scholarly journals Detection of low bottom water oxygen concentrations in the North Sea; implications for monitoring and assessment of ecosystem health

2009 ◽  
Vol 6 (4) ◽  
pp. 8411-8453 ◽  
Author(s):  
N. Greenwood ◽  
E. R. Parker ◽  
L. Fernand ◽  
D. B. Sivyer ◽  
K. Weston ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Oxygen Concentration ◽  
North Sea ◽  
Mixed Layer ◽  
Ecosystem Health ◽  
Bottom Water ◽  
Dissolved Oxygen Concentration ◽  
The North ◽  
The North Sea ◽  
Oxygen Concentrations

Abstract. This paper presents new results from high temporal resolution observations over two years (2007 and 2008) from instrumented moorings deployed in the central North Sea, at the Oyster Grounds and on the northern slope of Dogger Bank (North Dogger). The water column was stratified in the summer at both sites, leading to limited exchange of the water in the bottom mixed layer. Data from these moorings revealed the variable nature of summer oxygen depletion at the Oyster Grounds. The combination of in situ and ship-based measurements allowed the physical and biological conditions leading to decreasing dissolved oxygen concentrations in bottom water to be examined. The concentration of dissolved oxygen in the bottom water at both sites was observed to decrease throughout the summer period after the onset of stratification. Depleted dissolved oxygen concentration (6.5 mg l−1, 71% saturation) was measured at the North Dogger, a site which is not significantly influenced by anthropogenic nutrient inputs. Lower oxygen saturation (5.2 mg l−1, 60% saturation) was measured for short durations at the Oyster Grounds. Increasing bottom water temperature accounted for 55% of the decrease in dissolved oxygen concentration at the Oyster Grounds compared to 10% at North Dogger. Dissolved oxygen concentration in bottom water at the Oyster Grounds was shown to be strongly influenced by short term events including storm events and pulses of biomass input. In contrast, dissolved oxygen concentration in bottom water at the North Dogger reflected longer seasonal processes such as gradual temperature increases and a more steady supply of biomass to the bottom mixed layer. The differences between the study sites shows the need for an improved understanding of the mechanisms driving these processes if the use of oxygen in marine management and ensuring ecosystem health is to be meaningful and successful in the future. These observations provide greater understanding of the nature of the depletion in bottom oxygen concentration in the North Sea.

scholarly journals Detection of low bottom water oxygen concentrations in the North Sea; implications for monitoring and assessment of ecosystem health

2010 ◽  
Vol 7 (4) ◽  
pp. 1357-1373 ◽  
Author(s):  
N. Greenwood ◽  
E. R. Parker ◽  
L. Fernand ◽  
D. B. Sivyer ◽  
K. Weston ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Oxygen ◽  
Oxygen Concentration ◽  
North Sea ◽  
Particulate Organic Matter ◽  
Ecosystem Health ◽  
Bottom Water ◽  
Dissolved Oxygen Concentration ◽  
The North ◽  
The North Sea

Abstract. This paper presents new results from high temporal resolution observations over two years (2007 and 2008) from instrumented moorings deployed in the central North Sea, at the Oyster Grounds and on the northern slope of Dogger Bank (North Dogger). The water column was stratified in the summer at both sites, leading to limited exchange of the water in the bottom mixed layer. Data from these moorings revealed the variable nature of summer oxygen depletion at the Oyster Grounds. The combination of in situ and ship-based measurements allowed the physical and biological conditions leading to decreasing dissolved oxygen concentrations in bottom water to be examined. In 2007 and 2008, the concentration of dissolved oxygen in the bottom water at both sites was observed to decrease throughout the summer period after the onset of stratification. Depleted dissolved oxygen concentration (6.5 mg l−1, 71% saturation) was measured at the North Dogger, a site which is not significantly influenced by anthropogenic nutrient inputs. Lower oxygen saturation (5.2 mg l−1, 60% saturation) was measured for short durations at the Oyster Grounds. The seasonal increase in bottom water temperature accounted for 55% of the decrease in dissolved oxygen concentration at the Oyster Grounds compared to 10% at North Dogger. Dissolved oxygen concentration in bottom water at the Oyster Grounds was shown to be strongly influenced by short term events including storms and pulses of particulate organic matter input. In contrast, dissolved oxygen concentration in bottom water at the North Dogger reflected longer seasonal processes such as a gradual temperature increase over the summer and a more steady supply of particulate organic matter to the bottom mixed layer. The differences between the study sites shows the need for an improved understanding of the mechanisms driving these processes if the use of oxygen in marine management and ensuring ecosystem health is to be meaningful and successful in the future. These high frequency observations provide greater understanding of the nature of the depletion in bottom oxygen concentration in the North Sea.

