In this special issue we examine the biogeochemical conditions and marine ecosystems in the major marginal seas of the western North Pacific Ocean, namely, the East China Sea, the Japan/East Sea to its north and the South China Sea to its south. They are all subject to strong climate forcing as well as anthropogenic impacts. On the one hand, continental margins in this region are bordered by the world's most densely populated coastal communities and receive tremendous amount of land-derived materials. On the other hand, the Kuroshio, the strong western boundary current of the North Pacific Ocean, which is modulated by climate oscillation, exerts strong influences over all three marginal seas. Because these continental margins sustain arguably some of the most productive marine ecosystems in the world, changes in these stressed ecosystems may threaten the livelihood of a large population of humans. This special issue reports the latest observations of the biogeochemical conditions and ecosystem functions in the three marginal seas. The studies exemplify the many faceted ecosystem functions and biogeochemical expressions, but they reveal only a few long-term trends mainly due to lack of sufficiently long records of well-designed observations. It is critical to develop and sustain time series observations in order to detect biogeochemical changes and ecosystem responses in continental margins and to attribute the causes for better management of the environment and resources in these marginal seas.
Marginal seas in the western North Pacific Ocean. The contours are isobaths of 100 m (dotted), 200 m (dashed), 1000 m (thin solid) and 3000 m (thick solid). Sea floor deeper than 3000 m is shaded in grey. The Kuroshio is the strong western boundary current that flows through this region and interacts extensively with the three major marginal seas, namely, the South China Sea (SCS), East China Sea (ECS) and the Japan/East Sea. The ECS connects with the Yellow Sea, which in turn connects to the Bohai Sea, forming one of the largest contiguous continental shelves in the world. Four large rivers empty into the continental margins. The Mekong and the Pearl River discharge into the SCS; the Changjiang river discharges into the ECS, forming a distinct large river plume (Changjiang plume, CP) in summer; the Yellow River discharges into the Bohai Sea. The circulations within the marginal seas change seasonally. The stronger winter monsoon usually drives stronger currents, which are shown in solid curves. However, the weaker summer monsoon does cause some changes in currents; the more notable ones are shown as dashed curves. See Table 1 for abbreviations.
Continental margins in the western North Pacific Ocean are distinguished by the strong western boundary current, namely, the Kuroshio, and its intense interactions with the three marginal seas, namely, the South China Sea (SCS), East China Sea (ECS) and Japan/East Sea (JES, also EJS). Among the three, the SCS and ECS receive voluminous runoffs from some of the largest rivers in the world, while the SCS and JES have very deep basins making them like miniature oceans. The complicated environmental settings provide the three marginal seas with highly diverse habitats, which nurture some of the most productive large marine ecosystems in the world and sustain very active biogeochemical processes. The total fish catch exceeded 15 million tons in recent years (Anon, 2011; NOAA, 2013, 2011).
Biogeochemistry and ecosystems in the three marginal seas are sensitive to
atmospheric forcing and land-to-ocean fluxes (e.g., Tseng et al., 2011; Gong
et al., 2011; Kim et al., 2011). While the JES and SCS behave as miniature
oceans responsive to climate forcing, the East China Sea serves as the
quintessential example of effective CO
This special issue on “Biogeochemistry and ecosystems in the western north
Pacific continental margins under climate change and anthropogenic forcing” (Liu et al., 2014)
reports on the biogeochemistry and ecosystems, how they interact with each
other and how they respond to climate drivers and multiple anthropogenic
stressors in the three marginal seas. Such understanding will better prepare
our societies in facing the potentially adverse effects occurring in the
changing continental margins. We first describe the environmental settings
of the three marginal seas and then highlight notable findings in five
topical areas:
increasing atmospheric CO regional biogeochemical processes continental margin biota and their ecological characteristics physical forcing and nutrient transport phytoplankton responses to external forcing
All three marginal seas are significantly affected by the Kuroshio, which is the strong western boundary current in the North Pacific Ocean originating from a bifurcation of the North Equatorial Current to the east of the Luzon Island (Fig. 1). It flows northward off the eastern coast of Luzon and Taiwan, and along the shelf edge of the East China Sea and then turns eastward southwest of Kyushu. Along the way the Kuroshio or its branches intrude into all three marginal seas, first the SCS, then the ECS, and finally the JES, bringing strong influences on the hydrographic and biogeochemical properties. The two-way exchanges with the South and East China seas also result in significant modification of the Kuroshio water properties (Liu et al., 2010a, b).
