News: Significant new activity is occurring at the EPR 9N Integrated Studies Site (ISS). [TCS]

05 December 2006

Overview of EPR ISS Eruption Response Efforts

Click the link below to download a PDF copy of Dan Fornari's overview of the eruption response efforts.

• Download PDF (2.1 MB)

A full resolution copy (4.8 MB) is available upon request.

24 July 2006

Atlantis Response Cruise

Based on both Alvin diving and use of a new fiber optic TowCam system, the Atlantis response cruise team substantiated that very young lavas blanket a considerable portion of the seafloor throughout the EPR axis and crestal region between ~9° 46'-56'N. There are many similarities between the most recent (2005-2006) eruption(s) and the last major eruption documented in this area (1991-1992), including emplacement style, aerial extent, and decimation of existing hydrothermal/biological sites within the Axial Summit Trough (AST). However, the recent eruption(s) appear to be more voluminous, particularly in the north (9° 53'-55'N). An off-axis fissure eruption was documented at ~600 m east of the AST between 9° 53'-54.5'N. Visually, the young lavas are extremely glassy, similar to those erupted in 1991-1992, but appear to have fewer phenocrysts and vesicles. Two of the OBS's that were not recoverable on prior cruises were imaged and both had lava covering their base. Attempts to pull them free with a grappling hook on TowCam were unsuccessful.

Extant biological communities and some high temperature vents were covered by lava. In a few places, new flow covers the base of older chimneys and partially covers collapsed pieces of hydrothermal chimneys. None of the old Bio-Geo Transect Biomarkers deployed in 1992 were observed. Hi-T fluid loggers were recovered from M vent, Q vent and Ty vent, providing time series records that span from ~ 2 years before the eruption to a few months after it. Previously well-characterized geologic features within the AST were not easily recognized during Alvin dives or TowCam surveys. The new flows appear to be thin (~1 m thick) both within and proximal to the AST and on the EPR crestal plateau.

A series of vent fluid chemistry samples were obtained, with main emphasis in just a few locations and sparse coverage in the north and south portions of the new flow. Co-located chemical and biological measurements employed an in-situ electrochemical analyzer (ISEA) in combination with temperature and pH probes, and a McLane pump. This work focused on diffuse flow areas. One ISEA was set for a several-month deployment.

The microbial communities in three main habitats were investigated, including: a) sulfide chimneys, b) surfaces of newly exposed basalt, and c) fluids emanating from diffuse flow vents. Cultivators and substrates were deployed in diffuse flow areas, for recovery after several months. No snowblower vents were observed but there was abundant flocculent material in the bottom water within the AST in a number of places. Several samples were obtained for cultivation experiments. Colonization devices were deployed for a few days. Many water samples were inoculated and incubated at a variety of temperatures. DNA extractions from biofilms were also performed successfully.

Two sediment traps that had been deployed by the New Horizon team were recovered for larval studies. The traps were re-deployed and programmed for recovery by a cruise this Fall. The planned establishment of a new geo-bio transect could not be accomplished due to problems with marker deployment, so will have to await the next series of cruises. However, markers were deployed at quite a few of the sampling sites.

The majority of venting macrofaunal habitats observed are supported by hydrothermal activity through broken sheet flow and collapse talus. Nascent diffuse flow communities in fluids up to 30°C were described. No extant communities were seen during either the dive or towed camera programs on the Atlantis cruise. Empty Riftia tubes were clumped and scattered up to 200 m outside the western walls of the AST. Only a single ~0.75m live Riftia was observed on basalt at the base of P Vent.

Contacts:

• Karen Von Damm (chief scientist and vent fluid chemistry PI)
• Dan Fornari (EPR Site Coordinator and Volcanology PI)
• Tim Shank and Rich Lutz (Macrobiology PIs)
• Stefan Sievert and Craig Taylor (Microbiology PIs)
• George Luther (Chemistry PI)

Figure 1: Map of Camera Tows (CT), Vent locations (red dots), and the New Horizon heading (NH06) [click to download PDF version].

22 May 2006

First look at seismic data from EPR 9° 50' N Ocean Bottom Seismometers

Results from Knorr OBS turn-around
Author: Maya Tolstoy, LDEO

Preliminary analysis of the seismic data indicates that the most pronounced activity occurred in the time period of late January 2006. This is based primarily on visual inspection of the data and follow up work will detail the significance of this time period relative to other time periods. Present analysis is limited to two instruments, with one on axis, and so interpretation of the period of most intense activity may be geographically biased toward that on-axis instrument. For further details regarding the seismicity with respect to planning response efforts please contact Maya Tolstoy.

Figure 1: Side-by-side maps of all TowYos & vertical casts (left) and TowCam tracks (right).

