In situ measurements and a numerical model for the description of bottom-arrested currents are us... more In situ measurements and a numerical model for the description of bottom-arrested currents are used to elucidate aspects of the evolution of the Transient of the Eastern Mediterranean Basin.
The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has... more The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has been attributed to a westward contraction of the sub-polar gyre and stronger inflow of waters from the sub-tropical gyre. Temporal changes in the shape and strength of the two gyres have been related to the major mode of atmospheric variability in the Atlantic sector, the NAO. Hydrographic conditions along the Northwest European shelf are thus the result of different processes such as variations in transports, varying relative contributions of water masses from the two gyres and property trends in the source water masses.
An ensemble of regional climate change scenarios for the North Sea is validated and analyzed. Fiv... more An ensemble of regional climate change scenarios for the North Sea is validated and analyzed. Five Coupled Model Intercomparison Project Phase 5 (CMIP5) General Circulation Models (GCMs) using three different Representative Concentration Pathways (RCPs) have been downscaled with the coupled atmosphere–ice–ocean model RCA4-NEMO. Validation of sea surface temperature (SST) against different datasets suggests that the model results are well within the spread of observational datasets. The ensemble mean SST with a bias of less than 1 ∘ C is the solution that fits the observations best and underlines the importance of ensemble modeling. The exchange of momentum, heat, and freshwater between atmosphere and ocean in the regional, coupled model compares well with available datasets. The climatological seasonal cycles of these fluxes are within the 95% confidence limits of the datasets. Towards the end of the 21st century the projected North Sea SST increases by 1.5 ∘ C (RCP 2.6), 2 ∘ C (RCP...
In the framework of the German contribution to the Ship-of-Opportunity program (SOOP) temperature... more In the framework of the German contribution to the Ship-of-Opportunity program (SOOP) temperature measurements in the North Atlantic have been carried out since 1988. The timeseries of XBT measurements along the AX-03 line (English channel to Grand Banks, continuing to Halifax or New York) is without major interruptions and will be used to investigate interannual to decadal temperature changes in the highly variable transition region between the subtropical and subpolar gyre. Along the western part of the section changes of the separation latitude of the North Atlantic Current (NAC) are observed, showing a tendency for warmer waters to penetrate farther north between 1999-2006 compared to the period 1988-1998. However, interannual variability is on the same order of magnitude and masks the signal in some years. Based on XBT data only it is impossible to distinguish if the 1999-2006 warming is a trend or decadal variability. The variability in the eastern basin reveals a qualitative ...
Deep Sea Research Part I: Oceanographic Research Papers, 1995
ABSTRACT Adults of the lanternfish Ceratoscopelus maderensis have a broad depth distribution and ... more ABSTRACT Adults of the lanternfish Ceratoscopelus maderensis have a broad depth distribution and a primarily zonal distribution in the temperate-subtropical Atlantic, but are also high ranking in the Mauritanian upwelling area. The previous concept of a temperature-dependent distribution is questioned on the basis of hydrographic and fish larvae data from a new survey in combination with older data. The almost congruent horizontal distributions of adults and larvae coincide better with salinity characteristics in the lower-most daytime range of the adults, than with temperature. Adult C. maderensis live during daytime in deep water with Mediterranean influence. The southermost limit coincides also with oxygen deficiencies at the respective depth.
ABSTRACT Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variab... more ABSTRACT Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variability in the southeastern North Sea. In this study an atmospheric proxy for the observed sea level variability in the German Bight is introduced. Monthly mean sea level (MSL) time series from 13 tide gauges located in the German Bight and one virtual station record are evaluated in comparison to sea level pressure fields over the North Atlantic and Europe. A quasi-linear relationship between MSL in the German Bight and sea level pressure over Scandinavia and the Iberian Peninsula is found. This relationship is used (1) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871-2008 with data from the twentieth century reanalysis v2 (20CRv2), (2) to isolate the high frequency meteorological variability of MSL from longer-term changes, (3) to derive ensemble projections of the atmospheric contribution to MSL until 2100 with eight different coupled global atmosphere-ocean models (AOGCM's) under the A1B emission scenario and (4) two additional projections for one AOGCM (ECHAM5/MPI-OM) under the B1 and A2 emission scenarios. The hindcast produces a reasonable good reconstruction explaining approximately 80 % of the observed MSL variability over the period from 1871 to 2008. Observational features such as the divergent seasonal trend development in the second half of the twentieth century, i.e. larger trends from January to March compared to the rest of the year, and regional variations along the German North Sea coastline in trends and variability are well described. For the period from 1961 to 1990 the Kolmogorov-Smirnow test is used to evaluate the ability of the eight AOGCMs to reproduce the observed statistical properties of MSL variations. All models are able to reproduce the statistical distribution of atmospheric MSL. For the target year 2100 the models point to a slight increase in the atmospheric component of MSL with generally larger changes during winter months (October-March). Largest MSL changes in the order of ~5-6 cm are found for the high emission scenario A2, whereas the moderate B1 and intermediate A1B scenarios lead to moderate changes in the order of ~3 cm. All models point to an increasing atmospheric contribution to MSL in the German Bight, but the uncertainties are considerable, i.e. model and scenario uncertainties are in the same order of magnitude.
