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The sea level in the east of Luzon Strait along the latitudinal band (18°–22°N, 125°–170°E) demonstrates a unique decreasing trend during 1993–2020, with weakening of eddy kinetic energy (EKE), weaker Kuroshio transport and stronger looping pathway in the Luzon Strait. Neither the surface wind forcing (remote Rossby wave and local Ekman convergence/divergence) nor surface buoyancy forcing (heat flux and Ekman thermal advection) could explain the observed sea level and EKE decreasing trend. From the subsurface perspective, by using the observational data analysis and ventilated thermocline theory, we propose that the reduction of mode water in the subsurface ocean contributes to the above changes during the past ∼30 years. The mode water forms primarily in the mid‐latitude and then is carried by the thermocline circulation southwestward after it subducts into the subsurface ocean. It takes ∼5 years for the mode water to arrive at the latitudinal band of Luzon Strait and affect the vertical stratification by changing the slope of thermocline. When the volume of mode water shrinks, the slope of thermocline would flatten, making the upper thermocline lift along the Luzon Strait latitudinal band. Whereafter, the subtropical front weakens, reducing the vertical velocity shear between the surface eastward Subtropical Counter Current and subsurface westward North Equatorial Current and sea level due to the baroclinic adjustment. Besides, the flattened thermocline and weakened vertical velocity shear results in the EKE reduction, which will contribute to the decreasing of sea level due to the weakened eddy‐forcing. Plain Language Summary: Sea level change is an important and hot issue for the ocean and climate. In the past ∼30 years, the sea level in the east of Luzon Strait exhibits a unique band of decreasing trend, which affects the Kuroshio, one of the strongest ocean western boundary currents, and water exchange between the Western Pacific Ocean and the South China Sea. The decreasing of seal level can neither be explained by the surface wind forcing nor by the buoyancy forcing. Here we show that during 1993–2020, the reduction of mode water, a subsurface water mass between the upper and lower thermocline, contributes to the sea level decreasing along the latitudinal band of Luzon Strait. On the one hand, the volume shrinkage of mode water will reduce the tilt of thermocline and then the sea level. On the other hand, the decreasing of mode water and flattening of thermocline result in eddy activity reduction, which further lowers the sea level. Our study highlights the importance of subsurface forcing (The "subsurface forcing" means that we consider the forcing induced by mode water from a subsurface perspective in this study) induced by the mode water, in longer time scale. Key Points: The sea level along the latitude of Luzon Strait shows significant fine‐band structure of decrease during 1993–2020Neither the surface wind nor buoyancy forcing could explain the observed decreasing trend of the sea levelThe decreasing of subsurface mode water plays a key role for the decrease of sea level by changing the tilt of thermocline [ABSTRACT FROM AUTHOR]

Galectins are proteins that play a crucial role in the innate immune response against pathogenic microorganisms. Previous studies have suggested that Galectin-3 could be a candidate gene for antibacterial immunity in the large yellow croaker Larimichthys crocea. In this study, we cloned the Galectin-3 gene in the large yellow croaker, and named it LcGal-3. The deduced amino acid sequence of LcGal-3 contains a carbohydrate recognition domain with two conserved β-galactoside binding motifs. Quantitative reverse transcription PCR (qRT-PCR) analysis revealed that LcGal-3 was expressed in all the organs/tissues that were tested, with the highest expression level in the gill. In Larimichthys crocea kidney cell lines, LcGal-3 protein was distributed in both the cytoplasm and nucleus. Moreover, we found that the expression of LcGal-3 was significantly upregulated upon infection with Pseudomonas plecoglossicida, as demonstrated by qRT-PCR analyses. We also purified the LcGal-3 protein that was expressed in prokaryotes, and found that it has the ability to agglutinate large yellow croaker red blood cells in a Ca2+-independent manner. The agglutination activity of LcGal-3 was inhibited by lipopolysaccharides (LPS) in a concentration-dependent manner, as shown in the sugar inhibition test. Additionally, LcGal-3 exhibited agglutination and antibacterial activities against three Gram-negative bacteria, including P. plecoglossicida, Vibrio parahaemolyticus, and Vibrio harveyi. Furthermore, we studied the agglutination mechanism of the LcGal-3 protein using blood coagulation tests with LcGal-3 deletion and point mutation proteins. Our results indicate that LcGal-3 protein plays a critical role in the innate immunity of the large yellow croaker, providing a basis for further studies on the immune mechanism and disease-resistant breeding in L. crocea and other marine fish. [ABSTRACT FROM AUTHOR]