Change in Axial Summit Trough due to Eruption & Northern Extension

New Horizon data comparison
Authors: Dan Fornari & Adam Soule

Previous TowCam Axial Summit Trough rim depths are similar to what was measured during New Horizon studies, ~2496 meters, while Alvin AST rim depths were usually ~2500 m. It appears that there is an offset between TowCam and Alvin pressure depths. However, the trough appears to be about 10 m narrower and the floor depth perhaps 3-4 m shallower than the previous Alvin Imagenex data show. Shipboard analysis of TowCam images indicates that the northern extent of the flow is 9° 55.7' N. The width of the recent flow is not clear from these data, largely due to the small number of tow crossings.

Figure 2: AST crossing at Tica Vent
9° 50.42' N - 6NH TowCam#4

Preliminary Hydrothermal and Biological Results

Based on TowCam seafloor imaging surveys
Author: Tim Shank

Background The WHOI TowCam camera covers a relatively narrow swath (~6 x 4.5 meters at 5 m altitude). The camera was towed (with basically continuous coverage) from 9° 46' N to 9° 57.6' N resulting in a single swath within and just outside the Axial Summit Trough along this region of the seafloor. In order to improve this coverage, several camera dangles in specific areas, like the Bio9 area, north of the Biomarker 141 area, and the East Wall areas were conducted as well as survey lines that crossed the axis in several places just north of 9° 50' N (the Tica area). Hydrothermally active areas are defined as those in which venting was visually observed on the seafloor or that a ~0.5-2.0 increase in potential temperature was observed on the TowCam SBE25 CTD coincident with images of flocculent material in the water column (strongly suggesting that venting activity was just outside the cameras field of view). All tows were un-navigated, relying on ships GPS and layback calculations for final seafloor positions, rather than well-ranged transponder net. The likely error in seafloor positions given the estimated layback of the camera system is ~50 meters.

Distribution of Hydrothermal Venting Imaging surveys were conducted such that the survey coverage would be almost continuous (with overlapping latitudinal coverage linking separate tows) between 9° 46.0' N and 9° 57.5' N. The southernmost point of detected hydrothermal activity was at 9° 46.5' N and the northernmost at 9° 54.9' N. At the moment, it appears that the most spatially concentrated area of venting is between 9° 49.7' N and 9° 51.5' N with other relatively high-activity areas of venting near 9° 47.5' N and 9° 53.0' N. Near 9° 49.7' N and 9° 51.5' N where we had almost continuous coverage of the AST floor, these venting areas were most often separated by less than 10s of meters, particularly in the southern and northern end of this region. To date, only diffuse venting has been observed (see description below), but water column tow-yos indicate the presence of high-temperature venting.

Microbial mats and/or byproducts Extensive (apparent) microbial material existed in all areas of venting activity. From deep (i.e., several meters) within fissures to small cracks in the tops of lava remnants. Snow-blower type venting were observed in at least three locations. The large majority of venting was in the style of milky diffuse flow and not the snow-blower type. Extensive areas adjacent to and surrounding hydrothermally- active areas containing white apparent microbial mats and/or byproducts were laden with “olive-brown colored” mats (resembling webbing on the basalt surface in some areas). These appear to be the remnants or a later stage of the white microbial mats observed in venting activity. These apparent “olive” mats may indicate locations where venting was once vigorous and is now inactive. The distribution of the “olive” mats may indicate that diffuse flow has become reduced in extent relative to prior times.

Sessile Fauna No sessile faunal colonization was observed in newly-venting areas.

Tubeworm tubes (all apparently belonging to Riftia pachyptila) were observed in a few areas near 9° 49.2' N and 9° 50.5' N. Lone individual (empty) tubes were observed over 100 meters from the center of the axial trough (both east and west of the Tica area), suggesting some sort of off-axis transport via lava flow or the water column. Aggregations of tubes lying horizontally on the floor were observed near the base of the east wall between the East Wall and Tica area, and a stand of empty tubes surrounded by lava were imaged near 9° 49.2' N. None appeared mangled or scorched. Unlike following the 1991 eruption, no apparent shell debris was observed in any part of the surveyed area.

No live Tevnia, Riftia, or bivalves were observed. In fact, no live pre-existing communities were imaged. Subsequent Alvin dives are needed to locate communities that either survived the eruption in the eruptive area, identified as between 9° 46' N and 9° 55.7' N, or outside the eruptive area to provide important information on the nearest source populations.

Mobile Fauna With the exception of brachyuran crabs and zoarcid fish, all areas of extensive areas of diffuse flow were without megafaunal colonization. Brachyuran crabs increased in abundance proximal to venting activity. Galatheids were present in much fewer numbers than brachyurans, and their distribution seems unrelated to the distribution of venting.

Three non-cirrate octopods were imaged (one above the seafloor) on sheet flows close to venting areas.

