CMI Science focuses on how terrestrial vegetation and the oceans soak up carbon and thereby determine the fraction of the carbon dioxide (CO2) emitted into the atmosphere that actually stays there. CMI science features close collaboration with Princeton’s neighbor, the Geophysical Fluid Dynamics Laboratory (GFDL) of the US Department of Commerce. Together CMI and GFDL are improving the understanding of how climate variability and departures from the historical frequency of extreme events, such as heat waves, droughts, and hurricanes, impact business and society. Another initiative is providing simplified models for understanding the movement of ice through narrow straits, which can affect flow and mixing in the ocean.
Research Highlights – At a Glance
Stephen Pacala: Plants lose water and take up carbon through stomates, and the ability to simulate their behavior under various conditions is an essential part of global climate models. The Pacala group has developed and tested a new hypothesis of stomate regulation that improves upon current models in predicting stomate behavior during drought.
Jorge Sarmiento: Modeling studies suggest that the ocean around Antarctica acts as a key sink for atmospheric CO2 and heat, thus mitigating global temperature increases caused by rising levels of CO2. However, ship-based observations needed to understand the processes behind this uptake are scarce in the harsh and remote Southern Ocean, particularly in winter. To combat the data shortage, Jorge Sarmiento is directing the first large-scale deployment of robotic floats equipped with biogeochemical measurement instruments in this region. The project is enabling unprecedented observations of pH, biological productivity, carbon cycling, and phytoplankton dynamics in the Southern Ocean and improving our ability to predict its future.
François Morel: The ongoing increase in atmospheric CO2 acidifies the surface ocean. The Morel group has documented highly significant effects of ocean acidification on the bioavailability of essential trace metals such as iron and zinc, which are known to limit the growth of phytoplankton and, hence, the productivity of ecosystems in large areas of the oceans. A newly developed electrochemical analytical method is the first to show a quantitative correspondence between metal “lability” and rates of biological uptake in natural seawater.
Michael Bender: Ice core studies from the Allan Hills Blue Ice Area in Antarctica have yielded ice dating back to 2,000,000 years ago, the oldest ever retrieved. Analysis of ice dating to 1,000,000 years ago suggests that links between climate and CO2 are similar to those of more recent glacial cycles.
Howard Stone: Climate changes involve atmospheric motions, ocean flows, and evolution of ice on land and in the sea. These dynamics are necessarily interrelated; insights into individual processes can help to illuminate poorly understood aspects of global climate dynamics, such as factors affecting the maintenance of sea ice cover in the Arctic basin. Sea ice cover can impact fresh water fluxes, local ecology and ocean circulation. Over the past year, the Stone group has continued to study the physical mechanisms involved in the development of ice bridges in narrow straits and has succeeded in providing simple predictors for the conditions required for the bridge formation and maintenance. The approach accounts for processes on length scales below those normally resolved in climate models.
Modeling Stomatal Regulation Under Drought Conditions
Principal Investigator: Stephen Pacala
At a Glance
Plants lose water and take up carbon through stomates, and the ability to simulate their behavior under various conditions is an essential part of global climate models. The Pacala group has developed and tested a new hypothesis of stomate regulation that improves upon current models in predicting stomate behavior during drought.
Tiny valves on the surfaces of leaves, called stomates (Figure 1.1.), regulate carbon gain and water loss by plants, and are thus linchpins of the global carbon and water cycles. Amazingly, a simple equation regulates stomates worldwide. This equation is backed by enormous empirical data and a 40-year-old evolutionary explanation, and controls carbon gain and water loss in all Earth System models that predict climate. It is one of the most widely accepted paradigms in ecology and has been taught for decades in introductory biology courses worldwide, including Princeton’s.
Figure 1.1. A stomate on the surface of a cucumber leaf.
Nonetheless, neither the simple model nor the evolutionary hypothesis explains observed stomatal closure during drought. Moreover, the 40-year-old evolutionary hypothesis is not consistent with the current understanding of plant competition for water, and does not include recent discoveries about damage to plant hydraulic systems during drought.
The Pacala group developed an alternative hypothesis that includes plant competition and hydraulic damage, such as impaired water flow through xylem. The new hypothesis has the same empirical support as the classical hypothesis under non-drought conditions and also predicts observed stomatal closure during drought.
