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  • American Meteorological Society  (376)
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  • 1
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 11 pp.
    Publication Date: 2019-03-18
    Description: Dates of Cruise: 15.05. – 30.05.2018 Areas of Research: Physical, chemical, biological and fishery oceanography Port Calls: Riga. Latvia, 22.05.2018
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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  • 2
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 10 pp.
    Publication Date: 2019-02-15
    Description: Dates of Cruise: 16.04. – 29.04.2018 Areas of Research: Physical, chemical, biological and fishery oceanography Port Calls: Visby, Sweden, 21. - 22.04.2018
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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  • 3
    Publication Date: 2019-03-25
    Type: Software , NonPeerReviewed
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  • 4
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    American Meteorological Society
    In:  Journal of Climate, 32 (4). pp. 1101-1120.
    Publication Date: 2019-01-25
    Description: Proxy data and observations suggest that large tropical volcanic eruptions induce a poleward shift of the North Atlantic jet stream in boreal winter. However, there is far from universal agreement in models on this effect and its mechanism, and the possibilities of a corresponding jet shift in the Southern Hemisphere or the summer season have received little attention. Using a hierarchy of simplified atmospheric models, this study examines the impact of stratospheric aerosol on the extratropical circulation over the annual cycle. In particular, the models allow the separation of the dominant shortwave (surface cooling) and longwave (stratospheric warming) impacts of volcanic aerosol. It is found that stratospheric warming shifts the jet poleward in both summer and winter hemispheres. The experiments cannot definitively rule out the role of surface cooling, but provide no evidence that it shifts the jet poleward. Further study with simplified models demonstrates that the response to stratospheric warming is remarkably generic and does not depend critically on the boundary conditions (e.g., the planetary wave forcing) or the atmospheric physics (e.g., the treatment of radiative transfer and moist processes). It does, however, fundamentally involve both zonal-mean and eddy circulation feedbacks. The timescales, seasonality, and structure of the response provide further insight into the mechanism, as well as its connection to modes of intrinsic natural variability. These findings have implications for the interpretation of comprehensive model studies and for post-volcanic prediction
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  • 5
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 11 pp.
    Publication Date: 2019-06-26
    Description: R.V. Poseidon cruise no. 522 Dates, Ports: 10.04.2018 (Catania, Italy) – 29.04.2018 (Malaga, Spain) Research subject: Tephrostratigraphy of tsunami-related deposits at Stromboli Chief Scientist: Dr. Armin Freundt, GEOMAR, Kiel Number of Scientists: 11 Project: Stromboli tsunamis
    Type: Report , NonPeerReviewed
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  • 6
    Publication Date: 2019-07-25
    Type: Article , NonPeerReviewed
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  • 7
    Publication Date: 2019-08-16
    Description: Satellite observations and output from a high-resolution ocean model are used to investigate how the Loop Current in the Gulf of Mexico affects the Gulf Stream transport through the Florida Straits. We find that the expansion (contraction) of the Loop Current leads to lower (higher) transports through the Straits of Florida. The associated surface velocity anomalies are coherent from the southwestern tip of Florida to Cape Hatteras. A simple continuity-based argument can be used to explain the link between the Loop Current and the downstream Gulf Stream transport: as the Loop Current lengthens (shortens) its path in the Gulf of Mexico, the flow out of the Gulf decreases (increases). Anomalies in the surface velocity field are first seen to the southwest of Florida and within 4 weeks propagate through the Florida Straits up to Cape Hatteras and into the Gulf Stream Extension. In both the observations and the model this propagation can be seen as pulses in the surface velocities. We estimate that the Loop Current variability can be linked to a variability of several Sverdrups (1Sv = 10(6) m(3) s(-1)) through the Florida Straits. The exact timing of the Loop Current variability is largely unpredictable beyond a few weeks and its variability is therefore likely a major contributor to the chaotic/intrinsic variability of the Gulf Stream. However, the time lag between the Loop Current and the flow downstream of the Gulf of Mexico means that if a lengthening/shortening of the Loop Current is observed this introduces some predictability in the downstream flow for a few weeks.
    Type: Article , PeerReviewed
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  • 8
    Publication Date: 2019-08-19
    Description: Oceanic eddies are an important component in preconditioning the central Labrador Sea (LS) for deep convection and in restratifying the convected water. This study investigates the different sources and impacts of Eddy Kinetic Energy (EKE) and its temporal variability in the LS with the help of a 52-year long hindcast simulation of a 1/20° ocean model. Irminger Rings (IR) are generated in the West Greenland Current (WGC) between 60 and 62°N, mainly affect preconditioning and limit the northward extent of the convection area. The IR exhibit a seasonal cycle and decadal variations linked to the WGC strength, varying with the circulation of the subpolar gyre. The mean and temporal variations of IR generation can be attributed to changes in deep ocean baroclinic and upper ocean barotropic instabilities at comparable magnitudes. The main source of EKE and restratification in the central LS are Convective Eddies (CE). They are generated by baroclinic instabilities near the bottom of the mixed layer during and after convection. The CE have a mid-depth core and reflect the hydrographic properties of the convected water mass with a distinct minimum in potential vorticity. Their seasonal to decadal variability is tightly connected to the local atmospheric forcing and the associated air-sea heat fluxes. A third class of eddies in the LS are the Boundary Current Eddies shed from the Labrador Current (LC). Since they are mostly confined to the vicinity of the LC, these eddies appear to exert only minor influence on preconditioning and restratification.
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  • 9
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    GEOMAR
    In:  GEOMAR, 2 pp.
    Publication Date: 2019-08-26
    Description: DIPLANOAGAP (Distribution of plastics in the North Atlantic garbage patch), 17.08.-24.08.2019
    Type: Report , NonPeerReviewed
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  • 10
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    GEOMAR
    In:  GEOMAR Pressemitteilung , 03.09.2019 , 39/2019
    Publication Date: 2019-09-04
    Description: Umweltsensoren von GEOMAR und HZG wurden offenbar gewaltsam entfernt. 03.09.2019/Kiel. Im Dezember 2016 installierten das GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel und das Helmholtz-Zentrum Geesthacht in einem Sperrgebiet am Ausgang der Eckernförder Bucht ein Observatorium für Umweltmessungen am Meeresboden. Offenbar wurden die zwei, je 550 und 220 Kilogramm schweren Gestelle am 21. August mit großer Kraft von ihrer Position entfernt. Die Forscher fanden nur noch das zerfaserte Landanschlusskabel. Jetzt hoffen GEOMAR und HZG auf Hinweise, um die wertvollen Geräte zurückzuerhalten.
