次,通过对西赤道太平洋不同区域5个站位的HPLC藻类色素分析及CHEMTAX程序因子分析,获取了暖池区光合色素及浮游植物群落的垂直分布信息。结果显示在寡营养的暖池区,玉米黄素(Zeaxanthin)及乙二烯叶绿素a(DV Chl a)与叶绿素a浓度呈显著的正相关,浮游植物群落结构以蓝细菌、原绿球藻及定鞭金藻为优势藻纲,按对生物量的贡献率原绿球藻大于蓝细菌大于定鞭金藻的。蓝细菌和原绿球藻分布在真光层不同深度,而在营养盐丰富的次表层优势浮游藻类为定鞭金藻。     

The multifractal characters of temperature finestructures in the equatorial western Pacific Ocean

INTRODUCFIONTheknowledgeoffinestructureandmicrostructureplaysamajorroleintheresearchofoceanicdiapycnalmixing.Sofarastheliteratureisconcerned,finestructuresareroughlydefinedassmallstructuresdistributedonverticalscalesfromImto100m(Munk,1981),whereasmicrostructureshavesmallerscales.Forsimplicity,thesetwofeatureswillbecalledfinestructures ThestudywassupportedbytheNationalNaturalaudienceFoundationofChinaundercontractsNo.49376257,No.4950/6071andNo.49676275,andtheResearchFundfortutorialPngr…     

用小波变换研究赤道西太平洋温度细结构

使用小波变换分析了赤道西太平洋暖池区的CTD资料的温度序列,表明垂向温度细结构具有自相似特征,有可能使用分数维模型来描述.计算了温度序列的奇异性指数及其概率分布,发现此分布具有近似普适的形式.非零概率的负指数意味着温度剖面可能存在奇异点.对经小波变换后的序列的周期性统计表明周期△和尺度α遵从幂律标度△～αβ,β≈1.这提示着细结构背后可能存在简单的二分串级机制.小波变换的振幅反映了温度脉动的强弱.据此可以确定脉动能量的垂向分布和能谱密度,和传统方法的比较表明小波能谱较为光滑,有利于精确测定谱斜率.     

南海次表层盐度的低频变化及与太平洋年代际振荡的关系

南海是西北太平洋最大的边缘海, 是联系北太平洋和北印度洋的关键通道。黑潮北上经过吕宋海峡时会将来自西太平洋的信号传入南海, 进而影响南海的水动力环境。研究了南海次表层盐度的空间分布特征、低频变化规律及其与太平洋年代际振荡(Pacific Decadal Oscillation, PDO)的关系, 并进一步探究了次表层盐度近年来的变化。结果显示: 1)南海次表层高盐水的位势密度主要介于24~26σ_θ, 受次表层气旋式环流所驱动, 盐度气候态空间分布北高南低, 以吕宋海峡处为起点, 呈逆时针自北向南逐渐降低。2)次表层盐度低频变化显著, 与PDO呈显著的正相关关系。当PDO处于正位相时, 吕宋海峡处西向平流输送加强, 次表层盐度升高; 当PDO处于负位相时, 吕宋海峡处西向平流输送减弱, 次表层盐度降低, 盐度的变化受到水平环流场的直接影响。3)近年来, 南海次表层盐度呈现先降低后升高再降低的趋势, 滞后PDO约10个月, 2006— 2014年初, 盐度呈下降趋势; 2014—2017年初, 盐度呈上升趋势, 且上升速率远大于先前下降的速率; 2017年后盐度再次逐渐降低。     

Response of western equatorial Pacific to a westerly wind burst

INTRODUCTIONWindsWithhorizontalshearareliabletoinduceoceanicupwelling.Forexample,theresPOnseoftheoceantotheatmOSphericjetasshowninFig.Ihascausedacurlthatinducesupwellinginoneregion,downwellinginanother.IftheoceanisinfinitelydeepandhasconstantBrunt--V...     

Why are rings regularly shed in the western equatorial Atlantic but not in the western Pacific?