A statistical test was developed to explicitly separate the classical and new hypotheses, and assembled a global data set that could be used with the test. The results unanimously support the new hypothesis over the classical hypothesis. We have since built the new model of stomatal control into our Earth System Model. Early tests imply improvements in both the carbon and hydrologic cycles, particularly in tropical forests. This work is timely because of recent studies implying that drought has reduced the Amazon carbon sink.
Anderegg, W.R.L., A. Wolf, A. Arango-Velez, B. Choat, D.J. Chmura, S. Jansen, T. Kolb, S. Li, F. Meinzer, P. Pita, V. Resco de Dios, J.S. Sperry, B.T. Wolfe, and S.W. Pacala. Stomata are regulated to manage hydraulic damage: empirical evidence and global consequences. Nature, in revision.
Anderegg, W.R.L., A. Wolf, A. Arango-Velez, B. Choat, D.J. Chmura, S. Jansen, T. Kolb, S. Li, F. Meinzer, P. Pita, V. Resco de Dios, J.S. Sperry, B.T. Wolfe, and S.W. Pacala. Plant water potential improves prediction of stomatal models. Plant Cell Environ., in review.
Chou, C., L.O. Hedin, and S.W. Pacala. Functional groups, species, and light interact with nutrient limitation during tropical rainforest sapling bottleneck. J. Ecol., in revision.
Muller-Landau, H.C, and S.W. Pacala. What determines the abundance of lianas? In A. Dobson, D. Tilman, and R. Holt, Eds., for the volume Unsolved Problems in Ecology, in press.
Ocko, I.B., S.P. Hamburg, D.J. Jacob, D.W. Keith, N.O. Keohane, M. Oppenheimer, J.D. Roy-Mayhew, D.P. Schrag, and S.W. Pacala. Two-valued global warming potential effectively captures long- and short-term climate forcing. Science, in press.
Pellegrini, A.F.A, W.A. Hoffmann, G. Durigan, A.Tourgee, and S.W. Pacala. Overlapping woody plant composition and intermediate vegetation formations across savannas and forests in the Neotropical Brazilian Cerrado. Ecography, in review.
Uyehara, I.K.U., and S.W. Pacala. The role of succession in the evolution of flammability. Theor. Ecol., in review.
Xu, X., D. Medvigy, S.J. Wright, K. Kitajima, J. Wu, L. Albert, G. Martins, S. Saleska, and S.W. Pacala. Variations of leaf longevity in tropical evergreen forests predicted by a trait-driven carbon optimality model. Ecol. Lett., in revision.
Update on the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) Project
Principal Investigator: Jorge Sarmiento
At a Glance
Modeling studies suggest that the ocean around Antarctica acts as a key sink for atmospheric carbon dioxide (CO2) and heat, thus mitigating global temperature increases caused by rising levels of CO2. However, ship-based observations needed to understand the processes behind this uptake are scarce in the harsh and remote Southern Ocean, particularly in winter. To combat the data shortage, Jorge Sarmiento is directing the first large-scale deployment of robotic floats equipped with biogeochemical measurement instruments in this region. The project is enabling unprecedented observations of pH, biological productivity, carbon cycling, and phytoplankton dynamics in the Southern Ocean and improving our ability to predict its future.
CMI member Jorge Sarmiento directs the National Science Foundation-funded Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project, a multi-institutional effort to observe the poorly sampled ocean around Antarctica and increase our understanding of how it influences Earth’s climate and carbon cycles. CMI-supported modeling studies have indicated that the Southern Ocean is a large sink for atmospheric heat and carbon, as well as an important source of nutrients for low-latitudes, but efforts to observe the region directly are hampered by rough conditions that limit access by conventional research vessels. SOCCOM scientists are working to dramatically increase the number and variety of observations of the Southern Ocean through the world’s first large-scale deployment of biogeochemical (BGC) Argo floats (Figure 1.2.1.) – robotic floats equipped with newly developed biogeochemical sensors to measure pH, nitrate, and oxygen in addition to ocean temperature and salinity. The new observations are giving an unprecedented view of carbon cycling and biological productivity in this important region, and helping us to understand how these processes might change in the future.
