ALBERT

Description: In this study, the authors discuss two different parameterizations for the effect of mixed layer eddies, one based on ageostrophic linear stability analysis (ALS) and the other one based on a scaling of the potential energy release by eddies (PER). Both parameterizations contradict each other in two aspects. First, they predict different functional relationships between the magnitude of the eddy fluxes and the Richardson number (Ri) related to the background state. Second, they also predict different vertical structure functions for the horizontal eddy fluxes. Numerical simulations for two different configurations and for a large range of different background conditions are used to evaluate the parameterizations. It turns out that PER is better suited to capture the Ri dependency of the magnitude of the eddy fluxes. On the other hand, the vertical structure of the meridional eddy fluxes predicted by ALS is more accurate than that of PER, while the vertical structure of the vertical eddy fluxes is well predicted by both parameterizations. Therefore, this study suggests the use of the magnitude of PER and the vertical structure functions of ALS for an improved parameterization of mixed layer eddy fluxes.

Description: Northern Hemisphere stratospheric variability is investigated with respect to chaotic behavior using time series from three different variables extracted from four different reanalysis products and two numerical model runs with different forcing. The time series show red spectra at all frequencies and the probability distribution functions show persistent deviations from a Gaussian distribution. An exception is given by the numerical model forced with perpetual winter conditions—a case that shows more variability and follows a Gaussian distribution, suggesting that the deviation from Gaussianity found in the observations is due to the transition between summer and winter variability. To search for the presence of a chaotic attractor the correlation dimension and entropy, the Lyapunov spectrum, and the associated Kaplan–Yorke dimension are estimated. A finite value of the dimensions can be computed for each variable and data product, with the correlation dimension ranging between 3.0 and 4.0 and the Kaplan–Yorke dimension between 3.3 and 5.5. The correlation entropy varies between 0.6 and 1.1. The model runs show similar values for the correlation and Lyapunov dimensions for both the seasonally forced run and the perpetual-winter run, suggesting that the structure of a possible chaotic attractor is not determined by the seasonality in the forcing, but must be given by other mechanisms.

Description: Southern Hemisphere (SH) stratospheric variability is investigated with respect to chaotic behavior using time series from three different variables extracted from four different reanalysis products. The results are compared with the same analysis applied to the Northern Hemisphere (NH). The probability density functions (PDFs) for the SH show persistent deviations from a Gaussian distribution. The variability is given by white spectra for low frequencies, a slope of −1 for intermediate frequencies, and −3 slopes for high frequencies. Considering the time series for winter and summer separately, PDFs show a Gaussian distribution and the variability spectra change their slopes, indicating the role of the transition between winter and summer variability in shaping the time series. The correlation (D2) and the Kaplan–Yorke (DKY) dimensions are estimated. A finite value of the dimensions can be computed for each variable and data product, except for the NCEP zonal-mean zonal wind and temperature data, which violate the requirement D2 ≤ DKY, possibly owing to the presence of spurious trends and inconsistencies in the data. The value of D2 ranges between 2.6 and 3.9, while DKY ranges between 3.0 and 4.5. The results show that both D2 and DKY display large variability in their values both for different datasets and for different variables within the same dataset. The variability of the values of D2 and DKY thus leaves open the question about the existence of a low-dimensional attractor or if the finite dimensions of the system are the result of the projection of a larger attractor in a low-dimensional embedding space.

Description: The sensitivities of the Brewer–Dobson circulation (BDC) to different distributions of tropical SST heating are investigated in an idealized aquaplanet model. It is found that an increase in tropical SSTs generally leads to an acceleration of tropical upwelling and an associated reduction in the age of air (AOA) in the polar stratosphere and that the AOA near the subtropical tropopause is correlated with local isentropic mixing of tropospheric air with stratospheric air. The zonal distribution of SST perturbations has a major impact on the vertical and meridional structure of the BDC as compared with other SST characteristics. Zonally localized SST heatings tend to generate a shallow acceleration of the stratospheric residual circulation, enhanced isentropic mixing associated with a weakened stratospheric jet, and a reduction in AOA mostly within the polar vortex. In contrast, SST heatings with a zonally symmetric structure tend to produce a deep strengthening of the stratospheric residual circulation, suppressed isentropic mixing associated with a stronger stratospheric jet, and a decrease of AOA in the entire stratosphere. The shallow versus deep strengthening of the stratospheric residual circulation change has been linked to wave propagation and dissipation in the subtropical lower stratosphere rather than wave generation in the troposphere, and the former can be strongly affected by the vertical position of the subtropical jet. These results suggest that, while the longitudinally localized SST trends under climate change may contribute to the change in the shallow branch of the BDC, the upward shift of the subtropical jet associated with the zonal SST heating can impact the deep branch of the BDC.

Description: The authors test the hypothesis that recent observed trends in surface westerlies in the Southern Hemisphere are directly consequent on observed trends in the timing of stratospheric final warming events. The analysis begins by verifying that final warming events have an impact on tropospheric circulation in a simplified GCM driven by specified equilibrium temperature distributions. Seasonal variations are imposed in the stratosphere only. The model produces qualitatively realistic final warming events whose influence extends down to the surface, much like what has been reported in observational analyses. The authors then go on to study observed trends in surface westerlies composited with respect to the date of final warming events. If the considered hypothesis were correct, these trends would appear to be much weaker when composited with respect to the date of the final warming events. The authors find that this is not the case, and accordingly they conclude that the observed surface changes cannot be attributed simply to this shift toward later final warming events.

Description: Precipitation is highly variable in space and time; hence, rain gauge time series generally exhibit additional random small-scale variability compared to area averages. Therefore, differences between daily precipitation statistics simulated by climate models and gauge observations are generally not only caused by model biases, but also by the corresponding scale gap. Classical bias correction methods, in general, cannot bridge this gap; they do not account for small-scale random variability and may produce artifacts. Here, stochastic model output statistics is proposed as a bias correction framework to explicitly account for random small-scale variability. Daily precipitation simulated by a regional climate model (RCM) is employed to predict the probability distribution of local precipitation. The pairwise correspondence between predictor and predictand required for calibration is ensured by driving the RCM with perfect boundary conditions. Wet day probabilities are described by a logistic regression, and precipitation intensities are described by a mixture model consisting of a gamma distribution for moderate precipitation and a generalized Pareto distribution for extremes. The dependence of the model parameters on simulated precipitation is modeled by a vector generalized linear model. The proposed model effectively corrects systematic biases and correctly represents local-scale random variability for most gauges. Additionally, a simplified model is considered that disregards the separate tail model. This computationally efficient model proves to be a feasible alternative for precipitation up to moderately extreme intensities. The approach sets a new framework for bias correction that combines the advantages of weather generators and RCMs.

Description: There is an ongoing discussion in the community concerning the wave-averaged momentum equations in the hybrid vertically Lagrangian and horizontally Eulerian (VL) framework and, in particular, the form stress term (representing the residual effect of pressure perturbations) which is thought to restrict the handling of higher order waves in terms of a perturbation expansion. The present study shows that the traditional pressure-based form stress term can be transformed into a set of terms that do not contain any pressure quantities but do contain the time derivative of a wave-induced velocity. This wave-induced velocity is referred to as the pseudomomentum in the VL framework, as it is analogous to the generalized pseudomomentum in Andrews and McIntyre. This enables the second expression for the wave-averaged momentum equations in the VL framework (this time for the development of the total transport velocity minus the VL pseudomomentum) to be derived together with the vortex force. The velocity-based expression of the form stress term also contains the residual effect of the turbulent viscosity, which is useful for understanding the dissipation of wave energy leading to transfer of momentum from waves to circulation. It is found that the concept of the virtual wave stress of Longuet-Higgins is applicable to quite general situations: it does not matter whether there is wind forcing or not, the waves can have slow variations, and the viscosity coefficient can vary in the vertical. These results provide a basis for revisiting the surface boundary condition used in numerical circulation models.

Description: Mooring observations and model simulations point to an instability of the Labrador Current (LC) during winter, with enhanced eddy kinetic energy (EKE) at periods between 2 to 5 days, and much less EKE during other seasons. Linear stability analysis using vertical shear and stratification from the model reveals three dominant modes of instability in the LC: - a balanced interior mode with along-flow wavelengths of about 30–45 km, phase velocities of 0.3 m/s, maximal growth rates of 1 d−1 and surface intensified, but deep reaching amplitudes, - a balanced shallow mode with along-flow wavelengths of about 0.3–1.5 km, about three times larger phase speeds and growth rates, but amplitudes confined to the mixed layer (ML), - and an unbalanced symmetric mode with largest growth rates, vanishing phase speeds and along-flow structure, and very small cross-flow wavelengths, also confined to the ML. Both balanced modes are akin to baroclinic instability, but operate at moderate to small Richardson numbers Ri with much larger growth rates as for the quasi-geostrophic limit of Ri ≫ 1. The interior mode is found to be responsible for the instability of the LC during winter. Weak stratification and enhanced vertical shear due to local buoyancy loss and the advection of convective water masses from the interior result in small Ri within the LC, and to three times larger growth rates of the interior mode in March compared to summer and fall conditions. Both the shallow and the symmetric mode are not resolved by the model, but it is suggested that they might also play an important role for the instability in the LC and for lateral mixing.

Description: Sensible and latent heat fluxes were estimated from turbulence measurements gathered during several Atlantic transects of the R/V Polarstern. The inertial dissipation method was used to analyze the data. Resulting bulk transfer coefficients were then applied to the data from the ship’s meteorological system to get continuous time series of the heat fluxes. Combined to the measured downward solar and longwave radiation fluxes allows for an estimate of the total energy budget at the air-sea interface. Comparing these parameterized energy fluxes to ones based on the COARE 3.0 bulk flux algorithm show very strong agreement.

Description: The dynamical origin of the spectral and autocorrelation structure of annular variability in the troposphere is investigated by a deductive approach. Specifically, the structure of the power spectrum and autocorrelation function of the zonal-mean geopotential is analyzed for the case of a quasigeostrophic spherical atmosphere subject to a white noise mechanical forcing applied in a single Hough mode and concentrated at a particular level in the vertical, with vertically uniform Newtonian cooling and Rayleigh drag concentrated at a rigid lower boundary. Analytic expressions for the power spectrum are presented together with expressions for an approximate red noise (i.e., a Lorentzian-shaped) power spectrum. It is found that for an infinitely deep atmosphere the power spectrum can be well approximated by a red noise process for the first few Hough modes (associated with large Rossby heights), provided the distance from the forcing is not larger than about one Rossby height. When a frictional rigid lower boundary is included, however, the approximation is generally bad. The high-frequency part of the power spectrum exhibits near-exponential behavior and the autocorrelation function shows a transition from a rapid decay at short lags to a much slower decay at longer lags, if the thermal and mechanical damping time scales are sufficiently well separated. Since observed annular variability exhibits the same characteristics, the above results lead to the hypothesis that these characteristics may, to some extent, be intrinsic to the linear zonal-mean response problem—although the need for an additional contribution from eddy feedbacks is also implied by the results.

Description: A representation of an equatorial basin mode excited in a shallow water model for a single high order baroclinic vertical normal mode is used as a simple model for the equatorial deep jets. The model is linearized about both a state of rest and a barotropic mean flow corresponding to the observed Atlantic Equatorial Intermediate Current System. We found that the eastward mean flow associated with the North and South Intermediate Counter Currents (NICC and SICC, respectively) effectively shields the Equator from off-equatorial Rossby waves. The westward propagation of these waves is blocked and focusing on the Equator due to beta dispersion is prevented. This leads to less energetic jets along the Equator. On the other hand, the westward barotropic mean flow along the Equator reduces the gradient of absolute vorticity and hence widens the cross-equatorial structure of the basin mode. Increasing lateral viscosity predominantly affects the width of the basin modes’ Kelvin wave component in the presence of the mean flow while the Rossby wave is confined by the flanking NICC and SICC. Independent of the presence of the mean flow, the application of sufficient lateral mixing also hinders the focusing of off-equatorial Rossby waves, which is hence an unlikely feature of a low-frequency basin mode in the real ocean.

Description: A decadal change in the character of ENSO was observed around year 2000 toward weaker-amplitude, higher-frequency events with an increased occurrence of central Pacific El Niños. Here these changes are assessed in terms of the Bjerknes stability index (BJ index), which is a measure of the growth rate of ENSO-related SST anomalies. The individual terms of the index are calculated from ocean reanalysis products separately for the time periods 1980–99 and 2000–10. The spread between the products is large, but they show a robust weakening of the thermocline feedback due to a reduced thermocline slope response to anomalous zonal wind stress as well as a weakened wind stress response to eastern equatorial Pacific SST anomalies. These changes are consistent with changes in the background state of the tropical Pacific: cooler mean SST in the eastern and central equatorial Pacific results in reduced convection there together with a westward shift in the ascending branch of the Walker circulation. This shift leads to a weakening in the relationship between eastern Pacific SST and longitudinally averaged equatorial zonal wind stress. Also, despite a steeper mean thermocline slope in the more recent period, the thermocline slope response to wind stress anomalies weakened due to a smaller zonal wind fetch that results from ENSO-related wind anomalies being more confined to the western basin. As a result, the total BJ index is more negative, corresponding to a more strongly damped system in the past decade compared to the 1980s and 1990s.

