초록 ▼

○ 동중국해와 한반도 연안의 중장기 수온 변화 : HadSST 분석결과 동계 황해와 동중국해의 평균 해면 수온은 1980년대 후반 이후에 뚜렷한 온난화 경향을 보였다. 한반도 연안의 장기수온관측 분석 결과 0.02℃/year 이상의 온난화 추세를 보였다.
○ 동중국해 북부해역의 물리ㆍ생지화학적 특성의 계절 및 연변동 특성 : 03-10년까지 총 10회의 다학제 해양관측을 실시하였다. 동중국해 북부해역은 04년과 08년 춘계에 열염전선의 특성을, 06년 하계에는 07년보다 더 저염인 장강희석수와 황해저층냉수의 확장 특성을, 05

○ 동중국해와 한반도 연안의 중장기 수온 변화 : HadSST 분석결과 동계 황해와 동중국해의 평균 해면 수온은 1980년대 후반 이후에 뚜렷한 온난화 경향을 보였다. 한반도 연안의 장기수온관측 분석 결과 0.02℃/year 이상의 온난화 추세를 보였다.
○ 동중국해 북부해역의 물리ㆍ생지화학적 특성의 계절 및 연변동 특성 : 03-10년까지 총 10회의 다학제 해양관측을 실시하였다. 동중국해 북부해역은 04년과 08년 춘계에 열염전선의 특성을, 06년 하계에는 07년보다 더 저염인 장강희석수와 황해저층냉수의 확장 특성을, 05년 추계에는 혼합의 초기 특징을, 09년에는 바람장에 의한 수직환합 특성을 각각 나타냈다. 제주 서측 표층에서 관측된 봄과 가을의 비교적 높은 질산염과 인산염 농도는 수직혼합에 의한 저층으로부터의 공급에 기인하며, 여름의 뚜렷한 연간 변화는 하계 바람 방향의 변화에 의한 장강담수의 유입과 관계 깊은 것으로 파악되었다. 하계 질산염과 인산염 표층 분배가 규산염과 잘 일치하지 않는 이유는 샨샤댐 공사 이후 장강담수의 규소:질소 비율의 현저한 감소 결과에 의한 것으로 판단된다. 표층 이산화탄소의 분압은 열염전선의 서쪽과 동쪽에서, 또한 해황에 따라 동일 계절 내에서도 큰 연변동을 보인다. 겨울~여름동안 이산화탄소 분압은 대기중 2.2 ± 2.1 molm^-2yr^-1로 대기 이산화탄소의 강력한 흡수원으로 작용하는 것으로 나타났다.
○ 하위영양단계 생태계 계절 및 연변동 특성 : MODIS 자료를 이용, 03-09년의 월별 엽록소 a농도와 일차생산력의 장기변화를 분석하였다: 동죽국해의 엽록소 -a 농도는 증가 경향을 나타냈으며, 장강 하구역이 더욱 뚜렷하였다. 현장조사 결과 초미소 식물플라크톤의 생체량은 전체 식물플랑크톤의 약 30-50%를 차지하는 주요 일차-생산자로서 수온ㆍ염분과 밀접합 관계를 보였다. 식물플랑크톤의 색소 및 일차생산력도 장강희석수에 따라 변화를 나타냈다. 수온, 염분 및 일차 생산자에 의한 유기물 공급이 박테리아 생산력에 중요한 요인으로 나타났다. 동물플랑크톤 령균 생체량은 봄에 큰 피크, 가을에 작은 피크를 보였으며, 겨울에 가장 낮았다. 생체량의 연변화는 여름에 다소 감소하며, 봄과 가을에는 모두 증가하였다. 요각류가 개체수에 근거한 조성률에서 50%이상을 차지하며, 크기그룹별 생체량은 본 조사연도에 관계없이 대체로 1.0~2.0 mm 크기그룹의 생체량이 우세하였다.
○ 동국중국해 살오징어 유생의 수송과정과 연변동성 규명: 06-08년 7월에 살오징어 유생 채집 실시결과 총 91개 정점에서 292 개체의 유생이 출현하였다. 대부분 50 m 수온 15-22℃, 염분 32.7-34.6 psu의 제주 남동부와 큐슈 북부해역에서 발견되었으며, 전선역에서 높은 분포를 나타냈다. 해양순환모델을 이용하여 알과 유생의 초기 수송과정에 대해 모의 실험을 행하고 수송 경로를 추정하였다.
○ 기후변화 시나리오에 따른 동중국해의 미래 해양환경과 생지화학 특성 변화 예측 : IPCC 기후변화 시나리오에 따른 미래 기후조건을 이용하여 2030년대의 동중국해 수온, 염분, 해양혼합층과 해류 변화를 예측하였다. 지구시스템모델 예측결과를 이용하여 기후변화에 따른 2100년의 동중국해 생지화학 특성 변화를 전망하였다.

