Current Issue
2024 Vol. 43, No. 11
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2024, 43(11)
Abstract:
2024, 43(11): 1-11.
doi: 10.1007/s13131-024-2432-6
Abstract:
Based on in-situ observations in the East China Sea (ECS) during October 2021, we investigated a cross-shelf penetrating front (PF) in the inner shelf and explored its potential biogeochemical-ecological effects from a multidisciplinary perspective. The results show that a pronounced tongue-shaped PF was present at the southeast of the Hangzhou Bay, with salinity of 29−32 and a seaward horizontal penetration scale of ~200 km. It mainly occurred in the upper layers, and a spatial separation existed between this PF and the bottom salinity front in the northern coastal region off Zhejiang. In contrast, the salinity fronts at surface and bottom were well matched in the southern coastal area. Compared to the surface-to-bottom consistent coastal front in the southern region off Zhejiang, a stronger thermocline and halocline were sustained in the northern PF-dominated region, and suitable conditions could be achieved for phytoplankton growth and accumulation. The in-situ observed high-chlorophyll a (Chl a) zone in a seaward tongue shape was further an important indicator or signal for PF occurrence, and it was responsible for the decoupling of nutrient distributions and PF. The southern coastal front off Zhejiang might largely restrict the seaward transport of nutrients, and the dynamic environment under weak stratification in this region was disadvantageous for the growth of phytoplankton; thus the Chl a content was maintained at a relatively low level near the southern coastal region. Our results demonstrate that the PF combined with the coastal front may play an important role in shaping/regulating hydrodynamics, nutrient distributions and the Chl a regime over the inner ECS shelf.
Based on in-situ observations in the East China Sea (ECS) during October 2021, we investigated a cross-shelf penetrating front (PF) in the inner shelf and explored its potential biogeochemical-ecological effects from a multidisciplinary perspective. The results show that a pronounced tongue-shaped PF was present at the southeast of the Hangzhou Bay, with salinity of 29−32 and a seaward horizontal penetration scale of ~200 km. It mainly occurred in the upper layers, and a spatial separation existed between this PF and the bottom salinity front in the northern coastal region off Zhejiang. In contrast, the salinity fronts at surface and bottom were well matched in the southern coastal area. Compared to the surface-to-bottom consistent coastal front in the southern region off Zhejiang, a stronger thermocline and halocline were sustained in the northern PF-dominated region, and suitable conditions could be achieved for phytoplankton growth and accumulation. The in-situ observed high-chlorophyll a (Chl a) zone in a seaward tongue shape was further an important indicator or signal for PF occurrence, and it was responsible for the decoupling of nutrient distributions and PF. The southern coastal front off Zhejiang might largely restrict the seaward transport of nutrients, and the dynamic environment under weak stratification in this region was disadvantageous for the growth of phytoplankton; thus the Chl a content was maintained at a relatively low level near the southern coastal region. Our results demonstrate that the PF combined with the coastal front may play an important role in shaping/regulating hydrodynamics, nutrient distributions and the Chl a regime over the inner ECS shelf.
2024, 43(11): 12-25.
doi: 10.1007/s13131-024-2433-5
Abstract:
Estuaries are often a significant source of atmospheric CO2. However, studies of carbonate systems have predominantly focused on large estuaries, while smaller estuaries have scarcely been documented. In this study, we collected surface and bottom seawater carbonate samples in the subtropical Jiulong River Estuary across different tidal levels from 2019 to 2021. The results showed that estuarine mixing of freshwater from the river with seawater was the dominant factor influencing the estuarine carbonate system. Moreover, estuarine mixing is concomitantly impacted by the net metabolism of biological production and decomposition, groundwater input, release of CO2 from the estuary, and precipitation or dissolution of calcium carbonate. The estuarine partial pressure of CO2 (pCO2) varied from 530 μatm to7715 μatm, which represents a strong source of atmospheric CO2. The mean annual air-sea CO2 flux estimated from three different parameterized equations was approximately (25.63 ± 10.25) mol/(m2·a). Furthermore, the annual emission to the atmosphere was approximately (0.031 ± 0.012) Tg C, which accounts for a mere 0.0077 %−0.015% of global estuarine emissions. Dissolved inorganic carbon (DIC), total alkalinity (TA) and the pCO2 exhibited high variability throughout the tidal cycle across all cruises. Specifically, the disparities observed between DIC and TA during low and high tides at identical stations during all cruises ranged from approximately 15% to 30%. The variance in the pCO2 was even more pronounced, ranging from approximately 30% to 40%. Thus, tidal discrepancies may need to be taken into consideration to estimate the CO2 flux from estuarine systems more accurately.
