Carbon Mitigation Initiative
CMI

Carbon Science Group

Carbon Science Group
The Carbon Science Group uses both observational data and models to improve understanding of carbon sinks and predict the impact of climate change on the carbon cycle. The PI’s of the Science Group are Steve Pacala and Lars Hedin of the Department of Ecology and Evolutionary Biology, and Michael Bender, David Medvigy, Francois Morel and Jorge Sarmiento from the Department of Geosciences.

Exciting developments in 2012 include a new BP-sponsored program on near-term climate variability, breakthroughs in our understanding of the CO2 fertilization sink, and a potential world-class observing and modeling center for the Southern Ocean to be housed at Princeton.

Highlights

New Initiatives

  • A new BP-sponsored initiative will build the Carbon Science Group’s capacity to analyze, predict, and attribute changes in climate over the next 25 years.
  • The Sarmiento group prepared a large proposal for the National Science Foundation to form a Center for Southern Ocean Biogeochemical Observations and Modeling.

Controls on the Terrestrial Carbon Sink

  • A new analysis shows that, in the absence of a historical CO2 fertilization sink, the concentration of atmospheric CO2 would have been 80% greater than observed, and warming would have been 40% larger.
  • New models are explaining how nutrient limitation and nitrogen fixation affect CO2 fertilization, and predict that CO2 enhancement of the terrestrial carbon sink will continue.

Quantifying the Ocean Carbon Sink

  • A new set of climate models indicates that the Southern Ocean south of 30°S took up 71 ± 24% of the excess heat and 43 ± 3% of anthropogenic carbon over the period 1861 to 2005.
  • A new instrument for continuous, high precision measurements of the dissolved inorganic carbon concentration (DIC) of surface seawater has been deployed and validated.

New Modeling Tools

  • Simulation of ocean carbon cycling has been enhanced by a new model of bacterial cycling for global circulation models.
  • A new model explains how drought leads to tree mortality, which has been one of the largest sources of uncertainty in the carbon cycle.
  • A new model of fire in terrestrial systems is the first to effectively separate natural and anthropogenic fires at global scales.

Climate Change Impacts

  • Ocean acidification may decrease the fixation of nitrogen in the open ocean by decreasing the bioavailability of iron to nitrogen-fixing organisms.
  • New model studies predict a 20% reduction in fish size and likely tuna habitat reduction due to climate change and ocean warming.

Long-Term Climate Variability

  • Trends in the airborne fraction of anthropogenic CO2 are shown to be within the noise level when accounting for the decadal-scale influence of explosive volcanic eruptions, indicating that natural sinks are not decreasing as previous studies have found.
  • Million year-old ice from Antarctica is extending the ice core record of climate, and researchers are looking for even older ice.

New Initiatives

Program on near-term climate variability

To help anticipate the risks of near-term climate change, in 2012 BP agreed to sponsor a new research program at Princeton entitled “Climate Variability Over the Next 25 Years.” Headed by Steve Pacala and Elena Shevliakova, the program will involve collaborative research among BP, CMI, GFDL and the BP-sponsored team at Imperial College (IC). The researchers will use high- resolution climate models to predict climate variability, changes in climate variability and impacts of climate variability over the next quarter century. These studies will include hydrologic variability (i.e. rainfall, evapotranspiration, soil moisture, drought, river flow and flooding) and variability in natural and agricultural ecosystems (i.e. crop, biofuels, and forest production, carbon storage by ecosystems and carbon offsets, including effects of drought-induced fire). The first postdoc has been hired for this project and an offer has been extended to a second.

Proposed Center for Southern Ocean Biogeochemical Observations and Modeling

In the past 20 years, observational analysis and model simulations have transformed our understanding of the Southern Ocean, suggesting that the Ocean south of 30°S, occupying just 30% of the surface area, has profound influence on the Earth’s climate and ecosystems. The model studies underlying these results, however, are highly controversial and observational data is sparse in comparison to other areas of the world’s oceans.

