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  • 11
    Publication Date: 2023-11-29
    Description: Hydrothermal vent systems host microbial communities among which several microorganisms have been considered endemic to this type of habitat. It is still unclear how these organisms colonize geographically distant hydrothermal environments. Based on 16S rRNA gene sequences, we compare the bacterial communities of sixteen Atlantic hydrothermal vent samples with our own and publicly available global open ocean samples. Analysing sequences obtained from 63 million 16S rRNA genes, the genera we could identify in the open ocean waters contained 99.9% of the vent reads. This suggests that previously observed vent exclusiveness is, in most cases, probably an artefact of lower sequencing depth. These findings are a further step towards elucidating the role of the open ocean as a seed bank. They can explain the predicament of how species expected to be endemic to vent systems are able to colonize geographically distant hydrothermal habitats and contribute to our understanding of whether ‘everything is really everywhere’.
    Type: Article , PeerReviewed
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  • 12
    Publication Date: 2022-01-31
    Description: The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basin AMOC observational systems have been put in place to continuously monitor meridional volume transport variability, and in some cases, heat, freshwater and carbon transport. These observational programs have been used to diagnose the magnitude and origins of transport variability, and to investigate impacts of variability on essential climate variables such as sea surface temperature, ocean heat content and coastal sea level. AMOC observing approaches vary between the different systems, ranging from trans-basin arrays (OSNAP, RAPID 26 degrees N, 11 degrees S, SAMBA 34.5 degrees S) to arrays concentrating on western boundaries (e.g., RAPID WAVE, MOVE 16 degrees N). In this paper, we outline the different approaches (aims, strengths and limitations) and summarize the key results to date. We also discuss alternate approaches for capturing AMOC variability including direct estimates (e.g., using sea level, bottom pressure, and hydrography from autonomous profiling floats), indirect estimates applying budgetary approaches, state estimates or ocean reanalyses, and proxies. Based on the existing observations and their results, and the potential of new observational and formal synthesis approaches, we make suggestions as to how to evaluate a comprehensive, future-proof observational network of the AMOC to deepen our understanding of the AMOC and its role in global climate.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 13
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    In:  (PhD/ Doctoral thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 134 pp
    Publication Date: 2022-01-21
    Description: Observations at moored stations from the Labrador and Greenland Seas are analyzed under two major aspects: the interannual variability of convection and its relation to variability of the hydrographic, meteorological, and ice conditions, and the spatial and velocity scales of individual convective plumes compared to existing scaling arguments derived from numerical and laboratory experiments. The observations were carried out in the Labrador Sea between 1994 and 1999 and in the Greenland Sea between 1988 and 1995. The convection activity observed showed considerable interannual variability throughout the observational period, but no seesaw behavior correlated with the North Atlantic Oscillation index. In the Labrador Sea, the maximum depth of convection decreased from about 1800~m in 1995 to only 600~m in 1999. The water mass properties of the winter mixed layer shifted towards warmer and less saline conditions. A general warming of the upper 2000~m was observed. Evidence for convection activity in the Labrador Sea boundary current region could not be found. The measurements were analyzed for individual events of convective plumes. During periods of intense convection activity in the Labrador Sea, it was possible to directly measure the vertical heat flux. The observed velocity scales were found to be a function of the surface buoyancy flux and the mixed layer depth and not controlled by the Earth's rotation.
    Type: Thesis , NonPeerReviewed
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  • 14
    Publication Date: 2020-08-04
    Description: In 1997, a unique hydrographic and chlorofluorocarbon (CFC: component CFC-11) dataset was obtained in the subpolar North Atlantic. To estimate the synopticity of the 1997 data, the recent temporal evolution of the CFC and Labrador Sea Water (LSW) thickness fields are examined. In the western Atlantic north of 50°N, the LSW thickness decreased considerably from 1994–97, while the mean CFC concentrations did not change much. South of 50°N and in the eastern Atlantic, the CFC concentration increased with little or no change in the LSW thickness. On shorter timescales, local anomalies due to the presence of eddies are observed, but for space scales larger than the eddies the dataset can be treated as being synoptic over the 1997 observation period. The spreading of LSW in the subpolar North Atlantic is described in detail using gridded CFC and LSW thickness fields combined with Profiling Autonomous Lagrangian Circulation Explorer (PALACE) float trajectories. The gridded fields are also used to calculate the CFC-11 inventory in the LSW from 40° to 65°N, and from 10° to 60°W. In total, 2300 ± 250 tons of CFC-11 (equivalent to 16.6 million moles) were brought into the LSW by deep convection. In 1997, 28% of the inventory was still found in the Labrador Sea west of 45°W and 31% of the inventory was located in the eastern Atlantic. The CFC inventory in the LSW was used to estimate the lower limits of LSW formation rates. At a constant formation rate, a value of 4.4–5.6 Sv (Sv ≡ 106 m3 s−1) is obtained. If the denser modes of LSW are ventilated only in periods with intense convection, the minimum formation rate of LSW in 1988–94 is 8.1–10.8 Sv, and 1.8–2.4 Sv in 1995–97
    Type: Article , PeerReviewed
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  • 15
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 28 . pp. 1410-1424.
    Publication Date: 2018-04-06
    Description: In the Gulf of Lions, observations of deep convection have been sporadically carried out over the past three decades, showing significant interannual variability of convection activity. As long time series of meteorological observations of the region are available from coastal stations, heat flux time series for the Gulf of Lions for the individual winters from 1969 to 1994 are derived by calibrating these observations against direct measurements obtained over the convection site. These heat fluxes are also compared against heat fluxes obtained by the French PERIDOT weather model for the winter of 1991/92. A Kraus–Turner one-dimensional mixed layer model is initialized by climatological mean temperature and salinity profiles and then driven by the heat flux time series of the individual years. Resulting convection depths are in satisfactory agreement with existing observational evidence, showing the dominance of interannual variability of local forcing on convection variability. The interannual variability of convection depth causes interannual variations in deep-water properties, and these are also compared with the hydrographic database.
    Type: Article , PeerReviewed
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  • 16
    Publication Date: 2023-03-09
    Description: 19 March 2021 – 25 May 2021 Emden (Germany) – Emden (Germany) TRR181 / TRAFFIC / EVAR / BANINO
    Type: Report , NonPeerReviewed
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  • 17
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