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热带西太平洋海山浮游植物群落结构特征研究
Alternative TitleThe phytoplankton community structure on seamounts in the tropical Western Pacific
代晟
Subtype博士
Thesis Advisor孙晓霞
2021-05-21
Degree Grantor中国科学院大学
Place of Conferral中国科学院大学海洋研究所
Degree Name理学博士
Keyword海山 浮游植物 热带西太平洋 群落结构 初级生产力
Abstract

热带西太平洋上层水体常年存在严重的分层,是典型的寡营养海域,同时该海域也是海山分布最集中的区域之一。但是目前该海域海山的浮游植物研究仍处于起步阶段,海山浮游植物群落结构特征及海山对浮游植物的作用尚不明确。本研究系统揭示了热带西太平洋海山浮游植物群落结构特征及其与环境因子之间的关系,对有关浮游植物“海山效应”的相关假说和理论进行了检验,为研究热带寡营养海域的海山生态系统特征、初级生产过程、地球化学循环等奠定了基础。

本文对热带西太平洋的4座海山的浮游植物的生物量(以叶绿素a代表)、粒级结构、类群组成和初级生产力情况进行了5个航次的调查研究Y3海山:201412月;M2海山:20163月;C4海山:20178月、20195月;Kocebu海山:20183月),在此基础上浮游植物群落结构特征与环境因子的关系进行了分析;此外,对比研究了海山站位和周边站位的浮游植物群落结构的差异,并结合海山存在的物理过程和营养盐变化,分别分析了4海山的物理-化学-生物耦合过程研究得到以下结论:

       1. 热带西太平洋海山表层叶绿素a含量很低,随水深增加呈先增加后降低的趋势,叶绿素a最大值主要位于75 – 150 m,初级生产力水平较低。

受长期分层现象的影响,热带西太平洋海山区上层水体长期处于寡营养状态,浮游植物在上层水体的生长主要受到营养盐的限制,5个航次的表层叶绿素a浓度均维持在0.05 mg/m3左右,平均水柱叶绿素a的浓度范围为11.2 – 19.4 mg/m2。在温跃层,营养盐浓度逐渐升高,但是光照强度降低,导致了叶绿素a最大值通常位于温跃层起始位置的下方20 – 30 m处,叶绿素最大值的变化范围约为0.1 – 0.35 mg/m3。初级生产力在Y3M2C4海山均低于100 mgC/(m2×d)在北部的Kocebu海山最高,约为150 mgC/(m2×d)

       2. 温跃层以上以微微型的原绿球藻、聚球藻为优势类群,其次为微型浮游植物定鞭藻,随着水深的增加,聚球藻的优势地位逐渐被金藻和隐藻所取代,小型浮游植物硅藻、甲藻等对叶绿素a的相对贡献率在全水层较低。

M2C4Kocebu海山,微微型浮游植物如聚球藻、原绿球藻对叶绿素a的贡献率都达到了0.85左右,以定鞭藻、金藻和隐藻为主的微型浮游植物,其对叶绿素a的贡献率在0.1左右,而像硅藻、甲藻等小型浮游植物的叶绿素a浓度很低。在Y3海山,微微型浮游植物依然是优势类群,但其对叶绿素a的贡献率在0.55左右,微型浮游植物的贡献率接近0.3,小型浮游植物的贡献率在0.15左右。浮游植物类群组成的垂直变化为:温跃层以上以微微型的原绿球藻、聚球藻为主要的优势类群,其次为微型浮游植物定鞭藻,随着水深的增加,聚球藻的优势地位逐渐被金藻和隐藻所取代,小型浮游植物硅藻、甲藻等对叶绿素a的相对贡献率在全水层较低。浮游植物类群组成主要受光照和营养盐的影响,也与各类群的生活方式及生存策略相关。

