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  • 1
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    Short-term variability in euphotic zone biogeochemistry and primary productivity at Station ALOHA : a case study of summer 2012 (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 29 (2015): 1145–1164, doi:10.1002/2015GB005141.
    Description: Time-series observations are critical to understand the structure, function, and dynamics of marine ecosystems. The Hawaii Ocean Time-series program has maintained near-monthly sampling at Station ALOHA (22°45′N, 158°00′W) in the oligotrophic North Pacific Subtropical Gyre (NPSG) since 1988 and has identified ecosystem variability over seasonal to interannual timescales. To further extend the temporal resolution of these near-monthly time-series observations, an extensive field campaign was conducted during July–September 2012 at Station ALOHA with near-daily sampling of upper water-column biogeochemistry, phytoplankton abundance, and activity. The resulting data set provided biogeochemical measurements at high temporal resolution and documents two important events at Station ALOHA: (1) a prolonged period of low productivity when net community production in the mixed layer shifted to a net heterotrophic state and (2) detection of a distinct sea-surface salinity minimum feature which was prominent in the upper water column (0–50 m) for a period of approximately 30 days. The shipboard observations during July–September 2012 were supplemented with in situ measurements provided by Seagliders, profiling floats, and remote satellite observations that together revealed the extent of the low productivity and the sea-surface salinity minimum feature in the NPSG.
    Description: NOAA Climate Observation Division; National Science Foundation (NSF) Center for Microbial Oceanography: Research and Education (C-MORE) Grant Numbers: EF0424599, OCE-1153656, OCE-1260164; Gordon and Betty Moore Foundation Marine Microbiology Investigator
    Description: 2016-02-13
    Keywords: Primary productivity ; Microbial ecology ; Station ALOHA ; Temporal variability ; Biogeochemistry
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
    Format: application/msword
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    PAPER (OA)
  • 2
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    Evidence for the maintenance of slowly varying equatorial currents by intraseasonal variability (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 45 (2018): 1923–1929, doi:10.1002/2017GL076662.
    Description: Recent evidence from mooring data in the equatorial Atlantic reveals that semiannual and longer time scale ocean current variability is close to being resonant with equatorial basin modes. Here we show that intraseasonal variability, with time scales of tens of days, provides the energy to maintain these resonant basin modes against dissipation. The mechanism is analogous to that by which storm systems in the atmosphere act to maintain the atmospheric jet stream. We demonstrate the mechanism using an idealized model setup that exhibits equatorial deep jets. The results are supported by direct analysis of available mooring data from the equatorial Atlantic Ocean covering a depth range of several thousand meters. The analysis of the mooring data suggests that the same mechanism also helps maintain the seasonal variability.
    Description: This study was supported by the Deutsche Forschungsgemeinschaft as part of the Sonderforschungsbereich 754 “Climate‐Biogeochemistry Interactions in the Tropical Ocean” and through several research cruises with RV Meteor, RV Maria S. Merian, and RV L'Atalante, by the German Federal Ministry of Education and Research as part of the cooperative projects RACE (03F0605B), SACUS (03G0837A), and MiKlip2 (ATMOS‐MODINI; 01LP1517D) and by the European Union 7th Framework Programme (FP7 2007–2013) under grant agreement 603521 PREFACE project. Support for the moored observations was additionally provided by the U.S. National Science Foundation.
    Keywords: Equatorial deep jets ; Seasonal cycle ; Momentum flux convergence ; Tropical instability waves ; Equatorial basin mode resonance
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    PAPER (OA)
  • 3
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    The emergence of equatorial deep jets in an idealised primitive equation model: an interpretation in terms of basin modes (2017)
    Springer
    In:  Ocean Dynamics, 67 (12). pp. 1511-1522.
