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  • Numerical modeling  (8)
  • Carbon cycle  (6)
  • American Geophysical Union  (14)
  • 2010-2014  (14)
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  • 1
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    Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. 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 23 (2009): GB4028, doi:10.1029/2009GB003519.
    Description: Nitrogen cycle dynamics have the capacity to attenuate the magnitude of global terrestrial carbon sinks and sources driven by CO2 fertilization and changes in climate. In this study, two versions of the terrestrial carbon and nitrogen cycle components of the Integrated Science Assessment Model (ISAM) are used to evaluate how variation in nitrogen availability influences terrestrial carbon sinks and sources in response to changes over the 20th century in global environmental factors including atmospheric CO2 concentration, nitrogen inputs, temperature, precipitation and land use. The two versions of ISAM vary in their treatment of nitrogen availability: ISAM-NC has a terrestrial carbon cycle model coupled to a fully dynamic nitrogen cycle while ISAM-C has an identical carbon cycle model but nitrogen availability is always in sufficient supply. Overall, the two versions of the model estimate approximately the same amount of global mean carbon uptake over the 20th century. However, comparisons of results of ISAM-NC relative to ISAM-C reveal that nitrogen dynamics: (1) reduced the 1990s carbon sink associated with increasing atmospheric CO2 by 0.53 PgC yr−1 (1 Pg = 1015g), (2) reduced the 1990s carbon source associated with changes in temperature and precipitation of 0.34 PgC yr−1 in the 1990s, (3) an enhanced sink associated with nitrogen inputs by 0.26 PgC yr−1, and (4) enhanced the 1990s carbon source associated with changes in land use by 0.08 PgC yr−1 in the 1990s. These effects of nitrogen limitation influenced the spatial distribution of the estimated exchange of CO2 with greater sink activity in high latitudes associated with climate effects and a smaller sink of CO2 in the southeastern United States caused by N limitation associated with both CO2 fertilization and forest regrowth. These results indicate that the dynamics of nitrogen availability are important to consider in assessing the spatial distribution and temporal dynamics of terrestrial carbon sources and sinks.
    Description: We also acknowledge the financial support of the National Aeronautics and Space Administration Land Cover and Land Use Change Program (NNX08AK75G).
    Keywords: Nitrogen cycle ; Carbon cycle ; ISAM
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Magmatic and tectonic extension at mid-ocean ridges : 1. Controls on fault characteristics (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q08O10, doi:10.1029/2008GC001965.
    Description: We use 2-D numerical models to explore the thermal and mechanical effects of magma intrusion on fault initiation and growth at slow and intermediate spreading ridges. Magma intrusion is simulated by widening a vertical column of model elements located within the lithosphere at a rate equal to a fraction, M, of the total spreading rate (i.e., M = 1 for fully magmatic spreading). Heat is added in proportion to the rate of intrusion to simulate the thermal effects of magma crystallization and the injection of hot magma into the crust. We examine a range of intrusion rates and axial thermal structures by varying M, spreading rate, and the efficiency of crustal cooling by conduction and hydrothermal circulation. Fault development proceeds in a sequential manner, with deformation focused on a single active normal fault whose location alternates between the two sides of the ridge axis. Fault spacing and heave are primarily sensitive to M and secondarily sensitive to axial lithosphere thickness and the rate that the lithosphere thickens with distance from the axis. Contrary to what is often cited in the literature, but consistent with prior results of mechanical modeling, we find that thicker axial lithosphere tends to reduce fault spacing and heave. In addition, fault spacing and heave are predicted to increase with decreasing rates of off-axis lithospheric thickening. The combination of low M, particularly when M approaches 0.5, as well as a reduced rate of off-axis lithospheric thickening produces long-lived, large-offset faults, similar to oceanic core complexes. Such long-lived faults produce a highly asymmetric axial thermal structure, with thinner lithosphere on the side with the active fault. This across-axis variation in thermal structure may tend to stabilize the active fault for longer periods of time and could concentrate hydrothermal circulation in the footwall of oceanic core complexes.