Ventilation of bottom water in the North Sea–Baltic Sea transition zone

2009 ◽  
Vol 75 (1-2) ◽  
pp. 138-149 ◽  
Author(s):  
Jørgen Bendtsen ◽  
Karin E. Gustafsson ◽  
Johan Söderkvist ◽  
Jørgen L.S. Hansen
Keyword(s):  
Baltic Sea ◽  
Transition Zone ◽  
North Sea ◽  
Bottom Water ◽  
The North ◽  
The North Sea

Mixed-layer kaolinite-illite-vermiculite in North Sea shales

Clay Minerals ◽  
1999 ◽  
Vol 34 (2) ◽  
pp. 333-344 ◽  
Author(s):  
B. A. Sakharov ◽  
H. Lindgreen ◽  
A. L. Salyn ◽  
V. A. Drits
Keyword(s):  
North Sea ◽  
Mixed Layer ◽  
Coherent Scattering ◽  
Upper Jurassic ◽  
The North ◽  
Dominant Component ◽  
The North Sea ◽  
Xrd Patterns ◽  
Layer Mineral ◽  
Random Alternation

AbstractThe finest fractions of Upper Jurassic shales from the North Sea and onshore Denmark contain 80–90% of an illite-smectite-vermiculite (I-S-V) mixed-layer mineral and, in addition a phase which has X-ray diffraction (XRD) peaks at 7.20–7.26 Å and 3.56–3.58 Å in air- dried and glycolated specimens. This phase may be a fine kaolinite with a small thickness of coherent scattering domains (CSDs) or alternatively a mixed-layer mineral which has kaolinite as the dominant component. For one sample from the Norwegian well 9/4-3, these alternatives are investigated using the multi-specimen method by which agreement between the experimental pattern and the pattern calculated for one and the same structure is obtained for each of several specimens saturated with different cations and with/without glycolation. It is demonstrated that the modelled XRD patterns for a kaolinite-illite-vermiculite (K-I-V) structure having 0.94 kaolinite, 0.03 illite and 0.03 vermiculite layers and random alternation fit the experimental patterns.

scholarly journals An 18-year climatology of derechos in Germany

2019 ◽  
Author(s):  
Christoph P. Gatzen ◽  
Andreas H. Fink ◽  
David M. Schultz ◽  
Joaquim G. Pinto
Keyword(s):  
North Sea ◽  
Mixed Layer ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Warm Season ◽  
The United States ◽  
Cold Season ◽  
Central Germany ◽  
The North ◽  
The North Sea

Abstract. Derechos are high-impact convective wind events that can cause fatalities and widespread losses. In this study, 40 derechos affecting Germany between 1997 and 2014 are analysed to estimate the derecho risk. Similar to the United States, Germany is affected by two derecho types. The first derecho type forms in south-westerly 500-hPa flow downstream of intense west-European troughs and accounts for 22 of the 40 derechos. These derechos are named warm-season type due to their peak occurrence in June and July. Warm-season type derechos frequently start over southwestern Germany in the afternoon and move either eastward along the Alpine forelands or north-eastward across southern central Germany. Only one warm-season derecho moved across the North Sea and one moved across the Baltic Sea in the 18-year period. Proximity soundings of German warm-season type derechos indicate strong deep-layer vertical wind shear with a median of 20 m s−1 0–6-km shear and mixed-layer Convective Available Potential Energy (mixed-layer CAPE) between 20 and 2600 J kg−1 with a median around 500 J kg−1. The second derecho type forms in north-westerly 500-hPa flow and accounts for 18 of the 40 derechos. These derechos form in strong north-westerly flow, frequently in association with mid-tropospheric PV intrusions. They are named cold-season type because they are associated with a secondary peak from December to February. Cold-season type derechos start over or close to the North Sea and primarily affect north and central Germany; their start time is not strongly related to the peak of diurnal heating. Proximity soundings indicate high-shear–low-CAPE environments with a median 0–6-km shear of 35 m s−1 and a median mixed-layer CAPE of 3 J kg−1. Environmental CAPE is zero in almost half of cold-season type proximity soundings. Fifteen warm-season type and nine cold-season type derechos had wind gusts reaching 33 m s−1 in at least at three locations. Although warm-season derechos are more frequent, the path length of cold-season type derechos is on average 1.4 times longer. Thus, these two types of German derechos are likely to have similar impacts.

scholarly journals The impacts of physical processes on oxygen variations in the North Sea-Baltic Sea transition zone

2011 ◽  
Vol 8 (4) ◽  
pp. 1723-1755 ◽  
Author(s):  
L. Jonasson ◽  
Z. Wan ◽  
J. H. S. Hansen ◽  
J. She
Keyword(s):  
Dissolved Oxygen ◽  
Baltic Sea ◽  
Transition Zone ◽  
North Sea ◽  
Late Summer ◽  
Physical Processes ◽  
The North ◽  
The North Sea ◽  
Seasonal Hypoxia ◽  
Benthic Ecosystems

Abstract. The bottom water of the North Sea-Baltic Sea transition zone suffers from seasonal hypoxia, usually during late summer and autumn. These hypoxic events are critical for the benthic ecosystems and the concentration of dissolved oxygen is an important measure of the water quality. However, to model the subsurface dissolved oxygen is a major challenge, especially in estuaries and coastal regions. In this study a simple oxygen consumption model is coupled to a 3-D hydrodynamical model in order to analyse oxygen variations in the transition zone. The benthic and pelagic consumption of oxygen is modelled as a function of water temperature and oxygen concentration. A quantitative assessment of the model demonstrates that the model is able to resolve both seasonal and interannual variations in dissolved oxygen. Results from several experimental simulations highlight the importance of physical processes in the regulation of dissolved oxygen. Advective oxygen transport and wind induced mixing are two key processes that control the extent of hypoxia in the transition zone.

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