CMI Science

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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 atmospheric, oceanic and terrestrial carbon dioxide (CO2) and other greenhouse gases. The role of oceans as carbon and heat sinks is under investigation, with an emphasis on the relatively unexplored Southern Ocean. A growing effort is focused upon developing a better understanding of past tropical cyclone activity and intensity in order to improve the ability to predict future activity in response to changing climatic conditions. The study of surface waves at the interface between the atmosphere and ocean waters has important implications for improved understanding of climate and weather. Modeling of ice flows reveals new information about ocean mixing with implications for ocean ecology. Research on the role of terrestrial vegetation in the carbon cycle continues with additional focus on the hydrological cycle. An initiative launched in late 2017 investigates the physics of soil carbon dynamics to inform practical strategies for enhancing carbon storage in soils. In addition, a new supplementary award was announced to study methane sources and sinks in the atmosphere and on land.

Research Highlights – At a Glance

Jorge Sarmiento: Previous research using ocean observations and model results has suggested that the ocean around Antarctica acts as a key sink for atmospheric CO2, mitigating global temperature increases caused by increasing anthropogenic carbon emissions. However, ship-based observations to test these findings have been scarce and mostly limited to summertime measurements. New data from robotic floats that measure biogeochemistry year-round suggest that previous studies may have missed important wintertime outgassing in certain regions, resulting in overestimates of the size of the Southern Ocean sink. The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) researchers are working to extend such observations throughout the global ocean.

Gabriel Vecchi: Models project an increase in the rate of “rapid intensification” for tropical cyclones globally by the end of the 21st century. However, projections of changes in hurricane frequency in the Atlantic remain more uncertain, and model simulations and potential undercounts prior to available satellite data suggest observed long-term trends in hurricane counts are data artifact. The goal of this work is to reconcile these potential discrepancies and to improve the understanding of the mechanisms behind and limits to the predictability of tropical cyclone (TC) activity over the past few and next centuries. The work connects to broad questions in the climate science community, such as uncertainty over what TC changes are likely to occur over the coming century, and the extent to which intrinsic climate variability may be dominant over the impact of greenhouse forcing. 

Brandon Reichl: Surface waves at the atmosphere-ocean interface have important implications for climate and weather modeling. This research focuses on two topics related to surface waves. The first is improved coupled model performance through explicit consideration of physical processes related to surface gravity waves, including upper ocean turbulent mixing and interfacial fluxes of heat, momentum, and gases. The second is the investigation of changing surface wave characteristics in an evolving climate.

François Morel: The fixation of nitrogen gas by specialized organisms such as Trichodesmium is key to controlling photosynthetic production in marine ecosystems and may be impaired by ocean acidification. Recent studies sought to untangle the separate effects of high CO2 and low pH on Trichodesmium and found that the former accelerates photosynthesis and N2-fixation whereas the latter impairs these functions. Low ambient pH results in low intracellular pH, which decreases the efficiency of the nitrogenase enzyme.

Howard Stone: Climate changes involve atmospheric motions, ocean flows, and evolution of ice on land and in the sea. These dynamics are closely 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. The Stone group is providing simplified models for understanding the movement and distribution of ice during the formation of polynyas, which refer to localized regions of water surrounded by ice, and through narrow straits, which can affect flow, mixing and ecology in the ocean. The approach seeks to draw generalizations valid for various geometric and climate conditions. 

Stephen Pacala: The Pacala group’s work has continued to improve the representation of the carbon cycle in climate models, including empirical support for a new theory of evaporative water loss in plants and an explanation of tree behavior in response to drought. Additional work on the warming impacts of methane, including a collaboration with the Environmental Defense Fund, analyzed the methane budget of the US oil and gas infrastructure and provided new estimates for US emissions.

Elena Shevliakova: Human water management practices have a noticeable impact on the hydrological cycle. These include diverting water for irrigation, abstraction of groundwater, and construction of reservoirs. Hydrologic extremes, in particular, are heavily affected by water management practices, due to the existing stress on the system during droughts and floods. To prepare adaptation plans for hydrological extremes in the future, it is essential to account for water management and other human influences in state-of-the-art climate models.

Ian Bourg: An objective of the Bourg group is to resolve the physics of soil carbon storage. Field experiments indicate that the carbon storage capacity of soils increases significantly with their content in smectite clay minerals, but the cause of this relationship is unknown. The Bourg group is using atomistic-level simulations to predict the energetics of clay-organic interaction, the hydrology of clayey soils and sediments, and their dependence on aqueous chemistry. These results will enable more accurate Earth System Model predictions of soil carbon dynamics and inform practical strategies for enhancing the soil carbon sink.

François Morel (lead), Vaishali Naik, Elena Shevliakova, and Xinning Zhang: The CMI methane project, initiated in spring 2017, consists of three interconnected subprojects: an experimental project dealing with the critical issue of methane releases from wetlands, and two modeling projects aimed at quantifying the sources, sinks, and variations of methane in the atmosphere and on land. All three projects are now in full swing, following the hiring of postdoctoral researchers during the second half of 2017.

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