427 research outputs found
Ocean gyres and abrupt change in the thermohaline circulation: a conceptual analysis
Get PDFThe implications are investigated of representing ocean gyre circulations by a diffusion term in the Stommel and Rooth box models of the thermohaline circulation (THC) in one and two hemispheres, respectively. The approach includes mostly analytical solution and study of the bifurcation structure, but also numerical integration and feedback analysis. Sufficient diffusion (gyre strength) eliminates multiple equilibria from either model, highlighting the need for accurate gyre circulation strength in general circulation models (GCMs) when considering the potential for abrupt climate change associated with THC shutdown.With diffusion, steady-state flow strength in the Rooth model depends on freshwater forcing (i.e., implied atmospheric water vapor transport) in both hemispheres, not only on that in the upwelling hemisphere, as in the nondiffusive case. With asymmetric freshwater forcing, two solutions (strong stable and weak unstable) are found with sinking in the hemisphere with stronger forcing and one solution with sinking in the other hemisphere. Under increased freshwater forcing the two solutions in the hemisphere with stronger forcing meet in a saddle-node bifurcation (if diffusion is sufficiently strong to prevent a subcritical Hopf bifurcation first), followed by flow reversal. Thus, the bifurcation structure with respect to freshwater forcing of the diffusive Rooth model of two-hemisphere THC is similar to that of the Stommel model of single-hemisphere THC, albeit with a very different dynamical interpretation. Gyre circulations stabilize high-latitude sinking in the Stommel model. In the Rooth model, gyre circulations only stabilize high-latitude sinking if the freshwater forcing is weaker in the sinking hemisphere than in the upwelling hemisphere, by an amount that increases with diffusion. The values of diffusion and freshwater forcing at which qualitative change in behavior occurs correspond to the range of the values used in and obtained with GCMs, suggesting that this analysis can provide a conceptual foundation for analyzing the stability of the interhemispheric THC, and also for the potential of the Atlantic THC to undergo abrupt change
Economic Potential of Conservation Farming Annual Winter Forages for the Stocker Cattle Grazing Enterprise
Get PDFThe objective was to determine the expected net value of a no-till forage production and grazing system. Reduction in fuel and machinery costs offset the costs of herbicide application. The net value of the no-till system is $31 per acre, and is quite sensitive to relative differences in cattle performance.Farm Management, Land Economics/Use,
COVID-19 and the Internet: Lessons Learned
Get PDFThe COVID-19 pandemic has disrupted the ‘real’ world and substantially impacted the virtual world and thus the Internet ecosystem. It has caused a significant exogenous shock that offers a wealth of natural experiments and produced new data about broadband, clouds, and the Internet in times of crisis. In this chapter, we characterise and evaluate the evolving impact of the global COVID-19 crisis on traffic patterns and loads and the impact of those on Internet performance from multiple perspectives. While we place a particular focus on deriving insights into how we can better respond to crises and better plan for the post-COVID-19 ‘new normal’, we analyse the impact on and the responses by different actors of the Internet ecosystem across different jurisdictions. With a focus on the USA and Europe, we examine the responses of both public and private actors, with the latter including content and cloud providers, content delivery networks, and Internet service providers (ISPs). This chapter makes two contributions: first, we derive lessons learned for a future post-COVID-19 world to inform non-networking spheres and policy-making; second, the insights gained assist the networking community in better planning for the future.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Cyber Securit
Integrated mid-infrared spectroscopic sensing technology
No full textAuthor Gerald Stocker, MScDissertation Johannes Kepler Universität Linz 2022Arbeit nach Ablauf der Sperre auf den öffentlichen PCs in den Bibliotheken der JKU+Medizin abrufba
On the composition of firn air and its dependence on seasonally varying atmospheric boundary conditions and the firn structure
No full textThe dependence of the firn air composition on seasonally varying atmospheric boundary conditions and the firn structure has been studied based on firn air samples from two Antarctic sites, Halley and Kohnen.
The Halley data set consists of six profiles sampled in a two month resolution in the year 2003. Settling of the firn and snow accumulation led to a shift of the depth levels of both, the firn air sampling setup and the thermistors. Prediction of this sample level shift with a 1–dimensional box model developed in the frame of this study coincides with the decrease of the analyzed diurnal temperature cycle.
By forcing the temperature–diffusion model with the surface temperature history of Halley, temperature oscillations in the firn column originating from seasonal atmospheric temperature variations are reasonably well reproduced. Thus, the dependence of the thermal conductivity on firn density as derived by Schwander et al. [1997] is sufficient also on the seasonal scale.