3. 热带西太平洋海山区浮游植物群落结构在相同区域不同月份差异明显,而在同一月份,不同纬度差异不明显。

12月小型和微型浮游植物叶绿素a的相对贡献率最高,但叶绿素a和初级生产力水平最低。3月、5月和8月粒级结构及类群组成相近,3月和5月的叶绿素a水平要高于8月。在3月份,20 ˚N 左右的Kocebu海山表层叶绿素a浓度要稍高于10 ˚NM2海山,但叶绿素a最大值没有明显差异,两海山的粒级结构也没有区别。

4. Y3中等深度海山、C4浅海山及Kocebu深海山观测到浮游植物的生物量显著升高的现象。

       虽然在Y3C4浅海山及Kocebu深海上升流均受到分层的削弱,但由于浮游植物的分布较深,上升流补充的营养盐仍然在真光层底部对浮游植物的生物量起到了促进作用。其中,Y3海山的A断面和2017C4海山的两个断面均发现了浮游植物被显著增强的信号,在有些山坡站位,其叶绿素a最大值是周边站位的2倍以上。Y3海山和C4海山都存在较强的物理过程,其中Y3海山山顶处可能存在涡旋结构,而C4海山可能有泰勒帽存在。在叶绿素a的高值区观测到了等温线的抬升和营养盐向上输送的信号,存在很好的物理化学生物耦合过程。

       Kocebu深海山观测到等温线在山顶处产生的波动似乎被传递到温跃层,且营养盐在山顶站位有明显的抬升。不过与Y3C4海山不同的是,真光层观测到叶绿素a高值斑块并不位于山顶,而位于下游站位,与营养盐的200 m水柱浓度高值区有很好的耦合,可能是因为产生于Kocebu深海山的湍流或涡对水体的滞留或捕捉作用不能延伸至真光层,发生垂直混合的海水很快被流冲到下游,从而在下游形成高营养盐和高叶绿素a的斑块。

M2海山没有发现海山效应,通过对比其与Y3C4海山的区别,发现自东向西的北赤道流与主要呈南北走势的Y3C4海山有更强的相互作用,而水流方向与东西走势的M2海山平行,相互作用较弱。结合以往的研究,本文认为当洋流流向与海山走势垂直时,相互作用较强,更容易产生海山效应

5. 海山对浮游植物类群结构及分布存在一定影响。

Y3C4Kocebu海山发现了一些小型浮游植物或微型植物的叶绿素a浓度及贡献率升高的现象,如在Kocebu海山小型浮游植物叶绿素a在山顶处浓度最高,是周边海域的3倍左右,硅藻在两座山峰之间A5 – 8站位有较高的生物量;相似性分析结果表明,在2019C4海山浮游植物类群结构与对照组站位存在显著性差异。

       海山的物理过程(泰勒柱和上升流等)不仅可以一定程度上促进浮游植物的生长,像振幅较大的内波、次级环流以及埃克曼底边界流等过程也可以一定程度上加速浮游植物或颗粒物向海洋深处转移。考虑到西太平洋海山数量众多,海山对该区域的碳通量或地球化学循环的潜在贡献值得进一步关注和研究。

Other Abstract

The tropical western Pacific, one of the most oligotrophic seas on Earth, has a large number of seamounts. However, the phytoplankton study of seamount in this sea area is at the initial stage, and the community structure characteristics of seamount and the effect of seamount on phytoplankton are still unclear. The study of phytoplankton in seamount in this region is not only helpful to understand the characteristics of seamount ecosystem and primary production process in tropical oligotrophic waters, but also can support for understanding the mechanism of "seamount effect".

In this paper, phytoplankton biomass (in terms of chlorophyll a), group composition and primary productivity of four seamounts in the western tropical Pacific were investigated for five cruisesY3: December 2014M2: March 2016C4: August 2017 and May 2019KocebuMarch 2018. Based on this, the relationships between phytoplankton community structure characteristics and environmental factors were analyzed. In addition, the comparison of phytoplankton community structure between seamount and surrounding stations was performed, and the physical, chemical and biological coupling processes of each seamount were analyzed. The study drew the following conclusions

1. At study area, the concentration of chlorophyll a (Chl a) at surface layer is very low, and it increases above isotherms and then decreases with the increase of water depth. The deep Chl a maximum (DCM) is mainly located at 75-150 m, and the level of primary productivity is low.

