Monsoon Transition Research Articles

Crop yield and carbon sink potential with precipitation in maize and potato cropland ecosystems over the summertime monsoon transition zone of China

AbstractChina has significantly enhanced vegetation coverage and terrestrial carbon sink functions through ecological restoration. However, cropland ecosystems are sensitive to a changing climate over the summertime monsoon transition zone of China (SMTZC), which has implications for carbon cycling. For example, it is unclear how changes in precipitation will affect the cropland ecosystem carbon sinks (CSe) and carbon sink potential (CSp), and the mechanisms of tradeoffs that develop between plant and soil organic carbon (SOC) are unclear. Here, we integrated crop yield, total biomass (TB) and water coefficient in a combined field and modelling experimental. We explored the mechanisms of ecosystem carbon cycling and CSp in the SMTZC under different precipitation scenarios. We found that soil organic carbon sink (SOCs) was strongly correlated with the plant organic carbon sink (POCs) and discovered. Significant differences in CSp between ecosystems resulting from interannual precipitation. The C4 (maize, Zea mays) and C3 (potato, Solanum tuberosum L) carbon sinks (CSs) were 68.59, 190.73, 160.37 Mt and 10.21, 30.97, 14.59 Mt for the 3 years, respectively. Precipitation effectively increased TB and yield, but excessive precipitation in them, which was most obvious in C3 ecosystem (R2 > 0.60) and reduced POCs, evident in C4 ecosystem (R2 > 0.16). This study provides data and a scientific basis for increasing CS and achieving carbon neutrality in cropland.

Ecological Response to the Diluted Water in Guangxi during the Spring Monsoon Transition in 2021

Based on the field survey data of the Guangxi offshore voyage in May 2021, the distribution characteristics of the wind field during the spring monsoon transition period, the temporal and spatial changes in the diluted water path, and the corresponding ecological responses were analyzed. The results show the following: the core region of diluted water is located along the coast of Guangxi, and the diluted water expands to the east and west at the same time, where the thickness of the diluted water reaches 20 m. Under the combined action of the easterly wind and westward current, the westward expansion trend was stronger than the eastward expansion trend. The surface distribution of suspended solids, chlorophyll a, dissolved oxygen, and active silicon is similar to the dispersion range of the diluted water, and the high-value areas all appear near the estuary, which is basically consistent with the salinity distribution in the core region of the diluted water. Under the mixing caused by the wind and tide in the estuary area, the difference in dissolved oxygen between the surface and bottom layer is small, while in the nearshore area, the stratification of seawater hinders the dissolved oxygen’s downward transmission, resulting in a large difference in dissolved oxygen between the bottom and the surface.

Circulation structure and dynamic characteristics of Western Tropical Indian Ocean associated with monsoon transitions

The circulation structure in the western tropical Indian Ocean (WTIO) was investigated based on surface drifters and Simple Ocean Data Assimilation (SODA), with particular attention to the characteristics of the circulation structure associated with seasonal monsoon transitions. Surface drifter trajectories manifest three distinct seasonally dependent patterns of western boundary currents in the WTIO. The northward Somali Current (SC) flows across the equator to ∼10 °N in the boreal summer (June to August; JJA). The northward SC turns offshore near the equator during monsoon transitions. The southward SC feeds the South Equatorial Countercurrent together with the northward East African Coast Current in the boreal winter (December to February; DJF). While during the monsoon transition (MAM and SON), drifters prefer to turn eastward and feed the strong equatorial currents. Based on satellite observations, the results of a balanced diagnostic model demonstrate that the geostrophic component Uζ and the wind-driven componentUτ predominate the mean state and the seasonal variations of circulation in the WTIO. The vertical motion shows that upwelling primarily occurs along the coasts of Somali and Oman and is induced by offshore Ekman transport. Ekman transport and associated vertical motions constitute meridional overturning circulation. The SODA results confirm the existence of an equatorial roll in the boreal summer and winter. The results elucidate the dynamic relationships between 3-D circulation and monsoon transitions in the WTIO.

