Research

Research in the Barbeau lab is directed towards understanding the cycling of biologically active trace metals in marine systems. Much of our work has focused on iron, important as a limiting micronutrient in large areas of the ocean. Additional trace elements of interest in our research are copper and nickel. Trace metals are challenging to study in marine systems due to their complex chemistry and frequent occurrence at extremely low (picomolar to nanomolar) concentrations.  The relationships between trace metals and biota in the oceans are interactive, wide-ranging and can be perceived at molecular to ecosystem scales. My group has developed a strongly mechanistic and highly interdisciplinary approach to the study of marine trace metal biogeochemistry. We employ fundamental techniques in bioinorganic and analytical chemistry as well as microbial and molecular biology. Both fieldwork and laboratory work are essential to our program. We have made significant contributions to the understanding of trace element chemistry in seawater, the ecological effects of trace elements as limiting or co-limiting micronutrients in marine systems, and trace metal bioavailability to and cycling by marine microorganisms. Investigations in all of these areas are ongoing, and I welcome inquiries from prospective students and postdocs.

Chemistry of trace metal speciation in seawater

Although great strides have been made in the understanding of trace metal distributions and chemistry in seawater, significant analytical challenges remain and the determination of trace metal concentrations and chemical form (speciation) in seawater is far from routine. The Barbeau group is actively participating in current international efforts to intercalibrate analytical methods and develop effective standards for trace metal analysis in seawater, via the SAFe and GEOTRACES programs.  We employ primarily electrochemical and flow injection analysis methods for the study of iron, copper and nickel speciation in seawater. A particular area of interest is in the application of these methods in the context of mechanistic experiments to study biologically- or photochemically-mediated changes in trace metal speciation. We are pursuing experimental and observational studies of iron and copper speciation in pelagic regimes, coastal zones, and also copper-impacted sites like San Diego Bay and San Francisco Bay. Our work in this area has primarily been funded by NSF, and also by CALFED and DOE.

Recent Publications in this Area:

Earley, P.J., B.L. Swope, K. Barbeau, R. Bundy, J.A. McDonald and I. Rivera-Duarte. 2014. Life cycle contributions of copper from vessel painting and maintenance activities. Biofouling 30:51-68.

 

Bundy, R.M., D.V. Biller, K.N. Buck, K.W. Bruland, and K.A. Barbeau. 2014. Distinct pools of dissolved iron-binding ligands in the surface and benthic boundary layer of the California Current. Limnol. Oceanogr. 59(3): 769-787.

 

Bundy, R.M., M. Jiang, M. Carter and K.A. Barbeau. 2016. Iron-Binding Ligands in the Southern California Current System: Mechanistic Studies. Front. Mar. Sci. 3:27.

 

Ecological effects of trace metals as limiting/co-limiting micronutrients

My group has made progress in demonstrating the ecological significance of Fe availability in oceanic regimes where Fe limitation has not traditionally been thought to occur. One example of this is our work on Fe limitation in the Southern California Current System, a mesotrophic, relatively low-nutrient weak upwelling regime. Our incubation studies and measurements of Fe concentrations have provided evidence that while phytoplankton biomass in this regime is generally limited by the supply of nitrate, Fe supply influences macronutrient utilization, phytoplankton community species composition, and the spatial and temporal distribution of phytoplankton biomass, both at the surface and in the subsurface chlorophyll maximum. Our studies of iron biogeochemistry in this region have been funded by NASA, NSF-OCE and are ongoing as part of the NSF-funded California Current Ecosystem Long Term Ecological Research (CCE-LTER) site. We have also participated in studies of iron limitation off the Antarctic peninsula, in a region of natural iron fertilization, as part of a larger, multi-PI project funded by NSF-ANT and led by Greg Mitchell at SIO.

Recent Publications in this Area:

Hopkinson, B.M., B. Seegers, M. Hatta, C. I. Measures, B.G. Mitchell, and K. A. Barbeau. 2013. Planktonic C:Fe ratios and carrying capacity in the southern Drake Passage. Deep-Sea Res. II 90:102-111.

 

Ohman, MD, Barbeau K, Franks PJS, Goericke R, Landry MR, Miller AJ.  2013.  Ecological transitions in a coastal upwelling ecosystem. Oceanography. 26:210-219.

 

Brzezinski, M.A., J.W. Krause, R.M. Bundy, K.A. Barbeau, P. Franks, R. Goericke, M.R. Landry, and M.R. Stukel. 2015. Enhanced silica ballasting from iron stress sustains carbon export in a frontal zone within the California Current. J. Geophys. Res. Oceans. 120:4654-4669.

 

Semeniuk, D. M., R.L. Taylor, R.M. Bundy, W.K. Johnson, J.T. Cullen, M. Robert, K.A. Barbeau, and M.T. Maldonado. 2016. Iron-copper interactions in iron-limited phytoplankton in the northeast subarctic Pacific Ocean. Limnol. Oceanogr. 61:279-297.

 

Acquisition and transformation of trace metals by marine microorganisms

Knowledge of the genomic sequences of individual marine microbes as well as access to marine metagenomic data sets has greatly expanded in the last decade. This provides new opportunities to use this information to gain insight into fundamental biogeochemical processes in the ocean, including issues related to trace element cycling. With its strengths in the area of marine molecular biology, SIO is an ideal place to pursue these interests. An example of the application of genomics and molecular biology to studies of trace metal cycling in the marine environment is our work on receptor-mediated heme acquisition by marine bacteria. Uptake of exogenous heme complexes is a novel microbial Fe scavenging strategy in the context of marine systems, which has been identified by the Barbeau group. This project involves computational genomic studies, as well as gene expression studies and laboratory experiments with model bacterial strains.  Our ongoing efforts in this area seek to combine genomic information and molecular biology techniques with chemical measurements and experimentation to increase our understanding of Fe speciation and transformation in the ocean. We work with a variety of model marine bacteria strains in culture, including ecologically significant heterotrophs and cyanobacteria like Trichodesmium. Our work in this area has been funded by NSF and also the ACS Petroleum Research Fund.

Recent Publications in this Area:

Hogle, S.L., Barbeau, K. A. and M. Gledhill. 2014. Heme in the marine environment: from cells to the iron cycle. Metallomics 6(6): 1107-1120.

 

Roe, K.L. and K.A. Barbeau. 2014. Uptake mechanisms for inorganic iron and ferric citrate in Trichodesmium erythraeum IMS101. Metallomics. Accepted manuscript DOI: 10.1039/C4MT00026A

 

Hogle, S. L., J.C. Thrash, C.L. Dupont, and K.A. Barbeau. 2016. Trace metal acquisition by marine heterotrophic bacterioplankton with contrasting trophic strategies. Appl. Env. Microbiol. 82:1613-1624.

 

Hogle, S. L., R.M. Bundy, J.M. Blanton, E.E. Allen, and K.A. Barbeau. 2016. Copiotrophic marine bacteria are associated with strong iron-binding ligand production during phytoplankton blooms. Limnol. Oceanogr. Letters. doi: 10.1002/lol2.10026