Annual hypoxia dynamics in an enclosed gulf

Abstract. Hypoxia in coastal environments is a worldwide problem and is expected to worsen in future. Due to the stratification of the water column in many enclosed or semi-enclosed gulfs, deep waters are isolated and hypoxic or anoxic conditions frequently become dominant. The most common method for the oxygenation of these isolated anoxic water masses is vertical mixing. However, there are enclosed gulfs which rarely have the appropriate energy to ensure the mixing of the entire water column. The main purpose of this paper is to find if there are any other hydrodynamic processes which can cause oxygenation of deep waters, apart from vertical mixing. In order to achieve this aim, an enclosed gulf, Amvrakikos in Western Greece, was chosen to be the case study area and bimonthly physicochemical data were collected for one year and used in combination with a three-dimensional model in order to simulate the hydrodynamic circulation of the system. According to our results, another hydrodynamic process can lead to the oxygenation of the deepest water in an enclosed gulf. This process is the horizontal intrusion of well oxygenated water from the open sea. The key factor in determining the success of this horizontal intrusion is the density difference between the deepest area of the enclosed gulf and the open sea outside the gulf. From autumn to winter, when the open sea water is denser than that inside the gulf, the well oxygenated open sea water inflows into the gulf near the bottom sea floor and re-oxygenates the isolated deep waters through mixing. However, from spring to summer, when the deep water of the gulf is characterized by higher density in comparison with the open sea water, the inflow of well oxygenated water stops, causing the development of hypoxic/anoxic conditions during the summer months.

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Ocean carbon-cycle dynamics and atmospheric Pco 2

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1988.0039 ◽

1988 ◽

Vol 325 (1583) ◽

pp. 3-21 ◽

Cited By ~ 64

Keyword(s):

Surface Waters ◽

Three Dimensional ◽

Deep Ocean ◽

Relative Magnitude ◽

Total Carbon ◽

Three Dimensional Model ◽

Excess Carbon ◽

Deep Waters ◽

Rapid Changes ◽

Ocean Carbon

Mechanisms are identified whereby processes internal to the oceans can give rise to rapid changes in atmospheric P CO2 . One such mechanism involves exchange between the atmosphere and deep ocean through the high-latitude outcrop regions of the deep waters. The effectiveness of communication between the atmosphere and deep ocean is determined by the rate of exchange between the surface and deep ocean against the rate of biological uptake of the excess carbon brought up from the abyss by this exchange. Changes in the relative magnitude of these two processes can lead to atmospheric p co2 values ranging between 165 p.p.m. (by volume) and 425 p.p.m. compared with1 2 a pre-industrial value of 280 p.p.m. Another such mechanism involves the separation between regeneration of alkalinity and total carbon that occurs in the oceans because of the fact that organic carbon is regenerated primarily in the upper ocean whereas CaCO 3 is dissolved primarily in the deep ocean. The extent of separation depends on the rate of CaCO 3 formation at the surface against the rate of upward mixing of deep waters. This mechanism can lead to atmospheric values in excess of 20000 p.p.m., although values greater than 1100 p.p.m. are unlikely because calcareous organisms would have difficulty surviving in the undersaturated surface waters that develop at this point. A three-dimensional model that is being developed to further study these and other problems provides illustrations of them and also suggests the possibility that there is a long-lived form of non-sinking carbon playing a major role in carbon cycling.

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Relationship of Spatial Phytoplankton Variability during Spring with Eutrophic Inshore and Oligotrophic Offshore Waters in the East Sea, Including Dokdo, Korea

Journal of Marine Science and Engineering ◽

10.3390/jmse9121455 ◽

2021 ◽

Vol 9 (12) ◽

pp. 1455

Author(s):

Minji Lee ◽

Hyejoo Ro ◽

Yun-Bae Kim ◽

Chan-Hong Park ◽

Seung-Ho Baek

Keyword(s):

Water Column ◽

Vertical Mixing ◽

Early Spring ◽

Late Spring ◽

East Sea ◽

Water Column Stability ◽

Open Sea ◽

Phytoplankton Variability ◽

Abundance And Diversity ◽

Relationship Of

The area near the subpolar front of the East Sea has high primary productivity during the spring season. We conducted two surveys, one in early spring and another in late spring, to assess environmental factors that influence phytoplankton community structure during these times. During early spring, vertical mixing supplied abundant nutrients to the surface. Due to the well-mixed water column, there were high nutrient levels, but total phytoplankton abundances and diversity were relatively low and were dominated by the diatom Chaetoceros spp. During late spring, the water column gradually stratified, with relatively high levels of nutrients in the surface layers near the coastal areas. Phytoplankton abundance and diversity at that time were higher, and there were diatoms (Pseudo-nitzschia spp. and Chaetoceros spp.), cryptophytes, and small flagellates. Pseudo-nitzschia spp. were especially abundant in re-sampled areas. The presence of a stratified and stable water mass and sufficient nitrate led to high phytoplankton growth, even in the open sea during late spring. These findings provide a better understanding of how phytoplankton population dynamics in the East Sea depend on water column stability during both early and late spring seasons.

