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  • 1
    Book
    Book
    Entrainment in the Denmark Strait overflow plume by meso-scale eddies (2006)
    Hamburg
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    Keywords: Hochschulschrift
    Type of Medium: Book
    Pages: 80 S , Ill., graph. Darst.
    Language: English
    Note: Hamburg, Univ., FB Physik+Geowiss., Dipl., 2006
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  • 2
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    Entrainment in the Denmark Strait Overflow Plume by meso-scale Eddies (2007)
    In:  (Diploma thesis), Universität Hamburg, Hamburg, Germany, 80 pp
    Details
    Publication Date: 2015-06-11
    Type: Thesis , NonPeerReviewed
    Format: text
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    OceanRep: Thesis - not published by a publisher
  • 3
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    Eddies, topography, and the abyssal flow by the Kyushu-Palau Ridge near Velasco Reef (2020)
    The Oceanography Society
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Andres, M., Siegelman, M., Hormann, V., Musgrave, R. C., Merrifield, S. T., Rudnick, D. L., Merrifield, M. A., Alford, M. H., Voet, G., Wijesekera, H. W., MacKinnon, J. A., Centurioni, L., Nash, J. D., & Terrill, E. J. Eddies, topography, and the abyssal flow by the Kyushu-Palau Ridge near Velasco Reef. Oceanography, 32(4), (2019): 46-55, doi: 10.5670/oceanog.2019.410.
    Description: Palau, an island group in the tropical western North Pacific at the southern end of Kyushu-Palau Ridge, sits near the boundary between the westward-​flowing North Equatorial Current (NEC) and the eastward-flowing North Equatorial Countercurrent. Combining remote-sensing observations of the sea surface with an unprecedented in situ set of subsurface measurements, we examine the flow near Palau with a particular focus on the abyssal circulation and on the deep expression of mesoscale eddies in the region. We find that the deep currents time-averaged over 10 months are generally very weak north of Palau and not aligned with the NEC in the upper ocean. This weak abyssal flow is punctuated by the passing of mesoscale eddies, evident as sea surface height anomalies, that disrupt the mean flow from the surface to the seafloor. Eddy influence is observed to depths exceeding 4,200 m. These deep-​reaching mesoscale eddies typically propagate westward past Palau, and as they do, any associated deep flows must contend with the topography of the Kyushu-Palau Ridge. This interaction leads to vertical structure far below the main thermocline. Observations examined here for one particularly strong and well-sampled eddy suggest that the flow was equivalent barotropic in the far field east and west of the ridge, with a more complicated vertical structure in the immediate vicinity of the ridge by the tip of Velasco Reef.
    Description: We gratefully acknowledge the help of Captain David Murline and the crew of R/V Roger Revelle and the shore-based assistance of Lori Colin and Pat Colin of the Coral Reef Research Foundation. We sincerely thank Terri Paluszkiewicz for her steadfast support of basic research programs, including FLEAT, during her many years of service to the community as Office of Naval Research (ONR) Physical Oceanography Program Manager. MA was supported by ONR grant N000141612668, MS and MAM by N00014-16-1-2671, MHA and JAM by N00014-15-1-2264 and N00014-16-1-3070, GV by N00014-15-1-2592, DLR by N00014- 15-1-2488, and STM and EJT by N00014-15-1-2304. VH and LC were supported by ONR grant N00014-15-1-2286 and NOAA GDP grant NA15OAR4320071. RCM was supported by the Postdoctoral Scholar Program at the Wood Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship. We thank the Palau National Government for permission to carry out the research in Palau.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    A spatial geography of abyssal turbulent mixing in the Samoan passage (2020)
    Oceanography Society
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Carter, G. S., Voet, G., Alford, M. H., Girton, J. B., Mickett, J. B., Klymak, J. M., Pratt, L. J., Pearson-Potts, K. A., Cusack, J. M., & Tan, S. A spatial geography of abyssal turbulent mixing in the Samoan passage. Oceanography, 32(4), (2019): 194-203, doi: 10.5670/oceanog.2019.425.