    Description: Funding for this research was provided by NSF grants OCE-0327018 (M.D.B.), OCE-0548672 (M.D.B.), OCE- 0327051 (G.I.), and OCE-03-51234 (G.I.).
    Keywords: Mid-ocean ridges ; Faulting ; Magmatism ; Numerical modeling
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  • 3
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    Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean : results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2) (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 21 (2007): GB3007, doi:10.1029/2006GB002857.
    Description: Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (±1σ) downward flux of organic matter across 75 m depth is 17 ± 6 Pg C yr−1. Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.
    Description: R. G. N. and J. L. S. acknowledge the support of NASA grants NAG5-6451 and NAG5-6591, respectively, as part of the JGOFS Synthesis and Modeling Program. G. K. P. and F. J. acknowledge support by the Swiss National Science Foundation. European contributions were supported by the EU GOSAC Project (ENV4-CT97- 0495).
    Keywords: Export production ; Numerical modeling ; Ocean circulation
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  • 4
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    Enhanced CO2 outgassing in the Southern Ocean from a positive phase of the Southern Annular Mode (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 21 (2007): GB2026, doi:10.1029/2006GB002900.
    Description: We investigate the interannual variability in the flux of CO2 between the atmosphere and the Southern Ocean on the basis of hindcast simulations with a coupled physical-biogeochemical-ecological model with particular emphasis on the role of the Southern Annular Mode (SAM). The simulations are run under either pre-industrial or historical CO2 concentrations, permitting us to separately investigate natural, anthropogenic, and contemporary CO2 flux variability. We find large interannual variability (±0.19 PgC yr−1) in the contemporary air-sea CO2 flux from the Southern Ocean (〈35°S). Forty-three percent of the contemporary air-sea CO2 flux variance is coherent with SAM, mostly driven by variations in the flux of natural CO2, for which SAM explains 48%. Positive phases of the SAM are associated with anomalous outgassing of natural CO2 at a rate of 0.1 PgC yr−1 per standard deviation of the SAM. In contrast, we find an anomalous uptake of anthropogenic CO2 at a rate of 0.01 PgC yr−1 during positive phases of the SAM. This uptake of anthropogenic CO2 only slightly mitigates the outgassing of natural CO2, so that a positive SAM is associated with anomalous outgassing in contemporaneous times. The primary cause of the natural CO2 outgassing is anomalously high oceanic partial pressures of CO2 caused by elevated dissolved inorganic carbon (DIC) concentrations. These anomalies in DIC are primarily a result of the circulation changes associated with the southward shift and strengthening of the zonal winds during positive phases of the SAM. The secular, positive trend in the SAM has led to a reduction in the rate of increase of the uptake of CO2 by the Southern Ocean over the past 50 years.
    Description: This work was supported by NASA headquarters under the Earth System Science Fellowship Grant NNG05GP78H to N. S. L. and grants NAG5-12528 and NNG04GH53G to N. G. Both S. C. D. and I. D. L. were supported by NSF/ONR NOPP (N000140210370) and NASA (NNG05GG30G).
    Keywords: Southern Ocean ; Carbon cycle ; Southern Annular Mode
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  • 5
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    Sorted bed forms as self-organized patterns : 2. Complex forcing scenarios (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 112 (2007): F03016, doi:10.1029/2006JF000666.
    Description: We employ a numerical model to study the development of sorted bed forms under a variety of hydrodynamic and sedimentary conditions. Results indicate that increased variability in wave height decreases the growth rate of the features and can potentially give rise to complicated, a priori unpredictable, behavior. This happens because the system responds to a change in wave characteristics by attempting to self-organize into a patterned seabed of different geometry and spacing. The new wavelength might not have enough time to emerge before a new change in wave characteristics occurs, leading to less regular seabed configurations. The new seabed configuration is also highly dependent on the preexisting morphology, which further limits the possibility of predicting future behavior. For the same reasons, variability in the mean current magnitude and direction slows down the growth of features and causes patterns to develop that differ from classical sorted bed forms. Spatial variability in grain size distribution and different types of net sediment aggradation/degradation can also result in the development of sorted bed forms characterized by a less regular shape. Numerical simulations qualitatively agree with observed geometry (spacing and height) of sorted bed forms. Also in agreement with observations is that at shallower depths, sorted bed forms are more likely to be affected by changes in the forcing conditions, which might also explain why, in shallow waters, sorted bed forms are described as ephemeral features. Finally, simulations indicate that the different sorted bed form shapes and patterns observed in the field might not necessarily be related to diverse physical mechanisms. Instead, variations in sorted bed form characteristics may result from variations in local hydrodynamic and/or sedimentary conditions.