Abstract ▼

IV. Results

1. Long term temperature changes in the East China Sea and coastal regions of Korea

We analyzed a long term period of monthly SST data taken from the Hadley Center (Rayner et al.,. 2003) with the horizontal resolution of 1° x 1°. The variability of averaged SST over the Yel

IV. Results

1. Long term temperature changes in the East China Sea and coastal regions of Korea

We analyzed a long term period of monthly SST data taken from the Hadley Center (Rayner et al.,. 2003) with the horizontal resolution of 1° x 1°. The variability of averaged SST over the Yellow and East China Sea(22.5°N~42.5°N, 115.5°E~127.5°E) during winter time is characterized by a significant warming after the late 1980s. Using the Empirical Orthogonal Function(EOF) analysis we found that the spatial pattern of the first EOF SST is dominated by a basin scale over the Yellow and East China Sea. In addition, the maximum variance of SST appears in the east of Taiwan and the southern part of Korean peninsular with a northeast-southwest orientation. The principal component of the first EOF SST also indicates that the SST over the Yellow and East China Sea significantly warms after the late 1980s. We argued that such a warming may be due to a weakening of east Asia winter monsoon and associated changes in the atmospheric circulation.
It is found that the water temperature in the northern part of the East China Sea has been increased by analyzing observation data(WOD01). The increase of the winter temperature larger than that of the annual mean temperature implies that the amplitude of the annual variation has been decreased. Long-term variability in the coastal sea surface temperature(SST) in Korea was investigated to compare the above results by analyzing the coastal SST time series. Though a long term linear increasing trend is remarkable with the rate over 0.02℃/year at almost all the stations, it is also noticeable that SST is lower in the 1970s and early 1980s but higher in the 1990s and early 2000s after the increase in the late 1980s. The pattern of the interannual variability of SST is similar to that of air temperature.
The increasing trend of minimum SST in winter is obvious at most stations, but the linear trend of maximum SST in summer is less definite. Therefore, the decreasing tendency of annual amplitude is mainly due to the increasing tendency of SST in winter.

2. Variations of oceanic conditions and physical properties in the northern East China Sea

By carrying out a total of 10 times' ocean observation for the period of eight years from 2003 to 2010, we investigated seasonal characteristics of ocean circulation and water distribution in the northern area of the ECS (Spring: 3 times - April 2004, April 2008, April 2010; Summer: 4 times - August 2003, June 2005, July 2006, July 2007; Fall: 2 times - October 2004, November 2005; Winter: One time - February 2009).
In the spring season of 2004 and 2008 surface thermal and haline fronts formed from northwest to southeast in the survey area, corresponding each other. In spring 2004 the western part of the front showed lower salinities in the vertical profiles compared to 2008. However, temperatures were lower in spring 2008 than in 2004, showing the southward movement of coastal water along the Chinese coast.
In summer 2006 the Changjiang Diluted Water (CDW) extended to the Cheju Island in the surface layer with lower salinities(< 30 psu) than in 2007. Southward extension of the Yellow Sea Bottom Cold Water (YSBCW) were stronger in summer 2006 than in 2007.
It was featured that in a fall 2005 the previous summer stratification was broken to begin mixing. The area was, by the standard of the isothermal of 22.5 ℃ and the isohaline of 33 psu, divided into the eastern sea characterized by high temperature and salinity and the western sea characterized by low temperature and salinity, and revealed a simple pattern of temperature that is high(low) in the east(west) in comparison with summer. From sea surface to 50 m depth, the isohaline of 34 psu is, by the influence of Tsushima current, extended to the west of Jeju-do.
In winter 2009, bad weather restricted our observation to several areas near the Jeju-do. The winter water mass distribution shows a general feature that the surface layer and 50 m depth's layer are entirely mixed by strong winds. In the western sea of Jeju-do the thermohaline front, a general characteristic of winter, was formed.

