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).

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 index of the North Atlantic Oscillation, the dominant mode of climatic variability in the North Atlantic region, changed in the late 1980s (1987-1989) from a negative to a positive phase. This led to regime shifts in the ecology of the North Sea (NS) and the central Baltic Sea (CBS), which involved all trophic levels in the pelagial of these two neighbouring continental shelf seas. Increasing air and sea surface temperatures, which affected critical physical and biological processes, were the main direct and indirect driving forces. After 1987, phytoplankton biomass in both systems increased and the growing season was extended. The composition of phyto- and zooplankton communities in both seas changed conspicuously, e.g. dinoflagellate abundance increased and diatom abundance decreased in the CBS. Key copepod species that are essential in fish diets experienced pronounced changes in biomass. Abundance of Calanus finmarchicus (NS) and Pseudocalanus sp. (CBS) fell to low levels, whereas C. helgolondicus (NS) and Temora longicornis and Acartia spp. (CBS) were persistently abundant. These changes ill biomass of different copepod species had dramatic consequences on biomass, fisheries, and landings of key fish species: North Sea cod declined, cod in the CBS remained at low levels, and CBS sprat reached unprecedented high biomass levels resulting in high yields. The synchronous regime shifts in MS and CBS resulted in profound changes in both marine ecosystems. However, the reaction of fish populations to the bottom-up mechanisms caused by the same climatic shift was very different for the three fish stocks. (c) 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.

Rainfall erosivity is a crucial parameter for soil erosion assessment. It can trigger topsoil removal, leading to loss of agricultural potential and land degradation. This paper describes a new approach to derive the value for rainfall erosivity from weather radar data by using distributed cellular agents. Rainfall energy is used in standard erosion formulas such as the Universal Soil Loss Equation (USLE) and its regional variants as a means to measure rainfall erosivity. To calculate erosivity values, rainfall data need to be recorded. In cases where the entire area of interest cannot be covered, interpolation from the available data becomes necessary. When convective rainfall events are to be analysed, both a high spatial and a high temporal resolution is advisable.

The paper presents the results of a joint project combining numerical model studies and field work in order to investigate the dispersion of anthropogenic radioactivity in the Arctic Ocean. The results obtained underline the essential difference between the dispersion of dissolved contaminants in water and the transport of particulate material in sea ice. Coupled ice-ocean models on different spatial scales are applied to study the transit times and major pathways for radioactive contaminant transport in the water column. One of the main sources for radioactive pollution in the Arctic, the discharge of the Sellafield reprocessing plant, was simulated from 1965 until now. The results are compared with measurements and hypothetical release scenarios computed for the the dump sites of radioactive waste in the Kara Sea. Our comparison reveals that the Sellafield signal is by one or two orders of magnitude higher than any potential contamination from Kara Sea dump sites, even if a ’worst case’ scenario is assumed. In order to assess the role of sea ice in contaminant transport, sedimentological data from the Kara Sea and the Arctic Ocean were analysed. The results show that fine-grained Kara Sea sediments from dump site areas are predestined for entrainment into newly forming ice. Observed buoy drifts and simulated trajectories confirm that the Arctic Transpolar Ice Drift is a rather short pathway for pollutant dispersion from the Arctic Ocean to the adjacent Nordic Seas. However, compared to the large volume and contaminant flux in the ocean, the contaminant dispersion by sea ice plays a minor role.

This evaluation of the sea surface temperatures (SSTs) of the North Sea from December 1996 through November 1997 is based on SST grids derived from weekly composite SST analyses published by the Bundesamt für Seeschiffahrt und Hydrographie (BSH) since 1968. The 1971—1993 SST climatology computed from these SST grids is used to identify anomalies in the seasonal cycle and areal distribution of the SST in 1997.

