Associate Professor
Marine Organic Geochemistry

Contact Info

160 Marine Sciences Bldg.
Lab office:
165/167 Marine Sciences Bldg.
Lab phone:
(706) 542-6798

My expertise relies on the use of specific organic compounds, i.e., molecular biomarkers to investigate sources, transport, transformations, and fate of organic matter in the aquatic and atmospheric environments. Until recently, most of studies on the characterization of organic matter in environmental samples were primarily focused on the analysis of sediments and/or the particulate fraction. The utilization of Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) by the marine organic geochemistry community opened a new door to the analysis of the most abundant and biologically important fraction of organic matter: the dissolved fraction. The analysis of DOM (dissolved organic matter) using FT-ICR MS is now the main branch of my research and collaborations. Since 2010, hundreds of DOM samples were analyzed using FT-ICR MS encompassing various projects that my lab either led or collaborated with other groups in USA and Europe (see recent publications and Research below).


Medeiros Lab People:

  • Rachel Perry (Ph.D. student, 2018-ongoing)
  • Maria Letourneau (Ph.D. student, 2015-ongoing)
  • Erin Malsbury (Undergraduate student, 2018-ongoing)
  • Sylvia Schaefer (Research Associate, 2016-ongoing)

Medeiros Lab Alumni:

  • Michael Seidel (Postdoc, 2012-2015) - Now: Postdoc at ICBM, University of Oldenburg, Germany
  • Ding He (Postdoc, 2014-2016) - Now: Assistant Professor at Zhejiang University, China
  • Lydia ('Meg') Babcock-Adams (M.S. student, 2013-2016) - Now: Ph.D. student at MIT/WHOI Joint Program
  • Danielle Arnold (IDS undergraduate student, 2012-2013)
  • V. Ruth Pannill (IDS undergraduate student, 2016-2018)


  • Ph.D. 2006, Oregon State University (Environmental Sciences/Chemical Oceanography)

Simoneit BRT, Oros DR, Leif RN, Medeiros PM. 2019. Weathering and biodegradation of hydrothermal petroleum in the North Rift of Guaymas Basin, Gulf of California. Revista Mexicana de Ciencias Geológicas, in press.

Roebuck JA, Medeiros PM, Letourneau ML, Jaffe R. 2018. Hydrological controls on the seasonal variability of dissolved and particulate black carbon in the Altamaha River, GA. Journal of Geophysical Research - Biogeosciences. 123:3055-3071. DOI Google Scholar

Vorobev A, Sharma S, Yu M, Lee J, Washington BJ, Whitman WB, Ballantyne F, Medeiros PM, Moran MA. 2018. Identifying labile marine DOM through short-term depletion of bacterioplankton transcripts and chemical signals. Environmental Microbiology. 20:3012-3030. DOI Google Scholar

Galeron M-A, Radakovitch O, Charrière B, Vaultier F, Volkman JK, Bianchi TS, Ward ND, Medeiros PM, Sawakuchi HO, Tank S et al..  2018.  Lipoxygenase-induced autoxidative degradation of terrestrial particulate organic matter in estuaries: A widespread process enhanced at high and low latitude. Organic Geochemistry. 115:78-92. DOI Google Scholar 

Medeiros PM.  2018.  Encyclopedia of Geochemistry: Gas Chromatography-Mass Spectrometry (GC-MS). In: Encyclopedia of Earth Sciences Series. W.H. White (ed.). pp. 1-6. DOI Google Scholar (see the new Encyclopedia of Geochemistry here)

Babcock-Adams L, Chanton JP, Joye SB, Medeiros PM.  2017.  Hydrocarbon composition and concentrations in the Gulf of Mexico sediments in the 3 years following the Macondo well blowout. Environmental Pollution. 229:329-338. DOI Google Scholar 

Medeiros PM, Babcock-Adams L, Seidel M, Castelao RM, Di Iorio D, Hollibaugh JT, Dittmar T.  2017.  Export of terrigenous dissolved organic matter in a broad continental shelf. Limnology and Oceanography. 62:1718-1731. DOI Google Scholar 