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A High-Resolution Oil Drift Model on the Swedish Coast

International Oil Spill Conference Proceedings ◽

10.7901/2169-3358-1999-1-289 ◽

1999 ◽

Vol 1999 (1) ◽

pp. 289-293

Author(s):

Cecilia Ambjörn ◽

Olof Liungman ◽

Gustaf Törling

Keyword(s):

High Resolution ◽

West Coast ◽

Three Dimensional ◽

Coast Guard ◽

Geographical Information ◽

Local Model ◽

Three Dimensional Model ◽

Swedish West Coast ◽

Drift Model ◽

Open Sea

ABSTRACT The Swedish Meteorological and Hydrological Institute (SMHI) has developed a system for oil drift forecasting, which can be used by local authorities. The system shall predict where oil, coming from the open sea, hits the beaches or other parts of the archipelago. One crucial idea is that the system shall be easy to handle and also give fast calculations. An operational three-dimensional hydrodynamical model covering the North Sea and the Baltic Sea is run daily at SMHI. When oil is found in the open sea the Swedish Coast Guard makes an oil drift forecast based on the daily runs. The oil drift forecasts are used as input data to the high-resolution local model for the Swedish west coast, which calculates the transport, behaviour, and spreading of the oil. The whole calculation is made within a GIS system. That gives access to all the geographical information and information about vulnerable areas. In order not to be dependent on daily data transmission, the local model can choose between 71 different precalculated current fields. These fields are calculated using a three-dimensional model named PHOENICS, with a grid which is highly adapted to the coastal contours. Current measurements are performed for use as boundary values for the simulation of the precalculated current fields. This forecasting system is now developed for the northern part of the Swedish west coast (down to Gothenburg).

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Impact of Density Gradients on Net Sediment Transport into the Wadden Sea

Journal of Physical Oceanography ◽

10.1175/2007jpo3796.1 ◽

2008 ◽

Vol 38 (3) ◽

pp. 566-587 ◽

Cited By ~ 81

Author(s):

Hans Burchard ◽

Götz Flöser ◽

Joanna V. Staneva ◽

Thomas H. Badewien ◽

Rolf Riethmüller

Keyword(s):

Wadden Sea ◽

Sea Water ◽

Model Simulation ◽

Three Dimensional ◽

Field Studies ◽

Tidal Mixing ◽

Density Gradients ◽

Three Dimensional Model ◽

Model Simulations ◽

The North

Abstract This study tests the hypothesis that horizontal density gradients have the potential to significantly contribute to the accumulation of suspended particulate matter (SPM) in the Wadden Sea. It is shown by means of long-term observations at various positions in the Wadden Sea of the German Bight that the water in the inner regions of the Wadden Sea is typically about 0.5–1.0 kg m−3 less dense than the North Sea water. During winter this occurs mostly because of freshwater runoff and net precipitation; during summer it occurs mostly because of differential heating. It is demonstrated with idealized one-dimensional water column model simulations that the interaction of such small horizontal density gradients with tidal currents generates net onshore SPM fluxes. Major mechanisms for this are tidal straining, estuarine circulation, and tidal mixing asymmetries. Three-dimensional model simulations in a semienclosed Wadden Sea embayment with periodic tidal forcing show that SPM with sufficiently high settling velocity (ws = 10−3 m s−1) is accumulating in the Wadden Sea Bight because of density gradients. This is proven through a comparative model simulation in which the dynamic effects of the density gradients are switched off, with the consequence of no SPM accumulation. These numerical model results motivate future targeted field studies in different Wadden Sea regions with the aim to further support the hypothesis.

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Comparisons on Flow and Temperature Fields for Water-Collecting Box of Diesel Exhaust System

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.199-200.1532 ◽

2011 ◽

Vol 199-200 ◽

pp. 1532-1536 ◽

Cited By ~ 1

Author(s):

Xiao Chuan Wang ◽

Guo He ◽

Xing Long Pan ◽

Xiao Ying Shi

Keyword(s):

Sea Water ◽

Reverse Flow ◽

Temperature Drop ◽

Three Dimensional ◽

Exhaust System ◽

Temperature Fields ◽

Exhaust Gas ◽

Three Dimensional Model ◽

Computational Fluid Dynamics Cfd ◽

Storage Cells

The storage cells of conventional submarines are usually charged up by in the snorkeling state, when the diesel engines that charge the storage cells work underwater. The reverse flow of sea water into the diesel engine from the exhaust pipelines can be avoided effectively by using a water-collecting box (WCB), which has other functions as well. In this paper, a three-dimensional model of WCB was established and based on which the flow and temperature fields were studied by computational fluid dynamics (CFD) computations. From the comparison of distribution on interior fields for four different structural WCBs, an optimized scheme of enhancing the cooling effect and not raising the exhausting resistance was probed. The results show that the temperature drop of exhaust gas after washing the WCB IV (WCB with truncated tubes) is 40 percent higher than that of the WCB I, and the pressure drop has a low of 3 percent as well. The comprehensive characteristics of WCB IV are foremost between the four WCBs.