Galectins are proteins that are involved in the innate immune response against pathogenic microorganisms. In the present study, the gene expression pattern of galectin-1 (named as NaGal-1) and its function in mediating the defense response to bacterial attack were investigated. The tertiary structure of NaGal-1 protein consists of homodimers and each subunit has one carbohydrate recognition domain. Quantitative RT-PCR analysis indicated that NaGal-1 was ubiquitously distributed in all the detected tissues and highly expressed in the swim-bladder of Nibea albiflora, and its expression could be upregulated by the pathogenic Vibrio harveyi attack in the brain. Expression of NaGal-1 protein in HEK 293T cells was distributed in the cytoplasm as well as in the nucleus. The recombinant NaGal-1 protein by prokaryotic expression could agglutinate red blood cells from rabbit, Larimichthys crocea, and N. albiflora. The agglutination of N. albiflora red blood cells by the recombinant NaGal-1 protein was inhibited by peptidoglycan, lactose, D-galactose, and lipopolysaccharide in certain concentrations. In addition, the recombinant NaGal-1 protein agglutinated and killed some gram-negative bacteria including Edwardsiella tarda, Escherichia coli, Photobacterium phosphoreum, Aeromonas hydrophila, Pseudomonas aeruginosa, and Aeromonas veronii. These results set the stage for further studies of NaGal-1 protein in the innate immunity of N. albiflora. [ABSTRACT FROM AUTHOR]

Seasonality of the subtropical countercurrent (STCC) and associated surface eddy kinetic energy (EKE) near the western North Pacific boundary is investigated. Unlike the interior STCC region where the EKE peaks in late spring (May) interpreted by the vertical velocity shear between the STCC and underlying North Equatorial Current in early spring (March), the high EKE near the western boundary lasts from May to August with unclear mechanism. Other studies suggest that the wind, heat flux and mode water could contribute to the EKE seasonality along the STCC band. But all these mechanisms can barely explain the observed EKE seasonality near the western boundary comparing to the interior STCC region, since there are no seasonal phase changes in the above forcings. We found that the eddies provide significant contribution to the EKE and STCC seasonal variation near the western boundary. The westward propagating eddies are intensified by the background shear instability near the western boundary and then further induce the high EKE in summer through the EKE convergence. At the same time, the strong surface current by the enhanced eddy activity changes the seasonality of the STCC. The dynamics is different near the western boundary from that in the interior ocean, with eddies playing more important role in modulating the EKE and STCC seasonal variation. The finding of this study will contribute to a better understanding of the dynamics of eddy‐current interaction and ocean variability near the western boundary. Plain Language Summary: In the Northwestern Pacific subtropical gyre, an eastward current called the Subtropical Countercurrent (STCC) flows against the broad westward North Equatorial Current (NEC). Caused by the vertical velocity shear between the STCC and underlying NEC in early spring (March), the eddy kinetic energy (EKE) peaks in late spring (May) in the open ocean (east of 135°E). However, the EKE seasonality near western boundary is different, exhibiting high value from May to August with unclear mechanism. Our study shows that the westward propagating eddies modulate the seasonal phase changes of the EKE and STCC near the western boundary, comparing to the interior STCC region. When the eddies move from east to west and arrive at the western boundary, with absorbing energy from the background circulation, they intensify and induce the phase shift of the EKE and STCC seasonality through the EKE convergence. Our study shows eddies play more important role in modulating the EKE and STCC seasonal variation near the western boundary, rather than the external forcings, such as the wind, heat flux and mode water. The finding of this study will contribute to a better understanding of the dynamics of eddy‐current interaction and ocean variability near the western boundary. Key Points: The Eddy Kinetic Energy (EKE) and Subtropical Countercurrent (STCC) near the western boundary shows significant seasonal phase changesThe peak of EKE and STCC near the western boundary lasts from May to August, different from the peak in May in the interior oceanThe STCC seasonality near western boundary is modulated by westward propagating eddy through EKE convergence and baroclinic instability [ABSTRACT FROM AUTHOR]