Doherty M, Yager PL, Moran MAnn, Coles VJ, Fortunato CS, Krusche AV, Medeiros PM, Payet JP, Richey JE, Satinsky BM et al..  2017.  Bacterial biogeography across the Amazon River-ocean continuum. Frontiers in Microbiology. 8:882. doi:10.3389/fmicb.2017.00882  DOI Google Scholar 

Satinsky BM, Smith CB, Sharma S, Landa M, Medeiros PM, Coles VJ, Yager PL, Crump BC, Moran MAnn.  2017.  Expression patterns of elemental cycling genes in the Amazon River Plume. The ISME Journal. 11:1852-1864. DOI Google Scholar 

Medeiros PM, Seidel M, Gifford SM, Ballantyne F, Dittmar T, Whitman WB, Moran MAnn.  2017.  Microbially-mediated transformations of estuarine dissolved organic matter. Frontiers in Marine Science. 4:69. doi: 10.3389/fmars.2017.00069 DOI Google Scholar 

John DL, Medeiros PM, Babcock-Adams L, Walker SE.  2017.  Cambrian trilobites as archives for anthropocene biomarkers and other chemical compounds. Anthropocene. 17:99-106. DOI Google Scholar 

Ward ND, Bianchi TS, Medeiros PM, Seidel M, Richey JE, Keil RG, Sawakuchi HO.  2017.  Where carbon goes when water flows: Carbon cycling across the aquatic continuum. Frontiers in Marine Science (Review article). 4:7. doi:10.3389/fmars.2017.00007 DOI Google Scholar 

Cao F, Medeiros PM, Miller WL.  2016.  Optical characterization of dissolved organic matter in the Amazon River plume and the Adjacent Ocean: Examining the relative role of mixing, photochemistry, and microbial alterations. Marine Chemistry. 186:178-188. DOI Google Scholar

Seidel M, Dittmar T, Ward ND, Krusche AV, Richey JE, Yager PL, Medeiros PM.  2016.  Seasonal and spatial variability of dissolved organic matter composition in the lower Amazon River. Biogeochemistry. 131:281-302. DOI Google Scholar 

Craft C., Herbert E., Li F., Smith D., Schubauer-Berigan J., Widney S., Angeline C., Pennings S., Medeiros PM, Byers J. et al..  2016.  Climate change and the fate of coastal wetlands. Wetland Science & Practice. 33(3):70-73. Google Scholar 

Medeiros PM, Seidel M, Niggemann J, Spencer RGM, Hernes PJ, Yager PL, Miller WL, Dittmar T, Hansell DA.  2016.  A novel molecular approach for tracing terrigenous dissolved organic matter into the deep ocean. Global Biogeochemical Cycles. 30:689-699. DOI Google Scholar 

Seidel M, Kleindienst S, Dittmar T, Joye SB, Medeiros PM.  2016.  Biodegradation of crude oil and dispersants in deep seawater from the Gulf of Mexico: Insights from ultra-high resolution mass spectrometry. Deep Sea Research Part II: Topical Studies in Oceanography. 129:108-118. DOI Google Scholar 

Kleindienst S, Seidel M, Ziervogel K, Grim S, Loftis K, Harrison S, Malkin SY, Perkins MJ, Field J, Sogin ML et al..  2016.  Reply to Prince et al.: Ability of chemical dispersants to reduce oil spill impacts remains unclear. Proceedings of the National Academy of Sciences. 113(11):E1422-E1423. DOI Google Scholar BibTex XML

Loick-Wilde N, Weber SC, Conroy BJ, Capone DG, Coles VJ, Medeiros PM, Steinberg DK, Montoya JP.  2016.  Nitrogen sources and net growth efficiency of zooplankton in three Amazon River plume food webs. Limnology and Oceanography. 61:460-481. DOI Google Scholar 

Moran MAnn, Kujawinski EB, Stubbins A, Fatland R, Aluwihare LI, Buchan A, Crump BC, Dorrestein PC, Dyhrman ST, Hess NJ et al..  2016.  Deciphering ocean carbon in a changing world. Proceedings of the National Academy of Sciences. 113(12):3143-3151. DOI Google Scholar 

