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Salinity variability in the German Bight in relation to climate variability
Abstract
A relationship between observed variability in large-scale climate and salinity in the GermanBight is sought using a multivariate statistical approach. It is found that on an annual timescale,90% of the observed salinity variability is in-phase and correlated with a lag of several monthsto large-scale air pressure. The statistical model is used to estimate annual salinity anomaliesfrom large-scale air pressure back to 1900. The correlations between estimated and observedsalinities range from r=0.4 to r=0.7, depending on the position. It is shown that advectiveprecipitation is the mechanism that links air pressure and salinity anomalies. Advection ofAtlantic Water has only a minor impact on the annula mean in the examined coastal zone. Ifair pressure data from a climate change experiment is used as predictor, a slight drop of themean salinity level in the range of 0.2 to 0.3 psu is predicted for the near future. DOI: 10.1034/j.1600-0870.1998.00012.x
... Inter-annual variability of salinity in the North Sea is mainly driven by the inflow of highly saline Atlantic water in the north [61], [113], [114], [115] and river discharge from continental Europe in the south [116], [117]. A thorough study is needed to identify the primary salinity driver in the central and south-western North Sea, where the strong correlation with sprat stock variables was found. ...
... As we already mentioned, Atlantic water inflow is known to affect zooplankton composition in the North Sea [31], [62], [64]. Rivers discharge nutrient rich waters and strongly affect water stratification in the North Sea [117], both are important factors influencing primary and secondary productivity. A more detailed investigation of this bottom-up control of the sprat variability is needed to discover exact mechanism behind the correlations found in our study. ...
... One example would be the salinity of the southern and central North Sea, which was shown here to be a good environmental covariate of sprat SSB and recruitment. Schott [116] and Heyen and Dippner [117] showed that the salinity in the southern North Sea is correlated to river discharge with 1 year lag. Therefore, there is a potential to predict the sprat stock's dynamics with at least 1 year in advance based on the observations of river discharge. ...
Understanding of the processes affecting recruitment of commercially important fish species is one of the major challenges in fisheries science. Towards this aim, we investigated the relation between North Sea hydrography (temperature and salinity) and fish stock variables (recruitment, spawning stock biomass and pre-recruitment survival index) for 9 commercially important fishes using spatially-resolved cross-correlation analysis. We used high-resolution (0.2° × 0.2°) hydrographic data fields matching the maximal temporal extent of the fish population assessments (1948–2013). Our approach allowed for the identification of regions in the North Sea where environmental variables seem to be more influential on the fish stocks, as well as the regions of a lesser or nil influence. Our results confirmed previously demonstrated negative correlations between temperature and recruitment of cod and plaice and identified regions of the strongest correlations (German Bight for plaice and north-western North Sea for cod). We also revealed a positive correlation between herring spawning stock biomass and temperature in the Orkney-Shetland area, as well as a negative correlation between sole pre-recruitment survival index and temperature in the German Bight. A strong positive correlation between sprat stock variables and salinity in the central North Sea was also found. To our knowledge the results concerning correlations between North Sea hydrography and stocks’ dynamics of herring, sole and sprat are novel. The new information about spatial distribution of the correlation provides an additional help to identify mechanisms underlying these correlations. As an illustration of the utility of these results for fishery management, an example is provided that incorporates the identified environmental covariates in stock-recruitment models.
... On the other hand, salinity in the Fair Isle Current shows interannual variability and no clear long-term trend ( Fig. 3.2), being influenced by the fresher waters of the Scottish Coastal Current from west of Scotland. Coastal regions of the southern North Sea, notably the German Bight, are influenced by fluvial inputs (primarily from the rivers Rhine and Elbe) as well as Atlantic inflows (Heyen and Dippner 1998;Janssen 2002). Away from coastal waters, the influence of Atlantic inflow dominates. ...
... Away from coastal waters, the influence of Atlantic inflow dominates. For the German Bight, Heyen and Dippner (1998) reported no substantial trends in sea-surface salinity (SSS) for the period 1908-1995, a result confirmed by earlier analysis of Helgoland Roads SSS for the period 1873-1993 (Becker et al. 1997) and the analyses of Janssen (2002). German Bight studies (e.g. ...
This chapter discusses past and ongoing change in the following physical variables within the North Sea: temperature, salinity and stratification; currents and circulation; mean sea level; and extreme sea levels. Also considered are carbon dioxide; pH and nutrients; oxygen; suspended particulate matter and turbidity; coastal erosion, sedimentation and morphology; and sea ice. The distinctive character of the Wadden Sea is addressed, with a particular focus on nutrients and sediments. This chapter covers the past 200 years and focuses on the historical development of evidence (measurements, process understanding and models), the form, duration and accuracy of the evidence available, and what the evidence shows in terms of the state and trends in the respective variables. Much work has focused on detecting long-term change in the North Sea region, either from measurements or with models. Attempts to attribute such changes to, for example, anthropogenic forcing are still missing for the North Sea. Studies are urgently needed to assess consistency between observed changes and current expectations, in order to increase the level of confidence in projections of expected future conditions.
... The German Bight in the south-eastern North Sea extends from the East and North Frisian German Wadden Sea coast towards the White Bank (55°00 N; 6°00 E) in the north-west. The German Bight receives oceanic water from the British Channel (Heyen and Dippner, 1998), but also from the northwestern North Sea (Pohlmann, 2006). During transport along the Wadden Sea coasts the water masses are under strong riverine influence. ...
... Salinities increase from below 30 psu in front of river outlets to 31-32 psu at about 30 km distance from the coast. At Helgoland (i.e. about 50 km offshore) salinity fluctuates interannually between 31 and 33 psu (Wiltshire et al., 2008) while at about 75 km offshore the long-term mean salinity is N33 psu (Heyen and Dippner, 1998). The White Bank area is under the influence of central North Sea waters with relatively stable salinities of 34-35 psu (Skov and Prins, 2001). ...
