OS52A-01 10:25h
Particle Fluxes in the Marginal Seas of Antarctica: A 20-year Synthesis in Honor of Jack Dymond
One of Jack Dymond's long-standing scientific passions was the study of particles moving through the ocean water column. Jack's pioneering work in this area in the 1970's and generous mentoring of others throughout his career lead directly to the first authors involvement in sediment trap studies. Here we present a synthesis of 20 years of particle flux studies in coastal Antarctic (including the work of Collier and Dymond et al.) and highlight some of the important features and unresolved issues related to integrating particle trap interceptor data with other measures of production, transport, and deposition. The first sediment trap arrays were deployed on the Antarctic shelf in 1981 and 1982 in the Antarctic Peninsula. Simple instruments were also deployed in 1984 and 1986 in the Ross Sea. Since then, several nations (US, Italy, New Zealand) have recovered time series sediment trap data on moorings in both of these areas. This current synthesis makes use of data from approximately 22 sites, the majority of which are in the Ross Sea, and includes about 900 discrete samples of particles in vertical transit through the water column. We now have many complete time series that extend through the winter, allowing several important generalizations to be made. For example, annual particle-mediated organic C fluxes to below 200 meters in the Ross Sea average 4.4$\pm$3.3 g C m-2 yr-1. These values are significantly less than export fluxes calculated using short-term surface water mass balance approaches or Th isotope techniques yet are higher than seabed sediment accumulation rates. Intriguingly, seasonal seabed arrival rates of organic C estimated from in-situ summertime benthic respirometry studies yield C flux values similar in magnitude to those from sediment traps deployed at the same time, lending strong support to trap data. The cause of current disagreements between various methods of flux estimation may in fact not be solved until process studies are accomplished that extend through the austral autumn into winter and/or the biogeochemistry of Th is better understood in coastal area of the Southern Ocean. Nearly all Ross Sea particle flux time series show relative low sedimentation during the periods of highest primary production in surface waters followed by either events or periods of enhanced sedimentation during the latest austral summer and/or autumn. This high degree of decoupling between production and sedimentation is unusual and may well represent low grazing rates. It is likely that purely physical phenomena associated with the return of winter sea ice are responsible for enhanced autumn sedimentation in the Ross Sea. Compared to the Ross Sea region, biogenic fluxes in the Palmer Basin area of the Antarctic Peninsula are higher, but are more tightly coupled to productivity in surface waters. We conclude our synthesis by presenting a general model for particle production and deposition in several end-member environments of the Antarctic Margin.
OS52A-02 10:40h
MEDFLUX: Association of Organic Matter With Ballast Minerals in Sinking Particles
Recently we hypothesized that ballast minerals on sinking particles physically protect a fraction of their associated organic matter, and that the ratio of organic carbon to ballast is key to predicting variability in export fluxes and sinking velocities of organic carbon as estimated using radiotracers. To test this idea we collected sinking particles using sediment traps at the French JGOFS DYFAMED site in the western Mediterranean. We measured organic and inorganic carbon, and biogenic and total Si, Ca, Al and Ti, to characterize the organic and inorganic material in the particles. Using traditional assumptions to estimate organic matter, CaCO3, biogenic opal and the lithogenic fraction, we found that 20-30% of the material was unaccounted for. We will make wild and unsubstantiated speculations on what this material might be and how it might affect particle density.