    Description: High levels of turbulent mixing have long been suspected in the Samoan Passage, an important topographic constriction in the deep limb of the Pacific Meridional Overturning Circulation. Along the length of the passage, observations undertaken in 2012 and 2014 showed the bottom water warmed by ~55 millidegrees Celsius and decreased in density by 0.01 kg m–3. Spatial analysis of this first-ever microstructure survey conducted in the Samoan Passage confirmed there are multiple hotspots of elevated abyssal mixing. This mixing was not just confined to the four main sills—even between sills, the nature of the mixing processes appeared to differ: for example, one sill is clearly a classical hydraulically controlled overflow, whereas another is consistent with mode-2 hydraulic control. When microstructure casts were averaged into 0.1°C conservative temperature classes, the largest dissipation rates and diapycnal diffusivity values (〉10–7 W kg–1 and 10–2 m2 s–1, respectively) occurred immediately downstream of the northern sill in the eastern and deepest channel. Although topographic blocking is the primary reason that no water colder than Θ = 0.7°C is found in the western channel, intensive mixing at the entrance sills appeared to be responsible for eroding an approximately 100 m thick layer of Θ 〈 0.7°C water. Three examples highlighting weak temporal variability, and hence suggesting that the observed spatial patterns are robust, are presented. The spatial variability in mixing over short lateral scales suggests that any simple parameterization of mixing within the Samoan Passage may not be applicable.
    Description: This work was funded by the National Science Foundation under grants OCE-1029268, OCE-1029483, OCE-1657264, OCE-1657870, OCE-1658027, and OCE-1657795.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Internal wave breaking near the foot of a steep East-Pacific continental slope (2022)
    Elsevier
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    Publication Date: 2022-09-14
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in van Haren, H., Voet, G., Alford, M., & Torres, D. Internal wave breaking near the foot of a steep East-Pacific continental slope. Progress In Oceanography, 205, (2022): 102817, https://doi.org/10.1016/j.pocean.2022.102817.
    Description: The sloping sides of ocean basins are of particular interest for their potential importance for considerable turbulence generation via internal wave breaking and associated water circulation. The difference with the ocean interior may be manifest in a 10–100 m relatively thin layer above the seafloor. We set up an observational study with high-resolution stand-alone instrumentation attached to a custom-made release-anchor frame sampling to within 0.5 m from the seafloor up to 150 m above it. For two months, the taut wire moored instrumentation was tested in 1100 m water depth of the East-Pacific, off the coast of San Diego (CA, USA). The mooring was oceanward of an underwater bank and near the foot of its steep but gentle two-dimensional slope. Temperature sensor data demonstrate that internal waves peak at semidiurnal frequencies. While short (〈1 h) periods show complicated structure, tidally averaged turbulence dissipation rate monotonically increases towards the seafloor over two orders of magnitude. The largest turbulence dissipation rates are observed during the relatively warm phase of an internal wave. Although the local topographic slope is supercritical for semidiurnal internal waves, turbulent bores propagating up the slope and hydraulic jumps are not observed. Most of the turbulence appears to be dominated by shear production, but not related to steady frictional flow near the seafloor.
    Description: This work has been partially funded from NSF-grant OCE-1756264.
    Keywords: Pacific Ocean ; Sloping topography ; High-resolution instrumentation ; Internal wave breaking ; High turbulence intensity near seafloor
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Hydraulic control of flow in a multi-passage system connecting two basins (2022)
    Cambridge University Press
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    Publication Date: 2022-07-20
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tan, S., Pratt, L. J., Voet, G., Cusack, J. M., Helfrich, K. R., Alford, M. H., Girton, J. B., & Carter, G. S. Hydraulic control of flow in a multi-passage system connecting two basins. Journal of Fluid Mechanics, 940, (2022): A8, https://doi.org/10.1017/jfm.2022.212.
    Description: When a fluid stream in a conduit splits in order to pass around an obstruction, it is possible that one branch will be critically controlled while the other remains not so. This is apparently the situation in Pacific Ocean abyssal circulation, where most of the northward flow of Antarctic bottom water passes through the Samoan Passage, where it is hydraulically controlled, while the remainder is diverted around the Manihiki Plateau and is not controlled. These observations raise a number of questions concerning the dynamics necessary to support such a regime in the steady state, the nature of upstream influence and the usefulness of rotating hydraulic theory to predict the partitioning of volume transport between the two paths, which assumes the controlled branch is inviscid. Through the use of a theory for constant potential vorticity flow and accompanying numerical model, we show that a steady-state regime similar to what is observed is dynamically possible provided that sufficient bottom friction is present in the uncontrolled branch. In this case, the upstream influence that typically exists for rotating channel flow is transformed into influence into how the flow is partitioned. As a result, the partitioning of volume flux can still be reasonably well predicted with an inviscid theory that exploits the lack of upstream influence.
