Modelling water column processes in the North Sea

1993 ◽  
Vol 343 (1669) ◽  
pp. 509-517 ◽  
Keyword(s):  
Water Column ◽  
North Sea ◽  
Process Water ◽  
Phytoplankton Dynamics ◽  
Annual Cycles ◽  
The North ◽  
Field Investigations ◽  
Southern Central ◽  
The North Sea ◽  
Northern North Sea

In the North Sea advective transports are not negligible. Nevertheless, physical properties like sea surface temperature (SST) can be hindcasted with sufficient precision by vertical process water column models. Annual cycles of SST in the southern, central, and northern North Sea can be simulated using physical upper layer models with relatively small RMS errors. For the Fladenground Experiment (FLEX’76) in the northern North Sea the RMS error is less 0.3 °C for the 2 months of the experiment. This justifies the initial use, at least, of vertical process water column models in simulations for investigating transfer processes in the planktonic ecosystem. Experiments have shown that the simulated entrainment velocities at the bottom of the mixed layer during summer are critically dependent on the resolution of the forcing variables. The effects of this resolution on the annual phytoplankton dynamics will be discussed. Phytoplankton dynamics are strongly influenced by those of the zooplankton, and vice versa. Several field investigations have shown that, seemingly, phytoplankton cannot sustain the observed stock of zooplankton in the northern North Sea: there exists a gap between the abundance of phytoplankton and the need for it to maintain the zooplankton. Revisiting FLEX’76, the simulations with water column models of increasing complexity concerning detritus suggest that pelagic detritus can fill the gap in food availability for the zooplankton. If it is assumed that the zooplankton feeds also on detritus, the zooplankton experiences no food shortage.

scholarly journals Linked sediment and water-column methanotrophy at a man-made gas blowout in the North Sea: Implications for methane budgeting in seasonally stratified shallow seas

2016 ◽  
Vol 61 (S1) ◽  
pp. S367-S386 ◽  
Author(s):  
Lea Steinle ◽  
Mark Schmidt ◽  
Lee Bryant ◽  
Matthias Haeckel ◽  
Peter Linke ◽  
...  
Keyword(s):  
Water Column ◽  
North Sea ◽  
The North ◽  
The North Sea ◽  
Shallow Seas

Metabolic alkalinity release from the Elbe estuary to the North Sea

2021 ◽  
Author(s):  
Mona Norbisrath ◽  
Jeannette Hansen ◽  
Kirstin Dähnke ◽  
Tina Sanders ◽  
Justus E. E. van Beusekom ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Water Column ◽  
Fresh Water ◽  
North Sea ◽  
Total Alkalinity ◽  
Elbe Estuary ◽  
Metabolic Processes ◽  
The North ◽  
Carbon Species ◽  
The North Sea

<p>The Elbe is the largest river entering the German Bight. Its estuary is a heavily used waterway connecting the sea to Germany’s biggest port in Hamburg. The Elbe navigation channel is continuously dredged, and agricultural fertilizer input from the catchment ensuing large phytoplankton blooms in the river Elbe exerts additional anthropogenic pressure. Biogeochemistry in the estuary is additionally governed by the North Sea and its strong tidal cycles, which ensure an exchange of fresh and marine waters.</p><p>The aims were to quantify the release of the carbon species total alkalinity (TA) and dissolved inorganic carbon (DIC) along the Elbe estuary, and to estimate the contribution of aerobe and anaerobe metabolic processes. Therefore, we used water samples collected continuously during a cruise in June 2019, to measure TA and DIC, and the stable isotopes of nitrate. We applied mass balances, to characterize the metabolic activity and detect their effect on the carbon species</p><p>The Elbe estuary could be subdivided into two parts: 1) an outer marine driven part, which is dominated by conservative mixing, also visible in higher TA than DIC values, and 2) an inner fresh water part in which metabolic processes play an important role.</p><p>We found a strong increase in TA and DIC (several hundred µmol kg<sup>-1</sup>) in the Hamburg port area, with higher DIC than TA values. We unraveled the water column impacts of nitrification and denitrification on TA and DIC by analyzing the stable isotopes δ<sup>15</sup>N-NO<sub>3</sub><sup>-</sup> and δ<sup>18</sup>O-NO<sub>3</sub><sup>-</sup>, and identified water column nitrification as a dominant pelagic process in the port of Hamburg and in the fresh water part further downstream. Because nitrification cannot explain the significant increase of TA and DIC in the port region, anaerobic processes such as denitrification in the sediment also appear to play an important role.</p><p> </p>