To address this critical gap in understanding, the Sarmiento group has been involved in a major proposal for the National Science Foundation to form a Center for Southern Ocean Biogeochemical Observations and Modeling (C-SOBOM). If successful, the Center’s observations team will deploy over a hundred autonomous floats with biogeochemical sensors to gather data and provide unprecedented observations of the Southern Ocean, while the modeling team develops metrics to test and improve computer simulations of this region. The proposed center would involve researchers from Princeton, Scripps Institution of Oceanography, the University of Arizona, Rutgers, the University of Washington, the Monterey Bay Aquarium Research Institute, and both U.S. and international collaborators – Center awards will be announced in April 2013.

Controls on the Terrestrial Carbon Sink

The Pacala, Medvigy, Hedin, and Sarmiento groups are working to understand whether forest storage of carbon will be enhanced by increasing CO2 levels, what might limit “CO2 fertilization,” and the history and future of this component of the terrestrial carbon sink.

History of the terrestrial sink

The most important accomplishment of the Pacala climate modeling group in 2012 was an analysis of the value of the historical carbon sink in slowing the rise of atmospheric CO2 and warming. During 2012, Elena Shevliakova and Sergei Malyshev participated in development, evaluation, and analysis of the GFDL comprehensive Earth System Models ESM2M and ESM2G. In collaboration with the GFDL and CMI scientists, they explored interactions between historic land use and increased atmospheric CO2 concentrations and their implications for carbon cycle and climate. The researchers estimated for the first time that in the absence of historical CO2 fertilization, the concentration of atmospheric CO2 would have been 80% greater than observed, and the warming would have been 40% larger than observed. This work will appear in Proceedings of the National Academy of Sciences in 2013.

Nutrient limitation and the CO2 fertilization sink

Because elevated CO2 generally increases photosynthetic production, enhanced forest growth could scrub anthropogenic CO2 from the atmosphere and provide a negative feedback on climate change. It is commonly suggested that enhancement of the land sink by CO2 fertilization should be limited by the availability of nitrogen, yet forest free-air CO2 enhancement experiments (FACE) have shown continued CO2 fertilization despite nitrogen limitation Ray Dybzinski and Caroline Farrior have developed a new forest model that includes a previously unrecognized mechanism and explains the continuing CO2 fertilization in the FACE experiments. In their simulations, carbon allocation patterns are determined by competition. Enhanced carbon fixation under elevated CO2 resulted in elevated wood growth and height, but constant fractional allocation to wood, constant allocation to leaves, and elevated fractional and absolute fine root growth. This is positive news for carbon mitigation, as the new model predicts that the CO2 fertilization component of the land sink will continue for decades. The researchers are working to implement this model in the GFDL land model, LM3 to improve predictions of carbon cycling.

In a related collaboration with Steve Pacala, Ensheng Weng of the U.S. Forest Service developed a working version of a new model of the terrestrial biosphere and has written a manuscript that will be submitted soon. This model has a revolutionary structure, in that it models realistic competition among plant types and so should be able to predict the CO2 fertilization effects described above.

CO2 fertilization of recovering tropical forests

The Hedin/ Medvigy group is also focusing on understanding the competitive processes that affect the forest carbon sink, specifically the role of changes in resource availability and competitive dynamics among individuals following disturbances in the tropics. Tropical forests contribute a significant portion of the land carbon sink, but their future ability to sequester CO2 likely depends on how nutrients interact with forest recovery from cutting, agricultural land use, or natural disturbances. Recent observations place particular importance on this as yet unresolved interaction; first, it is becoming clear that a large fraction of tropical forests worldwide are recovering from some form of disturbance. Second, there is increasing evidence for exceptionally strong constraints by nutrients on carbon accumulation, but only at specific “bottleneck” periods during forest recovery. Third, results from models and empirical studies imply that nitrogen fixing trees may act to alleviate nitrogen limitation on plant growth during particular periods of forest recovery.

Although existing models of the tropical land carbon sink are exceptionally sensitive to potential interactions between carbon recovery and nutrient cycles, they have not been constructed to resolve some of the spatial and temporal scales that are fundamental to nutrient-driven processes. To address this problem, Jennifer Levy has developed a new framework for understanding nutrient cycling on the level of individual trees, and has successfully incorporated this framework into a terrestrial biosphere model, the Ecosystem Demography model 2 (ED2).