Shrimps distribution and their relationship to the environmental variables in Arafura Sea

Arafura Sea is well-known as the important area for commercial shrimp fisheries in Indonesia. The density of shrimps was highly influenced by their fishing pressure and environmental condition. The objective of this research was to study the distribution of shrimps based on its stock density and their relationship with the environmental variables. Trawling swept area method was used in 16 sampling sites of Arafura Sea during the transition monsoon in 2016. Some environmental variables in bottom layers as shrimp habitat were measured, including chlorophyll-a, dissolved oxygen, depth, salinity, temperature and pH. The results showed that the largest density of shrimps was found in the southern coast of Aru where it has the largest concentration of chlorophyll-a and dissolved oxygen. Among all the environmental variables, Chlorophyll-a was the main variable affected the density of shrimps. Three most dominant species were Penaeus semisulcatus, Metapenaeus endeavouri and Metapenaeus ensis. There was indication of the decreasing shrimp stock in Arafura Sea. The ecosystem-based fisheries management should be developed to rebuild the stock density and to enhance the environmental quality of Arafura Sea.

Seasonal and Year-To-Year Variability of Boundary Currents and Eddy Salt Flux along the Eastern and Southern Coasts of Sri Lanka Observed by PIES and Satellite Measurements

Abstract Boundary currents along the Sri Lankan eastern and southern coasts serve as a pathway for salt exchange between the Bay of Bengal and the Arabian Sea basins in the northern Indian Ocean, which are characterized by their contrasting salinities. Measurements from two pairs of pressure-sensing inverted echo sounders (PIES) deployed along the Sri Lankan eastern and southern coasts as well as satellite measurements are used to understand the variability of these boundary currents and the associated salt transport. The volume transport in the surface (0–200-m depth) layer exhibits a seasonal cycle associated with the monsoonal wind reversal and interannual variability associated with the Indian Ocean dipole (IOD). In this layer, the boundary currents transport low-salinity water out of the Bay of Bengal during the northeast monsoon and transport high-salinity water into the Bay of Bengal during the fall monsoon transition of some years (e.g., 2015 and 2018). The Bay of Bengal salt input increases during the 2016 negative IOD as the eastward flow of high-salinity water during the fall monsoon transition intensifies, whereas the effect of the 2015/16 El Niño on the Bay of Bengal salt input is still unclear. The time-mean eddy salt flux over the upper 200 m estimated for the April 2015–March 2019 period along the eastern coast accounts for 9% of the salt budget required to balance an estimated 0.13 Sv (1 Sv ≡ 106 m3 s−1) of annual freshwater input into the Bay of Bengal. The time-mean eddy salt flux over the upper 200 m estimated for the December 2015–November 2019 period along the southern coast accounts for 27% of that same salt budget. Significance Statement In the northern Indian Ocean, the highly saline Arabian Sea undergoes extreme evaporation while the Bay of Bengal (BoB) receives excess freshwater input. The focus of this study is the role of the observed time-variable circulation around Sri Lanka that permits the exchange between these basins to maintain their salinity distributions. The circulation fluctuates seasonally following the monsoon wind reversal and interannually in response to large-scale climate modes. The BoB freshwater export around Sri Lanka occurs during the northeast monsoon, whereas saline water import occurs during the fall monsoon transition of some years. However, rapid changes in both water volume transport and salt exchange can occur. The circulation over 0–200-m depth transports ∼9%–27% of the BoB salt budget.

Understanding the Mechanism of Currents through the Malacca Strait Study Case 2020 – 2022 : Mean state, Seasonal and Monthly Variation

The Malacca Strait is the importance waters for international shipping routes and more 200 cases of ship collisions in the period 1970-2015 in this strait. That is related to some a shallow depth waters with many small islands and strong current which is making this strait have a highest risk in certain seasons. The CMEMS data used to understanding of mechanism of current, illustrate the pattern and tranport volume. The research uses descriptive and the statistical methods to understanding of mechanism and variability of current. The analysis of current patterns and water level shows that during the monsoon winds active, the current always moves to the Andaman Sea, we called the southeast current system. The Northeast (NE) and Southwest (SW) monsoon wind is strongly influence to the mechanism of formation southeast current system, which causes the varition in sea level hight in eastern and western of Malacca Strait. During the NE monsoon season, the water masses of the South China Sea are push away into the Karimata Strait, causing the sea level in the eastern part to be higher than the western part and will increase the current speed. On the other hand, during the SW monsoon season, the water masses from the Karimata Strait is pushed away from the eastern part of the Malacca Strait which causes the sea level decrease and causes the current speed to weaken. Numbers eddies phenomenon were found at the Malacca Strait each season. The anticyclonic eddies occurred almost every season centered at 3° - 5° N, 97° - 100° E. Meanwhile anticyclonic eddies appear around the northern part of Sumatra centered at 4° - 5°N, 99° - 101°E during SW Monsoon season and the eddies formation also existed during the second transition monsoon season.