    Type: Newspaper report , NonPeerReviewed
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  • 11
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    GEOMAR
    In:  GEOMAR, 2 pp.
    Publication Date: 2019-09-02
    Description: 25.08.-01.09.2019
    Type: Report , NonPeerReviewed
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  • 12
    Publication Date: 2019-09-02
    Type: Article , NonPeerReviewed
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  • 13
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    GEOMAR
    In:  GEOMAR, 2 pp.
    Publication Date: 2019-09-10
    Description: 02.09.-08.09.2019
    Type: Report , NonPeerReviewed
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  • 14
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    GEOMAR
    In:  [Poster] In: deRSE19 - Konferenz für ForschungssoftwareentwicklerInnen in Deutschland, 04.-06.06.2019, Potsdam, Germany .
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 15
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    American Meteorological Society
    In:  Journal of Atmospheric and Oceanic Technology, 36 . pp. 281-296.
    Publication Date: 2019-09-23
    Description: The turbulent dissipation rate ɛ is a key parameter to many oceanographic processes. Recently gliders have been increasingly used as a carrier for microstructure sensors. Compared to conventional ship-based methods, glider-based microstructure observations allow for long duration measurements under adverse weather conditions, and at lower costs. The incident water velocity U is an input parameter for the calculation of the dissipation rate. Since U can not be measured using the standard glider sensor setup, the parameter is normally computed from a steady-state glider flight model. As ɛ scales with U2 or U4, depending whether it is computed from temperature or shear microstructure, flight model errors can introduce a significant bias. This study is the first to use measurements of in-situ glider flight, obtained with a profiling Doppler velocity log and an electromagnetic current meter, to test and calibrate a flight model, extended to include inertial terms. Compared to a previously suggested flight model, the calibrated model removes a bias of approximately 1 cm s−1 in the incident water velocity, which translates to roughly a factor of 1.2 in estimates of the dissipation rate. The results further indicate that 90% of the estimates of the dissipation rate from the calibrated model are within a factor of 1.1 and 1.2 for measurements derived from microstructure temperature sensors and shear probes, respectively. We further outline the range of applicability of the flight model.
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  • 16
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 9 pp.
    Publication Date: 2019-09-23
    Description: F.K. Littorina Cruise No.: L19-04 Date of cruise: 06.05. - 10.05.2019 Areas of research: Public relations and Aquarium West Shore Port Calls: Grenå DK (07.05. - 08.05. & 08.05 – 09.05.2019)
    Type: Report , NonPeerReviewed
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  • 17
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 3 pp.
    Publication Date: 2019-09-24
    Description: 09.09. bis 12.09.2019
    Type: Report , NonPeerReviewed
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  • 18
    Publication Date: 2019-10-08
    Description: In early 2017 we deployed eight KOSMOS [a] mesocosm units (53 m^3 each) close to ‘Isla San Lorenzo’ about 4.5 nm off-shore the Peruvian coastline (-12.0554667°, -077.2347667°). The aim of the study was to improve our mechanistic understanding of processes controlling plankton productivity, organic matter export, and particle stoichiometry in the coastal upwelling system off Peru. About 40 days into the study, Inca terns (Larosterna inca) – an abundant sea bird species in the region – discovered the mesocosms as suitable resting places. The birds were able to start and land on the very small areas lacking anti-bird spikes that were installed on the mesocosm roofs. Resting on the flotation frames as well as the opening of the mesocosm bags, they defecated into the enclosed water columns, adding new nutrients to the system. This orni-eutrophication from day 40 to 50 triggered intense phytoplankton blooms in the uppermost part of the enclosures where light was plentiful. This video illustrates the fertilizing effect of Inca tern defecation on phytoplankton communities during our mesocosm study in the upwelling system off Peru. [a] Kiel Off-Shore Mesocosms for Ocean Simulations
    Type: Video , NonPeerReviewed
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  • 19
    Publication Date: 2019-10-08
    Description: The reformed Common Fisheries Policy of the EU, in force since 2014, stipulates that overfishing by the fleets of its member states has to end latest in the year 2020. This study examines exploitation and status of 119 stocks fished by 20 countries in the Northeast Atlantic. In the year 2018, about 40% of the stocks were still subject to overfishing (F 〉 Fmsy), about 34% of the stocks were outside safe biological limits (B 〈 Bpa) and about 68% of the stocks were too depleted to produce maximum sustainable yields (B 〈 Bmsy). Reduction in the number of overfished stocks has stalled, possible because of an agreement between the European Commission (EC) and the International Council for the Exploration of the Seas (ICES), its advisory body for total allowed catches (TACs), wherein the EC requests ICES to give TAC advice leading to overfishing for many stocks. As a result, it is unlikely that overfishing will end in the Northeast Atlantic in 2020.
    Type: Report , NonPeerReviewed
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  • 20
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 7 pp.
    Publication Date: 2019-10-07
    Description: 23.09. - 27.09.2019
    Type: Report , NonPeerReviewed
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  • 21
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 4 pp.
    Publication Date: 2019-10-07
    Description: 18.-30.9.2019 The overall objective of this practical for students is to investigate the ecological role of gelatinous plankton in the Baltic Sea food webs and alongside the salinity gradient. To demonstrate the temporal as well as spatial variation of pelagic communities such as bacteria-, phyto and zooplankton as well as in the benthic food webs, different food web tracers will be used. Main focus here is therefore to obtain qualitative and quantitative sample sets of gelatinous zooplankton to investigate their distinct role on bentho-pelagic processes. Over the last several decades, a significant increase of both frequency and severity of jellyfish (JF) blooms were reported worldwide. Blooms of these organisms can extend for thousands of square kilometers, with drastic consequences and economic losses. When JF outbreak, they will not only affect the pelagic community by direct feeding on fish larvae, fish eggs or competing for the prey with bigger fishes, but only serve as organic matter source for benthic systems via sinking to the sea floor. Due to the scarcity of data on the potential role of gelatinous zooplankton from only few locations in the Baltic Sea, there is only a limited understanding on the role of JF in the bentho-pelagic food web of the Baltic Sea. A quantitative and qualitative assessment of gelatinous zooplankton in the BS systems and their functioning with regard to salinity gradient of the Baltic Sea , are now urgently needed to better account for the role of gelatinous zooplankton in the future of the system. Applicant and working group have performed this student research/educational cruise with the specific focus on jellyfish ecology every year and on a regular basis since 2013. During this two-week cruise students will perform the compulsory „Practical at Sea“. The general goal is to survey and characterize the temporal and special distribution of bacterial, phyto-, zooplankton and macroplankton specially jellyfish in Skagerrak and Baltic Sea
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  • 22
    Publication Date: 2019-10-07
    Description: 01.07. – 03.07.2019 Kiel (Germany) – Kiel (Germany) BiolOcPrac
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  • 23
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 3 pp.