3. Variations of biological and chemical properties in the northern East China Sea

A. Spatial and temporal variations in nutrient concentrations in the northern East China Sea

Nutrients, chlorophyll - a (Chi-a), and environmental conditions were extensively investigated in the northern East China Sea during eight research cruises from 2003 to 2010. In the eastern part of the study area, surface waters were characterized only by the Tsushima Current Water (TCW) during all five cruises. However, the western surface waters changed with season and were characterized by Yellow Sea Cold Water(YSCW) in spring, Changjiang Diluted Water(CDW)in summer, and Yellow Sea Mixed Water(YSMW) in autumn. In spring and autumn, relatively high concentrations of nitrate and phosphate were observed in the surface waters in the western part of the study area, where vertical mixing brought large supplies of nutrients from deep waters. Changes in wind direction occasionally varied the inflow of the Changjiang plume in summer, clearly causing the annual variation in surface nitrate and phosphate concentrations in summer. In summer, the surface distribution of nitrate and phosphate did not coincide with that of silicate in the study area, which probably resulted from the significant drop in the Si:N ratio in the Changjiang plume since construction of the Three Gorges Dam(TGD).

B. Seasonal variations of partial pressure of CO₂ in the surface water

Temperature, salinity, and sea-air differences of CO₂ partial pressure (△pCO₂) were extensively investigated in the northern ECS during eight research cruises from 2003 to 2010. The △pCO₂ showed large intraseasonal variation in spring and summer. In addition, △pCO₂ exhibited large seasonal variation with positive values in autumn and negative values in other seasons. The annually integrated sea-air CO₂ flux in the northern ECS was -2.2 ± 2.1 mol m^-2 yr^-1, which was more than two times lower than a previous estimate reported for the same region. This large difference was presumably the result of underestimation of winter CO₂ influx and the large intraseasonal variation of CO₂ flux in spring and summer. The CO₂ influx in the ECS was twice that estimated for continental shelves worldwide, suggesting that the ECS acts as a strong sink of atmospheric CO₂ compared to other continental shelves.

4. Variations of the characteristics of lower trophic level ecosystem in the northern ECS

A. Phytoplankton and bacteria

Nine research cruises were carried out in the northern ECS during 2003-2010 to help understand the effect of climate change to phytoplankton and bacterial ecosystem responses. Also, long-term variations were analysed for monthly composites of chlorophyll-a using MODIS data and for primary production calculated using VGPM model for the study period of 2003-2009.
The results of satellite data analysis showed an increasing trend for chlorophyll-a concentration in the ECS, and this increasing trend was clearer for the watershed area of of Chiangjiang River than the areas of the Ieodo Observatory Tower and the southern Jeju Island. The eight year average daily primary production was estimated to be 508.7土216.9 mgCm^-2d^-1, however the primary production also showed an increasing trend. Seasonally, large increases were observed in summer for the chlorophyll-a concentrations and primary production. The in-situ study carried out during the research cruises revealed that the contribution by picophytoplankton to total biomass of phytoplankton ranged about 30-50% suggesting its significance as an important primary producer. Its distribution seemed to be closely affected and varied depending on water temperature and salinity. Also, indicator pigments and primary production of phytoplankton were varied closely with the low-salinity waters from Chiangjiang water.
Bacterial abundances and productions showed large variations in summer, ranging from 0.2 to 4.8x10⁹ cells ℓ^-1 and from 0.05 to 20.9 mgC m^-3d^-1, respectively and temperature and salinity could be considered to be important factors regulating these variations. Further, the ratio of bacterial production to primary production integrated within the euphotic depths showed positive and negative relationships with temperature and salinity, respectively, suggesting that temperature and salinity can be important factors regulating the energy flow through microbial loop in the East China Sea.
These results suggest that input of Changjiang diluted water and sea water temperature increase due to global warming could affect not only microbial distribution and production but also foodweb structures of the East China Sea ecosystem.