The growth of phytoplankton in the upper water was mainly restricted by nutrients, and the concentrations of Chl a in the surface water were about 0.05 mg/m3, and the water column integrated concentration of Chl a ranged from 11.2 to 19.4 mg/m2. In the thermocline, nutrients gradually increased with depth, but the light intensity was low, resulting in the DCM were located 20 – 30 m below the initial depth of the thermocline, and the variation range of the (DCM) was about 0.1 – 0.35 mg/m3. Primary productivity at Y3, M2 and C4 seamounts were less than 100 mgC/(m2×d), and at Kocebu Seamount, it was about 150 mgC/(m2×d).

2. The dominant groups were picoplankton such as prochlorophytes and cyanobacteria (mainly Synechococcus) were the dominant groups, and followed by nanoplankton such as haptophytes, chrysophytes, cryptophytes.

At M2, C4 and Kocebu seamounts, picophytoplankton such as prochlorophytes and Synechococcus were the dominant groups, contributing approximately 0.85 of total Chl a. Nanophytoplankton such as haptophytes, chrysophytes, cryptophytes were followed, contributing about 0.10 of Chl a, and micro-phytoplankton such as diatoms and dinoflagellates contributed lowest Chl a. At Y3 seamount, picophytoplankton was still the dominant group, but its relative contribution to Chl a was lower than the other seamounts, and the relative contributions of nanophytoplankton and micro-phytoplankton were higher.

Cyanobacteria and prochlorophytes were dominated above the thermocline, and below thermocline, the dominant position of cyanobacteria was gradually replaced by chrysophytes and cryptophytes. Prochlorophytes was dominant group in the whole euphotic layer, and the haptophytes occupied a certain proportion in the euphotic layer.

3. In the sampling area, the changes of phytoplankton group composition were obvious in temporal dimensions.

The Chl a was lowest in December, and followed by August, and the Chl a concentrations were higher in March and May. The primary productivities were close in March, May and August, and it was the lowest in December. Micro and nanophytoplankton had highest relative contribution rate of Chl a in December, and the size-fractionated structures of phytoplankton were similar in March, May, and August. In the same month, the surface Chl a at Kocebu seamount was slightly higher than that at M2 seamount, while the the size-fractionated structures and DCM showed no significant difference between the two seamounts.

4. Enhanced phytoplankton was observed at Y3 Seamount, C4 Seamount and Kocebu Seamount.

Although the upwellings in Y3, C4, and Kocebu seamount were weakened by stratification, the nutrients supplemented still promoting phytoplankton biomasses at the bottom of eutrophic layer, due to the deep distribution of phytoplankton. Enhancements of phytoplankton were observed at section A of Y3 Seamount and both sections of C4 Seamount in 2017, with the DCM at some seamount stations were twice that of the surrounding water. There might were eddy at the peak of the Y3 Seamount, and "Taylor cap" may exist at C4 Seamount. At stations which existed high Chl a patches, the uplifted isotherm and nutrients was observed, which showed good physico-chemical-biological coupling process. The fluctuations of isotherms near the peak of Kocebu Seamount seemed to be transferred to the thermocline, and there is an obvious uplift of nutrients above the peak. Unlike Y3 and C4 seamounts, the high Chl a patches were observed at the downstream stations instead of the peak station, and that was consistent with the 200 m water column concentrations of nutrients. It may be because the effect of retention or capture of deep seamount will not extend to the euphotic layer, and the nutrient-supplemented water was rushed to the downstream in a short time, and formed high nutrient and Chl a pathes there.