    Publication Date: 2019-10-10
    Description: 02.09. bis 06.09.2019
    Type: Report , NonPeerReviewed
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  • 24
    Publication Date: 2019-10-30
    Description: 15 May – 30 May 2019, Kiel (Germany) – Kiel (Germany)
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  • 25
    Publication Date: 2019-11-07
    Description: Poseidon 533 – AIMAC (Atmosphere–ocean–island-biogeochemical interactions in the Macaronesian Archipelagos) investigated the influence of the Cape Verdes, the Canary Islands, and Madeira on the physics, chemistry and biology of the surrounding subtropical North- East Atlantic ocean. The air – sea exchange of halocarbons from marine sources impact tropospheric and stratospheric chemistry, and therewith air quality and human health. High oceanic and atmospheric concentrations of iodinated, brominated and chlorinated methanes are often found near coastlines. In particular, bromoform (CHBr3) was recently detected at unexpectedly high concentrations in seawater of subtropical coasts, e.g. at Miami and Tenerife beaches. Bromoform is produced naturally from macro algae and phytoplankton and is the major marine vector of organic bromine to the atmosphere. Together with dibromomethane (CH2Br2), it is the main contributor to natural stratospheric bromine, involved in ozone depletion. Bromoform is also a major product during disinfection of seawater for many industrial and recreational purposes and during desalination processes. While the bromoform production from phytoplankton generally leads to picomolar concentrations in seawater, macroalgal production yields nanomolar concentrations and disinfection processes involving seawater can increase concentrations to micromolar levels. The latter has led to the occasional application of this compound as tracer for the effluents of power plants and wastewater discharges. Other disinfection by-products (DBP) in the effluents can lead to unfavorable effects on the environment and human health. As bromoform shows large concentrations in urbanized and industrialized regions, the elevated concentrations at many coasts may have a major and increasing contribution to the global budget.. We hypothesize, that populated coastlines show elevated bromoform concentrations from disinfection activities, related to the amount of population and industrial activities. Coastal alongshore currents may additionally trap the compound inshore. Therefore, bromoform can be a good tracer of the terrestrial and anthropogenic signal in the island mass effect, which describes the increase in nutrients and biological productivity in the surrounding water masses of an island. POS533 investigated the bromoform distribution in ocean and atmosphere in the subtropical East Atlantic and the islands of Madeira, Tenerife, Gran Canaria and the Cape Verde Archipelago, considering physical and biogeochemical parameters, phytoplankton distribution and carbon chemistry. During the cruise new scientific tools where applied, to differentiate between the islands natural and anthropogenic interactions with ocean and atmosphere. The measurements deliver the first comprehensive biogeochemical data set of phytoplankton, microbiology, trace gases, carbon, oxygen and nutrient cycling from this region close the islands in exchange with the open ocean. Despite the novel knowledge, current climate chemistry and chemical transport models used to understand the anthropogenic signal of marine halocarbon emissions and their effects on tropospheric oxidation and stratospheric ozone will benefit from the expedition's dataset.
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  • 26
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 3 pp.
    Publication Date: 2019-11-04
    Description: M159 (29.10. – 20.11.2019) 1. Wochenbericht vom 3. November 2019
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  • 27
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 2 pp.
    Publication Date: 2019-11-11
    Description: M159 (29.10. – 20.11.2019) 2. Wochenbericht vom 10. November 2019
    Type: Report , NonPeerReviewed
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  • 28
    Publication Date: 2019-11-19
    Description: The RV Poseidon cruise 523 (POS523) is the second cruise to the work area as part of the observational program of the TRR 181 'Energy Transfers in Atmosphere and Ocean', and focussed on the energy transfer by low-mode internal waves. The goals of the cruise were to recover and redeploy a mooring to record the temporal variability of the internal wave field and associated energy fluxes, and to use time series CTD/LADCP/microstructure stations to assess locally the temporal variability of mixing, dissipation, and internal wave fluxes. The region south of the Azores in the east Atlantic is ideally suited for this kind of process study, because it is an area of a strong internal tide signal radiating away from the islands. The cruise track is located south of a chain of seamounts in a tidal beam formed by constructive interference of internal tides, and crosses the critical latitude for parametric subharmonic instability (PSI). During the cruise, we collected time series of CTD/LADCP and microstructure between 36 h and 52 h length on 5 stations in up to 4600 m water depth along the tidal beam between 29°20’N and 32°N latitude. In total 64 CTD/LADCP casts and 18 microstructure data sets were measured. The mooring equipped with current meter/temperature logger pairs and acoustic Doppler current profiler was successfully recovered and later redeployed along the track at 30°29’N, 30°12’W in a water depth of 4500 m (to be retrieved in 2019). All anticipated goals of the cruise were accomplished.
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  • 29
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 3 pp.
    Publication Date: 2019-11-18
    Description: M159 (29.10. – 20.11.2019) 3. Wochenbericht vom 17. November 2019
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  • 30
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 2 pp.
    Publication Date: 2019-12-11
    Description: 02.12.19 - 08.12.19
    Type: Report , NonPeerReviewed
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  • 31
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    American Meteorological Society
    In:  Journal of Physical Oceanography, 48 (2). pp. 261-281.