Floating objects facilitate the dispersal of marine and terrestrial species but also represent a major environmental hazard in the case of anthropogenic plastic litter. They can be found throughout the world's oceans but information on their abundance and the spatio-temporal dynamics is scarce for many regions of the world. This information, however, is essential to evaluate the ecological role of floating objects. Herein, we report the results from a ship-based visual survey on the abundance and composition of flotsam in the German Bight (North Sea) during the years 2006 to 2008. The aim of this study was to identify potential sources of floating objects and to relate spatio-temporal density variations to environmental conditions. Three major flotsam categories were identified: buoyant seaweed (mainly fucoid brown algae), natural wood and anthropogenic debris. Densities of these floating objects in the German Bight were similar to those reported from other coastal regions of the world. Temporal variations in flotsam densities are probably the result of seasonal growth cycles of seaweeds and fluctuating river runoff (wood). Higher abundances were often found in areas where coastal fronts and eddies develop during calm weather conditions. Accordingly, flotsam densities were often higher in the inner German Bight than in areas farther offshore. Import of floating objects and retention times in the German Bight are influenced by wind force and direction. Our results indicate that a substantial amount of floating objects is of coastal origin or introduced into the German Bight from western source areas such as the British Channel. Rapid transport of floating objects through the German Bight is driven by strong westerly winds and likely facilitates dispersal of associated organisms and gene flow among distant populations.
... A canonical correlation analysis (CCA) was performed between the leading eigenvectors of benthic animals, TNFs, and sediment variables (depth, grain size, LOI) using statistical downscaling methods (von Storch et al., 1993). This method has been applied e.g., to macrozoobenthos communities in the German Bight (Kröncke et al., 2013) or in the Gulf of Riga (Dippner and Ikauniece, 2001) and details on the method were given in Heyen and Dippner (1998). ...
During three cruises to the Bay of Gdansk, Baltic Sea, the fauna, porewater and bottom water were sampled at stations parallel to the shore and along a transect offshore. Diffusive porewater fluxes were calculated and related to the total net fluxes (TNF) of nutrients. The TNF comprise all nutrients that reach the bottom water from the sediment including diffusive nutrient efflux, discharge from macrozoobenthos and microbial activity. They were determined during in situ incubations using a benthic chamber lander, which is rarely done in coastal research. The lander restricts the physical influence of currents and waves on the sediments and only allows nutrient fluxes due to bioturbation by natural communities. Strong benthic-pelagic coupling in the shallow coastal zone suggested a crucial filter function for the bioturbated coastal sediments, which are separated from muddy deep sediments with little or no fauna at a depth of 50 m; in between is a small intermediate zone. While diffusive fluxes were highest at intermediate and offshore stations, TNF were highest at sandy coastal stations, where reservoirs of dissolved nutrients were small and sediments almost devoid of organic material. The greatest impact of macrofauna on sedimentary fluxes was found at stations whose communities were dominated by deep-burrowing polychaetes. The largest TNF were measured directly at the mouth of the Vistula River, where riverine food and nutrients supplies were highest. Macrofauna communities and sediment variables can thus serve as descriptive indicator to estimate the extent of the coastal filter. Finally, based on the total areal size of the different sediment types, annual efflux for the complete coastal zone of the Gdansk Bay was estimated to be 6.9 kt N, 19 kt Si, and 0.9 kt P. Compared to the muddy offshore area, which is twice as large, these amounts were similar for P and threefold higher for N and Si.
... Instead, it is possible to interpolate the relatively low varying formation factors computed from all values of the measured electrical conductivities (Fig. 6, bottom left panel) in a reliable way with a Kriging algorithm as shown in Fig. 6 Offshore sea water conductivity at 5 • C is assumed to be 3120 mS m −1 according to TDS of 35 000 mg l −1 , the mean salinity of the North Sea (e.g. Heyen and Dippner, 1998). To obtain supporting points for the sea region, additional apparent formation factors were gained by dividing sea water electrical conductivity by the corresponding HEM conductivity. ...
A numerical variable-density groundwater model is set up for the North Sea Island of Borkum to estimate climate change impacts on coastal aquifers and especially the situation of barrier islands in the Wadden Sea. The database includes information from boreholes, a seismic survey, a helicopter-borne electromagnetic survey (HEM), monitoring of the freshwater-saltwater boundary by vertical electrode chains in two boreholes, measurements of groundwater table, pumping and slug tests, as well as water samples. Based on a statistical analysis of borehole columns, seismic sections and HEM, a hydrogeological model is set up. The groundwater model is developed using the finite-element programme FEFLOW. The variable-density groundwater model is calibrated on the basis of hydraulic, hydrological and geophysical data, in particular spatial HEM and local monitoring data. Verification runs with the calibrated model show good agreement between measured and computed hydraulic heads. A good agreement is also obtained between measured and computed density or total dissolved solids data for both the entire freshwater lens on a large scale and in the area of the well fields on a small scale.
For simulating future changes in this coastal groundwater system until the end of the current century we use the climate scenario A2, specified by the Intergovernmental Panel on Climate Change and in particular the data for the German North Sea coast. Simulation runs show proceeding salinization with time beneath the well fields of the two waterworks Waterdelle and Ostland.
The modelling study shows that spreading of well fields is an appropriate protection measure against excessive salinization of the water supply until the end of the current century.
... Since 2001, the appearance of the blocking and Atlantic ridge patterns increased. Such changes in climate forcing should have an impact in the North Sea and the Baltic Sea because in various papers an impact of NAO to the physical ( Heyen and Dippner, 1998) and biological ( Kröncke et al., 1998) system of the North Sea and to the biological system of the Baltic Sea ( Dippner and Ikauniece, 2001;Dippner et al., 2000) have been demonstrated. Using monitoring data, we analyse two RS in different areas of North Sea and Baltic Sea. ...
... More relevant to our study, Heyen and Dippner (1998) proposed that in the German Bight, the interannual and interdecadal variability in surface salinity is correlated to river runoff rather than advection of Atlantic water. For the same area, Kröncke et al. (1998) found that the biomass, abundance and species number of macrozoobenthos is strongly affected by climate variability. ...
We compiled homogeneous long-term time series
comprising 39 variables representing the German Bight and
for the period 1975–2004. A diverse set of variables was
selected to cover multiple trophic levels and different
environmental forcing thus to examine long-term changes
in this coastal region. Previous studies have hypothesised
the presence of regime shifts in observations extending over
the entire North Sea. Focusing on a smaller spatial scale,
and closer to the coast, we investigated the major modes of
variability in the compiled time series using principal
component analysis. The results obtained confirm a
previously identified regime shift in the North Sea in
1987/1988 and suggest that the German Bight is dominantly
characterised by long-term modes of variability. In the
German Bight, the shift of 1987/1988 is driven primarily by
temperature, Gulf Stream index, frost days and Secchi
depth. Changes in some of the ecosystem variables
(plankton and fish) appear to be related to changes in these
driving variables. In particular, we documented strong
positive correlations between the long-term trend showed
by the first principal component and herring, Noctiluca
scintillans, and, to a lesser extent, Pleurobrachia pileus.