The SCS, which spans from 1.5 to 23
The ECS spans between China and the Ryukyu Islands with Taiwan as its
southern bound and the Yellow Sea (YS) and Bohai Sea (BS) as its northern
neighbor (Fig. 1). The ECS together with the YS and BS forms one of the
largest contiguous continental shelves in the world. The total area of the
shelf down to the isobath of 200 m is about 1 million km
The JES (Fig. 1) is a semi-enclosed marginal sea with only four narrow and
shallow (
All three marginal seas experience the southerly monsoon from May to August
and the northerly monsoon from October to March of the next year. The winter
monsoon is usually stronger than the summer monsoon. These seas are frequently
subject to typhoons, with the SCS seeing the highest number. From 1950 to
2001 there were on average 10 typhoons entering the SCS every year
(
Both the SCS and the ECS shelf receive large riverine discharges of water and
suspended sediments (Liu et al., 2010a). The Changjiang,
which has an estimated average discharge of 928 km
Aside from river discharges, all three marginal seas receive sizable contributions of macro- and micro-nutrients via dry and wet depositions from the atmosphere (e.g., Kim et al., 2011; Wang et al., 2012). The sources of the Aeolian fluxes are dusts and aerosols from industrial or biomass burning sources (Hsu et al., 2009; Lin et al., 2007, 2009).
The Kuroshio (Fig. 1) to the east of the Luzon Island has an estimated
transport of 14–16 Sv (Sverdrups) (Liu et al., 2010a). As the Kuroshio flows northward
passing the Luzon Strait, its path makes a slight detour intruding into the
SCS with only a small fraction (2–4 Sv) actually entering the interior,
mostly during winter. Passing by the east coast of Taiwan, the Kuroshio
enters the ECS with a mean transport of 21.5 Sv entering the ECS. As it
encounters the shelf edge of the ECS, the Kuroshio turns northeastward
following the isobaths, and separates from the shelf and flows around the
southern tip of Kyushu. The Kuroshio transport in the ECS (23.7
The currents within the SCS are rather weak with changing directions in responses to the forcing of alternating monsoons (Fig. 1), which drive a cyclonic gyre in winter and a reversed circulation in summer (Shaw and Chao, 1994; Chen et al., 2012). Aside from the Kuroshio intrusion in the upper water column through the Luzon Strait, the deep and intermediate water inflows induce a basin wide upwelling (Chao et al., 1996). The net inflow is balanced by outflow through other channels, including the Taiwan Strait and the Mindoro Strait in the north and the Karimata Strait in the south. The southern outflow forms the so-called SCS throughflow, which interacts with the Indonesian throughflow (Gordon et al., 2012).
List of abbreviations of geographic names and currents.
Passing by Taiwan, the Kuroshio branches off in several places along the ECS shelf break, most notably to the northeast of Taiwan and to the southwest of Kyushu. Off northeastern Taiwan, the intruding Kuroshio water forms a cyclonic eddy in the surface layer with the subsurface water onwelling along the slope and shelf bottom (Liu et al., 1992a, b) and some shelf water veering off the shelf. Therefore, this is a region of active exchange of water and geochemical materials between the shelf and the open ocean. An intruding Kuroshio Branch Current (KBC) combined with the northward flow from the Taiwan Strait forms the Taiwan Warm Current (Ichikawa and Beardsley, 2002). There is a persistent northward flow near the bottom through the Taiwan Strait from the SCS, while the surface flow is normally northward but changes direction when the northerly wind is strong and persistent in winter.
Southwest of Kyushu, a KBC intrudes onto the shelf to form the Tsushima Current, flowing towards the Tsushima/Korea Strait (Fig. 1). In summer, the Taiwan Warm Current also contributes to the Tsushima Current (Ichikawa and Beardsley, 2002). In winter (Fig. 1), the intruding Kuroshio Branch Current is the main source of the Tsushima Current, and also feeds into the Yellow Sea Warm Current (YSWC, Lie et al., 2001).
