겨울철 황해 난류 형성 및 난류를 통한 황해 내 질산염 유입에 관한 수치 실험 연구

학위논문(박사)--서울대학교 대학원 :자연과학대학 지구환경과학부,2020. 2. 조양기.The Yellow Sea (YS) is a shallow, semi-enclosed marginal sea surrounded by China and the Korean Peninsula. A deep trough is located in the central YS. The northwesterly wind drives the Yellow Sea Warm Current (YSWC) flows into the YS along the deep trough and two southward coastal currents occurs along the Chinese and Korean coasts in winter. Previous observations have shown that the path of the YSWC has shifted to the west from the deep trough one or two days after northerly wind bursts. However, exact evolution process of the YSWC remains unclear. Model results in this study suggested that the YSWC occurs along the deep trough one day after the wind burst. It shifts to the west of the trough two days later, which phenomenon is generally referred to as the westward shift of the YSWC. Previous studies have proposed a possibility that the westward shift can be driven by continental shelf waves (CSWs). Idealized models were performed to figure out the relationship between CSWs and the westward shift, and generation mechanism of the CSWs driving the shift. The westward shift appeared from the north to south with the propagation of sea surface height at a speed of 3 m/s that was consistent with the phase speed of the first mode CSW. CSWs driving the westward shift were generated on the northern slope primarily by scattering of barotropic Kelvin waves that developed due to northerly wind and propagated poleward into the YS along the eastern boundary off Korea. The YSWC plays an important role in the ecosystem of the YS, because it provides an external water mass in winter. A physical-biogeochemical coupled model and several sensitivity experiments were performed to reveal the role of the YSWC in nitrate (NO3) budget of the YS and quantify contributions of external sources and biological process to NO3 in the YS. Multiple sensitivity experiments revealed quantitative contribution of NO3 from the Changjiang River, Kuroshio Current (KC), run-off in the YS, and Taiwan Warm Current (TWC). 51 percent of total NO3 in the YS was estimated from the Changjiang River and 25 percent from the KC and rivers in the YS, respectively. The TWC contributed 8 percent. Change by nitrification process due to the biological activity was estimated less than 1 percent of the total NO3 in the YS. The estimation of NO3 flux into the YS suggested that 20 percent of total mass NO3 in the YS was supplied by the YSWC during winter. Relative NO3 contributions of the Changjiang River, KC, and TWC through the YSWC to the total inflow to the YS were 64, 29, and 10 percent, respectively.황해는 한반도와 중국 사이에 존재하는 반폐쇄성 해역이며 해역 중앙에는 수심 90 m 이상의 깊은 골이 존재한다. 겨울철 황해에 나타나는 주요 해류는, 북서계절풍으로 인해 중국 및 한국 연안에는 남향하는 흐름이 존재하며 깊은 골에는 바람의 반대 방향으로 북향하는 황해 난류가 나타난다. 관측을 통해 황해 난류의 경로는 황해 내부 깊은 골의 서쪽으로 치우쳐져 있고 바람이 분 뒤 하루나 이틀 뒤 강해진다고 보고되었으나, 형성과정에 대해선 자세히 보고된 바가 없다. 