Two gadoids, namely cod and saithe, showed negative
correlations with the observed long-term mode of variability.
Changes in the sum of five small calanoid copepods
were, however, less marked. Phosphate and ammonium
exhibited a decreasing trend over the last 30 years. Diatoms
and Calanus helgolandicus did not show evidence of
changes in concert to this trend. Specific analyses of the
data divided into three different subsets (biological, climatic
and chemical) characterise the climate of the German Bight
as highly dynamic also on short timescales (a few years) as
compared to much smoother biological and chemical
components. The dynamic regime of the German Bight
taken together with a low correlation between the major
mode of variability and phytoplankton and zooplankton
data suggests that the lower trophic levels of this ecosystem
are remarkably resilient.
... The vertical resolution is typically 10 m in the upper 100 m and 25 m below. See also Table 1 the Chinese coast (Cui & Zorita 1998) and salinity in the German Bight (Heyen & Dippner 1998). The general assumptions, problems and strategies of the statistical downscaling approach can be found, for instance, in Wilby & Wigley (1997). ...
The relationship between the low-frequency (annually averaged) salinity and oxygen concentrations in the last 30 yr in the Baltic Sea and the large-scale atmospheric circulation was statistically analyzed. Ii: was found that at these time scales the evolution of salinity and oxygen is guile homogeneous in depth, i.e. deviations from the long-term mean tend to be of the same sign in the upper and deeper layers simultaneously. Moreover, the evolution of the salinity and oxygen concentrations are negatively correlated within each layer: lower than normal salinities tend to be observed simultaneously with higher than normal oxygen concentrations, and vice versa. The statistical analysis seems to indicate that the forcing by the atmospheric circulation may be responsible for this anticorrelation between salinity and oxygen. A stronger meridional sea-level-pressure (SLP) gradient over the North Atlantic, and therefore stronger westerly winds, causes positive rainfall anomalies in the Baltic Sea catchment area and increase run-off giving rise to decreased salinities at all depths. The mechanisms by which a stronger zonal atmospheric circulation enhances the oxygen concentrations may be related either to a weakened stratification through the reduced salinity (at long time scales), or by stronger or more frequent inflows of North Sea waters (at short time scales). The influence of the atmospheric circulation can explain at these time scales of the order of 60 and 40 % of the variability of these hydrographic variables, respectively. The question of how salinity and oxygen in the Baltic Sea may respond to changes of the atmospheric circulation in a global climate change scenario is also addressed. For this purpose the intensities of the relevant atmospheric circulation patterns in a transient experiment with a coupled atmosphere-ocean general circulation model forced with increasing anthropogenic green house gas concentrations between the years 1860 and 2099 were estimated. In this integration the change of the atmospheric circulation most relevant for salinity and oxygen in the Baltic Sea seems to be an enhancement of the meridional SLP gradient in the North Atlantic. Thus, under the assumption that the statistical relationship between SLP and the hydrographic variables also holds in the future, this trend in the atmospheric circulation would lead to decreased salinity and improved oxygen conditions in the Baltic Sea.
... The freshwater inflow from the Elbe River, and to a minor extent from the Weser River, considerably influences the salinity of the German Bight, as indicated by a near-coastal low-salinity plume (Figure 2). Such a close relationship between river discharge and salinity is also described in earlier studies (Taylor et al., 1983;Radach and Berg, 1986;Heyen and Dippner, 1998). The relatively shallow German Bight (mean depth of 22.5 m) is characterized by strong tidal and wave dynamics, resulting in mixing of salt water and river-supplied fresh water. ...
On the basis of stable oxygen isotopes (8180), the summer sea-surface salinity of the German Bight, southeastern North Sea, was determined for the past 800 years. In this near-coastal area, salinity is mainly dependent on the freshwater input of the Elbe River discharging its large catchment, which covers an area of 149 000 km2 of central Europe. Therefore, a proxy for Elbe River discharge was reconstructed at the same time, and consequently the 8180 record is also mirroring variations in precipitation within the entire drainage basin. Significant variations in these palaeoenvironmental variables are linked to climatic changes.
... Becker & Pauly (1996) and Dippner (1998a) have shown that in nearly all areas of the North Sea the sea-surface temperature (SST) anomalies are correlated with the North Atlantic Oscillation (NAO) index. Heyen & Dippner (1996, 1998 demonstrated that the interannual and interdecadal variability in surface salinity at German light vessels is strongly correlated to the river runoff with a time lag between 2 and 4 mo. In ecological terms, it is important to identify the proportion of variance in bio-log~cal time series which may be attributed to climate variability. ...
Macrofaunal samples were collected seasonally from 1978 to 1995 in the subtidal zone off Norderney, one of the East Frisian barrier islands. Samples were taken with a 0.2 m(2) van Veen grab at 5 sites with water depths of 10 to 20 m. Interannual variability in biomass, abundance and species number of the biota were related to interannual climate variability using multivariate regression models. Changes in the biota were described in relation to human impact and seasonal and long-term meteorological variability. Our analyses suggest that macrofaunal communities are severely affected by cold winters, whereas storms and hot summers have no impact on the communities. It appears that mild meteorological conditions, probably acting in conjunction with eutrophication, have resulted in an increase in total biomass since 1989. A multivariate model found the following strong relationship: abundance. species number and (less clear) biomass in the second quarter are correlated with the North Atlantic Oscillation (NAO). The mediator between the NAO and benthos is probably the sea surface temperature (SST) in late winter and early spring. On the basis of our results, we suggest that most of the interannual variability in macrozoobenthos can be explained by climate variability.
... Boé et al. 2006;Najac et al. 2008). Several attempts applied to relatively small oceanic basins can be found in literature (e.g. the Baltic Sea, Heyen et al. 1996, Heyen andDippner 1998). Here we take up the challenge to set a scheme to reconstruct at best the surface ocean forcing variables for the entire Atlantic Ocean aiming at a better representation and understanding of the ocean variability for both present and future climates. ...