Dispersal of the Changjiang discharge varies seasonally (Lee and Chao, 2003). Normally the Changjiang freshwater discharge should drive a southward coastal jet, but, forced by the southwest monsoon in summer, the plume becomes diffuse and disperses towards the east or northeast and may enter the JES. Under the northerly monsoon in winter (Fig. 1), the plume follows a narrow coastal jet, extending southward (Lee and Chao, 2003), which is often named the China Coastal Current (CCC).
Observed partial pressure of CO
Trends of observed
There are four major currents in the JES (Senjyu, 1999), namely, the Tsushima
Warm Current (TWC), the East Korean Warm Current (EKWC), the Liman Current
(LC) and the North Korean Cold Current (NKCC) (Fig. 1). The Tsushima Warm
Current is the only significant source of water inflow to the JES. Unlike the
other two marginal seas, river discharges are not important to the JES. The
saline Tsushima Warm Current flows over the colder and less saline waters of
the homogeneous Proper Water and out to the Pacific through the Tsugaru and
Soya Straits. The north-flowing warm water forms a strong zonal polar front
around 40
Aragonite saturation (
Recent studies (e.g., Kang et al., 2010) clearly indicate that the JES has undergone a dramatic change in the last 50 years possibly due to climate forcing. The dissolved oxygen concentration in the deep Japan Basin has decreased significantly since the 1930s, and the oxygen minimum has been deepening successively since the late 1960s.
Schematic diagram showing the major biogeochemical features in the
river–shelf–boundary current systems observed in studies of this special
issue. Riverine nutrients-induced phytoplankton bloom in the river plume
draws down
The CO
Following the increasing CO
Chou et al. (2013a) reported dramatic changes in the seasonal patterns of
Aside from driving unusual changes in
An even lower degree of aragonite saturation (Fig. 3) has occurred in the bottom
water of the YS (Zhai et al., 2014). The data points shown in Fig. 3 are the
areal mean values, which show the lowest
Because estuaries and coastal regions are the most biogeochemically active zones, particularly in regions with rapid economic development and population growth (Jennerjahn, 2012), we have constructed a schematic diagram to illustrate the major biogeochemical features in the estuary-shelf-boundary current system (Fig. 4). Many findings reported in this special issue are presented in this figure, which is modified and amended following the diagrams of Y. F. Tseng et al. (2014), Tseng et al. (2011), and Cai and Lohrenz (2010).
In the Changjiang estuary and its outflow region in the East China Sea, the
two papers by Hung et al. (2013) and Hsiao et al. (2014) describe the fate
and importance of the mix of terrigenous and marine particles in the
continental shelf area. Hung et al. (2013) describes the particulate flux of
organic carbon from the sea surface to the bottom as measured by sediment
traps during summer. One major caveat of these measurements on continental
shelves is sediment resuspension (Fig. 4), because it modifies the export
flux and its chemical composition. Hung et al. (2013) uses a resuspension
model, which is able to provide an estimate of the resuspended fraction
collected in sediment traps. This fraction amounts from 27 to 93 % of the
total flux. Vertical POC fluxes range from 60 mg C m
Hsiao et al. (2014) concentrated on the Changjiang River plume and nitrification processes, which convert ammonium to nitrate. This process consumes oxygen in the reaction which may contribute to hypoxia in eutrophicated regions (e.g., Pearl River, Dai et al., 2006). Nitrification rates are correlated to ammonium concentration with a peak at a salinity of 29 psu (practical salinity unit) and they are larger in bulk water than particle-free water. Furthermore, when compared to community respiration, a measure of total oxygen consumption in a sample of water, it is shown that a significant share of oxygen consumption is used by the nitrification process. In half of the cases, this share exceeds the Redfield ratio (23 %) and in three occasions exceeds 100 % (up to 318 %). This is only possible if other oxidants can be used for nitrification (such as Mn or Fe oxides). These are abundant in the turbid plume of the Changjiang and deserve more attention in order to understand nitrogen cycling in turbid estuaries (Fig. 4).
On a smaller scale in the northwestern SCS, Li et al. (2014) studied the nutrient dynamics in a number of rivers and estuaries on the east coast of the Hainan Island. They found that all rivers are enriched in dissolved inorganic nitrogen relative to phosphate, due to high nitrate input. Based on a steady-state box model, riverine and groundwater inputs, with additional input from aquaculture effluents, were the major sources of nutrients to the east coast of the Hainan Island.