OS52A-03 INVITED 10:55h
Jack Dymond's "Fingerprints" on Sediment Chemistry, Biogeochemical Fluxes, and my Career
I first met Jack Dymond as a graduate student at Oregon State University. He wasn't my thesis advisor. He wasn't even on my committee. But his ever so gentle counsel and his low key advice did much to shape my career, as a student, as a scientist, and later as an administrator of science. At the time, Jack was wading through the analysis of a very large number of surface sediment samples from the Nazca Plate as part of an IDOE project. The number and density of sampling was extraordinary for the time and his work showed that the geochemistry of the sediments could be deconvolved to understand the contributions of sediment sources over the entire plate. I had been planning to analyze DSDP samples from the equatorial Pacific to understand the history of siliceous sedimentation in that region and I began to talk with Jack about how I could use geochemical signatures to estimate the non-biogenic fraction of the sediment. When Jack's Nazca Plate paper came out, Debra Stakes and I decided to analyze all of my sample residues for the same elements that Jack had studied. In the only piece of bad advice that he ever gave me, Jack told me that it was a waste of time because there wouldn't be high enough concentrations of transition metals in the calcareous and siliceous sediments to measure. We insisted and Jack, in typical fashion, agreed to pay for reagents and give us instrument time without charge anyway. The larger than expected concentrations, and the even more surprising match between the accumulation rates of some the metals and the accumulation rates of biogenic sediment were the subject of many discussions, all of which ended in the need for more information on the composition, fluxes and transformations of biogenic sediment in the water column and in recent sediments. This, of course, became another of Jack's specialties: his designs for sediment traps were important contributions to the evolution of this important sampling device. His studies of fluxes in a wide variety of environments - from hydrothermal vent fields to Crater Lake --were critical to the development of modern biogeochemical cycling experiments and thinking. And this, of course, was only one of the fields in which he made major contributions.
OS52A-04 11:10h
High-Resolution Holocene Records of Paleoceanographic and Paleoclimatic Variability from the Southern Alaskan Continental Margin
We are investigating sediments from the fjords and continental margin of southern Alaska to develop high-resolution climatic and oceanographic records for the Late Quaternary. Our goal is to better understand linkages between climatic, terrestrial and oceanic systems in this tectonically active and biologically productive region. A field program was conducted aboard the R/V Maurice Ewing in August/September 2004 utilizing geophysical surveys (high-resolution swath bathymetric and backscatter imaging, shallow sub-bottom profiling, and where permitted, high-resolution seismic reflection profiling), piston and multi-coring, and CTD/water sampling at about 30 sites in this region. Cores are being analyzed for sedimentological, microfossil, geochemical and stable isotopic proxies, with chronologies constrained by Pb-210, AMS radiocarbon, tephrochronolgic and paleomagnetic dating. Our preliminary results demonstrate that these rapidly accumulating sedimentary archives can resolve environmental changes on annual to decadal timescales. Records of recent changes in lithogenic sediment accumulation and biological productivity on the Gulf of Alaska shelf track historical climatic data that extends to the early 20th century in this region. The records also correlate with multi-decadal climate regimes during the Little Ice Age as suggested by tree-ring, glacial advance and salmon abundance records from nearby coastal sites. Jack Dymond's enthusiasm for collaborative, interdisciplinary research will help guide us in unraveling the fingerprints of key processes in this relatively unexplored region.
OS52A-05 INVITED 11:25h
Global and marine paleoproductivity over the last 4 glacial cycles, constrained by the triple isotope composition of atmospheric O2
Photochemical reactions in the stratosphere impart a mass-independent fractionation to O2 in the global atmosphere that is attenuated by photosynthesis and respiration. The mass-independent fractionation is approximated by the term D17O = d17O - 0.5 d18O; d17O and d18O are the normal delta terms, with values in per mil. One can calculate rates of photosynthesis and respiration by the biosphere from measurements of the triple isotope composition of paleoatmospheric O2 (accessed from ice cores) and estimates of relative rates of stratospheric photochemical reactions through time. This approach invokes the fact that the magnitude of D17O depends on relative rates of stratospheric reactions, which produce the anomaly, and biological processes, which consume anomalous ambient O2 and replace it with photosynthetic O2, which is normally fractionated (D17O = 0). We present a record of D17O of paleoatmospheric O2 back to 400 ka based on analyses of Vostok and other deep ice cores. We estimate rates of stratospheric reactions in the past, and use these results to estimate past variations in planetary fertility. The results lead to two significant conclusions. First, gross ocean productivity, estimated after subtracting inferred terrestrial productivity from the global value, was generally higher during the ice ages than in interglacial times. Second, global productivity was not strongly forced by orbital variations, in contrast to the Dole effect (d18O of atmospheric O2 - d18O of seawater). This discordance raises the question of how the isotopic composition of O2 in the atmosphere can vary independent of variations in production.