The links between the observed variability of the surface ocean variables estimated from reanalysis and the overlying atmosphere
decomposed in classes of large-scale atmospheric circulation via clustering are investigated over the Atlantic from 1958 to
2002. Daily 500hPa geopotential height and 1,000hPa wind anomaly maps are classified following a weather-typing approach
to describe the North Atlantic and tropical Atlantic atmospheric dynamics, respectively. The algorithm yields patterns that
correspond in the extratropics to the well-known North Atlantic-Europe weather regimes (NAE-WR) accounting for the barotropic
dynamics, and in the tropics to wind classes (T-WC) representing the alteration of the trades. 10-m wind and 2-m temperature
(T2) anomaly composites derived from regime/wind class occurrence are indicative of strong relationships between daily large-scale
atmospheric circulation and ocean surface over the entire Atlantic basin. High temporal correlation values are obtained basin-wide
at low frequency between the observed fields and their reconstruction by multiple linear regressions with the frequencies
of occurrence of both NAE-WR and T-WC used as sole predictors. Additional multiple linear regressions also emphasize the importance
of accounting for the strength of the daily anomalous atmospheric circulation estimated by the combined distances to all regimes
centroids in order to reproduce the daily to interannual variability of the Atlantic ocean. We show that for most of the North
Atlantic basin the occurrence of NAE-WR generally sets the sign of the ocean surface anomaly for a given day, and that the
inter-regime distances are valuable predictors for the magnitude of that anomaly. Finally, we provide evidence that a large
fraction of the low-frequency trends in the Atlantic observed at the surface over the last 50years can be traced back, except
for T2, to changes in occurrence of tropical and extratropical weather classes. All together, our findings are encouraging
for the prospects of basin-scale ocean dynamical downscaling using a weather-typing approach to reconstruct forcing fields
for high resolution ocean models (Part II) from coarse resolution climate models.
KeywordsWeather regimes–Climate variability–Atlantic Ocean–Oceanic forcing variables
... The author supports the hypothesis that the coastal areas are mainly driven by direct atmospheric forcing rather than, for instance, by inflow of Atlantic water (Cushing 1988(Cushing , 1990. More relevant to our study, Heyen and Dippner (1998) proposed that in the German Bight, the interannual and interdecadal variability in surface salinity is correlated to river runoff rather than advection of Atlantic water. For the same area, Kröncke et al. (1998) found that the biomass, abundance and species number of macrozoobenthos is strongly affected by climate variability. ...
We compiled homogeneous long-term time series comprising 39 variables representing the German Bight and for the period 1975–2004. A diverse set of variables was selected to cover multiple trophic levels and different environmental forcing thus to examine long-term changes in this coastal region. Previous studies have hypothesised the presence of regime shifts in observations extending over the entire North Sea. Focusing on a smaller spatial scale, and closer to the coast, we investigated the major modes of variability in the compiled time series using principal component analysis. The results obtained confirm a previously identified regime shift in the North Sea in 1987/1988 and suggest that the German Bight is dominantly characterised by long-term modes of variability. In the German Bight, the shift of 1987/1988 is driven primarily by temperature, Gulf Stream index, frost days and Secchi depth. Changes in some of the ecosystem variables (plankton and fish) appear to be related to changes in these driving variables. In particular, we documented strong positive correlations between the long-term trend showed by the first principal component and herring, Noctiluca scintillans, and, to a lesser extent, Pleurobrachia pileus. Two gadoids, namely cod and saithe, showed negative correlations with the observed long-term mode of variability. Changes in the sum of five small calanoid copepods were, however, less marked. Phosphate and ammonium exhibited a decreasing trend
over the last 30years. Diatoms and Calanus helgolandicus did not show evidence of changes in concert to this trend. Specific analyses of the data divided into three different subsets (biological, climatic and chemical) characterise the climate of the German Bight as highly dynamic also on short timescales (a few years) as compared to much smoother biological and chemical components. The dynamic regime of the German Bight taken together with a low correlation between the major mode of variability and phytoplankton and zooplankton data suggests that the lower trophic levels of this ecosystem are remarkably resilient.
... They concluded that variability was an oscillation caused by anomalies in the atmospheric NAO pattern, through anomalous surface heat fluxes and anomalous Ekman transports. Heyen and Dippner (1998) found that 90% of the observed salinity variability in near coastal areas, such as the German Bight, was linked to variability in air pressure by advective precipitation. It steadily becomes more and more clear that natural anomalies in physical parameters may have far reaching consequences in terms of climate and that these natural consequences are further amplified by the human population and its activities. ...
Between 1970 to 2000, the annual mean suspended matter (SPM) concentrations in the Vlie and Marsdiep tidal inlets of the Wadden Sea varied over five times. The present paper examines the possible relationship between SPM in the Wadden Sea and changing river Rhine discharges and dredging operations. The major short-term variations in annual mean SPM in part of the Wadden Sea appears to be a non-linear, exponential, function of river Rhine discharge and dredge spoil disposal (110 km to over 200 km from the area in front of the Dutch coast near the river Rhine outlet). Correlation coefficients (with SPM as the fixed and dredge disposal as the independent variable) ranged from r=0·8 (deep tidal inlet of Marsdiep) to r=0·2 (shallow inner area of Vlie) and weakened mainly as a function of distance to the disposal site. The best correlation with river discharge was for Marsdiep tidal inlet (r=0·45), indicating the superior effect of dredge disposal over river discharge-related processes. Taking the estimated regression equation as an explorative model, indicates that, without any disposal of dredge spoil, the expected SPM concentration levels in the tidal inlets of the Wadden Sea will be <15 g m−3 (comparable to the 1950s). The overall mean (and the highest mean) annual concentrations for the investigation period reached 42 (90) g m−3 at Marsdiep and 35 (75) g m−3 at Vlie. Assuming a 10% (220 m−3 s−1) increase in river Rhine discharge over the next 50 years, and unchanged dredging policy and other circumstances, SPM concentrations would increase 5–15% for Marsdiep and Vlie. Compared with the calculated (12·4 g m−3 SPM in Marsdiep and 14·8 g m−3 SPM in Vlie) and measured (15 g m−3 SPM in Marsdiep) background SPM concentrations, the expected overall mean increase since 1950 is at least 250% of background. The natural variation in river Rhine discharge will cause further inter-annual variation. Changes in SPM concentrations, due to expected changes in wind climate, combined with river discharge are estimated to increase SPM concentrations 20% above the present situation. The possible implications of changes in land use in combination with further increasing river discharge, changed wind fields and increased temperature are discussed. An important management conclusion is that increasing mean river discharge will significantly increase the need for dredging and spoil disposal, and result in further elevated SPM concentrations in the Dutch coastal zone and the Wadden Sea. The presented relationships offer possibilities for developing new management strategies in relation to dredging and its effects.