    Publication Date: 2019-02-01
    Description: Multi-year moored velocity observations of the Angola Current near 11°S reveal a weak southward mean flow superimposed by substantial intraseasonal to seasonal variability, including annual and semiannual cycles with distinct baroclinic structures. In the equatorial Atlantic these oscillations are associated with basin-mode resonances of the fourth and second baroclinic modes, respectively. Here, the role of basin-mode resonance and local forcing for the Angola Current seasonality are investigated. A suite of linear shallow-water models for the tropical Atlantic is employed, each model representing a single baroclinic mode forced at a specific period. The annually and semiannually oscillating forcing is given by 1) an idealized zonally uniform zonal forcing restricted to the equatorial band corresponding to a remote equatorial forcing or 2) realistic, spatially-varying Fourier components of wind stress data that include local forcing off Angola, particularly alongshore winds. Model-computed modal amplitudes are scaled to match moored velocity observations from the equatorial Atlantic. The observed annual cycle of alongshore velocity at 11°S is well reproduced by the remote equatorial forcing. Including local forcing slightly improves the agreement between observed and simulated semiannual oscillations at 11°S compared to the purely equatorial forcing. However, the model-computed semiannual cycle lacks amplitude at mid-depth. This could be the result of either underestimating the strength of the second equatorial basin-mode of the fourth baroclinic mode or other processes not accounted for in the shallow-water models. Overall, our findings underline the importance of large-scale linear equatorial wave dynamics for the seasonal variability of the boundary circulation off Angola.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 32
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 2 pp.
    Publication Date: 2018-03-05
    Description: Investigating deep water column biodiversity and ecology of the Cape Verde Islands Weekly report 21/2/2018-1/3/2018
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  • 33
    Publication Date: 2018-04-17
    Description: AtlantOS aims to improve ocean observing by strengthening international collaboration, sharing of ocean observing and by promoting engagement and innovation. The vision is to create together with the ocean community a coordinated, efficient, sustainable and purposeful system.
    Type: Video , NonPeerReviewed , info:eu-repo/semantics/other
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  • 34
    Publication Date: 2019-04-01
    Description: Benthic storms are important for both the energy budget of the ocean and for sediment resuspension and transport. Using 30 years of output from a high-resolution model of the North Atlantic, it is found that most of the benthic storms in the model occur near the western boundary in association with the Gulf Stream and the North Atlantic Current, in regions that are generally co-located with the peak near-bottom eddy kinetic energy. A common feature are meander troughs in the near-surface jets that are accompanied by deep low pressure anomalies spinning up deep cyclones with near-bottom velocities of up to more than 0.5 m/s. A case study of one of these events shows the importance of both baroclinic and barotropic instability of the jet, with energy being extracted from the jet in the upstream part of the meander trough and partly returned to the jet in the downstream part of the meander trough. This motivates examining the 30-year time mean of the energy transfer from the (annual mean) background flow into the eddy kinetic energy. This quantity is shown to be co-located well with the region in which benthic storms and large increases in deep cyclonic relative vorticity occur most frequently, suggesting an important role for mixed barotropic-baroclinic instability driven cyclogenesis in generating benthic storms throughout the model simulation. Regions of largest energy transfer and most frequent benthic storms are found to be the Gulf Stream west of the New England Seamounts and the North Atlantic Current near Flemish Cap.
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  • 35
    Publication Date: 2019-01-09
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  • 38
    Publication Date: 2018-01-19
    Description: Diese Broschüre und die gleichnamige Ausstellung befassen sich mit der Entwicklung des Echolots, für das der Kieler Physiker und Unternehmer Alexander Behm im Jahr 1913 das erste Patent erhielt. Erfahren Sie mehr über die Geschichte der Tiefenmessung im Ozean – von den ersten Handloten im alten Ägypten über die dampfgetriebenen Lotmaschinen des 19. Jahrhunderts, der Entwicklung der ozeanischen Tiefenkarten bis hin zur heutigen Vermessung des Meeresbodens mit modernen Fächerecholoten.
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  • 39
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    American Meteorological Society
    In:  Journal of the Atmospheric Sciences, 75 (8). pp. 2815-2826.
    Publication Date: 2019-03-01
    Description: The formation of secondary ice in clouds, i.e. ice particles that are created at temperatures above the limit for homogeneous freezing without the direct involvement of a heterogeneous ice nucleus is one of the longest standing puzzles in cloud physics. Here we present comprehensive laboratory investigations on the formation of small ice particles upon the freezing of drizzle-sized cloud droplets levitated in an electrodynamic balance. Four different categories of secondary ice formation (bubble bursting, jetting, cracking, breakup) could be detected and their respective frequencies of occurrence as a function of temperature and droplet size are given. We find that bubble bursting occurs more often than droplet splitting. While we do not observe the shattering of droplets into many large fragments, we find that the average number of small secondary ice particles released during freezing is strongly droplet-size dependent and may well exceed unity for droplets larger than 300 μm in diameter. This leaves droplet fragmentation an important secondary ice process effective at temperatures around -10 °C in clouds where large drizzle droplets are present.
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  • 40
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    American Meteorological Society
    In:  Journal of Climate, 31 (19). pp. 7969-7984.
    Publication Date: 2019-02-01
    Description: This study analyzes the response of the Atlantic meridional overturning circulation (AMOC) to different CO2 concentrations and two ice sheet configurations in simulations with the coupled climate model MPI-ESM. With preindustrial (PI) ice sheets, there are two different AMOC states within the studied CO2 range: one state with a strong and deep upper overturning cell at high CO2 concentrations and one state with a weak and shallow upper cell at low CO2 concentrations. Changes in AMOC variability with decreasing CO2 indicate two stability thresholds. The strong state is stable above the first threshold near 217 ppm, and the weak state is stable below the second threshold near 190 ppm. Between the two thresholds, both states are marginally unstable, and the AMOC oscillates between them on millennial time scales. The weak AMOC state is stable when Antarctic Bottom Water becomes dense and salty enough to replace North Atlantic Deep Water (NADW) in the deep North Atlantic and when the density gain over the North Atlantic becomes too weak to sustain continuous NADW formation. With Last Glacial Maximum (LGM) ice sheets, the density gain over the North Atlantic and the northward salt transport are enhanced with respect to the PI ice sheet case. This enables active NADW formation and a strong AMOC for the entire range of studied CO2 concentrations. The AMOC variability indicates that the simulated AMOC is far away from a stability threshold with LGM ice sheets. The nonlinear relationship among AMOC, CO2, and prescribed ice sheets provides an explanation for the large intermodel spread of AMOC states found in previous coupled LGM simulations.
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  • 41
    Publication Date: 2019-03-21
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  • 42
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 23 pp.
    Publication Date: 2019-04-04
    Description: 03.06.2018 – 15.06.2018
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  • 43
  • 44
    Publication Date: 2019-04-11
    Description: Laufzeit des Vorhabens: 01.01.2014-31.12.2017 : Berichtszeitraum: 01.01.2014-31.12.2017
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  • 45
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    American Meteorological Society
    In:  Earth Interactions, 22 (1). pp. 1-15.