Synaphobranchid eels were the most abundant demersal fish observed in all areas surveyed (gross estimate ~1 per 40 meters of imaged seafloor). Zoarcid fish were present in similar abundance as in April and May 1991, both directly in diffuse flow issuing from cracks coated in apparent microbial mats/byproduct as well as lying out on sheet and lobate lava flows 10s of meters from the axial trough. Along the base of M Vent (Fig 4b); based on the discovery of a HOBO high-temperature probe still in the orifice deployed in March 2004), two thick aggregations of bythidid fish were observed (as in the past) nose down in seafloor openings through which clear vent fluids emanated (Fig 4b). Only a few other bythidids (in seemingly random locations) were observed throughout the survey area.

Comparison to 1991 and estimates of time-zero From the more than 12,000 imaged reviewed, the venting and faunal composition and distribution is most similar to the period immediately following the 1991 eruption. The notable lack of apparent colonization (and/or growth) by Tevnia jerichonana (considered to be an early sessile colonizer of nascent venting; Shank et al., 1998) or other vent megafauna suggests that the initiation of activity was within the past ~3 to 9 months (aggregates of Tevnia seen 11 months after the 1991 eruption were up to 30cm in length). The initial colonization of Tevnia may be taking place. These areas appear as somewhat linear white objects (both sparse and in aggregations) in diffuse flow observed in the TowCam images, but are too small (estimated to be only a few cms in length) to be identified given the camera resolution, white background coloring, and venting activity (subsequent submersible imagery and sampling will be needed to identify these objects).

While faunal composition and distribution may be similar to that of April 1991, the style and type of apparent microbial mat/byproduct coating the seafloor is more reminiscent of 11 months following the 1991 eruption. The images of milky diffuse and snow-blower type venting in several locations within the 9° 49' N – 9° 51' N region that appear similar to March 1992. In April 1991, many of the microbial mats/byproducts were 10 cm thick and gelatinous in appearance and to the touch. We may have imaged one small area (less than a few meters by a few meters) in the 9° 49.3' N area that had this morphological appearance. The spatial extent of discrete vent areas with microbial mats/byproducts covering the seafloor was in between that observed in 1991 and 1992.

While two sulfide structures were documented in TowCam images near 9° 47.2' N and 9° 50.5' N (in the vicinity of V and M Vents, respectively), confirmed black smoker venting was not observed. The notable lack of black smoker venting and chimneys may be due to the fact that black smoker chimneys may be there and were not imaged, or that black to gray smoke issuing from around broken pieces of basalt could be diffuse (as in 1991) and thus difficult to observe in TowCam images. Chimney growth was not apparent immediately following the 1991 eruption given the lack of time for chimney formation, and active black smokers 11 months after the April 1991 eruption were several meters tall (e.g., P Vent and Bio9 Vent). Without the presence of chimney structures in April 1991, it was difficult to observe black smoker venting with Alvin until the sub was less than a few meters in front of the fluids issuing through cracks in the basalt. CTD tow-yos throughout the TowCam survey area documented rise heights of extensive hydrothermal plumes indicating the presence of high-temperature venting. An estimate of the time of eruption and the initiation of venting based on black smoker chimney growth can not currently be made based on the TowCam imaging surveys.

The lack of megafaunal colonization mentioned above and the observation that diffuse flow areas have experienced a focusing down of activity suggest that the eruption and the initiation of hydrothermal activity between 9° 46' N to 9° 57.6' N occurred within the last 6 months (since December 2005).

19 May 2006

Authors: Dr. Jim Cowen
Time: 19 May 2006, 4:26:33 PDT

Summary of the casts to date

• Cast 8: TowCam #4
• Cast 9: Vertical CTD cast
• Cast 10: Rock Dredge – 1
• Cast 11: Vertical CTD cast
• Cast 12: TowCam #5
• Sediment/Larval Trap Deployments
• Cast 13: CTD tow-yo
• Cast 14: TowCam #5
• Cast 15: Vertical TowCam–Pump–Electrochemical
• Deployment of Lagrangian Float

May 14, Cast #8 – TowCam #4
TowCam #4 was dedicated to conducting several cross-axis transects between 9° 53.4' N – 9° 53.1' N and 104° 18' W and 104° 17' W, starting from west to east and continuing in tightening right angle turns. Imagery acquired indicated that the previously known 5-7 meter deep axial summit trough (AST) in this area had recently filled with a new lava flow that spilled out and flowed east and west of the axis. The imagery shows extensive collapse over the AST, likely over the trace of the eruptive fissure due to drainback. The TowCam altimetry/depth profile shows that the AST is perhaps 10 m narrower in places (e.g., Tica Vent area) than it previously was and the floor depth a few meters shallower based on previous detailed mapping with Alvin. Extensive sheet flow areas of the new lava flow were observed in the photographs. Although the surveyed area contained well-studied hydrothermal hot spots, including Tica Vent, Bio9 Vent , P Vent and Ty Vent, and temperature anomalies were detected from the CTD in these spots, no visual confirmation of black smokers was found. However, more evidence of significant diffuse flow in this area is given by the presence of microbial mats. Four out of six rock cores were recovered, and water masses associated with temperature anomalies were sampled using four 5-liter niskin bottles. Ship-board methane analyses showed a values exceeding 800 nm in the area of Bio9 where a substantial deviation in potential temperature (from 1.9 to 2.6°C) was recorded on the TowCam CTD.