scholarly journals Looking beyond stratification: a model-based analysis of the biological drivers of oxygen deficiency in the North Sea

2016 ◽  
Vol 13 (8) ◽  
pp. 2511-2535 ◽  
Author(s):  
Fabian Große ◽  
Naomi Greenwood ◽  
Markus Kreus ◽  
Hermann-Josef Lenhart ◽  
Detlev Machoczek ◽  
...  
Keyword(s):  
North Sea ◽  
Oxygen Deficiency ◽  
Low Oxygen ◽  
The North ◽  
Oxygen Conditions ◽  
Southern Central ◽  
The North Sea ◽  
Central North Sea ◽  
The Impact ◽  
Oxygen Dynamics

Abstract. Low oxygen conditions, often referred to as oxygen deficiency, occur regularly in the North Sea, a temperate European shelf sea. Stratification represents a major process regulating the seasonal dynamics of bottom oxygen, yet, lowest oxygen conditions in the North Sea do not occur in the regions of strongest stratification. This suggests that stratification is an important prerequisite for oxygen deficiency, but that the complex interaction between hydrodynamics and the biological processes drives its evolution. In this study we use the ecosystem model HAMSOM-ECOHAM to provide a general characterisation of the different zones of the North Sea with respect to oxygen, and to quantify the impact of the different physical and biological factors driving the oxygen dynamics inside the entire sub-thermocline volume and directly above the bottom. With respect to oxygen dynamics, the North Sea can be subdivided into three different zones: (1) a highly productive, non-stratified coastal zone, (2) a productive, seasonally stratified zone with a small sub-thermocline volume, and (3) a productive, seasonally stratified zone with a large sub-thermocline volume. Type 2 reveals the highest susceptibility to oxygen deficiency due to sufficiently long stratification periods (>  60 days) accompanied by high surface productivity resulting in high biological consumption, and a small sub-thermocline volume implying both a small initial oxygen inventory and a strong influence of the biological consumption on the oxygen concentration. Year-to-year variations in the oxygen conditions are caused by variations in primary production, while spatial differences can be attributed to differences in stratification and water depth. The large sub-thermocline volume dominates the oxygen dynamics in the northern central and northern North Sea and makes this region insusceptible to oxygen deficiency. In the southern North Sea the strong tidal mixing inhibits the development of seasonal stratification which protects this area from the evolution of low oxygen conditions. In contrast, the southern central North Sea is highly susceptible to low oxygen conditions (type 2). We furthermore show that benthic diagenetic processes represent the main oxygen consumers in the bottom layer, consistently accounting for more than 50 % of the overall consumption. Thus, primary production followed by remineralisation of organic matter under stratified conditions constitutes the main driver for the evolution of oxygen deficiency in the southern central North Sea. By providing these valuable insights, we show that ecosystem models can be a useful tool for the interpretation of observations and the estimation of the impact of anthropogenic drivers on the North Sea oxygen conditions.

scholarly journals Large-scale forcing of the European Slope Current and associated inflows to the North Sea