    Publication Date: 2019-02-01
    Description: Predicting tropical cyclone (TC) activity becomes more important every year while the understanding of what factors impact them continues to be complicated. El Niño–Southern Oscillation (ENSO) is one of the primary factors impacting the activities in both the Pacific and the Atlantic, but an extensive examination of the fluctuation in this system has yet to be studied in its entirety. This article analyzes the ENSO impacts on the Atlantic tropical cyclone activity during the assessed warm and cold years to show the dominant centennial-scale variation impact. This study looks to plausibly link this variation to the Southern Ocean centennial variability, which is rarely mentioned in any factors affecting the Atlantic tropical cyclone activity. This centennial variability could be used to enhance future work related to predicting tropical cyclones.
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  • 46
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    American Meteorological Society
    In:  Journal of Physical Oceanography, 48 (12). pp. 2851-2865.
    Publication Date: 2019-02-01
    Description: Besides the zonal flow that dominates the seasonal and long-term variability in the equatorial Atlantic, energetic intraseasonal meridional velocity fluctuations are observed in large parts of the water column. We use 15 years of partly full-depth velocity data from an equatorial mooring at 23°W to investigate intraseasonal variability and specifically the downward propagation of intraseasonal energy from the near-surface into the deep ocean. Between 20 and 50 m, intraseasonal variability at 23°W peaks at periods between 30 and 40 days. It is associated with westward-propagating tropical instability waves, which undergo an annual intensification in August. At deeper levels down to about 2000 m considerable intraseasonal energy is still observed. A frequency–vertical mode decomposition reveals that meridional velocity fluctuations are more energetic than the zonal ones for periods 〈 50 days. The energy peak at 30–40 days and at vertical modes 2–5 excludes equatorial Rossby waves and suggests Yanai waves to be associated with the observed intraseasonal energy. Yanai waves that are considered to be generated by tropical instability waves propagate their energy from the near-surface west of 23°W downward and eastward to eventually reach the mooring location. The distribution of intraseasonal energy at the mooring position depends largely on the dominant frequency and the time, depth, and longitude of excitation, while the dominant vertical mode of the Yanai waves plays only a minor role. Observations also show the presence of weaker intraseasonal variability at 23°W below 2000 m that cannot be associated with tropical instability waves.
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  • 47
    Publication Date: 2019-03-26
    Description: This git repository contains all the scripts needed to reproduce our results from the study "Inter-chromosomal coupling between vision and pigmentation genes during genomic divergence" from raw data to figures. It contains all scripts referenced within the materials & methods section. Related datasets are deposited at ENA (raw sequencing data, acession nr. PRJEB27858) and dryad (genome annotation & genotypes, doi:10.5061/dryad.pg8q56g).
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  • 48
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 25 pp.
    Publication Date: 2019-03-05
    Description: 12.09.2018 – 22.09.2018
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  • 49
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 3 pp.
    Publication Date: 2018-02-26
    Description: Investigating deep water column biodiversity and ecology of the Cape Verde Islands Weekly report 14/2/2018-21/2/2018
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  • 50
    Publication Date: 2019-05-16
    Description: Downward wave coupling (DWC) is an important process that characterizes the dynamical coupling between the stratosphere and troposphere via planetary wave reflection. A recent modeling study indicated that natural forcing factors, including sea-surface temperature variability and quasi-biennial oscillation, influence DWC and the associated surface impact in the Northern Hemisphere (NH). In light of this, we further investigate how DWC in the NH is affected by anthropogenic forcings, using a fully coupled chemistry-climate model CESM1 (WACCM). The results indicate that the occurrence of DWC is significantly suppressed in the future, starting later in the seasonal cycle, with more events concentrated in late winter (February-March). The future decrease in DWC events is associated with enhanced wave absorption in the stratosphere due to increased greenhouse gases. The enhanced wave absorption is manifest as more absorbing types of stratospheric sudden warmings, with more events concentrated in early winter. This early winter condition leads to a delay in the development of the upper stratospheric reflecting surface, resulting in a shift in the seasonal cycle of DWC towards late winter. The tropospheric responses to DWC events in the future exhibit different spatial patterns compared to those of the past. In the North Atlantic sector, DWC-induced circulation changes are characterized by a poleward shift and an eastward extension of the tropospheric jet, while in the North Pacific sector, the circulation changes are characterized by a weakening of the tropospheric jet. These responses are consistent with a change in the pattern of DWC-induced synoptic-scale eddy-mean flow interaction.
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  • 51
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    American Meteorological Society
    In:  Journal of Physical Oceanography, 48 (4). pp. 757-771.
    Publication Date: 2019-05-27
    Description: The Eddy Kinetic Energy (EKE) associated with the Subtropical Countercurrent (STCC) in the western subtropical South Pacific is known to exhibit substantial seasonal and decadal variability. Using an eddy-permitting ocean general circulation model, which is able to reproduce the observed, salient features of the seasonal cycles of shear, stratification, baroclinic production and the associated EKE, we investigate the decadal changes of EKE. We show that the STCC region exhibits, uniquely among the subtropical gyres of the world’s oceans, significant, atmospherically forced, decadal EKE variability. The decadal variations are driven by changing vertical shear between the STCC in the upper 300 m and the South Equatorial Current below, predominantly caused by variations in STCC strength associated with a changing meridional density gradient. In the 1970s, an increased meridional density gradient results in EKE twice as large as in later decades in the model. Utilizing sensitivity experiments, decadal variations in the wind field are shown to be the essential driver. Local wind stress curl anomalies associated with the Interdecadal Pacific Oscillation (IPO) lead to up- and downwelling of the thermocline, inducing strengthening or weakening of the STCC and the associated EKE. Additionally, remote wind stress curl anomalies in the eastern subtropical South Pacific, which are not related to the IPO, generate density anomalies that propagate westward as Rossby waves and can account for up to 30–40 % of the density anomalies in the investigated region.