In diesem Kapitel werden die aktuellen Erkenntnisse bzgl. der vergangenen, derzeitigen und künftigen klimatischen Bedingungen in der Deutschen Bucht zusammengefasst und die Erkenntnisse des 1. Hamburger Klimaberichtes (kurz 1. HKB, von Storch und Claussen 2011) aktualisiert. Das Klima der Metropolregion Hamburg (MRH) wird maßgeblich von den ozeanographischen und meteorologischen Verhältnissen in und über der Nordsee beeinflusst, insbesondere aber von den Verhältnissen in der Deutschen Bucht. Diese grenzt direkt an die Metropolregion und ist auch die seewärtige Begrenzung der Tideelbe (◉ Abb. 4.1).
Résumé
La littérature scientifique de la dernière décennie contient un grand nombre de travaux qui détaillent le développement des méthodes de « désagrégation » (downscaling) de l’échelle globale à l’échelle hydrologique pour tenter d’estimer les impacts du changement global sur la disponibilité et la distribution des ressources en eau. Cet article présente une revue et une synthèse des méthodologies de « désagrégation climatique » présentées dans la littérature afin de simuler les réponses régionales au changement global du climat. L’accent est mis sur les avancées récentes et sur les problèmes reliés à l’application pratique des modèles dans les études d’impact. L’article présente également une discussion des avantages et limites des différentes approches, ainsi que quelques suggestions pour l’étude future des impacts du changement global sur les ressources en eau.
A multivariate statistical approach is presented that allows a systematic search for potential relationships between the variability in ecological time series and climate records. In this study, interannual variability in large- and mesoscale climate variables in the North Sea region is compared with variability in local zooplankton observations from Helgoland. The species Noctiluca scintillans (Protozoa), Temora longicornis and Acartia sp. (Copepoda), and spionid larvae (Polychaeta) are examined. The multivariate model detected several high correlations between zooplankton abundance and winter climate. Based on these correlations, complementary hypotheses about the causal relationships are discussed using available local data.
ABSTRACT: The pattern of temporal correlations between cod recruitment and sea temperature, in
conjuction with the climate variability of atmospheric pressure anomalies (NAO index) was investigated
by means of a combined use of principal component analysis (PCA) and canonical correlation
analysis (CCA), using time series collected in the area surrounding the Kola peninsula (Barents Sea)
and in the North Sea. The proposed data analysis strategy, namely to carry out a PCA of the temperature,
cod recruitment and NAO time series followed by a CCA between the component spaces of all
the possible data sets couples (recruitment vs temperature, recruitment vs NAO and NAO vs temperature),
allowed us to sketch a general model of correlation between climate and cod recruitment
dynamics. Two independent effects of temperature variability on cod recruitment emerged for the
Kola region, pointing to the existence of at least 2 different mechanisms of comparable importance by
which temperature may affect cod recruitment. In the North Sea the situation is somewhat simpler,
and the data are compatible with only 1 major interaction mechanism. Moreover, the general effect
of temperature on cod recruitment was opposite in the 2 regions: direct correlation for the Barents
Sea, inverse correlation for the North Sea. This is probably due to the existence of an optimal temperature
regime for cod recruitment lying in between the ‘cold’ Barents Sea and the ‘warm’ North
Sea.
A numerical, density dependent groundwater model is set up for the North Sea Island of Borkum to estimate climate change impacts on coastal aquifers and especially the situation of barrier islands in the Wadden Sea. The database includes information from boreholes, a seismic survey, a helicopter-borne electromagnetic (HEM) survey, monitoring of the freshwater-saltwater boundary by vertical electrode chains in two boreholes, measurements of groundwater table, pumping and slug tests, as well as water samples. Based on a statistical analysis of borehole columns, seismic sections and HEM, a hydrogeological model is set up. The groundwater model is developed using the finite-element programme FEFLOW. The density dependent groundwater model is calibrated on the basis of hydraulic, hydrological and geophysical data, in particular spatial HEM and local monitoring data. Verification runs with the calibrated model show good agreement between measured and computed hydraulic heads. A good agreement is also obtained between measured and computed density or total dissolved solids data for both the entire freshwater lens on a large scale and in the area of the well fields on a small scale.
For simulating future changes in this coastal groundwater system until the end of the current century, we use the climate scenario A2, specified by the Intergovernmental Panel on Climate Change and, in particular, the data for the German North Sea coast. Simulation runs show proceeding salinisation with time beneath the well fields of the two waterworks Waterdelle and Ostland.
The modelling study shows that the spreading of well fields is an appropriate protection measure against excessive salinisation of the water supply until the end of the current century.
The variability of April salinity at Helgoland Roads station (54.12°N, 7.9°E, Germany) is analysed in relationship with Elbe river discharge and the observed variability in large-scale atmospheric circulation for the period 1962–2000. It is shown that the main driver of salinity anomalies is the river discharge anomalies from the previous month. These discharge anomalies are strongly related with precipitation anomalies from the Elbe catchment area. Changes in the salinity, discharge and precipitation anomalies are accompanied by a wave train atmospheric circulation pattern that connects the tropical Atlantic Ocean with northern part of Europe, as well as with changes in large-scale water vapour transport over the whole German Bight. Positive sea-surface temperature anomalies, centred in the Caribbean region and the North Sea, are associated with positive salinity anomalies and negative anomalies of discharge and precipitation.
Long-term data of year class strengths of different commercially harvested fish stocks based on a virtual population analysis (VPA) are available from ICES. The anomalies of these long-term data sets of year class strength are analyzed using Empirical Orthogonal Functions (EOFs) and are related to climate variability: the anomalies of the sea surface temperature (SST) in the northern North Sea and the North Atlantic Oscillation (NAO) index. A Canonical Correlation Analysis (CCA) between the leading eigenmodes is performed. The results suggest that the variability in the fish recruitment of western mackerel and three gadoids, namely North Sea cod, North Sea saithe, and North Sea whiting is highly correlated to the variability of the North Sea SST which is directly influenced by the NAO. For North Sea haddock and herring no meaningful correlation exists to North Sea SST and NAO.
