Finished Research Projects

Flemish Pass | CarboChange | RACE | Upwelling in the Southern Ocean | Eddies and Fine Structure
SPP-1158 | Mixing at 16°N | Atlantic-Tracer | Helium-Solubility | SPP-1144 | 47°N-Mixing | SUMSUN
NBC-Rings | CARBOOCEAN | LAKRIS | CLIVAR | SF6 | SFB-460/TP-A7 | current research projects

         
       

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  observed velocity structure in Flemish Pass

observed velocity structure in Flemish Pass
  Transports and variability-driving mechanisms in Flemish Pass at the western boundary of the subpolar North Atlantic
(FLEPVAR, in cooperation with the Institute of Oceanography, University of Hamburg)

Funding: DFG
Period: 2012 - 2015

Labrador Sea Water (LSW) formed in the Labrador Sea constitutes the lightest contribution to North Atlantic Deep Water (NADW), a conglomerate of water masses that form the cold return flow of the Atlantic meridional overturning circulation (MOC). The Deep Western Boundary Current (DWBC) is the main southward pathway for newly formed LSW and leads it partly through Flemish Pass. Up to now, transports through Flemish Pass and their contribution to the MOC are still uncertain, the importance of the pass for the export of LSW and its associated variability are yet unknown. In this project the transports through Flemish Pass will be quantified, and mechanisms driving and governing the variability of the flow will be investigated.

 
       

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  change of the column inventory of anthropogenic carbon, 1997-2003

relative change of the column inventory of anthropogenic carbon between 1997 and 2003
  Storage of anthropogenic carbon and determination of oxygen consumption rates
(CarboChange, WP 1 & WP 5)

Funding: EU
Period: 2011 - 2015

The ocean plays a major role in the global carbon cycle, especially for the uptake and storage of anthropogenic CO2 emissions. Aim of this project is an improved quantification of the net ocean carbon uptake under changing climate conditions. Therefore both physical and biogeochemical processes will be investigated through a combination of observation and models. Contributions of the IUP are inferring changes of the oceanic inventory of anthropogenic carbon by repeated observations of transient tracers (CFC-12, SF6) and deriving a relation between water mass ages and oxygen consumption rates.

 
       

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  Applied measurement techniques

Field campaigns in the subpolar gyre
 
Large-scale fluctuations in the subpolar gyre of the North Atlantic

(Cooperative Project "RACE", WP 1.2)

Funding: BMBF
Period: 2012 - 2015

The subpolar gyre of the North Atlantic is the key region for the formation of water masses which participate in the global Meridional Overturning Circulation (MOC). Additionally warm and salty waters are transferred into the Nordic Seas, whereas water masses from the Nordic Seas are injected into the deep and cold lower limb of the MOC. This project deals with the estimation of transport variability in the subpolar gyre of the North Atlantic and the exchange of water masses between the subtropics and tropics. Both will be inferred by a combination of different methods and instrumental data (pressure inverted echosounders (PIES), altimetry, ship surveys, Argo-drifters, moorings). Formation rates of Labrador Sea Water will be derived from tracer inventories (chlorofluorocarbons in comparison to SF6).

 
       

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  Upwelling velocities, Weddell Sea

Determination of upwelling rates in the Weddell Sea
  Determination of upwelling rates in the Southern Ocean

Funding: DFG
Period: 2011 - 2014

Upwelling is an important process that has a strong impact on the properties of the oceanic mixed-layer. Upwelling allows gases, nutrients and other components from the ocean interior to enter the mixed-layer and thus to be released into the atmosphere. Strong upwelling can counteract the physical uptake of atmospheric gases like CO2 in the ocean. Since upwelling velocities are typically very small, they cannot be measured directly. Recently, imbalances of helium isotopes, as observed in the eastern equatorial Atlantic, were used to determine upwelling velocities, rates and heat fluxes between the ocean interior and the mixed-layer. These imbalances are caused by upwelling of 3He-rich waters from deeper levels in the ocean interior. This excess 3He enters the deep ocean through hydrothermal processes. In the framework of the project imbalances shall be analyzed based on historical data as well based on helium data collected during 'Polarstern' cruise ANT 27/2 (11/2010-02/2011) and 'Polarstern' cruise ANT 28/3 (01/2012-02/2012). These data will be used to determine upwelling velocities, rates and heat fluxes in the Weddell Sea and the Antarctic Circumpolar Current.

