Current Research Projects

RACE-II | TRR 181, W2 | MAR-Mixing | IRTG 1904 ArcTrain | Freshwater Budget | SPP 1889 "Sea Level"
Bremen Excellence-Cluster | Hydrothermadec | VV ''SOPRAN'' | finished research projects

         
       

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  NOAC-Longterm Ocean Observatory in the North Atlantic

NOAC-Longterm Ocean Observatory in the North Atlantic
 
Regional Atlantic Circulation and Global Change

(Cooperative Project "RACE-II", WP 1.2)

Funding: BMBF
Period: 2016 - 2018

The Atlantic Ocean and its marginal seas together with the wind field dominate climate and climate change in Western Europe. One of the main players is the ocean circulation and its variability, transporting heat from the tropics into higher latitudes and connecting the individual ocean basins into a joint global system. The most famous North Atlantic Current, the Gulf Stream, is thought to be the hot water heating system and responsible for the relatively mild climate in northern and western Europe. Systematic long-lasting changes in the Atlantic circulation - as envisioned under a warming world - could lead to basic climate changes in Germany and adjacent regions. To improve the projected changes, a better understanding of the mechanisms and processes involved in the Atlantic circulation is needed. The scientifc goals of RACE II are:

  • an improved understanding of processes that lead to changes in the circulation on interannual to decadal time scales
  • to study of the consequences and repercussions of circulation changes on the Atlantic climate system and on the European Shelf
  • to improve prediction of decadal and longer circulation changes and their impact on the climate system
 
       

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  Planned measurement campaign in tidal beam south of the Azores.

Planned measurement campaign in tidal beam south of the Azores.
Tidal beam data from satellite altimetry courtesy of B. Dushaw.
 
Energy transfer through low mode internal waves

(SFB/TRR 181, W2)

Funding: DFG
Period: 2016 - 2020

This project is part of the TRR 181 "Energy transfers in Atmosphere and Ocean" and aims to quantify the generation and propagation of internal waves in the global ocean, study the pathways of radiated low mode internal waves including processes operating along the pathways, identify regions of sources and sinks, and to quantify the contribution to local dissipation and identify the involved processes. For these purposes we will use (i) dedicated global high resolution (1/10° or higher) model runs, with idealised forcing mechanisms, (ii) use observations of internal wave energy fluxes along paths where satellite altimetry shows beams of converging low mode internal waves, and (iii) combine the model simulations with the available observations to produce the best estimate of the global distributions of sources and sinks needed for an energetically consistent model for the diapycnal diffusivity induced by breaking of internal waves.

 
       

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  Eddy kinetic energy at the sea surface from AVISO-satellite data and positions of the moorings

Eddy kinetic energy at the sea surface from AVISO-satellite data and positions of the moorings
  Temporal variability in the internal wave field and vertical mixing in the North Atlantic


Funding: DFG
Period: 2014 - 2017

The objective of this project is the investigation of temporal variability in internal wave energy and the intensity of vertical mixing in relation to the North Atlantic Current and its eddy field. Thereby 5-6 year long observations from moored current meters and temperature/conductivity recorders from four moorings along a section west of the Mid-Atlantic Ridge as well as shipboard LADCP/CTD measurements will be used. Specific scientific scientific questions are e.g. how large is the temporal variability in the energy in the internal wave field and what are the dominant processes (e.g. wind, topography, variability in the North Atlantic Current) responsible for the observed variability. Furthermore the intensity of vertical mixing will be analyzed using hydrographic shipmeasurements and Thorpe-scales from mooring data in order to study the regional and temporal variability in turbulent mixing.

 
       

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  Average surface velocity derived from satellite data, 1993-2008

Average surface velocity derived from satellite data, 1993-2008
  ArcTrain - Processes and impacts of climate change in the North Atlantic Ocean and the Canadian Arctic
(IRTG 1904 "ArcTrain", projects HB-5, HB-6, HB-7)

Funding: DFG
Period: 2013 - 2017

Within in the International Research Tranining Group ArcTrain PhD students and scientists of the University of Bremen (MARUM and IUP) and the Alfred-Wegener-Institute in Bremerhaven cooperate with 10 Canadian partner universities, to investigate in the framework of a strcutured doctoral program processes and impacts of climate change in the North Atlantic and the Canadian Arctic. Sub-projects residing at the Department of Oceanography deal with exchange processes between the Deep Western Boundary Current (DWBC) and the deep basins of the subpolar North Atlantic (HB-5), vertical mixing in the DWBC (HB-6), and horizontal mixing and stirring of water masses in the open subpolar North Atlantic (HB-7).

 
       

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  Major circulation branches of the North Atlantic Current

Major branches of the North Atlantic Current and
boxes used for reconstructing salinity profiles from Argo and altimetry data.
  Freshwater budget and salinity variability in the subpolar and suptropical gyres of the North Atlantic
(DFG Research Unit FOR 1740, WP 1.2)

Funding: DFG
Period: 2016 - 2019

In the first phase, high spatial (0.25° x 0.25°) and temporal (daily) resolution salinity time series (1992 - 2012) in the upper 700 m were constructed using Argo data and satellite altimetry. The objectives of the continuation proposal are based on the results of the first phase, and we will (i) analyse the monthly to multi-annual variability in the regional salinity contents; (ii) study the evolution and variability of surface and subsurface structures of fronts, meanders, and eddies, (iii) check whether the salinity reconstructions are valid in regions shallower than 1900 m depth in the Northeast Atlantic, and test whether the quality of the reconstructions of the salinity profile improve by adding satellite observations of surface salinity.