For the open SCS, Yang et al. (2014) estimated the fluxes of nitrate and
ammonium in atmospheric deposition at a remote island (Dongsha) in the
northern SCS and examined the potential sources of deposited nitrate from its
dual isotopic composition (
The two major pathways for energy and material flows in lower trophic levels
of pelagic ecosystems are the grazing food chain and the microbial food web
(e.g., Azam et al., 1983; Landry and Kirchman, 2002). The latter is based on bacterial
uptake of dissolved organic carbon (DOC), which may be provided by primary
production or by external sources, such as river discharge. Lai et al. (2014)
conducted two summer cruises in the northern SCS and found evidence to
support the malfunctioning microbial-loop hypothesis proposed by Thingstad et
al. (1997) that DOC accumulation occurs when bacterial production was low. In
contrast to the short DOC turnover time of 37–60 days observed in the inner
shelf near the mouth of the Pearl River, it was more than 100 days in the outer
shelf and basin region, where the inorganic nutrients were depleted and no
correlations were found among bacterial production (BP), DOC and
primary production (PP) in the shelf-to-basin transition zone (Fig. 4). Inside the
mid-shelf (bottom depth
Since the microbial food web composed by protists is likely functioning regardless of the seasons and areas, it is important to biogeochemical cycles and trophic dynamics in pelagic food webs (e.g., Shinada et al., 2001). Tsai et al. (2013) evaluated the impacts of viral lysis and nanoflagellate grazing on bacterial production in the ECS. They demonstrated that viral lysis was similar or more important than protozoan grazing for the dynamics of bacterial community. As significantly biogeochemical and ecological impacts have been emphasized for marine viruses (Fuhrman, 1999), trophic dynamics in microbial food web might be revised by including viruses.
On the other hand, phytoplankton growth and mortality are major drivers of biogeochemical cycles and material flow in pelagic food web. Guo et al. (2014) studied the growth and grazing rates of different picophytoplankton populations in the ECS in an attempt to understand the interactive mechanism of bottom-up and top-down control in regulating picophytoplankton biomass and composition and, consequently, the dynamics of biogeochemical cycling of carbon in the subtropical marginal seas. For the northern SCS, Chen et al. (2013a) compared growth and grazing mortality of phytoplankton community in different depths, seasons and sites using in situ experiments. While microzooplankton grazing was equivalent to more than half of the daily primary production as estimated before (Calbet and Landry, 2004), they were largely variable and decoupled by physical disturbances. The decoupling between growth and mortality may be the result of non-steady-state conditions due to physical forcing and food web complexity, which makes it difficult to predict the grazing mortality at global scales.
Chang et al. (2013) assumed that allometric scaling of phytoplankton cell size of natural assemblage to growth and mortality could be described by the metabolic theory of ecology (MTE). While their experiments in the ECS did not support the MTE, they suggested that the higher grazing impacts of large phytoplankton cells release the grazing mortality of small phytoplankton cells. Metazoans connect grazing and microbial food webs through their feeding on phytoplankton and protozoans (e.g., Kobari et al., 2003), suggesting that metazoan growth is an integration of production at lower trophic levels. Similarly to Chang et al. (2013), Lin et al. (2013) tested the MTE for a copepod community in the ECS. The results from their experiments generally agreed with the MTE because growth rates of the copepod community showed positive correlations with ambient temperature and negative to their body size. These findings suggest trophic interactions among the components are important for biological process of the pelagic ecosystems even in areas, such as the ECS, where the main drivers are external forcing like the Asian monsoon and Kuroshio.
Over the entire ECS, Chen et al. (2014) found that the abundance and community structure of larval fish assemblage changed between the two different monsoon seasons. Under the northeast monsoon in winter, there were two assemblages, the inshore and the offshore assemblages. Under the southwest monsoon in summer, the coverage of the inshore assemblage shrank covering the northern part of the Changjiang River plume, and that of the offshore assemblage expanded, whereas a coastal assemblage occupied the southern part of the Changjiang River plume and the coastal belt further south. They suggested that larval fish assemblage showed higher biodiversity and abundance under the southwest monsoon.