Phosphoribosyl pyrophosphate synthetases (EC 2.7.6.1) are key enzymes in the biological synthesis of phosphoribosyl pyrophosphate and are involved in diverse developmental processes. In our previous study, the PRPS1 gene was discovered as a key disease-resistance candidate gene in yellow drum, Nibea albiflora, in response to the infection of Vibrio harveyi, through genome-wide association analysis. This study mainly focused on the characteristics and its roles in immune responses of the PRPS1 gene in yellow drum. In the present study, the NaPRPS1 gene was cloned from yellow drum, encoding a protein of 320 amino acids. Bioinformatic analysis showed that NaPRPS1 was highly conserved during evolution. Quantitative RT-PCR demonstrated that NaPRPS1 was highly expressed in the head-kidney and brain, and its transcription and translation were significantly activated by V. harveyi infection examined by RT-qPCR and immunohistochemistry analysis, respectively. Subcellular localization revealed that NaPRPS1 was localized in cytoplasm. In addition, semi-in vivo pull-down assay coupled with mass spectrometry identified myeloid differentiation factor 88 (MyD88) as an NaPRPS1-interacting patterner, and their interaction was further supported by reciprocal pull-down assay and co-immunoprecipitation. The inducible expression of MyD88 by V. harveyi suggested that the linker molecule MyD88 in innate immune response may play together with NaPRPS1 to coordinate the immune signaling in yellow drum in response to the pathogenic infection. We provide new insights into important functions of PRPS1, especially PRPS1 in the innate immunity of teleost fishes, which will benefit the development of marine fish aquaculture. [ABSTRACT FROM AUTHOR]

Recent evidence shows that the North Pacific subtropical gyre and the Kuroshio Extension (KE) and Oyashio Extension (OE) fronts have moved poleward in the past few decades. However, changes of the North Pacific Subtropical Fronts (STFs), anchored by the North Pacific subtropical countercurrent in the southern subtropical gyre, remain to be quantified. By synthesizing observations, reanalysis, and eddy-resolving ocean hindcasts, we show that the STFs, especially their eastern part, weakened (20% ± 5%) and moved poleward (1.6° ± 0.4°) from 1980 to 2018. Changes of the STFs are modified by mode waters to the north. We find that the central mode water (CMW) (180°–160°W) shows most significant weakening (18% ± 7%) and poleward shifting (2.4° ± 0.9°) trends, while the eastern part of the subtropical mode water (STMW) (160°E–180°) has similar but moderate changes (10% ± 8%; 0.9° ± 0.4°). Trends of the western part of the STMW (140°–160°E) are not evident. The weakening and poleward shifting of mode waters and STFs are enhanced to the east and are mainly associated with changes of the northern deep mixed layers and outcrop lines—which have a growing northward shift as they elongate to the east. The eastern deep mixed layer shows the largest shallowing trend, where the subduction rate also decreases the most. The mixed layer and outcrop line changes are strongly coupled with the northward migration of the North Pacific subtropical gyre and the KE/OE jets as a result of the poleward expanded Hadley cell, indicating that the KE/OE fronts, mode waters, and STFs change as a whole system. [ABSTRACT FROM AUTHOR]

