How long to oceanic tracer and proxy equilibrium
TL;DR: In this paper, a global ocean circulation model, forced to least-square consistency with modern data, is used to find lower bounds for the time taken by surface-injected passive tracers to reach equilibrium.
About: This article is published in Quaternary Science Reviews.The article was published on 2008-04-01. It has received 90 citations till now. The article focuses on the topics: Thermohaline circulation & North Atlantic Deep Water.
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Earth System Research Laboratory1, University of California, Santa Cruz2, National Oceanic and Atmospheric Administration3, École Normale Supérieure4, Oregon State University5, George Washington University6, Scripps Institution of Oceanography7, Stazione Zoologica Anton Dohrn8, Institute of Arctic and Alpine Research9, Stony Brook University10, University of Washington11, Kent State University12, University of Connecticut13, University of Colorado Boulder14, Pacific Marine Environmental Laboratory15, Woods Hole Oceanographic Institution16
TL;DR: Examples from United States (U.S.) coasts applications are used to identify and describe the key requirements for an observational network that is needed to facilitate improved process understanding, as well as for sustaining operational ecosystem forecasting.
Abstract: Many coastal areas host rich marine ecosystems and are also centers of economic activities, including fishing, shipping and recreation. Due to the socioeconomic and ecological importance of these areas, predicting relevant indicators of the ecosystem state on sub-seasonal to interannual timescales is gaining increasing attention. Depending on the application, forecasts may be sought for variables and indicators spanning physics (e.g., sea level, temperature, currents), chemistry (e.g., nutrients, oxygen, pH), and biology (from viruses to top predators). Many components of the marine ecosystem are known to be influenced by leading modes of climate variability, which provide a physical basis for predictability. However, prediction capabilities remain limited by the lack of a clear understanding of the physical and biological processes involved, as well as by insufficient observations for forecast initialization and verification. The situation is further complicated by the influence of climate change on ocean conditions along coastal areas, including sea level rise, increased stratification, and shoaling of oxygen minimum zones. Observations are thus vital to all aspects of marine forecasting: statistical and/or dynamical model development, forecast initialization, and forecast validation, each of which has different observational requirements, which may be also specific to the study region. Here, we use examples from United States (U.S.) coastal applications to identify and describe the key requirements for an observational network that is needed to facilitate improved process understanding, as well as for sustaining operational ecosystem forecasting. We also describe new holistic observational approaches, e.g., approaches based on acoustics, inspired by Tara Oceans or by landscape ecology, which have the potential to support and expand ecosystem modeling and forecasting activities by bridging global and local observations.
32 citations
Cites background from "How long to oceanic tracer and prox..."
...…number of variables in the biogeochemical model relative to the physical model component the spin-up of the model biogeochemistry may require thousands of years (Wunsch and Heimbach, 2008) compared to weeks for the atmosphere and centuries for the ocean and ice components (Stouffer et al., 2004)....
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TL;DR: In this article, a tracer transport model of the modern-day ocean circulation is proposed to explain the interbasin lag of the last termination of the Last Termination.
Abstract: [1] The midpoint of the Last Termination occurred 4,000 years earlier in the deep Atlantic than the deep Pacific according to a pair of benthic foraminiferal δ18O records, seemingly implying an internal circulation shift because the lag is much longer than the deep radiocarbon age. Here a scenario where the lag is instead caused by regional surface boundary condition changes, delays due to oceanic transit timescales, and the interplay between temperature and seawater δ18O (δ18Ow) is quantified with a tracer transport model of the modern-day ocean circulation. Using an inverse method with individual Green functions for 2,806 surface sources, a time history of surface temperature andδ18Owis reconstructed for the last 30,000 years that is consistent with the foraminiferal oxygen-isotope data, Mg/Ca-derived deep temperature, and glacial pore water records. Thus, in the case that the ocean circulation was relatively unchanged between glacial and modern times, the interbasin lag could be explained by the relatively late local glacial maximum around Antarctica where surfaceδ18Ow continues to rise even after the North Atlantic δ18Owfalls. The arrival of the signal of the Termination is delayed at the Pacific core site due to the destructive interference of the still-rising Antarctic signal and the falling North Atlantic signal. This scenario is only possible because the ocean is not a single conveyor belt where all waters at the Pacific core site previously passed the Atlantic core site, but instead the Pacific core site is bathed more prominently by waters with a direct Antarctic source.
31 citations
TL;DR: In this article, a series of coupled climate experiments with different durations of the imposed intermittent mixing but where each has the same annual mean diffusivity is presented. And the results agree with a simple model of heat transfer for the upper ocean with a time-dependent vertical diffusion.