Description: In his comment, G. Bürger criticizes the conclusion that inflation of trends by quantile mapping is an adverse effect.He assumes that the argument would be ‘‘based on the belief that long-term trends and along with them future climate signals are to be large scale.’’ His line of argument reverts to the so-called inflated regression. Here it is shown, by referring to previous critiques of inflation and standard literature in statistical modeling as well as weather forecasting, that inflation is built upon a wrong understanding of explained versus unexplained variability and prediction versus simulation. It is argued that a sound regressionbased downscaling can in principle introduce systematic local variability in long-term trends, but inflation systematically deteriorates the representation of trends. Furthermore, it is demonstrated that inflation by construction deteriorates weather forecasts and is not able to correctly simulate small-scale spatiotemporal structure.

Description: The relationship between the Agulhas Current and the Agulhas leakage is not well understood. Here, this is investigated using two basin-scale and two global ocean models, of incrementally increasing resolution. The response of the Agulhas Current is evaluated under a series of sensitivity experiments, in which idealised anomalies, designed to geometrically modulate zonal trade wind stress, are applied across the Indian Ocean basin. The imposed wind stress changes exceed ±2 standard deviations from the annual mean trade winds and, in the case of intensification, are partially representative of recently observed trends. The Agulhas leakage is quantified using complimentary techniques based on Lagrangian virtual floats and Eulerian passive tracer flux. As resolution increases, model behavior converges and the sensitivity of the leakage to Agulhas Current transport anomalies is reduced. In the two eddy-resolving configurations tested, the leakage is insensitive to changes in Agulhas Current transport at 32°S, though substantial eddy kinetic energy anomalies are evident. Consistent with observations, the position of the retroflection remains stable. The decoupling of Agulhas Current variability from the Agulhas leakage suggests that, while correlations between the two may exist, they may not have a clear dynamical basis. It is suggested that present and future Agulhas leakage proxies be considered in the context of potentially transient forcing regimes.

Description: A surface diurnal warm layer is diagnosed from Seaglider observations, and develops on half the days in the CINDY/DYNAMO Indian Ocean experiment. The diurnal warm layer occurs on days of high solar radiation flux (〉 80 W m−2) and low wind speed (〈 6 m s−1), and preferentially in the inactive stage of the Madden–Julian Oscillation. Its diurnal harmonic has an exponential vertical structure with a depth scale of 4–5 m (dependent on chlorophyll concentration), consistent with forcing by absorption of solar radiation. The effective sea surface temperature (SST) anomaly due to the diurnal warm layer often reaches 0.8°C in the afternoon, with a daily mean of 0.2°C, rectifying the diurnal cycle onto longer time scales. This SST anomaly drives an anomalous flux of 4 W m−2 that cools the ocean. Alternatively, in a climate model where this process is unresolved, this represents an erroneous flux that warms the ocean. A simple model predicts a diurnal warm layer to occur on 30–50% of days across the tropical warm pool. On the remaining days, with low solar radiation and high wind speeds, a residual diurnal cycle is observed by the Seaglider, with a diurnal harmonic of temperature that decreases linearly with depth. As wind speed increases, this already weak temperature gradient decreases further, tending towards isothermal conditions.

Description: Sea surface temperature (SST) anomalies in the eastern equatorial Atlantic are connected to modulations in the strength of the South Atlantic subtropical high-pressure system, referred to as the South Atlantic Anticyclone (SAA). Using ocean and atmosphere reanalysis products we show here that the strength of the SAA from February to May impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial Atlantic (EEA) via anomalous tropical wind power. This modulation of the timing and amplitude of the seasonal cold tongue development manifests as anomalous SST events peaking between June and August. The timing and impact of this connection is not completely symmetric for warm and cold events. For cold events, an anomalously strong SAA in February and March leads to positive wind power anomalies from February to June resulting in an early cold tongue onset and subsequent cold SST anomalies in June and July. For warm events the anomalously weak SAA persists until May, generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm SST anomalies. Mechanisms by which SAA induced wind power variations south of the equator influence EEA SST are discussed, including ocean adjustment via Rossby and Kelvin wave propagation, meridional advection, and local intraseasonal wind variations

Description: We present a detailed quality assessment of a novel underwater sensor for the measurement of CO2 partial pressure (pCO2) based on surface water field deployments carried out between 2008 and 2011. The commercially available sensor, which is based on membrane equilibration and NDIR spectrometry is small and can be integrated into mobile platforms. It is calibrated in water against a proven flow-through pCO2 instrument within a custom-built calibration setup. The aspect of highest concern with respect to achievable data quality of the sensor is the compensation for signal drift inevitably connected to absorption measurements. We use three means to correct for drift effects: (i) a filter correlation or dual-beam setup, (ii) regular zero gas measurements realized automatically within the sensor and (iii) a zero-based transformation of two sensor calibrations flanking the time of sensor deployment. Three sensors were tested against an underway pCO2 system during two major research cruises providing an in situ temperature range from 7.4 to 30.1°C and pCO2 values between 289 and 445 μatm. The average difference between sensor and reference pCO2 was found to be -0.6 ± 3 μatm with a RMSE of 3.7 μatm.

Description: Ammassalik in southeast Greenland is known for strong wind events that can reach hurricane intensity and cause severe destruction in the local town. Yet, these winds and their impact on the nearby fjord and shelf region have not been studied in detail. Here, data from two meteorological stations and the European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim) are used to identify and characterize these strong downslope wind events, which are especially pronounced at a major east Greenland fjord, Sermilik Fjord, within Ammassalik. Their local and regional characteristics, their dynamics and their impacts on the regional sea ice cover, and air–sea fluxes are described. Based on a composite of the events it is concluded that wind events last for approximately a day, and seven to eight events occur each winter. Downslope wind events are associated with a deep synoptic-scale cyclone between Iceland and Greenland. During the events, cold dry air is advected down the ice sheet. The downslope flow is accelerated by gravitational acceleration, flow convergence inside the Ammassalik valley, and near the coast by an additional thermal and synoptic-scale pressure gradient acceleration. Wind events are associated with a large buoyancy loss over the Irminger Sea, and it is estimated that they drive one-fifth of the net wintertime loss. Also, the extreme winds drive sea ice out of the fjord and away from the shelf.

Description: In 2013, the vast majority of the monitored climate variables reported here maintained trends established in recent decades. ENSO was in a neutral state during the entire year, remaining mostly on the cool side of neutral with modest impacts on regional weather patterns' around the world. This follows several years dominated by the effects of either La Nina. or El Nino events. According to several independent analyses, 2013 was again among the 10 warmest years on record at the global scale, both at the Earth's surface and through the troposphere. Some regions in the Southern Hemispherehad record or near-record high temperatures for the year. Australia observed its hottest year on record, while Argentina and New Zealand reported their second and third hottest years, respectively. In Antarctica, Amundsen-Scott South Pole Station reported its highest annual temperature since records began in 1957 At the opposite pole, the Arctic observed its seventh warmest year since record's began in the early 20th century. At 20-m depth, record high temperatures were measured at some permafrost stations on the North Slope Of Alaska and in the Brooks Range. In the Northern Hemisphere extratropics, anomalous meridional atmospheric circulation occurred throughout much of the year leading to marked regional extremes of both temperature and precipitation. Cold temperature anomalies during Winter across Eurasia were followed by warm Spring temperature anomalies, which, were linked to a new record Eurasian snow cover extent in the May. Minimum sea ice extent in the :Arctic was the sixth lowest since satellite Observations began in 1979. Including 2013, all seven lowest extents on record have occurred in the past seven years Antarctica, on the other hand, had above average sea ice extent throughout 2013, with 116 days Of new daily high extent records, inclding a new daily maximum sea ice area of 19.57 million km(2) reached on 1 October. ENSO-neutral conditions in the eastern central Pacific Ocean and a negative Pacific decadal oscillation pattern in the North Pacific had the largest impacts on the global sea surface temperature in 2013: The North Pacific reached a historic high temperature in 2013 and on balance the globally-averaged sea surface temperature was among the 10 highest on record. Overall, the salt Content in near-surface ocean waters increased while in intermediate waters it decreased. Global mean sea level continued to rise during 2013, on pace with a trend of 3,2 mm yr(-1) over the past two decades. A portion of this trend (0.5 mm yr(-1)) has been attributed to natural variability associated with the Pacific decadal oscillation as Well as to ongoing contribution from the melting of glaciers and ice sheets and ocean warming. Global tropical cyclone frequency during 2013 was slightly above average with a total of 94 storms, although the North Atlantic Basin had its quietest hurricane season since 1994. In the Western North Pacific Basin, Super Typhoon Haiyan, the deadliest tropical Cyclone of 2013, had 1-minute sustained winds estimated to be 170 kt (OS m s(-1)) on 7 November, the highest Wind speed ever assigned to a tropical cyclone. High storm surge was also associated with Haiyan at it Made landfall over the central Philippines, an area where sea level is currently at historic highs increasing by 200 mm since 1970. In the atmosphere, carbon dioxide, methane, and nitrous oxide all Continued to increase in 2013. As in previous our years, each of these Major greenhouse gases once again reached historic high Concentrations. In the Arctic carbon dioxide and methane:, Increased at the same rate as:the global increase. These increases are likely due to export from lower latitudes rather than a consequence Of increases in Arctic sources such as thawing permafrost., At Mauna Loa, Hawaii, for the first time since measurement began in 1958, the daily average Mixing ratio Of carbon dioxide exceeded 400 ppm on 9 May. The state of these variables, along with dozens of others, and the 2013 climate conditions of regions around the world are discussed in further detail in this 24th, edition of the State of the Climate series

Description: The Denmark Strait Overflow (DSO) supplies about one-third of the North Atlantic Deep Water and is critical to global thermohaline circulation. Knowledge of the pathways of DSO through the Irminger Basin and its transformation there is still incomplete, however. The authors deploy over 10 000 Lagrangian particles at the Denmark Strait in a high-resolution ocean model to study these issues. First, the particle trajectories show that the mean position and potential density of dense waters cascading over the Denmark Strait sill evolve consistently with hydrographic observations. These sill particles transit the Irminger Basin to the Spill Jet section (65.25°N) in 5–7 days and to the Angmagssalik section (63.5°N) in 2–3 weeks. Second, the dense water pathways on the continental shelf are consistent with observations and particles released on the shelf in the strait constitute a significant fraction of the dense water particles recorded at the Angmagssalik section within 60 days (~25%). Some particles circulate on the shelf for several weeks before they spill off the shelf break and join the overflow from the sill. Third, there are two places where the water density following particle trajectories decreases rapidly due to intense mixing: to the southwest of the sill and southwest of the Kangerdlugssuaq Trough on the continental slope. After transformation in these places, the overflow particles exhibit a wide range of densities.

Description: Quantile mapping is routinely applied to correct biases of regional climate model simulations compared to observational data. If the observations are of similar resolution as the regional climate model, quantile mapping is a feasible approach. However, if the observations are of much higher resolution, quantile mapping also attempts to bridge this scale mismatch. Here, it is shown for daily precipitation that such quantile mapping-based downscaling is not feasible but introduces similar problems as inflation of perfect prognosis ("prog") downscaling: the spatial and temporal structure of the corrected time series is misrepresented, the drizzle effect for area means is overcorrected, area-mean extremes are overestimated, and trends are affected. To overcome these problems, stochastic bias correction is required.

Description: Previous attempts to derive the depth-dependent expression of the radiation stress have lead to a debate concerning (i) the applicability of Mellor’s approach to a sloping bottom, (ii) the introduction of the delta function at the mean sea surface in the later papers by Mellor, and (iii) a wave-induced pressure term derived in several recent studies. The authors use an equation system in vertically Lagrangian and horizontally Eulerian (VL) coordinates suitable for a concise treatment of the surface boundary, and obtain an expression for the depth-dependent radiation stress that is consistent with the vertically-integrated expression given by Longuet-Higgins and Stewart. Concerning (i)-(iii) in the above, the difficulty of handling a sloping bottom disappears when wave-averaged momentum equations in the VL coordinates are written for the development of (not the Lagrangian mean velocity but) the Eulerian mean velocity. There is also no delta function at the sea surface in the expression for the depth-dependent radiation stress. The connection between the wave-induced pressure term in the recent studies and the depth-dependent radiation stress term is easily shown by rewriting the pressure-based form stress term in the thickness-weighted-mean (TWM) momentum equations as a velocity-based term which contains the time derivative of the pseudomomentum in the TWM framework.