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Potential impact of iodinated replacement compounds CF<sub>3</sub>I and CH<sub>3</sub>I on atmospheric ozone: a three-dimensional modeling study

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-10129-2010 ◽

2010 ◽

Vol 10 (20) ◽

pp. 10129-10144 ◽

Cited By ~ 18

Author(s):

D. Youn ◽

K. O. Patten ◽

D. J. Wuebbles ◽

H. Lee ◽

C.-W. So

Keyword(s):

Transport Model ◽

Stratospheric Ozone ◽

Vertical Mixing ◽

Three Dimensional ◽

Convective Transport ◽

Atmospheric Ozone ◽

Dimensional Model ◽

Three Dimensional Model ◽

Model Calculations ◽

The Tropics

Abstract. The concept of Ozone Depletion Potentials (ODPs) is extensively used in policy considerations related to concerns about the effects of various halocarbons and other gases on stratospheric ozone. Many of the recent candidate replacement compounds have atmospheric lifetimes shorter than one year in order to limit their environmental effects, especially on stratospheric ozone. Using a three-dimensional global chemistry-transport model (CTM) of the troposphere and the stratosphere, the purpose of this study is to evaluate the potential effects of several very short-lived iodinated substances, namely iodotrifluoromethane (CF3I) and methyl iodide (CH3I), on atmospheric ozone. Like other chemicals with extremely short lifetimes, the stratospheric halogen loading and resulting ozone effects from these compounds are strongly dependent on the location of emissions. For CF3I, a possible replacement candidate for bromotrifluoromethane (CF3Br), ODPs derived by the three-dimensional model are 0.008 with chemical lifetime of 5.03 days and 0.016 with a lifetime of 1.13 days for emissions assumed to be evenly distributed over land surfaces at mid-latitudes and the tropics, respectively. While this is the first time the ODPs have been evaluated with a three-dimensional model, these values are in good agreement with those derived previously. The model calculations suggest that tropical convection could deliver a larger portion of the gas and their breakdown products to the upper troposphere and lower stratosphere if emission source is located in the tropics. The resulting ODP for CH3I, emitted from mid-latitudes, is 0.017 with lifetime of 13.59 days. Valid simulations of convective transport, vertical mixing and degradation chemistry of CH3I are shown that have good qualitative agreement between the model derived distribution of background CH3I, based on global source emission fluxes from previous studies, and available observations especially in vertical profiles.

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Circulation and mixing characteristics of a seasonally open tidal inlet: a field study

Marine and Freshwater Research ◽

10.1071/mf98037 ◽

1999 ◽

Vol 50 (4) ◽

pp. 281 ◽

Cited By ~ 25

Author(s):

Roshanka Ranasinghe ◽

Charitha Pattiaratchi

Keyword(s):

Field Study ◽

Sea Water ◽

Vertical Mixing ◽

Mixing Processes ◽

Convective Cooling ◽

Sea Breezes ◽

Open Sea ◽

Behavioural Patterns ◽

Mixing Characteristics ◽

Combined Action

Tidal inlets in microtidal, wave-dominated coastal environments tend to close to the ocean seasonally. This obstructs navigation and could cause degradation of water quality in the estuary/lagoon connected to the inlet. Hence, engineering solutions are often implemented to prevent inlet closure. However, a prior knowledge of circulation and mixing processes within the estuary is crucial for the sustainability of any engineering solution. This paper attempts to provide insight into circulation and mixing characteristics of seasonally open estuaries based on the results of a field study undertaken at Wilson Inlet, a typical seasonally open estuary, in south-western Australia. Results of the study indicate that this type of estuary may have two distinct behavioural patterns, in winter and in summer. During winter, solar heating causes density stratification during daytime, and convective cooling causes overnight de-stratification; a horizontal cyclonic gyre is established during winter by the combined action of the Coriolis force and streamflow. During summer, strong sea breezes (~10 m s–1 ) cause vertical mixing during daytime, and convective cooling vertically mixes the water column at night. When the inlet is open, sea water propagates into the estuary during flooding tides unless streamflows are very high.

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