The TowCam team was also pleasantly surprised when the system arrived on deck with a softball sized &lquo;volunteer&rquo; of the new glassy lava flow resting comfortably in the interior frame. Images later determined the geologic stowaway to be a result of the frame gently tapping an overhang at depth on the port side. Although Dan Fornari credits the acquisition to exceptional &lquo;telepathic&rquo; instrument navigation, the rest of the team is willing to concede that fate simply may have been kind.

May 14, Cast #9 – Vertical CTD cast
A vertical CTD cast was centered on the axial summit (9° 49.843' N, 104° 17.446' W) at the location where the first cross-axis CTD-tow-yo deployment crossed the axis (see Cast #3). Strong plume signals (temperature and particle anomalies) had been found at this site during both of the previous casts. A major objective of this cast was to perform large volume in situ pumping to collect large amounts of (bio)particles for extensive molecular genetic studies; thus a large stable plume was necessary to insure that we could continuously sample (pump) it for 1.5 hours. During this vertical cast we encountered a very intense particle plume that was large enough in area and depth so as to easily keep the instrument package within the particle peak for the entire 1.5 hour pumping period. Four niskin bottles were tripped also at this depth. Following the pumping operation, the package was lowered to ~15 m above the seafloor where the deepest water sample was collected. The rest of the bottles were collected at various depths during the ascent. Water chemistry samples collected showed very high methane concentrations in the near bottom samples (~350 nm), with lower but still substantial methane values in the upper plumes (~130-230 nM); methane values in the shallowest but most intense particle plume (pump depth) was ~140 nM. Much other forthcoming chemistry data should shed considerable light on the nature of the hydrothermal fluids, but we emphasize that these plume values for methane and those from the TowCam near bottom samples are very high for an unsedimented ridge hydrothermal system, and are higher than found within a year of the 1991 eruption in this area.

May 15, Cast #10 – Rock Dredge – 1
A rock dredge was deployed parallel to the ridge axis along a track from 9° 54.50 to 9° 54.70' N, along longitude 104° 18.70' W. The path intersected the previous TowCam route conducted in Cast #6 (TowCam#4), which had indicated new lava flow had traveled as far as 900 mm from the axis and ponded against an inward facing scarp. The intent was to hopefully acquire both older and new lava samples for comparison and analysis. Lining the dredge bag with burlap allowed a variety of rock sample sizes to be collected and ensured that the fine glassy fragments did not wash out of the dredge. Although further analyses are necessary, visual evidence suggests that several large (up to 30x30x10 cm) rock samples retrieved are believed to be older lava from older eruptions, while the glass fragments in the burlap which were lying under the larger fragments are likely to be a combination of both old and new lava. Shipboard inspection of the glass has culled out the freshest looking samples, which have a slight opalescent quality, consistent with very young volcanic glass. Despite a successful tow, the sea apparently shared her displeasure at having her bed disturbed by timing a thunderous squall to start and end exactly with the timing of the dredge retrieval.

May 15, Cast #11 – Vertical CTD cast
Based on previous CTD tow-yo (Cast 1) data, this second vertical CTD cast was performed at an axial location further north (9° 50.828' N, 104° 17.57' W) than the previous vertical cast (Cast 9), in the area of the previously known M-Vent and Q-Vent. Relatively high temperature anomalies were observed in the water column, especially at around 65 m above bottom, but the particle plumes were more modest than found elsewhere (ex. Cast 9). Another in situ high-volume pump sample was collected at ~2400 m depth within the particle plume maximum for this station. As before the pump system was attached to the CTD rosette and the resulting sample will be used for later analyses of molecular community diversity. Methane concentrations were also lower than in some samples from previous casts, though were still substantial (to >70 nM).

May 15, Cast #12 TowCam #5
This camera tow traversed along-axis tow covered the area of historical venting from the area of ~9° 49.4' N (just south of Tube Worm Pillar) to ~9° 50.9' N (the Bio Vent area), with several parallel tracks were made by letting the ship drift south to cover both east and west of the axis. Images show fresh lava flows, typically as thin veneers over older flows. The new lava has extensive areas of sheet flow within the area imaged on this camera tow, consistent with high eruption rates in the area and perhaps it being a locus of the eruption. Diffuse flow was evident through the sheet flows, although no animal colonization of the new lava was evident. The highest apparent potential temperature anomalies were recorded around the locations of the Q and M Vents. Water and rock core samples were also collected for analyses.

May 15, Sediment/Larval Trap Deployments
Two McLane Parflux Sediment traps were deployed at the Bio-9 and Tica (~9° 50.9' N) vent sites to collect hydrothermal vent particles. The traps were set to collect samples every two days and are scheduled to be retrieved in June 2006.

