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  1. Article ; Online: Circulation and overturning in the eastern North Atlantic subpolar gyre

    Koman, G. / Johns, W.E. / Houk, A. / Houpert, L. / Li, F.

    Progress in Oceanography. 2022 Nov., v. 208 p.102884-

    2022  

    Abstract: This study describes new transport estimates of the North Atlantic Current in the Iceland Basin, and uses these results along with other contemporaneous measurements to determine mass and overturning budgets for the eastern North Atlantic subpolar gyre. ... ...

    Abstract This study describes new transport estimates of the North Atlantic Current in the Iceland Basin, and uses these results along with other contemporaneous measurements to determine mass and overturning budgets for the eastern North Atlantic subpolar gyre. As part of the Overturning in the Subpolar North Atlantic Program (OSNAP), estimates of the North Atlantic Current are determined using three full-depth dynamic height moorings spanning the Iceland Basin and are supplemented by Argo and satellite altimetry data. Along with historical estimates of the exchanges over the Iceland-Scotland Ridge, additional OSNAP results from the Rockall Trough and Rockall-Hatton Bank regions are used to calculate transport budgets in different density layers over a broad portion of the eastern subpolar gyre. Results show that 13–14 Sv of the North Atlantic Current (σθ < 27.8 kg m⁻³) flow northward into the middle of the Iceland Basin through a primary baroclinic flow near 23.5°W and a secondary quasi-barotropic flow near 26°W. Together with the observed northward flow in the Rockall-Hatton area, we conclude that 19–20 Sv of the upper limb of the Atlantic Meridional Overturning Circulation (σθ < 27.56 kg m⁻³) flows into the region where nearly 40 % of it (7.3 Sv) is converted into the lower limb primarily through progressive water mass modification from atmospheric cooling. This accounts for nearly half of the strength of Atlantic Meridional Overturning Circulation defined by the full OSNAP array extending across the basin from Greenland to Scotland.
    Keywords basins ; cooling ; oceanography ; satellite altimetry ; Greenland ; Iceland ; Scotland
    Language English
    Dates of publication 2022-11
    Publishing place Elsevier Ltd
    Document type Article ; Online
    ISSN 0079-6611
    DOI 10.1016/j.pocean.2022.102884
    Database NAL-Catalogue (AGRICOLA)

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  2. Article: Transport and Evolution of the East Reykjanes Ridge Current

    Koman, G. / Johns, W. E. / Houk, A.

    Journal of geophysical research. 2020 Oct., v. 125, no. 10

    2020  

    Abstract: This study of the first continuous multiyear observations of the East Reykjanes Ridge Current (ERRC) reveals a highly variable, mostly barotropic southwestward flow with a mean transport of 10–13 Sv. The ERRC effectively acts as a western boundary ... ...

    Abstract This study of the first continuous multiyear observations of the East Reykjanes Ridge Current (ERRC) reveals a highly variable, mostly barotropic southwestward flow with a mean transport of 10–13 Sv. The ERRC effectively acts as a western boundary current in the Iceland Basin on the eastern flank of the Reykjanes Ridge. As part of the Overturning in the Subpolar North Atlantic Program (OSNAP), continuous measurements of the ERRC have been maintained for the first time using acoustic Doppler current profilers, current meters, and dynamic height moorings at six mooring sites near 58°N since 2014. Together with satellite altimetry and Argo profile and drift data, the mean transport, synoptic variability, water mass properties, and upstream and downstream pathways of the ERRC are examined. Results show that the ERRC forms in the northeastern Iceland Basin at the convergence of surface waters from the North Atlantic Current and deeper Icelandic Slope Water formed along the Iceland‐Faroe Ridge. The ERRC becomes denser as it cools and freshens along the northern and western topography of the Basin before retroflecting over the Reykjanes Ridge near 59°N into the Irminger Current. Analysis of the flow‐weighted density changes along the ERRC's path reveals that it is responsible for about one third of the net potential density change of waters circulating around the rim of the subpolar gyre.
    Keywords acoustics ; basins ; evolution ; geophysics ; research ; satellite altimetry ; topography ; Iceland
    Language English
    Dates of publication 2020-10
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1029/2020JC016377
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  3. Article: Moored Observations of the Iceland‐Scotland Overflow Plume Along the Eastern Flank of the Reykjanes Ridge

    Johns, W. E. / Devana, M. / Houk, A. / Zou, S.

