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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Dissertation•
01 Jan 2010
TL;DR: Thesis (S.M. as discussed by the authors ) in Climate Physics and Chemistry, Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010, 2010.
Abstract: Thesis (S.M. in Climate Physics and Chemistry)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.
3 citations
Cites background from "How long to oceanic tracer and prox..."
...In this experiment, the "dye" is completely passive, having no dynamical, chemical, or biological interactions and the color is just notional (Wunsch and Heimbach, 2008)....
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...but also because it would be one of the major regions of injection of glacial water melt, producing anomalies in tracers such as O 180 (Wunsch and Heimbach, 2008)....
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...Transit time distributions can be interpreted as Green functions of the tracer distribution equations (Wunsch and Heimbach, 2008)....
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...As a result, the AABW formation is not correctly presented here, with the North Atlantic region dominating the dye concentration of the deepest model layers (Wunsch and Heimbach, 2008)....
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..."The various time scales for distribution of tracers and proxies in the global ocean are critical to the interpretation of data from deep-sea cores" (Wunsch and Heimbach, 2008)....
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TL;DR: Here the ‘wicked problems’ of Anthropogenically induced climate change are addressed, posing challenges that currently seem to surpass the authors' ability to tackle them.
Abstract: Anthropogenically induced climate change has created a set of intriguing scientific problems pertaining to the Seas and the Oceans on earth that can be monitored, analysed, modelled and consequently understood at some level. The international research community is deeply engaged in this endeavour as exemplified by the United Nations Decade of Ocean Science for Sustainable Development (2021–2030). Even so, the types of problems caused by human activity are inherently difficult to solve, if solvable at all, making them equally difficult to approach and manage. Here we address these as ‘wicked problems’ (first discussed by Churchman 1967, and later defined and formalized regarding social and natural sciences by Rittel and Webber 1973), posing challenges that currently seem to surpass our ability to tackle them. We see the Sea and the Oceans, but mainly from above—we see only the surface. A curved and broken line that separates our world from the one below, from the life in and of the Sea. Seen from ashore, its beauty and incessant perplexity is staggering—an outlook which we increasingly seek refuge in, for recreation and for wellbeing (see for instance Bowen et al. 2014). Our land-based perspective is rewarding, but also limiting in its lack of three-dimensionality, because the vastness of the Seas and the Oceans is so much more than the surface we observe from a distance. It is what we cannot see which makes it so challenging to understand. Water stretches across basins and beneath ice shelves, extending all the way down to the abyssal depths. The Seas and Oceans cover over 70% of Earth’s surface or 3.61 9 10 km with a total mass of 1.4 9 10 kg (Vallis 2011). It has a mean depth of over 3.7 km, but even so all water on Earth can still be fitted in a sphere of only 1400 km in diameter. Despite big numbers, clean water is a scarce commodity that needs to be treated accordingly. Ocean circulation and overturning, processes that involve wind-driven gyres, turbulent diffusion and the sinking of surface water, are unevenly distributed globally. Gebbie and Huybers (2011) estimate that 15% of the total ocean’s surface accounts for 85% of the production of deep water. Despite the fact that this production is localized to a few high latitude areas, it still enables continued water mass exchange between the major interhemispheric basins. This vital engine helps maintain a balance in earth’s climate by constantly moderating it through uptake of heat and subsequent redistribution. On a human time scale, the ocean engine is slow, given the volume in question, explainingwhy it can take up to 1200–1500 years before submerged surface water in the PacificOcean reach the deepest parts of the basin (Gebbie and Huybers 2012) or even longer before it resurfaces, all depending on which ocean and water mass you examine (Wunsch and Heimbach 2008). It is that sluggishness we have come to rest the fundaments of our fast-growing and fast-living civilizations on because if the heat absorbed was released back from the ocean on shorter time scales the impact of our expanding footprint would be immediately evident. This is but one explanation for why we have taken the goods and services provided by the Seas and Oceans for granted through the centuries, a type of behaviour which has cemented a view that is hard to change. Numerous species have been decimated until saved in the last hour like the Antarctic blue whale (Attard et al. 2016) or the sea otter (Doroff et al. 2003). The list of threatened species is growing by the day which in effect makes the global marine ecosystem less resilient to further change (Levin and Lubchenco 2008).
