scholarly journals Variability of the Red River Plume in the Gulf of Tonkin as Revealed by Numerical Modeling and Clustering Analysis

2021 ◽  
Vol 8 ◽  
Author(s):  
Tung Nguyen-Duy ◽  
Nadia K. Ayoub ◽  
Patrick Marsaleix ◽  
Florence Toublanc ◽  
Pierre De Mey-Frémaux ◽  
...  
Keyword(s):  
Learning Algorithm ◽  
Early Summer ◽  
River Plume ◽  
Red River ◽  
Strong Wind ◽  
River Waters ◽  
Gulf Of Tonkin ◽  
Northeasterly Wind ◽  
Passive Tracers ◽  
Plume Flow

We study the daily to interannual variability of the Red River plume in the Gulf of Tonkin from numerical simulations at high resolution over 6 years (2011–2016). Compared with observational data, the model results show good performance. To identify the plume, passive tracers are used in order to (1) help distinguish the freshwater coming from different continental sources, including the Red River branches, and (2) avoid the low salinity effect due to precipitation. We first consider the buoyant plume formed by the Red River waters and three other nearby rivers along the Vietnamese coast. We show that the temporal evolution of the surface coverage of the plume is correlated with the runoff (within a lag), but that the runoff only cannot explain the variability of the river plume; other processes, such as winds and tides, are involved. Using a K-means unsupervised machine learning algorithm, the main patterns of the plume and their evolution in time are analyzed and linked to different environmental conditions. In winter, the plume is narrow and sticks along the coast most of the time due to the downcoast current and northeasterly wind. In early summer, the southwesterly monsoon wind makes the plume flow offshore. The plume reaches its highest coverage in September after the peak of runoff. Vertically, the plume thickness also shows seasonal variations. In winter, the plume is narrow and mixed over the whole water depth, while in summer, the plume can be detached both from the bottom and the coast. The plume can deepen offshore in summer, due to strong wind (in May, June) or specifically to a recurrent eddy occurring near 19°N (in August). This first analysis of the variability of the Red River plume can be used to provide a general picture of the transport of materials from the river to the ocean, for example in case of anthropogenic chemical substances leaked to the river. For this purpose, we provide maps of the receiving basins for the different river systems in the Gulf of Tonkin.

Variability of river plume in the Gulf of Tonkin

2021 ◽  
Author(s):  
Duy Tung Nguyen ◽  
Nadia Ayoub ◽  
Patrick Marsaleix ◽  
Florence Toublanc ◽  
Pierre De Mey-Fremaux ◽  
...  
Keyword(s):  
Time Scales ◽  
Marine Environment ◽  
Ocean Circulation ◽  
River Plume ◽  
Red River ◽  
Red River Delta ◽  
Large Variability ◽  
Gulf Of Tonkin ◽  
Estuarine Coastal ◽  
Coastal And Marine Environment

<p>The quality of estuarine, coastal and marine environment in the Gulf of Tonkin, in the South China Sea, is an essential issue to the ecosystems’ health and to the living conditions and economy of the Viet Nam population. The stakes are particularly high since the demographic density in the Red River delta is one of the highest in the world. Understanding the physical processes that drive the ocean circulation and its response to anthropic pressure there is therefore of primarily importance for enlightened resource management, as well as for designing adequate monitoring and forecasting systems.</p><p>As a first step toward a better understanding of the physical coastal and marine environment, we present here a study on the Red river plume variability in the Gulf of Tonkin over the period 2011-2016. The study is based on a numerical simulation, under realistic conditions, using the SYMPHONIE coastal model developed at LEGOS (Marsaleix et al., 2008). Compared with various data sources, the model results show good performances. The river plume is then identified and examined at different time scales. In general, the surface coverage of the river plume is strongly correlated with the runoff but with a 1-month lag. However, in some years, a higher peak in runoff does not create a higher peak of the plume area, suggesting that other forcings need to be taken into account to explain the variability of the river plume.</p><p>Using K-mean clustering, the main patterns of the plume are identified. The result shows that the plume has a large variability at both seasonal and interannual scales. Each pattern shows the plume under different forcing conditions.  Most of the time, the plume is narrow and sticks along the coast due to the downcoast current and northeasterly wind. In the summer, due to monsoon, the wind direction changes to southwesterly and helps the plume to spread offshore. The plume reaches its highest coverage in September after the peak of runoff; then its coverage decreases again when the monsoon reverses.</p><p>We also analyze events of offshore export of freshwater at daily time scales and show that they can be associated with recurrent coastal eddies during the summer monsoon. We investigate the respective role of wind and runoff in the eddies formation. Comparison with a run without river allows to identify the main impacts of the plume on the ocean states, for example in the current and sea surface elevation.</p>

Features of the Distribution of Abnormal Gasgeochemical Fields in the Red River Rift (Gulf of Tonkin, South China Sea)