The results allow the conclusion that is seems possible to predict long-term changes in the fish recruitment from climate change scenarios for North Sea cod, North Sea saithe and western mackerel. Furthermore, the results indicate the possibility of recruitment failure for North Sea cod, North Sea whiting, and western mackerel in the case of global warming.
Since 2001/2002, the correlation between North Atlantic Oscillation index and biological variables in the North Sea and Baltic Sea fails, which might be addressed to a global climate regime shift. To understand inter-annual and inter-decadal variability in environmental variables, a new multivariate index for the Baltic Sea is developed and presented here. The multivariate Baltic Sea Environmental (BSE) index is defined as the 1st principal component score of four z-transformed time series: the Arctic Oscillation index, the salinity between 120 and 200 m in the Gotland Sea, the integrated river runoff of all rivers draining into the Baltic Sea, and the relative vorticity of geostrophic wind over the Baltic Sea area. A statistical downscaling technique has been applied to project different climate indices to the sea surface temperature in the Gotland, to the Landsort gauge, and the sea ice extent. The new BSE index shows a better performance than all other climate indices and is equivalent to the Chen index for physical properties. An application of the new index to zooplankton time series from the central Baltic Sea (Latvian EEZ) shows an excellent skill in potential predictability of environmental time series.
Interannual variability of temperature in the Kola section (Barents Sea) and the abundance as 0-group (age 5 mo) and recruits (age 3 yr), spawning stock biomass, and survival of Arcto-Norwegian cod in the Barents Sea were related to climate variability using a multivariate regression model. The results show that in the Barents Sea the temperature anomalies are significantly and highly correlated to climate variables such as large-scale sea-level pressure fields and the North Atlantic Oscillation index. A significant and high correlation was detected between the temperature in the Barents Sea and both the 0-group index and recruitment of Arcto-Norwegian cod. A phase lag of 2 yr appears in recruitment. The high model skill and excellent correlation indicate that it is possible to predict the future development of Arcto-Norwegian cod stocks from climate-change scenarios.
Sclerochronological records of interannual shell growth variability were established for eight modern shells (26 to 163 years of age) of the bivalve Arctica islandica, which were sampled at one site in the inner German Bight. The records indicate generally low synchrony between individuals. Spectral analysis of the whole 163-yr masterchronology indicated a cyclic pattern with a period of 5 and 7 years. The masterchronology correlated poorly to time series of environmental parameters over the last 90 years. High environmental variability in time and space of the dynamic and complex German Bight hydrographic system results in an extraordinarily high noise' level in the shell growth pattern of Arctica islandica.
Many analyses of climate data sets suffer from high dimensions of the variables representing the state of the system at any given time. Often it is advisable to split the full phase space into two subspaces. The “signal” space is spanned by few characteristic patterns and is supposed to represent the dynamics of the considered process. The “noise subspace”, on the other hand, is high-dimensional and contains all processes which are purportedly irrelevant in their details for the “signal subspace”.
The term “downscaling” describes a procedure in which information about a process with a certain characteristic scale is derived from other processes with larger scales. The present paper identifies a relationship between the main components of the North Atlantic air-pressure anomalies at sea-level (characteristic length-scale > 1000 km) and the sea level anomalies at several Baltic Sea gauges (10 km−100 km) in winter. Monthly means from 20 observed winters are used to fit a statistical model that describes the dependence between both parameters. Further observations from this century are used to validate this model, which is able to estimate sea level anomalies from the air-pressure field to a good level of approximation. Sea level anomalies with periods from months to decades are reproduced well. As main forcing for the sea level anomalies, wind-stress with a strong zonal component is identified. For the past 89 years, we found that a slight decrease of mean sea level was induced by air-pressure. A slight increase is found when air-pressure from a GCM “greenhouse” experiment is downscaled. DOI: 10.1034/j.1600-0870.1996.t01-1-00008.x
This paper gives the physical oceanography background for the Bremerhaven Workshop on Biological Effects of Contaminants in the North Sea. Two main conclusions must be drawn: (1) The German Bight is an area characterized by strong mesoscale variability in physical properties such as fronts, meanders and eddies. This variability is also seen in the mobile superficial sediment and the resulting variability of the suspended matter content. (2) During the workshop the hydrographic situation in the German Bight was marked by highly saline inflows to the German Bight from the English Channel. The stations close to the East-Friesian coast are located within the contaminated Continental Coastal Water; the more offshore stations met more or less undiluted water originating from the English Channel, with a high portion of Atlantic Water. -from Authors
Macrofaunal samples were collected seasonally from 1978 to 1995 in the subtidal zone off Norderney, one of the East Frisian barrier islands. Samples were taken with a 0.2 m(2) van Veen grab at 5 sites with water depths of 10 to 20 m. Interannual variability in biomass, abundance and species number of the biota were related to interannual climate variability using multivariate regression models. Changes in the biota were described in relation to human impact and seasonal and long-term meteorological variability. Our analyses suggest that macrofaunal communities are severely affected by cold winters, whereas storms and hot summers have no impact on the communities. It appears that mild meteorological conditions, probably acting in conjunction with eutrophication, have resulted in an increase in total biomass since 1989. A multivariate model found the following strong relationship: abundance. species number and (less clear) biomass in the second quarter are correlated with the North Atlantic Oscillation (NAO). The mediator between the NAO and benthos is probably the sea surface temperature (SST) in late winter and early spring. On the basis of our results, we suggest that most of the interannual variability in macrozoobenthos can be explained by climate variability.
