OS51D-01 INVITED 08:05h
Jack Dymond's Deep Insights
Most people do not know that Jack Dymond was a major influence on several aspects of current deep-sea research. Along with Margaret Leinen and Jack, we were part of the first Alvin dive program on the Endeavour hydrothermal field in 1984. Jack was working with Rick, on a sediment-trap study of the overall carbon fluxes in the vicinity of the Endeavour hydrothermal systems in an effort to address a question that Cindy Lee had posed about the overall carbon production from hydrothermal vents. At the time we were recognizing and naming many of the 20- to 40-meter-high sulfide structures in the Endeavour field (Hulk, Grotto, Dante, Dudley, Bastille), Jack commented that it was a shame that the world could not see these magnificent edifices or watch endlessly awesome black smokers. His feeling was that some vent sites should be converted to National Parks to preserve them from invasion by enthusiastic scientists, yet he clearly had the vision that the public should be given a sense of the grandeur involved locally, as well as the vastness of the 70,000-km ridge-crest system running through every ocean. Within a year we started talking about the RIDGE Program, and Jack was an early and enthusiastic participant in the design and development of RIDGE. Jack was among the first to encourage multi-disciplinary research at the hydrothermal vent sites. Recognizing that deep currents are important to vent processes, he urged physical oceanographers to work with the chemists, biologists, and geologists and was personally responsible for Rick becoming interested in studying vents. We, the co-authors of this abstract, became close friends as a result of having been introduced to each other by Jack. Several years ago, we co-authored the first paper ever written on the possible influence of hydrothermal activity on the circulation of the Europan Ocean, a paper that we here dedicate to the memory of Jack. Finally, it was in part because of Jack's conviction that the world should know more about submarine hydrothermal systems, albeit in a manner we could not then imagine, that eventually led to developing the concept of a cabled ocean observatory. Technology evolved to allow us to design a system that would deliver considerable power and nearly inexhaustible bandwidth to major portions of the ocean basins, enabling an interactive form of oceanography that will be developed within the ORION program and that is now becoming a reality in the form of the Canadian NEPTUNE program. Within five years, these cabled systems will reach into the newly established Canadian Marine Protected area on the Endeavour Segment of the Juan de Fuca Ridge and will bring live-action high-definition video in stereo to anyone capable of logging onto the Internet. Jack Dymond was an inspiration to many communities, one of which was oceanography. We miss him tremendously.
OS51D-02 08:20h
Volatiles in Hydrothermal Systems: Then and Now
Jack Diamond was one of the principal investigators on the original proposal to dive on the Galapagos hydrothermal system. Jack participated on the cruise and, along with his graduate student (Richard Cobbler), made the first measurements of radon in hydrothermal systems. Louis I. Gordon and the author were also participants on this cruise and we made measurements of methane and hydrogen. In the ensuing 27 years much has been learned about volatiles in hydrothermal systems. For example, we have learned that phase separation and water/rock reactions play major roles in the volatile composition of hydrothermal fluids and that temporal variability is the rule rather than the exception. A summary of progress in this field will be given.
OS51D-03 08:35h
The use of 210Pb/Pb as a Tracer of Chemosynthetic and Photosynthetic Organic Carbon in Hydrothermal Vent Particles
Jack Dymond pioneered the use of sediment traps to understand the chemistry and flux of material emanating from submarine hydrothermal vents. For example, in one paper Roth and Dymond (1989) used the ratio of C$_org$/C$_CaCO3$ between traps to determine the fraction of chemosynthetically derived organic carbon (OC) in collected material. Knowledge of the relative proportion of chemosynthetic and photosynthetic OC is critical to mass balance calculations of hydrothermal OC inputs/exports and can also be determined from the 210Pb/Pb ratio measured in the sediment traps and suspended particles. The 210Pb/Pb ratio of particles in the ridge environment is diagnostic of the source and path of the particles. At the Endeavour Ridge, particles emanating directly from vents have a ratio close to that of the vent fluids and basalt ($\sim$0.5 dpm/$\mu$g) from where they are derived, and subsequently scavenge additional 210Pb as they disperse. It is therefore reasonable to assume that particles with a 210Pb/Pb ratio of 0.5 are "fresh" and any OC associated with them must be chemosynthetic in origin. This ratio is much smaller than that of typical (non-vent) seawater ($>$3 dpm/$\mu$g) and thus particles in the upper water column (or distant from vents) will have a high 210Pb/Pb ratio and contain OC predominantly from photosynthetic production. The 210Pb/Pb ratio of Endeavour particles increase markedly from $<$0.70 at a vent orifice, to 1.22 within the buoyant plume ($\sim$20 ma vent), to 1.4 downstream (~2 km) within the neutrally-buoyant plume at 2100 m depth. These plume particles are distinguished from those above the plume (at 1700 m with 210Pb/Pb = 3.2 dpm/$\mu$g) by lower 210Pb/Pb ratios but much higher 210Pb content. The high Pb content attests to a hydrothermal component of the plume particles. Therefore, the 210Pb/Pb ratio can be used to define two conservative endmembers for a particle population: those derived from the vents will have a ratio of 0.5 (with 100% chemosynthetic OC) and those derived from the surface ocean will have a ratio of 3.2 (from the 1700m trap, with 100% photosynthetic OC). With these endmembers, a linear relationship between the % chemosynthetic OC and 210Pb/Pb is: % OCchemo = -37 x (210Pb/Pb) + 118.45 The flux of OCchemo can be compared to the downward flux of photosynthetic OC from the surface ocean by another method utilizing 210Pb as a proxy of OC flux in the Pacific which was introduced in Moore and Dymond, (1988).
