969 research outputs found
The role of tectonic uplift, climate, and vegetation in the long-term terrestrial phosphorous cycle
Phosphorus (P) is a crucial element for life and therefore for maintaining ecosystem productivity. Its local availability to the terrestrial biosphere results from the interaction between climate, tectonic uplift, atmospheric transport, and biotic cycling. Here we present a mathematical model that describes the terrestrial P-cycle in a simple but comprehensive way. The resulting dynamical system can be solved analytically for steady-state conditions, allowing us to test the sensitivity of the P-availability to the key parameters and processes. Given constant inputs, we find that humid ecosystems exhibit lower P availability due to higher runoff and losses, and that tectonic uplift is a fundamental constraint. In particular, we find that in humid ecosystems the biotic cycling seem essential to maintain long-term P-availability. The time-dependent P dynamics for the Franz Josef and Hawaii chronosequences show how tectonic uplift is an important constraint on ecosystem productivity, while hydroclimatic conditions control the P-losses and speed towards steady-state. The model also helps describe how, with limited uplift and atmospheric input, as in the case of the Amazon Basin, ecosystems must rely on mechanisms that enhance P-availability and retention. Our novel model has a limited number of parameters and can be easily integrated into global climate models to provide a representation of the response of the terrestrial biosphere to global change
Transforming U.S. agriculture with crushed rock for CO sequestration and increased production
Enhanced weathering (EW) is a promising modification to current agricultural
practices that uses crushed silicate rocks to drive carbon dioxide removal
(CDR). If widely adopted on farmlands, it could help achieve net-zero or
negative emissions by 2050. We report detailed state-level analysis indicating
EW deployed on agricultural land could sequester 0.23-0.38 Gt CO yr
and meet 36-60 % of U.S. technological CDR goals. Average CDR costs vary
between state, being highest in the first decades before declining to a range
of 100-150 tCO by 2050, including for three states (Iowa,
Illinois, and Indiana) that contribute most to total national CDR. We identify
multiple electoral swing states as being essential for scaling EW that are also
key beneficiaries of the practice, indicating the need for strong bipartisan
support of this technology. Assessment the geochemical capacity of rivers and
oceans to carry dissolved EW products from soil drainage suggests EW provides
secure long-term CO removal on intergenerational time scales. We
additionally forecast mitigation of ground-level ozone increases expected with
future climate change, as an indirect benefit of EW, and consequent avoidance
of yield reductions. Our assessment supports EW as a practical innovation for
leveraging agriculture to enable positive action on climate change with
adherence to federal environmental justice priorities. However, implementing a
stage-gating framework as upscaling proceeds to safeguard against environmental
and biodiversity concerns will be essential
Multicentury changes in ocean and land contributions to the climate-carbon feedback
Author Posting. © American Geophysical Union, 2015. 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 29 (2015): 744–759, doi:10.1002/2014GB005079.Improved constraints on carbon cycle responses to climate change are needed to inform mitigation policy, yet our understanding of how these responses may evolve after 2100 remains highly uncertain. Using the Community Earth System Model (v1.0), we quantified climate-carbon feedbacks from 1850 to 2300 for the Representative Concentration Pathway 8.5 and its extension. In three simulations, land and ocean biogeochemical processes experienced the same trajectory of increasing atmospheric CO2. Each simulation had a different degree of radiative coupling for CO2 and other greenhouse gases and aerosols, enabling diagnosis of feedbacks. In a fully coupled simulation, global mean surface air temperature increased by 9.3 K from 1850 to 2300, with 4.4 K of this warming occurring after 2100. Excluding CO2, warming from other greenhouse gases and aerosols was 1.6 K by 2300, near a 2 K target needed to avoid dangerous anthropogenic interference with the climate system. Ocean contributions to the climate-carbon feedback increased considerably over time and exceeded contributions from land after 2100. The sensitivity of ocean carbon to climate change was found to be proportional to changes in ocean heat content, as a consequence of this heat modifying transport pathways for anthropogenic CO2 inflow and solubility of dissolved