Figure 1.2.1. SOCCOM float deployment from the R/V Nathaniel B. Palmer, January 2016. Float 12390 was named “KC Bell” by John Witherspoon Middle School students as part of SOCCOM’s adopt-a-float program. Photo credit: Climate Central.
Seventy-seven SOCCOM BGC floats (Figure 1.2.2.) are currently operating and have collectively made over 2 million observations in the Southern Ocean. The SOCCOM float data are made freely available to the public in near-real time, and have been incorporated into the global Argo data system used by hundreds of researchers around the world.
Complementing this observational effort, the SOCCOM team has developed model-based tools to study controls on Southern Ocean biogeochemistry and its response to climate change. To better understand the current workings of the Southern Ocean, SOCCOM researchers have assimilated observational data into an ocean model to produce a 3-D, physically realistic estimate of Southern Ocean biogeochemistry (B-SOSE) that is freely available to the oceanographic community. To improve predictions of future climate and carbon cycle changes, planning has been completed for a Southern Ocean Model Intercomparison Project (SOMIP) that will analyze differences among Earth system model forecasts from leading research groups.
Together, SOCCOM data and tools are providing unparalleled insights into the Southern Ocean. Wintertime and under-ice measurements never before available are yielding information on the annual variability of pH and carbonate saturation in the system, net community production, carbon export, air-sea fluxes of CO2 and O2, and bloom dynamics. For example, analyses of the new data have revealed that seasonal changes in CO2 fluxes and nutrient concentrations are much larger than previously estimated from ship-based data, which is biased toward the summer months. This insight has implications for our understanding of the magnitude, timing, and location of Southern Ocean carbon uptake, and also for model development, as current models of ocean biogeochemistry have been tuned to match the earlier, seasonally-biased estimates of carbon and nutrient distributions. These and other early research results, along with SOCCOM technology and methods, will be shared in a special issue of the Journal of Geophysical Research - Oceans this spring.
Figure 1.2.2. SOCCOM float locations and trajectories, February 2017. Red dots are locations of operating floats; blue are inoperative floats. Yellow lines indicate float trajectories since deployment. Credit: SOCCOM.
SOCCOM will continue to make progress on observational and modeling goals in the coming year. This September will mark the end of the group’s third cruise season, after which over 90 BGC floats will have been deployed, bringing SOCCOM nearly halfway to its goal of 200 floats deployed within six years. This year will also see SOCCOM float data incorporated into the biogeochemical state estimate and the initiation of SOMIP. Beyond SOCCOM, the team is working with international research partners to expand the SOCCOM network of BGC floats and create a global observing system for ocean health.
Johnson, K.S., J.N. Plant, L.D. Talley, and J.L. Sarmiento, 2017. Annual nitrate drawdown observed by SOCCOM profiling floats and the relationship to annual net community production. J. Geophys. Res.–Oceans., in review.
Tamsitt, V., H. Drake, A.K. Morrison, L.D. Talley, C.O. Dufour, A.R. Gray, S.M. Griffies, M.R. Mazloff, J.L. Sarmiento, J. Wang, and W. Weijer, 2017. Spiraling up: pathways of global deep waters to the surface of the Southern Ocean. Nat. Comm., in review.
Williams, N. L., L.W. Juranek, R.A Feely, K.S. Johnson, J.L. Sarmiento, L.D. Talley, A.G. Dickson, A.R. Gray, R. Wanninkhof, J.L. Russell, and S. C. Riser, 2017. Calculating surface ocean pCO2 from biogeochemical Argo floats equipped with pH: an uncertainty analysis. Global Biogeochem. Cy., in review.
Effects of Ocean Acidification on the Bioavailability of Essential Metals to Marine Phytoplankton
Principal Investigator: François Morel
At a Glance
The ongoing increase in atmospheric carbon dioxide (CO2) acidifies the surface ocean. The Morel group has documented highly significant effects of ocean acidification on the bioavailability of essential trace metals such as iron and zinc, which are known to limit the growth of phytoplankton and, hence, the productivity of ecosystems in large areas of the oceans. A newly developed electrochemical analytical method is the first to show a quantitative correspondence between metal “lability” and rates of biological uptake in natural seawater.