본 연구의 모델 수행 결과, 겨울철 황해에는 평균적으로 시계방향의 순환이 발생하였으며, 시간지연 상관관계 분석 결과, 황해 난류는 바람이 분 하루 뒤 깊은 골에 출현하였으며 이틀 뒤 골의 서쪽으로 편향되는 것으로 나타났다. 선행연구는 황해 난류의 서쪽 편향 현상이 대륙붕파에 의해 발생 할 수 있다고 주장하고 있다. 지형을 간소화한 모델을 통해 황해 난류의 서쪽 편향 현상과 편향 현상의 주 요인인 대륙붕파의 역할 및 형성 기작에 대해 연구하였다. 본 연구 결과, 황해 난류의 서쪽 편향 현상은 대륙붕파의 전파와 함께 발생하였으며 편향 현상의 전파 속도는 2.99 m/s 로 대륙붕파의 1번 모드 전파 속도와 일치하였다. 대륙붕파는 바람에 의해 경사가 있는 지역에서 발생할 수 있지만, 편향 현상을 주도하는 대륙붕파는 겨울철 북풍으로 인해 발생하는 캘빈 파가 황해의 북쪽 사면에서 산란 되면서 발생하는 것으로 나타났다. 황해 난류는 외부의 수괴를 황해 내부로 유입시키기 때문에 황해 생태계에도 중요한 역할을 한다. 물리-생지화학 접합 모델을 통해 황해 난류로 인한 질산염 유입량을 연구하였으며, 외부 유입원 및 질화 작용을 통한 생물학적인 공급량을 정량화 하였다. 관측 자료를 통해 황해 주변에 질산염 농도가 높은 수괴를 살펴본 결과, 황해 내부의 황해저층냉수와 쿠로시오 해류가 기원인 대한해협 중층수의 질산염 농도가 높았다. 민감도 실험을 통해 양자강, 쿠로시오 해류, 대만 난류, 황해 내부 강들의 효과, 그리고 질화 작용의 기여도를 각각 산정하였다. 황해 질산염의 51%가 양자강 기원이었으며, 쿠로시오 해류 그리고 황해 내부 강들이 전체 질산염의 약 25%씩 차지하고 있었고 대만난류로부터 기인한 질산염은 전체의 5% 정도로 적은 양이 유입되는 것을 알 수 있었다. 질화 작용을 통한 유입은 1% 아래로 낮게 나타났으며, 이는 황해에 존재하는 질산염은 생물학적인 공급보다 해류들로 인해 외부로부터 유입되는 것임을 의미한다. 각 기원의 공간적인 기여도를 살펴본 결과, 양자강 기원 질산염은 황해 중앙부 및 서쪽에서 기여도가 높게 나타났으며, 쿠로시오 해류 기원 질산염은 황해 중앙부에 존재하는 질산염에 부차적인 기여를 하는 것으로 나타났다. 황해 내부 강물에 의한 질산염 유입은 황해 동쪽 연안과 산둥반도 주변 연안에 국한되어 영향을 주었다. 황해 난류로 인해 유입되는 질산염 양은 0.137 Tg N 로 겨울철 황해 내부 평균 질산염 질량의 약 20% 정도가 황해 난류로 인해 유입되는 것으로 나타났다. 황해 난류로 인해 유입되는 질산염 중 양자강, 쿠로시오 해류, 대만난류 기원을 정량화한 결과, 각각 64%, 29%, 그리고 10%를 차지하고 있음을 알 수 있었다.1. General Introduction １ 2. Evolution of wind-driven flows in the Yellow Sea during winter 7 2.1. Introduction 7 2.2. Model configuration 8 2.3. Model validation 10 2.4. Model results 13 2.4.1 Mean flow in winter 13 2.4.2 Temporal variation of the YSWC 15 2.4.3 Correlation between northwesterly wind and meridional flow 19 2.4.4 Correlation between northwesterly wind and zonal flow 23 2.4.5 Evolution of actual flow in response to northwesterly wind burst 25 2.5. Summary 29 3. Numerical investigation of the generation of continental shelf waves and their role in the westward shift of the YSWC 31 3.1. Introduction 31 3.2. Model configuration 33 3.3. Results and Discussion 36 3.3.1 Westward shift of upwind flow with equatorward propagation of CSWs along the Chinese coast 36 3.3.2 Characteristics of CSWs driving westward shifting 42 3.3.3 Generation of CSWs driving the westward shift of the YSWC 47 3.3.4 Effects of periodic wind and the Shandong Peninsula on the westward shift of the upwind flow 57 3.3.5 Model application to realistic topography in the YS 64 3.4. Conclusion 71 4. Contribution of the YSWC to nitrate flux in the YS based on a 3-D physical-biogeochemical coupled model 73 4.1. Introduction 73 4.2. Data and Model configuration 75 4.3. Results and Discussion 86 4.3.1 Seasonal variations in temperature, salinity, chlorophyll, and NO3 in the YS 86 4.3.2 NO3 fluxes in the ECS 92 4.3.3 Water mass analysis to figure out the sources of NO3 94 4.3.4 Contribution of each origin of NO3 in the YS 97 4.3.5 Estimation of NO3 flux by the YSWC 103 4.3.6 Limitations of this study and future works 108 4.4. Conclusion 109 5. Summary and conclusion 112 References 115 Abstract (in Korean) 138Docto

