Biogeochemical Cycles

SS5.01: Metal Cycling in Coastal Wetlands
Organizer: Gabriel Filippelli, Indiana University/Purdue University Indianapolis (gfilippe@iupui.edu)

One legacy of industrial and population development has been the increased loading of metals (e.g., lead, copper, mercury, silver, cadmium) to both marine and freshwater coastal systems. One particularly sensitive ecosystem in this environment is wetlands, which harbor the majority of avian populations and provide a natural biogeochemical filtration of potentially harmful constituents in the interface between land and water. The input of metals from both overland and atmospheric sources to wetland settings, coupled with their incredible capacity to adsorb and collect these metals, has several implications. First, the high concentrations of particularly biotoxic metals in these environments can have a negative impact on ecosystems. Second, the storage capacity of wetlands is highly dependent on their hydrologic balance; modification or even restoration of these loaded systems has the potential to release potentially biotoxic metals to coastal systems on a wide scale. This special session would solicit papers on a wide range of topics dealing with metal cycling in wetland systems, including but limited to studies of deposition chemistry and rates of metals, internal cycling of metals in a variety hydrologic conditions, ecosystem dynamics in metal-loaded environments, estimates of release rates of metals under scenarios of disturbance/restoration, biological responses to individual biotoxic metals, and modeling of future conditions of metal cycling in coastal wetlands.

SS5.02: Elemental Cycling Under Suboxic/Anoxic Conditions
Organizers: James W. Murray, University of Washington (jmurray@u.washington.edu) and Mary Scranton, SUNY Stony Brook (mscranton@notes.cc.sunysb.edu)

Life on Earth emerged under anaerobic conditions and most of the fundamental biochemical and metabolic pathways evolved before the atmosphere contained oxygen. At present, true anoxic conditions are generally restricted to sediments and basins isolated from oxygenated deep-sea circulation, although enhanced oxygen consumption by organic matter decomposition and slow downward mixing and diffusion of dissolved oxygen from the surface waters can lead to oxygen-deficiency in the water column (OMZ) in highly productive waters. In the last couple of years, euxinic marine environments have become a topic of intensified attention of scientists from a broad range of disciplines. This increasing interest is reflected by a high number of cruises in different regions of the world ocean where oxygen-limited conditions occur, e.g. several cruises have recently been conducted to the Black Sea and Cariaco Basin with an emphasis on the biogeochemistry of the water column. The session will focus on four main topics: (i) nutrient and metal cycling at the oxic/anoxic interface, (ii) ecology of the oxic/anoxic interface, (iii) biogeochemistry of anaerobic methane oxidation, and (iv) oceanic anoxic events in the past.

SS5.03: The Biogeochemical Cycling of Iron in the Ocean – From Genes to Gyres
Organizers: Philip Boyd, National Institute of Water and Atmosphere, Dunedin, New Zealand (pboyd@alkali.otago.ac.nz), Mike McKay, Bowling Green State University, (rmmckay@bgnet.bgsu.edu), Steve Wilhelm, University of Tennessee (wilhelm@utk.edu), Russell Frew, University of Otago, Dunedin, New Zealand (rfrew@alkali.otago.ac.nz)

Research over the last decade has demonstrated the pivotal role that iron supply plays in controlling the physiology of both autotrophic and heterotrophic microbes, and its subsequent influence on ecosystem structure and the ocean carbon cycle. Studies over this period have yielded insights into the magnitude of iron supplied from both the atmosphere and the deep ocean. Others have investigated the nature of complex interactions between iron chemistry, photochemistry and iron acquisition strategies by the biota, and recently the first biogeochemical budgets have been constructed. In spite of many unknowns, they indicate that iron is recycled rapidly and efficiently in marine environments. In recent years, there has been a move away from solely employing iron perturbation studies to look at the role of iron supply in the oceans: investigators have begun to explore in detail aspects of iron biogeochemistry, with a view to elucidating the key fluxes and pools of iron in the ocean, and hence the construction of improved models through a better understanding of this biogeochemical cycle. New tools and approaches such as molecular probes and chemical tools, offer great potential in developing the field of iron biogeochemistry. In this session, we invite contributions from a wide range of disciplines ñ from physics to microbial physiology that provide insights into the key processes of the biogeochemical cycling of iron in the ocean, the identification and quantification of the main iron pools and fluxes, and how such controlling factors may vary both in time and space.