May 16, Cast #13 – CTD tow-yo
This final CTD tow-yo was conducted along axis but for most of the tract was offset ~150 m to the east of the axial summit trough. It was intended to cover the possibility that our earlier axial summit tow-yo (Cast #1) may have missed evidence of some venting due to the strong easterly currents that have clearly been carrying the hydrothermal plumes to the east. The tow track for Cast 13 was 9° 46.685' N, 104° 17.161' W to 9° 48.50' N, 104° 17.10' W and then to 9° 51.60' N,104° 17.65' W. The tow started slightly south of previous tows and, revealed significant plumes south of those encountered on previously cruises. Overall, comparison of the light scattering data from this cast and the earlier Cast #1 which was towed along the axial summit, indicate higher particle concentrations150 m to the east of the axial summit. Temperature anomaly data are forthcoming. Methane concentrations from Cast 13 samples (36 to 163 nM) were similar or perhaps slightly less than those from Cast 1 (57 to 255 nM).

May 17, Cast #14 – TowCam-5
The objective of this TowCam survey was to explore the EPR axis north of 9° 54' N for additional venting areas and to determine the northern limit of the new lava flow. The traverse along the axis began with the camera a few hundred meters east of the axis near 9° 53.9' N. At 17:12 a relative increase in temperature was observed. As the tow continued north, another temperature rise was seen at 17:24 near 9° 54.0' N, when the camera was closer to the topographic axis based on the EM300 bathymetry. Niskin #7 collected water from this site. The tow proceeded north along the axis and we observed mostly new lava in both lobate and sheet morphology with occasional exposures of older lobate lava. It is unclear from just this tow where the eruptive fissure is or if there are multiple fissures along axis where the flow issued from. Some of the lobes of the new flow were observed to have delicate fingers of glass extruded from the lobate surface probably as a late-stage pulse of magma broke the crust and extruded the fingers. The last image of the new lava flow was at 19:50:53 near 9° 55.7' N. From that point north to the end of the survey at 9° 57.8' N, the seafloor along the EPR axis was comprised of lobate to sheet lava with a dusting of sediment and variable areas of collapse. No diffuse flow or other hydrothermal indicators were observed. Niskin #8 was fired before leaving the bottom to get a background water sample away from a vent area.

May 17, Cast #15 – Vertical TowCam–Pump–Electrochemical
Fittingly, the final cast was a combined water column-seafloor, interdisciplinary effort. The in situ electrochemical analyzer and in situ large volume pumps were transferred from the CTD-rosette to the TowCam. The TowCam was deployed as a vertical cast at the same site as Cast #9, just north of the old Biomarker 141 area (9° 49.8' N 104° 17.42' W) where a large hydrothermal plume signal was detected in a previous tow-yo survey. The first objective was to position the TowCam within the plume and sample microbial communities via an autonomous pump and in-situ sulfide speciation via the ISEA (both instruments were mounted on TowCam). The TowCam was then lowered to ~3 m above the seafloor and allowed to float there while the ship attempted to maintain position; however, because the ship does not have dynamic positioning, the precise position of the ship varied and, consequently, the TowCam performed a random walk about the target position. This was in fact our intention in order to obtain many images of a limited area of the seafloor around a current hot spot and previously known vent site. Excellent coverage of the seafloor was obtained, revealing large (~10 x 10 meter) areas covered with apparent microbial mat/byproducts and significant diffuse flow, including snow-blower type venting from a crack at the base of a collapsed wall. Temperature anomalies were detected from the CTD in these locations. The electrodes of the electrochemistry analyzer were inserted into one of the 5 liter Niskin bottles. The idea here was to make in situ electrochemical (redox) measurements of hydrothermal plume water as it is collected in the Niskin and then throughout the rest of the cast (collection to surface) to directly observe changes in the redox chemistry over the time-frame that sample water is confined in the Niskin bottle. The results of this experiment were very interesting; for example, H₂S was readily observed in the sample at the time of collection and for a time afterward. But by the time the TowCam surfaced there was no longer any detectable sulfide. Methane concentrations from the same bottles were all high (>500 nM), one of which was >1 uM. The pH values were also low, as low as 7.3. In all, two 5-liter Niskin bottle collected near-bottom fluids associated with active venting areas, and a third Niskin bottle collected water from a turbidity plume at 2367 m (TowCam depth) during TowCams ascent to the surface.

May 17, Final Operation: Deployment of Lagrangian Float
Immediately following the recovery of the TowCam, we deployed the Lagrangian float (METOCEAN PROVOR). The float was lowered over the fantail just as we gained a little headway from our last cast site.

It was midnight as we concluded operations and headed for San Diego.

Figure 1: TowCam Run 4
TowCam #4 image from 9° 50.3'N area where bio9 vent was and where a water sample (Niksin #8) was taken. Onboard analysis indicated that the sample contained 900 nm methane.

