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  • 1
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    Assimilation of satellite color observations in a coupled ocean GCM-ecosystem model (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Monthly average coastal zone color scanner (CZCS) estimates of chlorophyll concentration were assimilated into an ocean global circulation model(GCM) containing a simple model of the pelagic ecosystem. The assimilation was performed in the simplest possible manner, to allow the assessment of whether there were major problems with the ecosystem model or with the assimilation procedure. The current ecosystem model performed well in some regions, but failed in others to assimilate chlorophyll estimates without disrupting important ecosystem properties. This experiment gave insight into those properties of the ecosystem model that must be changed to allow data assimilation to be generally successful, while raising other important issues about the assimilation procedure.
    Keywords: OCEANOGRAPHY
    Type: NASA-CR-191218 , NAS 1.26:191218
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Thorium isotopes, particle cycling models, and inverse calculations of model rate constants (1990)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research - Oceans, 95 (C9). pp. 16195-16206.
    Details
    Publication Date: 2016-07-12
    Description: Generalized models of thorium and particle cycling, data from Station P, and an inversion technique are used to obtain rate estimates of important biological and chemical transformations occurring in the water column. We first verify the inversion technique using an idealized data set generated by a finite difference model, and then apply the inversion technique to data from Station P. With the Station P data, predicted rate constants for adsorption and release of thorium between the dissolved and small particle phases are consistent with the results from other workers. The predicted rate constants for the interaction between small and large particles are smaller than previous estimates. The predicted concentration of large rapidly sinking particles is greater than the concentration of suspended non-sinking particles, whereas the reverse is usually assumed to be the case. The calculated sinking rate for the large particles is 20 m d−1. This sinking rate is an order of magnitude smaller than the large particle sinking rate inferred from sediment trap mass fluxes at two levels in the water column. The reason we predict a high large particle concentration and slow settling velocity has not been uniquely determined. Possible modifications of the current model that could help to reconcile the differences between observations and model predictions include: 1) two classes of rapidly sinking particles or rate constants that change with depth, 2) direct interactions between the large particle and dissolved phases, and 3) incorporation of a continuous distribution of particle size and settling velocity.
    Type: Article , PeerReviewed
    Format: text
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    PAPER (OCEANREP)
  • 3
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    Global Nitrous Oxide Production Determined by Oxygen Sensitivity of Nitrification and Denitrification (2018)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 32 (12). pp. 1790-1802.
    Details
    Publication Date: 2021-02-08
    Description: The ocean is estimated to contribute up to ~20% of global fluxes of atmospheric nitrous oxide (N2O), an important greenhouse gas and ozone depletion agent. Marine oxygen minimum zones contribute disproportionately to this flux. To further understand the partition of nitrification and denitrification and their environmental controls on marine N2O fluxes, we report new relationships between oxygen concentration and rates of N2O production from nitrification and denitrification directly measured with 15N tracers in the Eastern Tropical Pacific. Highest N2O production rates occurred near the oxic‐anoxic interface, where there is strong potential for N2O efflux to the atmosphere. The dominant N2O source in oxygen minimum zones was nitrate reduction, the rates of which were 1 to 2 orders of magnitude higher than those of ammonium oxidation. The presence of oxygen significantly inhibited the production of N2O from both nitrification and denitrification. These experimental data provide new constraints to a multicomponent global ocean biogeochemical model, which yielded annual oceanic N2O efflux of 1.7–4.4 Tg‐N (median 2.8 Tg‐N, 1 Tg = 1012 g), with denitrification contributing 20% to the oceanic flux. Thus, denitrification should be viewed as a net N2O production pathway in the marine environment.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    PAPER (OCEANREP)
  • 4
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    Role of Mesoscale Eddies in Cross-Frontal Transport of Heat and Biogeochemical Tracers in the Southern Ocean (2015)
    AMS (American Meteorological Society)
    Details
    Publication Date: 2022-03-09
    Description: This study examines the role of processes transporting tracers across the Polar Front (PF) in the depth interval between the surface and major topographic sills, which this study refers to as the “PF core.” A preindustrial control simulation of an eddying climate model coupled to a biogeochemical model [GFDL Climate Model, version 2.6 (CM2.6)– simplified version of the Biogeochemistry with Light Iron Nutrients and Gas (miniBLING) 0.1° ocean model] is used to investigate the transport of heat, carbon, oxygen, and phosphate across the PF core, with a particular focus on the role of mesoscale eddies. The authors find that the total transport across the PF core results from a ubiquitous Ekman transport that drives the upwelled tracers to the north and a localized opposing eddy transport that induces tracer leakages to the south at major topographic obstacles. In the Ekman layer, the southward eddy transport only partially compensates the northward Ekman transport, while below the Ekman layer, the southward eddy transport dominates the total transport but remains much smaller in magnitude than the near-surface northward transport. Most of the southward branch of the total transport is achieved below the PF core, mainly through geostrophic currents. This study finds that the eddy-diffusive transport reinforces the southward eddy-advective transport for carbon and heat, and opposes it for oxygen and phosphate. Eddy-advective transport is likely to be the leading-order component of eddy-induced transport for all four tracers. However, eddy-diffusive transport may provide a significant contribution to the southward eddy heat transport due to strong along-isopycnal temperature gradients.