SS5.04: Bioturbation: Who, When and Why?
Organizers: C.R. Smith, University of Hawaii, (csmith@soest.hawaii.edu) and B.P. Boudreau, Dalhousie University (bernie.boudreau@dal.ca)

Bioturbation has profound effects on the composition, fabric, and structure of sediments, as well as on sediment-dwelling biota. Specific examples of these effects include the promotion of diagenetic reactions that otherwise would not occur, the alteration of the apparent timing and magnitude of signals in the geological record, the modification of the faunal distributions, and the creation of density heterogeneities in sediments with important implications to acoustic imaging. While there have been great advances in our understanding of bioturbation, it has not been the focus of an intensive examination at an international meeting in the recent past. Thus, this special session offers a singular opportunity for scientists and engineers interested in the phenomenon of bioturbation to gather and discuss the modes and mechanics of bioturbation, the effects and feedbacks on the benthic ecology and sediment properties, and the models that can be employed to describe and predict these effects and consequences. The emphasis will be on recent advances in understanding the nature of bioturbation, its effects on sediments and benthos, and the use of cutting-edge technologies and models.

SS5.05: Sedimentary Indigestion: Bubbles and Ebullition
Organizers: B.P. Boudreau, Dalhousie University, (bernie.boudreau@dal.ca) and C. Martens, University of North Carolina (cmartens@marine.unc.edu)

Bubbles form in soft sediments when porewaters become supersaturated with respect to dissolved gases (methane, oxygen, carbon dioxide) as a result of in situ chemical reactions, such as the cases of methane through methanogenesis and oxygen via phytosynthesis, or the dissolution of gas hydrates, or transport from deeper sources. This session will examine the mechanisms of bubble formation from these sources, the modes and mechanics of bubbles rise and escape from sediments (ebullition), their relation to and influence on sediment physical and geochemical properties, the role of bubbles in the formation and dissolution of gas hydrates, novel methods for imaging bubbles in sediments, the mode of formation and significance of bubble creation in benthic biofilms, and the acculumation of bubbles into large unstable voids and their catastrophic failure (pockmarks). Experimental, observational, and theoretical studies are equally appropriate for this session.

SS5.06: Advances in Diagenetic Modelling
Organizers: Christof Meile, Indiana University – Bloomington (cmeile@indiana.edu), Philippe Van Cappellen, University of Utrecht (pvc@geo.uu.nl) and B. P. Boudreau, Dalhousie University (bernie.boudreau@dal.ca)

Mathematical modeling is a powerful approach to assess the nature and relative importance of diagenetic processes, to calculate fluxes across the sediment-water interface, to estimate in situ rates of diagenetic reactions, and to predict the geochemical evolution of sediments as a result of changes in inputs or other environmental conditions. Since their introduction, diagenetic models have progressed from simple linear steady-state models to an array of mathematically advanced forms, including coupled sets of non-linear partial differential equations, integro-differential equations, inverse models, stochastic differential equations and Monte Carlo simulations, and random-walk models. Current models attempt to capture the full complexity of coupled interactions between physical processes, chemical reactions and biological activity in sediments. This special session is designed to bring together researchers who develop diagenetic models with the community of (potential) users. The primary aim is to discuss, compare and evaluate advances in this field in the past decade, and to inform marine and environmental scientists and engineers of the vast range of germane problems that can be addressed through mathematical modeling. The secondary aim is to set directions for future developments in diagenetic modeling, through close collaboration with experimentalists. Contributions presenting novel methods and models, as well as their applications are encouraged. While the focus of the session is on aquatic sediments, contributions dealing with related reactive transport systems, e.g., biofilms, hydrothermal vent systems, aquifers, and estuaries, are also welcome.

SS5.07: Response of the Upper Ocean to Mesoscale Iron Enrichment
Organizer: Maurice Levasseur, Université Laval (maurice.levasseur@bio.ulaval.ca), Atsuschi Tsuda, University of Tokyo (tsuda@fra.affrc.go.jp), William Miller, Dalhousie University (william.miller@dal.ca), William Cochlan, Romberg Tiburon Center for Environmental Studies (cochlan@sfsu.edu) and Richard Rivkin, Memorial University of Newfoundland (rrivkin@mun.ca)

Mesoscale iron enrichment studies have been carried out in all the major HNLC biomes, i.e. the Southern Ocean, the Equatorial Pacific and the North East and North-West Sub-arctic North Pacific. These regions have different hydrographic regimes, temperatures, irradiance fields and planktonic food web structures, thus the ecosystem response to iron fertilization should also differ among regions and for different times of year. This special session invites papers on the physics, chemistry and biology for the mesoscale iron enrichment studies that have been carried out in the different HNLC regions, including related atmospheric/climatic responses. The goal of this session will be to compare the observed and modeled responses and identify the differences among HNLC regions. This is a necessary prerequisite for the modeling of the effect of in Fe input in the contemporary and future ocean under a changing global climate.