Description: The upper ocean, including the biologically productive euphotic zone and the mixed layer, has great relevance for studies of physical, biogeochemical, and ecosystem processes and their interaction. Observing this layer with a continuous presence, sampling many of the relevant variables, and with sufficient vertical resolution, has remained a challenge. Here a system is presented which can be deployed on the top of deep-ocean moorings, with a drive mechanism at depths of 150-200m, which mechanically winches a large sensor float and smaller communications float tethered above it to the surface and back down again, typically twice per day for periods up to 1 year. The sensor float can carry several sizeable sensors, and it has enough buoyancy to reach the near surface and for the communications float to pierce the surface even in the presence of strong currents. The system can survive mooring blow-over to 1000m depth. The battery-powered design is made possible by using a balanced energy-conserving principle. Reliability is enhanced with a drive assembly that employs a single rotating part that has no slip rings or rotating seals. The profiling bodies can break the surface to sample the near-surface layer and to establish satellite communication for data relay or reception of new commands. An inductive pass-through mode allows communication with other mooring components throughout the water column beneath the system. A number of successful demonstration deployments have been completed.

Description: In recent years, profiling floats, which form the basis of the successful international Argo observatory, are also being considered as platforms for marine biogeochemical research. This study showcases the utility of floats as a novel tool for combined gas measurements of CO2 partial pressure (pCO2) and O2. These float prototypes were equipped with a small-sized and submersible pCO2 sensor and an optode O2 sensor for high resolution measurements in the surface ocean layer. Four consecutive deployments were carried out during Nov. 2010 and June 2011 near the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic. The profiling float performed upcasts every 31 h while measuring pCO2, O2, salinity, temperature and hydrostatic pressure in the upper 200 m of the water column. In order to maintain accuracy, regular pCO2 sensor zeroings at depth and surface, as well as optode measurements in air, were performed for each profile. Through the application of data processing procedures (e.g., time-lag correction) accuracies of float-borne pCO2 measurements were greatly improved (10 – 15 μatm for water column and 5 μatm for surface measurements). O2 measurements yielded an accuracy of 2 μmol kg−1. First results of this pilot study show the possibility of using profiling floats as a platform for detailed and unattended observations of the marine carbon and oxygen cycle dynamics.

Description: The use of a coupled ocean/atmosphere/sea-ice model to hindcast (i.e. historical forecast) recent climate variability is described and illustrated for the cases of the 1976/77 and 1998/99 climate shift events in the Pacific. The initialization is achieved by running the coupled model in partially coupled mode whereby global observed wind stress anomalies are used to drive the ocean/sea-ice component of the coupled model while maintaining the thermodynamic coupling between the ocean/sea-ice and atmosphere components. Here we show that hindcast experiments can successfully capture many features associated with the 1976/77 and 1998/99 climate shifts. For instance, hindcast experiments started from the beginning of 1976 can capture sea surface temperature (SST) warming in the central-eastern equatorial Pacific and the positive phase of the Pacific Decadal Oscillation (PDO) throughout the 9 years following the 1976/77 climate shift, including the deepening of the Aleutian low pressure system. Hindcast experiments started from the beginning of 1998 can also capture part of the anomalous conditions during the 4 years after the 1998/99 climate. We argue that the dynamical adjustment of heat content anomalies that are present in the initial conditions in the tropics is important for the successful hindcast of the two climate shifts.

Description: One of the most remarkable features of the reproductive systems of eubrachyuran crabs is the presence of specialized organs for sperm storage, the seminal receptacles. Descriptions of seminal receptacle morphology, sperm storage time, sperm retention across molts, and the capacity to store multiple ejaculates from different males can help in understanding crab mating strategies as well as in preventing negative effects of male-biased fisheries of heavily harvested species. Metacarcinus edwardsii is the most harvested crab in Chile, but its reproductive biology is largely unstudied. In this study, the morphology of the seminal receptacles of M. edwardsii is characterized from the macroscopic to the microscopic level, during key points in the reproductive cycle. The receptacles of experimentally mated and wild-caught females were included in this analysis. Metacarcinus edwardsii has ventral-type seminal receptacles that are able to retain sperm after molting, and even after extrusion of the eggs. Stratification of multiple ejaculates is clearly observed. In general, the pattern of sperm storage indicates that populations of this species, like those of other cancrid crabs, could have high resilience to the negative effects of the selective harvest of males, principally because females have a great sperm storage capacity.

Description: The Arctic continental shelf seas hold a globally significant source of freshwater that impacts Arctic Ocean stratification, circulation, and climate. This freshwater can be injected below the surface mixed layer by intense turbulent kinetic energy dissipation events, as resolved by Laptev Sea microstructure observations. The tides provide a major source of energy that can be dissipated and hence drive diapycnal mixing in the Laptev Sea. Multiyear ADCP mooring records from locations across the shelf reveal that semidiurnal tides are dominated by theM2 and S2 constituents, with the largest amplitudes on the outer shelf. Throughoutmost of the shelf, tides are clockwise polarized and sheared by stratification, as characteristic near the M2 critical latitude. Interannual variations of the tidal and shear structures on the inner shelf aremainly determined by the stratification-setting Lena River freshwater plume. In all locations,M2 tides are enhanced under sea ice, and therefore changes in the seasonal ice cover may lead to changes in tides and water column structure. The main conclusions of this study are that (i) tides play a comparatively greater role year-round on the outer shelf relative to the inner shelf; (ii) a sea ice reduction will overall decrease the predictability of the currents, especially on the inner shelf; and (iii) the freshwater distribution directly impacts diapycnal mixing by setting the vertical tidal structure. These combined effects imply that future sea ice loss will increase the variability and vertical mixing of freshwater, particularly on the inner shelf, where the Lena River first enters the Laptev Sea.

Description: A large number of quantities have to be measured and processed to determine the atmospheric-state variables, which are the actual measurands, from aircraft-based measurements. A great part of the dependencies between these quantities depends on the aerodynamic state of the aircraft. Aircraft-based meteorological measurements, hence, require in-flight calibration. Most operators of research aircraft perform some kind of calibration, but the schemes used and the degree they are documented greatly vary. The flight maneuvers and calculation methods required, however, are published in a number of partly overlapping and partly contradictory publications. Some methods are only presented as a minor issue in publications mainly focused on atmospheric processes and are therefore hard to find. For an aircraft user, it is hence challenging to either perform or verify a calibration because of missing comprehensive guidance. This lack was stated on occasion of the in-flight calibration of the German research aircraft Polar5 carried out for the field experiment Investigation of Katabatic Winds and Polynyas during Summer (IKAPOS). In the present paper, a comprehensive review of the existing literature on this field and a practical guide to the wind calibration of a research aircraft to be used for turbulent flux measurements are given.

Description: Accurate projections of stratospheric ozone are required because ozone changes affect exposure to ultraviolet radiation and tropospheric climate. Unweighted multimodel ensemble-mean (uMMM) projections from chemistry–climate models (CCMs) are commonly used to project ozone in the twenty-first century, when ozone-depleting substances are expected to decline and greenhouse gases are expected to rise. Here, the authors address the question of whether Antarctic total column ozone projections in October given by the uMMM of CCM simulations can be improved by using a process-oriented multiple diagnostic ensemble regression (MDER) method. This method is based on the correlation between simulated future ozone and selected key processes relevant for stratospheric ozone under present-day conditions. The regression model is built using an algorithm that selects those process-oriented diagnostics that explain a significant fraction of the spread in the projected ozone among the CCMs. The regression model with observed diagnostics is then used to predict future ozone and associated uncertainty. The precision of the authors’ method is tested in a pseudoreality; that is, the prediction is validated against an independent CCM projection used to replace unavailable future observations. The tests show that MDER has higher precision than uMMM, suggesting an improvement in the estimate of future Antarctic ozone. The authors’ method projects that Antarctic total ozone will return to 1980 values at around 2055 with the 95% prediction interval ranging from 2035 to 2080. This reduces the range of return dates across the ensemble of CCMs by about a decade and suggests that the earliest simulated return dates are unlikely.

Description: Evidence is presented for the notion that some contribution to the recent decadal trends observed in the Southern Hemisphere, including the lack of a strong Southern Ocean surface warming, may have originated from longer-term internal centennial variability originating in the Southern Ocean. The existence of such centennial variability is supported by the instrumental sea surface temperatures (SSTs), a multimillennial reconstruction of Tasmanian summer temperatures from tree rings, and a millennial control integration of the Kiel Climate Model (KCM). The model variability was previously shown to be linked to changes in Weddell Sea deep convection. During phases of deep convection the surface Southern Ocean warms, the abyssal Southern Ocean cools, Antarctic sea ice extent retreats, and the low-level atmospheric circulation over the Southern Ocean weakens. After the halt of deep convection the surface Southern Ocean cools, the abyssal Southern Ocean warms, Antarctic sea ice expands, and the low-level atmospheric circulation over the Southern Ocean intensifies, consistent with what has been observed during the recent decades. A strong sensitivity of the time scale to model formulation is noted. In the KCM, the centennial variability is associated with global-average surface air temperature (SAT) changes of the order of a few tenths of a degree per century. The model results thus suggest that internal centennial variability originating in the Southern Ocean should be considered in addition to other internal variability and external forcing when discussing the climate of the twentieth century and projecting that of the twenty-first century.

Description: The wintertime northern annular mode (NAM) at the surface is known to undergo slow intraseasonal variations in association with stratospheric variability, which leads the surface signal by up to several weeks. The relative contributions, however, of potentially relevant stratosphere–troposphere coupling mechanisms are not yet fully understood. In this study the relative roles of (i) the downward effect of the zonal-mean secondary circulation induced by quasigeostrophic (QG) adjustment to stratospheric wave drag and radiative damping and (ii) wave drag local to the troposphere are estimated. For this purpose, a spectral tendency equation of the QG zonal-mean zonal wind is derived and used, in a first step, to obtain the external mechanical forcing that, in the QG framework, drives exactly the observed stratospheric and tropospheric daily NAM. In a second step, the equation is then integrated in time to reconstruct the daily NAM, but with the forcing restricted to either stratospheric or tropospheric levels, each case leaving a characteristic NAM surface signal. The relative roles of the above-mentioned mechanisms are found to be of similar quantitative importance, but to differ in a qualitative sense. The downward effect of stratospheric QG adjustment is responsible for the initiation of the NAM surface signal, whereas subsequently local tropospheric wave drag actively maintains and persists the signal over several weeks. Furthermore, the downward effect of QG adjustment to stratospheric radiative damping is shown to have only a minor impact, compared to that from stratospheric wave drag. The robustness of these conclusions is demonstrated by a sensitivity study with respect to various model parameters.

Description: The Agulhas Current plays a crucial role in the thermohaline circulation through its leakage into the South Atlantic. Under both past and present climates, the trade winds and westerlies could have the ability to modulate the amount of Indian-Atlantic inflow. Compelling arguments have been put forward suggesting that trade winds alone have little impact on the magnitude of Agulhas leakage. Here, employing three ocean models for robust analysis – a global coarse resolution, a regional eddy-permitting and a nested high-resolution eddy-resolving configuration – and systematically altering the position and intensity of the westerly wind belt in a series of sensitivity experiments, it is shown that the westerlies, in particular their intensity, control the leakage. Leakage responds proportionally to the westerlies intensity up to a certain point. Beyond this, through the adjustment of the large-scale circulation, energetic interactions occur between the Agulhas Return Current and the Antarctic Circumpolar Current that result in a state where leakage no longer increases. This adjustment takes place within 1 to 2 decades. Contrary to previous assertions, our results further show that an equatorward (poleward) shift in westerlies increases (decreases) leakage. This occurs due to the redistribution of momentum input by the winds. It is concluded that the reported present-day leakage increase could therefore reflect an unadjusted oceanic response mainly to the strengthening westerlies over the last few decades.

Description: For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.

Description: Mesoscale anticyclonic eddies in the Irminger Sea are observed using a mooring and a glider. Between 2002 and 2009, the mooring observed 53 anticyclones. Using a kinematic model, objective estimates of eddy length scales and velocity structure are made for 16 eddies. Anticyclones had a mean core diameter of 12 km, and their mean peak observed azimuthal speed was 0.1 m s(-1). They had core salinities and potential temperatures of 34.91-34.98 and 4.488-5.34 degrees C, respectively, making them warm and salty features. These properties represent a typical salinity anomaly of 0.03 and a temperature anomaly of 0.28 degrees C from noneddy values. All eddies had small (〈〈 1) Rossby numbers. In 2006, the glider observed two anticyclones having diameters of about 20 km and peak azimuthal speeds of about 0.3 m s(-1). Similar salinity anomalies were detected throughout the Irminger Sea by floats profiling in anticyclones. Two formation regions for the eddies are identified: one to the west of the Reykjanes Ridge and the other off the East Greenland Irminger Current near Cape Farewell close to the mooring. Observations indicate that eddies formed in the former region are larger than eddies observed at the mooring. A clear increase in eddy salinity is observed between 2002 and 2009. The observed breakup of these eddies in winter implies that they are a source of salt for the central gyre. The anticyclones are similar to those found in both the Labrador Sea and Norwegian Sea, making them a ubiquitous feature of the subpolar North Atlantic basins.

