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Sea Surface Topography and Mass Transport of the Antarctic Circumpolar Current (GEOTOP)

Das Projekt "Sea Surface Topography and Mass Transport of the Antarctic Circumpolar Current (GEOTOP)" wird vom Umweltbundesamt gefördert und von Technische Universität München, Institut für Astronomische und Physikalische Geodäsie durchgeführt. GeoTop3 is the third phase of a DFG project and belongs to the DFG priority progamme 1257 Mass Transport and Mass Distribution in the Earth System . It aims at the determination of the absolute, but temporally changing ocean circulation flow field and of associated mass and heat transports. It is based on a state-ofthe-art circulation model assimilating geodetic data of the dynamic ocean topography (DOT) and oceanographic in-situ data. The ocean model is focused on the Atlantic sector of the Antarctic Circumpolar Current (ACC) and the Weddell Sea. This is one of the most dynamic ocean areas and one of the most critical regions for global climate, due to the impact of circumpolar bottom water production on global deep sea circulation. The regional model is embedded into a coarser global model to avoid systematic distortions. The expected results of this project extension are: 1. A stationary DOT with highest achievable spatial resolution from GRACE and in particular GOCE geoid models and multi-mission altimeter data with error propagation for both, geoid and sea surface. 2. The geoid models will be combined with regional Antarctic gravity data for higher resolution. ICESat data will be used to deal with seasonal sea ice concentrations. 3. A time-variable DOT, sufficiently smoothed to reduce the signal-to-noise ratio and to match the spectral and spatial resolution characteristics of the numerical model. 4. A calculation of the sensitivity of major ocean features such as strength of the Weddell Gyre on the accuracy and resolution of the geoid (and dynamical height) determination in view of the high resolution GOCE geoid model and improved geoid estimates in Weddell Sea area. 5. Model runs, in particular for the mass and heat transport in the Antarctic Circumpolar Current and the Weddell Gyre, the mean oceanographic DOT and its variability as well as their interpretation and quality assessment.

Upwelling in the Atlantic sector of the Southern Ocean

Das Projekt "Upwelling in the Atlantic sector of the Southern Ocean" wird vom Umweltbundesamt gefördert und von Universität Bremen, Institut für Umweltphysik, Abteilung Ozeanographie durchgeführt. Upwelling is an important process in setting the characteristic of the mixed layer. Upwelling also provides a pathway for gases, nutrients, and other compounds from the ocean's interior into the mixed layer and ultimately into the atmosphere. Since the upwelling velocities are small, they cannot be measured directly. Recently, Rhein et al. (2010) exploited the helium isotope disequilibria found in the equatorial eastern Atlantic to infer upwelling speeds, upwelling rates, and vertical heat fluxes between the mixed layer and the ocean's interior. The disequilibrium in the mixed layer is caused by upwelling of 3He-enriched water from the interior. The surplus 3He is introduced into the deep ocean by hydrothermal activities.A first survey of historical Helium isotope data in the Antarctic Circumpolar Current (ACC) and the Weddell Sea showed, that the mixed layer is also enriched with 3He, which in summer months is supplied by upwelling of water from below the mixed layer. Although the first estimates of upwelling velocities from the historical data set look promising, the present Helium data lack a sufficient resolution in the upper 200-300m to determine the horizontal and vertical He gradients, necessary for the compilation of the upwelling velocity and of the contribution of diapycnal mixing. Here we propose to take the historical He data, and a new dedicated He data sets to be taken in November 2010 - February 2011 during the POLARSTERN cruise ANT 27/2 and January- February 2012 during POLARSTERN cruise ANT28/3 to calculate upwelling speeds and -rates in the Weddell Sea and the ACC, as well as heat fluxes between the interior and the mixed layer.This proposal is part of the Cluster ' Eddies and Upwelling: Major Factors in the Carbon Budget ofthe Southern Ocean'

Effects of eddy variability on the response of the ACC to global warming (R'Eddy)

