Turbulence mediates marine aggregate formation and destruction in the upper ocean.

Marine aggregates formed through particle coagulation, large ones (>0.05 cm) also called marine snow, make a significant contribution to the global carbon flux by sinking from the euphotic zone, impacting the Earth's climate. Since aggregate sinking velocity and carbon content are size-dependent, understanding the physical mechanisms controlling aggregate size distribution is fundamental to determining the biological carbon pump efficiency.

Seascapes: the world of aquatic organisms as determined by their particulate natures.

The interactions between planktonic organisms and their aquatic environment are mediated by diffusive processes on the scale of millimeters and smaller. The uptake of nutrients and food and the release of metabolic products creates localized patchiness that diffusive processes homogenize. Organism size determines, to a large extent, the character of these interactions.

Seasonal and annual reoccurrence in betaproteobacterial ammonia-oxidizing bacterial population structure.

Microbes exhibit remarkably high genetic diversity compared with plant and animal species. Many phylogenetically diverse but apparently functionally redundant microbial taxa are detectable within a cubic centimetre of mud or a millilitre of water, and the significance of this diversity, in terms of ecosystem function, has been difficult to understand. Thus it is not known whether temporal and spatial differences in microbial community composition are linked to particular environmental factors or might modulate ecosystem response to environmental change.

Particle aggregation.

A basic problem in marine biogeochemistry is understanding material and elemental distributions and fluxes in the oceans, and a key part of this problem is understanding the processes that affect particulate material in the ocean. Aggregation of particulate material is a primary process because it alters the transport properties of particulate material and provides a mechanism for transferring material from the dissolved into the particulate pools. Aggregation theory not only provides a framework for understanding these processes, but it also provides a means for making predictions and has been successfully used to predict maximum particle concentrations in the oceans and the fate of diatom blooms (including those from iron fertilization), the size spectra of particles in the oceans, and the size distributions of trace metals.

Sediment denitrifier community composition and nirS gene expression investigated with functional gene microarrays.

A functional gene microarray was used to investigate denitrifier community composition and nitrite reductase (nirS) gene expression in sediments along the estuarine gradient in Chesapeake Bay, USA. The nirS oligonucleotide probe set was designed to represent a sequence database containing 539 Chesapeake Bay clones, as well as sequences from many other environments. Greatest nirS diversity was detected at the freshwater station at the head of the bay and least diversity at the higher salinity station near the mouth of the Bay.

Ammonia-oxidizing bacterial community composition in estuarine and oceanic environments assessed using a functional gene microarray.

The relationship between environmental factors and functional gene diversity of ammonia-oxidizing bacteria (AOB) was investigated across a transect from the freshwater portions of the Chesapeake Bay and Choptank River out into the Sargasso Sea. Oligonucleotide probes (70-bp) designed to represent the diversity of ammonia monooxygenase (amoA) genes from Chesapeake Bay clone libraries and cultivated AOB were used to construct a glass slide microarray. Hybridization patterns among the probes in 14 samples along the transect showed clear variations in amoA community composition.

Small phytoplankton and carbon export from the surface ocean.

Autotrophic picoplankton dominate primary production over large oceanic regions but are believed to contribute relatively little to carbon export from surface layers. Using analyses of data from the equatorial Pacific Ocean and Arabian Sea, we show that the relative direct and indirect contribution of picoplankton to export is proportional to their total net primary production, despite their small size. We suggest that all primary producers, not just the large cells, can contribute to export from the surface layer of the ocean at rates proportional to their production rates.

Modeling steady-state particle size spectra.

Fractal dimensions of marine aggregates are often estimated from the measured slopes of particle size spectra. One technique uses dimensional analysis to determine the dependence of the spectrum's slope with fractal dimension. In this paper, we use numerical simulations to examine the assumptions underlying the dimensional analysis approach to particle size spectra.