    Journal of geophysical research. 2021 Aug., v. 126, no. 8

    2021  

    Abstract: Since 2014, an array of current meters deployed in the Iceland Basin as part of the Overturning in the Subpolar North Atlantic Program has provided new measurements of the southward flow of Iceland‐Scotland Overflow Water (ISOW) along the eastern flank ... ...

    Abstract Since 2014, an array of current meters deployed in the Iceland Basin as part of the Overturning in the Subpolar North Atlantic Program has provided new measurements of the southward flow of Iceland‐Scotland Overflow Water (ISOW) along the eastern flank of the Reykjanes Ridge. The location of the array, near 58–59°N, captures the ISOW plume at the farthest downstream location in the Iceland Basin before significant amounts of ISOW can flow into the Irminger Basin through deep fractures in the Reykjanes Ridge. The net transport of the ISOW plume at this location—approximately 5.3 Sv based on the first 4 years of observations—is significantly larger than previous values obtained farther north in the Iceland Basin, suggesting that either previous measurements did not fully capture the plume transport or that additional entrainment into the ISOW plume occurs as it approaches the southern tip of the Reykjanes Ridge. A detailed water mass analysis of the plume from continuous temperature/salinity observations shows that about 50% of the plume transport (2.6 Sv) is derived from dense waters flowing over the Nordic Sea sills into the Iceland Basin, while the remainder is made up of nearly equal parts of entrained Atlantic thermocline water and modified Labrador Sea Water. The overall results from this study suggest that the ISOW plume approximately doubles its transport through entrainment, similar to that of the Denmark Strait overflow plume in the Irminger Sea that forms the other major overflow source of North Atlantic Deep Water.
    Keywords basins ; geophysics ; research ; salinity ; seawater ; temperature ; Iceland
    Language English
    Dates of publication 2021-08
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1029/2021JC017524
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  4. Book ; Online: The contribution of eastern-boundary density variations to the Atlantic meridional overturning circulation at 26.5° N

    Chidichimo, M. P. / Kanzow, T. / Cunningham, S. A. / Johns, W. E. / Marotzke, J.

    eISSN: 1812-0792

    2018  

    Abstract: We study the contribution of eastern-boundary density variations to sub-seasonal and seasonal anomalies of the strength and vertical structure of the Atlantic Meridional Overturning Circulation (AMOC) at 26.5° N, by means of the RAPID/MOCHA mooring array ...

    Abstract We study the contribution of eastern-boundary density variations to sub-seasonal and seasonal anomalies of the strength and vertical structure of the Atlantic Meridional Overturning Circulation (AMOC) at 26.5° N, by means of the RAPID/MOCHA mooring array between April 2004 and October 2007. The major density anomalies are found in the upper 500 m, and they are often coherent down to 1400 m. The densities have 13-day fluctuations that are apparent down to 3500 m. The two strategies for measuring eastern-boundary density – a tall offshore mooring (EB1) and an array of moorings on the continental slope (EBH) – show little correspondence in terms of amplitude, vertical structure, and frequency distribution of the resulting basin-wide integrated transport fluctuations, implying that there are significant transport contributions between EB1 and EBH. Contrary to the original planning, measurements from EB1 cannot serve as backup or replacement for EBH: density needs to be measured directly at the continental slope to compute the full-basin density gradient. Fluctuations in density at EBH generate transport variability of 2 Sv rms in the AMOC, while the overall AMOC variability is 4.8 Sv rms. There is a pronounced deep-reaching seasonal cycle in density at the eastern boundary, which is apparent between 100 m and 1400 m, with maximum positive anomalies in spring and maximum negative anomalies in autumn. These changes drive anomalous southward upper mid-ocean flow in spring, implying maximum reduction of the AMOC, and vice-versa in autumn. The amplitude of the seasonal cycle of the AMOC arising from the eastern-boundary densities is 5.2 Sv peak-to-peak, dominating the 6.7 Sv peak-to-peak seasonal cycle of the total AMOC. Our analysis suggests that the seasonal cycle in density may be forced by the strong near-coastal seasonal cycle in wind stress curl.
    Subject code 551
    Language English
    Publishing date 2018-01-15
    Publishing country de
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article: Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre From Sustained Glider Observations

    Houpert, L. / Inall, M. E. / Dumont, E. / Gary, S. / Johnson, C. / Porter, M. / Johns, W. E. / Cunningham, S. A.