In order to simulate thermal fractionation of the different gas species, thermal diffusion factors αT are determined based on two different model approaches and the firn air data set: αT = 3.727 · 10−3 for the fractionation of 15N14N in N2, αT = 12.480·10−3 for 18O16O in air, αT = 7.321·10−3 for 16O2 in air, αT = 32.241·10−3 for 36Ar in air, αT = 45.516 · 10−3 for 40Ar in air, and 57.371 · 10−3 ≤ αT ≤ 67.811 · 10−3 for CO2 in air.
Seasonal oscillations observed in the firn air profiles of CO2 and the isotopic species δ15N, δ18O, and δ36Ar act as expected from theory during the entire year. The imprint of both, seasonal atmospheric temperature variations and atmospheric concentration oscillations is well reproduced by the diffusion–temperature model. Neither a seasonal variability of ±0.5 ppmv in the atmospheric CO2 concentration nor thermal diffusion forced by seasonal atmospheric temperature oscillations will lead to considerable changes of the CO2 concentration in air bubbles finally occluded in the ice.
An overestimation of the measured February amplitude of the isotopic profiles (δ15N, δ18O δ36Ar) by the diffusion–temperature model can be explained by surface convection. Based on a parametrisation approach of Severinghaus et al. [2001] and Kawamura et al. [2006], a convective column height of 0.28 ≤ zconv ≤ 0.43 m is derived for Halley firn of 2003. Convection turned out to be active between end of December and mid of February. The calculation of surface convection as Darcian air flow through the firn driven by a pressure field originating from dunes on the surface [Colbeck, 1989] confirms the size of the convective layer. However, the temporal forcing and monthly mean wind speeds measured in Halley do not clearly coincide.
Within the frame of thesis, firn and firn air have been sampled at the deep drilling site Kohnen in Austral summer 2005/06. Independently from the container type samples have a good quality with respect to the already analyzed species (isotopes, elemental ratios, CO2, noble gases and ozone depleting substances). The usage of a bladder tube of distinctly smaller diameter (by 15 mm) than the hole turned out to be problematic and thus, is not recommended for further experiments.
From the average of the 20 m temperature obtained from five borehole temperature profiles measured between November 2005 and January 2006, an annual mean temperature of –44.4°C could be derived for the Kohnen site.
Forcing the temperature model with atmospheric temperature data obtained from an automatic weather station near Kohnen Station leads to a good agreement between simulations and the bore hole temperatures. CO2 firn air data agree well with simulations based on the atmospheric CO2 history from South Pole and the measured temperatures. The best match between modeled and measured CO2 profiles was obtained by selecting the tortuosity parameters α and β to α = 0.85 and β = 2.5. The close–off density is determined to ρco = 825 kg m−3, which is slightly lower than the mean air isolation level of 833.4 kg m−3 derived according to Martinerie et al. [1992, 1994]. ρco corresponds to a close–off depth zco = 87.6 m. Effective diffusivity is determined to become terminated at the lock–in depth zli = 87.4 m. Kohnen firn has a non–diffusive zone of about 7 m length, where the deepest firn air sample is at zmax = 94.9 m.
CO2 firn air data agree with the simulation disregarding thermal diffusion rather than showing a thermal signal. Thus, Kohnen firn seems to have a convective zone attenuating the seasonal thermal amplitude.
The mean gas age at the close–off level is estimated by combining the mean gas ages of air originating from the open pore space and the air occluded in air bubbles. In order to determine the amount of occluded air, a mass balance is implemented in the diffusion–temperature model. Air enclosure is simulated from two different temporally constant enclosure functions. According to this approach a combined mean CO2 gas age at the close–off level of (65 +75/–50) or (74 +85/–56) years, respectively, is retrieved for present–day Kohnen firn. Depending on the enclosure functions the width of corresponding age distribution functions representing air occluded in air bubbles lies between ≈ 47 and ≈ 52 years. The width of the age distribution of the air originating from the open pore volume is ≈ 17 years.
Forcing effective diffusivity De with the open porosity sop instead of the total porosity s, leads to about 2 ppmv lower CO2 concentrations simulated for the depth range around and below the close–off region. Accordingly, the mean gas age is calculated to be 2 to 5 years lower than for De ∼ s.