The main objective of this research paper is to estimate the new-ice production in the Laptev Sea flaw lead during the 1991/1992 winter season. A one-dimensional energy balance model was applied to calculate ocean-to-atmosphere heat flux and the resulting new-ice formation over open water. For a detailed estimate of regional ice production, the flaw lead was divided into 14 sections based on the analysis of NOAA-satellite images and Russian ice charts. Opening and maintenance of the lead sections are controlled by offshore winds, whereas closing of open water is caused by onshore winds. Since the orientation of the lead varies from section to section, the same regional wind forcing can cause different local lead behavior. Model results reveal that the seasonally accumulated thickness of new ice formed in the different lead sections—under the assumption of instantaneous lateral new-ice removal from the water surface—varies from 1.3 m to 13 m over temporarily open water and may reach 20 m over permanently open water. The corresponding ice volume produced in the sections varies between 3.4 km3 and 59 km3 and amounts to 258 km3 for the entire lead. The significant regional variations in new-ice production are due to differences in (i) the number of days that a lead section is open (open-lead days), (ii) the oceanic heat loss during open-lead days, and (iii) the areal extent of the lead sections. As compared to other studies,—at least during 1991/1992 winter season—the Laptev Sea flaw lead produced between 28 and 617% more initial sea ice than the Kara, Barents, East Siberian and Chukchi leads. Despite its limited areal extent of roughly 36,000 km2, which represents only 8% of the entire Laptev Sea, the flaw lead produces about 32% of the annual shelf ice. The ice production in the flaw lead is 5.3 times higher than the remainder of the shelf (7.4 m vs. 1.4 m). Furthermore, the Laptev Sea flaw lead produces 2.6% of the ice annually formed the entire Arctic Mediterranean Sea and contributes about 9% to the volume of the Siberian branch of the Transpolar Drift Ice System. This makes the Laptev Sea flaw lead a significant producer of Arctic sea ice on local and regional scales, whereas the contribution of lead ice to the entire volume of annually formed pack in high northern latitudes amounts only to roughly 1.3%.

In this sequel paper, the investigation of the ice winter severity in the Western Baltic is continued in the frequency domain. Spectral analysis of the time series of the mass-related ice index (V-A Sigma) reveals prominent quasicycles with periods of 2.3, 5.8 and 7.8 years. The same cycles stand out in the variance spectrum of the winter North Atlantic Oscillation (NAG) index. Variations in the quasibiennial Q(2)(3) and intermediate I-5(10) periodicity ranges (indices give the range limits in years) account for 68.2% of the linear correlation (-0.46) between both time series. A maximum entropy subinterval analysis shows that the spectral variance composition of the V-A Sigma series undergoes significant temporal changes. The relative contribution of the Q(2)(3) range is down from 52.7% during 1899(+/-20) to almost half of this value during 1972(+/-20). The significance of the I-5(10) and of short periodic oscillations in the S-3(5) range has in turn increased from about 15% each to 36.8 and 30.7%, respectively. Predictions of ice winter severity based on the spectral characteristics of the full record are thus bound to fail. Some predictive skill for severe ice winters, which occurred with an overall frequency of 24.6%, may be realized from an apparent association with the 11-year solar activity cycle. This association has been most pronounced since the 1950s, about the time the 8-year rhythm started dominating variability. 9 out of 10 severe ice winters eventuated in phase with either high (3) or low solar activity (6). Moreover, almost all of the most severe ice winters occurred when the phase of the quasibiennial stratospheric wind oscillation (QBO) at the Equator was east (west) and, at the same time, solar activity was low (high). The peaks in the V-A Sigma spectrum after WWII reflect the dominance of singular 8-year ice events of modulated strength. This quasicyclic recurrence of strong ice winters in conjunction with the apparent statistical Solar Cycle-QBO-Ice Winter Severity relationship may be cautiously used in ice winter forecasting.

This brief evaluation of the sea surface temperatures (SSTs) of the North Sea from December 1995 through November 1996 is based on SST grids derived from weekly composite SST analyses published by the Bundesamt für Seeschiffahrt und Hydrographie (BSH) since 1968. The 1971–1993 SST climatology computed from these SST grids is used to identify anomalies in the seasonal cycle and areal distribution of the SST in 1996.