Estuaries are often a significant source of atmospheric CO2. However, studies of carbonate systems have predominantly focused on large estuaries, while smaller estuaries have scarcely been documented. In this study, we collected surface and bottom seawater carbonate samples in the subtropical Jiulong River Estuary across different tidal levels from 2019 to 2021. The results showed that estuarine mixing of freshwater from the river with seawater was the dominant factor influencing the estuarine carbonate system. Moreover, estuarine mixing is concomitantly impacted by the net metabolism of biological production and decomposition, groundwater input, release of CO2 from the estuary, and precipitation or dissolution of calcium carbonate. The estuarine partial pressure of CO2 (pCO2) varied from 530 μatm to
2024, 43(11): 26-33.
doi: 10.1007/s13131-024-2430-8
Abstract:
Trace metals emitted from human activities may have penetrated into the deep seas, and the underlying control mechanisms remain poorly understood. Sinking particles collected by moored time-series sediment traps from the northern South China Sea (NSCS) basin showed significant enrichment of anthropogenic aerosol Pb relative to lithogenic Fe. Total mass flux was primarily driven by seasonal primary production, and significant positive correlations were found between Pb/Fe flux and major biogenic components, indicating the crucial role of the biological pump in Pb/Fe scavenging in the water column. Notably, Pb exhibited 30−50 times higher affinity to biogenic components than Fe. A comparison was made between the enrichment factors of Fe and Pb in aerosols, euphotic particles, and sinking particles, which revealed that Pb exhibited significantly higher particle reactivity than Fe. This higher particle reactivity may encompass processes such as adsorption/desorption, bioaccumulation and decomposition release. The differential scavenging behavior of Pb suggested that the majority of Pb was rapidly scavenged in the euphotic zone and was preferentially released for accumulation in the twilight zone. This accumulation may further outflow through the Luzon Strait and result in the high dissolved Pb concentration observed in the subsurface water columns in both the NSCS and western Pacific Ocean. The rest of anthropogenic Pb in sinking particles tended to penetrate into deeper water layers and continue to be released below the twilight zone. These findings provide new insights into the biogeochemical cycling of trace metals originating from anthropogenic aerosols in marginal seas and serve as an example of the fate of other anthropogenic atmospheric pollutants.
Trace metals emitted from human activities may have penetrated into the deep seas, and the underlying control mechanisms remain poorly understood. Sinking particles collected by moored time-series sediment traps from the northern South China Sea (NSCS) basin showed significant enrichment of anthropogenic aerosol Pb relative to lithogenic Fe. Total mass flux was primarily driven by seasonal primary production, and significant positive correlations were found between Pb/Fe flux and major biogenic components, indicating the crucial role of the biological pump in Pb/Fe scavenging in the water column. Notably, Pb exhibited 30−50 times higher affinity to biogenic components than Fe. A comparison was made between the enrichment factors of Fe and Pb in aerosols, euphotic particles, and sinking particles, which revealed that Pb exhibited significantly higher particle reactivity than Fe. This higher particle reactivity may encompass processes such as adsorption/desorption, bioaccumulation and decomposition release. The differential scavenging behavior of Pb suggested that the majority of Pb was rapidly scavenged in the euphotic zone and was preferentially released for accumulation in the twilight zone. This accumulation may further outflow through the Luzon Strait and result in the high dissolved Pb concentration observed in the subsurface water columns in both the NSCS and western Pacific Ocean. The rest of anthropogenic Pb in sinking particles tended to penetrate into deeper water layers and continue to be released below the twilight zone. These findings provide new insights into the biogeochemical cycling of trace metals originating from anthropogenic aerosols in marginal seas and serve as an example of the fate of other anthropogenic atmospheric pollutants.