A statistical strategy to deduct regional-scale features from climate general circulation model (GCM) simulations has been designed and tested. The main idea is to interrelate the characteristic patterns of observed simultaneous variations of regional climate parameters and of large-scale atmospheric flow using the canonical correlation technique. The large-scale North Atlantic sea level pressure (SLP) is related to the regional, variable, winter (DJF) mean Iberian Peninsula rainfall. The skill of the resulting statistical model is shown by reproducing, to a good approximation, the winter mean Iberian rainfall from 1900 to present from the observed North Atlantic mean SLP distributions. It is shown that this observed relationship between these two variables is not well reproduced in the output of a general circulation model (GCM). The implications for Iberian rainfall changes as the response to increasing atmospheric greenhouse-gas concentrations simulated by two GCM experiments are examined with the proposed statistical model. In an instantaneous [open quotes]2 CO[sub 2][close quotes] doubling experiment, using the simulated change of the mean North Atlantic SLP field to predict Iberian rainfall yields, there is an insignificant increase of area-averaged rainfall of I mm/month, with maximum values of 4 mm/month in the northwest of the peninsula. In contrast, for the four GCM grid points representing the lberian Peninsula, the change is - 10 mm/month, with a minimum of - 19 mm/month in the southwest. In the second experiment, with the IPCC scenario A ([open quotes]business as usual[close quotes]) increase of CO[sub 2], the statistical-model results partially differ from the directly simulated rainfall changes: in the experimental range of 100 years, the area-averaged rainfall decreases by 7 mm/month (statistical model), and by 9 mm/month (GCM); at the same time the amplitude of the interdecadal variability is quite different. 17 refs., 10 figs.
Due to restrictions in the available computing resources and a lack of suitable observational data, transient climate change experiments with global coupled ocean-atmosphere models have been started from an initial state at equilibrium with the present day forcing. The historical development of greenhouse gas forcing from the onset of industrialization until the present has therefore been neglected. Studies with simplified models have shown that this cold start error leads to a serious underestimation of the anthropogenic global warming. In the present study, a 150-year integration has been carried out with a global coupled ocean-atmosphere model starting from the greenhouse gas concentration observed in 1935, i.e., at an early time of industrialization. The model was forced with observed greenhouse gas concentrations up to 1985, and with the equivalent C02 concentrations stipulated in Scenario A (Business as Usual) of the Intergovernmental Panel on Climate Change from 1985 to 2085. The early starting date alleviates some of the cold start problems. The global mean near surface temperature change in 2085 is about 0.3 K (ca. 10%) higher in the early industrialization experiment than in an integration with the same model and identical Scenario A greenhouse gas forcing, but with a start date in 1985. Comparisons between the experiments with early and late start dates show considerable differences in the amplitude of the regional climate change patterns, particularly for sea level. The early industrialization experiment can be used to obtain a first estimate of the detection time for a greenhouse-gas-induced near-surface temperature signal. Detection time estimates are obtained using globally and zonally averaged data from the experiment and a long control run, as well as principal component time series describing the evolution of the dominant signal and noise modes. The latter approach yields the earliest detection time (in the decade 1990–2000) for the time-evolving near-surface temperature signal. For global-mean temperatures or for temperatures averaged between 45N and 45S, the signal detection times are in the decades 2015–2025 and 2005–2015, respectively. The reduction of the cold start error in the early industrialization experiment makes it possible to separate the near-surface temperature signal from the noise about one decade earlier than in the experiment starting in 1985. We stress that these detection times are only valid in the context of the coupled model's internally-generated natural variability, which possibly underestimates low frequency fluctuations and does not incorporate the variance associated with changes in external forcing factors, such as anthropogenic sulfate aerosols, solar variability or volcanic dust.
Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major
source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in
one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold
conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes
since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and
parts of Scandinavia have generally experienced wetter than normal conditions.
Macrofaunal samples were collected regularly during springtime from 1978 to 1994 in the subtidal zone off Norderney, one of the East Frisian barrier islands. Sampling was carried out from a research vessel by means of a 0.2 m2 van-Veen grab at five sites with water depths of 10-20 m. Abundances, biomasses and species composition were analysed by cluster analysis and multidimensional scaling. The resulting patterns are discussed in terms of anthropogenic impact and varying meteorological conditions. Species survival is severely impaired by cold winters, whereas storms and hot summers have a minor impact. There is evidence that mild meteorological conditions and eutrophication have resulted in an increase in total biomass since 1989. In addition to environmental factors, the community is influenced by interspecific relationships, including competition.
Climate Change 1995--The Science of Climate Change is the most
comprehensive assessment available of current scientific understanding
of human influences on past, present and future climate. Prepared under
the auspices of the Intergovernmental Panel on Climate Change (IPCC),
each chapter is written by teams of lead authors and contributors
recognized internationally as leading experts in their field. Climate
Change 1995 is the first full sequel to the original 1990 IPCC
scientific assessment, bringing us completely up to date on the full
range of scientific aspects of climate change. This assessment forms the
standard scientific reference for all those concerned with climate
change and its consequences, including policy makers in governments and
industry worldwide, and researchers and senior-level students in
environmental science, meteorology, climatology, biology, ecology and
atmospheric chemistry.
The microreticulate resting cyst of the potentially toxic, chain-forming, unarmoured neritic dinoflagellate Gymnodinium catenatum Graham 1943, the planktonic stage of which is not known from North European waters, is reported for the first time from recent German coastal sediments of the North Sea and Baltic Sea. In sandy mud sediments of the German Bight, a maximum of 8.5 living cysts cm(-3) were found. In Kiel Bight sediments G.catenatum was found in maximum concentrations of 17.0 living cysts cm(-3). In surface waters of the German Bight resuspended G.catenatum cysts were observed at concentrations of up to 3.6 cysts l(-1). Successful germination experiments conducted with natural seawater show that the occurrence of a vegetative form of G.catenatum in northern Europe is very likely. The present study highlights that cyst surveys provide an important tool for the evaluation of areas with potential toxicity problems, as they may indicate the presence of hitherto overlooked species in the water column.
The data set extends from 1899-1977 but has originated from 8 different sources and discontinuities have been identified with every change in source. We have been documented corrections for many of these and have also catalogued 3263 serious errors. These have been corrected or set to missing. Most of these errors are over Asia and are predominant before 1922 or during World War II. -from Authors
Appropriate scenarios of future climate must be developed prior to any assessment of the impacts of climate change. The information needed by impact assessors was examined in consultation with those having experience in scenario use. Most assessors require regional scenarios with a temporal resolution of one day and a spatial resolution of around 100 km. Scenarios should contain one or more of: (1) general descriptive statistics of the major climate elements, (2) information about climatic anomalies such as drought, (3) statistics on the frequency and probability of events exceeding particular thresholds, and (4) general synoptic information. Techniques of climate analysis currently available were reviewed for their suitability to meet these scenario needs. The techniques were divided into a series of modules, groups of similar analysis techniques providing a scientifically sound piece of required information. A series of linked modules then provides the complete scenario. One set of modules emphasizes process models, another set uses empirical analyses. The final set involves linkage between the other two. For each module the needs and opportunities for research directed towards scenario development are discussed.
