Carbon Chemistry in the Mainstream of Kuroshio Current in Eastern Taiwan and Its Transport of Carbon into the East China Sea Shelf

Rapid increase of pCO2 and seawater acidification along Kuroshio at the east edge of the East China Sea

Rates of seawater acidification and rise of partial pressure of CO₂ (pCO₂) at ocean margins are highly uncertain. In this study, nine years of time-series data sampled during 2010-2018 along Kuroshio Current near the East China Sea (ECS) were investigated. We found trends of surface seawater pCO₂ at 3.70 ± 0.57 μatm year^-1 and pH at -0.0033 ± 0.0009 unityear^-1_, both of which were significantly greater than those reported from other oceanic time series. Mechanistic analysis showed that seawater warming caused rapid rates of pCO₂ increase and acidification under sustained DIC increase. The faster pCO₂ growth relative to the atmosphere resulted in the CO₂ uptake through the air-sea exchange declining by ~50 % (~-0.8 to -0.4 mol C m^-2 year^-1) over the study period. Our results imply that rapidly warming boundary currents could potentially present an elevated pCO₂ trend, leading to a gradual reduction and eventual loss of oceanic CO₂ uptake under climate change.

Plankton Community Respiration and Particulate Organic Carbon in the Kuroshio East of Taiwan

Biological organic carbon production and consumption play a fundamental role in the understanding of organic carbon cycling in oceans. However, studies on them in the Kuroshio, the western boundary current in the North Pacific Ocean, are scarce. To better understand the variations of plankton community respiration (CR) and particulate organic carbon (POC), eight cruises. which covered four seasons over a 2-year period, were surveyed across the Kuroshio at the KTV1 transect east of Taiwan. Spatially, a coastal uplift of isotherms (i.e., onshore lifting and offshore deepening) was observed along the KTV1 transect. During the uplift, the cold and nutrient-rich deep waters shoal to shallow water and enhance phytoplankton growth, resulting in higher values of phytoplankton, POC, and plankton CR on the onshore side. In this study, phytoplankton was dominated by picophytoplankton including Prochlorococcus, Synechococcus, and picoeukaryotes. Plankton CR was low, and its mean depth-normalized integrated rate (the upper 100 m water depth) ranged from 7.07 to 22.27 mg C m^-3 d^-1, to which the picophytoplankton and heterotrophic bacteria contributed the most. The mean depth-normalized integrated value of POC ranged from 12.7 to 21.6 μg C L^-1. POC is mainly associated with phytoplankton biomass with a mean carbon ratio of chlorophyll a/POC ≈ 1.03. All results suggest that plankton CR and POC variations may be associated with picoplankton dynamics in the Kuroshio.

Surface Current Variations and Hydrological Characteristics of the Penghu Channel in the Southeastern Taiwan Strait

Coastal ocean dynamics application radar (CODAR) SeaSonde high-frequency (HF) radars deployed along the coast of Taiwan were used to reveal ocean surface current variations both hourly and through climatological seasons in the Penghu Channel (PHC), southeastern Taiwan Strait (TS), from December 2014 to December 2020. The ocean current in the PHC has a semidiurnal tidal cycle, and the seasonal main flow, wind direction, and wind strength significantly affect the direction and speed of the flow passing through the PHC. The speed of the tidal current in the PHC area can reach more than 1 m/s, and the monthly average flow speed in the PHC is between 0.12 (winter) and 0.24 m/s (summer). Several buoys indicated that the southward flow along the western coast of Taiwan drifted through the PHC in fall and winter. The HF radar observations confirmed the same, implying that this occurred during the strong northeastern monsoon. For a weak northerly wind or even southerly wind, the flow in the PHC can be northward. Different wind directions can affect the speed of the flow passing through the PHC and the branch flow in the northern PHC. The HF radar results are highly consistent with the spatial characteristics of satellite data regarding the sea surface temperature, sea surface salinity, and chlorophyll concentrations; however, there are significant differences from the satellite-derived ocean current.