The ice age at the close–off level is determined to (905 ± 7) years from assigning documented volcanic events to peaks in the electrical conductivity record of the ice. Based on this depth–to–age relation an annual mean accumulation of 65 kg m−2 a−1 could be derived for the Kohnen site.
The ∆age, i.e. the difference between ice age and combined mean gas age, varies between (831 +85/–56) and (840 +76/–51) years for Kohnen firn subjected topresent–day conditions.
To the best of current knowledge Kohnen firn provides the oldest firn air that has ever been sampled so far. The age of the firn air at zmax = 94.9 m is determined to (114 +13/–10) years. The occurrence of such old firn air is attributed to a distinct stratification of Kohnen firn, which originates from a wind driven surface orography and is preserved down to the close–off region
Marketing channels for U.S. stocker cattle and the limited use of e-commerce
Get PDFabstract: We investigate the underlying reasons for producers’ choice of marketing channels for stocker cattle in the United States. In addition to traditional public auctions, private sales, video auctions, and Internet auctions have been recently used in the marketing of stocker cattle. We find that while the number of marketing options may have increased in recent years, only relatively large producers can actually take advantage of these options. The marketing options for smaller producers are still limited due to their relative size. We also find that the number of cattle marketed privately and through video and Internet auctions is positively correlated with herd size. In addition, the New Institutional Economics provides insights into how herd size influences the choice of marketing channels.Faculty working paper series (Morrison School of Agribusiness and Resource Management) ; MSABR 02-05Includes bibliographical references (p. 22-23)
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Nexos iconográficos entre las columnas de Tula y los discos de oro de Chichén Itzá. 26. Arqueología
No full text•Acosta,J.
1945. "La cuarta y quinta temporadas
de exploraciones arqueológicas en Tula, Hidalgo, 1943-44", en revista mexicana de estudios antropológicos, núm. 7, pp. 23-64.•Adams, R.E.W.
1977. Prehistoric Mesoamerica Boston, Little, Brown and Co.•Andrews .IV y E.Wyllys
1977. "Archaeology and Prehistory in
the Northern Maya Lowlands: An lntroduction ", en Handbook of Middle American indians, vol. 2, pp. 288-330.•Cabrera Castro, R.; S. Sugiyama y G.
Cowgill
1991. "The Templo de Quetzalcoatl Project at Teotihuacan", en Ancient Mesoomerica, núm. 2, pp. 77-92.•Cohodas, M.
1978. The greal ball court al Chichen ltza, Yucatan, Mexico, New York, Garland Publishing.•Cowgill, G.
1977. "Processes of Growth, Ili and Decline at Teotihuacán: The City and the State", en los procesos de cambio en Mesoamérica y áreas circunvecinas, XI Mesa redonda, vol. 1, México, Sociedad Mexicana de Antropología, pp. 183-193.•De la Fuente, B.; S.Treja y N.Gutiérrez
Solana
1988.Ecultura en piedra de Tula,. México, lnstituto de Investigaciones Estéticas-Universidad Nacional Autónoma de México.•Diehl, R.
1983. Tula:the Toltec capital of ancient, Mexico, EUA, Thames and Hudson , lnc.•Durán, O.
1964. The Aztecs, New York , Orion Press.•Edwards, O.y T.Stocker
2001. "Covariance of Poscclassic figurine styles, settllement patterns and political boundaries in the Basin of Mexico", en Tire New World figurine project, vol. 2, Stocker y C. Charlton (eds.), pp. 55-87.•Feldman. L.
1974. "Tollan in Hidalgo: native accounts of the Central Mexican Tolteca ", en Studies in ancient Tollan, R . Diehl (ed.), University of Missouri Monographs in Anthropology, núm. 1, pp. 130-149.•Gillespie, S.
1989. The Aztec kings, Tucson, University of Arizona .•Kaplan, J.
2000. "A great emblematic depiction of throned rule and royal sacrifice at Late PreClassic Kaminaljuyu" , en Ancient Mesoamerica, núm . 11, pp. 185-198.•Kelekna , P.
1998. "'War and Theocracy", en Chiefdoms and chieftaincy in the Americas, E. Redmond (ed.), Gainesville, Universiry of Florida Press, pp. 164-188.•Kelley, E.
1978. "The Temple of the Skulls at Alcavisca, Cha lchihuites", en Across the Chichimec sea, C. Riley y B. Hedrick (eds.), Carbondale, Souchern Illinois University Press, pp. 102-126.•Kristan-Graham .C.