    Description: G.C., M.O.G., and T.M.H. acknowledge funding from the (New Zealand) Foundation for Research, Science and Technology (contract C01X0401). The National Science Foundation (OCE0452178) supported A.B.M.
    Keywords: Self-organization ; Sorted bed forms ; Numerical modeling
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  • 6
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    Investigation of the summer Kara Sea circulation employing a variational data assimilation technique (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 112 (2007): C04S15, doi:10.1029/2006JC003728.
    Description: The summer circulations and hydrographic fields of the Kara Sea are reconstructed for mean, positive and negative Arctic Oscillation regimes employing a variational data assimilation technique which provides the best fit of reconstructed fields to climatological data and satisfies dynamical and kinematic constraints of a quasi-stationary primitive equation ocean circulation model. The reconstructed circulations agree well with the measurements and are characterized by inflow of 0.63, 0.8, 0.51 Sv through Kara Gate and 1.18, 1.1, 1.12 Sv between Novaya Zemlya and Franz Josef Land, for mean climatologic conditions, positive and negative AO indexes, respectively. The major regions of water outflow for these regimes are the St. Anna Trough (1.17, 1.21, 1.34 Sv) and Vilkitsky/Shokalsky Straits (0.52, 0.7, 0.51 Sv). The optimized velocity pattern for the mean climatological summer reveals a strong anticyclonic circulation in the central part of the Kara Sea (Region of Fresh Water Inflow, ROFI zone) and is confirmed by ADCP surveys and laboratory modeling. This circulation is well pronounced for both high and low AO phases, but in the positive AO phase it is shifted approximately 200 km west relatively to its climatological center. During the negative AO phase the ROFI locaion is close to its climatological position. The results of the variational data assimilation approach were compared with the simulated data from the Hamburg Shelf Ocean Model (HAMSOM) and Naval Postgraduate School 18 km resolution (NPS-18) model to validate these models.
    Description: This research is supported by the Frontier Research System for Global Change, through JAMSTEC, Japan, and by the National Science Foundation Office of Polar Programs (under cooperative agreements OPP-0002239 and OPP-0327664 with the International Arctic Research Center, University of Alaska Fairbanks). The development of the data assimilation system, utilized in this study, was also supported by NSF grant OCE-0118200.
    Keywords: Kara Sea ; Variational approach ; Numerical modeling
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  • 7
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    Constraining ventilation during deepwater formation using deep ocean measurements of the dissolved gas ratios 40Ar/36Ar, N2/Ar, and Kr/Ar (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2010. 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 115 (2010): C11015, doi:10.1029/2010JC006152.
    Description: The concentration of inert gases and their isotopes in the deep ocean are useful as tracers of air-sea gas exchange during deepwater formation. ΔKr/Ar, ΔN2/Ar, and δ40Ar were measured in deep profiles of samples collected in the northwest Pacific, subtropical North Pacific and tropical Atlantic oceans. For the ocean below 2000 m, we determined a mean ΔKr/Ar composition of −0.96% ± 0.16%, a mean ΔN2/Ar of 1.29% ± 0.21% relative to equilibrium saturation, and for δ40Ar a value of 1.188‰ ± 0.055‰ relative to air. These data are used to constrain high-latitude ventilation processes in the framework of three-box and seven-box ocean models. For the three-box model tracer data, we constrain the appropriate surface area of the high-latitude region in both models to be 3.6% (+2.5%, −1.7%) of ocean surface area and the bubble air injection rate to be 22.7 (+8.8, −7.3) mol air m−2 yr−1. Results for the seven-box model were similar, with a high-latitude area of 3.3% (+2.2%, −1.3%). Our results provide geochemical support for suggestions that the effective area of high-latitude ventilation is much smaller than the region of elevated preformed nutrients and demonstrate that noble gases strongly constrain the ocean solubility pump. Reducing high-latitude surface area weakens the CO2 solubility pump in the box models and limits communication between the atmosphere and deep ocean. These tracers should be useful constraints on high-latitude ventilation and the strength of the solubility pump in more complex ocean general circulation models.