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  • 52
    Publication Date: 2019-05-27
    Description: The eastern boundary region off Angola encompasses a highly productive ecosystem important for the food security of the coastal population. The fish-stock distribution, however, undergoes large variability on intraseasonal, interannual, and longer time scales. These fluctuations are partly associated with large-scale warm anomalies that are often forced remotely from the equatorial Atlantic and propagate southward, reaching the Benguela upwelling off Namibia. Such warm events, named Benguela Niños, occurred in 1995 and in 2011. Here we present results from an underexplored extensive in situ dataset that was analyzed in the framework of a capacity-strengthening effort. The dataset was acquired within the Nansen Programme executed by the Food and Agriculture Organization of the United Nations and funded by the Norwegian government. It consists of hydrographic and velocity data from the Angolan continental margin acquired biannually during the main downwelling and upwelling seasons over more than 20 years. The mean seasonal changes of the Angola Current from 6° to 17°S are presented. During austral summer the southward Angola Current is concentrated in the upper 150 m. It strengthens from north to south, reaching a velocity maximum just north of the Angola Benguela Front. During austral winter the Angola Current is weaker, but deeper reaching. While the southward strengthening of the Angola Current can be related to the wind forcing, its seasonal variability is most likely explained by coastally trapped waves. On interannual time scales, the hydrographic data reveal remarkable variability in subsurface upper-ocean heat content. In particular, the 2011 Benguela Niño was preceded by a strong subsurface warming of about 2 years’ duration.
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  • 53
    Publication Date: 2019-06-01
    Description: Decadal variabilities in Indian Ocean subsurface ocean heat content (OHC; 50–300 m) since the 1950s are examined using ocean reanalyses. This study elaborates on how Pacific variability modulates the Indian Ocean on decadal time scales through both oceanic and atmospheric pathways. High correlations between OHC and thermocline depth variations across the entire Indian Ocean Basin suggest that OHC variability is primarily driven by thermocline fluctuations. The spatial pattern of the leading mode of decadal Indian Ocean OHC variability closely matches the regression pattern of OHC on the interdecadal Pacific oscillation (IPO), emphasizing the role of the Pacific Ocean in determining Indian Ocean OHC decadal variability. Further analyses identify different mechanisms by which the Pacific influences the eastern and western Indian Ocean. IPO-related anomalies from the Pacific propagate mainly through oceanic pathways in the Maritime Continent to impact the eastern Indian Ocean. By contrast, in the western Indian Ocean, the IPO induces wind-driven Ekman pumping in the central Indian Ocean via the atmospheric bridge, which in turn modifies conditions in the southwestern Indian Ocean via westward-propagating Rossby waves. To confirm this, a linear Rossby wave model is forced with wind stresses and eastern boundary conditions based on reanalyses. This linear model skillfully reproduces observed sea surface height anomalies and highlights both the oceanic connection in the eastern Indian Ocean and the role of wind-driven Ekman pumping in the west. These findings are also reproduced by OGCM hindcast experiments forced by interannual atmospheric boundary conditions applied only over the Pacific and Indian Oceans, respectively.
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  • 54
  • 55
    Publication Date: 2019-09-23
    Description: The AUV Abyss post-processing workflow is published as Jupyter Notebooks complementing the IEEE OES AUV 2018 conference contribution "AUV Abyss workflow: autonomous deep sea exploration for ocean research" (Klischies et al., 2018). The publication explains the application and use of these Notebooks in detail. The purpose of the Juypter Notebooks is to share, adapt, execute and document post- processing of AUV Abyss MBES data.
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  • 56
  • 57
    Publication Date: 2019-09-23
    Description: The North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) describe the dominant part of the variability in the Northern Hemisphere extratropical troposphere. Due to the strong connection of these patterns with surface climate, recent years have shown an increased interest and an increasing skill in forecasting them. However, it is unclear what the intrinsic limits of short-term predictability for the NAO and AO patterns are. This study compares the variability and predictability of both patterns, using a range of data and index computation methods for the daily NAO/AO indices. Small deviations from Gaussianity are found and characteristic decorrelation time scales of around one week. In the analysis of the Lyapunov spectrum it is found that predictability is not significantly different between the AO and NAO or between reanalysis products. Differences exist however between the indices based on EOF analysis, which exhibit predictability time scales around 12 - 16 days, and the station-based indices, exhibiting a longer predictability of 18 - 20 days. Both of these time scales indicate predictability beyond that currently obtained in ensemble prediction models for short-term predictability. Additional longer-term predictability for these patterns may be gained through local feedbacks and remote forcing mechanisms for particular atmospheric conditions.
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  • 58
    Publication Date: 2019-09-23
    Description: The Lagrangian analysis of sets of particles advected with the flow fields of ocean models are used to study connectivity, i.e. exchange pathways, timescales and volume transports, between distinct oceanic regions. One important factor influencing the dispersion of fluid particles and hence connectivity is the Lagrangian eddy diffusivity, which quantifies the influence of turbulent processes on the rate of particle dispersal. Due to spatial and temporal discretization, turbulence is not fully resolved in modelled velocities, and the concept of eddy diffusivity is used to parametrize the impact of unresolved processes. However, the relations between observational- and model-based Lagrangian eddy diffusivity estimates as well as eddy parameterizations are not clear. This study presents an analysis of the spatially variable near-surface lateral eddy diffusivity estimates obtained from Lagrangian trajectories simulated with 5-day mean velocities from an eddy-resolving ocean model (INALT01) for the Agulhas system. INALT01 features diffusive regimes for dynamically different regions, some of which exhibit strong suppression of eddy mixing by mean flow, and is consistent with the pattern and magnitude of drifter-based eddy diffusivity estimates. Using monthly-mean velocities decreases the estimated diffusivities less than eddy kinetic energy, supporting the idea that large and persistent eddy features dominate eddy diffusivities. For a non-eddying ocean model (ORCA05), Lagrangian eddy diffusivities are greatly reduced, in particular when the Gent and McWilliams parameterization of mesoscale eddies is employed.
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  • 59
    Publication Date: 2019-09-23
    Description: Projekt im Rahmen des BMBF-Aufrufs "Förderung von Forschungs- und Entwicklungsvorhaben zum Thema Kipppunkte, Dynamik und Wechselwirkungen von sozialen und ökologischen Systemen (BioTip)" : Projektlaufzeit: 1. Juni 2017 bis 31. Mai 2018
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  • 60
    Publication Date: 2019-09-23
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  • 61
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    GEOMAR
    In:  AtlantOS Newsletter, 1 (4). p. 8.
    Publication Date: 2019-10-07
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  • 62
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    GEOMAR
    In:  GEOMAR News, 2017 (03). pp. 10-11.
    Publication Date: 2018-01-18
    Description: Seit mehr als 25 Jahren lernen, arbeiten und leben Meereswissenschaftlerinnen und Meereswissenschaftler auf dem Kieler Forschungsschiff ALKOR. 500 Expeditionen hat das 55 Meter lange Schiff mittlerweile absolviert. Es ist neben der POSEIDON das zweite „mittelgroße“ Forschungsschiff, das am GEOMAR stationiert ist.