The acidification (i.e., decreasing pH) of the surface ocean modifies its chemistry and, potentially, the bioavailability of nutrients. The Morel group has conducted both field and laboratory experiments to examine how the bioavailability of essential trace metals to phytoplankton changes over the range of pH values expected to occur in surface seawater over the next century.
The availability of trace metals to marine microorganisms depends on the extent to which they are bound to organic compounds, which in turn depends on ocean acidity. By increasing the organic binding of iron, ocean acidification decreases the bioavailability of one of the most important limiting nutrients in the oceans. For zinc, a metal that affects the assemblage of phytoplankton species that fuel marine food webs, the opposite result—an increase in bioavailability upon acidification—is expected and generally observed. Sometimes, however, a decrease in zinc bioavailability can result from competitive metal binding among organic compounds.
In laboratory experiments, a decrease in pH modified the bioavailability of iron and zinc in a way that was quantitatively consistent with the calculated change in their binding by the weak and strong organic complexing agents in the experimental medium. Extending these results to natural seawater is difficult, however, due to the presence of myriad organic compounds of unknown chemistry and affinity for the metals of interest.
To overcome this difficulty, the Morel group developed an electrochemical method to quantify the effects of acidification on metal availability in natural seawater in the presence of unknown metal-binding compounds. The new method distinguishes between the metal species available for biological uptake by phytoplankton and those that are not. These results will enable future assessments and predictions of how increases in CO2 concentration impact marine ecosystems.
The simplicity of the figure that illustrates these results (Figure 1.3.) belies their novelty and importance: it is the first time that a quantitative correspondence has been shown between chemical measurements of metal “lability” and rates of biological uptake in natural water samples.
Figure 1.3. The concentration of labile Zn (units: pM, or 10-12 moles per liter) measured by electrochemistry (anodic stripping voltammetry), and the short-term Zn uptake rate by phytoplankton (units: amol per hour per cell, amol = 10-18 moles) at pH 7.9 and pH 8.3 in coastal seawater.
Goldman, J.A.L., M.L. Bender, F.M.M. Morel, 2017. The effects of pH and pCO2 on photosynthesis and respiration in the diatom Thalassiosira weissflogii. Photosynth. Res., in press.
Hong, H., R. Shen, F. Zhang, Z. Wen, S. Chang, W.F. Lin, S.A. Kranz, Y.W. Luo, S.J. Kao, F.M.M. Morel, and D. Shi, 2017. The complex effects of ocean acidification on the dominant N2-fixing cyanobacterium Trichodesmium. Science, in review.
Climate Studies Based on Old Ice from Antarctica
Principal Investigator: Michael Bender
At a Glance
Ice core studies from the Allan Hills Blue Ice Area in Antarctica have yielded ice dating back to 2,000,000 years ago, the oldest ever retrieved. Analysis of ice dating to 1,000,000 years ago suggests that links between climate and carbon dioxide (CO2) are similar to those of more recent glacial cycles.
Many scientists have looked to characteristics of past climates as one guide to our planet’s future climate. A wide range of “paleoclimate” archives have been studied for this purpose. Of these archives, ice cores drilled through the Greenland and Antarctic ice sheets are unique in that they preserve fossil air that was trapped more or less when the snow fell. Ice core samples have been used to characterize variations in the CO2 concentration of air, among other properties. Through ice core studies, we have a detailed record of atmospheric CO2 variations back to 800,000 years ago. The results show that global climate varies closely with CO2 concentration changes during the ice ages. Heretofore, no older ice had been retrieved. This is a serious limitation, because glacial cycles were different before 800,000 years ago: earlier glacial cycles were less intense and lasted for a shorter time. We want to understand the difference in conditions between earlier ice ages (1,000,000-2,000,000 years ago) and the past 800,000 years.
My colleague John Higgins and I, working with a group from the University of Maine, along with graduate student Yuzhen Yan, have searched for old ice in a previously unexplored Antarctic environment: the Allan Hills Blue Ice Area. Preceding ice core studies have drilled cores where the ice age at the surface is zero, and age increases progressively with depth. In the Allan Hills, the Transantarctic Mountains block the flow of ice to the oceans. They guide old ice from the bottom of the ice sheet to the surface (Figure 1.4). In three expeditions to the Allan Hills over the past six of years, we have recovered ice dating back to 2,000,000.