    Type: Article , PeerReviewed
    Format: text
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  • 5
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    A transatlantic 14C-section near 40°N (1980)
    Bornträger
    Details
    Publication Date: 2022-06-24
    Description: 14C concentrations, as weil as 13C, hydrographic and nutrient data are reported for 5 hydrographic stations that form a transatlantic section near 40° N ("Meteor" cruise no. 23, 1971). Precision (for 14C ± 0.3% or better) and comparability with literature data are specified. A planned intercomparison with the US GEOSECS program within the Newfoundland Basin deep water failed because of variability of water characteristics. The observed 14C values decrease from about Δ 14C = + 80‰ at the surface to -70‰ at 2000 m depth. Deeper down, the values west of the Midatlantic Ridge remain similar, whereas those east of the ridge decrease further, to about -110‰. It is shown that bomb-14C is prominent down to about 1500 m depth. Beyond this depth the bomb 14C component is small and is negligible in the eastern basin below 2800 m. On the basis of the 14C-tritium correlation, the distribution of natural 14C below about 1500 m depth is derived from the observations. In the deep and bottom water east of the ridge the 14C-salinity relationship seemingly is non-linear. Contrary to expectation, the 14C concentration in the bottom water is not lower than found on an US GEOSECS station near 10° N. Apparently, lateral concentration differences in the Northeast Atlantic bottom water as well as nonlinearity of the 14C-salinity relationship at 40°N do not exceed 10‰ in Δ 14C.
    Type: Article , PeerReviewed
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  • 6
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    Nutrient Controls on Export Production in the Southern Ocean (2020)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-02-08
    Description: We use observations from novel biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling program to estimate annual net community production (ANCP; associated with carbon export) from the seasonal drawdown of mesopelagic oxygen and surface nitrate in the Southern Ocean. Our estimates agree with previous observations in showing an increase in ANCP in the vicinity of the polar front (∼3 mol C m−2 y−1), compared to lower rates in the subtropical zone (≤ 1 mol C m−2 y−1) and the seasonal ice zone (〈2 mol C m−2 y−1). Paradoxically, the increase in ANCP south of the subtropical front is associated with elevated surface nitrate and silicate concentrations, but decreasing surface iron. We hypothesize that iron limitation promotes silicification in diatoms, which is evidenced by the low silicate to nitrate ratio of surface waters around the Antarctic polar front. High diatom silicification increases the ballasting effect of particulate organic carbon and overall ANCP in this region. A model-based assessment of our methods shows a good agreement between ANCP estimates based on oxygen and nitrate drawdown and the modeled downward organic carbon flux at 100 m. This agreement supports the presumption that net biological consumption is the dominant process affecting the drawdown of these chemical tracers and that, given sufficient data, ANCP can be inferred from observations of oxygen and/or nitrate drawdown in the Southern Ocean.
    Keywords: Course of study: MSc Biological Oceanography
    Type: Article , PeerReviewed
    Format: text
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