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  • Wiley  (6)
  • AMS (American Meteorological Society)  (5)
  • GEOMAR  (1)
  • 1
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    Winter to summer oceanographic observations in the Arctic Ocean north of Svalbard (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 122 (8). pp. 6218-6237.
    Details
    Publication Date: 2020-02-06
    Description: Oceanographic observations from the Eurasian Basin north of Svalbard collected between January and June 2015 from the N-ICE2015 drifting expedition are presented. The unique winter observations are a key contribution to existing climatologies of the Arctic Ocean, and show a ∼100 m deep winter mixed layer likely due to high sea ice growth rates in local leads. Current observations for the upper ∼200 m show mostly a barotropic flow, enhanced over the shallow Yermak Plateau. The two branches of inflowing Atlantic Water are partly captured, confirming that the outer Yermak Branch follows the perimeter of the plateau, and the inner Svalbard Branch the coast. Atlantic Water observed to be warmer and shallower than in the climatology, is found directly below the mixed layer down to 800 m depth, and is warmest along the slope, while its properties inside the basin are quite homogeneous. From late May onwards, the drift was continually close to the ice edge and a thinner surface mixed layer and shallower Atlantic Water coincided with significant sea ice melt being observed.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2016JC012391
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    The surface diurnal warm layer in the Indian Ocean during CINDY/DYNAMO (2014)
    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 . pp. 9101-9122.
    Details
    Publication Date: 2015-11-24
    Description: A surface diurnal warm layer is diagnosed from Seaglider observations, and develops on half the days in the CINDY/DYNAMO Indian Ocean experiment. The diurnal warm layer occurs on days of high solar radiation flux (〉 80 W m−2) and low wind speed (〈 6 m s−1), and preferentially in the inactive stage of the Madden–Julian Oscillation. Its diurnal harmonic has an exponential vertical structure with a depth scale of 4–5 m (dependent on chlorophyll concentration), consistent with forcing by absorption of solar radiation. The effective sea surface temperature (SST) anomaly due to the diurnal warm layer often reaches 0.8°C in the afternoon, with a daily mean of 0.2°C, rectifying the diurnal cycle onto longer time scales. This SST anomaly drives an anomalous flux of 4 W m−2 that cools the ocean. Alternatively, in a climate model where this process is unresolved, this represents an erroneous flux that warms the ocean. A simple model predicts a diurnal warm layer to occur on 30–50% of days across the tropical warm pool. On the remaining days, with low solar radiation and high wind speeds, a residual diurnal cycle is observed by the Seaglider, with a diurnal harmonic of temperature that decreases linearly with depth. As wind speed increases, this already weak temperature gradient decreases further, tending towards isothermal conditions.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/jcli-d-14-00222.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Seaglider observations of equatorial Indian Ocean Rossby waves associated with the Madden-Julian Oscillation (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (6). pp. 3714-3731.
    Details
    Publication Date: 2018-02-26
    Description: During the CINDY–DYNAMO field campaign of September 2011–January 2012, a Seaglider was deployed at 80°E and completed 10 north-south sections between 3 and 4°S, measuring temperature, salinity, dissolved oxygen concentration, and chlorophyll fluorescence. These high-resolution subsurface observations provide insight into equatorial ocean Rossby wave activity forced by three Madden-Julian Oscillation (MJO) events during this time period. These Rossby waves generate variability in temperature O(1°C), salinity O(0.2 g kg−1), density O(0.2 kg m−3), and oxygen concentration O(10 μmol kg−1), associated with 10 m vertical displacements of the thermocline. The variability extends down to 1000 m, the greatest depth of the Seaglider observations, highlighting the importance of surface forcing for the deep equatorial ocean. The temperature variability observed by the Seaglider is greater than that simulated in the ECCO-JPL reanalysis, especially at depth. There is also marked variability in chlorophyll fluorescence at the surface and at the depth of the chlorophyll maximum. Upwelling from Rossby waves and local wind stress curl leads to an enhanced shoaling of the chlorophyll maximum by 10–25 m in response to the increased availability of nutrients and light. This influence of the MJO on primary production via equatorial ocean Rossby waves has not previously been recognized.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2013JC009657
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Multidecadal Warming and Shoaling of Antarctic Intermediate Water (2012)
    AMS (American Meteorological Society)
    In:  Journal of Climate, 25 (1). pp. 207-221.
    Details
    Publication Date: 2014-10-21
    Description: Antarctic Intermediate Water (AAIW) is a dominant Southern Hemisphere water mass that spreads from its formation regions just north of the Antarctic Circumpolar Current (ACC) to at least 20°S in all oceans. This study uses an isopycnal climatology constructed from Argo conductivity–temperature–depth (CTD) profile data to define the current state of the AAIW salinity minimum (its core) and thence compute anomalies of AAIW core pressure, potential temperature, salinity, and potential density since the mid-1970s from ship-based CTD profiles. The results are used to calculate maps of temporal property trends at the AAIW core, where statistically significant strong circumpolar shoaling (30–50 dbar decade−1), warming (0.05°–0.15°C decade−1), and density reductions [up to −0.03 (kg m−3) decade−1] are found. These trends are strongest just north of the ACC in the southeast Pacific and Atlantic Oceans and decrease equatorward. Salinity trends are generally small, with their sign varying regionally. Bottle data are used to extend the AAIW core potential temperature anomaly analysis back to 1925 in the Atlantic and to ~1960 elsewhere. The modern warm AAIW core conditions appear largely unprecedented in the historical record: biennially and zonally binned median AAIW core potential temperatures within each ocean basin are, with the notable exception of the subtropical South Atlantic in the 1950s–70s, 0.2–1°C colder than modern values. Zonally averaged sea surface temperature anomalies around the AAIW formation latitudes in each ocean and sectoral southern annular mode indices are used to put the AAIW core property trends and variations into context.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/JCLI-D-11-00021.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    The North Pacific Oxygen Uptake Rates Over the Past Half-Century (2016)
    AMS (American Meteorological Society)
    In:  Journal of Climate, 29 (1). pp. 61-76.