The morphodynamics of wave on a monsoon-dominated coasts: West coast of GoT

Globally, coastal areas are eroding due to climate change, which influences sea level rise, storm surge, cyclones, and hurricanes. During the past two decades, the coastline areas bordering the Gulf of Thailand have been gradually eroded and extended, with no indication of subsiding, specifically during the northeast monsoon storm season. Subsequently, this research aims to determine how beaches alter along the west coast of Gulf of Thailand during different monsoon seasons. Beach profile surveys were performed throughout the southwest monsoon, the transition monsoon, and the northeast monsoon. The complexity of coastal dynamics, such as wave parameters, was applied to examine the wave features in the five (5) sampling stations along the west coast of Gulf of Thailand during the monsoon seasons to comprehend the issue better. The numerical modelling with MIKE 21 SW illustrates Gulf of Thailand’s West Coast beaches, primarily erosional beaches subject to monsoon wave conditions, especially at Singhanakhon beach, with a great loss of −9.15 m3 of sand volume. Nevertheless, erosion persisted as a concern resulting from interactions of coastal structures with few processes such as wave characteristics and sediment budget. Hence, comprehending coastal features and hydrodynamic processes is essential for bridging the issue’s knowledge gap and offering alternatives in sustainable coastal management.

Frontogenesis and estuarine circulation at the shallow sill of a tropical fjord: Insights from Ambon Bay, eastern Indonesia

Surface water flushing of the tropical fjord of Ambon Bay is linked to stratification and frontogenesis that vary with tidal and seasonal cycles. Tidal- and seasonal-based​ deployments of CTD casts and bottom-mounted current meters in 2019 coupled with an analytical model were employed to investigate estuarine circulation (i.e. flood/ebb-mean transport) at the sill of Ambon Bay. Spring tides produce a large (flood/ebb-mean) horizontal salinity gradient, ∂S/∂x, (up to 13 × 10−4‰/m) across the sill, intensifying estuarine circulation. This intensification of ∂S/∂x is driven by strong (flood/ebb-mean) stratification at the inshore sill, associated with buoyant frontogenesis (indicated by densimetric Froude number, Fo2≥ 0.3) during the related strong flood tides. Estuarine circulation is stronger in the easterly monsoon (July) than in the transitional monsoon (October) since buoyant fronts are larger in thickness and horizontal extension along the sill in the easterly monsoon following high freshwater input. The estuarine circulation was intensified by a deep-water renewal process in which deep water from the adjacent open sea is upwelled to the sill by internal waves.Flushing of inner Ambon Bay (IAB, the fjord basin) due to estuarine circulation at the sill only occurs at the surface layer of IAB. Within a spring–neap sequence (∼2 weeks), the net oceanic inflow due to estuarine circulation at the sill replenished 73% and 41% volume of the surface layer of IAB in the easterly monsoon and the transitional season, respectively. The knowledge of flushing of IAB due to net oceanic inflow presented here has application for the mitigation of pollution build-up and for understanding of oceanic nutrient supply in the basin.

Response of extreme precipitation to climatic warming in the Weihe river basin, China and its mechanism

Abstract As global warming continues, extreme precipitation events occur frequently in inland areas, seriously affecting human security and the ecological environment. Spatiotemporal evolution of extreme precipitation as well as response of extreme precipitation to climatic warming and its mechanism were investigated by considering the Weihe river basin in a monsoon transition zone of China as a research object. The results indicate that while the annual average temperature of the Weihe river basin increased with fluctuations from 1966 to 2017, except for the consecutive dry days (CDD) and simple daily intensity index that increased slightly, the other extreme precipitation indices (consecutive wet days, R25, and Rx5day) tended to decrease. Moreover, except for the CDD, the other four indices gradually increased from the northwest to the southeast, showing a similar trend to the temperature. The relationship between the 95th percentile threshold and temperature (hereinafter referred to as the P 95d–T relationship) in the Weihe river basin demonstrates the hook structure and its strength in terms of response is mainly dominated by the super-Clausius–Clapeyron (C–C) and C–C scaling. Furthermore, the peak temperature rises gradually from the northwest to the southeast. The results can provide important reference for the prediction of climate change and future studies of disaster risk in the Weihe river basin.