Abstract: [1] Tropical cyclones (TC) represent a powerful, albeit highly transient forcing able to redistribute ocean heat content locally. Recent studies suggest that TC-induced ocean mixing can have global climate impacts as well, including changes in poleward heat transport, ocean circulation, and thermal structure. In several previous modeling studies devoted to this problem, the TC mixing was treated as a permanent (constant in time) source of additional vertical diffusion in the upper ocean. In contrast, this study aims to explore the highly intermittent character of the mixing. We present results from a series of coupled climate experiments with different durations of the imposed intermittent mixing but where each has the same annual mean diffusivity. All simulations show robust changes in sea surface temperature and ocean subsurface temperature, independent of the duration of the mixing that varies between the experiments from a few days to a full year. Simulated temperature anomalies are characterized by a cooling in the subtropics, a moderate warming in middle to high latitudes, a pronounced warming of the equatorial cold tongue, and a deepening of the tropical thermocline. These effects are paralleled by substantial changes in ocean and atmosphere circulation and heat transports. While the general patterns of changes remain the same from one experiment to the next, their magnitude depends on the relative duration of the mixing. Stronger mixing, but of a shorter duration, has less of an impact. These results agree with a simple model of heat transfer for the upper ocean with a time-dependent vertical diffusivity.
31 citations
Cites background from "How long to oceanic tracer and prox..."
...The deep ocean continues its adjustment on longer time scales (centennial to millennial) that should involve diapycnal diffusion throughout the global ocean [Wunsch and Heimbach, 2008] and processes in the Southern Ocean [Haertel and Fedorov, 2011; Allison et al., 2011]....
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...fusion throughout the global ocean [Wunsch and Heimbach, 2008] and processes in the Southern Ocean [Haertel and Fedorov, 2011; Allison et al....
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TL;DR: In this article, the authors describe the protocol used to spin up the UK Earth system model (UKESM1) with respect to pre-industrial forcing for use in the 6th Coupled Model Intercomparison Project (CMIP6).
Abstract: For simulations intended to study the influence of anthropogenic forcing on climate, temporal stability of the Earth's natural heat, freshwater and biogeochemical budgets is critical. Achieving such coupled model equilibration is scientifically and computationally challenging. We describe the protocol used to spin‐up the UK Earth system model (UKESM1) with respect to pre‐industrial forcing for use in the 6th Coupled Model Intercomparison Project (CMIP6). Due to the high computational cost of UKESM1's atmospheric model, especially when running with interactive full chemistry and aerosols, spin‐up primarily used parallel configurations using only ocean/land components. For the ocean, the resulting spin‐up permitted the carbon and heat contents of the ocean's full volume to approach equilibrium over ~5000 years. On land, a spin‐up of ~1000 years brought UKESM1's dynamic vegetation and soil carbon reservoirs towards near‐equilibrium. The end‐states of these parallel ocean‐ and land‐only phases then initialised a multi‐centennial period of spin‐up with the full Earth system model, prior to this simulation continuing as the UKESM1 CMIP6 pre‐industrial control (piControl). The realism of the fully‐coupled spin‐up was assessed for a range of ocean and land properties, as was the degree of equilibration for key variables. Lessons drawn include the importance of consistent interface physics across ocean‐ and land‐only models and the coupled (parent) model, the extreme simulation duration required to approach equilibration targets, and the occurrence of significant regional land carbon drifts despite global‐scale equilibration. Overall, the UKESM1 spin‐up underscores the expense involved and argues in favour of future development of more efficient spin‐up techniques.
30 citations
Cites background from "How long to oceanic tracer and prox..."
...For example, estimated from radiocarbon and from inverse models, the waters of the deep North Pacific have a ventilation age of 1,200–1,500 years (Gebbie & Huybers, 2012; Khatiwala et al., 2012), with some model studies suggesting much longer timescales (Wunsch & Heimbach, 2008)....
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TL;DR: In this article, the authors investigated whether pore fluid profiles can constrain ocean δ18O and salinity at other times and, simultaneously, their ability to constrain the LGM ǫ o 2 and o 2, respectively.
Abstract: Paleoceanographic proxies indicate that the ocean state during the Last Glacial Maximum (LGM) differed from the modern ocean state. Depth profiles of ocean sediment pore fluid δ18O and [Cl−] have been used to reconstruct the δ18O and salinity at the LGM. Here, it is investigated whether pore fluid profiles can constrain ocean δ18O and salinity at other times and, simultaneously, their ability to constrain the LGM δ18O and salinity. An inverse framework is developed that relies on Bayesian parameter estimation, thus allowing formal separation of prior assumptions from the information in observations. Synthetic problems are used to explore the information about past ocean tracers that can be recovered from pore fluid profiles. It is concluded that prior knowledge of deep ocean mixing time scales is essential to an accurate inverse estimate of LGM ocean salinity and δ18O from modern pore fluid profiles. The most recent 10 000 years of ocean salinity and δ18O and the error in their estimates are bette...