Transport of FNPP1-derived radiocaesium from subtropical mode water in the western North Pacific Ocean to the Sea of Japan

This study investigated the spatio-temporal variations in activity concentrations in the Sea of Japan (SOJ) of 137Cs and these transport process from the North Pacific Ocean to the SOJ through the East China Sea (ECS) during 2012–2016. The 137Cs activity concentrations in the SOJ have been increasing since 2012–2013 and reached a maximum in 2015–2016 of approximately 3.4&thinsp;Bq&thinsp;m−3, more than twice the pre-Fukushima accident 137Cs activity concentration of  ∼ 1.5&thinsp;Bq&thinsp;m−3. The 134Cs&thinsp;∕&thinsp;137Cs activity ratios ranged from 0.36 to 0.51 in 2016. After taking into account radioactive decay and ocean mixing, we concluded that these 134Cs&thinsp;∕&thinsp;137Cs activity ratios were evidence that the Fukushima accident caused the increase in the 137Cs activity concentrations. In the North Pacific south of Japan (NPSJ), the highest 137Cs activities in 2012–2013 were observed in water from a depth of 300&thinsp;m, the potential water density anomaly (σθ) of which corresponded to subtropical mode water (STMW). In the ECS, a clear increase in the 137Cs activity concentration started at a depth of 140&thinsp;m (σθ = &thinsp;25.2&thinsp;kg&thinsp;m−3) in April 2013, propagated to the surface layers at depths of roughly 0–50&thinsp;m, reached a maximum in 2015 and decreased in subsequent years. In the ECS, the Fukushima-derived radiocaesium activity concentration in surface water reached a maximum in 2014–2015, whereas the concentration in the SOJ reached a maximum in 2015–2016. The propagation of Fukushima-derived radiocaesium in surface seawater from the ECS into the SOJ therefore required approximately 1 year. These temporal changes in 137Cs activity concentrations and 134Cs&thinsp;∕&thinsp;137Cs activity ratios indicated that part of the 137Cs and 134Cs derived from the Fukushima accident (FNPP1-derived 137Cs and134Cs) was transported within several years to the ECS and then to the SOJ via STMW from the NPSJ. The integrated amount of FNPP1-derived 137Cs that entered the SOJ before 2016 was estimated to be 0.21±0.01&thinsp;PBq, 5.0&thinsp;% of the estimated total amount of FNPP1-derived 137Cs in the STMW. The integrated amount of FNPP1-derived 137Cs that returned to the North Pacific Ocean through the Tsugaru Strait was estimated to be 0.09±0.01&thinsp;Bq, 43&thinsp;% of the total amount of FNPP1-derived 137Cs transported to the SOJ and 2.1&thinsp;% of the estimated total amount of FNPP1-derived 137Cs in the STMW.</p

Satellite-Based Fog Detection: A Dynamic Retrieval Method for Europe Based on Machine Learning

Fog has many economic as well as ecological impacts and it directly affects human life in many ways. The large number of fog influence factors shows that a comprehensive understanding of its causes and a precise mapping of the spatio-temporal distribution patterns are of great interest. Since there are justifiable concerns about the general applicability of existing fog retrieval methods, this thesis investigates new techniques of satellite based fog detection and the derivation of spatio-temporal information on fog distribution in Europe. The central novelties of this study are: - No static assumptions about microphysical properties were used during fog retrieval. - A novel hybrid approach based on machine learning methods was developed that can be continuously applied 24 hours a day. - The algorithm covers all fog types. Areas of different fog types could also be differentiated indirectly from the generated product due to their typical diurnal and annual frequency cycles. - For the first time, fog frequency maps for Europe could be produced for different general weather situations separately for each fog type

Methane dynamics in the coastal–Continental shelf transition zone of the Gulf of Cadiz