2019 ◽  
Vol 484 (2) ◽  
pp. 181-184 ◽  
Author(s):  
R. B. Shakirov ◽  
Duong Quoc Hung ◽  
N. S. Syrbu ◽  
Le Duc Anh ◽  
A. I. Obzhirov ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Red River ◽  
China Sea ◽  
Gulf Of Tonkin

scholarly journals Seasonal measurements of total OH reactivity fluxes, total ozone loss rates and missing emissions from Norway spruce in 2011

2012 ◽  
Vol 9 (10) ◽  
pp. 13497-13536
Author(s):  
A.C. Nölscher ◽  
E. Bourtsoukidis ◽  
B. Bonn ◽  
J. Kesselmeier ◽  
J. Lelieveld ◽  
...  
Keyword(s):  
Heat Stress ◽  
Norway Spruce ◽  
Total Ozone ◽  
Late Summer ◽  
Early Summer ◽  
Unknown Primary ◽  
Oh Radicals ◽  
Strong Wind ◽  
Emission Rates ◽  
Loss Rates

Abstract. Numerous reactive volatile organic compounds (VOCs) are emitted into the atmosphere by vegetation. Most biogenic VOCs are highly reactive towards the atmosphere's most important oxidant, the hydroxyl (OH) radical. One way to investigate the chemical interplay between biosphere and atmosphere is through the measurement of total OH reactivity, the total loss rate of OH radicals. This study presents the first determination of total OH reactivity emission rates (measurements via the Comparative Reactivity Method) based on a branch cuvette enclosure system mounted on a Norway spruce (Picea abies) throughout spring, summer and autumn 2011. In parallel separate VOC emission rates were monitored by a Proton Transfer Reaction-Mass Spectrometer (PTR-MS), and total ozone (O3) loss rates were obtained inside the cuvette. Total OH reactivity emission rates were in general temperature and light dependent, showing strong diel cycles with highest values during daytime. Monoterpene emissions contributed most, accounting for 56–69% of the measured total OH reactivity flux in spring and early summer. However, during late summer and autumn the monoterpene contribution decreased to 11–16%. At this time, a large missing fraction of the total OH reactivity emission rate (70–84%) was found when compared to the VOC budget measured by PTR-MS. Total OH reactivity and missing total OH reactivity emission rates reached maximum values in late summer corresponding to the period of highest temperature. Total O3 loss rates within the closed cuvette showed similar diel profiles and comparable seasonality to the total OH reactivity fluxes. Total OH reactivity fluxes were also compared to emissions from needle storage pools predicted by a temperature-only dependent algorithm. Deviations of total OH reactivity fluxes from the temperature-only dependent emission algorithm were observed for occasions of mechanical and heat stress. While for mechanical stress, induced by strong wind, measured VOCs could explain total OH reactivity emissions, during heat stress they could not. The temperature driven algorithm matched the diel course much better in spring than in summer, indicating a different production and emission scheme for summer and early autumn. During these times, unmeasured and possibly unknown primary biogenic emissions contributed significantly to the observed total OH reactivity flux.

Pesticides in the Red River and its Tributaries in Southern Manitoba: 1993—95

1999 ◽  
Vol 34 (2) ◽  
pp. 183-220 ◽  
Author(s):  
Dorothea F.K. Rawn ◽  
Thor H.J. Halldorson ◽  
Robert N. Woychuk ◽  
Derek C.G. Muir
Keyword(s):  
Water Quality ◽  
Drainage Basin ◽  
Sampling Site ◽  
Early Summer ◽  
Red River ◽  
Aquatic Life ◽  
Quality Guidelines ◽  
A Minor ◽  
River Drainage Basin ◽  
Minor Extent

Abstract Pesticide concentrations and loadings at three locations along the Red River and on seven of its tributaries in southern Manitoba were determined over a three year period. Samples (18 L) were collected on a biweekly schedule between spring and late autumn in 1994 and 1995 and triweekly throughout the initial year of the study (1993) between June and October. Pesticide recoveries ranged from 14 to 115%, and those with < 80% recovery (bromoxynil, 2,4-D,diclofop, MPCA and triclopyr) were recovery corrected. Maximun concentrations were related to regional use periods, despite greatest runoff occurring during spring melt and early summer rains. Pesticides were not present at elevated levels during this period. The pesticides detected in the highest frequency in the Red River tributaries generally were those used most extensively (e.g., MCPA). MCPA concentaraions for all sites ranged from < 0.01 to990 ng/L. MCPA had the largest loadings of all herbicides in each tributary, although loads were low (9-3100 g) compared to usage. Atrazine and alachlor were frequently detected in the Red River. Atrazine is widely used in the neighbouring U.S. states, and loadings of this chemical in the Red River were similar to loadings of the highly used and less persistant phenoxyacids, although it was used only to a minor extent in Manitoba. Alachor, althiugh not in used in Canada, was present (<0.060-150 ng/L) in the Red River at each sampling site, which reflected U.S. usage of this product. Urban usage of chlorpyrifos, 2,4 D and MCLA contributed to loadings along the Red River. Pesticide concentrations generally were well below Canadian water quality guidelines in the Red River drainage basin; however, chlorpyrifos concentrations occassionally exceeded guideline levels for the production of freshwater aquatic life.

