Institutional Repository of Key Laboratory of Marine Ecology & Environmental Sciences, CAS
|Alternative Title||Exploration of "seamount effect" on the biogenic elements in the seamount waters of the Western Pacific Ocean|
|Place of Conferral||中国科学院海洋研究所|
1. Y3、M4和M5海山区真光层中生源要素含量显著增高，存在“海山效应”，而M2和Magellan海山区无“海山效应”。 “海山效应”受北赤道流（NEC）与海山地形的相互作用的影响，在Y3和M5海山A断面最为显著，由于M4海山周围存在环流，A和B断面均存在“海山效应”。
在Y3和M5海山区，各站位200 m水柱中颗粒态氮磷的平均浓度在A断面中出现从山顶向东西两侧逐渐降低的“海山效应”，而Y3海山区的B断面及M5海山区的B和C断面则未出现该现象。5个海山区所在区域的0-200 m的上层水体主要受自东向西的NEC的影响，故在东西方向的A断面更易引起上升流，进而使颗粒态氮磷等参数出现显著的隆起。M4海山区中A和B断面中都出现了山顶附近颗粒态氮磷的平均浓度较高的“海山效应”，即在M4海山周围不仅存在上升流，还存在显著的环流，造成了无机态氮磷硅以O站位为中心向四周“辐射降低”以及颗粒态氮磷A和B断面山顶浓度较高的“海山效应”的现象。
NPTW中，浮游植物的光合作用和微生物的分解作用占主导作用。5个海山区的NPTW中分布着DCML，是浮游植物活动最为剧烈的区域，造成了与之密切的NO2-N和DOC大量增加。该区域有机物大量生成，使颗粒态有机氮（PON）/总颗粒态氮（TPN）和颗粒态有机磷（POP）/总颗粒态磷（TPP）显著提高，同时浮游植物的代谢可能造成了DIN: PO4-P和SiO3-Si: DIN转变成磷和硅限制。微生物分解有机物消耗O2，导致 溶解氧（DO）相较于SW分别下降了1.32、0.55、0.10、1.54和0.55 mg/L，表观耗氧量（AOU）也显著增加。 DIC受到了浮游植物光合作用和微生物分解作用的共同影响。浮游植物光合作用造成DIC的降低。然而DIC浓度总体随水深的增加不断增加，说明有机物分解对DIC的补充速率远高于DIC的消耗速率。
NPIW中，微生物的分解作用占主导作用。该区域与大洋低氧带的范围基本重合，微生物分解有机物大量消耗DO，导致生源要素从有机态向无机态的迅速转化，颗粒物中的PON/TPN和POP/TPP逐渐降低。同时，DO的急剧降低对氮循环意义重大，有利于反硝化作用充分进行，作该过程中间产物的NO2-N迅速降低，NO3-N加速转化为N2溢出，使得DIN: PO4-P降低，而SiO3-Si: DIN升高。
DW中，微生物的分解作用趋于结束，生源要素受大洋热盐环流的影响大。大洋热盐环流携带富含DO的南极DW使得5个海山区DO出现明显回升，而AOU则显著降低。同时，由于水体的交换，大洋热盐环流还对生源要素的分布产生深远的影响。特别地，颗粒态氮磷和POC浓度略有升高，一方面可能受沉积物再悬浮作用的影响，另一方面也可能受到大洋热盐环流水体交换的影响。同时，微生物的分解作用趋于结束使PON/TPN、POP/TPP、 DIN: PO4-P和SiO3-Si: DIN保持稳定。而NO2-N作为反硝化作用的中间环节，也因该区域减弱的反硝化作用而浓度较低并保持稳定。DW中，较低的水温和较大的压强使得CaCO3加速溶解，使得该区域的DIC持续增高。
3. 发现M4海山区有典型的泰勒柱现象，该海山区等温线和等盐度线、流速和流向数据及理论计算共同证实了泰勒柱的存在。同时，泰勒柱导致了该海山区周围营养盐、叶绿素a（Chl a）和异养细菌等值线的隆起，使200 m水深以上水柱环境参数的平均浓度在山顶附近显著高于山坡水域。
当水流流经海山时，形成的水文动力过程十分复杂，而泰勒柱是其中最重要的水文特征之一。基于等温线和等盐度线隆起的上升流，基于水流数据的反气旋环流以及基于海山周围环境条件的理论计算的结果表明，在调查期间，M4海山周围确实存在泰勒柱。 温度和盐度断面图中海山周围等温线和等盐度线的隆起表明上升流的存在。同时，流速和流向断面图显示200-300 m的水层中海山东西方向和南北方向的水流方向大致相反，而水流的简要平面图进一步直观地反映了该区域反气旋环流的存在。此外，理论计算结果表明，阻塞参数和罗斯贝数分别为4.922和0.195，表明环境条件足以支持M4海山泰勒柱的形成。
生物物理耦合在海山周围很常见，M4海山泰勒柱的生态环境效应十分显著。营养盐、Chl a和异养细菌的等值线在A断面山顶西侧和B断面山顶上方显示出与等温线和等盐度线大致一致的隆起，表明上升流影响了这些参数的分布。同时，200 m以上水柱中营养盐、Chl a和异养细菌的平均值在海山周围的站位较高，表明泰勒柱提高了海山周围的生产力，可用“经典理论”来解释。 此外，受泰勒柱影响显著的A6站位与其他5个站的营养盐浓度、Chl a浓度和异养细菌丰度之比往往大于1.0，进一步表明了泰勒柱的作用。此外，基于各站位Chl a浓度比1.0的粗略估算，M4海山泰勒柱的范围是以O站位（140.13°E，10.48°N）为中心，半径为6.1 km。
Seamount is a unique landform in the deep ocean, which has a unique ecosystem. As the material basis of the marine ecosystem, the study of the biogenic elements in the seamounts is of great significance to reveal the uniqueness of the biogenic elements in the seamounts, to clarify the mechanism of the "seamount effect", and to clarify the key processes of the material cycling and energy flow in the seamount ecosystem. Based on surveys of five seamount areas in the Western Pacific Ocean (37.62-153.42 ° E, 8.76-17.78 ° N) including Y3, M2, M4, Magellan and M5 (peak depths were 315, 34, 110, 1195 and 106 m, respectively), this study systematically described the distribution characteristics of the biogenic elements in the seamounts, and explored the coupling relationship between the biogenic elements and the ecological environment in the seamounts. A series of results and understandings are as follows:
1. The distribution of biogenic elements in euphotic zone of the Y3, M4, and M5 seamounts had a significant relationship with the seamount terrain, forming the "seamount effect", while there were no significant "seamount effect" in the M2 and Magellan seamounts. The "seamount effect" was controlled by the interaction between North Equatorial Current (NEC) and the seamount terrain, and was more prominent in the section A of the Y3 and M5 seamount. However, the "seamount effect" existed in both sections A and B of the M4 seamount due to a circulation around the seamount.
The upwelling around the seamount is one of the important drivers of the "seamount effect", and the uplift of the isotherm or the salinity line is the main reference for judging the upwelling. There were uplifts of the isotherms or isalilines at different depths in the five seamount areas, and the amplitudes and positions of the isotherm and the isalilines were similar, indicating the existence of upwelling.
Y3, M4 and M5 (northern part) seamounts were all shallow or medium-depth seamounts, and the upwellings near the summit were more significant. The response of NO3-N, PO4-P, SiO3-Si and DIC to the upwelling was the most significant, and the isolines of the concentrations of these parameters tended to show similar uplifts as the isotherms or isalilines, indicating that they were affected by the strong upwelling. The average concentrations of most biogenic elements on stations near the summits of the Y3, M4, and M5 seamouns areas were often higher than those on staions far from the seamount, further confirming that upwelling around the seamount was beneficial to increase NO3-N, PO4-P, SiO3-Si and DIC concentration. Particulate nitrogen and phosphorus and NO2-N, DOC and POC were relatively weak in the effect of upwelling due to their high concentration in the upper waters. However, the average concentrations of these parameters were higher near the seamount summit, and there was still a certain "seamount effect".
In the Y3 and M5 seamount areas, the average concentrations of particulate nitrogen and phosphorus in the 200 m water column in section A showed a "seamount effect", there were not these phenomenons in the other sections. The upper waters in the depth of 0-200 m in this area was mainly affected by NEC from east to west, so the section A in the east-west direction was more likely to cause upwelling, which in turn caused significant uplifts of parameters such as particulate nitrogen and phosphorus. The “seamount effect” with high average concentration of particulate nitrogen and phosphorus occurred both in section A and section B in the M4 seamount area, that is, not only an upwelling, but also a significant circulation around the M4 seamount, causing the stronger "seamount effect" in the M4 seamount area.
2. In the Western Pacific Warm Pool region where the five seamount areas were located, the water layer could be divided into Surface Water (SW, except Magellan seamount), North Pacific Tropic Water (NPTW), North Pacific Intermediate Water (NPIW) and Deep Water (DW). The biogeochemical processes and typically environmental characteristics such as high salinity zone and thermocline, oceanic hypoxic zone, and Deep Chlorophyll Maximum Layer (DCML) in water layers controlled the morphology, distribution and cycling of the biogenic elements.