1989. Art, rulership and tire Mesoamerican body p olitic al Tula and Chichen Itza, UCLA, dissercation.•Kubler, G.
1984. The art and orclritecture of ancient America: the Mexican, Maya and Andean peoples , New York, Penguin Books.•Luján, L.; R.Cobean y A.G. Mastache
1995. Xochicalco y Tula, México, Jaca Book.
•Mandeville, M.
1974. "Chipped Stone points from Tula'', en Studies in oncimt To/Ion, R. Diehl (ed.), Univers iry of Missiuri Monographs in Anchropology , pp. 95-104.•Mílbrath S.
1999. Star gods of the Mayo astronomy in art,folklore and calendars, Austin, Universicy of Texas Press.•Miller M.
1999. Maya art and architecture, New York, Thames and Hudson.•Proskouriakoff, T.
1974. Jades from the Cenote of Sa crifice, Chichen ltza, Yucacan, en Memoirs o/ the Peabody Museum of Ar chaeology and Ethnology, vol. 1O, núm. 1, Cambridge, Harvard University.•Ringle, W., T. Negrón y G.Bey 111
1998. "The return of Queczalcoacl", en Ancient Mesoamerica, núm. 9, pp. 183-232.•Schele, L
1998. "The iconography of Maya architectural facades during the Late classic period'', en Function and meaning in Classic Maya architecture, S. Houscon (ed.), Washington, D.C., Dumbarton Oaks, pp. 479-518.•Schmookler .A.
1984. Parable o/ the tribes: theproblem
of social evolution, Boscon, Houghron
Mifflin.•Stocker, T.
1974. "A small temple in che Tula residential zone", en Studies in ancient Tollan, R. Diehl (ed.), Uni versity of Missouri Monographs in An chropology, núm . 1, pp. 25-31.1983. Figurines from Tula, Hidalgo, Mexi
co, tesis, Universicy of Illinois, Urbana.
1987. "Conquesc, tribute and che rise of the state", en Studies in the neolithic and urban revolutions, L. Manzanilla (ed.), BAR Internacional Series 349, pp. 365-376.1991. "lntroduccion", en The New Worldfigurine project,vol. 1, Stocker (ed.),_Provo, Research Press, pp. 1-2.1993a. "Contradicrlons in religious myts: Tezcatlipoca and his existence at Tula, Hidalgo, Mexico", en Notas Mesoamericanas, 14, pp. 63-92.1993b. Who were che Toltecs and what did they do?, ponencia presen tada en la XIII reunión de IAES, México.2000a . "Ethnohistorical input for the Mesoamerican obsidian indus try", en Nahua Newsletter, núm . 30, pp. 27-31.2000b. "Reconsidering commems on Sahagún's 260 day signs", Nahua Newsletter, núm. 30, pp. 25-26.2001a. "Further coments on Townsend's the Azcecs, en Nahua Newsletter, en prensa.2001b. A walk through an Aztec dream , Taejon, South Korea, Heliot House.2002 "The Aztec Trickster on Display", en www.tr ickster.org
s.f. The Aztec augury table, manuscrito original.•Stocker, T.y D.James
1988. "Semiotic analysis of Prehistoric texts, en Semiotics, J.Deely (ed.), N.Y., Un iversity Press of Amer ica, 1987, pp. 183-192.
•Slocker, T. y E.Kylar
1984. "Aztec warfare. Sacrifice and cannibalism", en The Explorers Journal, mím 62, pp. 126-133.•Stocker, T., S. Meltzoff y S.Armsev
1979. "Further incerpretations in
Formative period iconography", en American antiquity , núm. 45, pp. 740-58.•Stocker T.y M.Spence
1974. "Obsidian eccencrics from Central Mexico'', en Studies in ancient Tollan, R. Diehl (ed.), University of Missouri Monographs in Anthropology, núm. l, pp. 88-94.•Tezozomoc , Hernando Alvarado
1975. Crónica mexicayotl , México,
UNAM.•Tozzer ,A.
1957. "Chichén Itzá and its Cenote of Sacrifice: A comparative scudy of contemporaneous Maya and Toltec",
en Memoirs of the Peobody Museum of Archaeologyond Ethnology, vols. 11-12.•Umberger, E.