Warming Trend and Cloud Responses over the Indochina Peninsula during Monsoon Transition

An exacerbated precipitation–temperature relationship can lead to compound extremes. The role of clouds in such a relationship is relatively uncertain. Here, we investigate the cloud–precipitation–temperature relationships over the Indochina Peninsula during the summer monsoon transition. The negative correlation between cloudiness/precipitation and surface maximum temperature is valid on seasonal and interannual timescales. The near-surface temperature exhibits interdecadal variability and a long-term warming trend. The warming trend has accelerated in the past two decades. In the anomalous warm years, the remarkably strong western Pacific subtropical high inhibits the development of clouds, especially the middle and high cloud-top regimes, leading to the suppression of deep convection and precipitation. There are more optically thin (moderate to thick) clouds with smaller (larger) effective radii in the high cloud-top regime for the warm (cold) years. The dominance of shallow cumulus is a distinct feature in the warm years. The daytime heating of enhanced surface insolation due to decreased cloudiness is worsened by the dry condition of the precipitation deficit. The water vapor warming effect can prevent an efficient drop in nighttime temperature, thereby exacerbating the warm condition under the warming trend. The cloud–precipitation–temperature relationships coupling with the monsoon development can be used to diagnose the regional scale cloud–climate interactions in climate models.

Community structure of zooplankton during the southwest-northeast monsoon transition period in the southeastern East China Sea

Abstract The assessment of zooplankton spatial structure is critical to quantifying plankton production and biochemical cycling. Here, we show the effect of monsoon-driven hydrographic changes on the spatial patterns of zooplankton at regional scales. Based on a field survey conducted during the monsoon transition, we assess the community structure and ash-free dry weight above 100 m depth in the Kuroshio edge area, southeastern East China Sea. The zooplankton community was dominated by copepods, with calanoids as the most abundant taxon followed by poecilostomatoids. Copepod assemblages comprised 81 species belonging to 41 families, and 23 genera, with Undinula vulgaris as the most abundant species. The richness of zooplankton taxa showed a mounting trend from the coast to offshore, which was opposite to the spatial variation of total zooplankton biomass. Our results suggest a leading influence of the Kuroshio Current during the southwest-northeast monsoon transition period in the southeastern East China Sea.

Recent interdecadal changes in the Tropospheric Biennial Oscillation of the East Asian summer monsoon

This paper focuses on the interdecadal changes in the biennial East Asian summer monsoon (EASM) transition related to the Tropospheric Biennial Oscillation (TBO), which has major impacts on East Asian climate. During 1958–2020, the TBO signal in the EASM exhibits noticeable interdecadal changes around the late 1970s and late 1990s. Among the three periods [1958–1979 (P1), 1980–2000 (P2), 2001–2020 (P3)], the TBO signal is the strongest in P2 and the weakest in P1. Such changes are closely associated with changes in the amplitude and position of wind anomalies over the western North Pacific (WNP). Further analysis indicates that the regime shifts in ENSO properties, including intensity, period, and location of ENSO-related sea surface temperature (SST) anomalies, play a crucial role. Compared with P1, the warm SST anomalies in the central Pacific and North Indian Ocean SST associated with the slowly decaying ENSO together induce the stronger WNP wind anomalies in both P2 and P3. However, such SST warming is relatively weaker in P3 compared with those in P2, which is consistent with the weak intensity and short period of ENSO in P3. In comparison, the anomalous circulation over the WNP is thus relatively weaker in P3 than in P2. Therefore, these anomalous SSTs associated with the shift in the ENSO regime are suggested to induce circulation anomalies over the WNP that subsequently contributed to the changes in the EASM TBO around the late 1970s and late 1990s.

Precipitation-Use Efficiency and Its Conversion with Climate Types in Mainland China

The impacts of climate change on ecosystem productivity and water resources over a long term in China are not well quantified. Precipitation-use efficiency (PUE) is a key parameter that describes carbon and water exchange in terrestrial ecosystems. Research on the response of regional PUE to climate change and its driving forces is of great significance to climate-change mitigation and the sustainable development of regional ecology. Based on an improved actual evapotranspiration (ETa) model, the responses of ETa, net primary productivity (NPP), and PUE to climate change in different climatic regions of China were analyzed; the contributions of various environmental factors to PUE changes were quantified; and the conversion characteristics and regulatory mechanisms of the PUE regime in different climatic regions were identified. The results indicate that the improved ETa model, after considering the limiting effect of energy on ETa in humid regions, can simulate the ETa distribution in China well. Over the past 58 years (1960–2017), ETa and NPP have increased in the western regions and decreased in the eastern regions, with the boundary at 103° E. PUE presents a “low-high-low” spatial distribution from northwest to southeast in China. It is noteworthy that there was a zonal distribution for a high value area of PUE, which coincided with the summer monsoon transition zone. The soil moisture (SM) increase in arid regions is the main driving force of the PUE increase, whereas the annual net radiation (Rn) change in humid regions is the main driving force of the PUE change. The transition zone is the conversion zone, where the prevailing factor limiting vegetation growth transitions from water to energy.