inorganic carbon. By 2300, climate change reduced cumulative ocean uptake by 330 Pg C, from 1410 Pg C to 1080 Pg C. Land fluxes similarly diverged over time, with climate change reducing stocks by 232 Pg C. Regional influence of climate change on carbon stocks was largest in the North Atlantic Ocean and tropical forests of South America. Our analysis suggests that after 2100, oceans may become as important as terrestrial ecosystems in regulating the magnitude of the climate-carbon feedback.We are grateful for support from the U.S. Department of Energy Office of Science and the National Science Foundation (NSF). J.T.R. and F.H. received support from the Regional and Global Climate Modeling Program in the Climate and Environmental Sciences Division of the Biological and Environmental Research (BER) Program in the U.S. Department of Energy Office of Science. J.T.R., K.L., E.M., W.F., J.K.M., S.C.D., and N.N.M. received funding from the NSF project “Collaborative Research: Improved Regional and Decadal Predictions of the Carbon Cycle“ (AGS-1048827, AGS-1021776, and AGS-1048890). The Community Earth System Modeling project receives support from both NSF and BER.2015-12-0
Global Biology Research Program: Program plan
Biological processes which play a dominant role in these cycles which transform and transfer much of this material throughout the biosphere are examined. A greater understanding of planetary biological processes as revealed by the interaction of the biota and the environment. The rationale, scope, research strategy, and research priorities of the global biology is presented
Inconsistent strategies to spin up models in CMIP5: implications for ocean biogeochemical model performance assessment
International audienceDuring the fifth phase of the Coupled Model Inter-comparison Project (CMIP5) substantial efforts were made to systematically assess the skill of Earth system models. One goal was to check how realistically representative marine biogeochemical tracer distributions could be reproduced by models. In routine assessments model historical hind-casts were compared with available modern biogeochemi-cal observations. However, these assessments considered neither how close modeled biogeochemical reservoirs were to equilibrium nor the sensitivity of model performance to initial conditions or to the spin-up protocols. Here, we explore how the large diversity in spin-up protocols used for marine biogeochemistry in CMIP5 Earth system models (ESMs) contributes to model-to-model differences in the simulated fields. We take advantage of a 500-year spin-up simulation of IPSL-CM5A-LR to quantify the influence of the spin-up protocol on model ability to reproduce relevant data fields. Amplification of biases in selected biogeochemical fields (O2, NO3, Alk-DIC) is assessed as a function of spin-up duration. We demonstrate that a relationship between spin-up duration and assessment metrics emerges from our model results and holds when confronted with a larger ensemble of CMIP5 models. This shows that drift has implications for performance assessment in addition to possibly aliasing estimates of climate change impact. Our study suggests that differences in spin-up protocols could explain a substantial part of model disparities, constituting a source of model-to-model uncertainty
Phytoplankton temporal strategies increase entropy production in a marine food web model
We develop a trait-based model founded on the hypothesis that biological
systems evolve and organize to maximize entropy production by dissipating
chemical and electromagnetic potentials over longer time scales than abiotic
processes by implementing temporal strategies. A marine food web consisting of
phytoplankton, bacteria and consumer functional groups is used to explore how
temporal strategies, or the lack there of, change entropy production in a
shallow pond that receives a continuous flow of reduced organic carbon plus
inorganic nitrogen and illumination from solar radiation with diel and seasonal
dynamics. Results show that a temporal strategy that employs an explicit
circadian clock produces more entropy than a passive strategy that uses
internal carbon storage or a balanced growth strategy that requires
phytoplankton to grow with fixed stoichiometry. When the community is forced to
operate at high specific growth rates near 2 d-1, the optimization-guided model
selects for phytoplankton ecotypes that exhibit complementary for winter versus
summer environmental conditions to increase entropy production. We also present
a new type of trait-based modeling where trait values are determined by
maximizing entropy production rather than by random selection.Comment: 39 pp. including Supplementary Material, 6 Figure
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