SS5.08: Dynamics of Dissolved Organic Material in Marine and Freshwater Environments
Organizers: James McManus, Oregon State University (mcmanus@coas.oregonstate.edu) and James Cotner, University of Minnesota (cotne002@umn.edu)

Dissolved organic matter (DOM) is one of the largest reservoirs of carbon on the planet and the cycling of dissolved organic carbon and nutrients can play an essential, if not dominant, role in regulating ecosystem carbon flow. Furthermore, DOM plays a key role in connecting terrestrial systems to both freshwater and marine systems. For example, in a variety of typically oligotrophic systems, respiration outpaces particulate carbon production, and one common mechanism to sustain this apparent imbalance is through an allochthonous dissolved organic subsidy. Also, for some systems inorganic nutrient availability may be sufficiently low that primary production relies on dissolved organic nutrients. This session seeks abstracts that focus on the importance of DOM cycling in both marine and freshwater systems. Abstracts that compare/contrast these two regimes are particularly encouraged.

SS5.09: Dynamic interactions between particulate and dissolved mineral and organic matter
Organizers: Yoshimi Suzuki, Shizuoka University, Shizuoka, Japan (seysuzu@ipc.shizuoka.ac.jp) and Rob Armstrong, Stony Brook University, Marine Sciences Research Center (rarmstrong@notes.cc.sunysb.edu).

This session will focus on processes that determine elemental and compound ratios in particulate and dissolved organic matter. Of special interest are the ratios of carbonate minerals and biogenic silica to organic carbon in sinking particulate matter, the roles of mineral dissolution in the degradation of organic matter, and the effects of mineral materials on the interconversion of particulate organic matter and dissolved organic matter. Contributions reporting results from field work, laboratory experimentation, and/or modeling are welcomed.

SS5.10: Marine Biodiversity and Ecosystem Functioning
Organizer: John J. Stachowicz, University of California at Davis (jjstachowicz@ucdavis.edu) and J. Emmett Duffy, Virginia Institute of Marine Science (jeduffy@vims.edu)

Human activities are currently causing a loss of biodiversity on a global scale equivalent to that of previous mass extinction events. Even on a local scale, biodiversity of many ecosystems is declining as a result of habitat destruction, eutrophication, and overharvesting. Because different species often participate in different biogeochemical cycles, have unique nutrient requirements or fill unique consumer niches, the loss of species could cause a major disruption in the function of ecosystems. The functional consequence of biodiversity loss is a major research focus in terrestrial plant ecosystems. In contrast, our understanding of the consequences of biodiversity reductions in aquatic systems is more diffuse and comes from fields as diverse as microbial ecology, biogeochemistry, benthic ecology and fisheries science. Further, the greater average intensity of trophic interactions, and consequently greater emphasis thereon, in aquatic systems has the potential to increase the breadth of our understanding of the consequences of biodiversity loss beyond the producer level being studied by terrestrial ecologists. This is especially critical given that species in higher trophic levels appear disproportionately prone to extinction. However, potential insights from aquatic systems will only be realized if researchers from these diverse approaches interact and a synthesis can be achieved. This special session represents a start toward that end. Contributed papers are invited that touch on the relationships between species diversity and key ecosystem functions including (but by no means limited to) primary or secondary production, nutrient cycling, carbon flux, and ecosystem stability or resistance to invasion, disturbance or environmental change. Any study of functional differentiation among species can potentially be brought to bear on this critical question. Organizers hope to bring together a group of oceanographers, biogeochemists and ecologists whose research addresses the common theme of the role of species diversity in ecosystems.

SS5.12: Interactions and Feedbacks Among Marine Pelagic Ecosystems, Biogeochemical Cycles and Climate, in a Globally Changing Environment
Organizers: Richard B. Rivkin, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada (rrivkin@mun.ca) and Louis Legendre, Laboratoire d'Oceanographie de Villefranche, Villefranche-sur-Mer, France (legendre@obs-vlfr.fr)

For over a decade, it has been recognized that there are relationships between food web structure and biogeochemical cycles. It is only recently however that these interactions has begun to be quantified. Moreover, it is through their interactions with biogeochemical cycles that marine food webs feedback to the climate. This special session will examine the observational, experimental, and conceptual and numerical modeling studies of the interactions and feedbacks among food-web, biogeochemical and climate processes.