30 citations
Cites background from "How long to oceanic tracer and prox..."
...ocean equilibration time scales may be up to 10000 years or even longer (Wunsch and Heimbach 2008)....
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...…stable until 19–14ka BP (Clark et al. 2009), which calls into question both the idea of a synchronous LGM in the ocean and the timing of the LGM at any site in the ocean, particularly given that the ocean equilibration time scales may be up to 10000 years or even longer (Wunsch and Heimbach 2008)....
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...However, Wunsch and Heimbach (2008) dem- onstrate that radiocarbon ages can be misleading; the ocean may need up to 10 000 years to reach a new equilibrium in response to regional changes in surface forcing....
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...However, Wunsch and Heimbach (2008) demonstrate that radiocarbon ages can be misleading; the ocean may need up to 10 000 years to reach a new equilibrium in response to regional changes in surface forcing....
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References
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TL;DR: The NCEP/NCAR 40-yr reanalysis uses a frozen state-of-the-art global data assimilation system and a database as complete as possible, except that the horizontal resolution is T62 (about 210 km) as discussed by the authors.
Abstract: The NCEP and NCAR are cooperating in a project (denoted “reanalysis”) to produce a 40-year record of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involves the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data; quality controlling and assimilating these data with a data assimilation system that is kept unchanged over the reanalysis period 1957–96. This eliminates perceived climate jumps associated with changes in the data assimilation system. The NCEP/NCAR 40-yr reanalysis uses a frozen state-of-the-art global data assimilation system and a database as complete as possible. The data assimilation and the model used are identical to the global system implemented operationally at the NCEP on 11 January 1995, except that the horizontal resolution is T62 (about 210 km). The database has been enhanced with many sources of observations not available in real time for operations, provided b...
28,145 citations
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31 Dec 1959
TL;DR: In this paper, a classic account describes the known exact solutions of problems of heat flow, with detailed discussion of all the most important boundary value problems, including boundary value maximization.
Abstract: This classic account describes the known exact solutions of problems of heat flow, with detailed discussion of all the most important boundary value problems.
21,807 citations
TL;DR: In this article, a new parameterization of oceanic boundary layer mixing is developed to accommodate some of this physics, including a scheme for determining the boundary layer depth h, where the turbulent contribution to the vertical shear of a bulk Richardson number is parameterized.
Abstract: If model parameterizations of unresolved physics, such as the variety of upper ocean mixing processes, are to hold over the large range of time and space scales of importance to climate, they must be strongly physically based. Observations, theories, and models of oceanic vertical mixing are surveyed. Two distinct regimes are identified: ocean mixing in the boundary layer near the surface under a variety of surface forcing conditions (stabilizing, destabilizing, and wind driven), and mixing in the ocean interior due to internal waves, shear instability, and double diffusion (arising from the different molecular diffusion rates of heat and salt). Mixing schemes commonly applied to the upper ocean are shown not to contain some potentially important boundary layer physics. Therefore a new parameterization of oceanic boundary layer mixing is developed to accommodate some of this physics. It includes a scheme for determining the boundary layer depth h, where the turbulent contribution to the vertical shear of a bulk Richardson number is parameterized. Expressions for diffusivity and nonlocal transport throughout the boundary layer are given. The diffusivity is formulated to agree with similarity theory of turbulence in the surface layer and is subject to the conditions that both it and its vertical gradient match the interior values at h. This nonlocal “K profile parameterization” (KPP) is then verified and compared to alternatives, including its atmospheric counterparts. Its most important feature is shown to be the capability of the boundary layer to penetrate well into a stable thermocline in both convective and wind-driven situations. The diffusivities of the aforementioned three interior mixing processes are modeled as constants, functions of a gradient Richardson number (a measure of the relative importance of stratification to destabilizing shear), and functions of the double-diffusion density ratio, Rρ. Oceanic simulations of convective penetration, wind deepening, and diurnal cycling are used to determine appropriate values for various model parameters as weak functions of vertical resolution. Annual cycle simulations at ocean weather station Papa for 1961 and 1969–1974 are used to test the complete suite of parameterizations. Model and observed temperatures at all depths are shown to agree very well into September, after which systematic advective cooling in the ocean produces expected differences. It is argued that this cooling and a steady salt advection into the model are needed to balance the net annual surface heating and freshwater input. With these advections, good multiyear simulations of temperature and salinity can be achieved. These results and KPP simulations of the diurnal cycle at the Long-Term Upper Ocean Study (LOTUS) site are compared with the results of other models. It is demonstrated that the KPP model exchanges properties between the mixed layer and thermocline in a manner consistent with observations, and at least as well or better than alternatives.