Unlike conventional ecosystem models, ED2 resolves (1) heterogeneity in resource environments and (2) resource competition between trees of different sizes and functional types. Because of these two factors, it is possible to scale understanding of nitrogen fixation and nutrient limitation from individual trees to ecosystem-level properties. Furthermore, because field studies often measure properties of individual trees, there is a wealth of data that can be used to challenge and evaluate the new model. The researchers are currently using measurements of nitrogen fixation and the results of nutrient fertilization experiments for this purpose. The resulting validated model will be an important tool for assessing the capacity of tropical forests to act as carbon sinks.

The Medvigy and Hedin labs are in the process of expanding this model by adding a phosphorus algorithm to enable simulation of carbon, nitrogen, and phosphorus interactions. Once this algorithm is ready, it will be easily transferrable into LM3 and other similar models in use Princeton.

North-South variation of nitrogen fixation and terrestrial carbon uptake

This year Duncan Menge used forest inventory data from the USA and Mexico to show that nitrogen- fixing plants comprise ~10% of trees south of 35 degrees latitude but only ~1% of trees north of 35 degrees. Furthermore, the dominant type of nitrogen-fixing tree switches at this same threshold. Menge’s research also showed that this transition from 10% to 1% can be explained by a concomitant transition in the nitrogen-fixing “strategy,” from rapid tuning of nitrogen fixation in the south to slow or no tuning in the north. The dominant types in the north versus south are thought to have these different strategies, lending support to the hypothesis that these different strategies explain the transition. This is important for climate change because plants that tune nitrogen fixation rapidly (the southern type) remove more carbon dioxide from the atmosphere, whereas plants that do not tune nitrogen fixation (the northern type) remove less carbon dioxide.

Understanding temporal shifts in terrestrial uptake of atmospheric CO2

figure 1

In 2011, Jorge Sarmiento and colleagues reported that an abrupt shift in the net land carbon sink, estimated as the residual between fossil fuel emissions, the growth rate of atmospheric CO2 at Mauna Loa, and modeled ocean carbon uptake, occurred in the late 1980s. The land carbon uptake appears to have remained relatively constant for three decades and to have increased rapidly after 1988/1989.

In collaboration with researchers at UCLA, NASA and the Medvigy group as part of a study supported by a NASA Carbon Cycle Science grant, this year the Sarmiento group analyzed a suite of simulations of primary productivity from the terrestrial biogeochemical model CASA and upscaled FluxNet data to identify independently regions/ecosystems in which carbon uptake is consistent with the timing and magnitude of carbon sinks derived from previous studies. Results show that globally, the net primary productivity (NPP) increased by about 1 Pg C/yr (or 1 billion metric tons of carbon per year) after 1989. The gross primary productivity also increased of approximately 2

Pg C/yr at the same time. These estimates are consistent with the shift in net land carbon uptake detected in previous work. Results further suggest that three key regions are contributing to the abrupt increase in productivity in the late 1980s: Northern Eurasia, Tropical Africa and Tropical South America (see Figure 1).

The group found that these changes may be climate-constrained. Results showed that the productivity changes observed in the three regions seem influenced by different climatic factors: a) warming in Northern Eurasia (from late 1980s onwards), b) increased precipitation in Tropical Africa (from late 1980s/early 1990s onwards) and c) increased solar radiation over Tropical South America (from mid- 1990s onwards).

Claudie Beaulieu in the Sarmiento group is currently analyzing additional CASA simulations to study sensitivity of the results to different forcing data sets. Furthermore, the group is analyzing net ecosystem exchange runs to verify whether the key regions have actually gained carbon or if this increase is due to changes in respiration.

Quantifying the Ocean Carbon Sink

The Sarmiento and Bender groups use observations and modeling to study the role of the ocean in the carbon cycle and gain insight into history and future of the ocean carbon sink.

Understanding the Southern Ocean’s impact on carbon and climate

As part of their NSF proposal (see “New Initiatives” above), the Sarmiento group carried out a CMI analysis focusing on oceanic heat and carbon uptake in a new set of 19 IPCC-class climate models over the period 1861 to 2005. The model intercomparison study shows that 71 ± 24% of the excess heat and 43 ± 3% of anthropogenic carbon is entering the Southern Ocean south of 30°S (Figure 2), although the Southern Ocean only covers 30% of the global ocean surface area. Overall, multi-model variability in CO2 uptake remains largest over the Southern Ocean, but the multi-model spread is significantly reduced compared to earlier generation models.

figure 2

Moving forward, the group plans to investigate the response of the Southern Ocean carbon cycle to changing Southern Ocean winds in response to changes in stratospheric ozone levels and greenhouse gas concentrations.