There is no "seamount effect" in M2 Seamount. Comparing to M2 Seamount, Y3 and C4, which are elongated along the N-S axis, seem to interact more strongly with westward-flowing currents than does M2, and these interactions serve to drive the biological responses.

5. Seamounts affect the phytoplankton groups composition and distribution.

at Y3, C4 and Kocebu seamount, some nano- or micro-phytoplankton Chl a concentrations increased, For example, above the summit of Kocebu Seamount, the concentration of micro-Chl a was the highest, which was about three times that in the surrounding water, and Diatoms had a higher biomass at the A5-8 station between the two peaks. The results of similarity analysis showed that phytoplankton group composition at C4 seamount were significant differences from that at control stations in 2019.

Seamounts can not only promote the growth of phytoplankton by upwellings and Taylor column, but also accelerate the transfer of phytoplankton or organic particles to the deep ocean by some vertical processes such as internal waves with large amplitude, secondary circulation, and Ekman bottom boundary ow. Given there are numerous seamounts in the tropical Western Pacific, the potential contribution of seamounts to carbon fluxes or geochemical cycles in the region deserves further attention and study.

 

Subject Area海洋科学
MOST Discipline Catalogue理学::海洋科学
Language中文
Table of Contents

1  引言... 1

1.1  浮游植物概述... 1

1.2  海山研究概述... 3

1.2.1  海山的基本特征... 4

1.2.2  海山研究历史... 5

1.2.3  海山物理过程... 6

1.2.4  海山浮游植物研究... 8

1.3  研究区域的环境特征... 10

1.4  研究内容及意义... 11

2  材料与方法... 14

2.1  采样站位... 14

2.2  环境因子... 17

2.3  分粒级叶绿素a. 17

2.4  浮游植物类群组成... 17

2.5  初级生产力... 18

2.6  数据分析与作图... 19

3  Y3海山浮游植物群落结构特征... 20

3.1  Y3海山环境因子... 20

3.2  Y3海山分粒级叶绿素a. 22

3.3  Y3海山海山效应”. 25

4  M2海山浮游植物群落结构特征... 29

4.1  M2海山环境因子... 29

4.2  M2海山分粒级叶绿素a. 31

4.3  M2海山对浮游植物的影响... 32

5  C4海山浮游植物群落结构特征... 34

5.1  20178C4海山浮游植物群落结构特征... 34

5.1.1  环境因子... 34

5.1.2  分粒级叶绿素a. 37

5.1.3  浮游植物类群组成... 38

5.1.4  2017C4海山海山效应”. 43

5.2  20195C4海山浮游植物群落结构特征... 46

5.2.1  环境因子... 46

5.2.2  分粒级叶绿素a. 50

5.2.3  浮游植物类群组成... 53

5.2.4  物理化学生物耦合... 58

6  Kocebu海山浮游植物群落结构特征... 61

6.1  环境因子... 61

6.2  分粒级叶绿素a. 64

6.3  浮游植物类群组成... 66

6.4  “海山效应”. 70

7  不同海山浮游植物群落结构特征的对比研究... 74

7.1  4座海山浮游植物群落结构的共同特征... 74

7.1.1  生物量和初级生产力水平... 74

7.1.2  叶绿素最大层... 76

7.1.3  浮游植物类群组成... 79

7.1.4  类群组成的垂直变化... 80

7.2  不同海山浮游植物群落结构特征的差异... 82

7.3  不同海山的海山效应”. 84

8  结论与创新... 89

8.1  结论... 89

8.2  创新点... 91

8.3  不足与展望... 91

参考文献... 92

  ... 100

... 104

作者简历及攻读学位期间发表的学术论文与研究成果    106

Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/170721
Collection胶州湾海洋生态系统国家野外研究站
Recommended Citation
GB/T 7714
代晟. 热带西太平洋海山浮游植物群落结构特征研究[D]. 中国科学院大学海洋研究所. 中国科学院大学,2021.
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