15 May 2006

Authors: Dr. Jim Cowen; map, images, captions – Dan Fornari & Tim Shank
Time: 15 May 2006, 8:58:13 PDT

Summary of the casts to date:

• Cast 1: CTD, along axis (9.783° N to 9.875° N)
• Cast 2: TowCam #1, along axis (9.818° N to 9.881° N)
• Cast 3: CTD, cross axis at ~9.833° N (104.326° W to 104.250°W)
• Cast 4: TowCam #2, along axis (9.767° N to 9.63° N)
• Cast 5: CTD, cross axis from (9.843° N, 104.311° W to 9.874° N, 104.253° W)
• Cast 6: TowCam #3, along axis from (9.870°N, 104.296°W) to (9.917°N, 104.302°W) (just completed)
• Cast 7: CTD, along axis from 9° 52.00' N to 9° 54.22' N and then turning to a heading of 060 degrees

Details of the casts:

May 10, ~2230 hr: Arrive on station —
~2300 hr: Cast 1: CTD-rosette tow-yo along the axial summit trough of the ridge, including the axial region between 9°49' – 51'N where 8 Ocean Bottom Seismometers (OBSs) had stopped communicating and another 3 would not release. The CTD package was towed from 9° 47.000'N, 104° 16.920'W directly over the axial summit trough to near 9° 52.500'N, 104° 17.820'W and verified the presence of extensive and intense hydrothermal particle plumes. Hydrothermal plumes were observed over the entire tow, but were clearly most intense in the northern portion of the tow over the OBS study area near 9°50'N. Plume intensity and vertical structure was quite variable throughout the tow. Analyses of the corresponding temperature anomalies are underway, but the most substantial T anomalies are near bottom (to ~30 mab) from ~9° 49.7' to 9° 50.5' N. In situ water samples have been collected for analysis of a wide variety of gas, other chemical and microbial constituents. Ship-board methane analyses reveal plume methane concentrations twice those previously measured in samples collected from the same area in the post-1991time period. Although ship-board analyses indicate no detectable hydrogen sulfide in water samples collected so far, an in situ electrochemical analyzer frequently did detect sulfide in portions of the plume.

May 11, ~1145 hr: Cast #2, a TowCam, a deep-sea, bottom imaging digital cameral sled that also carries 4 5-liter niskin bottles and 6 wax cores. This first TowCam survey was between 9° 49'N to 9° 52.88'N along the trace of the axial summit trough (AST), imaging ~80% of the track with overlapping images from altitudes of ~4-5 m. Seafloor depths along the track were quite consistent at 2496-7 m. This depth is ~ 5-10 m shallower than previous measured depths along the AST floor in this area based on high-resolution, near bottom bathymetric data. Images at the start of the survey document black, glassy, fresh lava flows (lobates, pillows, and sheets) and murky or turbid bottom water (absence of much flocculent debris). Brachyuran crabs were observed but not in great numbers. The new lava flow was imaged in most of the photographs acquired on this traverse. The temperature anomalies that were detected (potential temperatures up to ~3°C, 5 meters above the bottom) with TowCams CTD corresponded well with previous sites of venting, including the Tube Worm Pillar, Ty Vent, Bio9 Vent, Tica Vent, and Q Vent. However, no markers or experiments (e.g., Biomarkers, Temperature probes, or OBSs) were observed. No black smokers were directly observed. Two snow-blower like vents were observed, but these areas of high hydrothermal flux, flow and microbial-like floc do not appear to be as intense or abundant as those documented from Alvin diving in the eruptive area in April 1991. The areas mentioned above appear much like the vents did in 1992, with remnant hydrothermal/sulfide staining in cracks and crevices where microbial biomass was likely high following the cooling of the lava. Empty tubeworm tubes were observed (both as clumps and as stray tubes) in the Tica and Q Vent region. The new lava flow is present to the end of the tow, near 9° 52.88'N. Two rock core samples were recovered along with two, 5-liter niskin bottles, in the areas of highest temperature anomalies. Based on comparisons of the 1990 images collected on TowCam#1, to still and video imagery taken from Alvin in March 1992, we can confirm that a recent eruption has occurred, although the actual time frame of the flow is still uncertain. We tentatively suggest, based on the fresh, glassy character of the lava surfaces compared with the underlying lava that the eruption may have occurred between 1 and 6 months ago.

~ 2246 hr: Cast #3, a cross-axis CTD-rosette tow-yo (104.326 W to 104.250W at ~9.833) followed the TowCam. This cast found only very low-level hydrothermal plumes to the east of the axial summit; however, right at and, especially, off-axis the plumes were strong. The off-axis (east only) particle plume extended vertically in places from 2250 m to greater than 2500 m. Methane concentrations were higher (33 to 123 nM) than those reported from November 1991 (Mottl et al. 1995) although not so high as found in Cast #1 axial samples. Methane carbon stable isotope values (on shore) will help to determine the degree to which these lower concentrations reflect microbial methane oxidation versus different (venting from source vents to the North or South) concentrations. An in situ electrochemical analyzer detected H₂S in some samples, whereas ship board analysis of Niskin bottle samples did not.

