Click here for my research interests.
Click here for my teaching interests.
Click here for a list of my publications.
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A central focus of my research is the role of the ocean in global biogeochemical cycles and climate. The marine carbon cycle, through its effect on atmospheric CO2 levels, provides the motivation for much of this research. I make inferences about the marine carbon cycle by synthesizing and analyzing data sets for carbon dioxide and related chemical species, particularly dissolved oxygen and nutrients. I often use numerical models to interpret these observational data sets. I am also interested in the air-sea fluxes of gases that influence atmospheric chemistry, such as carbon monoxide, carbonyl sulfide and dimethyl sulfide. In the past I have worked in paleoceanography (no pun intended), particularly on the role of changes in bathymetry on the long term cooling that has occurred during the Cenozoic Era (the past 65 million years). Finally, I am conducting research on the physical and biogeochemical dynamics of Chesapeake Bay and its watershed, and am particularly interested in the effect of anthropogenic activity on these systems. Here are some of my current projects:
Consortium for Atlantic Regional Assessment (CARA). The goal of this EPA-funded project is to provide climate information to stakeholders in the Mid- and Upper-Atlantic Region of the United States. For details, go to the CARA web site.
Measuring and modeling sources and sinks of dimethylsulfide (DMS). DMS is a source of cloud condenstation nuclei and is derived mainly from phytoplankton. My collaborators and I made time-series measurements in the Sargasso Sea and off the Palmer Peninsula (Antarctica) and we are now modeling these systems. Team leader Paty Matrai has a nice web site on the Palmer part of the project, including one of my log entries.
The carbon budget of the US Eastern Continental Shelf. With a combination of numerical models, historical data sets and satellite data we are attempting to constrain rates of carbon cycling on the US Eastern Continental Shelf. More details of this NASA-funded project can be found here.
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Here's a summary of courses I've taught:
Introductory Meteorology (Meteo 003). The main goal of this general education course is to provide the student with a basic understanding of the earth's atmosphere. If successful, the student should be able to comprehend at least the following by the end of this course: the blue sky, global warming, the greenhouse effect, fronts, mirages, dew formation, cloud formation, the jet stream, El Niño, lightning, thunderstorms, hurricanes, tornadoes and the ozone hole.
The Oceans (Meteo 022). The aim of this course is to gain a basic understanding of how seawater moves in the form of currents, waves and tides and how these motions are part of the Earth System. In particular, ocean currents in light of their effect on climate and marine ecosystems are emphasized. Successful completion of this course means that students will have learned, among other things, why Northern Europe is anomalously warm, why marine climates are so moderate, why Peruvian fisheries are so productive (usually), why the open ocean is considered to be a biological desert, why currents are stronger on the western sides of ocean basins, why tides occur twice a day, and why waves break parallel to the beach. The approach is conceptual and intuitive, as opposed to highly mathematical and abstract. Diagrams and some basic principles of physics are used instead of equations to reason one's way through the machinery of ocean circulation. This is a task that is not easy, but is one that everyone can master given hard work, patience and enthusiasm. I do my best to make it a fun, stimulating and satisfying journey. 2 credits. No prerequisites.
Survey of the Atmosphere (Meteo 300). The main purpose of this class is to provide a formal overview of the atmosphere to meteorology and other science and engineering majors. This course differs from the general education course Meteo 002/003 (Weather and Society/Introduction to Meteorology) in that it is far more quantitative. We will routinely use the tools of calculus and physics to understand the atmosphere. The course will serve meteorology majors by placing into context core courses that will be taken in their third and fourth years. Other majors should benefit by seeing how meteorology is related to other fields, such as oceanography and geochemistry.
Introduction to Physical Oceanography (Meteo 451). The main goal of this course is to describe ocean circulation on basin-wide and global scales and present a theoretical basis for understanding it. Topics covered include: Conservation of mass, momentum, salt and heat in the ocean; The effect of the earth's rotation on ocean currents; Wind-driven upwelling; Subtropical gyres; Western boundary currents (e.g., The Gulf Stream); El Niño; Heat transport and storage by the ocean; Role of the ocean in climate change; Sea level rise; Air-Sea heat and freshwater fluxes; The thermohaline circulation; The ocean's temperature and salinity distributions; Chemical tracers of ocean circulation; Tides and other waves. 3 credits. Prerequisites: Meteo 421.