The northern ECS is an important spawning and nursery ground for many species
of fish and squid. Umezawa et al. (2014) uses
The Kuroshio is the most important nutrient supplier in the western North
Pacific Ocean. Based on the absolute geostrophic velocity, which was
calculated from the repeated hydrographic data, and nitrate concentration
measurements across five sections along the Kuroshio downstream during at
least the last decade, Guo et al. (2013) computed the nitrate transport by
the Kuroshio Current from the ECS to south of Japan. Their estimated net
nitrate transport crossing the PN line within the Okinawa Trough (Fig. 1) is
178.8 kmol s
The rather rich nutrient reserve in the ECS shelf water could serve as a
sizable nutrient supply to the oligotrophic northern SCS in winter as
suggested by Han et al. (2013). Based on field observations covering both the
ECS and the northern SCS, they examined southward long-range transport of
nutrients from the ECS to the northeastern SCS carried by the China Coastal
Current (CCC) driven by the prevailing northeast monsoon in winter. They
estimated a DIN transport of 1430
Aside from affecting the basin-wide upwelling (Liu et al., 2013), the intrusion of the Kuroshio into the SCS has more direct consequences as demonstrated by Du et al. (2013). They used an isopycnal mixing model to quantify the extent of the Kuroshio intrusion and its impact on the nutrient inventory in the northern SCS. Results show that the nutrient inventory in the upper 100 m of the northern SCS is overall negatively correlated to the Kuroshio water fraction, because the Kuroshio surface water is depleted in nutrients. Consequently, the Kuroshio intrusion has complicated and significant influences on nutrient distribution in the SCS and its seasonal variation.
In the study area of this special issue, external forcing, like the
Changjiang River discharge, the East Asian monsoon and the Kuroshio, affects
greatly and variously the pelagic ecosystems. The maintenance of high primary
production in the Ulleung Basin of the JES has been explained by wind-driven
coastal upwelling (Hyun et al., 2009; Yoo and Park, 2009), mesoscale eddies,
which are often associated with the branch currents of the Kuroshio (Hyun et
al., 2009; Kim et al., 2012; Lim et al., 2012), and hydrographic conditions
(Kwak et al., 2013a). Kwak et al. (2013b) measured the primary and new
productivities in the UB throughout a year. The vertical structure of the
water column in the basin is characterized by two distinct features:
well-stratified in summer–autumn and well-mixed in winter–spring. Nutrient
distributions in euphotic zone show seasonal shift from oligotrophic to
eutrophic. Diatoms were in general the most dominant phytoplankton. The
annual primary, new and regenerated production in the Ulleung Basin were
273.0 g C m
In contrast to previous studies on the primary production and chlorophyll
For the ECS the study of Chen et al. (2013b) also reveals the dramatic
changes before and after the spring transition period. They surveyed the ECS
in April of 2009 and 2010, and obtained contrasting results of community
respiration (CR). In 2009 the CR ranged from
15 to 307 mg C m
Sun et al. (2014) describes the distribution of living coccolithophores in the YS and the ECS in summer and winter, and correlation between species and environmental parameters. As observed, the living coccolithophores in the surface layer occurred mainly in the coastal belt and the shelf region south of the mouth of the Changjiang; in winter they were abundant in the continental shelf area along the PN line (Fig. 1). Spatial comparison indicates lower species diversity and less abundance in the YS than those in the ECS in both seasons. They suggest that temperature and the nitrate concentration may be the major environmental factors controlling the distribution and species composition of living coccolithophores. While this is little studied for other seasons, more studies on the seasonal distribution of coccolithophores should be pursued in the future because coccolithophores take on major roles in the marine carbon cycle.