B. Zooplankton

Zooplankton samples were collected from 2004 to 2009 in the northern East China Sea to understand the potential changes of zooplankton(mainly mesozooplankton) community structure in relation to climate change and/or environmental changes. Sampling seasons were rather different among the years.
Total biomass of zooplankton showed a peak in spring followed by in fall and it was the lowest in winter. This seasonal variation of total zooplankton biomass agreed with that in the temperate region. Regarding the inter-annual variation of zooplankton biomass, the biomass in spring and fall have increased compared to the previous same season, but decreased a little in summer. Copepods dominated the zooplankton in terms of abundance through the sampling period, with over 50% of composition. Small sized copepods including Paracalanus copepodite, Paracalanus parvus, Oithona similis dominated in copepod group. However, decapoda larvae and radiolarian dominated in zooplankton in fall. The size group of 1.0〜2.0 mm of zooplankton was the highest in size-fractionated zooplankton biomass from 2006 to 2009 regardless of season.
Production of the copepod Calanus sinicus was measured in April 2004 Egg production rate was averaged at 5.8 egg s/female/day, similar with the previous result from the southern part of the Yellow Sea. Contribution of egg production to total production (somatic production + egg production) was 3%, indicating low contribution of egg production in total production of Calanus sinicus. Total production of Calanus sinicus was significantly correlated with mean water temperature and
chlorophyll-a concentration. The production decreased with increasing water temperature and increased with increasing chlorophyll-a concentration.
Anomaly of mean abundance of copepods in February from 1978 to 2005 based on the oceanographic observation(314 line) by NFRDI in the southern coast of Jeju Island showed that the abundance of copepods was lower in the El Nino periods (i.e. 1982/1983 and 1997/1998) than the mean abundance of copepods for the 27 years. However, we still have difficulty to understand the relationship between the lower copepod abundance and El Nino events.

C. Protozoa

То investigate grazing impacts and community structure of heterotrophic protozoa, we collected water sample from surface in ECS. Communities of planktonic protozoa were classified into four groups such as hetero trophic nanoflagellates (HNF), ciliates, and hetero trophic dinoflagellates (HDF). In 2006 year(summer) and 2007 year(summer), carbon biomass of planktonic protozoa ranging from 6.1 to 14.7 ugC ℓ^-1 (average, 8.7 ugC ℓ^-1 and from 3.8 to 40 ugC ℓ^-1 (average, 11.2 ug ℓ^-1), respectively. Also, carbon biomass of planktonic protozoa in spring(2007) ranging from 9.2 to 60 ugC ℓ^-1 z (average, 17 ugC ℓ^-1). Spatial distribution of planktonic protozoan carbon biomass was relatively high in the west-southern part of this study area because of CDW. Carbon biomass of hetero trophic protozoa and phytoplankton biomass showed strong positive correlation in the study area. Therefore, planktonic protozoa appears to be primarily governed by phytoplankton concentration as a food source. Biomass of HNF comprised 23% of the planktonic protozoan biomass in summer, and 17% in spring. Biomass of ciliates in summer and spring comprised 44% and 62% of the planktonic protozoan biomass, respectively. Biomass of HDF comprised 33% of the planktonic protists biomass in summer, and 21% in spring. Therefore, ciliates was the most dominant component in this study area. Grazing impacts of heterotrophic protozoa on potential chlorophyll-a production ranged from 55% to 93%, and was relatively low in west-southern part of this study area.

5. Inter-annual variability on larval dispersion of common squid Todarodes Pacificus during 2000s

To examine the horizontal distribution pattern and transport process of common squid larvae, surveys were conducted in the northern East China Sea and Korea/Tsushima Strait during July 2006-2008. Most larvae were occurred in the southeastern Jeju Island and the north of Kyushu Island. Larval abundance was highest at the inshore edge of the frontal zone(18-20℃), where Tsushima Warm Current ana inshore waters meet.
Regional Ocean Modeling System(ROMs) based on reanalyzed data was applied to investigate transport process and distribution pattern of eggs and larvae of common squid from the spawning areas to the nurseries. We modified the particle - tracking module of a three-dimensional circulation model for the northwest Pacific to incorporate simple larval behaviors such as diel vertical migration. We used the model to simulate dispersal of common squid larvae during summer spawning season. In order to estimate the origin of common squid larvae that inhabits the southeastern Jeju Island and north of Kyushu Island, particles were released at the each sampling position and were transported backward for 7 to 30 day, considering larval growth rate. Based on backward experiment, particles were released at the inferred spawning area and tracked for 90 days. We also addressed intra- and interannual variability in dispersal by repeating the simulations with larval release occurring during different seasons and years for 2000s

6. Model analysis of climate change scenario and downscaling experiment of ocean climate change

A. Analysis of climate change projections in the East China Sea and Yellow Sea using the IPCC climate system model simulations

For 23 climate system models submitted in the AR4, we estimated a performance of models on the basis of the variation of sea surface temperature in the ECS and Yellow Sea, and predicted the future temperature variation there mainly using MPI_echam5, IPSL_cm4, MIROC_hires, and NCAR_ccsm3.0. The sea surface temperature difference between the early 21st century (2001-2050) and the whole 20th century for the respective models reveals an increase by 0.6~1℃ in MPI_echam5 and IPSL_cm4 and by higher than 0.8~1.2℃ in NCAR_ccsm3.0 for the whole ECS and Yellow Sea, and by higher than 2℃ for the northwestern ESC and the central Yellow Sea in MIROC_hires.