Ocean Science ◽  
2017 ◽  
Vol 13 (2) ◽  
pp. 315-335 ◽  
Author(s):  
Robert Marsh ◽  
Ivan D. Haigh ◽  
Stuart A. Cunningham ◽  
Mark E. Inall ◽  
Marie Porter ◽  
...  
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Tide Gauge ◽  
Density Gradients ◽  
Current Transport ◽  
Tide Gauge Records ◽  
The North ◽  
Wide Range ◽  
The North Sea ◽  
Northern North Sea

Abstract. The European Slope Current provides a shelf-edge conduit for Atlantic Water, a substantial fraction of which is destined for the northern North Sea, with implications for regional hydrography and ecosystems. Drifters drogued at 50 m in the European Slope Current at the Hebridean shelf break follow a wide range of pathways, indicating highly variable Atlantic inflow to the North Sea. Slope Current pathways, timescales and transports over 1988–2007 are further quantified in an eddy-resolving ocean model hindcast. Particle trajectories calculated with model currents indicate that Slope Current water is largely recruited from the eastern subpolar North Atlantic. Observations of absolute dynamic topography and climatological density support theoretical expectations that Slope Current transport is to first order associated with meridional density gradients in the eastern subpolar gyre, which support a geostrophic inflow towards the slope. In the model hindcast, Slope Current transport variability is dominated by abrupt 25–50 % reductions of these density gradients over 1996–1998. Concurrent changes in wind forcing, expressed in terms of density gradients, act in the same sense to reduce Slope Current transport. This indicates that coordinated regional changes of buoyancy and wind forcing acted together to reduce Slope Current transport during the 1990s. Particle trajectories further show that 10–40 % of Slope Current water is destined for the northern North Sea within 6 months of passing to the west of Scotland, with a general decline in this percentage over 1988–2007. Salinities in the Slope Current correspondingly decreased, evidenced in ocean analysis data. Further to the north, in the Atlantic Water conveyed by the Slope Current through the Faroe–Shetland Channel (FSC), salinity is observed to increase over this period while declining in the hindcast. The observed trend may have broadly compensated for a decline in the Atlantic inflow, limiting salinity changes in the northern North Sea during this period. Proxies for both Slope Current transport and Atlantic inflow to the North Sea are sought in sea level height differences across the FSC and between Shetland and the Scottish mainland (Wick). Variability of Slope Current transport on a wide range of timescales, from seasonal to multi-decadal, is implicit in sea level differences between Lerwick (Shetland) and Tórshavn (Faroes), in both tide gauge records from 1957 and a longer model hindcast spanning 1958–2012. Wick–Lerwick sea level differences in tide gauge records from 1965 indicate considerable decadal variability in the Fair Isle Current transport that dominates Atlantic inflow to the northwest North Sea, while sea level differences in the hindcast are dominated by strong seasonal variability. Uncertainties in the Wick tide gauge record limit confidence in this proxy.

scholarly journals Opportunistically recorded acoustic data support Northeast Atlantic mackerel expansion theory

2015 ◽  
Vol 73 (4) ◽  
pp. 1115-1126 ◽  
Author(s):  
Jeroen van der Kooij ◽  
Sascha M.M. Fässler ◽  
David Stephens ◽  
Lisa Readdy ◽  
Beth E. Scott ◽  
...  
Keyword(s):  
North Sea ◽  
Stock Assessment ◽  
Detection Algorithm ◽  
Trawl Survey ◽  
Northeast Atlantic ◽  
Acoustic Data ◽  
The North ◽  
The North Sea ◽  
Northern North Sea ◽  
Feeding Grounds