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  • 63
    Publication Date: 2019-04-04
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  • 64
    Publication Date: 2019-04-11
    Description: Laufzeit des Vorhabens:01.06.2015-30.11.2017
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  • 65
    Publication Date: 2019-02-01
    Description: The Weddell Sea polynya is a large opening in the open-ocean sea ice cover associated with intense deep convection in the ocean. A necessary condition to form and maintain a polynya is the presence of a strong subsurface heat reservoir. This study investigates the processes that control the stratification and hence the buildup of the subsurface heat reservoir in the Weddell Sea. To do so, a climate model run for 200 years under preindustrial forcing with two eddying resolutions in the ocean (0.25° CM2.5 and 0.10° CM2.6) is investigated. Over the course of the simulation, CM2.6 develops two polynyas in the Weddell Sea, while CM2.5 exhibits quasi-continuous deep convection but no polynyas, exemplifying that deep convection is not a sufficient condition for a polynya to occur. CM2.5 features a weaker subsurface heat reservoir than CM2.6 owing to weak stratification associated with episodes of gravitational instability and enhanced vertical mixing of heat, resulting in an erosion of the reservoir. In contrast, in CM2.6, the water column is more stably stratified, allowing the subsurface heat reservoir to build up. The enhanced stratification in CM2.6 arises from its refined horizontal grid spacing and resolution of topography, which allows, in particular, a better representation of the restratifying effect by transient mesoscale eddies and of the overflows of dense waters along the continental slope.
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  • 66
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    American Meteorological Society
    In:  Journal of Climate, 30 (22). pp. 8913-8927.
    Publication Date: 2019-02-01
    Description: The regional climate model COSMOin Climate Limited-AreaMode (COSMO-CLM or CCLM) is used with a high resolution of 15km for the entire Arctic for all winters 2002/03–2014/15. The simulations show a high spatial and temporal variability of the recent 2-m air temperature increase in the Arctic. The maximum warming occurs north of Novaya Zemlya in the Kara Sea and Barents Sea between March 2003 and 2012 and is responsible for up to a 208C increase. Land-based observations confirm the increase but do not cover the maximum regions that are located over the ocean and sea ice.Also, the 30-km version of theArctic SystemReanalysis (ASR) is used to verify the CCLM for the overlapping time period 2002/03–2011/12. The differences between CCLM and ASR 2-m air temperatures vary slightly within 18C for the ocean and sea ice area. Thus,ASR captures the extreme warming as well. The monthly 2-m air temperatures of observations and ERA-Interim data show a large variability for the winters 1979–2016. Nevertheless, the air temperature rise since the beginning of the twenty-first century is up to 8 times higher than in the decades before. The sea ice decrease is identified as the likely reason for the warming. The vertical temperature profiles show that the warming has a maximum near the surface, but a 0.58Cyr21 increase is found up to 2 km. CCLM, ASR, and also the coarser resolved ERA-Interim data show that February and March are the months with the highest 2-m air temperature increases, averaged over the ocean and sea ice area north of 708N; for CCLM the warming amounts to an average of almost 58C for 2002/03–2011/12.
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  • 67
    Publication Date: 2019-04-24
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  • 68
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    American Meteorological Society
    In:  Journal of Physical Oceanography, 47 (7). pp. 1685-1699.
    Publication Date: 2019-02-01
    Description: Seasonal variability in pathways of warm water masses toward the Kangerdlugssuaq Fjord-Glacier system (KF/KG), southeast Greenland, is investigated by backtracking Lagrangian particles seeded at the fjord mouth in a high-resolution regional ocean model simulation in the ice-free and the ice-covered seasons. The waters at KF are a mixture of Atlantic-origin water advected from the Irminger Basin (FF for Faxaflói), the deep waters from the Denmark Strait and the waters from the Arctic Ocean, both represented by the Kögur section (KO). Below 200m depth, the warm water is a mixture of FF and KO water masses, and is warmer in winter than in summer. We find that seasonal differences in pathways double the fraction of FF particles in winter, causing the seasonal warming and salinification. Seasonal temperature variations at the upstream sections (FF and KO) have a negligible impact on temperature variations near the fjord. Successful monitoring of heat flux to the fjord therefore needs to take place close to the fjord, and cannot be inferred from upstream conditions.
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  • 69
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 2 pp.
    Publication Date: 2017-06-07
    Description: Wochenbericht der Forschungsreise mit R.V. „Alkor“ AL 493 13.05.2017 – 20.05.2017
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  • 70
    Publication Date: 2017-08-11
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  • 71
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    American Meteorological Society
    In:  Journal of Climate, 30 (8). pp. 2921-2935.
    Publication Date: 2019-02-01
    Description: The ratio of global mean surface air temperature change to cumulative CO2 emissions, referred to as transient climate response to cumulative CO2 emissions (TCRE), has been shown to be approximately constant on centennial time scales. The mechanisms behind this constancy are not well understood, but previous studies suggest that compensating effects of ocean heat and carbon fluxes, which are governed by the same ocean mixing processes, could be one cause for this approximate constancy. This hypothesis is investigated by forcing different versions of the University of Victoria Earth System Climate Model, which differ in the ocean mixing parameterization, with an idealized scenario of 1% annually increasing atmospheric CO2 until quadrupling of the preindustrial CO2 concentration and constant concentration thereafter. The relationship between surface air warming and cumulative emissions remains close to linear, but the TCRE varies between model versions, spanning the range of 1.2°–2.1°C EgC−1 at the time of CO2 doubling. For all model versions, the TCRE is not constant over time while atmospheric CO2 concentrations increase. It is constant after atmospheric CO2 stabilizes at 1120 ppm, because of compensating changes in temperature sensitivity (temperature change per unit radiative forcing) and cumulative airborne fraction. The TCRE remains approximately constant over time even if temperature sensitivity, determined by ocean heat flux, and cumulative airborne fraction, determined by ocean carbon flux, are taken from different model versions with different ocean mixing settings. This can partially be explained with temperature sensitivity and cumulative airborne fraction following similar trajectories, which suggests ocean heat and carbon fluxes scale approximately linearly with changes in vertical mixing.