Das Projekt "Effects of eddy variability on the response of the ACC to global warming (R'Eddy)" wird vom Umweltbundesamt gefördert und von Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR), Forschungsbereich 1: Ozeanzirkulation und Klimadynamik, Forschungseinheit Theorie und Modellierung durchgeführt. Observations show a significant intensification of the Southern Hemisphere Westerlies over the past decades. A continuation of this trend is projected by climate models for the 21st century if greenhouse gas emissions continue to grow. The dynamic response of the Antarctic Circumpolar Current (ACC) to the atmospheric forcing depends on an intricate balance between wind-driven (Ekman) transports, eddy-induced transports, and changes in the meridional density contrast due to concomitant anomalies in the buoyancy fluxes. Climate model studies generally show a progressive increase in the ACC transport as well as in its meridional overturning circulation, behaviour of critical importance for the carbon dioxide uptake in the Southern Ocean. This picture is under debate, because the Ekman effect is thought to be opposed by wind-induced increases in eddy fluxes, an effect that may not be captured in current eddy transport parameterizations. The aim of this project is to examine the impact of explicitly resolved eddies on the Southern Ocean's response to global warming by conducting a sequence of global climate model simulations with successively increased resolutions (up to 1/12° to 1/15°) in the ACC regime of the ocean component. The results of the high-resolution experiments will provide a benchmark for the reliability of eddy parameterization schemes in non-eddy resolving climate and carbon cycle models.

Eddy-driven transports in the Antarctic Circumpolar Current

Das Projekt "Eddy-driven transports in the Antarctic Circumpolar Current" wird vom Umweltbundesamt gefördert und von IFM-GEOMAR Leibniz-Institut für Meereswissenschaften durchgeführt. In the Southern Ocean, eddy-driven transports can be as large as mean transports. In particular the meridional, cross frontal transports are affected or even controlled by meso-scale eddy activity. On the other hand, these transports set the role of the Southern Ocean as a major oceanic sink in the global carbon cycle. In ocean models, such variability has to be adequately resolved or parameterised. The parameterisation by Gent and McWilliams (1990) is currently used to account for such eddy-driven transports, in which the so-called thickness diffusivity K has to be specified. Only a rough order of I magnitude is currently known for ', but, in particular in the Southern Ocean, the choice of K strongly affects meridional transports of mass and tracers and is therefore of crucial importance to quantify the role of the Southern Ocean in the climate system and the global carbon cycle. It is proposed to estimate the thickness diffusivity K in the Southern Ocean from synthetic data of an existing realistic eddy-resolving ocean model. While previous attempts highlight the problem of rotational eddy fluxes which complicate the estimation procedure, it has been recently shown that the definition and use of physically meaningful rotational fluxes reduces this problem. Therefore, reliable estimates of K in the Southern Ocean appear possible for the first time. Furthermore, it is proposed to estimate relations between mean quantities predicted by ocean models and thickness diffusivity, necessary in order to build a self-consistent eddy parameterisation.

Cenozoic Antarctic glaciation: An integrated atmosphere - Ocean - Ice Sheet Model Approach

Das Projekt "Cenozoic Antarctic glaciation: An integrated atmosphere - Ocean - Ice Sheet Model Approach" wird vom Umweltbundesamt gefördert und von Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung - Fachbereich Klimawissenschaften durchgeführt. The widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene-Oligocene boundary (about 35 million years ago) represents one of the most fundamental reorganisations of global climate in the earth s history. During the same time, the opening of the Southern Ocean gateways, the Drake Passage and the Tasman Gateway, led to the formation of the Antarctic Circumpolar Current and hence to the isolation of the Antarctic continent. Apart from the oceanic regime, other global phenomena such as the declining atmospheric carbon dioxide concentration and the orbital configuration, contributed to the onset of a persistent Antarctic glaciation. With this project we address the impact of each of these processes on the formation of the Antarctic Ice Sheet. We put special emphasis on the ocean circulation, latent heat transport as well as on ice sheet dynamics in an integrated modelling approach. Shifts in atmospheric circulation, temperature changes, and snow accumulation over Antarctica and their forcing factors will be analysed in detail. The identification of thresholds for the Antarctic ice sheet development will yield novel views for palaeoclimatic records at the Eocene-Oligocene transition.