Impacts of ocean acidification on phytoplankton

A third of the anthropogenic CO2 released to the atmosphere dissolves into the surface ocean, reducing its pH. What effects this ocean acidification will have on the ocean biota is a focus of research in the Morel group. Among the manifold potential effects of ocean acidification is a change in the cycling of nitrogen, the principal limiting nutrient for marine ecosystems.

The major input of “new” nitrogen in the open ocean is through nitrogen fixation, which is effected by a few species of cyanobacteria. In experiments with the dominant nitrogen-fixing species, Trichodesmium (Figure 3), Morel and colleagues demonstrated that lowering pH decreases both Fe uptake and, independently, the efficiency of N2-fixation. Because the nitrogenase enzyme, which catalyzes the reduction of N2 to NH4+, contains a very large number of iron atoms, and N2 fixing organisms thrive in regions where iron is scarce, these two effects may act synergistically to decrease the input of new nitrogen to marine ecosystems and impact global productivity.

Measuring dissolved CO2 in the ocean

To help quantify the fluxes of carbon into and out of the surface ocean, Michael Bender and colleagues have developed a new instrument for continuous, high precision measurements of the dissolved inorganic carbon concentration (DIC) of surface seawater. The DIC instrument achieves high precision using a method called isotope dilution, which allows concentrations to be determined by an isotope ratio measurement that is much easier and more accurate that the normal concentration measurements.

figure 3

During 2012, the instrument was validated and successfully deployed on 3 cruises. It has since been modified, using a so-called “doublespike” technique, in a way that achieves higher precision while at the same time greatly simplifying the implementation. During the coming year, the group will use this instrument to characterize DIC on cruises in the Southern Ocean and the Arctic Ocean. Other groups have expressed interest in copying this instrument. The researchers expect that it will be widely used for measurements along cruise tracks of oceanographic ships, both to characterize the invasion of fossil fuel CO2 into ocean surface waters and to track the seasonal imprint on DIC of the annual cycle of biological activity.

New Modeling Tools

Since CMI’s inception, the Carbon Science Group has worked on developing new tools to improve modeling of the carbon cycle. This year the Pacala and Sarmiento groups have developed new approaches to the impacts of drought and forest fires, as well as carbon cycling in the ocean.

Linking drought and tree mortality

Adam Wolf is developing models and observations that link the water cycle, and particularly drought, to the carbon cycle, particularly mortality. Wolf has developed a unique observation system that monitors the biosphere (including microclimate and tree physiology) and reports these data in real time over cellular networks using electronics designed in-house. These observations help constrain a key uncertainty in the model depiction of plant physiology, namely the sensitivity of leaf photosynthesis and evaporation to drought among diverse species. Together, this work aims to identify which species gain and which species lose in a changing climate, and what impacts these demographic shifts will have on the global carbon cycle.

Better depiction of fire in land models

Vegetation fire is a significant contributor of greenhouse gases and other compounds that affect the climate, especially in tropical nations. Sam Rabin and Elena Shevliakova are working on a model of vegetation fire that will simulate the amount of burning on different vegetation types around the world — especially on human-managed lands — for inclusion in a global climate and vegetation model. This separation of fire types, thus far unique in the fire modeling literature, will help the research community better understand how interventions might be undertaken to reduce the impact of fire on the climate. In 2012, the researchers helped develop and publish details of a method that revealed, based on maps of land cover and satellite-observed burned area, how the timing of fire activity within a year differs between agricultural and non-agricultural lands. Development of advanced methods that allow more accurate estimation of the amount of burning on cropland, pasture, and other lands is under way.