SS5.13: Eutrophication of Coastal Waters
Organizer: Alice Newton, University of Algarve, Faro, Portugal (anewton@ualg.pt)

Eutrophication in coastal waters is manifesting itself as a global problem. Well-studied systems include the Chesapeake Bay, the Gulf of Mexico, the Baltic and the Venice (Italy) lagoon although many estuaries and coastal waters are now affected, increasingly in developing countries. While the reports of eutrophication continue to increase the point sources of nutrients are being addressed by engineering solutions but the diffuse sources, such as the atmosphere and agricultural runoff, are still a challenge. Eutrophication of coastal waters is fundamentally a “holistic” problem of oceanography that involves mechanisms such as river and atmospheric inputs, tidal dilution and transport, as well as the biological oceanography of phytoplankton blooms. Nevertheless, the problems caused have serious socio-economic impacts on the valuable coastal zone and solutions also must address socio-economic aspects of industry and agriculture.

SS5.14: The Aquatic Gel Phase: Its Role in Biogeochemical Cycles
Organizer: Pedro Verdugo, University of Washington (verdugo@u.washington.edu)

This symposium focuses on the intricate combination of biological and physicochemical processes by which dissolved organic matter (DOM) is formed and cycled in the ocean. Despite its part-per-million concentration, seawater DOM is of interest as: (a) a necessary intermediate for the assimilation of most substrates by marine heterotrophs, (b) one of the largest pools (~700 x 1015 g C) of actively cycling reduced carbon on earth, (c) an active component of seawater that affects such bulk properties as light transmission, trace metal transfer and organism behavior, and (d) a molecular Rosetta stone (provided by the most slowly cycling components) to the selectivities of the major removal processes. The interlinked biological and physical processes by which bioactive elements are cycled in the ocean represent on of the most complicated and critical systems on earth. Although living organisms are the ultimate source and sink of the organic matter in which these elements primarily cycle, the major currency for both their active transfer and long-term storage in the ocean is as small, nonliving organic molecules. This “molecular prerogative” results because the biomacromolecules (e.g. polysaccharides and proteins) composing organisms and tissues must be broken down to inert subunits (e.g. oligosaccharides and oligopeptides of 5-10 units) of less than about 600 amu (daltons) to pass bacterial cell walls prior to complete intracellular respiration. In the ocean, much of this molecular dismantling is accomplished by bacterial exoenzymes operating on submicron units of dissolved organic substrate. Nutrient elements carried through this “bacterial loop” become available for conversion back to living particulate form either through photosynthesis or via transfer of bacterial production up food webs through protists and zooplankton. Such biologically mediated cycling between dissolved and particulate organic forms is critical on a larger scale to the transfer and fate of nutrients because only particles can sink to selectively transport bioactive elements from the lighted surface ocean into deep storage below the thermocline. The latter transport process has become known as the “biological pump” for removing climatically active elements (such as carbon) from direct contact with the atmosphere. Dissolved organic molecules that for some reason have been “stranded” between the living and assimilable size extremes (~1000-1 nm), constitute the most abundant form of remnant biochemical in the sea, outweighing total living biomass by a factor of roughly 200 (Hedges and Oades, 1997). Recent evidence for spontaneous assembly of colloidal marine molecules into microscopic polymer gels (Chin et al., 1998) has fundamentally changed the way that oceanographers think about processes linking the microbial loop and biological pump to the rest of the biosphere and the geosphere (Wells, 1998). The observation that colloidal-size organic molecules found in surface seawater can spontaneously self assemble forming microscopic networks has been recently found to also take place in riverine water (Kerner et al 2003). The implications of a self assembly process of DOM biopolymeric material, and the role of the resulting microgels as well as the role of larger gel material found in sea and riverine water are very broad and represent a critically important aspect of biogeochemical cycling. This interdisciplinary symposium will start with a tutorial on the physics of polymer gels, and will include geochemists, marine microbiologists, and geophysicists dealing with particle hydrodynamics in seawater.

SS5.15: Biogeochemical Processes Within Freshwater Influenced Coastal Systems
Organizer: Joseph E. Salisbury, University of New Hampshire (joe.salisbury@unh.edu)

Biogeochemical processes within freshwater-influenced coastal systems coastal systems influenced by freshwater discharge are regions of intense biogeochemical cycling and trophic exchanges. The diagenic pathway and fate of terrestrial carbon in the ocean is an open question. Important questions remain concerning the status of coastal systems as global sources or sinks for carbon, and the role that human activity and climate change will play in the future. It is also unclear what effect changes in biological community structure have on the cycling of biogeochemical constituents and trophic status of these systems. This session will include papers that address the processes that control the delivery, transformation, transport and fate of bioactive constituents in freshwater-influenced coastal systems. Papers reporting on process studies, modeling, and observations are all encouraged.