    Description: Funding was provided by NSF‐OCE‐0647979.
    Keywords: Noble gases ; Ventilation ; Carbon cycle ; Solubility pump ; Gas exchange
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  • 8
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    Reply to comment by M. Ortega-Sánchez et al. on “High-angle wave instability and emergent shoreline shapes : 1. Modeling of sand waves, flying spits, and capes” (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): F01006, doi:10.1029/2007JF000885.
    Keywords: Coastline evolution ; Morphodynamic instabilities ; Numerical modeling
    Repository Name: Woods Hole Open Access Server
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  • 9
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    High-angle wave instability and emergent shoreline shapes : 1. Modeling of sand waves, flying spits, and capes (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): F04011, doi:10.1029/2005JF000422.
    Description: Contrary to traditional findings, the deepwater angle of wave approach strongly affects plan view coastal evolution, giving rise to an antidiffusional “high wave angle” instability for sufficiently oblique deepwater waves (with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport, ∼45°). A one-contour-line numerical model shows that a predominance of high-angle waves can cause a shoreline to self-organize into regular, quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers. The numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash, which is assumed to maintain a minimum barrier width. Systematic analysis shows that the wave climate determines the form of coastal response. For nearly symmetric wave climates (small net alongshore sediment transport), cuspate coasts develop that exhibit increasing relative cross-shore amplitude and pointier tips as the proportion of high-angle waves is increased. For asymmetrical wave climates, shoreline features migrate in the downdrift direction, either as subtle alongshore sand waves or as offshore-extending “flying spits,” depending on the proportion of high-angle waves. Numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude, a rate that is insensitive to the proportion of high-angle waves. The proportion of high-angle waves determines the offshore versus alongshore aspect ratio of self-organized shoreline undulations.
    Description: This research was funded by the Andrew W. Mellon Foundation and NSF grants DEB-05-07987 and EAR-04-44792.
    Keywords: Coastline evolution ; Morphodynamic instabilities ; Numerical modeling
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  • 10
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    Historic 2005 toxic bloom of Alexandrium fundyense in the western Gulf of Maine : 2. Coupled biophysical numerical modeling (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C07040, doi:10.1029/2007JC004602.
    Description: A coupled physical/biological modeling system was used to hindcast a massive Alexandrium fundyense bloom that occurred in the western Gulf of Maine in 2005 and to investigate the relative importance of factors governing the bloom's initiation and development. The coupled system consists of a state-of-the-art, free-surface primitive equation Regional Ocean Modeling System (ROMS) tailored for the Gulf of Maine (GOM) using a multinested configuration, and a population dynamics model for A. fundyense. The system was forced by realistic momentum and buoyancy fluxes, tides, river runoff, observed A. fundyense benthic cyst abundance, and climatological nutrient fields. Extensive comparisons were made between simulated (both physical and biological) fields and in situ observations, revealing that the hindcast model is capable of reproducing the temporal evolution and spatial distribution of the 2005 bloom. Sensitivity experiments were then performed to distinguish the roles of three major factors hypothesized to contribute to the bloom: (1) the high abundance of cysts in western GOM sediments; (2) strong ‘northeaster' storms with prevailing downwelling-favorable winds; and (3) a large amount of fresh water input due to abundant rainfall and heavy snowmelt. Model results suggest the following. (1) The high abundance of cysts in western GOM was the primary factor of the 2005 bloom. (2) Wind-forcing was an important regulator, as episodic bursts of northeast winds caused onshore advection of offshore populations. These downwelling favorable winds accelerated the alongshore flow, resulting in transport of high cell concentrations into Massachusetts Bay. A large regional bloom would still have happened, however, even with normal or typical winds for that period. (3) Anomalously high river runoff in 2005 resulted in stronger buoyant plumes/currents, which facilitated the transport of cell population to the western GOM. While affecting nearshore cell abundance in Massachusetts Bay, the buoyant plumes were confined near to the coast, and had limited impact on the gulf-wide bloom distribution.