The western equatorial Atlantic is characterized by the formation and shedding of 3–4 large anticyclonic rings per year. These rings originate from the North Brazil Current which, in response to the vanishing wind stress curl (over the ocean interior), retroflects and turns eastward at around 4°N. After their formation and shedding the rings propagate toward the northwest along the South American coast carrying an annual average of about 4Sv. As such, the rings constitute an important part of the meridional heat flux in the Atlantic.The same cannot be said, however, of the western equatorial Pacific. Here, the situation is entirely different even though the South Equatorial Current retroflects at roughly the same latitude as its Atlantic counterpart, the North Brazil Current. Although the South Equatorial Current retroflection is flanked by two quasi-permanent eddies (the so-called Halmahera and the Mindanao eddies), these eddies are an integral part of the current itself and are not shed. Consequently, they are not associated with any meridional heat flux. An important question is, then, why the two oceans behave in such a fundamentally different way even though the source of the rings, the retroflected currents, are very similar in the two oceans.To answer this question, the two oceans are compared using recently developed analytical and numerical models for the western equatorial oceans. It is first pointed out that, according to recent developments in the modelling of the western equatorial Atlantic, the North Brazil Current retroflection rings are formed, shed and drift to the west because, in the Atlantic, this is the only way by which the momentum flux of the approaching and retroflecting current can be balanced. In this scenario, the northwestward flow force exerted by the approaching and retroflecting North Brazil Current (analogous to the force created by a rocket) is balanced by the southwestward force exerted by the rings as they are formed (analogous in some sense to the kickback associated with a firing gun).On the other hand, in the western equatorial Pacific, the formation and shedding of rings is unnecessary because the southward flowing Mindanao Current provides an alternative mechanism for balancing the northward momentum flux of the South Equatorial Current. This implies that it is the absence of a counter current (such as the Mindanao) in the western Atlantic that causes the formation and shedding of North Brazil Current rings. A remaining difficulty with the above scenario is that most colliding and retroflecting currents (i.e. the Mindanao and South Equatorial currents) are not “balanced” in the sense that they cannot be stationary but rather must drift along the coast. It is shown that, in the case of the western Pacific, the long-shore migration is arrested by the Indonesian Throughflow which allows the “unbalanced” fraction of the approaching currents to leak out into the Indian Ocean. This resolves the above difficulty and allows the retroflection to be approximately steady.     

Relationship between time-series diatom fluxes in the central and western equatorial Pacific and ENSO-associated migrations of the Western Pacific Warm Pool

The water masses of the central and western equatorial Pacific can be divided into two parts: the Western Pacific Warm Pool (WPWP) and the Equatorial Upwelling Region (EUR). The behavior of the WPWP plays a significant role in global climate changes such as the El Niño-Southern Oscillation (ENSO), and it drastically modifies the oceanographic conditions in the area every few years. It is important to evaluate changes in time-series diatom fluxes during both the El Niño and the La Niña events. As a part of the Global Carbon Cycle and Related Mapping based on Satellite Imagery (GCMAPS) Program, time-series sediment trap moorings were deployed and recovered along the Equator at seven stations (Sites MT1–MT7) during five R/V Mirai cruises in the central and western Pacific during January 1999–January 2003. The entire length of this study is divided into two phases depending on the oceanographic conditions: the La Niña event (1999 and 2000); and the El Niño event (2002). Site MT3 was located in the WPWP and Sites MT5–MT7 were in the EUR. Annual means of total diatom fluxes increased towards the east in each year. The fluxes observed at Sites MT4–MT6 decreased from the La Niña event to the El Niño event. However, the fluxes observed at Site MT3 in 2001 and 2002 were higher than those in 2000. Total diatom fluxes showed different seasonal patterns at all sites. The diatom assemblages in the WPWP differed from those of the EUR. Pennate diatoms (e.g., Nitzschia bicapitata, Thalassionema nitzschioides) dominated in the WPWP, while the relative abundances of centric diatoms (e.g., Rhizosolenia bergonii, Azpeitia spp., Thalassiosira spp.) were higher than those of pennate diatoms in the EUR. The diatom fluxes during the La Niña event reflected seasonal oscillation of the WPWP in spatial extent. At Site MT3 during El Niño, terrestrial materials appeared to have been transported by subsurface currents, which might be a secondary influence on total diatom fluxes. The spatial extent of the WPWP reached Site MT7 in 2002, when total diatom fluxes decreased in the sediment traps located in the eastern region including Site MT7. Therefore, we conclude that the relationships between the ENSO and diatoms fluxes in the western and central equatorial Pacific can be explained by the geographic (west–east) expansion or contraction of the WPWP.