Impact of physically relevant and numerically induced diapycnal mixing and meso-scale dissipation on meridional mass and tracer transports in the Southern Ocean

Das Projekt "Impact of physically relevant and numerically induced diapycnal mixing and meso-scale dissipation on meridional mass and tracer transports in the Southern Ocean" wird vom Umweltbundesamt gefördert und von Leibniz-Institut für Ostseeforschung durchgeführt. The Meridional Overturning Circulation (MOC) in the Southern Ocean (SO) is composed of two limbs, the Upper Circumpolar Deep Water (UCDW) flows polewards and upwards across the Antarctic Circumpolar Current (ACC), upwells to the surface at the poleward flank of the ACC and then returns equatorwards as a near surface current. This upper limb is known to be largely adiabatic. In contrast to that, the lower limb of the MOC formed by the Lower Circumpolar Deep Water (LCDW) upwells closer to Antarctica, cools down substantially near the surface and convects down at high turbulent mixing to form the Antarctic Bottom Water (AABW). While the adiabatic upper limb is driven by an imbalance of a northward Ekman transport and an opposing meso-scale eddy transport, the dynamics of the lower limb is more complex due to the additional significance of diapycnal mixing. Thus, a good quantification of these dynamics requires a correct representation of both small-scale (diapycnal) and meso-scale (lateral) eddy mixing. On the other hand, it has long been known that in particular in the SO, large numerical mixing and dissipation in ocean circulation models due to the discretisation of the advection terms obscures the representation of diapycnal mixing and thus strongly limits the predictability of ocean models. It is therefore the aim of this project to use and to further develop a novel analysis tools for numerical mixing and dissipation to quantify effective mixing and dissipation, given by the sum of explicitly parameterised and numerically induced values. By estimating realistic effective mixing and dissipation rates, using our combined expertise of numerical mathematics and small-scale turbulence parameterisation and large-scale high-resolution modelling, we are able to the first time to assess the sensitivity of realistic models of the SO to diapycnal mixing and numerical dissipation and to understand the interplay between meso-scale (lateral) and small-scale (diapycnal) eddy mixing on the lower limb of the MOC.

Paläoklima Südamerikas und Paläozeanographie des Südostpazifiks

Das Projekt "Paläoklima Südamerikas und Paläozeanographie des Südostpazifiks" wird vom Umweltbundesamt gefördert und von Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum durchgeführt. Das Klima Südchiles wird maßgeblich von der südhemisphärischen Westwindzone und dem antarktischen Zirkumpolarstrom bestimmt. Damit ist dieses Gebiet für die Rekonstruktion von Klimaveränderungen auf der Südhemisphäre besonders wichtig und geeignet. Untersuchungen an marinen und terrestrischen Archiven aus dieser Region haben gezeigt, dass die Breitenverlagerung der atmosphärischen und ozeanischen Systeme als wichtiger Teil dieser Veränderungen zu verstehen ist. Ziel dieses Projekts ist es, für diese Region in einem breiten methodischen Ansatz Änderungen in z.B. der Temperatur, dem Niederschlag und der Vegetation während des Spätglazials und des Holozäns zu erfassen.

Molekulare Phylogeographie und Ökologie von kleinen Antarktischen Calanoida (Copepoda, Crustacea)

Das Projekt "Molekulare Phylogeographie und Ökologie von kleinen Antarktischen Calanoida (Copepoda, Crustacea)" wird vom Umweltbundesamt gefördert und von Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung durchgeführt. At present little is known about the oceanographic processes and biological traits that influence the dispersal of these planktonic species, and thus connectivity, in Antarctic waters. In the Antarctic marine pelagic species or species with pelagic life stages (e.g. larvae) are often considered to have a circumpolar distribution due to the absence of obvious barriers. The strong Antarctic Circumpolar Current is thought to facilitate the dispersal of specimens around Antarctica. However, recent investigations have shown genetic diversifications in planktonic organism on a worldwide geographical scale. To understand the importance of geographical differences in planktonic species it is necessary to detect morphologically cryptic taxa in order to investigate the physical processes and biological traits that lead to genetic diversification in pelagic Antarctic waters. For the presented project five abundant, but little studied, smaller species of calanoid copepods in the Southern Ocean have been chosen to study their phylogeography and ecology. These species have a similiar size range, but show different patterns of distribution (worldwide - endemic), depth habitats (epipelagic - mesopelagic - bathypelagic) and feeding modes (herbivorous - omnivorous). Their biogeographical patterns and rates of evolutionary diversification will be investigated with the help of mitochondrial and nuclear genes, AFLP fingerprints and 454 sequencing.

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