Global Biogeochemical Cycles (Meteo 475W). We often think of the biosphere as a system that reacts to the external forcing of climate and chemical composition. In fact, the biosphere has a profound impact on the environment itself, and the two are therefore a coupled system, sometimes known as the Earth System. Global biogeochemical cycles are a part of the Earth System, and are defined as the study of the transport and transformation of chemical substances on the global scale. Global biogeochemical cycles usually involve those elements that are important to life, such as carbon, nitrogen, oxygen, sulfur, and phosphorus, to name a few. Having taken this course, one should have an appreciation of the following: The role of the biosphere in the Earth System; The interdisciplinary nature of global biogeochemical cycles; Current areas and methods of research in global biogeochemical cycles; The importance of global biogeochemistry to a variety of current environmental issues, such as acid rain, stratospheric ozone depletion, climate change, air and water quality, and global food production. 3 credits. Prerequisites: Techniques of Calculus (Math 110) or Calculus with Analytical Geometry (Math 140); Chemical Principles (Chem 012).
Marine Biogeochemistry (Geosc 410). The chemistry of the oceans profoundly affects marine life, atmospheric composition and global climate. In turn, marine biological processes and ocean circulation determine the distributions and fluxes of many chemical species in the ocean. Marine biogeochemistry is the study of this complex interplay between chemical and biological processes in the ocean's physical environment. The main goal of this course is to describe and present a theoretical basis for understanding the large-scale biogeochemical cycles of carbon, oxygen, nitrogen, phosphorus, silicon, calcium, sulfur and related elements and to discuss their relevance to biological productivity, atmospheric composition and the earth's climate. 3 credits.
Oceans and Climate Seminar (Meteo 588). The oceans affect climate by exchanging heat, fresh water, carbon dioxide and other chemical species with the atmosphere. In this graduate seminar, students lead discussions on research articles about these interactions. Past topics in this seminar have been: the thermohaline circulation, biogenic sulfur and cloudiness, and the uptake of anthropogenic CO2 by the ocean and terrestrial biosphere. 2 credits.
Geophysical Fluid Dynamics (Meteo 520). This is the introductory fluid dynamics course for meteorology graduate students. The basics of fluid motion are discussed, particularly those aspects that are relevant for geophysical flows. Topics include: kinematics, conservation laws, vorticity dynamics, gravity waves, dynamic similarity, laminar flow, and an introduction to instability. 3 credits.
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Journal Articles
Najjar, R. G., C. R. Pyke, M. B. Adams, D. Breitburg, M. Kemp, C. Hershner, R. Howarth, M. Mulholland, M. Paolisso, D. Secor, K. Sellner, D. Wardrop, and R. Wood. 2009. Potential climate-change impacts on the Chesapeake Bay. Estuarine, Coastal, and Shelf Science, in press.
Shorr, N., A. Amato, S. Graham, and R. Najjar. 2008. Climate change impacts on household heating and cooling in the Northeast US compared to those of purposive behaviors. Climate Research, in press.
Najjar, R. G., L. Patterson and S. Graham. 2009. Climate simulations of major estuarine watersheds in the Mid-Atlantic region of the United States. Climatic Change, 95, 139-168.
Wu, S.-Y., R. G. Najjar, and J. Siewert. 2009. Potential impacts of sea-level rise on the Mid- and Upper-Atlantic Region of the United States. Climatic Change, 95,121-138.
Fennel, K., J. Wilkin, M. Previdi, and R. Najjar. 2008. Denitrification effects on air-sea CO2 flux in the coastal ocean: Simulations for the northwest North Atlantic. Geophys. Res. Lett., 35, L24608, doi: 10.1029/2008GL036147.
Hilton, T. H., R. G. Najjar, L. Zhong, and M Li. 2008. Is there a signal of sea-level rise in Chesapeake Bay salinity? Journal of Geophysical Research., 113, C09002, doi: 10.1029/2007JC00427.