In SW, there were strong light, high water temperature and massive heterotrophic bacteria. Strong light and high water temperature were the main reasons for the distribution of phytoplankton in the subsurface layers, which in turn affected the distribution of biogenic elements such as NO2-N and DOC. High temperature also reduced the solubility of CO2, making the concentration of DIC lower. The overlap between high salinity zone and thermocline below the SW restricted the upward transport of biogenic elements at the bottom, which was an important reason for the extremely low levels of NO3-N, PO4-P and SiO3-Si in the SW. The proliferation of heterotrophic bacteria might cause DIN: PO4-P to be much lower than 16: 1, and SiO3-Si: DIN to be much higher than 1: 1, exacerbating the nitrogen deficiency in seawater.
In NPTW, photosynthesis by phytoplankton and decomposition by microorganisms were strong. DCML mainly distributed in the NPTW of the five seamount areas, which was the area with the most intense phytoplankton activity, causing a large increase in NO2-N and DOC. Massive organic matter was generated in this area, significantly improving the PON/TPN and POP/TPP. Meanwhile, the metabolism of phytoplankton might cause DIN:PO4-P and SiO3-Si: DIN turn into phosphorus and silicon limitation. The decomposition of organic matter consumed O2, resulting in a decrease in DO of 1.32, 0.55, 0.10, 1.54, and 0.55 mg/L, and a significant increase in AOU compared to SW. DIC was affected by both photosynthesis and decomposition. Photosynthesis caused a decrease in DIC. However, the overall DIC concentration increased continuously with the increase of water depth, indicating that the rate of supplementation of DIC by organic matter decomposition was much higher than the consumption rate of DIC.
In NPIW, the decomposition by microorganisms was dominant. The area basically coincidds with the range of the oceanic hypoxic zone, where the DO was consumed in large quantities. Decomposition of organic matter by microorganisms caused rapid conversion of biogenic elements from organic to inorganic, and the PON/TPN and POP/TPP gradually decreased. Meanwhile, dramatic reduction in DO was significant for the nitrogen cycle, which was beneficial for the more completed enitrification, and the NO2-N, as the intermediate product in this process, rapidly reduced. Meanwhile, the conversion of NO3-N to N2 was also accelerated, causing the lower DIN: PO4-P and higher SiO3- Si: DIN.
In DW, the decomposition by microorganisms tended to the end, and the biogenic elements were greatly affected by the oceanic thermohaline circulation, which could carry DO-rich Antarctic bottom water to increase the DO and decrease the AOU in the five seamount areas. Meanwhile, the oceanic thermohaline circulation also had a profound impact on the distribution of biogenic elements due to water exchange. In particular, the particulate nitrogen and phosphorus, and POC concentrations increased slightly. On the one hand, they may be affected by sediment resuspension, on the other hand, they may also be affected by oceanic thermohaline circulation. The weak decomposition by microorganisms kept the PON/TPN, POP/TPP, DIN:PO4-P, and SiO3-Si:DIN stable. The NO2-N also remained stable due to the attenuated denitrification. In DW, the lower water temperature and higher pressure made CaCO3 accelerate the dissolution, which made the DIC in this area continue to increase.
3. There was a significant Taylor column phenomenon in the M4 seamount. The isotherms and isalilines, Acoustic Doppler Current Profilers (ADCP) data and theoretical calculations together indicated the existence of the Taylor column in the M4 seamount. The Taylor column led to the isolines uplifts of nutrients, Chlorophyll a (Chl a) and heterotrophic bacteria around the M4 seamount, and the higher average concentrations of these parameters in the 200 m water column near the semount summit.