May 12, ~1212 hr: Cast #4, a TowCam (TC2) towed from 9.767 N to 9.63 N.
TowCam#2 traversed the terrain along the axial summit trough between ~9° 46'N to 9° 49.3'N with the intent of surveying the southern extent of new lava flow along the ridge axis. Preliminary analysis of the photos indicates that new lava flow is present at 9° 47'N, but not further south. The camera track passed over A, L, and Marker 21 vent locations with no evidence of high-temperature venting (either imaged by TowCam or detected via its CTD), and no chimneys were observed in these areas. However, several areas of high hydrothermal flux with temperature anomalies of ~>2°C measured by TowCams CTD were observed. At these sites, flow and microbial floc were present. The most intense activity occurs near ~9° 47.5'N, 9° 48'N and 9° 48.3'N. In many places, on this and TowCam#1, the new flow is observed to be <1 m thick based on exposures of older lobate and sheet flow surfaces adjacent to the new glassy, black lobate and sheet lava flows. At the end of Tow#2, we traversed east of the AST near 9° 49.3'W and observed that the new lava flow terminated ~250 m from the AST along the camera track. Two 5-liter Niskin samples and six rock cores were collected along the traverse.

~1951 hr: Cast #5, a CTD tow-yo. This was another cross-axis tow (9.843 N, 104.311 W to 9.874 N, 104.253 W).
We encountered the most intense particle plumes yet during this tow-yo, and again the strongest signals were about one km east of the axial summit. A similar pattern had been encountered during the first cross-axis tow further to the south (Cast 3), although the highest-level particle signals were less than during this cast. The source of the very intense plume is currently unclear, since the strong off-axis plumes are not consistent with the plumes encountered so far. The off-axis plumes also extend to greater than 2525 m, deeper than the bottom depth at the ridge summit to the west. Given the patterns of the plumes to date, it is clear that there is a very strong easterly bottom current, however the pattern also suggests a strong southerly component as well (SE to SSE). It is possible that the first axial CTD tow-yo (and TowCam) did not adequately reflect the venting intensity along this portion of the ridge. However, another likely scenario (especially given the deeper depths of some of the off-axis plumes) is that there might be another source for the off-axis plumes further north on the axis than we have yet towed. Therefore the next CamTow was directed to tow along the section of axial summit trough north of 9.870 N.

May 13, ~0550 hr: Cast #6, a TowCam.
TowCam#3 traversed the terrain along the axial summit trough from ~9° 51.5'N to 9° 54.3'N with the goal to assess the northern extent of the new lava flow, and search for hydrothermal activity that could be a source for observed off-axis plumes in CTD TowYo data (6NH-05) collected the previous evening. The most intense activity, up to ~2°C anomaly, occurred in a ~50 to100 m long segment of the axis centered at ~9° 53.0'N. Images from this area reveal active diffuse venting through cracks in broken sheet flows and pillow basalts. All active vent openings were coated with material resembling microbial mats and/or their byproducts, with no apparent faunal colonization (exceptions include demersal fish and brachyuran crabs). As in TowCam#1 and #2 surveys, no black smokers were documented. Three rock cores acquired along the survey track recovered basalt pieces, and four 5-liter Niskin bottles collected near bottom water associated with observed temperature anomalies. No activity was observed between 9°53.3'N and 9° 53.4'N. At 9° 54.3'N, our survey track turned east to assess the off axis extent of the new flows, including whether lavas had reached the first inward facing scarp located 1 km from the axis based on DSL-120A sidescan data. TowCam images document tongues of the new flow along the easterly traverse. The new lava flow was observed to pond against the base of the scarp. The survey continued several hundred meters east of the scarp, documenting much older, sedimented lobate, pillow, and collapse lava terrain.