Bailey, K. E., D. A. Toole, B. Blomquist, R. G. Najjar, B. Huebert, D. J. Kieber, R. P. Kiene, P. Matrai, G. R. Westby, and D. A. del Valle. 2008. Dimethylsulfide production in Sargasso Sea eddies. Deep-Sea Res. II, 55, 1491-1504.
Gabric, A. J., P. Matrai, R. Cropp, J. Dacey, J. DiTullio, D. J. Kieber, R. P. Kiene, R. G. Najjar, R. Simó, and D. A. Toole. 2008. Factors determining the vertical profile of dimethylsulfide in the Sargasso Sea during summer. Deep-Sea Res. II, 55, 1505-1518.
Hoffman, E., J.-N. Druon, K. Fennel, M. Friedrichs, D. Haidvogel, C. Lee, A. Mannino, C. McClain, R. Najjar, J. O'Reilly, D. Pollard, M. Previdi, S. Seitzinger, J. Siewert, S. Signorini, and J. Wilkin. 2008. Eastern US continental shelf carbon budget: Integrating models, data assimilation, and analysis. Oceanography, 21(1), 86-104.
Zafiriou, O. C., H. Xie, N. B. Nelson, and R. G. Najjar. 2008. Carbon monoxide distributions reveal upper-ocean diel- and seasonal-scale photochemistry, biogeochemistry and mixing. Limnol. Oceanogr., 53, 835-850.
Najjar, R. G., and 22 others. 2007. Impact of circulation on export production, dissolved organic matter and dissolved oxygen in the ocean: Results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2), Global Biogeochem. Cycles, 21, GB3007, doi:10.1029/2006GB002857. PDF file.
Berelson, W. M., W. M. Balch, R. Najjar, R. A. Feely, C. Sabine, K. Lee. 2007. Relating estimates of CaCO3 production, export, and dissolution in the water column to measurements of CaCO3 rain into sediment traps and dissolution on the sea floor: A revised global carbonate budget. Global Biogeochem. Cycles, 21, GB1024, doi: 10.1029/2006GB002803. PDF file.
Jin, X., R. G. Najjar, F. Louanchi, and S. C. Doney. 2007. A modeling study of the seasonal oxygen budget of the global ocean. J. Geophys. Res. 112, C05017, doi:10.1029/2006JC003731. PDF file.
Friis, K., R. G. Najjar, M. J. Follows, S. Dutkiewicz, A. Kortzinger and K. M. Johnson. 2007. Dissolution of calcium carbonate: Observations and model results in the North Atlantic. Biogeosciences, 4, 205-213. PDF file.
Friis, K., R. G. Najjar, M. J. Follows, and S. Dutkiewicz. 2006. Possible overestimation of shallow-depth calcium carbonate dissolution in the ocean. Global Biogeochem. Cycles, 20, GB4019, doi:10.1029/2006GB002727. PDF file.
Reed, P. M., R. P. Brooks, K. J. Davis, D. R. DeWalle, K. A. Dressler, C. J. Duffy, H. Lin, D. A. Miller, R. G. Najjar, K. M. Salvage, T. Wagener, and B. Yarnal. 2006. Bridging river basin scales and processes to assess human-climate impacts and the terrestrial hydrologic system. Water Resources Research, 42, W07418, doi:10.1029/2005WR004153. PDF file.
Orr, J. C. and 26 others. 2005. Anthropogenic ocean acidification over the 21st Century and its impact on marine calcifying organisms. Nature, 437, 681-686. PDF file.
Matsumoto, K. and 31 others. 2004. Evaluation of ocean carbon cycle models with data-based metrics. Geophys. Res. Lett., 31, doi:10.1029/2003GL018970. PDF file.
Doney, S.C. and 27 others. 2004. Evaluating global ocean carbon models: the importance of realistic physics, Global Biogeochem. Cycles, 18, GB3017, doi:10.1029/2003GB002150. PDF file.
von Hobe, M., R. G. Najjar, A. J. Kettle and M. O. Andreae. 2003. Photochemical and physical modeling of carbonyl sulfide in the ocean. J. Geophys. Res., 108, 3229-3244. PDF file.