2024, 43(11): 34-44.
doi: 10.1007/s13131-024-2397-5
Abstract:
Ridges are common features found on continental shelves and understanding their formation processes is crucial for sedimentology, stratigraphy, and geological engineering. This study investigates the development of ridges on the broad shelf of the East China Sea using a core (DH03) and associated seismic profile. Lithology analysis of the core revealed a 50 m thick shallow sandy sequence which consisted mainly of silty fine sands with intercalations of mud beds composed of sand-mud couplets. Benthic foraminifera examination indicated the offshore species were dominant. The seismic profile indicated that the ridges were separated from the older delta layers due to a boundary formed by river erosion during the last glacial maximum. Radiocarbon dating of the sandy sequence revealed an irregular chronological sequence, with most age ranges falling within the past 3 ka. Based on the chronological data from DH03 and other cores, we propose that the ridges, which were formed during the early Holocene transgression, have been active on a shelf scale in the recent 3–2 ka. Synthetic analysis of the shelf-scale ridge formation processes indicates that the sea-level fluctuations during the mid-late Holocene sea-level highstand triggered the ridge activities. A center for ridge activity developed in the southern shelf, facilitated by thicker ridge deposits in the paleo-Changjiang River Estuary and stronger currents (tidal currents and possibly internal waves) induced by the remaining funnel-shaped estuary topography. Based on these findings, we propose a conceptual model for ridge development, which includes a ridge formation stage during the early Holocene transgression and a ridge activation stage during the mid-late Holocene sea-level highstand.
Ridges are common features found on continental shelves and understanding their formation processes is crucial for sedimentology, stratigraphy, and geological engineering. This study investigates the development of ridges on the broad shelf of the East China Sea using a core (DH03) and associated seismic profile. Lithology analysis of the core revealed a 50 m thick shallow sandy sequence which consisted mainly of silty fine sands with intercalations of mud beds composed of sand-mud couplets. Benthic foraminifera examination indicated the offshore species were dominant. The seismic profile indicated that the ridges were separated from the older delta layers due to a boundary formed by river erosion during the last glacial maximum. Radiocarbon dating of the sandy sequence revealed an irregular chronological sequence, with most age ranges falling within the past 3 ka. Based on the chronological data from DH03 and other cores, we propose that the ridges, which were formed during the early Holocene transgression, have been active on a shelf scale in the recent 3–2 ka. Synthetic analysis of the shelf-scale ridge formation processes indicates that the sea-level fluctuations during the mid-late Holocene sea-level highstand triggered the ridge activities. A center for ridge activity developed in the southern shelf, facilitated by thicker ridge deposits in the paleo-Changjiang River Estuary and stronger currents (tidal currents and possibly internal waves) induced by the remaining funnel-shaped estuary topography. Based on these findings, we propose a conceptual model for ridge development, which includes a ridge formation stage during the early Holocene transgression and a ridge activation stage during the mid-late Holocene sea-level highstand.