An improved model of bacterial cycling in the ocean

Sinking organic particles composed of detrital materials including dead phytoplankton and zooplankton fecal pellets are one of the main ways carbon is transported to the deep ocean as part of the biological pump. Most sinking particles are remineralized, transformed from organic carbon to CO2, in the mesopelagic zone (150 to 1000 m depth) due to the metabolic activity of heterotrophic bacteria. The Sarmiento group has developed a model to better understand the mechanisms connecting heterotrophic bacteria with these sinking particles in the mesopelagic zone. The 1-dimensional idealized model of a sinking particle includes free-living and attached heterotrophic bacteria, particulate and dissolved organic matter, extracellular enzyme, and hydrolysate. In the past year, a major development in the project has been to add quorum sensing, a signaling system used by bacteria to assess population density, to regulate extracellular enzyme production and particle detachment rates to the model. This new parameterization has dramatically improved the model predictions of carbon flux at the Bermuda Atlantic Time Series station, which is located in the North Atlantic subtropical gyre.

One of the benefits of this model is that it can be integrated with the dynamics of existing models, i.e. the Martin Curve and the ballast model, currently used in IPCC-class models to predict particle attenuation in the deep ocean. The ultimate goal of this project is to improve predictions of the effects of future climate change on carbon sequestration in the ocean.

Model development is nearing completion so the next phase will be to conduct sensitivity studies of key parameters and implement the model in geographic locations with different environmental characteristics.

Climate Change Impacts

The Sarmiento group studies the impacts of anthropogenic CO2 emissions and climate change on ocean chemistry and sea life.

Impact of climate change and ocean warming on fish body size

figure 4

Changes in temperature, oxygen content, and other ocean biogeochemical properties also directly affect the ecophysiology of marine water-breathing organisms. Previous studies suggest that the most prominent biological responses are changes in distribution, phenology, and productivity. Both theory and empirical observations also support the hypothesis that warming and reduced oxygen will reduce body size of marine fishes. However, the extent to which such changes would exacerbate the impacts of climate and ocean changes on global marine ecosystems remains unexplored.

In collaboration with researchers at the University of British Columbia, the Sarmiento group employed a model to examine the integrated biological responses of over 600 species of marine fishes due to changes in distribution, abundance and body size. The model has an explicit representation of ecophysiology, dispersal, distribution, and population dynamics. The model results show that assemblage-averaged maximum body weight is expected to shrink by 14–24% globally from 2000 to 2050 in a warmer less oxygenated ocean under a high-emission scenario (Figure 4). About half of this shrinkage is due to change in distribution and abundance, the remainder to changes in physiology. The tropical and intermediate latitudinal areas will be heavily impacted, with an average reduction of more than 20%. The results of this study provide a new dimension to understanding the integrated impacts of climate change on marine ecosystems.

Impact of oceanic O2, CO2, and temperature changes on tuna habitats

Predicting the effects of climate change on habitat utilization in the ocean environment requires identification of underlying physiological mechanisms influenced by environmental conditions.Hemoglobin-oxygenation is hypothesized to be one of these underlying mechanisms. Oxygen extraction from seawater and delivery to tissues, a fundamental process which depends on hemoglobin, is a necessity for tuna survival, as the globe-traveling fish utilize many different regions and depths in the ocean while foraging for food.

All of the environmental factors associated with hemoglobin-oxygenation are predicted to change in the future: temperature is predicted to increase with climate change, oxygen is predicted to decrease as increases in temperature cause water column stratification to increase, and carbon dioxide is predicted to increase with ocean acidification. It is hypothesized that these changes will result in habitat compression for tuna, but the magnitude and biogeography of the compression will be different among the species of tuna. The Sarmiento group is using the P50 depth, the depth at which 50% of hemoglobin is oxygenated, as the threshold restricting tuna habitat utilization in global datasets and IPCC-class earth system model results. Preliminary results from two earth system models indicate that future climate change will have neutral to negative impacts on the habitat size of Thunnus albacares, the yellowfin tuna, by 2100.

The plan for the next year is to evaluate seven additional IPCC-class earth system models. There are many variations in how the physics, chemistry, and biology of an earth system model is constructed and also differences in the parameterizations selected for each model, all of which contribute to uncertainty in the results. For this reason, it is important to use multiple earth system models to account for the uncertainty resulting from different model formulations. The analysis will also be expanded to include all the tuna species in the genus Thunnus.