Description: In this article we address the causes of the large-scale tropical sea level pressure (SLP) changes during climate change. The analysis we present is based on model simulations, observed trends and the seasonal cycle. In all three cases the regional changes of tropospheric temperature (Ttropos) and SLP are strongly related to each other (considerably stronger than (sea) surface temperature and SLP). This relationship basically follows the Bjerknes Circulation Theorem, with relatively low regional SLP where we have relatively high Ttropos and vice versa. A simple physical model suggests a tropical SLP response to horizontally inhomogeneous warming in the tropical Ttropos, with a sensitivity coefficient of about -1.7 hPa/K. This relationship explains a large fraction of observed and predicted changes in the tropical SLP. It is shown that in climate change model simulations the tropospheric land-sea warming contrast is the most significant structure in the regional Ttropos changes relative to the tropical mean changes. Since the land-sea warming contrast exists in the absent of any atmospheric circulation changes it can be argued that the large-scale response of tropical SLP changes is to first order a response to the tropical land-sea warming contrast. Further, as land-sea warming contrast is mostly available moisture dependent, the models predict a stronger warming and decreasing SLP in the drier regions from South America to Africa and a weaker warming and increasing SLP over the wetter Indo-Pacific warm pool region. This suggests an increase in the potential for deep convection conditions over the Atlantic Sector and a decrease over the Indo-Pacific warm pool region in the future.

Description: Variations in eastern Indian Ocean upper-ocean thermal properties are assessed for the period 1970–2004, with a particular focus on asymmetric features related to opposite phases of Indian Ocean Dipole events, using high-resolution ocean model hindcasts. Sensitivity experiments, where atmospheric forcing variability is restricted to the Indian or Pacific Ocean only, support the interpretation of forcing mechanisms for large-scale asymmetric behavior in eastern Indian Ocean variability. Years are classified according to eastern Indian Ocean subsurface heat content (HC) as proxy of thermocline variations. Years characterized by anomalous low HC feature a zonal gradient in upper-ocean properties near the equator, while high events have a meridional gradient from the tropics into the subtropics. The spatial and temporal characteristics of the seasonal evolution of HC anomalies for the two cases is distinct, as is the relative contribution from Indian Ocean atmospheric forcing versus remote influences from Pacific wind forcing: low events develop rapidly during austral winter/spring in response to Indian Ocean wind forcing associated with an enhanced southeasterly monsoon driving coastal upwelling and a shoaling thermocline in the east; in contrast, formation of anomalous high eastern Indian Ocean HC is more gradual, with anomalies earlier in the year expanding from the Indonesian Throughflow (ITF) region, initiated by remote Pacific wind forcing and transmitted through the ITF via coastal wave dynamics. Implications for seasonal predictions arise with high HC events offering extended lead times for predicting thermocline variations and upper-ocean properties across the eastern Indian Ocean.

Description: European Polar Low Working Group This workshop summarized the current state of PL research in the Arctic and Antarctic. A couple of related projects are in the planning phase or already funded. The creation of a PL database for the Norwegian Sea in the frame of the Sea Surface Temperature and Altimeter Synergy (STARS) project (http://projects.met.no stars) will provide a valuable resource for future research and, potentially, predictability improvements. The maintenance of this database and the creation of similar databases for other polar areas including satellite and NWP data are highly recommended. There is also a need for free and timely access to satellite data, in particular to SAR data to fill the gap caused by the mission end of Envisat. With the increasing resolution of climate models, mesoscale processes such as polar MCs will have to be considered in international research programs such as the World Climate Research Programme (WCRP) Polar Climate Predictability Initiative and the World Weather Research Programme (WWRP) Polar Predictability Project.

Description: The mechanisms involved in setting the annual cycle of the Florida Current transport are revisited using an adjoint model approach. Adjoint sensitivities of the Florida Current transport to wind stress reproduce a realistic seasonal cycle with an amplitude of ~1.2 Sv (1 Sv ≡ 106 m3 s−1). The annual cycle is predominantly determined by wind stress forcing and related coastal upwelling (downwelling) north of the Florida Strait along the shelf off the North American coast. Fast barotropic waves propagate these anomalies southward and reach the Florida Strait within a month, causing an amplitude of ~1 Sv. Long baroclinic planetary Rossby waves originating from the interior are responsible for an amplitude of ~0.8 Sv but have a different phase. The sensitivities corresponding to the first baroclinic mode propagate westward and are highly influenced by topography. Considerable sensitivities are only found west of the Mid-Atlantic Ridge, with maximum values at the western shelf edge. The second baroclinic mode also has an impact on the Florida Current variability, but only when a mean flow is present. A second-mode wave train propagates southwestward from the ocean bottom on the western side of the Mid-Atlantic Ridge between ~36° and 46°N and at Flemish Cap, where the mean flow interacts with topography, to the surface. Other processes such as baroclinic waves along the shelf and local forcing within the Florida Strait are of minor importance.

Description: The residual effect of surface gravity waves on mean flows in the upper ocean is investigated using thickness weighted mean (TWM) theory applied in a vertically Lagrangian and horizontally Eulerian coordinate system. Depth-dependent equations for the conservation of volume, momentum, and energy are derived. These equations allow for (i) finite amplitude fluid motions, (ii) the horizontal divergence of currents and (iii) a concise treatment of both the kinematic and viscous boundary conditions at the sea surface. Under the assumptions of steady and monochromatic waves and a uniform turbulent viscosity, the TWM momentum equations are used to illustrate the pressure- and viscosity-induced momentum fluxes through the surface that are implicit in previous studies of the wave-induced modification of the classical Ekman spiral problem. The TWM approach clarifies, in particular, the surface momentum flux associated with the so-called virtual wave stress of Longuet-Higgins. Overall the TWM framework can be regarded as an alternative to the three-dimensional Lagrangian mean framework of Pierson. Moreover the TWM framework can be used to include the residual effect of surface waves in large-scale circulation models. In specific models that carry the TWM velocity appropriate for advecting tracers as their velocity variable, the turbulent viscosity term should be modified so that the viscosity acts only on the Eulerian mean velocity.

Description: Many aspects of barnacle body form are known to be developmentally plastic. Perhaps the most striking examples of such plasticity occur in their feeding legs and unusually long penises, the sizes and shapes of which can change dramatically and adaptively with changes in conspecific density and local water flow conditions. However, whether variation in overall appendage form is mirrored by structural responses in cuticle and muscle is not known. In order to determine how structural variation underlies phenotypic plasticity in barnacle appendages, we examined barnacles occurring at low and high population densities from one wave-protected and one wave-exposed site. We used histological sectioning and fluorescence microscopy of feeding legs and penises to compare cuticle thickness, muscle thickness, and muscle organization, and artificial penis inflation to compare penis extensibility. We observed striking differences in cuticle thickness, muscle thickness, and muscle organization between sites that differed in water velocity, but we found no clear differences associated with variation in conspecific density. Penis extensibility also did not differ consistently between sites. These results are consistent with an adaptive explanation for much of the remarkable and complex variation in barnacle feeding leg and penis morphology among sites that differ in water velocity.

Description: The tropical Atlantic wind response to El Niño forcing is robust, with weakened northeast trade winds north of the equator and strengthened southeast trade winds along and south of the equator. However, the relationship between sea surface temperature (SST) anomalies in the eastern equatorial Pacific and Atlantic is inconsistent, with El Niño events followed sometimes by warm and other times by cold boreal summer anomalies in the Atlantic cold tongue region. Using observational data and a hindcast simulation of the Nucleus for European Modeling of the Ocean (NEMO) global model at 0.5° resolution (NEMO-ORCA05), this inconsistent SST relationship is shown to be at least partly attributable to a delayed negative feedback in the tropical Atlantic that is active in years with a warm or neutral response in the eastern equatorial Atlantic. In these years, the boreal spring warming in the northern tropical Atlantic that is a typical response to El Niño is pronounced, setting up a strong meridional SST gradient. This leads to a negative wind stress curl anomaly to the north of the equator that generates downwelling Rossby waves. When these waves reach the western boundary, they are reflected into downwelling equatorial Kelvin waves that reach the cold tongue region in late boreal summer to counteract the initial cooling that is due to the boreal winter wind stress response to El Niño. In contrast, this initial cooling persists or is amplified in years in which the boreal spring northern tropical Atlantic warming is weak or absent either because of a positive North Atlantic Oscillation (NAO) phase or an early termination of the Pacific El Niño event.

Description: Initial-value predictability measures the degree to which the initial state can influence predictions. In this paper, the initial-value predictability of six atmosphere–ocean general circulation models in the North Pacific and North Atlantic is quantified and contrasted by analyzing long control integrations with time invariant external conditions. Through the application of analog and multivariate linear regression methodologies, average predictability properties are estimated for forecasts initiated from every state on the control trajectories. For basinwide measures of predictability, the influence of the initial state tends to last for roughly a decade in both basins, but this limit varies widely among the models, especially in the North Atlantic. Within each basin, predictability varies regionally by as much as a factor of 10 for a given model, and the locations of highest predictability are different for each model. Model-to-model variations in predictability are also seen in the behavior of prominent intrinsic basin modes. Predictability is primarily determined by the mean of forecast distributions rather than the spread about the mean. Horizontal propagation plays a large role in the evolution of these signals and is therefore a key factor in differentiating the predictability of the various models.

Description: Sudden stratospheric warmings are prominent examples of dynamical wave–mean flow interactions in the Arctic stratosphere during Northern Hemisphere winter. They are characterized by a strong temperature increase on time scales of a few days and a strongly disturbed stratospheric vortex. This work investigates a wide class of supervised learning methods with respect to their ability to classify stratospheric warmings, using temperature anomalies from the Arctic stratosphere and atmospheric forcings such as ENSO, the quasi-biennial oscillation (QBO), and the solar cycle. It is demonstrated that one representative of the supervised learning methods family, namely nonlinear neural networks, is able to reliably classify stratospheric warmings. Within this framework, one can estimate temporal onset, duration, and intensity of stratospheric warming events independently of a particular pressure level. In contrast to classification methods based on the zonal-mean zonal wind, the approach herein distinguishes major, minor, and final warmings. Instead of a binary measure, it provides continuous conditional probabilities for each warming event representing the amount of deviation from an undisturbed polar vortex. Additionally, the statistical importance of the atmospheric factors is estimated. It is shown how marginalized probability distributions can give insights into the interrelationships between external factors. This approach is applied to 40-yr and interim ECMWF (ERA-40/ERA-Interim) and NCEP–NCAR reanalysis data for the period from 1958 through 2010.

Description: To analyze the probability density distributions of surface turbulent heat fluxes, the authors apply the twoparametric modified Fisher–Tippett (MFT) distribution to the sensible and latent turbulent heat fluxes recomputed from 6-hourly NCEP–NCAR reanalysis state variables for the period from 1948 to 2008. They derived the mean climatology and seasonal cycle of the location and scale parameters of the MFT distribution. Analysis of the parameters of probability distributions identified the areas where similar surface turbulent fluxes are determined by the very different shape of probability density functions. Estimated extreme turbulent heat fluxes amount to 1500–2000 W m22 (for the 99th percentile) and can exceed 2000 W m22 for higher percentiles in the subpolar latitudes and western boundary current regions. Analysis of linear trends and interannual variability in the mean and extreme fluxes shows that the strongest trends in extreme fluxes (more than 15 W m22 decade21) in the western boundary current regions are associated with the changes in the shape of distribution. In many regions changes in extreme fluxes may be different from those for the mean fluxes at interannual and decadal time scales. The correlation between interannual variability of themean and extreme fluxes is relatively low in the tropics, the SouthernOcean, and the Kuroshio Extension region.Analysis of probability distributions in turbulent fluxes has also been used in assessing the impact of sampling errors in theVoluntaryObserving Ship (VOS)-based surface flux climatologies, allowed for the estimation of the impact of sampling in extreme fluxes. Although sampling does not have a visible systematic effect onmean fluxes, sampling uncertainties result in the underestimation of extreme flux values exceeding 100 W m22 in poorly sampled regions.

Description: Antarctic Intermediate Water (AAIW) is a dominant Southern Hemisphere water mass that spreads from its formation regions just north of the Antarctic Circumpolar Current (ACC) to at least 20°S in all oceans. This study uses an isopycnal climatology constructed from Argo conductivity–temperature–depth (CTD) profile data to define the current state of the AAIW salinity minimum (its core) and thence compute anomalies of AAIW core pressure, potential temperature, salinity, and potential density since the mid-1970s from ship-based CTD profiles. The results are used to calculate maps of temporal property trends at the AAIW core, where statistically significant strong circumpolar shoaling (30–50 dbar decade−1), warming (0.05°–0.15°C decade−1), and density reductions [up to −0.03 (kg m−3) decade−1] are found. These trends are strongest just north of the ACC in the southeast Pacific and Atlantic Oceans and decrease equatorward. Salinity trends are generally small, with their sign varying regionally. Bottle data are used to extend the AAIW core potential temperature anomaly analysis back to 1925 in the Atlantic and to ~1960 elsewhere. The modern warm AAIW core conditions appear largely unprecedented in the historical record: biennially and zonally binned median AAIW core potential temperatures within each ocean basin are, with the notable exception of the subtropical South Atlantic in the 1950s–70s, 0.2–1°C colder than modern values. Zonally averaged sea surface temperature anomalies around the AAIW formation latitudes in each ocean and sectoral southern annular mode indices are used to put the AAIW core property trends and variations into context.