We have analyzed ice dating to 1,000,000 years ago for CO2, methane (CH4), and other properties. The data suggest that links between climate and CO2 are similar to those of more recent glacial cycles. During the last expedition (austral summer of 2015-2016), we recovered ice as old as 2,000,000 years. To date we have focused on the time-consuming process of dating the ice. Our Maine collaborators have analyzed the isotopic composition of the ice, which turns out to reflect past temperatures of the study region. We will begin making analyses of greenhouse gases (CO2 and CH4) shortly.
Figure 1.4. Left: A cartoon illustrating ice flow in the Allan Hills, Antarctica. The glacier flows east (solid lines with arrows) but runs up against the Allan Hills of the Transantarctic Mountains, which guides deeply buried old ice to the surface. Credit: Whillans and Cassidy, 1983. Right: A photo looking north. The dark areas to the extreme right side of the photo are the peaks of the Transantarctic Mountains. Note the contrast between (old) blue ice in the upper half of the photo and modern snow in the lower part. Snowmobile for scale. Photo credit: Yuzhen Yan.
Studies of million-year-old ice showed that, at that time, Earth’s climate properties co-varied as during more recent times. For example, the relation between CO2 and Antarctic temperature was the same 1,000,000 years ago as during the larger climate fluctuations of more recent times. With our new samples, we will determine if this pattern holds true further back in time. We will also be able to test the hypothesis that the long-term climate cooling of the last 3,000,000 years ago was a consequence of declining levels of CO2 in air. Overall, this research will contribute to the objective of studying Earth’s past climates to advance our understanding of the response of climate to changing levels of CO2 and other greenhouse gases.
Modeling Ice Bridges to Obtain Results Beyond the Resolution of Climate Models
Principal Investigators: Howard Stone
At a Glance
Climate changes involve atmospheric motions, ocean flows, and evolution of ice on land and in the sea. These dynamics are necessarily interrelated; insights into individual processes can help to illuminate poorly understood aspects of global climate dynamics, such as factors affecting the maintenance of sea ice cover in the Arctic basin. Sea ice cover can impact fresh water fluxes, local ecology and ocean circulation. Over the past year, the Stone group has continued to study the physical mechanisms involved in the development of ice bridges in narrow straits and has succeeded in providing simple predictors for the conditions required for the bridge formation and maintenance. The approach accounts for processes on length scales below those normally resolved in climate models.
Ice bridges are stationary, rigid structures composed of sea ice, which are commonly formed in the many straits and channels throughout the Canadian Arctic Archipelago. Under certain conditions, the ice bridges are stable and span the width of the strait, connecting the two neighboring landmasses. These ice bridges appear seasonally and persist for several months, impacting both the local climate and ecology in two significant ways. First, since they are solid structures spanning the strait, they inhibit the flow of sea ice from colder regions into warmer waters. Second, by regulating the motion of ice, they affect the dynamics of flow and mixing in the ocean, thus influencing ocean salinity and regulating the transport of gases and nutrients that are crucial for ecological processes (e.g., the growth of photosynthetic plankton that form the base of marine food chains).
While ice bridges are regularly and predictably observed in the field, the precise mechanical conditions under which they form are not well understood. Improved models for predicting the dynamics of ice bridges would lead to a fuller picture of global changes in sea ice and fill in gaps in common large-scale climate models, which typically fail to resolve dynamics at the scale of a narrow strait. Failure to form an ice bridge during a particular season can, for instance, result in an irrecoverable loss of sea ice through flow into warm oceans and subsequent melting. Since 2015, the Stone group has studied the physical mechanisms involved in the bridge formation process and has succeeded in providing simple predictors for the conditions required for the formation and maintenance of ice bridges.
Although most studies of ice flows implement numerical models, the mechanics community has a long history of developing simplified models for studying flow in narrow geometries. Over the past year, the Stone group has used these techniques to provide a mathematical model that includes the role of mechanical stresses in the ice in response to wind, which is more central to ice bridge formation than other secondary processes such as the rotation of the Earth, or ice melting and freezing; water flow has also been included. This model will provide oceanographers and climate scientists with tools by which to understand the complex dynamics of sea ice, while speaking more broadly to the scientific community on problems of global importance. The group produced a new
theory to predict the flux of ice expected in situations without ice bridges, which agrees well both with field measurements and large-scale computational models. The theory also makes predictions for the critical ice thickness (defined to account for the wind stress, the compressive strength of the ice and the channel width) beyond which the flow becomes entirely arrested, which is also consistent with numerical studies.