Abstract Fisheries independent monitoring of widely distributed pelagic fish species which conduct large seasonal migrations is logistically complex and expensive. One of the commercially most important examples of such a species in the Northeast Atlantic Ocean is mackerel for which up to recently only an international triennial egg survey contributed to the stock assessment. In this study, we explore whether fisheries acoustic data, recorded opportunistically during the English component of the North Sea International Bottom Trawl Survey, can contribute to an improved understanding of mackerel distribution and provide supplementary data to existing dedicated monitoring surveys. Using a previously published multifrequency acoustic mackerel detection algorithm, we extracted the distribution and abundance of schooling mackerel for the whole of the North Sea during August and September between 2007 and 2013. The spatio-temporal coverage of this unique dataset is of particular interest because it includes part of the unsurveyed summer mackerel feeding grounds in the northern North Sea. Recent increases in landings in Icelandic waters during this season suggested that changes have occurred in the mackerel feeding distribution. Thus far it is poorly understood whether these changes are due to a shift, i.e. mackerel moving away from their traditional feeding grounds in the northern North Sea and southern Norwegian Sea, or whether the species' distribution has expanded. We therefore explored whether acoustically derived biomass of schooling mackerel declined in the northern North Sea during the study period, which would suggest a shift in mackerel distribution rather than an expansion. The results of this study show that in the North Sea, schooling mackerel abundance has increased and that its distribution in this area has not changed over this period. Both of these findings provide, to our knowledge, the first evidence in support of the hypothesis that mackerel have expanded their distribution rather than moved away.

Climatic and oceanic influences on the abundance of gelatinous zooplankton in the North Sea

2009 ◽  
Vol 90 (6) ◽  
pp. 1153-1159 ◽  
Author(s):  
C.P. Lynam ◽  
M.J. Attrill ◽  
M.D. Skogen
Keyword(s):  
North Sea ◽  
Biological Response ◽  
Winter Precipitation ◽  
Gelatinous Zooplankton ◽  
Aurelia Aurita ◽  
Future Research ◽  
Long Term Effects ◽  
The North ◽  
The North Sea ◽  
Northern North Sea

Oceanographically based mechanisms are shown to explain the spatial variation in the climatic relationship between the abundance of medusae (Aurelia aurita and Cyanea spp. of the class Scyphozoa), in the North Sea between 1971 and 1986 during June–August, and the winter (December–March) North Atlantic Oscillation Index (NAOI). A scyphomedusa population to the west of Denmark shows a strong inverse relationship between medusa abundance and fluctuations in the NAOI; the NAOI correlates strongly (P < 0.001) with both annual sea surface temperature (SST) at 6.5°E 56.5°N (1950–2008) and with winter precipitation on the Danish coast at Nordby (1900–2008) suggesting a direct link between the influence of climate and medusae abundance. In contrast, scyphomedusa abundance and distribution in the northern North Sea appears to be influenced by oceanic and mixed water inflow, which may overwhelm or mask any direct climatic influence on jellyfish abundance. Similarly, advection can also explain much of the interannual variability (1959–2000) in the abundance of other gelatinous zooplankton taxa (Cnidaria, Ctenophora and Siphonophora) in the northern North Sea as identified by the capture of gelatinous tissue and nematocysts (stinging cells) in Continuous Plankton Recorder samples. Jellyfish (Scyphozoa) in the southern North Sea may benefit from low temperature anomalies and the long-term effects of global warming might suppress Aurelia aurita and Cyanea spp. populations there. However, the biological response to temperature is complex and future research is required in this area.

Clay mineral distribution and provenance in Mesozoic and Tertiary mudrocks of the Moray Firth and northern North Sea

Clay Minerals ◽  
1990 ◽  
Vol 25 (4) ◽  
pp. 519-541 ◽  
Author(s):  
M. J. Pearson
Keyword(s):  
Clay Mineral ◽  
North Sea ◽  
Volcanic Activity ◽  
Volcanic Material ◽  
The North ◽  
Moray Firth ◽  
History Of ◽  
The North Sea ◽  
Northern North Sea ◽  
And Control