Natural Climate Variability

The Sarmiento and Bender groups examine climate change in the context of long-term natural variability. Sarmiento and colleagues are working to separate anthropogenic signatures on atmospheric carbon from the background noise of natural events, while the Bender group looks to ancient sea ice to better understand the carbon cycle.

Atmospheric CO2 response to volcanic eruptions

In previous work, the Sarmiento group has shown that tropical volcanic eruptions are one of the most important natural factors that significantly impact the climate system and the carbon cycle on annual to multi-decadal time scales. The three largest explosive volcanic eruptions in the last 50 years – Agung, El Chichón, and Pinatubo – occurred in spring-summer in conjunction with El Niño events and left distinct negative signals in the observational temperature and CO2 records. However, confounding factors such as seasonal variability and El Niño-Southern Oscillation (ENSO) may obscure the forcing-response relationship.

In this study, Thomas Frölicher in the Sarmiento group determined for the first time the extent to which initial conditions, i.e. season and phase of the ENSO, and internal variability influence the coupled climate and carbon cycle response to volcanic forcing, and how this affects estimates of the terrestrial and ocean carbon sinks. Ensemble simulations with the Earth System Model CSM1.4- carbon predict that the atmospheric response is ~60% larger when a volcanic eruption occurs during El Niño and in winter than during La Niña conditions (Figure 5). The simulations suggest that the Pinatubo eruptions contributed 11 ± 6% to the 25 Pg terrestrial carbon sink inferred over the decade 1990-1999 and -2 ± 1% to the 22 Pg oceanic carbon sink.

figure 5

Recent studies have indicated a possible positive trend in the airborne anthropogenic CO2 fraction, suggesting a worrying decrease in the efficiency of the ocean and land carbon sinks. In contrast to these claims, this study indicates that accounting for the decadal-scale influence of explosive volcanism and related uncertainties removes the positive trend in the airborne fraction of anthropogenic carbon. The results highlight the importance of considering the role of natural variability in the carbon cycle for interpretation of observations and for data-model intercomparison.

Extending the record of ancient CO2 levels

The deepest ice cores yet drilled, targeted to encompass the longest possible continuous records, end at ice 800,000 years old. To extend this record, Michael Bender and colleagues have been searching Antarctic sites where, because of complex glacier flows influenced by the Transantarctic Mountains, older ice may be present near the surface (Figure 6). In the Allan Hills, the researchers have discovered million year old ice that will enable Bender’s group to extend back ice core records of CO2 and climate beyond the oldest ice otherwise available. The team plans to do additional prospecting for even older ice in the region. The hope is that this work will yield ice that can be used to extend the climate record back into the “40 k world” of shorter, less intense climate cycles that prevailed from about 2.5-1 million years ago.

Bender has also written a book, Paleoclimate, to be published by Princeton University Press in 2013. The book covers natural climate change and CO2's role in climate throughout geologic time.

figure 6

Carbon Science Publications

Beaulieu, C., J. Chen, J.L. Sarmiento. “Change-point analysis as a tool to detect abrupt climate variations.” Philosoph. Transactions of the Royal Socciety A, 370: 1228-1249; doi:10.1098/rsta.2011.0383. 2012

Beaulieu, C., J.L. Sarmiento, J.L., S. E. Mikaloff Fletcher, J. Chen, D. Medvigy. “Identification and characterization of abrupt changes in the land uptake of carbon.” Global Biogeochem. Cycles, 26: GB1007, doi:10.1029/2010GB004024. 2012. Beaulieu, C., S.A. Henson, J.L. Sarmiento, J.P. Dunne, S.C. Doney, R.R. Rykaczewski and L. Bopp. “Factors challenging our ability to detect long-term trends in ocean chlorophyll.” Biogeosciences Discuss., 9: 1649- 16456, doi:10.5194/bgd-9-14589-2012. 2012.

Brookshire, E.N.J., S. Gerber, D.N.L. Menge and L.O. Hedin. “Large losses of inorganic nitrogen from tropical rainforests suggest a lack of nitrogen limitation.” Ecology Letters 15(1): 9-16. doi: 10.1111/j.1461- 0248.2011-01701.x. 2012.