Figure 1.5. (A) Map showing the Nares Strait between northwestern Greenland and Ellesmere Island, Canada. The Nares Strait is a site for seasonal ice bridge formation. Credit: Environment Canada, Government of Canada. (B) Satellite image indicating the location of a stable ice bridge in the Nares Strait (from May 25, 2001), marking the boundary between (a) the ice sheet and (b) open water in the strait. Image adapted from: Dumont, D., Y. Gratton, and T. E. Arbetter, 2009. Modeling the dynamics of the North Water Polynya ice bridge. J. Phys. Oceanogr., 39: 1448–1461. (C) The formation of ice bridges depends on the ice thickness h, the maximum and minimum widths of the strait wmin and wmax, respectively, the wind stress t and the compressive strength of the ice S. Shaded regions are theoretical predictions, and symbols are numerical results for the flow state as a function of the ice thickness, which includes icebridge formation. The conditions for ice bridge formation are more restrictive in simulations than in the theory due to dynamic instabilities of the bridge that arise from a tendency of the ice to continue flowing during incipient stages of bridge formation. (D) Ice velocity as a function of the wind stress in Nares Strait, indicating theoretical predictions for different ice thicknesses (lines) and the field data of Samelson et al. 2006 GRL (symbols), which span a range of thicknesses that is not measured. The sign of t denotes the direction of the wind, with positive t representing the dominant northerly winds towards the Atlantic Ocean. Concurrent measurements of ice properties and forcing conditions will allow the theory to predict sea ice fluxes through straits.
The Stone group’s current efforts are focused on modeling the process by which the flow becomes arrested, eventually leading to the formation of an ice bridge. Such behavior also arises in other engineering and science problems, such as the flow of granular materials, including soil, in confined geometries, which suggests a broader scope for understanding other physical and geological processes. Additionally, our theory provides a means to calibrate existing models of sea ice dynamics against field observations without the need to run detailed simulations. Thus, our theoretical efforts not only explain a complex geophysical flow phenomenon in straits, but also provide a means to refine the modeling of sea ice in the more general context of Arctic and Antarctic ice flows.
In the future, the group aims to tackle ice accumulation and flow past islands, which are other significant aspects of dynamics in the arctic. A long-term goal is to understand the eventual breakup of ice bridges and dynamics of formation and flow using a model that incorporates processes such as wind forcing, ice melting and water flow.
Lai, C.-Y., Z. Zheng, E. Dressaire, G. Ramon, H.E. Huppert, and H.A. Stone, 2017. Elastic relaxation of fluid-driven cracks and the resulting backflow. Phys. Rev. Lett., in press.
Liu, Y., Z. Zheng, and H.A. Stone, 2017. The influence of capillary effects on the drainage of a viscous gravity current into a deep porous medium. J. Fluid Mech., in review.
Rallabandi, B., Z. Zheng, M. Winton, and H.A. Stone, 2017. Wind-driven formation of ice bridges in straits, in review.
Yu, Y., Z. Zheng, and H.A. Stone, 2017. Coupled drainage from both a permeable base and an edge of a porous reservoir. Phys. Rev. Fluids., in review.
Behrenfeld, M.J., Y. Hu, R. T. O’Malley, E. S. Boss, C.A. Hostetler, D.A. Siegel, J. Sarmiento, J. Schulien, J.W. Hair, X. Lu, S. Rodier, and A.J. Scarino, 2016. Annual boom–bust cycles of polar phytoplankton biomass revealed by space-based lidar. Nat. Geosci., 10: 118–122. doi.org/10.1038/ngeo2861.
Bender, M.L., B. Tilbrook, N. Cassar, B. Jonsson, A. Poisson, and T.W. Trull, 2016. Ocean productivity south of Australia during spring and summer. Deep-Sea Res., 112: 68- 78. doi:10.1016/j.dsr.2016.02.018.