OS51D-04 08:50h
The Impact of Microbes on the Composition of the Ocean Crust and Seawater
Microbes attack volcanic glass and primary igneous minerals in aqueous environments and they participate in the transformation of glass and minerals into secondary minerals such as clay. This transformation also proceeds in the absence of microbes. In either case some elements go into solution and others are sequestered in secondary minerals. Our hypothesis is that in the ocean crust secondary minerals produced by abiotic reactions are chemically distinct from those produced by microbial attack. If this is true, then microbial attack on volcanic rocks could affect the composition of the ocean crust and sea water. The best source of deep sea volcanic rocks to test this hypotheses is the Ocean Drilling Program's archived collection. We selected several samples from this collection and used an electron microprobe to measure the composition of secondary clays that were deemed to be produced either bioticly or abioticly. Abundance measurements were obtained for eleven elements (Na, Mg, Al, Si, P, Cl, K, Ca, Ti, Mn, and Fe). We used Principal Component Analysis to extract three factors that were linear combinations of the eleven elements and that accounted for more than 80% of the data variance. These three factors were used as inputs to a stochastic, non-linear, Artificial Neural Network that demonstrates that abiotic secondary minerals are chemically distinct from biotic secondary minerals. Significant differences in clay compositions were found for MgO (0.2), MnO (0.3), K$_{2}$O (3), CaO (2), TiO$_{2}$ (3), and possibly FeO (1.2). (Numbers in parentheses are biotic:abiotic oxide wt. % ratios.) This result suggests that biotic alteration of the ocean crust will release more MgO and MnO from the rocks and sequester more K$_{2}$O, CaO, TiO$_{2}$, and possibly FeO in clay than abiotic alteration. The impact of microbial alteration on the composition of the crust therefore depends on the fraction of basalt alteration that is caused by microbes. The impact of microbial alteration on the composition of sea water, also depends on this fraction, and whether released elements Mg and K are sequestered elsewhere in the crust or are vented to the ocean.
OS51D-05 09:05h
Using the Silica Cycle to Re-assess the Role of Continental Margin Systems in the Deep Biological Carbon Pump
Predictions of future climate require that the long-term partitioning of carbon dioxide between the oceans and atmosphere be estimated. Deep sea sediments receive only a small amount of organic carbon and waters above the base of the main thermocline exchange with the atmosphere on time scales of generally less than a few decades. Therefore, the most important oceanic reservoir for carbon storage on climate-change time-scales is oceanic deep water. Studies of the biological pump must focus on those ecosystems that supply the majority of the flux to the deep ocean, i.e. to below approximately 1000 m. Previous studies of deep organic fluxes based on benthic flux compilations have indicated that regions near continental boundaries, particularly those that experience significant, wind-driven coastal upwelling, supply a disproportionately large proportion of the organic carbon to the deep ocean. Margin systems in general were estimated to account for approximately 1/2 of the total deep biological pump. Despite this potential role, process studies of carbon fluxes have not focused on these environments. Because processes such as benthic exchange, iron input from shelf sediments, denitrification, and nepheloid layer transport are unique to margin systems, open ocean process studies may not provide an accurate assessment of carbon dynamics in margin settings. Recent publications report that 1. POC and opal fluxes are not strongly correlated in open ocean sediment trap samples, 2. measured opal fluxes in traps are less than those inferred from a global circulation model (GCM) and 3. silica burial is greater in continental margin sediments and less in the southern ocean than previously reported. Here we present a compilation of benthic flux chamber results from margin systems that confirm a strong correlation between POC and opal fluxes, consistent with ecological models. These results support the conclusion that there is a strong link between organic carbon and Si cycles and suggest that the discrepancy between GCM and open ocean trap fluxes may be balanced by an opal flux along continental margins. Taken together, these results support previous benthic flux studies that suggest that continental margin systems significantly contribute to the deep biological carbon pump.