2024, 43(11): 45-56.
doi: 10.1007/s13131-024-2313-z
Abstract:
The deltas serve as the primary interactive zone where terrestrial and marine environments converge, playing a pivotal role in the coastal deposition. In the Holocene, climate changes and sea level fluctuation are the principal driving factors in the evolution of deltas. However, human activities such as the construction of dams and reservoirs in the Anthropocene have significantly altered sediment transport in rivers, leading to depositional pattern variation during deltaic evolution. In this study, we have conducted a comparative analysis of the morphological variations (1986–2021) in the barrier system of the Hanjiang River Delta (HRD) using satellite remote sensing (SRS) method. Additionally, we have examined the lithological changes and facies alterations observed in eight boreholes on the present barrier spit. Our findings indicate that the intensification of anthropogenic activities led to a significant reduction in the sediment flux of the Hanjiang River (HR), resulting in depocenter landward migration at the estuary. SRS analysis reveals their periodical morphological characteristics and spatial variations of estuarine sandbars (1986–1992), barrier islands-lagoons (1993–2009), and barrier spits (2010–2021) during 1986 to 2021. The stratigraphy of boreholes demonstrates a south-to-north facies transition from lagoon to lagoon-barrier spit and barrier spit in vertical lithology. Therefore, the depositional evolution of the HRD barrier system is categorized into three phases: estuarine sandbar-barrier island phase (1986–1998); barrier island-lagoon phase (1999–2009); and barrier spit phase (2010–2021). During the estuarine sandbar-barrier island phase, fluvial processes played a predominate role in the deposition. Consequently, with a significant decrease in river sediment load, the dominant factors driving depositional processes shifted towards wave action and alongshore current. Based on the conceptual model in the Holocene, we propose a modified depositional model of wave-dominated deltas during Anthropocene that encompasses three evolutionary phases: estuarine sandbars and delta front platforms, barrier island-lagoon formation and landward migration of barrier spits. This pattern highlights that human-induced reduction in river sediment flux has led to a seaward deltaic progradation driven by barrier landward migration.
The deltas serve as the primary interactive zone where terrestrial and marine environments converge, playing a pivotal role in the coastal deposition. In the Holocene, climate changes and sea level fluctuation are the principal driving factors in the evolution of deltas. However, human activities such as the construction of dams and reservoirs in the Anthropocene have significantly altered sediment transport in rivers, leading to depositional pattern variation during deltaic evolution. In this study, we have conducted a comparative analysis of the morphological variations (1986–2021) in the barrier system of the Hanjiang River Delta (HRD) using satellite remote sensing (SRS) method. Additionally, we have examined the lithological changes and facies alterations observed in eight boreholes on the present barrier spit. Our findings indicate that the intensification of anthropogenic activities led to a significant reduction in the sediment flux of the Hanjiang River (HR), resulting in depocenter landward migration at the estuary. SRS analysis reveals their periodical morphological characteristics and spatial variations of estuarine sandbars (1986–1992), barrier islands-lagoons (1993–2009), and barrier spits (2010–2021) during 1986 to 2021. The stratigraphy of boreholes demonstrates a south-to-north facies transition from lagoon to lagoon-barrier spit and barrier spit in vertical lithology. Therefore, the depositional evolution of the HRD barrier system is categorized into three phases: estuarine sandbar-barrier island phase (1986–1998); barrier island-lagoon phase (1999–2009); and barrier spit phase (2010–2021). During the estuarine sandbar-barrier island phase, fluvial processes played a predominate role in the deposition. Consequently, with a significant decrease in river sediment load, the dominant factors driving depositional processes shifted towards wave action and alongshore current. Based on the conceptual model in the Holocene, we propose a modified depositional model of wave-dominated deltas during Anthropocene that encompasses three evolutionary phases: estuarine sandbars and delta front platforms, barrier island-lagoon formation and landward migration of barrier spits. This pattern highlights that human-induced reduction in river sediment flux has led to a seaward deltaic progradation driven by barrier landward migration.