Dengue fever occurrence in India, Brazil, Paraguay, Philippines and Singapore using Google trends

Background. Dengue is a mosquito-borne disease and its occurrence is a worldwide problem. The health seekers may turn to the Internet based data for possible complications and various therapeutic approaches for the treatment. Therefore, our objective is to identify and characterize the seasonal transition of dengue fever using Google Trends. Methods. This was a cross-sectional study of dengue fever internet searches between 2004 and 2017. The Google was indexed the aggregated web data and ranked based on the search volume with respect to time. The countries selected for the study include India, Brazil, Paraguay, Philippines and Singapore based on the maximum number of cases across world. The selected regions were further classified in to seasonal time points and the relative search volume ranks were categorized to two season variables. Mann–Whitney U test was applied to identify the statistical significance. Results. The summer to monsoon transitions were showed highest number cases beginning from 2004 in the selected regions. Furthermore, dengue searches were peaked in both the seasons of summer and monsoon in selected regions. The analyses of data further revealed that 16.2 % of variation in dengue trends is associated with the time between 2004 and 2017.

Energy Distribution Characteristics and Environmental Impact Factors in Different Regions of the Summer Monsoon Transition Zone

The summer monsoon transitional zone is a typical transitional ecosystem that is, also ecologically fragile. It is critical to explore the land surface energy balance and the water and heat transfer processes in this region for water resource management. However, the processes of surface water and heat transfer throughout the transition zone and the effects of environmental factors on energy distribution are understudied. Therefore, we analyzed the surface energy distribution and the environmental factors influencing it in the eastern and western transition zone from July to September, and compared the differing effects of meteorological factors and vegetation on the energy distribution between the two regions. The results show that the main consumption item of the available energy in the west of the transition zone is the latent heat flux. The same is true in the eastern region from July to August, but it changes to sensible heat flux in September. The factors influencing the Bowen ratio in the two regions were ground temperature difference, vapor pressure deficit, shallow soil water content, and drought stress index. Nevertheless, the Bowen ratio in the western region was more sensitive to water factors, whereas that in the eastern region was more sensitive to energy factors. The relationship between the Bowen ratio and the normalized difference vegetation index in the eastern region was more regular. This study provides a scientific basis for reasonably guiding agricultural production in the transition area.

STUDY OF SNPP-VIIRS SATELLITE IMAGE FOR ESTIMATION SURFACE GILL NETS FISHING GROUND IN SEMARANG WATERS, CENTRAL JAVA, INDONESIA

Gillnet fishermen in Semarang often have difficulty determining the fishing grounds. The aims of the study were to analysed the spatial and temporal distribution of sea surface temperature (SST) and chlorophyll-a, to analysed the relationship between variables and to study the estimation of fishing grounds. The data collection method used purposive sampling. Map processing using the Inverse Distance Weighted (IDW) method. The data processing method uses normality test, classical assumption test and linear regression test. Analysis of image data spatially (4 miles from the shoreline) and temporally (west, east and transition monsoons). SST and chlorophyll-a tend to be high near the shore. The lowest SST (28.82OC) and the highest chlorophyll-a (5.11 mg/L) occurred in the east monsoon. The highest SST (31.74OC) and the lowest chlorophyll-a occurred in the west monsoon (1.31 mg/L). SST and chlorophyll-a have an erratic distribution pattern during the transitional monsoon. The value of SST and chlorophyll-a correlation partially to catch was 14.3% (weak) and 74% (very strong). The correlation value of SST to chlorophyll-a is 30.2% (medium). The correlation value of SST and chlorophyll-a simultaneously with catch is 75.3% (very strong). Determination of fishing areas based on high chlorophyll-a1 values and low SST. The coordinates for determining the fishing ground include 6° 53' 24,858" South Latitude 110° 26' 0.071" east west monsoon, 6° 55' 43,941" LS 110° 24' 47,903" east longitude transitional monsoon I, 6° 55' 29,439" latitude 110° 25' 54,790" east longitude, and 6° 55' 11,394" latitude 110° 26' 15,904" east longitude of transitional monsoon II.