This brief evaluation of the sea surface temperatures (SSTs) of the North Sea from December 1993 through November 1994 is based on SST grids derived from weekly composite in situ SST analyses published by the “Bundesamt für Seeschiffahrt und Hydrographie” (BSH) since 1968. The 1971–1993 SST climatology computed from these SST grids is used to identify anomalies in the seasonal, cycle and areal distribution of the SST in 1994. The summer 1994 SST distribution stands out as the strongest warm anomaly on record since 1976.

This brief evaluation of the sea surface temperatures (SSTs) of the North Sea from December 1994 through November 1995 is based on SST grids derived from weekly composite SST analyses published by the Bundesamt für Seeschiffahrt und Hydrographie (BSH) since 1968. The 1971–1993 SST climatology computed from these SST grids is used to identify anomalies in the seasonal cycle and areal distribution of the SST in 1995.

The variability of the severity of ice winters in the Western Baltic between 1879 and 1992 is statistically investigated using a time series of the accumulated areal ice volume (or VAΣ) from the Baltic coast of Schleswig-Holstein. Lowpass filtering of the original time series shows the level of ice production in the mid 1980s to have been the same as that almost 100 years ago. A vivid interpretation is made possible of the variations in ice production by classifying VAΣ according to ice winter severity types. The increased variability of ice production since the 1920s is seen in the more frequent occurrence both of very strong and weak ice winters, while moderate and strong ice winters have decreased. The time series of the accumulated areal ice volume is negatively correlated with a temporally corresponding series of the NAO winter index, a measure of the strength of the zonal atmospheric circulation above the North Atlantic. Pearson's correlation coefficient, rp = -0.47, exceeds the 99.9% confidence limit. In addition, a contingency table analysis revealed that this inverse correlation is due to the preferential occurrence of (a) weak ice winters with strong westerlies (NAO winter index >; 1) and (b) strong to very strong ice winters with weak westerlies (NAO winter index > — 1).

The variability of the severity of ice winters in the Western Baltic between 1879 and 1992 is statistically investigated using a time series of the accumulated areal ice volume (or V(ASIGMA) from the Baltic coast of Schleswig-Holstein. Lowpass filtering of the original time series shows the level of ice production in the mid 1980s to have been the same as that almost 100 years ago. A vivid interpretation is made possible of the variations in ice production by classifying V(ASIGMA) according to ice winter severity types. The increased variability of ice production since the 1920s is seen in the more frequent occurrence both of very strong and weak ice winters, while moderate and strong ice winters have decreased. The time series of the accumulated areal ice volume is negatively correlated with a temporally corresponding series of the NAO winter index, a measure of the strength of the zonal atmospheric circulation above the North Atlantic. Pearson's correlation coefficient, r(p) = -0.47. exceeds the 99.9 % confidence limit. In addition, a contingency table analysis revealed that this inverse correlation is due to the preferential occurrence of (a) weak ice winters with strong westerlies (NAO winter index > 1 ) and (b) strong to very strong ice winters with weak westerlies (NAO winter index < - 1).

Recent general circulation model studies1–3 performed to assess the equilibrium climate response to doubling atmospheric CO2 suggested a global mean surface warming of 3.5–4.2 °C. Part of this warming was attributed to a change in cloud cover1. But all of these studies neglected changes of cloud optical properties which were shown to provide a substantial negative feedback in radiative-convective models if the cloud liquid water content was assumed to increase with increasing temperature4,5. This hypothesis is examined in a climate model where clouds are simulated interactively with dynamics, radiation and hydrological cycle6. The thermal forcing is introduced by a 2% increase of the solar constant which is equivalent to a doubling of CO21. The results show the anticipated increase of cloud liquid water and cloud optical depth. A feedback analysis of the simulated climate change supports earlier suggestions of the importance of cloud optical depth feedbacks4,5. The net effect of clouds is to provide a negative feedback on surface temperature, rather than the positive feedback found in earlier general circulation model studies without considering cloud optical depth feedbacks1.