 
       

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  Finestructure variability in the eddy field of the NAC

Finestructure variability in the eddy field of the NAC
 
Eddies and finestructure variability in the NAC


Funding: DFG
Period: 2010 - 2014

Observational estimates of elevated vertical diffusivity in regions of high mesoscale eddy activity point toward the relevance of energy loss from eddies to maintain the ocean stratification. Estimates of net energy transfers between the internal wave field and a mesoscale eddy field indicate wave-eddy coupling as an important source of internal wave energy, and thus mixing, in the deep ocean. In this project, we investigate the relation of the subpolar front and the associated eddies in the energetic North Atlantic Current (NAC) to finescale variability of the internal wave field observed in vertical profiles of density and velocity. The study has the objectives to study the finescale variance and possible changes of water mass transformation and mixing patterns in the North Atlantic as a response of shifts in position of the NAC, and to examine the role of the temporal variability of the atmospheric forcing.

 
       

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  Vertical tracer distribution along Greenwich Meridian

Vertical tracer distribution along Greenwich Meridian
 
Inventories of anthropogenic carbon and their variability in the Atlantic sector of the Southern Ocean, 1984-2010

(SPP 1158)

Funding: DFG
Period: 2004 - 2013

The Atlantic sector of the Southern Ocean is a key area for the formation of bottom, and deep water. Climate relevant anthropogenic carbon (Cant) is taken up at the atmospheric interface and exported from the atmosphere during Antarctic Bottom Water (AABW) formation. In turn, formation of these waters are influenced by climate change. Despite their importance, Cant inventories and related formation rates of AABW and AAIW in that area are not well known, and estimates of the temporal variability are quite uncertain. Based on transient tracer (CFC) data the formation rates of AABW and the Cant inventories in the Atlantic Southern Ocean will be determined and their variability during the last two decades will be assessed.

 
       

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  Temperature variance at 16°N

Time series of high-frequency temperature fluctuations at 16°N
  Turbulent Mixing in the Deep Western Boundary Current of the North Atlantic at 16°N

Funding: DFG
Period: 2007 - 2013

Turbulent mixing in the ocean belongs to the key parameters that control the meridional overturning circulation. The spatial distribution of turbulent vertical fluxes and especially their intensification along the ocean boundaries are essential to reproduce the overturning circulation in ocean models. Recent investigations concentrated on how tidal energy is converted into turbulent motion above rough bathymetry. But for several regions in the Atlantic, there is evidence for intensified mixing along the western boundary, especially in the boundary current region. In this project we study the variability of internal waves and diapycnal mixing in the Deep Western Boundary Current of the tropical Atlantic at 16°N. Using time series measurements of currents and stratification as well as CTD and LADCP data the following questions are addressed:

  • How do the physical characteristics of the Deep Western Boundary Current and their temporal variability influence the internal wave field?
  • How do wind and tides influence the local generation of internal waves? What are the differences between boundary region, the Mid-Atlantic Ridge, and the ocean interior?
  • Is critical layer absorption a relevant process, and is temporal variability of importance in this context?
  • Do we observe relevant interaction between the internal waves and the mean flow?
 
       

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  Age distribution of young DSOW

Age distribution of young DSOW
  Changes in anthropogenic carbon inventories and formation rates of deep and intermediate waters inferred from large-scale transient tracer distributions in the Atlantic, 2010-2011

Funding: DFG
Period: 2010 - 2013

Dutch and Spanish cooperation partners conduct several large-scale expeditions in 2010 and 2011, aiming at surveying the Atlantic Ocean along two zonal and one meridional basin-wide sections. Measurements of noble gas concentrations and anthropogenic tracers at these sections deliver valuable data suitable to calculate the inventory of anthropogenic carbon in Antarctic Intermediate Water (AAIW) and in North Atlantic Deep Water (NADW). Furthermore, propagation velocities, dilution and mixing of these water masses will be analyzed. Tracer and noble gase data also serve to estimate the import of intermediate and deep water from the Pacific Ocean that cross 50°S towards north in the Atlantic Ocean.