1987. Antiques, revivals, and references to the pase in the Aztec are, en Res, núm. 13, pp. 61-105.•Van de Guchte, M.
1999. "The Inca cognition of landscape", en Archaeologies of landscape: Contemporary perspectives, T. Ashmore y B. Knapp (eds.), Oxford, Blackwell
Recommended from our members
Steady-state and transient modeling of tracer and nutrient distributions in the global ocean
Get PDFThe deep circulation model developed by Wright and Stocker has been used to represent the latitude-depth distributions of temperature, salinity, radiocarbon and color'' tracers in the Pacific, Atlantic and Indian Oceans. Restoring temperature and salinity to observed surface data the model shows a global thermohaline circulation where deep water is formed in the North Atlantic and in the Southern Ocean. A parameter study reveals that the high-latitude surface salinity determines the composition of deep water and its flow in the global ocean. Increasing Southern Ocean surface salinity by 0.4 ppt the circulation changes from a present-day mode where North Atlantic Deep Water is one where Antarctic Bottom Water is dominant. An inorganic carbon cycle with surface carbonate chemistry is included, and gas exchange is parameterized in terms of pCO{sub 2} differences. Pre- industrial conditions are achieved by adjusting the basin-mean alkalinity. A classical 2{times}CO{sub 2} experiment yields the intrinsic time scales for carbon uptake of the ocean; they agree with those obtained from simple box models or 3-dimensional ocean general circulation models. Using the estimated industrial anthropogenic input of CO{sub 2} into the atmosphere the model requires, consistent with other model studies, an additional carbon flux to match the observed increase of atmospheric pCO{sub 2}. We use more realistic surface boundary conditions which reduce sensitivity to freshwater discharges into the ocean. In a glacial-to-interglacial experiment rapid transitions of the deep circulation between two different states occur in conjunction with a severe reduction of the meridional heat flux and sea surface temperature during peak melting. After the melting the conveyor belt circulation restarts
Large-scale ocean circulation, air-sea gas exchange, and carbon isotopes in a three-dimensional, computationally efficient ocean model
No full textThis thesis focuses on the intermediate-complexity modelling of the large-scale ocean circulation and the oceanic carbon cycle. The main objective is the development of a model of intermediate complexity by combining, evaluating and extending existing formulations of the single components within a coherent setting. The model should be suited to perform long integrations over the timescales of interest in climate research in short periods of time, also permitting to employ Monte-Carlo and other ensemble techniques.
In Chapter 2 the development of the physical core of the Bern3D ocean model is presented. First, the frictional-geostrophic balance ocean model of Edwards et al. [1998] is reviewed. This model has been designed to be computationally efficient and is used as the oceanic com ponent in the coupled atmosphere - sea ice - ocean model "C-GOLDSTEIN" [Edwards and Marsh, 2005] and is also applied as the oceanic component of the grid-based Earth system model GENIE (http://www. genie. ac.uk). The Bern3D ocean model is largely based on the ocean model described by Edwards et al. [1998] with updates as described in Edwards and Marsh [2005]. First, the governing equations describing the large scale ocean circulation and tracer transport are introduced. Then, specific extensions and modifications of the original ocean model constituting the development of the physical core of the Bern3D ocean model are described in detail. The Bern3D ocean model features seasonal boundary conditions and a high vertical resolution. In comparison to the ocean model used in Edwards and Marsh [2005], the mixing scheme for isopycnal diffusion and eddy-induced transport has been enhanced and an altered convection scheme has been implemented. Further, results from the standard simulation and the sensitivity of the steady state circulation to the mixing parameters are examined and presented. Also the simulated barotropic transport for a simulation with opened Indonesian Passage and increased latitudinal resolution is presented and compared to the standard solution.
The large scale circulation and the resulting distribution of water masses as simulated with the Bern3D ocean model has been examined and probed using a set of tracers governed by decadal to multi-century timescales [Müller et al., 2006] (Chapter 3). Modelled tracers are the 39Ar/Ar ratio and natural radiocarbon, both influenced by radioactive decay with different mean life times, as well as bomb-produced radiocarbon, CFC-11, and anthropogenic carbon, all influenced by their transient atmospheric boundary conditions. For all of these tracers exist measurements or data-based reconstructions of their distribution inside the ocean. Simulated distributions and inventories of temperature, salinity and the other tracers are compared with data-based estimates and reasonable agreement is found for a simulation performed with the Bern3D ocean model tuned towards data-based metrics, including the natural radiocarbon signatures of typical water masses and the inventories of CFC-11 for the mid-l 990s in the Indopacific. The model has also been applied to examine the importance of different surface to-deep transport mechanisms for the simulated distribution of natural radiocarbon and the uptake of CFC-11. Deep equatorial upwelling has been found to be sensitive to the vertical model resolution, reduced deep equatorial upwelling strength is found for a higher vertical resolution. Furthermore, the carbon budget for the industrial period was closed by simulating an uptake of anthropogenic carbon by the ocean of 18.9 GtC and 19.7 GtC for the 1980s and 1990s, respectively, and inferring land-atmosphere fluxes, in agreement with data-based estimates.