Focusing on the same area plus the BS, He at al. (2013) investigated
long-term changes in the occurrence of phytoplankton blooms using a 14-year
time series of satellite-derived surface chlorophyll data. They obtained the
spatially resolved time series of satellite chlorophyll by merging SeaWiFS
and MODIS data and validating it against two in situ data sets from large
cruises covering the ECS, YS and BS. By applying an algorithm for the
identification of phytoplankton blooms, He et al. (2013) is able to analyze
spatial and temporal patterns in bloom distribution. They find a doubling in
bloom intensity in the YS and BS over the past 14 years, which they attribute
to a doubling in the supply of nitrate and phosphate primarily due to
increased nutrient loads from the adjacent rivers. However, in the Changjiang
outflow region in the ECS, they find no long-term change in bloom intensity
in spite of the reported increase of Changjiang DIN load in the last few
decades (Yan et al., 2010). This lack of long-term trend could be due to the
same reason mentioned earlier for the lack of long-term trend of
Although the Changjiang discharge provides ample amount of DIN to the
receiving water body, the lack of proportional DIP load in the discharge may
induce potential P-stress for phytoplankton. In order to address this issue,
Y. F. Tseng et al. (2014) conducted a cruise in the Changjiang plume during summer
2011 to survey distributions of nutrients, chlorophyll
It is well known that the variability of surface chlorophyll concentrations in the SCS basin is related to wind forcing, especially during winter monsoon, which leads to a pronounced seasonal cycle in chlorophyll (Liu et al., 2002). Liu et al. (2013) shows that after removing the seasonal cycle, surface chlorophyll responds asymmetrically to wind forcing under El Niño and La Niña conditions. For this purpose, Liu et al. (2013) produced a time series of satellite-derived chlorophyll for a location in the central northern SCS around the SEATS station by merging SeaWiFS and MODIS products in this region and validating it against in situ chlorophyll data from SEATS. Under El Niño conditions, surface chlorophyll is strongly correlated with wind forcing, while under La Niña conditions the correlation is weak (Liu et al., 2013). The weak correlation during La Niña is explained by the deeper thermocline due to weakened SCS throughflow, which diminishes the importance of wind-driven nutrient pumping.
Shang et al. (2014) examines the question of how different chlorophyll
products from the MODIS satellite compare to each other and how consistent
they are in revealing temporal and spatial patterns in the SCS. This is an
important question, especially for optically complex coastal waters in
nearshore regions where the accuracy of satellite-derived chlorophyll
estimates is likely lower than in the open ocean, because chlorophyll is
often not the dominant constituent influencing optical properties. Shang et
al. (2014) compares products from three different algorithms that are
routinely made available to the oceanographic community by NASA and finds that
all three algorithms capture essential features such as winter peaks in
chlorophyll
The three major marginal seas in the western North Pacific Ocean, namely, the
Japan/East Sea (JES), the East China Sea (ECS) and the South China Sea (SCS),
are experiencing multiple stressors induced by anthropogenic as well as
natural drivers. However, few long-term trends in biogeochemical conditions
or ecosystem functions can be determined mainly due to lack of long-term
observations. The only notable long-term biogeochemical trends are the
increase of
The only long-term trends in ecosystem function are the doubling of the algal
bloom intensity in the Bohai Sea and Yellow Sea, attributable to
increasing anthropogenic nutrient loads from rivers. At the same time,
eutrophication-induced high primary production in the ECS leads to enhanced
acidification in the bottom waters. This notion is corroborated by the
observed very high POC fluxes, up to 785 mg C m
More important than nutrient supplies from land, the Kuroshio carries a DIN
load of 179 kmol N s
The Changjiang River plume and its interaction with the shelf water and the Kuroshio are closely examined in this special issue. The major features here and in some of the Pearl River outflow region are summarized in Fig. 4. In the turbid estuary and inner shelf, the high concentrations of suspended particulate matter (SPM) support very high nitrification rates, which exceed the values expected from oxygen consumption in half of the samples, suggesting that iron or manganese oxides associated with SPM could have served as oxidants for nitrification.
The potential P-limitation in the river plume due to the imbalance of the
N
It has been increasingly recognized in recent years that time series
observations are critical for detecting and attributing environmental changes and ecosystem
responses, especially in continental margins (Levin et al., 2015). One good
example is the CARIACO time series program in the Cariaco Basin
(
Therefore, the existing time series programs in the marginal sea, namely, the
EAST-I (East Asian Seas Time-series) program for the JES (e.g., Kang et al.,
2003) and the SEATS program for the
SCS (Wong et al., 2007) should be sustained and expanded in scope, especially
in ecosystem observations. For the ECS, a program similar to the CalCOFI
(California Cooperative Oceanic Fisheries Investigations) program
(
We wish to thank the three reviewers, whose comments helped us improve the paper significantly. We are grateful to the funding agencies (including Ministry of Science and Technology, Taiwan, NSF-C, etc.) that have supported the research projects which have produced the rich outcomes presented in this special issue. We wish to thank most sincerely all of the authors of this special issue, who initially submitted more than 35 contributions. K.-K. Liu acknowledges the support of the Ministry of Science and Technology, Taiwan (grant NSC 102-2611-M-008 -002). Edited by: C.-K. Kang