    Journal of geophysical research. 2018 Aug., v. 123, no. 8

    2018  

    Abstract: Repeat glider sections obtained during 2014–2016, as part of the Overturning in the Subpolar North Atlantic Program, are used to quantify the circulation and transport of North Atlantic Current (NAC) branches over the Rockall Plateau. Using 16 glider ... ...

    Abstract Repeat glider sections obtained during 2014–2016, as part of the Overturning in the Subpolar North Atlantic Program, are used to quantify the circulation and transport of North Atlantic Current (NAC) branches over the Rockall Plateau. Using 16 glider sections collected along 58°N and between 21°W and 15°W, absolute geostrophic velocities are calculated, and subsequently the horizontal and vertical structure of the transport are characterized. The annual mean northward transport (± standard deviation) is 5.1 ± 3.2 Sv over the Rockall Plateau. During summer (May to October), the mean northward transport is stronger and reaches 6.7 ± 2.6 Sv. This accounts for 43% of the total NAC transport of upper‐ocean waters (σO<27.55 kg/m³) estimated by Sarafanov et al. (2012, https://doi.org/10.1029/2011JC007572) along 59.5°N, between the Reykjanes Ridge and Scotland. Two quasi‐permanent northward flowing branches of the NAC are identified: (i) the Hatton Bank Jet (6.3 ± 2.1 Sv) over the eastern flank of the Iceland Basin (20.5°W to 18.5°W) and (ii) the Rockall Bank Jet (1.5 ± 0.7 Sv) over the eastern flank of the Hatton‐Rockall Basin (16°W to 15°W). Transport associated with the Rockall Bank Jet is mostly depth independent during summer, while 30% of the Hatton Bank Jet transport is due to vertical geostrophic shear. Uncertainties are estimated for each individual glider section using a Monte Carlo approach, and mean uncertainties of the absolute transport are less than 0.5 Sv. Although comparisons with altimetry‐based estimates indicate similar large‐scale circulation patterns, altimetry data do not resolve small mesoscale current bands in the Hatton‐Rockall Basin which are strongly needed for the right transport estimates.
    Keywords altimetry ; basins ; geophysics ; research ; standard deviation ; summer ; Iceland ; Scotland
    Language English
    Dates of publication 2018-08
    Size p. 6019-6038.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1029/2018JC014162
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  6. Article ; Online: Tropical Atlantic variability and coupled model climate biases

    Johns, W. E. / Brandt, Peter / Chang, P.

    results from the Tropical Atlantic Climate Experiment (TACE)

    2014  

    Language English
    Publisher Springer
    Publishing country de
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  7. Article: Zonal structure and seasonal variability of the Atlantic Equatorial Undercurrent

    Johns, W. E / Brandt, P / Bourlès, B / Tantet, A / Papapostolou, A / Houk, A

    Climate dynamics. 2014 Dec., v. 43, no. 11

    2014  

    Abstract: Simultaneous mooring arrays were maintained along the path of the Equatorial Undercurrent (EUC) at three longitudes (23°W, 10°W, and 0°E), from October 2007 to June 2011, as part of the CLIVAR Tropical Atlantic Climate Experiment. The measurements allow ... ...

    Abstract Simultaneous mooring arrays were maintained along the path of the Equatorial Undercurrent (EUC) at three longitudes (23°W, 10°W, and 0°E), from October 2007 to June 2011, as part of the CLIVAR Tropical Atlantic Climate Experiment. The measurements allow for the first time a description of the seasonal cycle and interannual variability of the EUC across the Atlantic basin. The mean transport of the EUC at 23°W is 14.3 ± 0.6 Sv, decreasing to 12.1 ± 0.9 and 9.4 ± 0.6 Sv at 10°W and 0°E, respectively. The EUC shows a changing seasonal cycle across the basin: at 23°W, the strongest EUC transport occurs in boreal fall in association with maximum easterly wind stress, at 10°W the EUC transport shows a semiannual cycle with a maximum in boreal spring and fall, while at 0°E the EUC has a single spring maximum. At all locations the EUC core exhibits a similar seasonal vertical migration, with shallowest core depths occurring in boreal spring and deepest core depths in boreal fall. The maximum core intensity occurs in boreal spring all across the basin, when the EUC is shallow, during the annual wind relaxation. The weakest EUC core intensity occurs during the boreal summer cold tongue phase, especially in the eastern part of the basin. At both 23°W and 10°W, a deep extension of the EUC occurs in boreal summer, which increases the transport in the lower thermocline and partially offsets the weaker upper EUC transport during boreal summer. No clear linkage could be established between the interannual variability of the EUC in the eastern part of the basin and the intensity of the summer cold tongue, despite evidence for such a linkage in the western part of the basin.
    Keywords climate ; seasonal variation ; spring ; summer ; wind
    Language English
    Dates of publication 2014-12
    Size p. 3047-3069.
    Publishing place Springer-Verlag
    Document type Article
    ZDB-ID 1471747-5
    ISSN 1432-0894 ; 0930-7575
    ISSN (online) 1432-0894
    ISSN 0930-7575
    DOI 10.1007/s00382-014-2136-2
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  8. Article ; Online: The importance of deep, basinwide measurements in optimized Atlantic Meridional Overturning Circulation observing arrays