2024, 43(11): 57-67.
doi: 10.1007/s13131-024-2434-4
Abstract:
The establishment of effective proxies for the differentiation of sedimentary facies in the tide-dominated river mouth is fundamental to the delineation of stratigraphy and the study of paleoenvironments. Geochemical signatures of the acetic acid (HAc) extractive phases of alkaline earth metals, such as Sr, Ba, and Ca, are closely related to sedimentary environments and thus provide a novel method for discriminating the sedimentary facies of river mouth. In this study, 50 surface water and surface sediment samples were obtained from different geomorphological units of the Jiulong River mouth, i.e., river channel, distributary channel, delta front, delta front slope, prodelta, and shallow marine area, and the salinity of the water, the grain size, and the Sr, Ba, and Ca contents and Sr/Ba molar ratio (Sr/Ba) in HAc leachates of the sediments were determined. Contents of alkaline earth metals in HAc leachates of surface sediments from the Changjiang (Yangtze) River coast were also collated. The goals of this study were to reveal the spatial distribution of alkaline earth metals in the Jiulong River mouth, define their depositional mechanisms, and search for effective geochemical proxies for identification of the various sedimentary facies in the fluvial to marine transition zone. The results revealed several land-to-sea gradients. The Ba content decreased rapidly from the distributary channel to the sea, and the Sr and Ca contents and Sr/Ba increased gradually with the increase in salinity. Salinity, marine biomass, and sedimentary dynamic processes, were speculated to be the main reasons for the differences in their spatial distributions. There were significant differences in Ba, Sr, Ca, and Sr/Ba between the river channel and the distributary channel, in Ca and Ba between the distributary channel and the delta front (slope), and in Sr, Ca, and Sr/Ba between the delta front (slope) and the prodelta–shallow marine region. The Sr–Ba scatterplot showed that the sediments of the river channel and alluvial plain were located as a high Ba and low Sr element-defined end-member, whereas samples of the prodelta and shallow marine formed a high Sr and low Ba end-member. These can be used as characteristic end-members indicating terrestrial facies and marine facies, respectively. The sediments of the delta plain, tidal river, distributary channel, delta front, and delta front slope are located between these two end-member regions of the scatterplot, and this region of the diagram can be used to identify land–sea transitional sedimentary facies.
The establishment of effective proxies for the differentiation of sedimentary facies in the tide-dominated river mouth is fundamental to the delineation of stratigraphy and the study of paleoenvironments. Geochemical signatures of the acetic acid (HAc) extractive phases of alkaline earth metals, such as Sr, Ba, and Ca, are closely related to sedimentary environments and thus provide a novel method for discriminating the sedimentary facies of river mouth. In this study, 50 surface water and surface sediment samples were obtained from different geomorphological units of the Jiulong River mouth, i.e., river channel, distributary channel, delta front, delta front slope, prodelta, and shallow marine area, and the salinity of the water, the grain size, and the Sr, Ba, and Ca contents and Sr/Ba molar ratio (Sr/Ba) in HAc leachates of the sediments were determined. Contents of alkaline earth metals in HAc leachates of surface sediments from the Changjiang (Yangtze) River coast were also collated. The goals of this study were to reveal the spatial distribution of alkaline earth metals in the Jiulong River mouth, define their depositional mechanisms, and search for effective geochemical proxies for identification of the various sedimentary facies in the fluvial to marine transition zone. The results revealed several land-to-sea gradients. The Ba content decreased rapidly from the distributary channel to the sea, and the Sr and Ca contents and Sr/Ba increased gradually with the increase in salinity. Salinity, marine biomass, and sedimentary dynamic processes, were speculated to be the main reasons for the differences in their spatial distributions. There were significant differences in Ba, Sr, Ca, and Sr/Ba between the river channel and the distributary channel, in Ca and Ba between the distributary channel and the delta front (slope), and in Sr, Ca, and Sr/Ba between the delta front (slope) and the prodelta–shallow marine region. The Sr–Ba scatterplot showed that the sediments of the river channel and alluvial plain were located as a high Ba and low Sr element-defined end-member, whereas samples of the prodelta and shallow marine formed a high Sr and low Ba end-member. These can be used as characteristic end-members indicating terrestrial facies and marine facies, respectively. The sediments of the delta plain, tidal river, distributary channel, delta front, and delta front slope are located between these two end-member regions of the scatterplot, and this region of the diagram can be used to identify land–sea transitional sedimentary facies.