Cadotte, M.W., L.R. Mehrkens and D.N.L. Menge. “Gauging the impact of meta-analysis on ecology.” Evolutionary Ecology 26(5): 1153-1167. doi: 10.1007/s10682-012-9585-z. 2012.

Cheung, W.W.L., J.L. Sarmiento, J. Dunne, T.L. Frölicher, V. Lam, M.L.D. Palomares, R. Watson, and D. Pauly. “Shrinking of fishes exacerbates impacts of global ocean changes on marine ecosystems.” Nature Climate Change, doi:10.1038/nclimate1691. 2012.

Cocco, V., F. Joos, M. Steinacher, T.L. Frölicher, L. Bopp, J. Dunne, M. Gehlen, C. Heinze, J. Orr, A. Oschlies, B. Schneider, J. Segschneider, J. Tjiputra. “Oxygen and indicators of stress for marine life in multi-model global warming projections.” Biogeosciences Discuss., 9, 10785-10845, doi:10.5194/bgd-9-10785-2012

Dunne, J.P., J. John, A. Adcroft, S. M Griffies, R.W. Hallberg, E. Shevliakova, R.J. Stouffer, W.F. Cooke, K.A. Dunne, M.J. Harrison, J.P. Krasting, S. Malyshev, P.C.D. Milly, P. Phillipps, L.T. Sentman, B.L. Samuels, M.J. Spelman, M. Winton, A.T Wittenberg, and N. Zadeh. “GFDL’s ESM2 global coupled climate-carbon Earth System Models Part I: Physical formulation and baseline simulation characteristics.” Journal of Climate, 25(19), doiI:10.1175/JCLI-D-11-00560.1. 2012.

Dunne, J.P., J. John, E. Shevliakova, R.J. Stouffer, J.P. Krasting, S. Malyshev, P.C.D. Milly, L.T. Sentman, A. Adcroft, W.F. Cooke, K.A. Dunne, S.M. Griffies, R.W. Hallberg, M.J. Harrison, H. Levy II, A.T. Wittenberg, P.Phillipps, and N. Zadeh. “GFDL’s ESM2 global coupled climate-carbon Earth System Models Part II: Carbon system formulation and baseline simulation characteristics”. Journal of Climate. doi:10.1175/ JCLI-D-12-00150.1. 10/12. 2012.

Duteil, O., W. Koeve, A. Oschlies, O. Aumont, D. Bianchi, L. Bopp, E. Galbraith, R. Matear, J.K. Moore, J.L. Sarmiento, and J. Segschneider. “Preformed and regenerated phosphate in ocean general circulation models: can right total concentrations be wrong?” Biogeosciences 9: 1797-2012, doi:10.5194/bg-9-1797- 2012.

Dybzinski, R., C. Farrior, S. Ollinger and S. W. Pacala. “Physiological shifts within- and competitive shifts between-species explain independence of leaf nitrogen from soil available nitrogen in broadleaf trees”. In Review. 2013.

Dybzinski, R., N. Beckman and D. Tilman. “Neighborhoods have little effect on pre-dispersal fungal or insect seed predation in a grassland biodiversity experiment”. In Review. 2012.

Farrior, C., D. Tilman, R. Dybzinski, P.B. Reich, and S.W. Pacala. “Resource limitation in a competitive context determines complex plant responses to experimental resource additions. In Review. 2013.

Farrior, C., R. Dybzinski, S. Levin, and S.W. Pacala. “Competition for water and light in closed-canopy forests: a tractable model of carbon allocation with implications for carbon sinks.” The American Naturalist. In Press. 2013.

Frölicher, T.L., F. Joos, C.C. Raible, and J.L. Sarmiento. “Atmospheric CO2 response to volcanic eruptions: the role of ENSO, season, and variability.” Global Biogeochem. Cycles. Accepted. 2013.

Gruber, N., C. Hauri, Z. Lachkar, D. Loher, T. L. Frölicher, G.-K. Plattner. “Rapid progression of ocean acidification in the California Current System.” Science, 337(6091), 220-223, doi: 10.1126/science.1216773. 2012.

Hibbard, K., T. Wilson, K. Averyt, R. Harriss, R. Newmark, S. Rose, E. Shevliakova, V. Tidwell Chapter 10, “Water, Energy, and Land Use”, The National Climate Assessment Report, http://www.globalchange.gov/ what-we-do/assessment. Under public review. 2013.