B. Downscaling experiment of environmental changes in the East China Sea due to the global warming

We simulated and compared the present and future ocean circulation in the East China Sea using an East Asia Regional Ocean model because the global climate models with coarse spatial resolutions do not properly resolve the ocean circulation in the East China Sea. Mean climate states for 1990〜1999 and 2030〜2039 were used as surface conditions for simulations of the present and future ocean circulation, which were derived from the simulation results of the global climate models for 20th century and those of the future the 21st century projected by the IPCC SRES AlB. Six experiments were conducted with six different surface conditions, three for the present and three for the future climate conditions, extracted from the simulation results of three different global climate models, ECHAM5-MPI, GFDL-CM2.0 and MIROC3.2_hires.
Compared to the global climate models, East Asia Regional Ocean model simulated the detailed patterns of temperature, salinity and current fields under the present and future climate conditions and their change instead of simple structures. There are consistent ocean circulation changes derived from three pairs corresponding to the global climate model such as that surface temperature increases in winter and bottom temperature in summer, that surface temperature increases in summer except in some region, and that temperature and salinity changes are prominent near the Chinease coast and in the Changjiang bank.
However, the simulated circulations are different each other depending on the prescribed atmospheric conditions not only under the present climate but also the future climate. Circulation changes between the present and future simulation derived from three pairs corresponding to the global climate model are as well inconsistent It implies that more simulations with different pairs are needed.
Warming experiments with three different surface forcing (ECHAM5/MPI-OM, MIROC_hires, and GFDL CM2.0) project a overall mixed layer depth (MLD) decrease in the ECS. The MLD decrease is attributed to weakened wind, surface-intensified stratification increase by surface warming and freshening. However, magnitude of the MLD change depends highly on imposed surface conditions and some areas show different signs in MLD changes depending on imposed warming conditions. Kuroshio-related high salinity water also an important contributor to MLD and its change in the ECS, especially in the Yellow Sea.

7. A biogeochemical modeling and long term projection of primary production in the East China Sea

A. Numerical experiment of the phytoplankton bloom in the northern East China Sea in summer 2006 using a physical-biogeochemical model

A two-dimensional biogeochemical model linked to a circulation model was established to understand the dynamics of the phytoplankton bloom in the northern ECS in summer. The ECS circulation model is based on the Regional Ocean Modeling System(ROMS) and coupled to the ecosystem model in one way fashion. Wind stress data from QuickSCAT in 2006 were used. The simulated results capture well the two times of phytoplankton bloom events observed in July 2006. Model result shows that the upwelling caused by the southwesterly monsoon in the Chinese coastal area had greater impacts on the offshore phytoplankton bloom than the Changjiang Diluted Water. Bottom water supplied by the upwelling is estimated to be 150 times more than the Changjiang discharge in July 2006. The nitrates supplied by the upwelling could be 9.30 times more than that by the Changjiang discharge.

B. Projection of primary production in the East China Sea using an earth system model simulation

Using results from an earth system model, the response of the East China Sea primary production under the A1B emission scenario has been investigated. As the global warming progresses, the sea water becomes warmer and the stratification intensifies so nutrient supply from the deep ocean weakens. Therefore, the primary production reduces. In addition to the progressive warming there are strong interdecadal variabilities as well as year to year variabilities, and there are decades when the change is rapid or slow. The warming tendency thus could become prominent only after a few decades. A temperature front can be found along the edge of the Kuroshio where the primary production is high. This high production lowers the oceanic CO₂ partial pressure which in turn enhances air-sea CO₂ exchange. The content and the partial pressure of CO₂ in the ocean become higher along with the atmospheric concentration of CO₂. The air-sea CO₂ exchange, however, does not show notable increase. The year-to-year variation is always large enough to overwhelm the signal due to the warming.