The concentration of CH4 in water was measured along five transects in the Gulf of Cadiz (Trafalgar, Sancti Petri, Guadalquivir, Tinto - Odiel and Guadiana) during four cruises throughout the months of March, June, September and December 2016. For two of the cruises water overlying three mud volcanoes situated in the Gulf of Cadiz were also sampled (San Petersburgo, 860 m; Pipoca, 460 m; and Anastasya, 500 m. In addition, the stable carbon isotopic compositions of dissolved CH4 (δ13C) were measured in the study area in June and December 2016. The mean CH4 value for the whole water column was 10.5 ± 4.3 nmol L−1, with large spatial and temporal variations. The highest values were found in June 2016 and the lowest in March 2016. In surface waters, the mean dissolved methane concentration was of 9.6 ± 2.6 nmol L−1. In most of the sampling area, high concentrations of CH4 were found in subsurface waters at depths close to the thermocline and at the coastal stations. The highest concentrations were obtained from the bottom waters above the Anastasya mud volcano (125 nmol L−1). The stable carbon isotope compositions ranged between - 29.2 and - 58.4‰, and the least negative values were associated with the highest CH4 concentrations in samples from above the mud volcanoes, related to thermogenic values. The sea-air fluxes of CH4 ranged from 12.4 to 37.7 μmol m−2 d−1, showing that the study area acts as a source of CH4 to the atmosphere

Marine Nitrogen Fixation and Phytoplankton Ecology

Many oceans are currently undergoing rapid changes in environmental conditions such as warming temperature, acidic water condition, coastal hypoxia, etc. These changes could lead to dramatic changes in the biology and ecology of phytoplankton and consequently impact the entire marine ecosystems and global biogeochemical cycles. Marine phytoplankton can be an important indicator for the changes in marine environments and ecosystems since they are major primary producers that consolidate solar energy into various organic matter transferred to marine ecosystems throughout the food-webs. Similarly, the N2 fixers (diazotrophs) are also vulnerable to changing environmental conditions. It has been found that the polar regions can be introduced to diazotrophic activity under warming conditions and the increased N availability can lead to elevated primary productivity. Considering the fundamental roles of phytoplankton in marine ecosystems and global biogeochemical cycles, it is important to understand phytoplankton ecology and N2 fixation as a potential N source in various oceans. This Special Issue provides ecological and biogeochemical baselines in a wide range of geographic study regions for the changes in marine environments and ecosystems driven by global climate changes

Do bacteria thrive when the ocean acidifies? Results from an off-­shore mesocosm study

Marine bacteria are the main consumers of the freshly produced organic matter. In order to meet their carbon demand, bacteria release hydrolytic extracellular enzymes that break down large polymers into small usable subunits. Accordingly, rates of enzymatic hydrolysis have a high potential to affect bacterial organic matter recycling and carbon turnover in the ocean. Many of these enzymatic processes were shown to be pH sensitive in previous studies. Due to the continuous rise in atmospheric CO2 concentration, seawater pH is presently decreasing at a rate unprecedented during the last 300 million years with so-far unknown consequences for microbial physiology, organic matter cycling and marine biogeochemistry. We studied the effects of elevated seawater pCO2 on a natural plankton community during a large-scale mesocosm study in a Norwegian fjord. Nine 25m-long Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging from ca. 280 to 3000 µatm by stepwise addition of CO2 saturated seawater. After CO2 addition, samples were taken every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. Our results indicate that marine bacteria benefit directly and indirectly from decreasing seawater pH. During both phytoplankton blooms, more transparent exopolymer particles were formed in the high pCO2 mesocosms. The total and cell-specific activities of the protein-degrading enzyme leucine aminopeptidase were elevated under low pH conditions. The combination of enhanced enzymatic hydrolysis of organic matter and increased availability of gel particles as substrate supported higher bacterial abundance in the high pCO2 treatments. We conclude that ocean acidification has the potential to stimulate the bacterial community and facilitate the microbial recycling of freshly produced organic matter, thus strengthening the role of the microbial loop in the surface ocean