Vents Program

Accomplishments in FY 99

The second annual expedition to the NeMO (New Millenium Observatory) site in the vicinity of Axial Volcano was conducted in June and July, 1999 from the R/V’s Thomas G. Thompson and Wecoma. Twenty-one dives were made this year at NeMO in the area of Axial Volcano with the Canadian ROV ROPOS. While the Axial Volcano continued in a post-eruptive phase following the eruptive activity of January, 1998, many interesting investigations continue at the site. Among them were:

The discovery of several previously unknown hydrothermal vents south of Axial caldera in a new lava flow.
High-resolution sea-floor mapping in the northern portion of the new lava flow using the Imagenex sonar system mounted on ROPOS
An array of seafloor miniature temperature recorders (SMTRs) was deployed near several seafloor vents in the Axial caldera to monitor trends in individual vent temperatures, to correlate temperature changes with geophysical events, if possible, and to compare seafloor temperature changes to changes observed in the water column by annual ship surveys and in situ temperature recording moorings to assess the impact of hydrothermal fluxes from the Axial Volcano.
Using ROPOS, engineers freed from the new lava the Volcanic Systems Monitor that that had been embedded in lava following the January, 1998 eruption.
For the first time, images and data from a remote seafloor-mounted camera and array of temperature sensors were transmitted in near-realtime via acoustic telemetry and satellite to the laboratory.
1999 marked the second year (and third cruise) of monitoring hydrothermal changes resulting from the 1998 eruption on Axial Volcano. A series of CTD tows and casts found that the inventory of hydrothermal heat and particulate matter in the water column over Axial continued to decline. The decrease of both species can be modeled as a power law, with the rate of decline similar to that observed at CoAxial following the 1993 eruption.
Between the 1998 and 1999 field seasons, Vents scientists improved on the prototype hydrothermal fluid and particle sampler (HFPS) and then used it to collect 120 samples during 5 ROPOS dives at Axial Volcano. A major emphasis of the NEMO project is the investigation of the sub-seafloor microbial biotope, and the HFPS is the primary tool to recover samples. 1999 was our second year of studying the hydrothermal effects of the January, 1998, volcanic eruption. The time series and spatial extent of our diffuse vent fluid sampling in the eruption area are unprecedented, and we are gaining new insight to the chemical and microbiological importance of low-temperature reaction particle samples was characterized and revealed very high diversity in both particle-attached and "free-living" microbes.
The Cleft segment time series plume chemistry studies continued in 1999. Total CO2 measurements were added to the suite of analytes, to provide background values for future eruptive events in this area.
The Axial Volcano post eruption monitoring continued in 1999 as well. Significant decreases from 1998 were observed in CO2, Fe, and Mn.
The primary objective of the VENTS Suspended Matter Project is to provide a better understanding of the evolution of particulate hydrothermal chemical species, including S and Fe, near deep-sea vents. These chemical species provide the metabolic energy resources for hydrothermal particle-bound bacteria, and the resulting vent-related ecosystems. Towards this end, we are focussing on hydrothermal sources and sinks for particulate sulfur. We have developed a procedure for collection, preservation and analysis of particulate non-volatile and volatile sulfur by x-ray fluorescence spectrometry. Coupled with our SEM methods, these procedures help us to differentiate between biotic and abiotic forms of sulfur (Figure 1). We are working closely with the microbiologists at UW and WWU to identify particle-bound bacteria. Together with the micobiological results, we will elucidate the efficiency of the microbial systems with respect to the chemical species emanating from deep-sea vents.

Other major activities and accomplishments included:

Autonomous hydrophones were deployed in the North Atlantic to monitor seismic activity in the mid-Atlantic Ridge. Another array of hydrophones was deployed in the North Pacific and Gulf of Alaska to aid in studying the behavior of marine mammals in that region.
Thermistor and current measurements at Axial Volcano were used in a inverse calculation to infer active-vent locations that might have been overlooked by sea floor towed-instrument surveys. Results suggest, among other things, the likelihood of hydrothermal sources on the eastern flank of the volcano during 1998, but ones which ceased discharging by summer 1999.
Numerical experiments of buoyant convection from line segment sources were undertaken for both laboratory and ocean scalings to examine the number of individual bolues into which rising event plumes might break. At ocean rotation rates and stratification, breakup is borderline. Results suggest an event plume source must be actively discharging along more than several kilometers of seafloor before even two plumes at the level of neutral buoyancy could be created.
Publication of a paper in Earth Planetary Science Letters addressing the way in which event plumes, or megaplumes, are produced during magmatic events on mid-ocean ridges. This paper relied on the helium and heat content in these event plumes to place constraints on the mechanism of their formation.
Completion of a major expedition exploring hydrothermal vent sites along the southern East Pacific Rise using the deep submersible Alvin.