Interannual to Interdecadal Variability of the Southern Yellow Sea Cold Water Mass and Establishment of “Forcing Mechanism Bridge”

The Yellow Sea cold water mass (YSCWM) occupies a wide region below the Yellow Sea (YS) thermocline in summer which is the most conservative water and may contain clearer climate signals than any other water masses in the YS. This study investigated the low-frequency variability of the southern YSCWM (SYSCWM) and established the “forcing mechanism bridge” using correlation analysis and singular value decomposition. On the interannual timescale, the southern oscillation can affect the SYSCWM through both the local winter monsoon (WM) and the sea surface net heat flux. On the decadal timescale, the Pacific decadal oscillation (PDO) can affect the SYSCWM via two “bridges”. First, the PDO affects the SYSCWM intensity by Aleutian low (AL), WM, and surface air temperature (SAT). Second, the PDO affects the SYSCWM by AL, WM, Kuroshio heat transport, and Yellow Sea warm current. The Arctic oscillation (AO) affects the SYSCWM by the Mongolian high, WM, and SAT. Before and after the 1980s, the consistent phase change of the PDO and the AO contributed to the significant decadal variability of the SYSCWM. Finally, one simple formula for predicting the decadal variability of SYSCWM intensity was established using key influencing factors.

Changes in detrital sediment supply to the central Yellow Sea since the last deglaciation

The sediment supply to the central Yellow Sea since the last deglaciation was uncovered through clay mineralogy and geochemical analysis of core 11YS-PCL14 in the Central Yellow Sea Mud (CYSM). The core can be divided into four units based on the various proxies, such as grain size, clay mineralogy, geochemistry, and Sr and Nd isotopes: Unit 4 (700–520 cm; 15.5–14.8 ka), Unit 3 (520–310 cm; 14.8–12.8 ka), Unit 2 (310–130 cm; 12.8–8.8 ka), and Unit 1 (130–0 cm; <8.8 ka). Unit 2 is subdivided into two subunits, Unit 2-2 (310–210 cm; 12.8–10.5 ka) and Unit 2-1 (210–130 cm; 10.5–8.8 ka), according to smectite content. Comparison of the clay mineral compositions, rare earth elements, and εNd indicate distinct provenance shifts in core 11YS-PCL14. Moreover, the integration of clay mineralogical and geochemical indices show different origins according to particle size. During the late last deglaciation (Units 3 and 4, 15.5–12.8 ka), Unit 4 sediments originated from all potential provenance rivers, such as the Huanghe, Changjiang, and western Korean rivers, while the source of coarse sediments changed to the Huanghe beginning with Unit 3. Fine-grained sediment was still supplied from all rivers during the deposition of Unit 3. Early Holocene (Unit 2) sediments were characterized by oscillating grain size, clay minerals, and moderate εNd values. In this period, the dominant fine-sediment provenance changed from the Huanghe to the Changjiang, whereas coarse sediments most likely originated from western Korean rivers. The Unit 1 CYSM sediments were sourced primarily from the Changjiang, along with minor contributions from the western Korean rivers. Possible transport mechanisms concerning such changes in the sediment provenance include paleo-river pathways, tidal stress evolution, and the development of the Yellow Sea Warm Current and coastal circulation systems, depending on the sea level fluctuations.

The Yellow Sea Warm Current flushes the Bohai Sea microbial community in winter

The effect of the Yellow Sea Warm Current (YSWC) on virio- and bacterioplankton communities in the Bohai Sea is unknown. In this study, the composition and dynamic changes of virio- and bacterioplankton at the entrance of the Bohai Sea were measured to determine the influence of the YSWC on those communities and vice versa. In the Bohai Strait, there were east to west gradients of water chemistry and hydrology. The turbulent mixing between the deep north-western ‘warm’ current, which is 9°C, and the cold, nutrient-rich Bohai Sea water at 7–8°C appears to stimulate the abundance of both viruses and heterotrophic bacteria, with numbers at the junction of ‘warm’ and cold water being almost 10-fold greater than in the low-thermohaline areas, and peaking where the temperature is the highest. The average viral and bacterial abundances in the north-eastern area are much higher than in the south-western area. It proved that the YSWC entered the Bohai Sea with poor biomass and exited with rich biomass, which, in turn, enriches the Yellow Sea microbial loop. Our results showed the dramatic effect of temperature rise and increasing eutrophication on microbial abundance and marine microbial communities.

Dispersal Characteristics and Pathways of Japanese Glass Eel in the East Asian Continental Shelf

The Japanese eel Anguilla japonica is an important aquaculture fish species in the East Asian countries of Japan, China, Korea, and Taiwan. All glass eel fry are captured from the wild and understanding the recruitment patterns of the glass eel is important. The larvae of A. japonica are passively transported to the East Asian Continental Shelf by the North Equatorial Current, the Kuroshio, the Kuroshio intrusion currents, and coastal currents. In each location, recruitment time is diverse: It is November in Taiwan and April in the Yalu River. How the glass eels reach recruitment areas remains poorly understood. Here, we combine information from larval ages based on otolith increments, simulated drifting paths on the East Asian Continental Shelf, and main fishing seasons in each location of East Asia. We identify five main recruitment blocks: (1) The main Kuroshio, (2) The Taiwan Strait Warm Current, (3) The Taiwan Warm Current, (4) The Yellow Sea Warm Current and (5) The branch of Yellow Sea Warm Current. The counted age of the glass eels is significantly underestimated for the later recruits, possibly due to the cessation of the otolith edge growth under low water temperatures. This study clarifies the eel’s larval characteristics and transport mechanisms in the East Asia Continental Shelf, providing important information for its recruitment dynamics in the marine stage.