Description: Anthropogenic emissions of greenhouse gases could lead to undesirable effects on oceans in coming centuries. Drawing on recommendations published by the German Advisory Council on Global Change, levels of unacceptable global marine change (so-called guardrails) are defined in terms of global mean temperature, sea level rise, and ocean acidification. A global-mean climate model [the Aggregated Carbon Cycle, Atmospheric Chemistry and Climate Model (ACC2)] is coupled with an economic module [taken from the Dynamic Integrated Climate–Economy Model (DICE)] to conduct a cost-effectiveness analysis to derive CO2 emission pathways that both minimize abatement costs and are compatible with these guardrails. Additionally, the “tolerable windows approach” is used to calculate a range of CO2 emissions paths that obey the guardrails as well as a restriction on mitigation rate. Prospects of meeting the global mean temperature change guardrail (2° and 0.2°C decade−1 relative to preindustrial) depend strongly on assumed values for climate sensitivity: at climate sensitivities 〉3°C the guardrail cannot be attained under any CO2 emissions reduction strategy without mitigation of non-CO2 greenhouse gases. The ocean acidification guardrail (0.2 unit pH decline relative to preindustrial) is less restrictive than the absolute temperature guardrail at climate sensitivities 〉2.5°C but becomes more constraining at lower climate sensitivities. The sea level rise and rate of rise guardrails (1 m and 5 cm decade−1) are substantially less stringent for ice sheet sensitivities derived in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, but they may already be committed to violation if ice sheet sensitivities consistent with semiempirical sea level rise projections are assumed.

Description: Historical hydrographic data (1940s–2010) show a distinct cross-slope difference of the lower halocline water (LHW) over the Laptev Sea continental margins. Over the slope, the LHW is on average warmer and saltier by 0.2°C and 0.5 psu, respectively, relative to the off-slope LHW. The LHW temperature time series constructed from the on-slope historical records are related to the temperature of the Atlantic Water (AW) boundary current transporting warm water from the North Atlantic Ocean. In contrast, the on-slope LHW salinity is linked to the sea ice and wind forcing over the potential upstream source region in the Barents and northern Kara Seas, as also indicated by hydrodynamic model results. Over the Laptev Sea continental margin, saltier LHW favors weaker salinity stratification that, in turn, contributes to enhanced vertical mixing with underlying AW.

Description: The equatorial deep jets (EDJ) are a striking feature of the equatorial ocean circulation. In the Atlantic Ocean, the EDJ are associated with a vertical scale of between 300 and 700 m, a time scale of roughly 4.5 years and upward energy propagation to the surface. It has been found that the meridional width of the EDJ is roughly 1.5 times larger than expected based on their vertical scale. Here we use a shallow water model for a high order baroclinic vertical normal mode to argue that mixing of momentum along isopycnals can explain the enhanced width. A lateral eddy viscosity of 300 m2 s−1 10 is found to be sufficient to account for the width implied by observations.

Description: The suggestion is advanced that the remarkably low static stability of Antarctic surface waters may arise from a feedback loop involving global deep-water temperatures. If deep-water temperatures are too warm, this promotes Antarctic convection, thereby strengthening the inflow of Antarctic Bottom Water into the ocean interior and cooling the deep ocean. If deep waters are too cold, this promotes Antarctic stratification allowing the deep ocean to warm because of the input of North Atlantic Deep Water. A steady-state deep-water temperature is achieved such that the Antarctic surface can barely undergo convection. A two-box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts, such as the bounds on the operation of this loop. The model illustrates the possible dominating influence of Antarctic upwelling rate and Antarctic freshwater balance on global deep-water temperatures.

Description: The importance of decadal climate variability (DCV) research is being increasingly recognized, including by the World Climate Research Program (WCRP) and the Intergovernmental Panel on Climate Change (IPCC). An improved understanding of DCV is very important because stakeholders and policymakers want to know the likely climate trajectory for the coming decades for applications to water resources, agriculture, energy, and infrastructure development. Responding to this demand, many climate modeling groups in the United States, Europe, Japan, and elsewhere are gearing up to assess the potential for decadal climate predictions. The magnitudes of regional DCV often exceed those associated with the trends resulting from anthropogenic changes. Therefore, differentiating between the two is also very important for planning, implementation, and national and international treaties.

Description: Simple idealized layered models and primitive equation models show that the meridional gradient of the zonally averaged pressure has no direct relation with the meridional flow. This demonstrates a contradiction in an often-used parameterization in zonally averaged models. The failure of this parameterization reflects the inconsistency between the model of Stommel and Arons and the box model of Stommel, as previously pointed out by Straub. A new closure is proposed. The ocean is divided in two dynamically different regimes: a narrow western boundary layer and an interior ocean; zonally averaged quantities over these regions are considered. In the averaged equations three unknowns appear: the interior zonal pressure difference Delta p(i), the zonal pressure difference Delta p(b) of the boundary layer, and the zonal velocity us at the interface between the two regions. Here Delta p(i) is parameterized using a frictionless vorticity balance, Delta p(b), by the difference of the mean pressure in the interior and western boundary, and u(delta) by the mean zonal velocity of the western boundary layer. Zonally resolved models, a layer model, and a primitive equation model validate the new parameterization by comparing with the respective zonally averaged counterparts. It turns out that the zonally averaged models reproduce well the buoyancy distribution and the meridional flow in the zonally resolved model versions with respect to the mean and time changes.

Description: Continuous estimates of the oceanic meridional heat transport in the Atlantic are derived from the Rapid Climate Change–Meridional Overturning Circulation (MOC) and Heatflux Array (RAPID–MOCHA) observing system deployed along 26.5°N, for the period from April 2004 to October 2007. The basinwide meridional heat transport (MHT) is derived by combining temperature transports (relative to a common reference) from 1) the Gulf Stream in the Straits of Florida; 2) the western boundary region offshore of Abaco, Bahamas; 3) the Ekman layer [derived from Quick Scatterometer (QuikSCAT) wind stresses]; and 4) the interior ocean monitored by “endpoint” dynamic height moorings. The interior eddy heat transport arising from spatial covariance of the velocity and temperature fields is estimated independently from repeat hydrographic and expendable bathythermograph (XBT) sections and can also be approximated by the array. The results for the 3.5 yr of data thus far available show a mean MHT of 1.33 ± 0.40 PW for 10-day-averaged estimates, on which time scale a basinwide mass balance can be reasonably assumed. The associated MOC strength and variability is 18.5 ± 4.9 Sv (1 Sv ≡ 106 m3 s−1). The continuous heat transport estimates range from a minimum of 0.2 to a maximum of 2.5 PW, with approximately half of the variance caused by Ekman transport changes and half caused by changes in the geostrophic circulation. The data suggest a seasonal cycle of the MHT with a maximum in summer (July–September) and minimum in late winter (March–April), with an annual range of 0.6 PW. A breakdown of the MHT into “overturning” and “gyre” components shows that the overturning component carries 88% of the total heat transport. The overall uncertainty of the annual mean MHT for the 3.5-yr record is 0.14 PW or about 10% of the mean value.

Description: The water mass structure of the Arctic Ocean is remarkable, for its intermediate (depth range ~150–900 m) layer is filled with warm (temperature 〉0°C) and salty water of Atlantic origin (usually called the Atlantic Water, AW). This water is carried into and through the Arctic Ocean by the pan-Arctic boundary current, which moves cyclonically along the basins’ margins (Fig. 1). This system provides the largest input of water, heat, and salt into the Arctic Ocean; the total quantity of heat is substantial, enough to melt the Arctic sea ice cover several times over. By utilizing an extensive archive of recently collected observational data, this study provides a cohesive picture of recent large-scale changes in the AW layer of the Arctic Ocean. These recent observations show the warm pulse of AW that entered the Arctic Ocean in the early 1990s finally reached the Canada Basin during the 2000s. The second warm pulse that entered the Arctic Ocean in the mid-2000s has moved through the Eurasian Basin and is en route downstream. One of the most intriguing results of these observations is the realization of the possibility of uptake of anomalous AW heat by overlying layers, with possible implications for an already-reduced Arctic ice cover.

Description: Vertical mixing in the bottom boundary layer and pycnocline of the Laptev Sea is evaluated from a rapidly sampled 12-h time series of microstructure temperature, conductivity, and shear observations collected under 100% sea ice during October 2008. The bottom boundary turbulent kinetic energy dissipation was observed to be enhanced (ϵ ∼ 10−4 W m−3) beyond background levels (ϵ ∼ 10−6 W m−3), extending up to 10 m above the seabed when simulated tidal currents were directed on slope. Upward heat fluxes into the halocline-class waters along the Laptev Sea seabed peaked at ∼4–8 W m−2, averaging out to ∼2 W m−2 over the 12-h sampling period. In the Laptev Sea pycnocline, an isolated 2-h episode of intense dissipation (ϵ ∼ 10−3 W m−3) and vertical diffusivities was observed that was not due to a localized wind event. Observations from an acoustic Doppler current meter moored in the central Laptev Sea near the M2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under-ice stress vector. Upward cross-pycnocline heat fluxes from the Arctic halocline peaked at ∼54 W m−2, resulting in a 12-h average of ∼12 W m−2. These results highlight the intermittent nature of Arctic shelf sea mixing processes and how these processes can impact the transformation of Arctic Ocean water masses. The observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near-inertial kinetic energy to drive vertical mixing on the Arctic shelves.

Description: Lambert, cosmological letters, fixed stars, nebulae, island universe, teleology, teleological, enlightenment, enlightened, romanticism, romantic, hypothesis, physical-teleological, speculation, imagination, stability, solar system, cosmology, astronomy, comet, magic, alchemy, pietism, science, arts, philosophy, Newtonian. - Johann Heinrich Lamberts Cosmological Letters was published 1761 in Augsburg. Lambert tried to expose a theory of the structure of the universe as a whole, that is, a theory that was able to involucrate all sorts of observed celestial bodies, like 'fixed stars' und nebulae. Lambert tackles his task mixing two disciplines, which in principle seem to be incompatible: Newtonian physics and teleology. Lambert's speculative and imaginative way to formulate his hypotheses shows resemblances to the way of making science developed during the romantic period, disagreeing with the methods of enlightenment, movement to which Lambert is usually associated. A central aspect of this thesis is to study Lambert's figure in relation to this two traditions, with the finality to deal with the compression of his ideas in depth, in light of the transition between the enlightened vision of the world and the romantic one.

Description: thesis

Description: The different benthic foraminiferal species (epibenthic as well as endobenthic) colonize wide areas of the ocean floor and are widely used for paleoceanographic reconstructions. To improve these reconstructions, it is an important part in research to continuously develop and refine proxies by e.g. improving measuring techniques as well as introducing other species in paleoceanograhpy. The main focus of the presented thesis is a regional examination of the trace element ratios of the rarely used benthic foraminifer Oridorsalis umbonatus and the investigation of their suitability for paleoceanographic applications. Since O. umbonatus is not very abundant in the sediments, it was necessary . as a prerequisite for such studies . to investigate, whether laser ablation ICP-MS can be used for trace element measurements on benthic foraminifera. Therefore, as a first step, trace elements were measured using laser ablation ICP-MS on a set of modern core top samples collected along a depth transect on the continental slope off Namibia at 25.5.S (320 . 2300m water depth; 2.9. to 10.4.C). The Mg/Ca ratios where than calibrated against bottom water temperatures (BWT). The study demonstrates clearly that benthic foraminiferal trace elements can be reliably measured with the laser ablation technique and that the Mg/Ca ratio of O. umbonatus has the potential to be used as a proxy for BWTs...

Description: thesis

Description: In the early 1990`s the first IPCC report stated the effect of anthropogenic CO2 emissions on global warming and John Martin`s Iron Hypothesis (Martin and J.H 1990), relating atmospheric dust deposition, a major source of iron to the surface ocean, to the CO2 concentration in the atmosphere and the last ice age, culminating in the well known sentence Give me (half) a tanker of iron and I’ll give you a new ice age!. Since then, several large-scale in situ Fe fertilisation experiments revealed that in large areas of the ocean, the so called high nutrient low chlorophyll (HNLC) areas, phytoplankton growth is partly limited by depleted Fe conditions (Geider et al. 1994; De Baar and Boyed 2000; Boyd et al. 2007). The ocean receives Fe from upwelling, riverine input, melting icebergs, atmospheric dust input, input from anoxic sediments, hydrothermal vents and direct recycling by organisms(Tovar-Sanchez et al. 2007). However, in HNLC regions the Fe input to surface waters is very low resulting in Fe limitation of phytoplankton growth. Fe is an important nutrient for marine phytoplankton (Geider et al. 1994; Falkowski et al. 1998; Morel and Price 2003), being essential in metabolic reactions like the photosynthetic electron transport and the assimilation of nitrogen. It is also required for the synthesis of chlorophyll (Martin et al. 1988; Maldonado et al. 1999) as well as for the functioning of the enzyme superoxide dismutase which inhibits the breakdown of chlorophyll by superoxide radicals (Coale 1991)...