There are complex hydrological dynamic when the current flows through the seamount, and the Taylor column is one of the most primary hydrology features in seamount. The three separate parts, the upwelling based on the uplifts of isotherms and isohalines, the anti-cyclonic circulation based on current data, and the theory calculation based on the environmental conditions around the seamount showed that the Taylor column indeed exists around the M4 seamount during our cruise. The uplifts of isotherms and isohalines around the seamount in temperature and salinity profiles indicated the existence of upwelling. Meanwhile, the ADCP profiles showed the approximately opposite current directions on east-west sides and north-south sides of the seamount at the water layers ranged from 200 to 300 m, and a brief current plot planar further indicated an anti-cyclonic circulation in this region intuitively. In addition, the theory calculation results showed that values of Blocking Parameter and Rossby Number was 4.922 and 0.195, indicating the environmental conditions were sufficient enough to support a formation of Taylor column in M4 seamount. The biophysical coupling was common around the seamount due to the influence of hydrological dynamic on biological processes. The isolines of the nutrients, Chl a and heterotrophic bacteria showed approximately consistent uplifts with isotherms and isohalines on the west of the summit in section A and above the two summits in section B, indicating the effect of the biophysical coupling, especially the upwelling was strong enough to influence the distribution of these parameters. Meanwhile, the planar graphs of nutrients, Chl a and heterotrophic bacteria in water column above 200 m showed the relatively high values around the seamount, indicating the effect of Taylor column on the enhancement of productivity, which could be explained by the “classic theory”. Moreover, the ratios of nutrients concentrations, Chl a concentrations and heterotrophic bacteria abundances between A6 station and the other five stations were always greater than 1.0, further indicating the effect of biophysical coupling. Furthermore, the range of the effect of biophysical coupling in M4 seamount was with O station (140.13°E，10.48°N) as center point and 6.1 km as radius, roughly estimated based on a standard of Chl a concentration ratio ~ 1.0.
|MOST Discipline Catalogue||工学::环境科学与工程（可授工学、理学、农学学位）|
|Funding Project||Strategic Priority Research Program of the Chinese Academy of Sciences[XDA19060401] ; Strategic Priority Research Program of the Chinese Academy of Sciences[XDA11030202] ; Special Project of Science and Technology Basic Resources Survey - China Ministry of Science and Technology[2017FY100802] ; Aoshan Science and Technology Innovation Project of Qingdao Ocean Science and Technology National Laboratory[2016ASKJ14] ; Aoshan Science and Technology Innovation Project of Qingdao Ocean Science and Technology National Laboratory[2016ASKJ14] ; Special Project of Science and Technology Basic Resources Survey - China Ministry of Science and Technology[2017FY100802] ; Strategic Priority Research Program of the Chinese Academy of Sciences[XDA11030202] ; Strategic Priority Research Program of the Chinese Academy of Sciences[XDA19060401]|
|Table of Contents|
第1章 绪论... 1
1.1 大洋海山研究进展.. 1
1.1.1 海山的研究历史... 1
1.1.2 海山的分类... 3
1.1.3 海山的生态环境特征... 5
1.1.4 海山生态系统的运作机制... 8
1.1.5 海山研究的发展方向... 11
1.2 海水中生源要素研究概述.. 12
1.2.1 溶解无机态氮磷硅... 13
1.2.2 颗粒态氮磷... 15
1.2.3 溶解性无机碳、溶解性有机碳和颗粒态有机碳... 16
1.3 论文的选题意义及主要研究内容.. 18
1.4 研究区概况及研究方法.. 19
1.4.1 西太平洋概况... 19
1.4.2 样品采集与分析... 21
第2章 西太平洋海山区海水中的生源要素与生态环境... 27
2.1 海山区海水中环境要素特征.. 27
2.1.1 温度和盐度... 27
2.1.2 溶解氧和表观耗氧量... 34
2.1.3 pH.. 37
2.1.4 叶绿素a和异养细菌... 39
2.2 海山区海水中生源要素特征.. 41
2.2.1 溶解无机态氮磷硅... 41
2.2.2 颗粒态氮磷... 50
2.2.3 溶解性无机碳、溶解性有机碳和颗粒态有机碳... 62
2.3 海山区海水中生源要素与生态环境的关系.. 66
2.3.1 “海山效应”与生源要素... 66
2.3.2 水层中的生物地球化学过程与生源要素... 70
2.3.3 典型环境特征与生源要素... 78
第3章 海山区生源要素与生态环境的耦合效应—M4海山泰勒柱... 82
3.1 M4海山存在泰勒柱的证据.. 82
3.1.1 等温线和等盐度线隆起... 82
3.1.2 流速和流向数据解析... 84
3.1.3 泰勒柱的理论计算... 86
3.2 M4海山泰勒柱的生态环境效应.. 87
3.2.1 营养盐、叶绿素a和异养细菌等参数的分布... 87
3.2.2 各参数在200 m水柱中的平均浓度... 90
3.2.3 泰勒柱影响范围的估算... 92
第4章 结语与创新... 95
4.1 结论.. 95
4.2 创新点.. 98
致 谢... 113
|马骏. 西太平洋海山区“海山效应”对海水生源要素影响的探析[D]. 中国科学院海洋研究所. 中国科学院大学,2020.|
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