    Details
    Publication Date: 2019-02-01
    Description: The transport of dissolved oxygen (O2) from the surface ocean into the interior is a critical process sustaining aerobic life in mesopelagic ecosystems, but its rates and sensitivity to climate variations are poorly understood. Using a circulation model constrained to historical variability by assimilation of observations, we show that the North Pacific thermocline effectively takes up O2 primarily by expanding the area through which O2-rich mixed layer water is detrained into the thermocline. The outcrop area during the critical winter season varies in concert with the Pacific Decadal Oscillation (PDO). When the central North Pacific Ocean is in a cold phase, the winter outcrop window for the Central Mode Water class (CMW; a neutral density range of γ = 25.6 - 26.6) expands southward allowing more O2-rich surface water to enter the ocean’s interior. An increase in volume flux of water to the CMW density class is partly compensated by a reduced supply to the shallower densities of Subtropical Mode Water (γ = 24.0 - 25.5). The thermocline has become better oxygenated since the 1980s due partly to strong O2 uptake. Positive O2 anomalies appear first near the outcrop and subsequently downstream in the subtropical gyre. In contrast to the O2 variations within the ventilated thermocline, observed O2 in Intermediate Water (density range of γ = 26.7 – 27.2) shows a declining trend over the past half-century, a trend not explained by the open ocean water mass formation rate.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/JCLI-D-14-00157.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    The ocean mixed-layer under Southern Ocean sea-ice: Seasonal cycle and forcing (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 122 (2). pp. 1608-1633.
    Details
    Publication Date: 2020-02-06
    Description: The oceanic mixed-layer is the gateway for the exchanges between the atmosphere and the ocean; in this layer all hydrographic ocean properties are set for months to millennia. A vast area of the Southern Ocean is seasonally capped by sea-ice, which alters the characteristics of the ocean mixed-layer. The interaction between the ocean mixed-layer and sea-ice plays a key role for water-mass transformation, the carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the under-ice mixed-layer are poorly understood due to the sparseness of in-situ observations and measurements. In this study, we combine distinct sources of observations to overcome this lack in our understanding of the Polar Regions. Working with Elephant Seal-derived observations, ship-based and Argo float observations, we describe the seasonal cycle of the ocean mixed-layer characteristics and stability of the ocean mixed-layer over the Southern Ocean and specifically under sea-ice. Mixed-layer heat and freshwater budgets are used to investigate the main forcing mechanisms of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget, and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity and vertical entrainment play only secondary roles.Our results suggest that changes in regional sea-ice distribution and annual duration, as currently observed, widely affect the buoyancy budget of the underlying mixed-layer, and impact large-scale water-mass formation and transformation with far reaching consequences for ocean ventilation.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2016JC011970
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    The Southern Ocean Observing System (SOOS) (2015)
    AMS (American Meteorological Society)
    In:  Bulletin of the American Meteorological Society, 96, Special supplement (7). S157-S160.
    Details
    Publication Date: 2018-06-20
    Description: [in “State of the Climate in 2014” : Special Supplement to the Bulletin of the American Meteorological Society Vol. 96, No. 7, July 2015]
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    BMBF-Verbundvorhaben "MIKLIP" : Abschlussbericht des Teilprojekt OCEANOBS am GEOMAR : verification of ensembles and initialization fields for decadal climate predictions via ocean observation systems (2016)
    GEOMAR
    In:  GEOMAR, Kiel, Germany, 15 pp.
    Details
    Publication Date: 2019-04-11
    Type: Report , NonPeerReviewed
    Format: text
    DOI: 10.2314/GBV:892789085
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    OceanRep: Report - other report
  • 9
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    The Atlantic Subtropical Cells inferred from observations (2019)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2022-02-18
    Description: The Atlantic Subtropical Cells (STCs) are shallow wind‐driven overturning circulations connecting the tropical upwelling areas to the subtropical subduction regions. In both hemispheres they are characterized by equatorward transport at thermocline level, upwelling at the equator and poleward Ekman transport in the surface layer. This study uses recent data from Argo oats complemented by ship sections at the western boundary as well as reanalysis products to estimate the meridional water mass transports and to investigate the vertical and horizontal structure of the STCs from an observational perspective. The seasonally varying depth of meridional velocity reversal is used as the interface between the surface poleward ow and the thermocline equatorward ow. The latter is bounded by the 26.0 kg m‐3 isopycnal at depth. We find that the thermocline layer convergence is dominated by the southern hemisphere water mass transport (9.0 ±1.1 Sv from the southern hemisphere compared to 2.9 ±1.3 Sv from the northern hemisphere) and that this transport is mostly confined to the western boundary. Compared to the asymmetric convergence at thermocline level, the wind‐driven Ekman divergence in the surface layer is more symmetric, being 20.4 ±3.1 Sv between 10°N and 10°S. The net poleward transports (Ekman minus geostrophy) in the surface layer concur with values derived from reanalysis data (5.5 ±0.8 Sv at 10°S and 6.4 ±1.4 Sv at 10°N). A diapycnal transport of about 4 Sv across the 26.0 kg m‐3 isopycnal is required in order to maintain the mass balance in the STC circulation.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    The Weddell Gyre, Southern Ocean: Present Knowledge and Future Challenges (2019)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-03-09
    Description: The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures, and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide, and global modeling efforts—thereby enhancing predictions of the WG in global ocean circulation and climate.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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