Description: thesis

Description: Mg/Ca ratios in benthic foraminiferal shells are frequently used in paleoceanographic studies to estimate past bottom water temperatures. Apart from temperature, other factors may exert additional influences on foraminiferal Mg/Ca. These include the Mg/Ca ratio of seawater, partial dissolution of shell calcite, salinity, physiological effects, and, probably of capital importance, the carbonate chemistry of seawater. In this context, the seperate effects of temperature and seawater carbonate chemistry on the magnesium incorporation into benthic foraminideral calcite are unraveled and quantified in this thesis...

Description: thesis

Description: Organic-walled dinoflagellate cysts, oxidation, degradation, organic matter. - Species-selective aerobic decomposition affects fossil organic-walled dinoflagellate cyst (dinocyst) records and hence dinocyst-based interpretations of primary productivity and oceanographic conditions. However, since the recognition of dinocyst species sensitive and resistant to oxic degradation (S- and R-cysts, respectively) it has become apparent that R-cysts may still serve as reliable productivity and oceanographic conditions proxies. On the other hand S-cysts provide a way to quantify aerobic degradation of organic matter (OM) and past bottom-water O2 concentrations. OM degradation plays a key role in global carbon cycling and is important for global climate change. Therefore dinocysts are a valuable tool for estimating the rate of diagenetic process. Questions concerning species-selective aerobic degradation still remain and will be adressed here. To obtain information on the rate of S-cyst decomposition, the relationship between S-cyst degradation and O2 concentrations, and the aerobic degradation of extinct dinocyst species, a natural exposure experiment has been conducted and studies of both Quaternary and pre-Quaternary material from sediment cores were executed. The exposure experiment was conducted in the natural setting of the Eastern Mediterranean. During a 15 month exposure period to oxic water masses, concentrations of S-cysts (Brigantedinium spp. and Echinidinium granulatum) decreased by 24 to 57%. However, taxa such as Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum and Impagidinium aculeatum demonstrated a slight increase in concentration, indicating resistance to aerobic degradation. These results show that even short-term exposure to oxygen may cause considerable changes in the dinocyst assemblage ...

Description: thesis

Description: Marine snow, underwater cameras, particle flux, aggregation, suspended particulate matter, particle transport. - This study focusses on the vertical distribution and transportation pathways of marine particles off NW-Africa with aid of optical methodologies. A profiling camera system and a remotely operated vehicle (ROV) was used for in-situ observations on the distribution, transport processes and sinking behaviour of marine particulate matter. Between the regional areas of investigation Cape Blanc, Dakhla and Cape Bojador significant differences could be observed with respect to distribution and transportation patterns. These differences are primarily related to the different primary production conditions between the investigation areas. Primary production is the most important factor for the abundance of particulate matter, where highest particle concentrations in the entire water column were seen off Cape Blanc. Next to primary production, water depth, currents and density gradients are factors influencing the particle distribution patterns. With respect to the prevailing transport processes, the Cape Blanc region is characterised by vertically orientated transport patterns. In addition to the continuous supply of large, relatively fast sinking particle aggregates a sinking event could be documented for the first time in-situ in the water column. These events deliver huge amounts of particulate matter from the ocean surface ...

Description: thesis

Description: The dissolution kinetics of gypsum and anhydrite have been measured under various conditions. For gypsum an almost linear rate equation R=ks1(1-c/ceq)n1 is valid, where R is the surface rate, n1 1 is the kinetics order, c is the total calcium concentration at the surface, and ceq the equilibrium concentration with respect to gypsum. For the determination of the entire dissolution kinetics a batch set-up was used. This batch experiment reveals a dissolution rate equation R=ks1(1-c/ceq)n1 which switch close to equilibrium to a nonlinear rate equation R=ks2(1-c/ceq)n2 with n2 4.5. The experimentally observed dissolution rates from the batch experiment could be fitted by only minor variations with a mixed kinetics model. The rotating disk experiment on anhydrite reveals a surface controlled rate equation. For anhydrite the observed experimentally dissolution rates by a batch experiment are described by R=ks(1-c/ceq})n, where ks is the surface rate constant and n 4.2 is the kinetic order. Furthermore, a method for the determination of the rate equation parameters was developed ...

Description: thesis

Description: Madagascar; Jurassic; Karoo; Gondwana; Breakup; Rift; Microfauna; Macrofauna; Ammonites; Indian Ocean. - The breakup of Gondwana along the former East African Orogen is widely interpreted to have lasted from the Late Palaeozoic to the Callovian. The present study indicates that the Permian-Triassic or Karoo phase of rifting was not responsible for the separation of East- and West-Gondwana, since that rift system failed in the Late Triassic. Instead the breakup of Gondwana occurred in the Late Liassic. The pre-rift phase in the Morondava Basin is represented by the Karoo deposits, and the syn-rift phase is recorded by Toarcian marine shales, locally overlain by Aalenian sandstones. A major Early Bajocian unconformity is interpreted as the breakup unconformity. The initial post-rift or drift phase is represented by the Bajocian-Bathonian carbonates, marls and sandstones of coastal plain environment and a coastal barrier/lagoon complex. During the Bathonian the siliciclastic shoreface system moved basinward. Callovian-Early Kimmeridgian shales with interbedded iron-oolites represent ...

Description: thesis

Description: Turbulence, ice ridge, polynja, drag coefficient. - Polarstern (PS) cruise ARK XII led into the Laptev Sea and into the Kara Sea. Measurements of atmospheric processes within the polar surface layer were performed by a turbulence probe mounted at the bow crane of the ship.The meteorological conditions during the cruise were characterised by moderate winds and low temperature differences between the atmosphere and the underlying surface.Detailed information about the variation of meteorological parameters and of the surface fluxes were achieved as a function of the surface characteristics. The measurements are used to analyse ...

Description: thesis

Description: thesis

Description: thesis

Description: thesis

Description: This thesis describes the adaptive shallow water model PLASMA-FEMmE. It solves on the sphere the shallow water equations, the prototype for partial differential equations in atmospheric modeling, using a semi-implicit semi-Lagrangian time step and linear finite elements. Both statically and dynamically adapted grids created by the grid generator amatos are investigated. The results are compared with those of the predecessor model FEMmE that uses a static uniform grid. The outcome demonstrates the capability of the chosen approach as well as its limits. Grid adaptation can easily be achieved with amatos. No reflexions at the grid interfaces are observed. Though in one test case instabilities are released at the grid interfaces. The numerical errors are reduced without a considerable enhancement of the computational effort in another test case with a well-known analytical solution. In respect to the conservation properties the results are more complicated. Mass conservation can be achieved in one test case with an appropriate static grid. In case of complex flow regimes all conservation properties are weakened during the simulation using dynamic grid adaptation...

Description: thesis

Description: The polar ice sheets are unique paleoclimatic archives and play an important role in recent and future climate. The melting of the big freshwater reservoirs will not only increase the global sea level, but will also influence the ocean currents. Therefore, it will be of particular interest to improve the currently available numeric climate models to achieve more accurate statements about climatic change and its consequences. In this work, the evaluation and the different applications of GPS and altimetry data will be described in respect to enhance models. The antarctic area of investigation, Dronning Maud Land (DML), is of particular interest for German polar research, because both the overwintering station Neumayer and the summer station Kohnen are located within it. In the surroundings of these two stations, highly accurate kinematic GPS measurement were made, which will be the basis for the digital elevation model presented here. Because these data are spatially limited, they are supplemened with remotely sensed data. For this purpose, two airborne altimetry data sets and spaceborne laser altimetry data of the Ice, Cloud, and land Elevation Satellite (ICESat) are used...

Description: thesis

Description: Marine sediments, diagenesis, anoxic environments, paleomagnetism, low-temperature magnetism, magnetic Fe-Ti-Oxides. - Magnetic particles usually occur in very minor concentrations in igneous and sedimentary rocks, soils, volcanic ashes, dusts and even in living organisms. Many of these magnetic grains are capable of carrying a stable permanent magnetization and therefore act as recorders of the recent and ancient Earth's magnetic field. Thus paleomagnetism refers to the study of this remanent magnetization in sedimentary and volcanic rocks through time. From this magnetization, directional intensity information can be recovered concerning the geomagnetic field that prevailed at the sample location at the time of the rock formation. The magnetic parameter on which such paleomagnetic studies are based is the natural remanent magnetization (NRM). In continental margin regions the remanence acquisition process is often complicated by post-depositional modifications of the original magnetic material. After deposition magnetic minerals can be altered or new magnetic phases can be formed. Consequently the original NRM might be obscured or even fully erased. The process of diagenesis and authigenesis may thus seriously compromise paleomagnetic interpretation. Therefore our knowledge of the geomagnetic field behavior based on sediment records from continental margin regions remains limited. To obtain fully reliable information about the geomagnetic field or paleoenvironmental conditions from continental margin regions, the effect of early diagenetic processes occurring after deposition of the sediment must be understood in detail.

Description: thesis

Description: Anaerobe Oxidation of Methane, AOM, methanotrophy, stable isotope labeling, stable isotope probing, carbon assimilation, flow-through columns, ANME, Seep-SRB, Gullfaks, Tommeliten. - Anaerobic oxidation of methane (AOM) performed by consortia of methanotrophic archaea (ANME) and sulfate reducing bacteria (SRB) is the major sink of methane in marine sediments. This thesis describes methane consumption at two of the most active North Sea cold seeps (Gullfaks, Tommeliten), their microbial community and the resulting lipid biomarker patterns. Experiments in flow-through setups are presented, focusing on physiological parameters of AOM activity such as different methane and sulfate concentrations and on the tolerance of AOM to starvation periods. The roles of inorganic carbon (DIC) and methane as carbon sources for the microbial community performing AOM were examined combining stable isotope probing and lipid biomarker analyses. For archaea substantial uptake of carbon from DIC and methane was found, indicting a novel carbon assimilation pathway. Biomass from SRB was exclusively labeled by DIC indicating a methane dependent, but autotrophic growth consortial SRB.

Description: thesis

Description: Black Sea, seafloor seepage, mud volcanoes, seeps, fluid migration, gas hydrates, diapirs. - The Black Sea is the worldwide largest anoxic basin with thick gas rich sediments facilitating seafloor seepage, which is widely distributed along the continental slopes of the Black Sea. In two areas, the Sorokin Trough off Crimea and at the continental slope off Batumi (Georgia), the distribution, structure and evolution of two different vent systems and their relation to fluid migration pathways and gas/gas hydrate occurrences have been investigated by means of high resolution multichannel seismic data. In both regions, the distribution of seafloor seepage is controlled by fluid migration along permeable pathways associated with diapiric uplift in the subsurface. In the Sorokin Trough, seepage is expressed by intensive material upflow and the formation of mud volcanoes; offshore Batumi, gas seeps with low material flux dominate. In the Sorokin Trough, most mud volcanoes are associated with near-subsurface mud diapirs. The great morphological variability of the mud volcanoes reflects different driving mechanisms, which depend on the availability of permeable fluid migration pathways and the depositional environment. A 3D seismic dataset images the detailed three-dimensional ...

Description: thesis

Description: Ozone, balloon-borne measurements, atmospheric trace gases, concentration profiles, climate change. - In the frame of this work, a new small-size balloon-borne sonde was developed. A miniature grating spectrometer in the sonde measures simultaneously the solar spectral irradiance at a wide wavelength range from 200 to 850. As a first application, ozone profiles have been determined by measuring the changes in the spectral irradiance, caused by ozone absorption in the Huggins band. The wide spectral coverage of the spectrometer offers the possibility for measurements of other trace gases which absorb within the wavelength range, e.g. NO2 and BrO. The low weight of the new sonde (1.7 kg), the moderate price, and the autonomous portable telemetry system makes it a very versatile tool for satellite validation and for case studies, which requires a high number of launches. The newly developed sonde works well without temperature stabilisation, even so the spectrometer experiences rather large temperature changes (15 - 20 K) during the ascent through the atmosphere. Laboratory measurements were performed in ...

Description: thesis

Description: Photooxidants play an important role for the oxidation capacity of the troposphere. The presented work deals with seasonal changes of atmospheric photooxidants like hydrogen peroxide (H2O2), methylhydroperoxide (MHP) and formaldehyde (HCHO). The principal purpose was to follow and quantify the mixing-ratios of these photochemical species for the first time over a complete annual cycle in Antarctica. During two field campaigns at the German Antarctic station Neumayer (overwintering campaign from January 1997 until March 1998 and a shorter campaign from January to March 1999) continuous measurements of atmospheric mixing-ratios were performed. A continuous wet-chemical technique was used for peroxides and formaldehyde sampling and analysis. Species were quantified by fluorescence detection. In order to compare the results and measurements with well-known reaction mechanisms a photochemical box model was applied. The obtained time series show a pronounced seasonal variation with higher values during summer. For the first time atmospheric concentrations of H2O2, MHP and HCHO were documented during polar night in winter. The mixing-ratios were significantly higher than expected due to missing actinic radiation essential for photochemical production. Trajectory analyses and calculations with a three-dimensional model showed that during winter the mixing-ratios of photooxidants are mainly affected by long-range transport in the free troposphere. Investigations during the Antarctic ó́zone hole period ́́show no significant impact of the increased UV-B radiation on the photooxidants. The findings of this work contribute to a better understanding of the photochemistry of the investigated trace gases in the clean troposphere of Antarctica and provide a useful data record for further photochemical modeling.