The western North Pacific Subtropical Countercurrent (WSTCC), anchored by the western subtropical front (WSTF), varies from seasonal to multidecadal time scales and affects the climate variability in the North Pacific. However, conflicting views exist for physical mechanisms of the decadal to multidecadal variability of the WSTF/WSTCC. While many previous studies attribute the WSTF/WSTCC decadal variability to the anomalous wind forcing by the Pacific Decadal Oscillation, by synthesizing observations, reanalysis products and the pre‐industrial model simulation experiment, the present study demonstrates that they are controlled by the Atlantic Multidecadal Oscillation (AMO) through the Subtropical Mode Water (STMW) variability. The AMO induced decadal temperature and volume anomalies of the STMW are stored in the subsurface ocean through the subduction process south of the Kuroshio Extension. Then these anomalies propagate southwestward along the thermocline circulation and reaches the northern flank of the WSTCC in about 5 years. During the AMO‐positive phase, the anomalous warm and thin STMW flattens the upper thermocline, reduces the meridional temperature gradient and weakens the WSTF intensity, lagging 5 years behind the AMO index. Subsequently, the WSTCC decreases and moves southward, and vice versa for the AMO‐negative phase. Our results provide a potential predictability for the WSTF and WSTCC decadal to multidecadal variability and are important for the North Pacific climate change and the biogeochemical processes. Plain Language Summary: The North Pacific subtropical countercurrent (STCC) is a shallow eastward jet stretching from the western Pacific to the north of Hawaii, accompanied by the subtropical front (STF) in the upper 200 m. Specifically, the western branch (western North Pacific Subtropical Countercurrent [WSTCC] and western subtropical front [WSTF]) is much stronger and broader than the eastern part. Decadal to multidecadal variability of the WSTCC and WSTF is known to have significant effects on the North Pacific climate change and biogeochemical processes. However, conflicting views exist for physical mechanisms of the decadal to multidecadal variability of the WSTF/WSTCC. While many previous studies attribute the WSTF/WSTCC decadal to multidecadal variability to the anomalous wind forcing by the Pacific Decadal Oscillation, the present study demonstrates that they are controlled by the Atlantic Multidecadal Oscillation (AMO) through the Subtropical Mode Water (STMW) variability. The STMW anomalies caused by the AMO are stored in the subsurface ocean and would propagate southwestward along the circulation, reach the WSTF/WSTCC region in about 5 years and influence the current's decadal to multidecadal variations. Our results provide a potential predictability for the WSTF and WSTCC variability on decadal to multidecadal time scales and are important for the North Pacific climate change and the biogeochemical processes. Key Points: The decadal‐multidecadal variation of the western North Pacific subtropical front and countercurrent is controlled by the Atlantic Multidecadal Oscillation (AMO)The AMO modulates the Subtropical Mode Water (STMW) variability, which controls the upper pycnocline slope and dominates the intensity of the countercurrentIt takes ∼5 years for the STMW to reach the countercurrent region, corresponding to the time lag of the frontal changes with the AMO [ABSTRACT FROM AUTHOR]

The meridional shift of the Kuroshio Extension (KE) front and changes in the formation of the North Pacific Subtropical Mode Water (STMW) during 1979–2018 are reported. The surface-to-subsurface structure of the KE front averaged over 142°–165°E has shifted poleward at a rate of ~0.23° ± 0.16° decade−1. The shift was caused mainly by the poleward shift of the downstream KE front (153°–165°E, ~0.41° ± 0.29° decade−1) and barely by the upstream KE front (142°–153°E). The long-term shift trend of the KE front showed two distinct behaviors before and after 2002. Before 2002, the surface KE front moved northward with a faster rate than the subsurface. After 2002, the surface KE front showed no obvious trend, but the subsurface KE front continued to move northward. The ventilation zone of the STMW, defined by the area between the 16° and 18°C isotherms or between the 25 and 25.5 kg m−3 isopycnals, contracted and displaced northward with a shoaling of the mixed layer depth hm before 2002 when the KE front moved northward. The STMW subduction rate was reduced by 0.76 Sv (63%; 1 Sv ≡ = 106 m3 s−1) during 1979–2018, most of which occurred before 2002. Of the three components affecting the total subduction rate, the temporal induction (−∂hm/∂t) was dominant accounting for 91% of the rate reduction, while the vertical pumping (−wmb) amounted to 8% and the lateral induction (−umb ⋅ ∇hm) was insignificant. The reduced temporal induction was attributed to both the contracted ventilation zone and the shallowed hm that were incurred by the poleward shift of KE front. [ABSTRACT FROM AUTHOR]

Abstract: The meridional shift of Oyashio Extension (OE) front in the past 36 years was analyzed by using the high‐resolution Optimum Interpolation SST data. The annual mean OE front has moved northward in its eastern part (between 157°E and 172°E) by 0.018°/year but no obvious poleward shift in the western OE front (between 145°E and 157°E). It is shown that the trade wind became stronger and broader, and the whole wind field moved northward in the past 36 years, shifting the zero wind stress curl line (or the zero Sverdrup streamline) and the eastern OE front northward. The above mechanism is confirmed by a 1.5‐layer reduced‐gravity model simulation as well as the altimetry data. Meanwhile, the local Ekman heat transport anomaly due to the wind field changes is found to be one of the contributors to the northward shift of the eastern OE front. However, both wind stress curl and local Ekman heat transport anomalies do not favor northward shift of the western OE front. [ABSTRACT FROM AUTHOR]