The Bern3D ocean model has been complemented with standard formulations of the abiotic, organic matter, and calcite carbon cycle (Chapter 4), as formulated for the phase two of the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP-2) [Orr, 2000]. Further, the formulations of the OCMIP-2 have been extended to include the radiocarbon fluxes in the organic matter and calcite cycles and the 13C fluxes for the whole oceanic carbon cycle formulation. Results have been compared with data-based estimates and are found to reasonably reproduce the main large-scale features as observed in the data. The oceanic carbon-cycle model component has been complemented with a 4-box formulation for the land biosphere following Siegenthaler and Oeschger [1987], in order to calculate the radiocarbon production rate by inversion of atmospheric Ll14C reconstructions from tree rings [Reimer et al., 2004, McCormac et al., 2004] with a global carbon cycle model.
The magnitude of the global mean air-sea gas exchange rate for CO2 has been discussed and debated over the last few decades in the scientific literature. In a contribution to this discussion (manuscript in preparation, Chapter 5) the natural radiocarbon distribution, basin-wide inventories of excess radiocarbon, the Earth system budget of radiocarbon, and basin-wide inventories of CFC-11 have been simulated using the gas-exchange formulation of the OCMIP-2 in an extensive sensitivity study varying the magnitude of the gas-exchange rate and oceanic transport strength. The results are compared to recent data-based estimates. It is demonstrated that the rate-limiting process for the uptake of excess radiocarbon is the gas-exchange rate and that the uptake of CFC-11 is dominated by oceanic transport and mixing. A target consisting of the data-based basin-wide inventories of excess radiocarbon in the Pacific, Indian Ocean, and Southern Atlantic for different points in time, the natural radiocarbon distribution in the surface ocean, and the Earth system budget of radiocarbon is defined and is best matched if the gas-transfer field from the OCMIP-2 is scaled down by (26 ± 16)%. Simulated column inventories are found to be similar in all basins, in contrast to data-based estimates, where the North Atlantic inventories are significantly higher than in the other basins. Estimates for inventories of excess radiocarbon, using the downscaled gas transfer rate of (15.7 ± 3.3) cm hr-1, are presented.
In a publication by Muscheler et al. [2007] (Chapter 6), the radiocarbon production rate records calculated by different carbon-cycle models and reconstructions of 10Be from ice cores are used together with records of the geomagnetic field intensity to infer the solar magnetic modulation, which is linked to the solar activity. The solar modulation parameter record is compared to irradiance records. In this publication, the radiocarbon production rate calculated with the Bern3D model is presented and compared with other radiocarbon production rate reconstructions using carbon-cycle models featuring a box model representation of the ocean. In comparison to the box models of the ocean, the Bern3D model provides a more realistic boundary condition at the surface ocean for the air-sea gas exchange of radiocarbon. ∆14C reconstructions for the northern and southern hemispheres, which differ owing to a gradient in atmospheric ∆14C at the equator, can thus be included as boundary conditions of the respective oceanic domains. In the box models of the ocean, which do not resolve the two hemispheres, the atmospheric ∆14C boundary condition has to be an averaged value of the two hemispheric records. The results using the different modelling approaches to calculate radiocarbon production are found to agree well.
An outlook regarding ongoing and possible future model development extending the Bern3D ocean model into various directions and applications thereof is given in Chapter 7. The Appendix details the construction of smooth atmospheric pC02 records as applied in the studies presented in this thesis and also their projection into the future in the form of idealised stabilisation scenarios as used for projections of climate change commitment using Earth system models of intermediate complexity for the upcoming Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) and e. g. in Plattner et al. [submitted] and Knutti et al. [2005]. Furthermore, a publication [Muscheler et al., 2005] contributing to a discussion that was initiated following the publication of a paper by Solanki et al. [2004] is attached in the Appendix. There, using radiocarbon production rate based reconstructions of the solar modulation parameter, Muscheler et al. [2005] find that the solar modulation parameter was comparable to or even exceeds today's values during several periods in the last 500 years
- …