In situ measurements and a numerical model for the description of bottom-arrested currents are us... more In situ measurements and a numerical model for the description of bottom-arrested currents are used to elucidate aspects of the evolution of the Transient of the Eastern Mediterranean Basin.
The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has... more The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has been attributed to a westward contraction of the sub-polar gyre and stronger inflow of waters from the sub-tropical gyre. Temporal changes in the shape and strength of the two gyres have been related to the major mode of atmospheric variability in the Atlantic sector, the NAO. Hydrographic conditions along the Northwest European shelf are thus the result of different processes such as variations in transports, varying relative contributions of water masses from the two gyres and property trends in the source water masses.
An ensemble of regional climate change scenarios for the North Sea is validated and analyzed. Fiv... more An ensemble of regional climate change scenarios for the North Sea is validated and analyzed. Five Coupled Model Intercomparison Project Phase 5 (CMIP5) General Circulation Models (GCMs) using three different Representative Concentration Pathways (RCPs) have been downscaled with the coupled atmosphere–ice–ocean model RCA4-NEMO. Validation of sea surface temperature (SST) against different datasets suggests that the model results are well within the spread of observational datasets. The ensemble mean SST with a bias of less than 1 ∘ C is the solution that fits the observations best and underlines the importance of ensemble modeling. The exchange of momentum, heat, and freshwater between atmosphere and ocean in the regional, coupled model compares well with available datasets. The climatological seasonal cycles of these fluxes are within the 95% confidence limits of the datasets. Towards the end of the 21st century the projected North Sea SST increases by 1.5 ∘ C (RCP 2.6), 2 ∘ C (RCP...
In the framework of the German contribution to the Ship-of-Opportunity program (SOOP) temperature... more In the framework of the German contribution to the Ship-of-Opportunity program (SOOP) temperature measurements in the North Atlantic have been carried out since 1988. The timeseries of XBT measurements along the AX-03 line (English channel to Grand Banks, continuing to Halifax or New York) is without major interruptions and will be used to investigate interannual to decadal temperature changes in the highly variable transition region between the subtropical and subpolar gyre. Along the western part of the section changes of the separation latitude of the North Atlantic Current (NAC) are observed, showing a tendency for warmer waters to penetrate farther north between 1999-2006 compared to the period 1988-1998. However, interannual variability is on the same order of magnitude and masks the signal in some years. Based on XBT data only it is impossible to distinguish if the 1999-2006 warming is a trend or decadal variability. The variability in the eastern basin reveals a qualitative ...
Deep Sea Research Part I: Oceanographic Research Papers, 1995
ABSTRACT Adults of the lanternfish Ceratoscopelus maderensis have a broad depth distribution and ... more ABSTRACT Adults of the lanternfish Ceratoscopelus maderensis have a broad depth distribution and a primarily zonal distribution in the temperate-subtropical Atlantic, but are also high ranking in the Mauritanian upwelling area. The previous concept of a temperature-dependent distribution is questioned on the basis of hydrographic and fish larvae data from a new survey in combination with older data. The almost congruent horizontal distributions of adults and larvae coincide better with salinity characteristics in the lower-most daytime range of the adults, than with temperature. Adult C. maderensis live during daytime in deep water with Mediterranean influence. The southermost limit coincides also with oxygen deficiencies at the respective depth.
ABSTRACT Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variab... more ABSTRACT Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variability in the southeastern North Sea. In this study an atmospheric proxy for the observed sea level variability in the German Bight is introduced. Monthly mean sea level (MSL) time series from 13 tide gauges located in the German Bight and one virtual station record are evaluated in comparison to sea level pressure fields over the North Atlantic and Europe. A quasi-linear relationship between MSL in the German Bight and sea level pressure over Scandinavia and the Iberian Peninsula is found. This relationship is used (1) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871-2008 with data from the twentieth century reanalysis v2 (20CRv2), (2) to isolate the high frequency meteorological variability of MSL from longer-term changes, (3) to derive ensemble projections of the atmospheric contribution to MSL until 2100 with eight different coupled global atmosphere-ocean models (AOGCM's) under the A1B emission scenario and (4) two additional projections for one AOGCM (ECHAM5/MPI-OM) under the B1 and A2 emission scenarios. The hindcast produces a reasonable good reconstruction explaining approximately 80 % of the observed MSL variability over the period from 1871 to 2008. Observational features such as the divergent seasonal trend development in the second half of the twentieth century, i.e. larger trends from January to March compared to the rest of the year, and regional variations along the German North Sea coastline in trends and variability are well described. For the period from 1961 to 1990 the Kolmogorov-Smirnow test is used to evaluate the ability of the eight AOGCMs to reproduce the observed statistical properties of MSL variations. All models are able to reproduce the statistical distribution of atmospheric MSL. For the target year 2100 the models point to a slight increase in the atmospheric component of MSL with generally larger changes during winter months (October-March). Largest MSL changes in the order of ~5-6 cm are found for the high emission scenario A2, whereas the moderate B1 and intermediate A1B scenarios lead to moderate changes in the order of ~3 cm. All models point to an increasing atmospheric contribution to MSL in the German Bight, but the uncertainties are considerable, i.e. model and scenario uncertainties are in the same order of magnitude.
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Papers by Birgit Klein