    Description: This work was supported by the National Science Foundation under grants OCE-1029268, OCE-1029483, OCE-1657264, OCE-1657795, OCE-1657870 and OCE-1658027.
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Pacific abyssal transport and mixing: Through the Samoan Passage versus around the Manihiki Plateau (2019)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 49(6), (2019): 1577-1592, doi:10.1175/JPO-D-18-0124.1.
    Description: The main source feeding the abyssal circulation of the North Pacific is the deep, northward flow of 5–6 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) through the Samoan Passage. A recent field campaign has shown that this flow is hydraulically controlled and that it experiences hydraulic jumps accompanied by strong mixing and dissipation concentrated near several deep sills. By our estimates, the diapycnal density flux associated with this mixing is considerably larger than the diapycnal flux across a typical isopycnal surface extending over the abyssal North Pacific. According to historical hydrographic observations, a second source of abyssal water for the North Pacific is 2.3–2.8 Sv of the dense flow that is diverted around the Manihiki Plateau to the east, bypassing the Samoan Passage. This bypass flow is not confined to a channel and is therefore less likely to experience the strong mixing that is associated with hydraulic transitions. The partitioning of flux between the two branches of the deep flow could therefore be relevant to the distribution of Pacific abyssal mixing. To gain insight into the factors that control the partitioning between these two branches, we develop an abyssal and equator-proximal extension of the “island rule.” Novel features include provisions for the presence of hydraulic jumps as well as identification of an appropriate integration circuit for an abyssal layer to the east of the island. Evaluation of the corresponding circulation integral leads to a prediction of 0.4–2.4 Sv of bypass flow. The circulation integral clearly identifies dissipation and frictional drag effects within the Samoan Passage as crucial elements in partitioning the flow.
    Description: This work was supported by the National Science Foundation under Grants OCE-1029268, OCE-1029483, OCE-1657264, OCE-1657870, OCE-1658027, and OCE-1657795. We thank the captain, crew, and engineers at APL/UW for their hard work and skill.
    Description: 2020-06-11
    Keywords: Abyssal circulation ; Bottom currents ; Boundary currents ; Channel flows ; Mixing ; Transport
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
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    Persistent turbulence in the Samoan Passage (2020)
    American Meteorological Society
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cusack, J. M., Voet, G., Alford, M. H., Girton, J. B., Carter, G. S., Pratt, L. J., Pearson-Potts, K. A., & Tan, S. Persistent turbulence in the Samoan Passage. Journal of Physical Oceanography, 49(12), (2019): 3179-3197, doi: 10.1175/JPO-D-19-0116.1.
    Description: Abyssal waters forming the lower limb of the global overturning circulation flow through the Samoan Passage and are modified by intense mixing. Thorpe-scale-based estimates of dissipation from moored profilers deployed on top of two sills for 17 months reveal that turbulence is continuously generated in the passage. Overturns were observed in a density band in which the Richardson number was often smaller than ¼, consistent with shear instability occurring at the upper interface of the fast-flowing bottom water layer. The magnitude of dissipation was found to be stable on long time scales from weeks to months. A second array of 12 moored profilers deployed for a shorter duration but profiling at higher frequency was able to resolve variability in dissipation on time scales from days to hours. At some mooring locations, near-inertial and tidal modulation of the dissipation rate was observed. However, the modulation was not spatially coherent across the passage. The magnitude and vertical structure of dissipation from observations at one of the major sills is compared with an idealized 2D numerical simulation that includes a barotropic tidal forcing. Depth-integrated dissipation rates agree between model and observations to within a factor of 3. The tide has a negligible effect on the mean dissipation. These observations reinforce the notion that the Samoan Passage is an important mixing hot spot in the global ocean where waters are being transformed continuously.