2024, 43(11): 68-87.
doi: 10.1007/s13131-024-2380-1
Abstract:
The biological pump, driven by phytoplankton production and death, plays a crucial role in the ocean’s sequestration of atmospheric CO2. In particular, marginal seas with high primary productivity show a significant capacity for carbon fixation. Variations in phytoplankton biomass and community structure are key factors influencing the efficiency of the marine biological pump. The Taiwan Strait (TS) is a unique shallow conduit that connects the East China Sea (ECS) and the South China Sea (SCS), which are subject to seasonal monsoons and episodic events (e.g., typhoons and floods). Thus, its planktonic ecosystem is significantly influenced by physical processes such as strong ocean currents, coastal upwelling and river discharge, resulting in noticeable seasonal variability. In this study, we examined spatiotemporal patterns of phytoplankton biomass and community structure using phytoplankton-sourced biomarkers from suspended particles in surface waters across all four seasons from 2019 to 2020 in the TS. The findings highlight notable seasonal disparities in phytoplankton biomass, with spring and summer exhibiting significantly higher levels compared to autumn and winter. In order to determine phytoplankton ecosystem responses to various physical and biological processes on a seasonal scale, we used Empirical Orthogonal/Eigen Function (EOF) analysis to investigate the covarying spatiotemporal patterns of: marine-sourced biomarkers and terrestrial-sourced biomarkers in surface suspended particles, a biomass indicator (Chl a), water-mass indicators [sea surface temperature (SST), sea surface salinity (SSS), nutrients], and a hydrodynamic indicator [total suspended solids at surface/bottom water, (TSS_S and TSS_B)]. The results identified six physical-biological coupling modes that influence seasonal variations in marine phytoplankton ecosystems within the energetic strait system. Additionally, an in-depth understanding of the coupling between physical process and lipid biomarker signals from suspended particles in the contemporary marine environment can offer valuable insights for interpreting ancient sediment records of phytoplankton ecosystem evolution in the TS.
The biological pump, driven by phytoplankton production and death, plays a crucial role in the ocean’s sequestration of atmospheric CO2. In particular, marginal seas with high primary productivity show a significant capacity for carbon fixation. Variations in phytoplankton biomass and community structure are key factors influencing the efficiency of the marine biological pump. The Taiwan Strait (TS) is a unique shallow conduit that connects the East China Sea (ECS) and the South China Sea (SCS), which are subject to seasonal monsoons and episodic events (e.g., typhoons and floods). Thus, its planktonic ecosystem is significantly influenced by physical processes such as strong ocean currents, coastal upwelling and river discharge, resulting in noticeable seasonal variability. In this study, we examined spatiotemporal patterns of phytoplankton biomass and community structure using phytoplankton-sourced biomarkers from suspended particles in surface waters across all four seasons from 2019 to 2020 in the TS. The findings highlight notable seasonal disparities in phytoplankton biomass, with spring and summer exhibiting significantly higher levels compared to autumn and winter. In order to determine phytoplankton ecosystem responses to various physical and biological processes on a seasonal scale, we used Empirical Orthogonal/Eigen Function (EOF) analysis to investigate the covarying spatiotemporal patterns of: marine-sourced biomarkers and terrestrial-sourced biomarkers in surface suspended particles, a biomass indicator (Chl a), water-mass indicators [sea surface temperature (SST), sea surface salinity (SSS), nutrients], and a hydrodynamic indicator [total suspended solids at surface/bottom water, (TSS_S and TSS_B)]. The results identified six physical-biological coupling modes that influence seasonal variations in marine phytoplankton ecosystems within the energetic strait system. Additionally, an in-depth understanding of the coupling between physical process and lipid biomarker signals from suspended particles in the contemporary marine environment can offer valuable insights for interpreting ancient sediment records of phytoplankton ecosystem evolution in the TS.