3 citations
Cites background from "How long to oceanic tracer and prox..."
...…in question, explainingwhy it can take up to 1200–1500 years before submerged surface water in the PacificOcean reach the deepest parts of the basin (Gebbie and Huybers 2012) or even longer before it resurfaces, all depending on which ocean and water mass you examine (Wunsch and Heimbach 2008)....
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TL;DR: In this article , the authors quantify the typical amplitude of past global temperature fluctuations on time scales from hundreds to tens of millions of years and use it to assess the presence or absence of long-term stabilizing feedbacks in the climate system.
Abstract: The question of how Earth’s climate is stabilized on geologic time scales is important for understanding Earth’s history, long-term consequences of anthropogenic climate change, and planetary habitability. Here, we quantify the typical amplitude of past global temperature fluctuations on time scales from hundreds to tens of millions of years and use it to assess the presence or absence of long-term stabilizing feedbacks in the climate system. On time scales between 4 and 400 ka, fluctuations fail to grow with time scale, suggesting that stabilizing mechanisms like the hypothesized “weathering feedback” have exerted dominant control in this regime. Fluctuations grow on longer time scales, potentially due to tectonically or biologically driven changes that make weathering act as a climate forcing and a feedback. These slower fluctuations show no evidence of being damped, implying that chance may still have played a nonnegligible role in maintaining the long-term habitability of Earth.
3 citations
TL;DR: In this paper, a method for computing marginal probability distributions of passive tracer dispersal from Lagrangian observations is developed using a pseudotrack approach, and probability distributions for the domain of occupation and transit time are developed, complimenting more frequently used bulk statistics for average transit time and overall crossing probability.
Abstract: Probability distribution functions of displacement are central to Lagrangian statistics and the study of fluid dispersal. A method for computing marginal probability distributions of passive tracer dispersal from Lagrangian observations is developed. Using a pseudotrack approach, probability distributions for the domain of occupation and transit time are developed, complimenting more frequently used bulk statistics for average transit time and overall crossing probability. To demonstrate application of this technique to observations, likelihoods and time scales of dispersal from the Gulf Stream to the Azores are quantified using World Ocean Circulation Experiment (WOCE) Surface Velocity Program (SVP) near-surface drifter data for the years 1992–2008. Over observable time scales, the transit of a particle in the near-surface ocean from the Gulf Stream to the Azores occurs across a spectrum of time scales, from tens to hundreds of days, with an overall likelihood of 42% ± 4% and a mean time scale of...
2 citations
01 Jun 2016
TL;DR: In this paper, the same methodology is applied to δ18Ow in the upper 100m of four deep-sea cores, and results are very sensitive, with conventional diffusion values, to the assumed initial conditions at −100 ky and a long list of noise (uncertainty) assumptions.
Abstract: . An earlier analysis of pore-water salinity (chlorinity) in two deep-sea cores, using terminal constraint methods of control theory, concluded that although a salinity amplification in the abyss was possible during the LGM, it was not required by the data. Here the same methodology is applied to δ18Ow in the upper 100 m of four deep-sea cores. An ice volume amplification to the isotopic ratio is, again, consistent with the data but not required by it. In particular, results are very sensitive, with conventional diffusion values, to the assumed initial conditions at −100 ky and a long list of noise (uncertainty) assumptions. If the calcite values of δ18O are fully reliable, then published enriched values of the ratio in seawater are necessary to preclude sub-freezing temperatures, but the seawater δ18O in pore fluids does not independently require the conclusion.
2 citations
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
Book•
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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