Rushdi AI, Oros DR, Al-Mutlaq KF, He D, Medeiros PM, Simoneit BRT.  2016.  Lipid, sterol and saccharide sources and dynamics in surface soils during an annual cycle in a temperate climate region. Applied Geochemistry. 66:1-13. DOI Google Scholar 

Kleindienst S, Seidel M, Ziervogel K, Grim S, Loftis K, Harrison S, Malkin SY, Perkins MJ, Field J, Sogin ML et al..  2015.  Chemical dispersants can suppress the activity of natural oil-degrading microorganisms. Proceedings of the National Academy of Sciences. 112:14900-14905. DOI Google Scholar 

Medeiros PM, Seidel M, Dittmar T, Whitman WB, Moran MA.  2015.  Drought-induced variability in dissolved organic matter composition in a marsh-dominated estuary. Geophysical Research Letters. 42:6446-6453. DOI Google Scholar 

Seidel M, Yager PL, Ward ND, Carpenter EJ, Gomes HR, Krusche AV, Richey JE, Dittmar T, Medeiros PM.  2015.  Molecular-level changes of dissolved organic matter along the Amazon River-to-ocean continuum. Marine Chemistry. 177:218-231. DOI Google Scholar 

Medeiros PM, Seidel M, Ward ND, Carpenter EJ, Gomes HR, Niggemann J, Krusche AV, Richey JE, Yager PL, Dittmar T.  2015.  Fate of the Amazon River dissolved organic matter in the tropical Atlantic Ocean. Global Biogeochemical Cycles. 29:677-690. DOI Google Scholar 

Medeiros PM, Seidel M, Powers LC, Dittmar T, Hansell DA, Miller WL.  2015.  Dissolved organic matter composition and photochemical transformations in the northern North Pacific Ocean. Geophysical Research Letters. 42:863-870. DOI Google Scholar 

Simoneit BRT, Oros DR, Medeiros PM.  2014.  Organic matter provenance and paleoenvironment in the Cretaceous on the Manihiki Plateau, South Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology. 409:48-56. DOI Google Scholar 

Landa M., Cottrell M.T, Kirchman D.L, Kaiser K., Medeiros PM, Tremblay L., Batailler N., Caparros J., Catala P., Escoubeyrou K. et al..  2014.  Phylogenetic and structural response of heterotrophic bacteria to dissolved organic matter of different chemical composition in a continuous culture study. Environmental Microbiology. 16(6):1668-1681. DOI Google Scholar 

Satinsky B.M, Crump B.C, Smith C.B, Sharma S., Zielinski B.L, Doherty M., Meng J., Sun S., Medeiros PM, Paul J.H et al..  2014.  Microspatial gene expression patterns in the Amazon River Plume. Proceedings of the National Academy of Sciences. 111(30):11085–11090. DOI Google Scholar 

Ward ND, Keil RG, Medeiros PM, Brito DC, Cunha AC, Dittmar T, Yager PL, Krusche AV, Richey JE.  2013.  Degradation of terrestrially derived macromolecules in the Amazon River. Nature Geoscience. 6(7):530-533. DOI Google Scholar 

Sikes EL, Medeiros PM, Augustinus P, Wilmshurst JM, Freeman KR.  2013.  Seasonal variations in aridity and temperature characterize changing climate during the last deglaciation in New Zealand. Quaternary Science Reviews. 74:245-256. DOI Google Scholar 

Medeiros PM, Sikes EL, Thomas B, Freeman KH.  2012.  Flow discharge influences on input and transport of particulate and sedimentary organic carbon along a small temperate river. Geochimica et Cosmochimica Acta. 77:317-334. DO Google Scholar 


Research Interests:

Organic and isotope geochemistry:

1. Sources, transport, alterations and fate of organic compounds in aquatic and atmospheric environments;

2. Molecular characterization of marine/estuarine dissolved organic matter (DOM); 

3. Microbial- and photochemical-derived changes in DOM composition.


See complete list of publications here.