2024, 43(11): 88-98.
doi: 10.1007/s13131-024-2381-0
Abstract:
The characteristics of the terrain of a strait can lead to a “fine tube” effect that enhances a monsoon and thereby affects the physical, chemical, and biological processes of marine ecosystems. This effect is a highly dynamic and complex phenomenon involving interactions among atmospheric, oceanic, and terrestrial systems, as well as biogeochemical cycles and biological responses driven by it. However, current understanding has been focused mainly on the differences between monsoons, and there have been few studies concerned with the weakening or strengthening of monsoons. To explore the biogeochemical and phytoplankton responses during varying intensities of the northeast (NE) monsoon in the Taiwan Strait, high-resolution, across-front observations combined with FerryBox online data and satellite observations were conducted in this study during a strong, moderate, and weak NE monsoon. The spatiotemporal changes of nutrient concentrations and phytoplankton communities were regulated by the dynamics of ocean currents forced by NE winds. The weakening of the NE monsoon caused shrinkage of the coastal currents that led to a reduction of nutrient concentrations and an alteration of the distribution patterns of phytoplankton communities along cross-front sections. Specifically, there was a notable decrease in the proportions of dinoflagellates and cryptophytes in inshore regions and of prasinophytes in offshore areas. This study showed for the first time the dynamics of phytoplankton with changes of ocean currents during varying intensities of the NE monsoon in a strait system. The findings helped to elucidate the general spatial patterns of the phytoplankton community based on satellite-derived surface temperature and wind patterns and further enhanced the understanding of biogeochemical cycles in marine systems.
The characteristics of the terrain of a strait can lead to a “fine tube” effect that enhances a monsoon and thereby affects the physical, chemical, and biological processes of marine ecosystems. This effect is a highly dynamic and complex phenomenon involving interactions among atmospheric, oceanic, and terrestrial systems, as well as biogeochemical cycles and biological responses driven by it. However, current understanding has been focused mainly on the differences between monsoons, and there have been few studies concerned with the weakening or strengthening of monsoons. To explore the biogeochemical and phytoplankton responses during varying intensities of the northeast (NE) monsoon in the Taiwan Strait, high-resolution, across-front observations combined with FerryBox online data and satellite observations were conducted in this study during a strong, moderate, and weak NE monsoon. The spatiotemporal changes of nutrient concentrations and phytoplankton communities were regulated by the dynamics of ocean currents forced by NE winds. The weakening of the NE monsoon caused shrinkage of the coastal currents that led to a reduction of nutrient concentrations and an alteration of the distribution patterns of phytoplankton communities along cross-front sections. Specifically, there was a notable decrease in the proportions of dinoflagellates and cryptophytes in inshore regions and of prasinophytes in offshore areas. This study showed for the first time the dynamics of phytoplankton with changes of ocean currents during varying intensities of the NE monsoon in a strait system. The findings helped to elucidate the general spatial patterns of the phytoplankton community based on satellite-derived surface temperature and wind patterns and further enhanced the understanding of biogeochemical cycles in marine systems.
2024, 43(11): 99-117.
doi: 10.1007/s13131-024-2431-7
Abstract:
As the most important component of marine siliceous organisms, diatoms are vital primary producers of the ocean that are often used as indicators of paleoenvironmental change. To understand the response of sedimental diatoms to regional environmental changes and the factors affecting the distribution of sedimental diatoms in the Taiwan Strait, this study quantified and classified the diatoms found in surface sediments collected during four surveys from 2019 to 2020. Overall, 118 diatom taxa and 44 genera were identified with total diatom abundance of 8–27 353 valves/g. Four diatom assemblages representing different environments were identified. Among them, assemblage Ⅰ represented a coastal environment, assemblage Ⅱ comprised warm water species of a coastal environment, Assemblage Ⅲ represented a coastal environment affected markedly by exorheism, Assemblage Ⅳ represented a group with lowest diatom abundance. Seasonal variation in total diatom abundance was controlled by seven environmental factors: depth, sea surface salinity, mean grain size, silicate, nitrite, nitrate, and phosphate. Spatiotemporal variation in each of the diatom assemblages was substantial and strongly affected by various currents, upwelling, and low-salinity water. Specifically, it was found that the succession of diatom assemblages reflects change in the range of influence of local warm currents.