 
       

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  gassing chamber for determining the solubility of helium

gassing chamber for determining the solubility of helium
  Determining solubility of helium in water

Funding: DFG
Period: 2010 - 2012

The focus of the project is to determine the solubility of helium (and neon) with an accuracy of 0.2%, where older publications quote values around 1%. This will be done using a newly developed gassing system equipped with highly accurate sensors to control the operating parameters and experimental conditions. The Bremen mass spectrometer, which will be used for the measurement of the produced water samples, is very sensitive to these noble gases. The obtained data can then be used to quantify fresh water fluxes of melted Antarctic continental ice and investigate their pathways in the ocean. Also, the air-sea interaction can be studied in more detail using the disequilibrium of noble gases. The apparatus is furthermore able to produce water samples of well defined concentrations of these noble gases. These samples should be used for intercalibration of measurement systems run at various international laboratories analyzing noble gases.

 
       

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  Temperature anomalies close to hydrothermal vents

Temperature anomalies close to hydrothermal vents
 
Vertical mixing and helium fluxes at hydrothermal vents

(SPP 1144)

Funding: DFG
Period: 2003 - 2011

Hydrothermal vents belong to the energy sources of the oceans and are important suppliers of primordial helium-3. This project aims at estimating the vertical mixing near hydrothermal vents which are located at the Mid-Atlantic Ridge between 5°S and 11°S. Fluxes of heat and helium will be estimated for this region.

 
       

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  Vertical mixing at 47°N

Vertical mixing at 47°N
  Mixing Processes in the Deep Western Boundary Current at 47°N

Funding: DFG
Period: 2007 - 2010

The goal of this project is to qualitatively and quantitatively study the diapycnal mixing associated with Deep Western Boundary Currents (DWBC). To this end, we supplement existing hydrographic data from the DWBC region off Flemish Cap with a small scale hydrographic survey and a moored array. In particular, the following questions will be addressed:

  • Is there a temporal variability in the strength of the mixing?
  • Which external parameter are linked to the variability?
  • What is the role of the local topography for the mixing pattern?
  • Is the exchange between the DWBC and the interior dominated by diapycnal or isopynal fluxes?
 
       

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  Investigation sites in the Okinawa Trough, Pacific Ocean

Investigation sites in the Okinawa Trough, Pacific Ocean
  Turbulence, currents and He-isotopes in the near field of CO2 emission sites at Okinawa Trough
(SUMSUN)

Funding: BMBF
Period: 2008 - 2010

The main goal of this project ist to study the reaction of a deep sea environment on the emission of CO2, including the associated change in pH. The focus is on the geochemical balance in the water column and sediment and on the adaption strategies of the ecosystem. The study area includes three hydrothermal systems in the Okinawa Trough, East Pacific, where CO2 venting occurs naturally, the Izena Hole, Hatoma Knoll, and Yoneguni Knoll. The Bremen oceanography group is responsible for the measurements of turbulence, stratification and the flow field in the near field of the CO2 emission, as well as additional mapping of primordial Helium in the far field of the hydrothermal plume as a tracer for the hydrothermal output.