Satellite Observed Spatial and Temporal Variabilities of Particulate Organic Carbon in the East China Sea

In this study, we investigate spatial and temporal variabilities of particulate organic carbon (POC) in the East China Sea (ECS) and explore the dominant influencing factors for its three subregions—coastal, continental shelf and open sea—by analyzing satellite derived POC from 2001 to 2011 after calibration against in situ samplings. The analysis reveals that the largest POC occurs in spring at the coastal region with a value of 297.5 mg m−3, and the smallest in summer at the open sea region with a value of 108.9 mg m−3. POC in the coastal region is dominated by biological activity related to river discharge of nutrients and organic matter, and is regulated by sediment discharge variation due to the Three Gorge Project and chemical fertilizer application along the Changjiang River watershed; the open sea region is dominated by water exchange with the Kuroshio current, which results in the highest sea surface temperature and the lowest chlorophyll and POC among the three subregions; POC in the continental shelf region is driven by the seasonal competition between the influence of the coastal ocean and the Kuroshio current through biological activity and water exchange. A method to estimate the organic matter reserve in the ECS was developed based on satellite data and in situ samplings. Organic carbon storage was estimated at 4.08 × 1013 g, which could be used as a baseline for future estimates. An improved estimation could be found with additional in situ data and with the use of a more sophisticated algorithm for satellite POC analysis.

Impacts of the Kuroshio and Tidal Currents on the Hydrological Characteristics of Yilan Bay, Northeastern Taiwan

Yilan Bay is in the northeast corner of Taiwan at the junction of the East China Sea (ECS) and the Pacific Ocean. This study clarified the composition of water masses adjacent to Yilan Bay. The upper seawater in the bay is characterized by Kuroshio surface water, Taiwan warm current water, and shelf mixed water masses. The flow field in this area is mainly determined by the inter-actions among the northeastern Taiwan countercurrent, Kuroshio Current (KC), and tidal currents. The fall season is the main rainfall period in Yilan Bay, which causes a large amount of river runoff and a further increase in chlorophyll concentration, and the salinity of the upper water layer is observed much lower than other seasons. Water with a high chlorophyll concentration can flow into the ECS with ebb currents and the KC with ebb and flood currents. Combining hourly geosynchronous ocean color imager data and numerical simulation flow field helps us understand short-term changes of chlorophyll concentration. The trajectories of the drifters and virtual particle simulations help us understand the sources and movement of ocean currents in Yilan Bay. The seasonal swing of the KC path outside the bay is an important factor affecting the flow field and hydrological characteristics.

The Impact of an Environmental Way of Customer’s Thinking on a Range of Choice from Transport Routes in Maritime Transport

The paper deals with the impact that an environmental way of thinking has on shipping and transport company customers regarding their preferences in choosing a transport route. Nowadays, maritime transport plays a very important role mainly in transoceanic container transport. It also deals with the statistics focused on container shipping, especially between North America and Europe. These statistics contribute to a general description of the development of container shipping on the route that is applicated in this case study. The significant impact of this kind of transport also reflects the estimation of the future development of container transport on the selected transport route. In this view, the least square method is used in this paper. This method can present the trend of development according to statistics. Thanks to these materials, this paper estimates a slight increase of the number of containers transported between North America and Europe in the near future. This increase will have a certain effect on the environment. Thus, as part of their business policy of sustainability and environment protection, customers will prefer a mode of transport and transport routes featuring a smaller effect on the environment in the future. The relevance of such a change in preferences in planning transport routes for the customer is reflected in the case study presented in this paper. So, one part of this paper is also dedicated to information about the impact of maritime transport on the environment. This part also explains the impact according to different studies that have been published in the last few years. The main contribution of this paper is also to point out the importance of this factor for the preferences of customers via the multi-criteria decision method. Using a multi-criteria decision method, it outlines how the factor of the impact on the environment can significantly change the offer made by a transport or shipping company, and thus how it represents a key element of whether the customer would prefer the given offer or focus on a competitor’s offer.

East China Sea increasingly gains limiting nutrient P from South China Sea

The Taiwan Strait (TS) directly connects two of the richest fishing grounds in the world - the East China Sea (ECS) and the South China Sea (SCS). Carbon and nutrient supplies are essential for primary production and the Yangtze River is an important source for the ECS. However the ECS is severely P-limited. The TS transports an order of magnitude more carbon and a factor of two more phosphate (P) to the ECS than the Yangtze River does. To evaluate the temporal variability of these supplies, the total alkalinity (TA), dissolved inorganic carbon (DIC), nitrate plus nitrite (N), P, and silicate (Si) fluxes through the TS were estimated using empirical equations for these parameters and the current velocity, which was estimated using the Hybrid Coordinate Ocean Model (HYCOM). These empirical equations were derived from in situ salinity and temperature and measured chemical concentrations that were collected during 57 cruises (1995–2014) with a total of 2096 bottle samples. The 24-month moving averages of water, carbon, and nutrient fluxes significantly increase with time, so does the satellite chlorophyll a concentration. More importantly, the increased supply of the badly needed P from the TS is more than that from the Yangtze River.