Dissolved PAHs impacted by air-sea interactions: Net volatilization and strong surface current transport in the Eastern Indian Ocean

In the Indian Ocean, the marine fate of polycyclic aromatic hydrocarbons (PAHs) is impacted by the unique air-sea interactions with great monsoon characters. By collecting water-column samples during the monsoon transition period, we found PAHs (∑8PAH: 1.1–27 ng L−1) showed significantly different distributions from the Bay of Bengal, Equatorial Indian Ocean, Eastern Indian Ocean, and the South China Sea (p < 0.001). Their vertical profiles showed natural logarithm relationships with depth in the Bay of Bengal and Equatorial Indian Ocean. PAHs were mainly from wood/coal combustion and vehicle emission. The estimation of PAHs’ air-seawater exchange flux revealed net volatilizations from seawater except in the Eastern Indian Ocean. The Wyrtki Jet, a surface current driven by the westerly wind, was observed in the equatorial area. This swift current could transport PAHs eastward efficiently with a mass flux of 636 ± 188 g s−1. The subsurface current, Equatorial Undercurrent, played a less crucial role in PAHs’ lateral transport with a flux of 115 ± 31.3 g s−1. This study preliminarily revealed the role of air-sea interactions on PAHs’ transport and fate in the open ocean. The coupled air-sea interactions with biogeochemical processes should be considered in future work.

Amplitude modulation of relative humidity by wind in Northeast China: the formation of variance annual cycle in relative humidity

Relative humidity has an important impact not only on climate change and ecosystems but also on human life. The intensity of high-frequency fluctuations in surface relative humidity over Northeast China shows a predominant seasonally dependent structure, which may be closely related to regional monsoon activities. However, the factors responsible for this phenomenon remain unknown. This study defines the variance annual cycle (VAC) to describe this seasonally dependent intensity structure of high-frequency relative humidity fluctuations. Relative humidity VAC shows a high correlation with low-frequency oscillations of surface wind speed. We examine the instantaneous amplitude-phase correlation map and amplitude modulation (AM) index between surface relative humidity and surface wind speed. We find that the surface wind speed with a period around 140–420 days has a significant amplitude modulation effect on the surface relative humidity with a period of around 2–90 days over most regions in Northeast China, which reveals that the low-frequency oscillations of surface wind speed amplitude modulate on the high-frequency fluctuations of surface relative humidity. To explore the physical mechanism behind this modulation, we examine the monthly mean patterns of the surface wind and sea level pressure fields. The patterns indicate that this amplitude modulation is induced by the evolution and transition of East Asian winter monsoon and summer monsoon.

Southwesterly Water Vapor Transport Induced by Tropical Cyclones over the Bay of Bengal during the South Asian Monsoon Transition Period

Southwesterly Water Vapor Transport Induced by Tropical Cyclones over the Bay of Bengal during the South Asian Monsoon Transition Period

Optimum Multiparameter Analysis of Water Mass Structure off Western Guangdong during Spring Monsoon Transition

Water masses and their variability play vital roles in regulating ocean circulation, material exchanges and biogeochemical processes. However, there is still a lack of quantitative analysis of water mass distributions in coastal waters of the South China Sea. Here, two oceanographic cruise observations in April and May 2016 are used to quantify water mass distributions, pathways and mixture, and their intraseasonal variability off western Guangdong during the spring monsoon transition. Temperature and salinity observations qualitatively reveal that there are three types of water masses: the Pearl River diluted water (PRDW, salinity (S) = 22 psu, potential temperature (θ) = 25 °C), the South China Sea surface water (SCSSW, S = 34 psu, θ = 28 °C) and the South China Sea subsurface water mass (SCSSUW, S = 34.5 psu, θ = 17 °C). Their relative contributions and intraseasonal variability are quantified using the Optimum Multiparameter (OMP) method. The PRDW is largely confined to the upper 10 m layer in shallow nearshore waters (depths &lt; 30 m), with a maximum contribution &gt;90% near the Pearl River Estuary. The SCSSW mainly dominates the rest of the surface layer above 20 m, with a contribution &gt;50% in offshore regions. The layer below 20 m is primarily composed of ~60% SCSSW and ~40% SCSSUW. A comparison between the two different observations suggests that the PRDW tends to expand southwestward and the SCSSUW spreads offshore, whereas the SCSSW moves landward and is situated underneath the surface fresh PRDW. These characteristics are very likely associated with the wind transition from weak southeasterly in April to strong northeasterly in May, which enhances the southwestward coastal current and the onshore surface Ekman transport from offshore waters.