Description: thesis

Description: Besides measurements of atmospheric trace gases and laboratory studies of chemical reactions, modelling has been recognised to be of increasing importance to improve our knowledge of the atmosphere and the capabilities of photochemical models. Main scope of this work was the development of a photochemical atmospheric model, which was especielly designed for the interpretation of Differential Optical Absorption measurments (DOAS). This model has been used to improve our knowledge of atmospheric chemistry. For example, for the first time it was possible to demonstrate that a significant amount of IO in a range of 0.65 to 0.8 pptv is present in the stratosphere in the polar region (Ny-Alesund,Spitzbergen). Moreover it has been shown that such amounts of stratospheric IO lead to an additional Ozone loss in the range of 10 % in cold arctic winters.

Description: thesis

Description: Ozone profile retrieval, ERS-2, GOME, FURM, ozone decline, Northern hemisphere. - Measurements of stratospheric ozone over the Northern hemisphere forthe winter/spring periods of 1997 to 2000 taken with the GOMEinstrument were used to derive the chemical ozone depletion inside thepolar vortex. GOME onboard the ERS-2 satellite measures radiationcoming from the Earth in the UV/vis spectral range.To discern the chemical depletion from dynamical influences, a modelwas developed to calculate vortex averaged diabatic descent ratesusing the radiative transfer model MIDRAD and the FURM ozoneprofiles. The permeability of the Arctic vortex was analysed by usingthe trajectory model TANGO in conjunction with a reverse domainfilling algorithm, developed within the framework of this thesis.The chemical ozone ...

Description: thesis

Description: Sea ice is a very important component of the climate system. While the Arctic sea ice extent has retreated during the past 20 years, it has remained constant in the Antarctic. In order to better understand the role of sea ice in the climate system in the context of global warming currently used coupled Atmosphere-Ocean Global Circulation Models have to be improved. This requires to know the sea ice concentration C for a long period for both hemispheres and at the best possible spatial resolution. Currently used methods to obtain C like the NASA Team (NT) algorithm are based on data acquired by the Special Sensor Microwave/Imager (SSM/I) at 19 and 37GHz. The SEA LION (SL) algorithm presented here allows to infer C from the polarization P at 85GHz taking advantage of the higher spatial resolution at this frequency. However, the decrease of P caused by the weather influence leads to an overestimation of C. Therefore, P is corrected using a radiative transfer model and atmospheric data taken from Numerical Weather Prediction models and/or derived from SSM/I measurements. The various sea ice and snow properties are considered calculating monthly sea ice tie points. The average standard deviation of C derived with the SL algorithm is 12% for C 〈 50% and below 5% for C 〉 90%. The SL ice edge agrees within 10km with the one evident in VIS/IR images. The SL ice concentration gradient across the marginal ice zone (MIZ) agrees much better with the one evident in SAR images compared to results of the NT algorithm. Using the higher spatial resolution at 85GHz the SL algorithm allows to detect smaller open water areas than known algorithms. A major limitation of the SL algorithm arises from the quality of atmospheric data needed for the weather correction. A spatial resolution of these data lower than the 85GHz SSM/I channels and/or a time lag larger than half an hour between both data sets can cause relative errors above 100%, particulary in the cloud-covered parts of the MIZ.

Description: thesis

Description: Ozone chemistry, tracer measurements, radiometry, airborne,submillimeterwave, Arctic, stratosphere. - The Airborne Submillimeter Radiometer (ASUR) is a passive heterodyne instrument using a superconducting detector with an instrumental frequency range from 604.3 to 662.3 GHz.Operating onboard an aircraft to avoid absorption by tropospheric water vapor key species of the stratospheric ozone chemistry can be detected for a vertical altitude range from 15 to 55 km. In the winter 1999/2000 the ASUR instrument participated in the THESEO 2000/SOLVE project onboard the NASA research aircraft DC-8. Three deployments were carried ...

Description: thesis

Description: thesis

Description: WSDW, water mass spreading, numerical model, lagrangian trajectories, Weddell Scotia Confluence. - The deep Scotia Sea is filled with ventilated Weddell Sea Deep Water (WSDW). This in turn is an essential contributor to the ventilation of the World Ocean abyss. A primitive equation, hydrostatic, ocean general circulation model (BRIOS1.1) with terrain-following coordinate is used to investigate the water mass export from the Weddell Sea. The model is circumpolar focusing on the Weddell Sea, with particularly high resolution (2̃0 km) in the DOVETAIL area. The northern limb of the Weddell Gyre exhibits an eastward Weddell Sea Deep Water transport across 44ʿW of 24 Sv. Export rates of Weddell Sea Deep Water through gaps in theSouth Scotia Ridge are estimated to be 6.4 Sv with a semi-annual cycle of ± 0.6 Sv, which can be correlated to atmospheric cyclone activity and Weddell Gyre strength. Sensitivity studies considering extreme sea ice conditions in the Weddell Sea show higher (lower) exports in years of minimum (maximum) winter sea ice extent. This can be attributed to the local change of the surface stress achieved by wind and ice. Lagrangian ...

Description: thesis

Description: Carbon export; SeaWiFS; variability; upwelling; Atlantic Ocean; chlorophyll filament; SeaWiFS; SST. - The North Atlantic off NW Africa is characterized by the trade wind induced upwelling of cold and nutrient rich waters. As one of most strongest eastern boundary upwelling areas it is marked by low sea surface temperature and high bio-production, both subject to strong seasonal and interannual variations.Satellite measurements of sea surface temperature (SST) and chlorophyll-a (Chl-a) in the upper water-column were used to (a) recognize the upwelling of deep water and its distribution and mixing in the surface, (b) identify the development of phytoplankton blooms and (c) provide further insights in the characteristics of its variations.Measurements of surface Chl-a were compared to deep-sea fluxes of organic carbon in order to determine the relationship between both parameters and to further calculate the export of Corg and the export variation strength.The off-shore extension of SST-defined upwelling from 1988 through 1999 between 18ʿ and 25ʿN shows maxima in January and May/June with an average area of 140,000 km2 (standard deviation of 20,000 km2). Minima in August exhibit an extension of 43,000 km2 (15,000 km2 standard deviation). A correlation between ...

Description: thesis

Description: Thermohaline circulation, variability, energy and moisture balance model, paleoceanography. - Freshening of high latitude surface water can change the large scale oceanic transport of heat and salt. Consequently, atmospheric and sea ice perturbations over the deep water production sites excite a large scale response establishing an oceanic t̀̀eleconnection'' with time scales of years to centuries. To study these feed-backs, an atmospheric energy and moisture balance model (EMBM), predicting the heat and fresh water fluxes at the surface, and a thermodynamic sea ice model were constructed and coupled to the GFDL ocean model MOM2. The heat and moisture transports by transient eddies in the EMBM are parameterized by diffusion. The coupled model reproduces many aspects of today's oceanic circulation. The most interesting features of the coupled model are the sensitivity of the thermohaline circulation to changes in the configuration, the multidecadal variability in the ocean-sea ice system, and the behaviour of the thermohaline circulation during transitions between glacial and interglacial periods. A very strong thermohaline circulation develops in the coupled system that is not evident in the stand-alone ocean model. An interesting aspect of this behaviour is the existence of a maximum strength in the overturning. Beyond this maximum, evaporation in the subtropics cannot balance the northward salt-transport. As a result, the watermasses over the deep water production sites become fresher, leading to a collapse of the thermohaline circulation. The associated changes in the sea ice cover prevent the system to recover. ...

Description: thesis

Description: This study focuses on the interactions between climate and ice sheets in order to obtain a better understanding of the processes involved. Two periods in the geological past are explored; the Middle Miocene and the mid-Pliocene. For both periods, foraminiferal oxygen-isotope records from deep-sea sediment cores as well as stratigraphical data, suggest a global sea-level lowering. The magnitude of these reductions in sea level indicate large-scale ice-sheet build-up. However, the origin of these events and even the geographic locations of the ice sheets, are still under discussion. The ice sheet-climate model developed in this study provides a tool to test some of the hypotheses brought forward to explain the ice-sheet expansion events. It describes the Antarctic ice sheet and is forced by a climate component based on energy and mass balances. Further more, the model computes the oxygen-isotopic composition of the ice-sheet, thereby providing the possibility to compare numerical results directly to deep-sea sediment records. Numerical experiments focus on the interactions between atmospheric CO2, temperature, ice volume (sea-level equivalent) and the isotopic composition of sea water...

Description: thesis

Description: The Late BarremianLate Aptian interval was characterised by several major changes in the ocean/climate system related to the onset of the Mid-Cretaceous greenhouse world. North Africansedimentary deposits offer excellent archives of the ecological changes on the southern Tethyscontinental margin during this time interval. In the present phD thesis sedimentology, palaeontology,biostratigraphy, chemostratigraphy, and geochemistry are combined to reconstruct the palaeoenvironmental evolution and sea-level changes of the Tunisian carbonate platform margin.Respect is paid to major palaeoceanographic and palaeoclimatic events including the late Early Aptian Oceanic Anoxic Event 1a (OAE 1a) and two time intervals associated with widespread carbonate platform drowning in the early- and mid-Late Aptian. The last chapter deals with the cephalopod fauna of the platform margin. Results of the detailed regional investigations are compared to global marine palaeoenvironments and discussed in a broad geological context...

Description: thesis

Description: ICP-MS, Time of Flight, laser ablation, solid and liquid samples, ice cores, Antarctica, mineral dust, trace element analysis. - The analysis of the inorganic composition of climatic archives provides proxies for climate reconstruction. For many applications commercially available inductively coupled plasma quadrupole mass spectrometry (ICP-Q-MS) systems are used for investigations. One aim of this thesis was to test the laser ablation (LA)-ICP-Q-MS method for the analysis of different sample matrices (polar ice cores, bivalves, frozen lake sediment cores). The main limitation of LA-ICP-Q-MS measurements is the number of analysed isotopes, especially for point scan analysis of embedded particles in the ice matrix and the analysis of growth bands of bivalve shells. Analysing as many isotopes as possible is of interest to deduce e.g. the corresponding source region of embedded particles in the ice matrix. The quasi-simultaneous detection of several isotopes of transient signals is realised in ICP-Time of Flight-MS (ICP-TOF-MS) systems. The applicability of the newly developed ICP-TOF-MS system for ice core analysis in climatic research was explored in this thesis. With the present experimental setup the analysis of trace elements in ice core samples is only possible for liquid samples. The accuracy and precision compares to well established ICP-Q-MS systems. Using the Aridus II as sample introduction system the signal sensitivity was 2-10 times lower for the ICP-TOF-MS compared to ICP-Q-MS systems. Calibration studies and investigation of reference materials showed that the calibration range is limited to an order of magnitude of about 10exp4 to 10exp5 except for m/z ratios between 23 amu and 72 amu where it is even lower. The observed ...

Description: thesis

Description: Sea-ice, Finite Element Sea-Ice Model, Kalman Filter, Data Assimilation. - The Arctic region is sensitive to climate change. Since the Arctic sea-ice cover influences the surface heat budget of the Earth the observed sea-ice decline is seen as an indication of global warming. Furthermore, the dynamics of sea ice plays an important role for the sea-ice mass distribution in the Arctic, for the production of dense, cold, and salty water in the Arctic Ocean, which contributes to the thermohaline circulation, and also for the freshwater budget of the Nordic Seas. Thus, a realistic description of sea-ice motion is important to draw conclusions for the mass transport and sea-ice mass distribution. The Finite-Element Sea-Ice Model simulates the large-scale physical sea-ice processes like the sea-ice growth and circulation realistically. The model domain covers the entire Arctic Ocean and its marginal seas. Together with the Singular Evolutive Interpolated Kalman (SEIK) Filter and remotely sensed sea-ice drift observations this sea-ice model is applied for data assimilation to investigate details of the sea-ice dynamics. So far, drift assimilation has been carried out to analyze and modify only the drift field with subsequent computation of the advection or redistribution of ice mass which corresponds more to the physical model behavior than a statistical analysis that the SEIK Filter provides. The sea-ice drift data assimilation with the SEIK Filter achieves drift modification and furthermore changes in the two other sea-ice variables concentration and thickness. The modifications of these "unobserved variables" (within the meaning of data assimilation) are validated and it is found that they are in good agreement for at least 2 months for the sea-ice thickness and even 4 months for the sea-ice concentration which is the longest period examined. The drift improvement is achieved due to the sea-ice concentration and ...