OS51D-06 09:20h
Evolution of Iron Along the Conveyor Belt: North Atlantic to North Pacific
We have obtained three new full water-column profiles of iron in the ocean from regions where no data was previously available: in the western North Atlantic (10$\deg$N 45$\deg$W and 24.5$\deg$S 37$\deg$W), and in the central North Pacific (26$\deg$N 175$\deg$W). Together with other profiles in the literature, we now can describe the large-scale deepwater ($>$2500 m)distribution of Fe with some confidence. In the North Atlantic, deepwater Fe is $\sim$0.7 nmol/kg; by the time NADW has traveled to 24.5$\deg$S in the western Atlantic, Fe has decreased to $\sim$0.5 nmol/kg. The salinity and micronutrients are the same at the northern and southern sites, so we attribute the Fe decrease to particulate scavenging as the water travels south. Using C14 estimates for the transit time between these sites, we estimate a deepwater scavenging residence time of 270 +/- 140 years. Most of the decrease occurs in the 0.02-0.4 um colloidal fraction. By the time deepwater has reached the north Pacific, Fe has decreased slightly; three stations (two at HOT-ALOHA near Hawaii and the other further to the northeast) show deepwater Fe levels of 0.45 +/- 0.05 nmol/kg; $>$75% of this Fe is in the soluble $<$0.02 um fraction. These deepwater data help put to rest the notion that "dissolved" ($<$0.4 um) deepwater Fe is fixed at $\sim$0.6 nmol/kg, but raises the question of whether deepwater "soluble" ($<$0.02 um) iron is fixed at $\sim$0.4 nmol/kg, with most of the deepwater reactivity confined to the colloidal fraction.
OS51D-07 09:35h
The trace element fingerprint of phytoplankton in ocean particulate matter: positive ID or smudged residue?
The biogeochemical cycles of many trace metals are directly or indirectly driven by the growth, vertical transport, and remineralization of phytoplankton. One of Jack Dymond's research interests was how the geochemical signals of biological processes determine the composition of sinking particulate matter and ultimately the sedimentary record. It seems obvious that there must be links between fundamental aspects of the physiology and biochemistry of phytoplankton growing under a range of oceanic conditions, and the composition of bulk oceanic particulate matter. However, too few attempts have been made to use experimental or observational elemental data to constrain predictions of particulate metal fluxes and their relationship to primary biological processes. On one hand, laboratory-determined metal quotas may suffer from unrealistic species composition and metal availability, and on the other hand attempts to analyze phytoplankton in field samples are typically frustrated by the inability to separate living cells from the abundant organic and inorganic nonliving particles found in most natural waters. Using multi-element analyses of suspended particles in Mid-Atlantic Bight shelf-slope surface waters, and correction factors for non-living particles, we argue that phytoplankton dominate bulk particulate composition for some metals (Zn, Cu, Cd), that non-living particles dominate for other metals (Ti, Fe), and that some metals may fall into either group (Mn, Co). The results show quantitative consistencies with results from diatom lab cultures, and hold promise for improved predictions of vertical metal fluxes associated with carbon export from the euphotic zone of characteristic oceanic regimes.
OS51D-08 09:50h
Prospects For a Carbon ARGO [ II ]
Understanding the dynamics and sedimentation of biologically fixed particulate organic and inorganic carbon (POC and PIC) is fundamental to the prediction of future levels of atmospheric carbon dioxide. Over the last four years LBNL has been working to bridge a major 'space-time' gap in upper ocean carbon cycle observations. We have launched twelve robotic Carbon Explorers built on SIO's Orbcomm/GPS enhanced Sounding Oceanographic Lagrangian Observer (SOLO). These 'souped up' versions of ocean-profiling ARGO floats, operating in remote and stormy seas, have returned in real-time year-long high-frequency records of POC variability and recently have explored the systematics of carbon sedimentation to kilometer depths. We briefly recap the success of a new fast profiling optical sensor for PIC (sensitivity better than 0.1 $\mu$M) which was deployed during routine CTD/rosette casts during the R/V Ron Brown June - July 2003 reoccupation of WOCE A16N (Iceland to Madiera) in the N Atlantic Ocean. Our primary aim is to report on the development of paired autonomous imaging sediment traps designed to optically record hourly variations of POC and PIC flux at depth for weeks to months. Preliminary analysis of 22 days of observations achieved this year near Hawaii indicate a major contribution of zooplankton parts to carbon flux at station ALOHA. We further recorded multiple events of simultaneous arrival of fecal material and associated zooplankton feeders. This supports the importance of such animals in determining the attenuation of carbon flux to the deep sea. The success of the Carbon Explorers, the new PIC sensor, and the developing capability for season to year-long high frequency records of POC and PIC carbon sedimentation in the very observation-poor but biologically-active upper kilometers of the ocean suggest excellent prospects for a 'Carbon-ARGO'.