AbstractClay mineral abundances in Mesozoic and Tertiary argillaceous strata from 15 exploration wells in the Inner and Outer Moray Firth, Viking Graben and East Shetland Basins of the northern North Sea have been determined in <0·2 µm fractions of cuttings samples. The clay assemblages of more deeply-buried samples cannot be unambiguously related to sedimentary input because of the diagenetic overprint which may account for much of the chlorite and related interstratified minerals. Other sediments, discussed on a regional basis and related to the geological history of the basins, are interpreted in terms of clay mineral provenance and control by climate, tectonic and volcanic activity. The distribution of illite-smectite can often be related to volcanic activity both in the Forties area during the M. Jurassic, and on the NE Atlantic continental margin during the U. Cretaceous-Early Tertiary which affected the North Sea more widely and left a prominent record in the Viking Graben and East Shetland Basin. Kaolinite associated with lignite-bearing sediments in the Outer Moray Firth Basin was probably derived by alteration of volcanic material in lagoonal or deltaic environments. Some U. Jurassic and L. Cretaceous sediments of the Inner Moray Basin are rich in illite-smectite, the origin of which is not clear.

scholarly journals Vertical distribution of pre-settled sandeel (Ammodytes marinus) in the North Sea in relation to size and environmental variables

2003 ◽  
Vol 60 (6) ◽  
pp. 1342-1351 ◽  
Author(s):  
Henrik Jensen ◽  
Peter J Wright ◽  
Peter Munk
Keyword(s):  
Vertical Distribution ◽  
Water Column ◽  
North Sea ◽  
Distribution Patterns ◽  
Food Concentration ◽  
The North ◽  
Vertical Distributions ◽  
The North Sea ◽  
Drift Trajectory ◽  
Vertical Positioning

Abstract Vertical distribution patterns of larval and juvenile sandeels were investigated at four locations in the North Sea. Sandeels between 6 and 65 mm were found to depths of 80 m, with vertical distributions dependent on both length and environmental factors. At one location with a stratified water column, the highest densities were found during the day in midwater where food concentration was also highest. In areas without marked vertical hydrographic gradients, larvae were relatively more abundant in surface waters during the day. At all locations, larvae of all sizes were generally more homogeneously distributed in the water column during night than during day. The extent of vertical migration, as measured by the standard deviation of the mean depth, increased generally with length. Gear avoidance was evident for larvae ≥20 mm. Catch efficiency generally depended on both length class and surface light intensity. A simulated drift pattern of larvae, based on ADCP current measurements from two locations, predicts that the horizontal drift trajectory would only be affected slightly by the vertical positioning of the larvae in the water column during the time of sampling. The implication of vertical migrations for dispersal of larvae away from the spawning grounds is discussed.

Spatial and temporal dynamics of European hake (Merluccius merluccius) in the North Sea

2018 ◽  
Vol 75 (6) ◽  
pp. 2033-2044 ◽  
Author(s):  
Arved Staby ◽  
Jon Egil Skjæraasen ◽  
Audrey J Geffen ◽  
Daniel Howell
Keyword(s):  
North Sea ◽  
Temporal Dynamics ◽  
Trawl Survey ◽  
Merluccius Merluccius ◽  
Frequency Distributions ◽  
The North ◽  
The North Sea ◽  
Northern North Sea ◽  
Central North Sea ◽  
European Hake

Abstract Catches of European hake (Merluccius merluccius) in the North Sea have increased substantially during the last decade, even though there is no directed commercial fishery of hake in this area. We analysed the spatial distributions of hake in the northern the parts of its range, (where it is less well-studied), using ICES international bottom trawl survey data from 1997 to 2015. We examine length-frequency distributions for (i) distinct modes enabling the assignment of fish into categories which likely corresponded to the ages 1, 2, and 3+ and (ii) patterns of seasonal spatial distribution for the different groups. Age categories 1 and 2 fish were most abundant in the northern North Sea, and appear to remain in the North Sea until 2 years of age, when they move into deeper waters. Their distribution has expanded into the western-central North Sea in the last decade. Age category 3+ fish were most abundant in the northern and central North Sea during summer, indicating a seasonal influx of large individuals into this area likely associated with spawning activity. The distribution of these older fish has gradually expanded westward in both seasons.

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