A 10-year record of the 500 mb geopotential height for the Northern
Hemisphere has been expanded into spherical harmonics and filtered in
the time domain. Maps of the root-mean-square (rms) height have been
constructed corresponding to different spatial scales and frequency
bands. The spatial scales and frequency bands were chosen to emphasize
blocking and cyclogenesis and to help isolate spurious, high-frequency
parts of the field from the physically meaningful parts. We find that
low-frequency fields are dominated by planetary-scale waves at high
latitudes and by synoptic-scale waves at mid-latitudes. The
medium-frequency fields get substantial contributions from the waves of
synoptic scale and shorter.Power spectra of the spherical harmonic
expansion coefficients are presented, as well as quadrature spectra for
each pair of cosine and sine expansion coefficients. We find large-scale
waves have a large amount of low-frequency power and a spectrum rapidly
decreasing with frequency. Shorter waves have less low-frequency power
but have more slowly decreasing power with frequency. We also find
westward propagation dominating the longer waves while the shorter waves
propagate eastward.All calculations are performed for both the winter
and summer seasons.
Blocking activity was especially frequent and persistent over Northern Europe during all seasons from late 1958 through 1959 and 1960. Some effects of the blocking on seasonal precipitation are discussed. The initiation and persistent recurrence of the blocking is studied with the help of various mean seasonal charts, particularly those for mid-tropospheric levels.It is suggested that the physical causes of the blocks lie in complex feed-back phenomena between the atmosphere, the North Atlantic sea surface and the Scandinavian Peninsula (particularly its lack of cold-season snow). The latter two factors appear to serve as conservative links in a feed-back chain, thus providing restorative forcing elements on the general circulation over the area.Some precursory signs of such long period blocking are suggested by an analysis of the wintertime meridional flow prevailing between southern Greenland and southern Scandinavia.
In a high resolving (mean grid size 11 km) barotropic numerical model of the North Sea tides the M2-tide is computed. Nonlinearities of the Navier-Stokesequation yield, in connection with an annual mean wind stress, a residual circulation fitting well to observational data. Some effects of this circulation are discussed in connection with pollution problems.In einem hochauflsenden (mittlerer Gitterabstand 11 km) barotropen Modell fr die Gezeiten der Nordsee wird die M2-Gezeit berechnet. Verschiedene Nichtlinearitten der Bewegungsgleichungen fhren in Verbindung mit einem mittleren Windschub zu einer Restzirkulation, die mit Beobachtungen in Einklang steht. Einige Effekte dieser Zirkulation in Zusammenhang mit Verschmutzungsproblemen werden diskutiert.L'onde mare M2 est calcule dans un modle numrique barotropique de la mer du Nord de haute rsolution (l'espacement moyen entre les lignes de quadrillage tant de 11 km). Des non-linarits de l'quation Navier-Stokes produisent, en connection avec une force moyenne annuelle du vent, une circulation rsiduelle s'accordant bien avec les donnes observes. Certains effects de cette circulation sont discuts, en relation avec les problmes de pollution.
For the practical use of hydrodynamic numeric methods in surge forecasting the meteorological input data are assumed to be available as grid point values originating from numerical models of the atmosphere.
In the present investigation an attempt has been made to introduce into a HN model of the Hansen-type covering the North Sea, the Skagerrak and the Kattegat, the fields of pressure gradient and real wind near sea surface, which are derived from grid point distributions of surface pressure and temperature of air and sea.
It appears that a linear relation between geostrophic and real wind velocity near surface, as is suggested by other authors, is not sufficient for the highest wind velocities, but it might suitably be replaced by a square root function.
The model was tested by three major storm surge situations in the North Sea and the verification of the results is illustrated in diagrams comparing the time variation of the computed residual with hourly records from selected tide gauges.
Furthermore, a quality test has been carried out by means of a statistical analysis of computed residuals and hourly values of recorded residual from 16 tide gauges.
Regarding the representation of the meteorological data in the model the following demands should be met:1.
The grid point distance of the meteorological field must not exceed 150 km.
2.
The input data from meteorological models have to be given at least for every three hours.
An analysis of the 65-year record of surface salinity, for the European shelf seas has shown that during this century, these seas have experienced a striking and fairly regular alternation between periods of low and of high salinity. Typically, when the seasonal variation in salinity is removed, each high salinity period is shown to be the end-point of a more or less continuous rise in the anomalies of salinity over a period of 3–4 years. The chronology of these interannual changes is described, showing that the timing of high and low-salinity periods is essentially similar in all areas of the shelf seas.
Conditions of high salinity in the shelf seas are shown to be associated with the periodic re-establishment over the North Atlantic sector of an anomalous and persistent atmospheric circulation pattern. The persistence of this type of circulation has been suggested by Namias to be due to ocean/atmosphere feedback effects. Advective changes induced in the eastern Atlantic by this circulation pattern, resulting in an increased flux of salt to the shelf seas, are held to be primarily responsible for each sustained salinification of these seas; in addition, changes in precipitation and evaporation associated with the anomalous pressure-field are capable of making a further direct contribution to the rising anomalies of salinity.
Contemporary counterparts to these salinity fluctuations are also found in the deep current to the Transition Area and Baltic, and there is some evidence of similar fluctuations in the Norwegian Atlantic current and in the North Cape-Murman current.
Mesoscale variability of the German Bight - an atlas of circulation, density distribution and sea surface height
- J W Dippner
Detection of anthropogenic climate change using a fingerprint method
- K Hasselmann
- L Bengtsson
- U Cubasch
- G C Hegerl
- H Rodhe
- E Roeckner
- H Von Storch
- R Voss
- J Waszkewitz
Climate change 1995. The science of climate change. Contribution of working group Ito the 2nd assessment report of the IPCC
- J T Houghton
- L G Meira Filho
- B A Callander
- N Harris
Influence of climate on recruitment and migration of fish stocks in the North Sea
- E Svendsen
- A Aglen
- S A Iversen
- D W Skagen
- O Smedstadt