 
       

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  Drift ice nea Greenland (Photo M. Rhein)

Drift ice near Greenland (Photo M. Rhein)
  Estimates of basal melt water from Greenland: a driver for sea level changes
(SPP 1889 "Regional Sea Level Change and Society")

Funding: DFG
Period: 2016 - 2019

The mass loss rate of the Greenland Ice Sheet almost quadrupled in the last 20 years. One of the main process is the inflow of warm water from the subtropics into the Greenland fjords. There, warm water comes into contact with the bottom of the floating ice tongues. The increases of the melt rates lead to an increase in global sea level, but also influence the dynamics of the ocean, modifying the regional sea level. By measuring the distribution of helium and neon isotopes in the ocean, the until now unknown pathways of Greenland melt water into the boundary current and into the key regions of the ocean will be detected and the fraction of melt water quantified. This will help to estimate the changes in the circulation and thus in the regional sea level.

 
       

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  Climatological mixed-layer depths in March

Climatological mixed-layer depths in March
  Variability of Deep Water Formation in the North Atlantic
(Bremen Exzellenz-Cluster "The Ocean as Part of the Earth's System - MARUM" )

Funding: DFG (Bremen Excellence-Cluster "MARUM")
Period: 2012 - 2017

Climate model experiments suggest that deep-water formation in the North Atlantic may drop in the 21st century (IPCC, 2007). Evidence from geological records suggests that the oceanic meridional overturning circulation had almost ceased at various times in the geological past, and these shut-downs were linked to abrupt climate changes. Using an integrated approach of data and model simulations, we will examine the processes in the atmosphere-ocean-sea ice system responsible for the fluctuations in deep water formation rates on interannual to longer time scales. We identify sensitive sites for the ocean circulation changes. The formation of deep water masses north of Iceland and in the Labrador Sea may have different effects for the strength of the large-scale ocean circulation: the dense water formed north of Iceland results in the overflow water, whereas open ocean convection dominates in the Labrador Sea. Finally, these changes are compared to recent salinity anomaly events.

 
       

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  Research Vessel ''Sonne'' (Photo J. Köhler)

Research Vessel Sonne (Photo J. Köhler)
  Hydrothermadec - Geochemical and ecological impacts of hydrothermal processes at intraoceanic volcanic arcs studied exemplary on the Kermadec Arc, SW-Pacific

Funding: BMBF, Auswerteantrag So253, PI W. Bach/MARUM
Period: 2016 - 2019

Hydrothermal systems along volcanic island arcs are different to those at mid-ocean ridges because of their mostly shallow water depth and strong magmatic input into their fluids and hydrothermal plumes. As these plumes often reach up into the photic zone they discharge large quantities of material into the surface water layers. The goals of our proposal include the characterization of hydrothermal systems at the Kermadec Arc and the understanding of their role for the global elemental budget of the ocean and for local chemical and biological processes in the water column and at the seafloor. Specific focus will be on the role of chemical speciation (redox speciation, organic complexation) and the influence of biological processes on the export and bioavailability of these elements. To achieve these goals, we plan to investigate hydrothermal fluids, solid phases, and plumes, and biological communities from a number of different hydrothermal systems at the southern and middle Kermadec Arc. We will use the ROV Quest, CTD/rosette water samplers, and multicorer or grab systems in this interdisciplinary approach.

 
       

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  Vertical velocities in the Mauritanian upwelling area

Vertical velocities in the Mauritanian upwelling area
 
Upwelling velocities inferred from helium isotope disequilibrium

Verbundvorhaben SOPRAN III

Funding: BMBF
Period: 2013 - 2016

Upwelling is an important factor for the exchange of biogeochemical properties between the mixed layer and the ocean interior. It plays an important role for the nutrient supply of the euphotic zone and also has a cooling effect on the mixed layer. Trace gases as bromoforme and nitrous oxide (N2O) are produced underneath the oceanic mixed layer, transported towards the surface by upwelling and outgassing into the atmosphere. As upwelling velocities are in the order of 10^-5 m/s, they cannot measured directly. Within SOPRAN, the helium-3 disequilibrium of the surface waters has been used to indirectly infer the magnitude of the upwelling. This method has been applied to the equatorial eastern Atlantic and the area off the Mauritanian coast during the earlier stages of SOPRAN. The mean upwelling in the coastal region is determined by the Ekman divergence, whereas further offshore the helium method indicates eddy induced upwelling. During SOPRAN III, the strength of the Peruvian upwelling will be investigated and compared with the other two SOPRAN regions. By including diapycnal diffusivities, the total fluxes of heat, nutrients and trace gases into the mixed layer will be estimated.

 
       

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