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  • 72
    Publication Date: 2019-02-01
    Description: Arctic sea ice area (SIA) during late summer and early fall decreased substantially over the last four decades, and its decline accelerated beginning in the early 2000s. Statistical analyses of observations show that enhanced poleward moisture transport from the North Pacific to the Arctic Ocean contributed to the accelerated SIA decrease during the most recent period. As a consequence, specific humidity in the Arctic Pacific sector significantly increased along with an increase of downward longwave radiation beginning in 2002, which led to a significant acceleration in the decline of SIA in the Arctic Pacific sector. The resulting sea ice loss led to increased evaporation in the Arctic Ocean, resulting in a further increase of the specific humidity in mid-to-late fall, thus acting as a positive feedback to the sea ice loss. The overall set of processes is also found in a long control simulation of a coupled climate model.
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  • 73
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 17 pp.
    Publication Date: 2018-01-22
    Description: 14.08. – 25.08.2017 Port Calls: Gdynia, Poland: 19.08. – 20.08.2017
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  • 74
    Publication Date: 2017-12-13
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  • 75
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    American Meteorological Society
    In:  Journal of Climate, 30 (2). pp. 509-525.
    Publication Date: 2019-02-01
    Description: By performing two sets of high-resolution atmospheric general circulation model (AGCM) experiments, we find that the atmospheric response to a sea surface temperature (SST) anomaly in the extratropical North Pacific is sensitive to decadal variations of the background SST on which the SST anomaly is superimposed. The response in the first set of experiments, in which the SST anomaly is superimposed on the observed daily SST of 1981-1990, strongly differs from the response in the second experiment, in which the same SST anomaly is superimposed on the observed daily SST of 1991-2000. The atmospheric response over the North Pacific during 1981-1990 is eddy-mediated, equivalent barotropic and concentrated in the east. In contrast, the atmospheric response during 1991-2000 is weaker and strongest in the west. The results are discussed in terms of Rossby wave dynamics, with the proposed primary wave source switching from baroclinic eddy vorticity forcing over the eastern North Pacific in 1981-1990 to mean flow divergence over the western North Pacific in 1991-2000. The wave source changes are linked to the decadal reduction of daily SST variability over the eastern North Pacific and strengthening of the Oyashio Extension front over the western North Pacific. Thus, both daily and frontal aspects of the background SST variability in determining the atmospheric response to extratropical North Pacific SST anomalies are emphasized by our AGCM experiments.
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  • 76
    Publication Date: 2019-02-25
    Description: The Indian Ocean has sustained robust surface warming in recent decades, but the role of multi-decadal variability remains unclear. Using ocean model hindcasts, characteristics of low-frequency Indian Ocean temperature variations are explored. Simulated upper-ocean temperature changes across the Indian Ocean in the hindcast are consistent with those recorded in observational products and ocean reanalyses. Indian Ocean temperatures exhibit strong warming trends since the 1950s limited to the surface and south of 30°S, while extensive subsurface cooling occurs over much of the tropical Indian Ocean. Previous work focused on diagnosing causes of these long-term trends in the Indian Ocean over the second half of the 20th Century. Instead, the temporal evolution of Indian Ocean subsurface heat content is shown here to reveal distinct multi-decadal variations associated with the Pacific Decadal Oscillation and the long-term trends are thus interpreted to result from aliasing of the low-frequency variability. Transmission of the multi-decadal signal occurs via an oceanic pathway through the Indonesian Throughflow and is manifest across the Indian Ocean centered along 12°S as westward propagating Rossby waves modulating thermocline and subsurface heat content variations. Resulting low-frequency changes in the eastern Indian Ocean thermocline depth are associated with decadal variations in the frequency of Indian Ocean Dipole (IOD) events, with positive IOD events unusually common in the 1960s and 1990s with a relatively shallow thermocline. In contrast, the deeper thermocline depth in the 1970s and 1980s is associated with frequent negative IOD and rare positive IOD events. Changes in Pacific wind forcing in recent decades and associated rapid increases in Indian Ocean subsurface heat content can thus affect the basin’s leading mode of variability, with implications for regional climate and vulnerable societies in surrounding countries.
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  • 77
    Publication Date: 2019-02-01
    Description: For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.
    Type: Article , PeerReviewed
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  • 78
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    American Meteorological Society
    In:  Journal of Climate, 30 (22). pp. 9321-9337.
    Publication Date: 2019-05-27
    Description: In the present study, the influence of some major tropical modes of variability on northern hemisphere regional blocking frequency variability during boreal winter is investigated. Reanalysis data and an ensemble experiment with the ECMWF model using relaxation towards the ERA-Interim reanalysis data inside the tropics are used. The tropical modes under investigation are El Niño Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO) and the upper tropospheric equatorial zonal-mean zonal wind . An early (late) MJO phase refers to the part of the MJO cycle when enhanced (suppressed) precipitation occurs over the western Indian Ocean and suppressed (enhanced) precipitation occurs over the Maritime Continent and the western tropical Pacific. Over the North Pacific sector, it is found that enhanced (suppressed) high latitude blocking occurs in association with El Niño (La Niña) events, late (early) MJO phases and westerly (easterly) . Over central to southern Europe and the east Atlantic, it is found that late MJO phases, as well as a suppressed MJO are leading to enhanced blocking frequency. Furthermore, early (late) MJO phases are followed by blocking anomalies over the western North Atlantic region, similar to those associated with a positive (negative) North Atlantic Oscillation. Over northern Europe, the easterly (westerly) phase of is associated with enhanced (suppressed) blocking. These results are largely confirmed by both the reanalysis and the model experiment.
    Type: Article , PeerReviewed
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  • 79
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    American Meteorological Society
    In:  Journal of Climate, 30 (12). pp. 4337-4350.
    Publication Date: 2019-05-27
    Description: Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in the Weddell and Ross Seas melt at rates orders of magnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet.
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  • 80
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    GEOMAR
    In:  GEOMAR, Kiel, Germany, 18 pp.
    Publication Date: 2019-06-28
    Description: Dates, Ports: 09.05.2017 (Heraklion, Crete) – 24.05.2017 (Heraklion, Crete) Research subject: Tephrostratigraphy along the Aegean arc Chief Scientist: Dr. Armin Freundt, GEOMAR, Kiel Number of Scientists: 11 Project: Aegean Tephras
    Type: Report , NonPeerReviewed
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  • 81
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    Unknown
    American Meteorological Society
    In:  Journal of Climate, 30 (14). pp. 5491-5512.
    Publication Date: 2019-09-23