    Details
    Publication Date: 2020-02-06
    Description: Ocean circulation models do not generally exhibit equatorial deep jets (EDJs), even though EDJs are a recognised feature of the observed ocean circulation along the equator and they are thought to be important for tracer transport along the equator and even equatorial climate. EDJs are nevertheless found in nonlinear primitive equation models with idealised box geometry. Here we analyse several such model runs. We note that the variability of the zonal velocity in the model is dominated by the gravest linear equatorial basin mode for a wide range of baroclinic vertical normal modes and that the EDJs in the model are dominated by energy contained in vertical modes between 10 and 20. The emergence of the EDJs is shown to involve the linear superposition of several such neighbouring basin modes. Furthermore, the phase of these basin modes is set at the start of the model run and, in the case of the reference experiment, the same basin modes can be found in a companion experiment in which the amplitude of the forcing has been reduced by a factor of 1000. We also argue that following the spin-up, energy must be transferred between different vertical modes. This is because the model simulations are dominated by downward phase propagation following the spin-up whereas our reconstructions imply episodes of upward and downward propagation. The transfer of energy between the vertical modes is associated with a decadal modulation of the EDJs.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1007/s10236-017-1111-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Evidence for the maintenance of slowly varying equatorial currents by intraseasonal variability (2018)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 45 (4). pp. 1923-1929.
    Details
    Publication Date: 2021-05-18
    Description: Recent evidence from mooring data in the equatorial Atlantic reveals that semi-annual and longer time scale ocean current variability is close to being resonant with equatorial basin modes. Here we show that intraseasonal variability, with time scales of 10's of days, provides the energy to maintain these resonant basin modes against dissipation. The mechanism is analogous to that by which storm systems in the atmosphere act to maintain the atmospheric jet stream. We demonstrate the mechanism using an idealised model set-up that exhibits equatorial deep jets. The results are supported by direct analysis of available mooring data from the equatorial Atlantic Ocean covering a depth range of several thousand meters. The analysis of the mooring data suggests that the same mechanism also helps maintain the seasonal variability.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1002/2017GL076662
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    The deep equatorial ocean circulation in wind-forced numerical solutions (2015)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 45 . pp. 1709-1734.
    Details
    Publication Date: 2021-05-18
    Description: We perform eddy-resolving and high-vertical-resolution numerical simulations of the circulation in an idealized equatorial Atlantic Ocean in order to explore the formation of the deep equatorial circulation (DEC) in this basin. Unlike in previous studies, the deep equatorial intraseasonal variability (DEIV) that is believed to be the source of the DEC is generated internally by instabilities of the upper ocean currents. Two main simulations are discussed: Solution 1, configured with a rectangular basin and with wind forcing that is zonally and temporally uniform; and Solution 2, with realistic coastlines and with an annual cycle of wind forcing varying zonally. Somewhat surprisingly, Solution 1 produces the more realistic DEC: The large-vertical-scale currents (Equatorial Intermediate Currents or EICs) are found over a large zonal portion of the basin, and the small-vertical-scale equatorial currents (Equatorial Deep Jets or EDJs) form low-frequency, quasi-resonant, baroclinic equatorial basin modes with phase propagating mostly downward, consistent with observations. We demonstrate that both types of currents arise from the rectification of DEIV, consistent with previous theories. We also find that the EDJs contribute to maintaining the EICs, suggesting that the nonlinear energy transfer is more complex than previously thought. In Solution 2, the DEC is unrealistically weak and less spatially coherent than in the first simulation probably because of its weaker DEIV. Using intermediate solutions, we find that the main reason for this weaker DEIV is the use of realistic coastlines in Solution 2. It remains to be determined, what needs to be modified or included to obtain a realistic DEC in the more realistic configuration.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1175/JPO-D-14-0171.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Equatorial Deep Jets in the Atlantic Ocean studied by observations and ocean general circulation models (2018)
    Details
    Publication Date: 2022-02-18
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Talk
  • 7
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    Equatorial Deep Jets in the Atlantic Ocean studied by observations and ocean general circulation models (2017)
    In:  [Talk] In: IAPSO Assembly, 27.08.-01.09.2017, Cape Town, South Africa .
    Details
    Publication Date: 2018-11-09
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
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