Jeong, S.J., D. Medvigy, E. Shevliakova and S. Malyshev. “Predicting changes in temperate forest budburst using continental-scale observations and models”. Geophysical Research Letters. doi:10.1029/2012GL054431. 12/12. In press. 2012a.

Jones, C., E. Robertson, V. Arora, P. Friedlingstein, E. Shevliakova, L. Bopp; V. Brovkin, T. Hajima, E. Kato, M. Kawamiya, S. Liddicoat, K. Lindsay, C. Reick, C. Roelandt, J. Segschneider, J. Tjiputra. “21st Century compatible CO2 emissions and airborne fraction simulated by CMIP5 Earth System models under 4 Representative Concentration Pathways”, Journal of Climate. In press. 2013.

Joos, F., R. Roth, J.S. Fuglestvedt, G.P. Peters, I.G. Enting, W. von Bloh, V. Brovkin, E.J. Burke, M. Eby, N.R. Edwards, T. Friedrich, T. L. Frölicher, P.R. Halloran, P.B. Holden, C. Jones, T. Kleinen, F. Mackenzie, K. Matsumoto, M. Meinshausen, G.-K. Plattner, A. Reisinger, J. Segschneider, G. Shaffer, M. Steinacher, K. Strassmann, K. Tanaka, A. Timmermann, A.J. Weaver, “Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: A multi-model analysis.” Atmos. Chem. Phys. Discuss., 12, 19799-19869, doi:10.5194/acpd-12-19799-2012. 2012.

Keller, K.M., F. Joos, C.C. Raible, V. Cocco, T. L. Frölicher, J.P. Dunne, M. Gehlen, T. Roy, L. Bopp, J.C. Orr, J. Tjiputra, C. Heinze, J. Segschneider, N. Metzl. “Variability of the Ocean Carbon Cycle in Response to the North Atlantic Oscillation.” Tellus B, 64, 18738. 2012.

Magi, B.I., S. Rabin, E. Shevliakova, and S.W. Pacala. “Separating agricultural and non-agricultural fire seasonality at regional scales”. Biogeosciences, 9, 3003-3012, doi:10.5194/bg-9-3003-2012. 2012.

Menge, B.A. and D.N.L. Menge. “Dynamics of coastal meta-ecosystems: the intermittent upwelling hypothesis and a test in rocky intertidal regions”. Ecological Monographs. In revision. 2013.

Menge, D.N.L., L.O. Hedin, and S.W. Pacala. “Nitrogen and phosphorus limitation over long-term ecosystem development in terrestrial ecosystems.” PLoS ONE 7(8): e42045. doi: 10.1371/journal. pone.0042045. 2012.

Plancherel, Y., K.B. Rodgers, R.M. Key, A.R. Jacobson, and J.L. Sarmiento. “Role of regression model selection and station distribution on the estimation of oceanic anthropogenic carbon change by eMLR.” Biogeosciences Discuss. 9: 14589-14638. Submitted, 2012.

Raupach, M.R., M. Gloor, J.L. Sarmiento, J.G. Canadell, T.L. Frölicher, T. Gasser, R. A. Houghton, C. L. LeQuéré, C. M. Trudinger. “Diagnosis and attribution of observed changes in the global carbon cycle over the last 50 years.” Nature Climate Change. Submitted, 2012.

Shi, D., S. A. Kranz, J.-M. Kim and F. M. M. Morel. “Ocean acidification slows nitrogen fixation and growth in the dominant diazotroph Trichodesmium under low-iron conditions”, PNAS, 109 (45) 18255- 18256; E3094-E3100 DOI: 10.1073/pnas. 2012.

Vitousek, P.M., D.N.L. Menge, S.C. Reed, and C.C. Cleveland. “Biological nitrogen fixation: Rates, patterns, and ecological controls in terrestrial ecosystems.” Philosophical Transactions of the Royal Society-B. In revision. 2013.

Yin, L., R. Fu, E. Shevliakova, R.E. Dickinson. “How well can CMIP5 simulate precipitation and its controlling processes over tropical South America?” Climate Dynamics. Submitted. 2012.

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