    Description: Research support was provided through the Woods Hole Center for Oceans and Human Health, National Science Foundation (NSF) grant OCE-0430723 and National Institute of Environmental Health Science (NIEHS) grant 1-P50-ES012742-01, ECOHAB program through NSF grant OCE-9808173 and NOAA grant NA96OP0099, and GOMTOX program through NOAA grant NA06NOS4780245.
    Keywords: Gulf of Maine ; Harmful algal bloom ; Numerical modeling
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  • 11
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    Barotropic tides on the southeast New England shelf : a view from a hybrid data assimilative modeling approach (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): C08002, doi:10.1029/2005JC003254.
    Description: A high-resolution hybrid data assimilative (DA) modeling system is used to study barotropic tides and tidal dynamics on the southeast New England shelf. In situ observations include tidal harmonics of 5 major tidal constituents [M2, S2, N2, O1, and K1] analyzed from coastal sea level and bottom pressure gauges. The DA system consists of both forward and inverse models. The former is the three-dimensional, finite difference, nonlinear Regional Ocean Modeling System (ROMS). The latter is a three-dimensional linearized, frequency domain, finite element model TRUXTON. The DA system assimilates in situ observations via the inversion for the barotropic tidal open boundary conditions (OBCs). Model skill is evaluated by comparing the misfits between the observed and modeled tidal harmonics. The assimilation scheme is found effective and efficient in correcting the tidal OBCs, which in turn improve ROMS tidal solutions. Up to 50% decreases of model/data misfits are achieved after inverse data assimilation. Co-amplitude and co-phase maps and tidal current ellipses for each of 5 tidal constituents are generated, revealing complex tidal variability in this transition region between the tidally amplified Gulf of Maine in the northeast and the tidally much less energetic Middle Atlantic Bight in the southwest. Detailed examinations on the residual circulation, energetics, and momentum balances of the M2 tide reveal the key roles of the unique bottom bathymetry of Nantucket Shoals and the complex coastal geometry in affecting the regional tidal dynamics.
    Description: This work was supported by WHOI Coastal Ocean Institute Research Award. J.W. acknowledges support of the Office of Naval Research.
    Keywords: Continental shelf ; Barotropic tides ; Numerical modeling ; Data assimilation
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  • 12
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    How does ocean biology affect atmospheric pCO2? Theory and models (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C07032, doi:10.1029/2007JC004598.
    Description: This paper examines the sensitivity of atmospheric pCO2 to changes in ocean biology that result in drawdown of nutrients at the ocean surface. We show that the global inventory of preformed nutrients is the key determinant of atmospheric pCO2 and the oceanic carbon storage due to the soft-tissue pump (OCS soft ). We develop a new theory showing that under conditions of perfect equilibrium between atmosphere and ocean, atmospheric pCO2 can be written as a sum of exponential functions of OCS soft . The theory also demonstrates how the sensitivity of atmospheric pCO2 to changes in the soft-tissue pump depends on the preformed nutrient inventory and on surface buffer chemistry. We validate our theory against simulations of nutrient depletion in a suite of realistic general circulation models (GCMs). The decrease in atmospheric pCO2 following surface nutrient depletion depends on the oceanic circulation in the models. Increasing deep ocean ventilation by increasing vertical mixing or Southern Ocean winds increases the atmospheric pCO2 sensitivity to surface nutrient forcing. Conversely, stratifying the Southern Ocean decreases the atmospheric CO2 sensitivity to surface nutrient depletion. Surface CO2 disequilibrium due to the slow gas exchange with the atmosphere acts to make atmospheric pCO2 more sensitive to nutrient depletion in high-ventilation models and less sensitive to nutrient depletion in low-ventilation models. Our findings have potentially important implications for both past and future climates.