Najjar, R. G., G. Nong, D. Seidov and W. Peterson. 2002. Modeling geographic impacts on early Eocene ocean temperature. Geophys. Res. Lett., 29, 10.1029/2001GL014438. PDF file.
Dutay, J.-C. and 28 others. 2002. Evaluation of ocean model ventilation with CFC-11: comparison of 13 global ocean models. Ocean Modelling, 4, 89-120. PDF file.
Gabric, A., W. Gregg, R. G. Najjar and D. J. Erickson III. 2001. Modelling the biogeochemical cycle of dimethylsulfide in the upper ocean: A review. Chemosphere - Global Change Science, 3, 377-392. PDF file.
Louanchi, F. and R. G. Najjar. 2001. The mean annual cycle of nutrients and oxygen in the North Atlantic Ocean. Deep-Sea Res. II., 48, 2155-2171. PDF file.
Ono, S., A. Ennyu, R. G. Najjar and N. R. Bates. 2001. Shallow remineralization in the Sargasso Sea estimated from seasonal variations in oxygen, dissolved inorganic carbon and nitrate. Deep-Sea Res. II, 48, 1567-1582. PDF file.
Hotinski, R. M., K. L. Bice, L. R. Kump, R. G. Najjar and M. A. Arthur. 2001. Ocean stagnation and end-Permian anoxia. Geology, 29, 7-10. PDF file.
Gibson, J. and R. G. Najjar. 2000. The response of Chesapeake Bay salinity to climate-induced changes in streamflow. Limnol. Oceanogr., 45, 1764-1772. PDF file.
Nong, G. T., R. G. Najjar, D. Seidov and W. H. Peterson. 2000. Simulation of ocean temperature change due to the opening of Drake Passage. Geophys. Res. Lett., 27, 2689-2692. PDF file.
Louanchi, F. and R. G. Najjar. 2000. A global monthly mean climatology of phosphate, nitrate and silicate in the upper ocean: Spring-summer production and shallow remineralization. Global Biogeochem. Cycles., 14, 957-977. PDF file.
Najjar, R. G. and R. F. Keeling. 2000. Mean annual cycle of the air-sea oxygen flux: A global view. Global Biogeochem. Cycles, 14, 573-584. PDF file.
Najjar, R.G., H.A. Walker, P.J. Anderson, E.J. Barron, R. Bord, J. Gibson, V.S. Kennedy, C.G. Knight, P. Megonigal, R. O'Connor, C.D. Polsky, N.P. Psuty, B. Richards, L.G. Sorenson, E. Steele, and R.S. Swanson. 2000. The potential impacts of climate change on the Mid-Atlantic Coastal Region. Climate Res., 14, 219-233. PDF file.
Hotinski, R. M., L. R. Kump and R. G. Najjar. 2000. Opening Pandora's Box: The impact of open system modeling on interpretations of anoxia. Paleoceanogr., 15, 267-279.
Neff R., H. Chang, C.G. Knight, R.G. Najjar, B. Yarnal and H.A. Walker. 2000. Impact of climate variation and change on Mid-Atlantic Region hydrology and water resources. Climate Res., 14,, 207-218. PDF file.
Preiswerk, D. and R. G. Najjar. 2000. A global, open ocean model of OCS and its air-sea flux. Global Biogeochem. Cycles, 14, 585-598. PDF file.
Najjar, R. G. 1999. The water balance of the Susquehanna River Basin and its response to climate change. J. Hydrol., 219, 7-19. PDF file.
Keeling, R. F., B. B. Stephens, R. G. Najjar, S. C. Doney, D. Archer, and M. Heimann. 1998. Seasonal variations in the atmospheric O2/N2 ratio in relation to the kinetics of air-sea gas exchange. Global Biogeochem. Cycles, 12, 141-164. PDF file.
Najjar, R. G. and R. F. Keeling. 1997. Analysis of the mean annual cycle of the dissolved oxygen anomaly in the World Ocean. J. Mar. Res., 55, 117-151. PDF file.