Carter, B.R., T.L. Frölicher, J.P. Dunne, K.B. Rodgers, R.D. Slater, and J. L. Sarmiento, 2016. When can ocean acidification impacts be detected from decadal alkalinity measurements? Global Biogeochem. Cy., 30: 595-612. doi:10.1002/2015GB005308
Farrior, C.E., S.A. Bohlman, S. Hubbell, and S.W. Pacala, 2016. Dominance of the suppressed: Power-law size structure in tropical forests. Science, 351(6269): 155-157. doi: 10.1126/science.aad0592.
Guo, B., Z. Zheng, M.A. Celia, K.W. Bandilla, and H.A. Stone, 2016. Flow regime analysis for geologic CO2 sequestration and other subsurface fluid injections. Intl. J. Greenhouse Gas Control, 53: 284-291. doi:10.1016/j. ijggc.2016.08.007.
Guo, D., Z. Zheng, M. Celia, and H.A. Stone, 2016. Axisymmetric flows from fluid injection into a confined porous medium. Phys. Fluids, 28: 022107. doi:10.1063/1.4941400.
Kim, J.M., O. Baars, and F.M.M. Morel, 2016. The effect of acidification on the bioavailability and electrochemical lability of zinc in seawater. Philos. T. R. Soc. A. 374: 20150296. doi: 10.1098/rsta.2015.0296.
Lai, C.-Y., Z. Zheng, E. Dressaire, and H.A. Stone, 2016. Fluid-driven cracks in an elastic matrix in the toughness-dominated limit. Phil. Trans. Roy. Soc. A, 374: 20150425. doi:10.1098/rsta.2015.0425.
Morrison, A.K., S.M. Griffies, M. Winton, W.G. Anderson, and J.L. Sarmiento, 2016. Mechanisms of Southern Ocean Heat Uptake and Transport in a Global Eddying Climate Model. J. Climate, 29(6), 2059–2075. doi:10.1175/JCLI-D-15-0579.1.
Pellegrini, A.F.A., W.R.L. Anderegg, C.E.T. Paine, W.A. Hoffmann, T. Kartzinel, S. Rabin, D. Sheil, A.C. Franco, and S.W. Pacala, 2016. Convergence of bark investment according to fire and climate structures ecosystem vulnerability to future change. Ecol. Lett., 20(3): 307-316. doi: 10.1111/ele.12725.
Weng, E.S., C.E. Farrior, R. Dybzinski, and S.W. Pacala, 2016. Predicting vegetation type through physiological and environmental interactions with leaf traits: evergreen and deciduous forests in an earth system modeling framework. Glob. Chang. Biol., doi:10.1111/gcb.13542.
Williams, N.L., L. W. Juranek, K.S. Johnson, R.A. Feely, S.C. Riser, L.D. Talley, J.L. Russell, J. L. Sarmiento, and R. Wanninkhof, 2016. Empirical algorithms to estimate water column pH in the Southern Ocean. Geophys. Res. Lett., 43(7): 3415-3422. doi:10.1002/2016GL068539.
Wolf, A., W.R.L. Anderegg, and S.W. Pacala, 2016. Optimal stomatal behavior with competition for water and risk of hydraulic impairment. Proc. Natl. Acad. Sci., 113(46): E7222-E7230. doi: 10.1111/pce.12852.
Yau, A.M., M.L. Bender, T. Blunier, and J. Jouzel, 2016. Setting a chronology for the basal ice at Dye-3 and GRIP: Implications
for the long-term stability of the Greenland Ice Sheet. Earth Planet. Sc. Lett., 451: 1-9. doi:10.1016/j.epsl.2016.06.053.
Yau, A.M., M.L. Bender, A. Robinson, and E.J. Brook, 2016. Reconstructing the last interglacial at Summit, Greenland: Insights from GISP2. Proc. Natl. Acad. Sci., 113: 9710- 9715. doi: 10.1073/pnas.1524766113.
Young, J.N., A.M.C. Heureux, R.E. Sharwood, R.E.M. Rickaby, F.M.M. Morel, and S.M. Whitney. Large variations in the Rubisco kinetics of diatoms reveals diversity among their carbon concentrating mechanisms, 2016. J. Exp. Bot., 67(11): 3445-3456. doi:10.1093/ jxb/erw163.