    Description: While at MIT, I.M. was supported by the NOAA Postdoctoral Program in Climate and Global Change, administered by the University Corporation for Atmospheric Research.
    Keywords: Carbon cycle ; Preformed nutrient ; Nutrient depletion
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  • 13
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    Inverse estimates of anthropogenic CO2 uptake, transport, and storage by the ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2006. 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 20 (2006): GB2002, doi:10.1029/2005GB002530.
    Description: Regional air-sea fluxes of anthropogenic CO2 are estimated using a Green's function inversion method that combines data-based estimates of anthropogenic CO2 in the ocean with information about ocean transport and mixing from a suite of Ocean General Circulation Models (OGCMs). In order to quantify the uncertainty associated with the estimated fluxes owing to modeled transport and errors in the data, we employ 10 OGCMs and three scenarios representing biases in the data-based anthropogenic CO2 estimates. On the basis of the prescribed anthropogenic CO2 storage, we find a global uptake of 2.2 ± 0.25 Pg C yr−1, scaled to 1995. This error estimate represents the standard deviation of the models weighted by a CFC-based model skill score, which reduces the error range and emphasizes those models that have been shown to reproduce observed tracer concentrations most accurately. The greatest anthropogenic CO2 uptake occurs in the Southern Ocean and in the tropics. The flux estimates imply vigorous northward transport in the Southern Hemisphere, northward cross-equatorial transport, and equatorward transport at high northern latitudes. Compared with forward simulations, we find substantially more uptake in the Southern Ocean, less uptake in the Pacific Ocean, and less global uptake. The large-scale spatial pattern of the estimated flux is generally insensitive to possible biases in the data and the models employed. However, the global uptake scales approximately linearly with changes in the global anthropogenic CO2 inventory. Considerable uncertainties remain in some regions, particularly the Southern Ocean.
    Description: This research was financially supported by the National Aeronautics and Space Administration under grant NAG5- 12528. N. G. also acknowledges support by the National Science Foundation (OCE-0137274). Climate and Environmental Physics, Bern acknowledges support by the European Union through the Integrated Project CarboOcean and the Swiss National Science Foundation.
    Keywords: Anthropogenic CO2 ; Carbon cycle ; Inverse modeling
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  • 14
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    Interannual variations in continental-scale net carbon exchange and sensitivity to observing networks estimated from atmospheric CO2 inversions for the period 1980 to 2005 (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2008. 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 22 (2008): GB3025, doi:10.1029/2007GB003082.
    Description: Interannually varying net carbon exchange fluxes from the TransCom 3 Level 2 Atmospheric Inversion Intercomparison Experiment are presented for the 1980 to 2005 time period. The fluxes represent the model mean, net carbon exchange for 11 land and 11 ocean regions after subtraction of fossil fuel CO2 emissions. Both aggregated regional totals and the individual regional estimates are accompanied by a model uncertainty and model spread. We find that interannual variability is larger on the land than the ocean, with total land exchange correlated to the timing of both El Niño/Southern Oscillation (ENSO) as well as the eruption of Mt. Pinatubo. The post-Pinatubo negative flux anomaly is evident across much of the tropical and northern extratropical land regions. In the oceans, the tropics tend to exhibit the greatest level of interannual variability, while on land, the interannual variability is slightly greater in the tropics and northern extratropics. The interannual variation in carbon flux estimates aggregated by land and ocean across latitudinal bands remains consistent across eight different CO2 observing networks. The interannual variation in carbon flux estimates for individual flux regions remains mostly consistent across the individual observing networks. At all scales, there is considerable consistency in the interannual variations among the 13 participating model groups. Finally, consistent with other studies using different techniques, we find a considerable positive net carbon flux anomaly in the tropical land during the period of the large ENSO in 1997/1998 which is evident in the Tropical Asia, Temperate Asia, Northern African, and Southern Africa land regions. Negative anomalies are estimated for the East Pacific Ocean and South Pacific Ocean regions. Earlier ENSO events of the 1980s are most evident in southern land positive flux anomalies.
    Keywords: Carbon cycle ; Atmospheric inversion ; Interannual variability
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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