Doney, S. C., D. M. Glover, and R. G. Najjar. 1996. A new coupled, one-dimensional biological-physical model for the upper ocean: Application to the JGOFS Bermuda Atlantic Time-series Study (BATS) site. Deep-Sea Res. II, 43, 591-624.
Doney, S. C., R. G. Najjar, and S. Stewart. 1995. Photochemistry, mixing, and diurnal cycles in the upper ocean. J. Mar. Res., 53, 341-369. PDF file.
Keeling, R. F., R. G. Najjar, M. L. Bender and P. P. Tans. 1993. What atmospheric oxygen measurements can tell us about the global carbon cycle. Global Biogeochem. Cycles, 7, 37-67.
Levitus, S., J. Reid, M. E. Conkright, R. G. Najjar, and A. Mantyla. 1993. Distribution of phosphate, nitrate and silicate in the world oceans. Prog. Oceanogr., 31, 245-273.
Najjar, R. G., J. L. Sarmiento and J. R. Toggweiler. 1992. Downward transport and fate of organic matter in the ocean: simulations with a general circulation model. Global Biogeochem. Cycles, 6, 45-76.
Sarmiento, J. L., J. R. Toggweiler and R. G. Najjar. 1988. Ocean carbon-cycle dynamics and atmospheric pCO2. Phil. Trans. R. Soc. Lond., A 325, 3-21.
Najjar, R. G. and C. Laohakul. 1986. An approximate solution to the Graetz problem with axial conduction and prescribed wall heat flux. International Communications in Heat and Mass Transfer, 13, 315-324.
Book Chapters
Najjar, R. G. 1992. Marine Biogeochemistry. In: Climate System Modeling, Trenberth, K. (ed.), Cambridge University Press, Cambridge, England, 241-280.
Najjar, R. G., D. J. Erickson III, and S. Madronich. 1995. Modeling the air-sea fluxes of gases formed from the decomposition of dissolved organic matter: Carbonyl sulfide and carbon monoxide. In: The Role of Non-living Organic Matter in the Earth's Carbon Cycle, Zepp, R. and C. Sonntag (eds.), 106-132, John Wiley, New York.
Technical Reports, Conference Proceedings, etc.
Pyke, C. R., R. G. Najjar, M. B. Adams, D. Breitburg, M. Kemp, C. Hershner, R. Howarth, M. Mulholland, M. Paolisso, D. Secor, K. Sellner, D. Wardrop, and R. Wood. 2008. Climate Change and the Chesapeake Bay: State-of-the-Science Review and Recommendations. A Report from the Chesapeake Bay Program Science and Technical Advisory Committee (STAC), Annapolis, MD. 59 pp. PDF file.
Najjar, R. G., N. Gruber and J. C. Orr. 2001. Predicting the ocean's response to rising CO2: The Ocean Carbon Cycle Model Intercomparison Project. U.S. JGOFS News, 11(1), 1-4.
Orr, J. C., P. Monfray, E. Maier-Reimer, J. R. Palmer and R. G. Najjar. 1997. Transition time for ocean carbon-cycle model comparison. Research GAIM, 1 (2), 8-11.
Najjar, R. G. 1995. Three-dimensional models of the marine carbon cycle. In: Speranza, A., S. Tibaldi and R. Fantechi, Global Change, Proceedings of the First Demetra Meeting, Chianciano, Italy, pp. 246-264. European Commission, Luxembourg.
Najjar, R. G. and J. R. Toggweiler. 1993. Reply to the comment by Jackson. Limnol. Oceanogr., 38, 1331-1332.
Najjar, R. G. 1990. Simulations of the phosphorus and oxygen cycles in the world ocean using a general circulation model, Ph.D. thesis, Princeton University, 190 pp.
Sarmiento, J. L., M. Fasham, U. Siegenthaler, R. Najjar and J. R. Toggweiler. 1989. Models of chemical cycling in the oceans II: a progress report. Ocean Tracers Laboratory Technical Report # 6, Princeton University.
Toggweiler, J. R., J. L. Sarmiento, R. Najjar and D. Papademetriou. 1987. Models of chemical cycling in the oceans: a progress report. Ocean Tracers Laboratory Technical Report #4, Princeton University.
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Send email to: najjar@meteo.psu.edu