scholarly journals Seasonal measurements of total OH reactivity emission rates from Norway spruce in 2011

2013 ◽  
Vol 10 (6) ◽  
pp. 4241-4257 ◽  
Author(s):  
A.C. Nölscher ◽  
E. Bourtsoukidis ◽  
B. Bonn ◽  
J. Kesselmeier ◽  
J. Lelieveld ◽  
...  
Keyword(s):  
Heat Stress ◽  
Norway Spruce ◽  
Late Summer ◽  
Early Summer ◽  
Unknown Primary ◽  
Oh Radicals ◽  
Diel Variation ◽  
Strong Wind ◽  
Emission Rates ◽  
Loss Rates

Abstract. Numerous reactive volatile organic compounds (VOCs) are emitted into the atmosphere by vegetation. Most biogenic VOCs are highly reactive towards the atmosphere's most important oxidant, the hydroxyl (OH) radical. One way to investigate the chemical interplay between biosphere and atmosphere is through the measurement of total OH reactivity, the total loss rate of OH radicals. This study presents the first determination of total OH reactivity emission rates (measurements via the comparative reactivity method) based on a branch cuvette enclosure system mounted on a Norway spruce (Picea abies) throughout spring, summer and autumn 2011. In parallel VOC emission rates were monitored by a second proton-transfer-reaction mass spectrometer (PTR-MS), and total ozone (O3) loss rates were obtained inside the cuvette. Total OH reactivity emission rates were in general temperature and light dependent, showing strong diel cycles with highest values during daytime. Monoterpene emissions contributed most, accounting for 56–69% of the measured total OH reactivity flux in spring and early summer. However, during late summer and autumn the monoterpene contribution decreased to 11–16%. At this time, a large missing fraction of the total OH reactivity emission rate (70–84%) was found when compared to the VOC budget measured by PTR-MS. Total OH reactivity and missing total OH reactivity emission rates reached maximum values in late summer corresponding to the period of highest temperature. Total O3 loss rates within the closed cuvette showed similar diel profiles and comparable seasonality to the total OH reactivity fluxes. Total OH reactivity fluxes were also compared to emissions from needle storage pools predicted by a temperature-only-dependent algorithm. Deviations of total OH reactivity fluxes from the temperature-only-dependent emission algorithm were observed for occasions of mechanical and heat stress. While for mechanical stress, induced by strong wind, measured VOCs could explain total OH reactivity emissions, during heat stress they could not. The temperature-driven algorithm matched the diel variation of total OH reactivity emission rates much better in spring than in summer, indicating a different production and emission scheme for summer and early autumn. During these times, unmeasured and possibly unknown primary biogenic emissions contributed significantly to the observed total OH reactivity flux.

scholarly journals Response of an Antarctic Peninsula Fjord to Summer Katabatic Wind Events

2019 ◽  
Vol 49 (6) ◽  
pp. 1485-1502 ◽  
Author(s):  
Øyvind Lundesgaard ◽  
Brian Powell ◽  
Mark Merrifield ◽  
Lisa Hahn-Woernle ◽  
Peter Winsor
Keyword(s):  
Antarctic Peninsula ◽  
Upper Ocean ◽  
Katabatic Wind ◽  
Strong Wind ◽  
Deep Basin ◽  
Wind Event ◽  
Salinity Increase ◽  
Strong Winds ◽  
Wind Events ◽  
Passive Tracers

AbstractFjords along the western Antarctic Peninsula are episodically exposed to strong winds flowing down marine-terminating glaciers and out over the ocean. These wind events could potentially be an important mechanism for the ventilation of fjord waters. A strong wind event was observed in Andvord Bay in December 2015, and was associated with significant increases in upper-ocean salinity. We examine the dynamical impacts of such wind events during the ice-free summer season using a numerical model. Passive tracers are used to identify water mass pathways and quantify exchange with the outer ocean. Upwelling and outflow in the model fjord generate an average salinity increase of 0.3 in the upper ocean during the event, similar to observations from Andvord Bay. Down-fjord wind events are a highly efficient mechanism for flushing out the upper fjord waters, but have little net impact on deep waters in the inner fjord. As such, summer episodic wind events likely have a large effect on fjord phytoplankton dynamics and export of glacially modified upper waters, but are an unlikely mechanism for the replenishment of deep basin waters and oceanic heat transport toward inner-fjord glaciers.

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