As the most important component of marine siliceous organisms, diatoms are vital primary producers of the ocean that are often used as indicators of paleoenvironmental change. To understand the response of sedimental diatoms to regional environmental changes and the factors affecting the distribution of sedimental diatoms in the Taiwan Strait, this study quantified and classified the diatoms found in surface sediments collected during four surveys from 2019 to 2020. Overall, 118 diatom taxa and 44 genera were identified with total diatom abundance of 8–27 353 valves/g. Four diatom assemblages representing different environments were identified. Among them, assemblage Ⅰ represented a coastal environment, assemblage Ⅱ comprised warm water species of a coastal environment, Assemblage Ⅲ represented a coastal environment affected markedly by exorheism, Assemblage Ⅳ represented a group with lowest diatom abundance. Seasonal variation in total diatom abundance was controlled by seven environmental factors: depth, sea surface salinity, mean grain size, silicate, nitrite, nitrate, and phosphate. Spatiotemporal variation in each of the diatom assemblages was substantial and strongly affected by various currents, upwelling, and low-salinity water. Specifically, it was found that the succession of diatom assemblages reflects change in the range of influence of local warm currents.
2024, 43(11): 118-130.
doi: 10.1007/s13131-024-2437-1
Abstract:
The Macao Special Administrative Region is located in the southeastern coastal area of China. The region of Macao was narrow in the history, so land reclamation has become a main means of expanding its geographical scope. Exploring the significance of land reclamation for the planning and urban construction of the Macao region provides valuable references. (1) The Google Earth Engine (GEE) cloud processing platform is used in this study to calculate the modified normalized difference water index (MNDWI) based on Landsat data from 1986 to 2021; (2) the Jenks natural index classification method is used to extract the water body range, and the water body boundary as well as area at different periods is calculated combined with the neural network classification method in the environment for visualizing images (ENVI) software; (3) this study then combines the patch-generating land use simulation (PLUS) model to predict the future trend of shoreline changes in the study area in 2036. The result indicates that the MNDWI and neural net classification method lead to a high classification accuracy with both the overall accuracy (OA) and Kappa coefficient being higher than 87%. Land reclamation activities in Macao were gradually intense from 1986 to 2021, with social and economic conditions such as transportation being main influencing factors, which provides valuable references and inspiration for the regional planning of the Macao Special Administrative Region.
The Macao Special Administrative Region is located in the southeastern coastal area of China. The region of Macao was narrow in the history, so land reclamation has become a main means of expanding its geographical scope. Exploring the significance of land reclamation for the planning and urban construction of the Macao region provides valuable references. (1) The Google Earth Engine (GEE) cloud processing platform is used in this study to calculate the modified normalized difference water index (MNDWI) based on Landsat data from 1986 to 2021; (2) the Jenks natural index classification method is used to extract the water body range, and the water body boundary as well as area at different periods is calculated combined with the neural network classification method in the environment for visualizing images (ENVI) software; (3) this study then combines the patch-generating land use simulation (PLUS) model to predict the future trend of shoreline changes in the study area in 2036. The result indicates that the MNDWI and neural net classification method lead to a high classification accuracy with both the overall accuracy (OA) and Kappa coefficient being higher than 87%. Land reclamation activities in Macao were gradually intense from 1986 to 2021, with social and economic conditions such as transportation being main influencing factors, which provides valuable references and inspiration for the regional planning of the Macao Special Administrative Region.