Description: thesis

Description: Tectonics, marine geophysics, plate-tectonic reconstruction, new zealand, antarctica, seismic refraction/wide-angle reflection, Gondwana break-up. - The last supercontinent fell into pieces with the break-up of Gondwana. In this context, the separation of the microcontinent of New Zealand from Antarctica is a jigsaw puzzle of many pieces. Its parts lay at the convergent margin of East Gondwana, which changed into a divergent margin within a geologically short time. That is why the microcontinent of New Zealand experienced different tectonic regimes and phases of the Wilson cycle. Although it is a good object of investigation due to its changing history, remarkably little is known about the submerged parts of the microcontinent. Knowledge of the magmatic-tectonic development of the submarine plateaux such as Campbell Plateau and Chatham Rise will improve the understanding of the processes that led to the late Gondwana break-up, and, in turn, lead to better reconstructions of East Gondwana, as Zealandia is a key piece in plate-kinematic reconstructions of this part of Gondwana. The central part of this thesis deals with the separation process of Zealandia from Antarctica leading to an improved reconstruction of New Zealand with emphasis on the submarine plateaux. Bounty Trough separating Chatham Rise from Campbell Plateau, and the Great South Basin separating Campbell Plateau from the South Island are investigated with seismic refraction and reflection methods. They are interpreted jointly with magnetic and gravity data. The results of crustal thickness modelling based on satellite gravity data are combined with existing information about crustal thickness of Zealandia. With these data ...

Description: thesis

Description: Dinoflagellate cysts, paleoceanography, paleoenvironment, Late Quaternary, Norwegian-Greenland Sea. - Dinoflagellate cysts have been investigated in nine short sediment cores as well as two long sediment cores from the Norwegian-Greenland Sea and the North Atlantic to reconstruct the surface water paleoenvironment of the last climatic cycle and the Holocene. Holocene sea-surface temperatures and salinities during summer and winter and the extent of sea-ice cover were reconstructed. On the Rockall Plateau, higher cyst concentrations indicating favourable conditions and increased productivity only occur during parts of stage 5, 4-2, and the Holocene. Only sparse occurrences of dinocysts have been observed in the Norwegian-Greenland Sea before 10000 yr BP. Later, high abundances of O. centrocarpum and N. labyrinthus indicate the increased inflow of relatively warm Atlantic. A change in dominance of these species as well as a distinct increase in cyst concentrations marks the onset of the recent circulation system. In the Norwegian Sea, O. centrocarpum dominates the assemblages since about 7000 yr BP, while assemblages in the Iceland and the Greenland Sea are more complex due to the influence of different surface currents.

Description: thesis

Description: Slope stability, submarine slides, Svalbard, Arctic Ocean, Sophia Basin. - With increasing interest in slope stability issues on continental shelves the causes and trigger mechanism of submarine slides get more and more into the scientific focus. Within the ESF EUROMARGINS project 'Slope Stabilities on Europe's passive continental Margin' (SPACOMA) sediment dynamics of megaslides along the passive continental margin north of Svalbard have been investigated. The study concentrated on identification and sedimentological characterisation of megafailure events, their dating and interpretation in relation to paleoceanography and climate history of the Svalbard archipelago. Integrated interpretation of multibeam bathymetric, sediment-penetrating acoustic (PARASOUND) and seismic data shows a multiple slope failure on the northern European continental margin, north of Spitsbergen. One huge submarine slide has been identified which was first described by Cherkis et al. (1999) - the Yermak Slide (later named Hinlopen/Yermak Megaslide). The extent of the Hinlopen/Yermak Megaslide has been revised based on new acoustic and detailed bathymetric data. Details from the side's internal structure give evidence for one main slide event followed by repeated minor events. The first slide event occurred during MIS 3 around 30 cal. kyr. BP and was characterised by highly dynamic and rapid evacuation of ca. 1.250 kmÃÂđ of sediment from the lower to the upper part of the shelf slope. During this megaslide event, headwalls up to 1600 m have been created and ca. 1150 kmÃÂđ material from hemipelagic sediments and from the lower preexisting trough mouth fan has been entrained and transported into the semi-enclosed Sophia Basin. This megaslide was followed by a secondary evacuation of debris material to the Nansen Basin accomplished by funnelling of the debris through the Littke Channel between Polarstern Seamount and the adjacent continental slope. The main slide debris is overlain by a set of fining-upwards sequences as evidence for the associated suspension cloud and ...

Description: thesis

Description: Sea ice, surface emissivity, emitting layer temperature, temperature profile, microwave radiometry. - Polar regions play a key role in the global climate. The information on atmospheric parameters in these regions is sparse. Among the polar surfaces, sea ice varies in extent and physical properties with region and season and so does the surface emissivity. In the present study a method to retrieve the emissivity is applied over two selected regions in the Arctic, one covered by first-year ice and the other by multiyear ice and it investigates the application of them in the improvement of temperature profile retrieval ver sea ice. The retrieval of surface emissivity is done by combining simulated brightness temperatures with the satellite measured brightness temperature. In order to determine the surface emissivity of sea ice, the observations of the microwave instruments amsu (Advanced Microwave Sounding Unit) and amsr-e (Advanced Microwave Scanning Radiometer- Earth Observing System) are used. Determination of emissivity requires the knowledge of the temperature of the emitting layer. The penetration depth of microwaves in sea ice varies between millimeters and decimeters depending on the frequency and micro-physical structure. A year-round observation of temperature profiles of sea ice from the Surface Heat Budget of the Arctic Ocean (sheba) campaign at a first-year and a multiyear ice site is used to derive a set of coefficients a and b to linearly relate ...

Description: thesis

Description: Reflection seismics, sediment drifts, bottom currents. - The region south of South Africa has been a crucial gateway for large scale Thermohaline Circulations since late Eocene times. Here, three of the most important currents for maintaining the global heat exchange, namely the warm and surface related Agulhas Current (AC), and the cold and denser North Atlantic Deep Water (NADW) as well as the Atlantic Bottom Water (AABW), flow around South Africa. Due to the special tectonic and geologic situation, a huge amount of the deep and bottom water masses that flow around South Africa have to pass the narrow Agulhas Passage, located between the South African continental shelf and the submarine Agulhas Plateau. As a result, the sedimentary infill of the Transkei Basin, which is located east of the Agulhas Plateau, has been predominantly influenced by NADW and AABW activity since ~36 Ma. Via the analysis of this sedimentary infill, a palaeo current reconstruction of (proto-) NADW and (proto-) AABW revealed changing flow paths and flow strengths since then. These variations in current attributes were triggered by large scale effects, such as the opening of the Tasman Gateway and the Drake Passage in the Late Eocene, or the closure of the Isthmus of Panama in the Pliocene. A more detailed analysis of the Transkei Basin's depocentre locations and interface outlines resulted in a palaeo flow path reconstruction for this region. Moreover, palaeo climate conditions from the Late Cretaceous were partially reconstructed ...

Description: thesis

Description: Ice, microstructures, subgrain boundaries, recrystallization, flow, deformation. - The primary objective of this thesis is the investigation of microstructures obtained from samples from the EPICA Dronning Maud Land ice core from Antarctica. The goal is to gain understanding of deformation processes an deformation-related recrystallization mechanisms using these structures. The structures are visualized with the new microstructure mapping method using the preferred sublimation along defect regions in the crystal. This method enables observation in high resolution as well as overview over a significant sample volume. In order to provide unambiguous proof of their deformational origin and to offer interpretation and characterization, experimental reproduction of the microstructural features are performed using creep tests. Subgrain boundaries and grain-boundary morphology are identified as the most direct effects of deformation and recrystallization processes, which are still easily observable. They can be used additionally to the conventional parameters (grain size, crystal-orientation distribution) to determine these mechanisms. Different sbugrain-boundary types observed in experimentally deformed samples as well as in natural ice indicate several formation processes. Results obtained from this new and novel data suggest a profound reconsideration of the classical tripartition of recrystallization regimes described in the literature in ice sheets. Instead, dynamic recrystallization in two of its forms (rotation recrystallization and strain-induced migration recrystallization) dominates the microstructure evolution in all depth regions of the EDML ice core. Results of systematic microstructure analysis of creep-test samples demonstrate ...

Description: thesis

Description: The hyperspectral UV-vis-NIR spectrometer SCIAMACHY will be launched aboard the European satellite Envisat. Its limb measurements will provide vertically resolved profiles of trace gases and other atmospheric parameters. No retrieval algorithms and radiative transfer models have been established for these measurements yet.In this thesis, a unique, fast radiative transfer model for UV-vis-NIR limb radiances has been developed, implemented, and validated. It takes into account the sphericity of the atmosphere and up to two orders of scattering and surface reflection. The weighting functions for all parameters are calculated from analytical formulae. A realistic instrument model with field-of-view integration and signal-to-noise computation and retrieval algorithms have also been implemented. All have been combined in the new program package SCIARAYS. The package has been applied for the characterisation of the limb measurements in several ways:The simulated weighting functions agree well with those due to full multiple scattering. Thus they may be used to calculate theoretical precision estimates and averaging kernels. In conformance with this, test retrievals with approximate weighting functions converge correctly. Therefore, the approximate weighting functions of SCIARAYS are well suited for retrievals from SCIAMACHYś limb measurements.Detailed theoretical retrieval precisions have been calculated for SCIAMACHYś trace gas targets. The conclusion is that a UV-vis-NIR limb sensor like SCIAMACHY is well suited for studying the vertical structure of the stratosphere and also of the upper troposphere above cloud top.Further investigations show that the vertical resolution of retrievals from SCIAMACHYś limb measurements can be improved beyond its geometrical limits. As a trade-off for better vertical resolution, the retrieval precision gets worse. Thus O3 profile features with 1km vertical extent will be detectable with a precision of 20-30%.

Description: thesis

Description: GIS, Geoinformatik, Spatial Theory, Face Intersection, Polygon Clipping, Diagramatic Reasoning. - A Geographic Information System (GIS) is used to handle, analyse and visualize ‘facts’ of the ‘real world’. These ‘facts’ are assumed to be spatial in the sense that they are located at the earth’s surface. The first chapter outlines that the recent success of applied GIS is based on this ‘real world’ approach, which conforms to the tradition of geography as a scientific discipline. While most GIS-applications are pragmatically oriented in solving ‘real-world-problems’, each attempt to implement ‘spatial theories’ of GIS ends up in the well known geographical dilemma ...

Description: thesis

Description: Deep-sea fan, early diagenesis, susceptibility, anaerobic oxidation of methane, black shale, anoxia, oceanic anoxic event, trace elements, iron, phosphorus, sediment source, redox changes, enrichment factors, sequential extraction. - In the context of present-day changes of atmo-, hydro-, geo- and biosphere processes, there is growing interest to decipher rapid paleoenvironmental changes in the geological past. Marine deposits provide valuable insights into paleoenvironmental conditions that prevailed during their deposition, if we know how to read the respective signals in the sedimentary record. However, caution is demanded as primary signals of past environmental conditions can be altered by postdepositional diagenetic processes. In the presented work, we will show the potentials, but also limitations of inorganic geochemical proxies to record signals of abrupt paleoenvironmental shifts in the terrestrially dominated Late Quaternary deposits of the Zambesi deep-sea fan (SE African margin), and in a fully marine Late Cretaceous black shale succession on Demerara Rise (NW South American margin).

Description: thesis

Description: Carbon, Upwelling, Namibia, shelf, sediments. - This PhD thesis is an essential component of the 'Namibia Gas' (NAMIBGAS) project, which aims to improve the understanding of the rate and fluxes of hydrogen sulfide and methane to the sediment surface and into the water column on the Namibian shelf, which is one of the most productive upwelling systems on Earth. Organic matter degradation in the sediment drives hydrogen sulfide production, the maintenance of anoxia, and methane formation. Therefore, the primary aims of the thesis are to study carbon transformation processes within the sediment, determine the reactivity of organic carbon in the sediment and, investigate the control of microbial community structure and activity by the amount and accessibility of carbon sources. The emphasis is on linking microbial community structure (identity) to their function (activity) to provide new insights into the microbial ecology that controls carbon turnover in these upwelling sediments. By studying the stepwise degradation of organic carbon a complete process overview of organic carbon mineralization could be obtained. Firstly, the diagenetic transformation of dissolved organic carbon (DOC), in particular dissolved carbohydrates, was studied by using both biogeochemical methods and molecular techniques. The bulk sediment composition, pore water chemistry, polysaccharide hydrolysis rates, 35S-sulfate reduction rates, and the abundance of active bacteria involved in the initial and terminal processes of organic carbon degradation within the top 15 cm of the sediment from two sampling stations were determined (Chapter 2). Secondly, the diversity of bacteria from the same ...

Description: thesis

Description: High-resolution climate reconstruction, North Sea, annual banded proxy, Arctica islandica. - Until now, there has been no published documentation of North Sea year-to-year climate variability during the last 8000 to 10000 years. High-resolution instrumental time series of climatic and environmental data for the North Sea and the adjacent North Atlantic are only available for the last decades or a century at best. Long term paleoclimatic reconstructions in higher latitudes have been predominantly undertaken using land-based annually banded archives, such as trees, varves, glaciers, and speleothems. A suitable long-term environmental archive with annual may be provided by CaCO3-skeletons of long-lived marine invertebrates. This study evaluates whether recent and subfossil shells of the long-lived bivalve Arctica islandica from the North Sea carry feasible information on Holocene climatic and oceanographic conditions. I compared modern shells of Arctica islandica from two very different habitats, a near-coastal shallow site (German Bight) and a northerly, more central, deep site (Fladen Ground). From the latter, subfossil shells were analysed, also. This study demonstrates that Arctica from both sites provides suitable archives of marine environmental conditions in the form of (i) variations in annual shell ...

Description: thesis