3,756 citations
TL;DR: In this paper, a subgrid-scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non-eddy-resolving ocean circulation models.
Abstract: A subgrid-scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non-eddy-resolving ocean circulation models. The mixing is applied in isopycnal coordinates to isopycnal layer thickness, or inverse density gradient, as well as to passive scalars, temperature and salinity. The transformation of these mixing forms to physical coordinates is also presented.
3,107 citations
"How long to oceanic tracer and prox..." refers methods in this paper
...The underlying numerical code is that of Marshall et al. (1997) as modified by the ECCO projects in the interim, and includes the Large et al. (1994) mixed layer formulation, and the Gent and McWilliams (1990) eddy-flux parameterization....
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TL;DR: A preconditioner is used which, in the hydrostatic limit, is an exact integral of the Poisson operator and so leads to a single algorithm that seamlessly moves from nonhydrostatic to hydrostatic limits, competitive with the fastest ocean climate models in use today.
Abstract: The numerical implementation of an ocean model based on the incompressible Navier Stokes equations which is designed for studies of the ocean circulation on horizontal scales less than the depth of the ocean right up to global scale is described. A "pressure correction" method is used which is solved as a Poisson equation for the pressure field with Neumann boundary conditions in a geometry as complicated as that of the ocean basins. A major objective of the study is to make this inversion, and hence nonhydrostatic ocean modeling, efficient on parallel computers. The pressure field is separated into surface, hydrostatic, and nonhydrostatic components. First, as in hydrostatic models, a two-dimensional problem is inverted for the surface pressure which is then made use of in the three-dimensional inversion for the nonhydrostatic pressure. Preconditioned conjugate-gradient iteration is used to invert symmetric elliptic operators in both two and three dimensions. Physically motivated preconditioners are designed which are efficient at reducing computation and minimizing communication between processors. Our method exploits the fact that as the horizontal scale of the motion becomes very much larger than the vertical scale, the motion becomes more and more hydrostatic and the three- dimensional Poisson operator becomes increasingly anisotropic and dominated by the vertical axis. Accordingly, a preconditioner is used which, in the hydrostatic limit, is an exact integral of the Poisson operator and so leads to a single algorithm that seamlessly moves from nonhydrostatic to hydrostatic limits. Thus in the hydrostatic limit the model is "fast," competitive with the fastest ocean climate models in use today based on the hydrostatic primitive equations. But as the resolution is increased, the model dynamics asymptote smoothly to the Navier Stokes equations and so can be used to address small- scale processes. A "finite-volume" approach is employed to discretize the model in space in which property fluxes are defined normal to faces that delineate the volumes. The method makes possible a novel treatment of the boundary in which cells abutting the bottom or coast may take on irregular shapes and be "shaved" to fit the boundary. The algorithm can conveniently exploit massively parallel computers and suggests a domain decomposition which allocates vertical columns of ocean to each processing unit. The resulting model, which can handle arbitrarily complex geometry, is efficient and scalable and has been mapped on to massively parallel multiprocessors such as the Connection Machine (CM5) using data-parallel FORTRAN and the Massachusetts Institute of Technology data-flow machine MONSOON using the implicitly parallel language Id. Details of the numerical implementation of a model which has been designed for the study of dynamical processes in the ocean from the convective, through the geostrophic eddy, up to global scale are set out. The "kernel" algorithm solves the incompressible Navier Stokes equations on the sphere, in a geometry as complicated as that of the ocean basins with ir- regular coastlines and islands. (Here we use the term "Navier Stokes" to signify that the full nonhydrostatic equations are being employed; it does not imply a particular constitutive relation. The relevant equations for modeling the full complex- ity of the ocean include, as here, active tracers such as tem- perature and salt.) It builds on ideas developed in the compu- tational fluid community. The numerical challenge is to ensure that the evolving velocity field remains nondivergent. Most
2,315 citations
"How long to oceanic tracer and prox..." refers methods in this paper
...The underlying numerical code is that of Marshall et al. (1997) as modified by the ECCO projects in the interim, and includes the Large et al. (1994) mixed layer formulation, and the Gent and McWilliams (1990) eddy-flux parameterization....
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