 
       

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  Contribution of South Atlantic Water and meridional velocity component along 16°N

Contribution of South Atlantic Water and meridional velocity component along 16°N
 
Transport pathways and mechanisms of decay for North Brazil Current Rings in the tropical North Atlantic


Funding: DFG
Period: 2008 - 2010

An important contribution to the upper, warm branch of the Meridional Overturning Circulation (MOC) in the tropical Atlantic is performed by NBC rings. These large-scale eddies (diameter of 250-350 km) carry a high amount of South Atlantic Waters in their core, which remains in the northern hemisphere after the decay of the eddies. NBC rings occur at the western boundary of the tropical North Atlantic Ocean and may reach the eastern Caribbean Sea; their transport contributes to the Gulf Stream System. The formation and propagation of NBC rings as well as their interaction at topographic boundaries (namely the Lesser Antilles) are the topics of this research project. The questions are addressed using the high resolution FLAME model and observational data from Argo floats.

 
       

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  Column inventory of anthropogenic carbon in 1997

Column inventory of anthropogenic carbon in 1997
 
Estimation of anthropogenic CO2-Inventories

(CARBOOCEAN Integrated Project)

Funding: EU
Period: 2005 - 2009

The greenhouse gas CO2 is an important factor for global warming. In order to recommend appropriate reduction rates for CO2 emissions, it is necessary to know the amount and relative importance of the oceanic sources and sinks under current and future environmental conditions (higher temperature, higher atmospheric CO2 concentrations).
This project aims at estimating the oceanic sinks and sources of anthropogenic CO2 in the Atlantic Ocean and in the Southen Ocean. The respective time frame is +/- 200 years from now.

 
       

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  Logo of project LAKRIS  
Sea ice, circulation, and zoo plankton abundances

(LAKRIS)

Funding: BMBF
Period: 2004 - 2009

This project deals with temporal changes in the occurrence of krill with respect to the dependence on physical parameters like sea ice cover, water mass properties or circulations patterns. This is done by analyzing three-dimensional time series of krill abundance and vertical migration derived from the back scatter signal of shipboard and moored ADCPs (Acoustic Doppler Current Profilers).

 
       

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  Mooring array to determine the inflow into the Caribbean Sea

Mooring array to determine the inflow into the Caribbean Sea
 
Strength of the upper limb of the Meridional Overturning Circulation

(CLIVAR)

Funding: BMBF, DFG
Period: 2002 - 2008

The upper limb of the Meridional Overturning Circulation (MOC) consists of warm waters and intermediate waters from the southern hemisphere. The major part of theses waters crossing the equator recirculates and flows back into the South Atlantic. The warm water remaining in the northern hemisphere is thought to enter the Caribbean Sea to later join the Florida Current.
The strength of the MOC and its variability is investigated in the inflow region into the Caribbean Sea south of Guadeloupe and across 16°N.

 
       

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  Temporal evolution of atmospheric tracer concentrations

Temporal evolution of atmospheric tracer concentrations
 
Building a sea-going analysis system for measuring sulphurhexafluoride (SF6) in seawater


Funding: DFG
Period: 2005 - 2007

Due to the declining trend of atmospheric chlorofluorocarbons (CFCs) and the rising atmospheric concentrarions of sulphurhexafluoride (SF6) the latter tracer is a promising parameter for future estimations of deep water formation rates derived from their respective tracer inventories.
A sea-going analysis system for simultaneous measurements of CFCs and SF6 in seawater will be built in the framework of this project. The system will be tested and improved at sea. First samples will be taken and interpreted in the subpolar North Atlantic.

 
       

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  Tracer inventory of Labrador Sea Water (LSW), 1997

Tracer inventory of Labrador Sea Water, 1997
 
Water Mass Transformation and Variability in the subpolar North Atlantic

(SFB-460/TP A7)

Funding: DFG
Period: 2002 - 2006

Data from recent years have indicated that the properties of water masses formed in the North Atlantic have considerably changed from year to year. These changes are analyzed with respect to identifying water mass spreading pathways and spreading times scales. By means of repeated large-scale ship surveys (hydrography and tracers) changes in the chlorofluorocarbon (CFC) inventories of Labrador Sea Water (LSW) have been quantified. These results are used to infer water mass formation rates. The application of the tracer inventory method using CFCs is one of the main objectives of this project. Furthermore, the spreading of water masses in the subpolar North Atlantic and the exchange between the western and the eastern basins of the North Atlantic are investigated.