OS52A-06 11:40h
Barium, Barite, and Export Production - Lessons in the Development of a New Proxy
The quantitative application of Ba as a proxy for export production in the ocean, first suggested by Dymond et al., (1992), is widely used for paleoproductivity studies at different oceanic settings and time scales. As for any promising and exciting proxy, the more we look the more complex it becomes. It is rare that in a first publication all of the potential complications and pit falls are identified and laid out. The evolution - from prediction, through testing, and refinement to better understanding and application, of the Ba, barite, productivity proxy, following the detailed outline of Jack's intuition and understanding will be presented. New trace element (Sr/Ba, SeO4/SO4) and isotope data (del44Ca) and barite accumulation rate results, that shed light on the mechanisms of barite formation and relation to export production will be discussed.
OS52A-07 11:55h
The Dymond Legacy: Oceans to Lakes and Back Again
Jack Dymond was an extremely unique scientist and colleague. His high level of professional ambition, risk-taking, and accomplishment were largely hidden behind a gentle and open-minded demeanor which always had room for thoughtful consideration of new ideas and different points of view. Although very different in personality, Jack shared with Degens and Edmonds the ability to encourage us to think broadly, globally, and to apply our expertise and knowledge to systems with which we might not be so familiar or comfortable. Jack believed that studying multiple systems was the best way to truly unravel the geochemical fingerprints recorded in sediments and rocks, thus leading us to a better understanding of how the earth, how Gaia, really works. To this end, Jack applied oceanographic techniques and concepts of marine geochemical cycling to large lakes of the world and encouraged a new generation of oceanographers to do the same. His exhaustive study of Crater Lake involving numerous oceanographic colleagues, and his collaboration with Siberian scientists working on Lake Baikal, provided extraordinary new insights into lacustrine hydrothermal systems which generated significant worldwide interest. Jack was an integrated thinker, an enthusiastic collaborator, and a great source of support and encouragement for his colleagues. His big picture view of the earth and its processes, many of which he knew intimately, was never intimidating, only enlightening. He drew upon his vast research experience and systems approach to demystify for his students and the public the important feed-backs between the biosphere, atmosphere, and lithosphere. In this manner, he made some of his most important contributions to science by providing the public and young scientists with an understanding and appreciation of the dynamic links between earth processes and global climate change.
OS52A-08 12:10h
Modeling the Effects of Changing Seasonal River Flow Rates on the Mixing of Reverse Osmosis Plant Effluent into the Pasquotank River in North Carolina
The goal of this research, begun Fall 2004, is to assess the seasonal impact of effluent from a reverse osmosis (RO) plant on the water of the Pasquotank River, a trunk river of Albemarle Sound in northeast North Carolina. Currently, the plant discharges about 103,000 gallons of high salinity (16 ppt) processed groundwater into Chantilly Bay in the Pasquotank River (0-3 ppt, depending on season) over an eight-hour operational day. The impact of the RO effluent on water chemistry and physical properties along the river bottom depends on the flow rate of the river. The Pasquotank is slower flowing (anecdotally, reverse flowing at times) during the generally dry summer season and faster flowing during the rainy winter season. This varying river flow rate may result in various effluent zones: a pool of effluent on the riverbed, a plume of effluent dissipating with downstream distance, or a minimal effluent signal near the outlet manifold. Modeling of seasonal data for the current rate of effluent discharge allows prediction of the effects of tripling the daily volume of RO plant discharge through round-the-clock plant operation, an outcome that seems likely in the near future due to residential growth in the county served by the plant. Data from fall and early winter 2004 will be presented. Water parameters (salinity/conductivity, temperature, pH, turbidity, Secchi depth, dissolved oxygen content, and dissolved major cation concentrations) are measured biweekly at nine surface stations (three water depths at each station) in the general vicinity of the effluent discharge outlet. Similar parameters are measured biweekly for Pasquotank River water at two stations upstream and two stations downstream of the outlet. River flow rates and discharge rates are measured weekly. The results of modeling using a two-end member mixing model and a normative analysis treatment will be presented. Additionally, modeling results for various possible changes (relocation of discharge outlet, outlet manifold redesign, reselection of wells for plant influent, rescheduling of discharge periods, effluent pre-discharge dilution, etc.) will be discussed.