    Description: The authors thank Zhongxiang Xao and Jody Klymak, who provided earlier setups of the numerical model, and also Arjun Jagannathan for insightful discussions on the subject of flow over topography. We also thank John Mickett and Eric Boget for their assistance in designing, deploying, and recovering the moorings. In addition, we also thank the crew and scientists aboard the R/V Revelle and R/V Thompson, without whom the data presented in this paper could not have been gathered. Ilker Fer and two anonymous reviewers provided thoughtful feedback that improved the paper. This work was supported by the National Science Foundation under Grants OCE-1029268, OCE-1029483, OCE-1657264, OCE-1657795, OCE-1657870, and OCE-1658027.
    Keywords: Gravity waves ; Turbulence ; Abyssal circulation ; Mixing ; Tides
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
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    Frequency content of sea surface height variability from internal gravity waves to mesoscale eddies (2017)
    John Wiley & Sons
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 2519–2538, doi:10.1002/2016JC012331.
    Description: High horizontal-resolution (1=12:5° and 1=25°) 41-layer global simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea surface height (SSH) variability. The HYCOM output is separated into steric and nonsteric and into subtidal, diurnal, semidiurnal, and supertidal frequency bands. The model SSH output is compared to two data sets that offer some geographical coverage and that also cover a wide range of frequencies—a set of 351 tide gauges that measure full SSH and a set of 14 in situ vertical profilers from which steric SSH can be calculated. Three of the global maps are of interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) two-dimensional swath altimeter mission: (1) maps of the total and (2) nonstationary internal tidal signal (the latter calculated after removing the stationary internal tidal signal via harmonic analysis), with an average variance of 1:05 and 0:43 cm2, respectively, for the semidiurnal band, and (3) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum, with an average variance of 0:15 cm2. Stationary internal tides (which are predictable), nonstationary internal tides (which will be harder to predict), and nontidal internal gravity waves (which will be very difficult to predict) may all be important sources of high-frequency ‘‘noise’’ that could mask lower frequency phenomena in SSH measurements made by the SWOT mission.
    Description: Office of Naval Research Grant Numbers: N00014-11-1-0487 , N00014-15-1-2288; NASA Earth and Space Science Grant Number: NNX16AO23H; University of Michigan; National Aeronautics and Space Administration Grant Numbers: NNX13AD95Q , NNX16AH79G; National Science Foundation Grant Number: OCE-1351837; National Aeronautics and Space Administration Grant Numbers: NNX13AE32G , NNX16AH76G , NNX13AE46G
    Description: 2017-09-28
    Keywords: Internal gravity waves ; Internal tides ; Spectral density
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
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    Spectral decomposition of internal gravity wave sea surface height in global models (2017)
    John Wiley & Sons
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 7803–7821, doi:10.1002/2017JC013009.
    Description: Two global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space and time scales of sea surface height (SSH) signals associated with internal gravity waves (IGWs). Frequency-horizontal wavenumber SSH spectral densities are computed over seven regions of the world ocean from two simulations of the HYbrid Coordinate Ocean Model (HYCOM) and three simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). High wavenumber, high-frequency SSH variance follows the predicted IGW linear dispersion curves. The realism of high-frequency motions (〉0:87 cpd) in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest-resolution runs of each model (1/25° HYCOM and 1/48° MITgcm) with dynamic height variance frequency spectral density computed from nine in situ profiling instruments. These high-frequency motions are of particular interest because of their contributions to the small-scale SSH variability that will be observed on a global scale in the upcoming Surface Water and Ocean Topography (SWOT) satellite altimetry mission. The variance at supertidal frequencies can be comparable to the tidal and low-frequency variance for high wavenumbers (length scales smaller than ∼50 km), especially in the higher-resolution simulations. In the highest-resolution simulations, the high-frequency variance can be greater than the low-frequency variance at these scales.
    Description: National Aeronautics and Space Administration (NASA) Earth and Space Science Fellowship Grant Number: NNX16AO23H Margaret and Herman Sokol Faculty; Office of Naval Research (ONR) Grant Numbers: N00014-15-1-2288 , N00014-11-1-0487; National Science Foundation (NSF) Grant Numbers: OCE-0968783 , OCE-1351837 , NNX13AE32G , NNX16AH76G , NNX13AE46 , NNX13AD95Q , NNX16AH79G
    Description: 2018-04-10
    Keywords: Internal gravity waves ; Internal tides ; Sea surface height variability ; High-resolution ocean models
    Repository Name: Woods Hole Open Access Server
    Type: Article
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