    McCarthy, G. D. / Menary, M. B. / Mecking, J. V. / Moat, Ben / Johns, W. E. / Andrews, M. B. / Rayner, D. / Smeed, D. A.

    Journal of geophysical research. 2017 Mar., v. 122, no. 3 p.1808-1826

    2017  

    Abstract: The Atlantic Meridional Overturning Circulation (AMOC) is a key process in the global redistribution of heat. The AMOC is defined as the maximum of the overturning stream function, which typically occurs near 30°N in the North Atlantic. The RAPID mooring ...

    Abstract The Atlantic Meridional Overturning Circulation (AMOC) is a key process in the global redistribution of heat. The AMOC is defined as the maximum of the overturning stream function, which typically occurs near 30°N in the North Atlantic. The RAPID mooring array has provided full‐depth, basinwide, continuous estimates of this quantity since 2004. Motivated by both the need to deliver near real‐time data and optimization of the array to reduce costs, we consider alternative configurations of the mooring array. Results suggest that the variability observed since 2004 could be reproduced by a single tall mooring on the western boundary and a mooring to 1500 m on the eastern boundary. We consider the potential future evolution of the AMOC in two generations of the Hadley Centre climate models and a suite of additional CMIP5 models. The modeling studies show that deep, basinwide measurements are essential to capture correctly the future decline of the AMOC. We conclude that, while a reduced array could be useful for estimates of the AMOC on subseasonal to decadal time scales as part of a near real‐time data delivery system, extreme caution must be applied to avoid the potential misinterpretation or absence of a climate time scale AMOC decline that is a key motivation for the maintenance of these observations.
    Keywords climate ; decline ; evolution ; geophysics ; heat ; motivation ; research
    Language English
    Dates of publication 2017-03
    Size p. 1808-1826.
    Publishing place John Wiley & Sons, Ltd
    Document type Article ; Online
    Note JOURNAL ARTICLE
    ZDB-ID 161667-5
    ISSN 2169-9291 ; 2169-9275 ; 0148-0227 ; 0196-2256
    ISSN (online) 2169-9291
    ISSN 2169-9275 ; 0148-0227 ; 0196-2256
    DOI 10.1002/2016JC012200
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  9. Article ; Online: Author Correction: Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation.

    Li, F / Lozier, M S / Bacon, S / Bower, A S / Cunningham, S A / de Jong, M F / deYoung, B / Fraser, N / Fried, N / Han, G / Holliday, N P / Holte, J / Houpert, L / Inall, M E / Johns, W E / Jones, S / Johnson, C / Karstensen, J / Le Bras, I A /
    Lherminier, P / Lin, X / Mercier, H / Oltmanns, M / Pacini, A / Petit, T / Pickart, R S / Rayner, D / Straneo, F / Thierry, V / Visbeck, M / Yashayaev, I / Zhou, C

    Nature communications

    2022  Volume 13, Issue 1, Page(s) 739

    Language English
    Publishing date 2022-02-02
    Publishing country England
    Document type Published Erratum
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-022-28397-3
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Book: Biggles

    Bergèse, Francis / Johns, W. E

    1994  

    Author's details Bergèse; Johns
    Size 48 S, überwiegend Ill
    Edition 1. Aufl
    Publisher Comicplus
    Publishing place Hamburg
    Document type Book
    ISBN 3894740426 ; 9783894740429
    Database Former special subject collection: coastal and deep sea fishing

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