~1510 hrs: Cast #7; CTD tow-yo.
This cast started out retracing the track line of the previous casts TowCam operation. The CTD was initially towed along the axial summit from 9° 52.00' N to 9° 54.22' N; however, only occasional small plumes (limited depth range and only modest intensity) were detected within the water column at a depth of ~2460 m. At 9° 54.22' N, the ship bore to the right of the axial track-line to a heading of 060°. On this heading we encountered only small plumes for the first 1.5 kms off-axis before finding more intense plumes that persisted for another 1.5 kms further east of the axial summit. A distinct vertically structured particle plume was observed from 1.5 to 3.0 km off-axis at depths extending from deeper than 2600 m to ~2260 m. This depth can be compared to the depth of the axial summit (~2550 m) due west of this off-axis plume. Consequently, the source(s) of the intense, vertically-extended off-axis plumes observed during Casts 3, 5, and 7 are still uncertain. So far it appears that the most convenient explanation is rigorous axial venting further to the north or south of the portion of the ridge summit surveyed so far during this cruise (i.e., north of 9° 54' N or south of 9° 46' N). Alternatively, venting and resulting plumes along this axial section could be more vigorous than indicated by present data or venting could conceivably have been temporally variable within the time frame recorded in the plume, although in both cases there would have to be a significant deepening of the off-axis isopycnal surfaces. Previous work in this area (Nov. 1991, Mottl et al. 1995) indicate strong latitudinal differences in chemical signals (e.g., CH₄/Mn ratios), with the plumes over the 1991 eruption standing out relative to ridge sections to the immediate south or north. Shipboard methane data and shore-based analyses of collected samples for Mn, Fe and other constituents may help to identify differences or similarities between the off-axis plumes and nearby and more distant axial plumes. Site-time depending, we will also try to sample ridge areas further to the north and south.

A number of additional CTD and TowCam tows are planned for the remaining 2-3 days, as well as rock dredges and mooring and langrangian float deployments.

Images

(Click the image for the full resolution version)

Figure 1: Location map

Figure 2: Cast 2, TowCam Run 1
9° 50.212'N, 104° 17.468'W, seafloor depth 2498 m, 4 m altitude.
Newly erupted (2006?) glassy lobate lava flow overlying older lobate lava on the EPR crest.

Figure 3: Cast 2, TowCam Run 1
9° 51.547N, 104° 17.746'W, seafloor depth 2511 m, 5 m altitude.
Post-eruptive diffuse vent fluids emanating through cracks in broken sheet flow and over lava surfaces covered by white microbial mats and/or the remnants of microbial activity. Few confirmed macrofaunal species, including, fish, like the synaphobranchid eel at upper right and sparsely-distributed brachyuran crabs, were observed in this and similar nascent venting areas within the region. Horizontal distance at the middle of the image is ~5m.

Figure 4a: Cast 2, TowCam Run 1
M vent at 9° 50.7'N surrounded by new lava. Note at middle bottom small instrument housing. It is the hiT Hobo logger (#6) that was instrumenting the vent.

Figure 4b: Cast 2, TowCam Run 1
M vent at 9° 50.7'N surrounded by new lava. Close up of the hiT Hobo logger (#6) that was instrumenting the vent.

Figure 5: Cast 4, TowCam Run 2
Southern terminus of new lava found on TowCam#2 near 9° 47.3'N. New lava is lobate and older flow surface in this location is a curtain-folded sheet flow.

Figure 6: Cast 4, TowCam Run 2
Active venting with extensive bacterial mats and particulates in the bottom water near V-vent (~9° 47'N).

Figure 7: Cast 4, TowCam Run 2
New flow with exposure to older lobate surface with broken crusts, from near mid point of Knorr dredge track. This photo, and others suggest the new flow is thin (<1 m) in most places and also that the material sampled in the Knorr dredge might contain both older and new lava.

Figure 8: Cast 4, TowCam Run 2
One of the last photos taken on Tow#2 as the camera was traversing seafloor about 250 meters east of the AST near 9° 49'N showing distal lobe of new lava flowing over older lobate flow.

12 May 2006

Author: Dr. Jim Cowen
Time: 12 May 2006, 8:51:57 PDT

Within twenty-four hours of arriving on station at the 9° 50' N EPR R2K Integrated Study Site (ISS), we have completed one CTD TowYo and one TowCam deep-sea camera tow along the axial summit trough of the ridge, including the axial region between 9°49-51'N where 8 Ocean Bottom Seismometers (OBSs) had stopped communicating and another 3 would not release. Overall, the preliminary analysis of water column, shipboard chemical and photographic data strongly support the contention that this site has experienced a recent seafloor eruption.

The CTD tow-yo (9° 47.000'N, 104° 16.920'W to 9° 52.500'N, 104° 17.820'W) verified the presence of extensive and intense hydrothermal particle plumes. Hydrothermal plumes were observed over the entire tow, but were clearly most intense in the northern portion of the tow over the OBS study area near 9°50'N. Plume intensity and vertical structure was quite variable throughout the tow. Analyses of the corresponding temperature anomalies are underway, but the most substantial T anomalies are near bottom (to ~30 mab) from ~9° 49.7' to 9° 50.5' N. In situ water samples have been collected for analysis of a wide variety of gas, other chemical and microbial constituents. Ship-board methane analyses reveal plume methane concentrations twice those previously measured in samples collected from the same area in the post-1991 time period. Although ship-board analyses indicate no detectable hydrogen sulfide in water samples collected so far, an in situ electrochemical analyzer frequently did detect sulfide in portions of the plume.

The camera tow, from 9° 49.09'N to 9° 52.88'N centrally aligned over the area known to be an axial summit trough, has provided dramatic photo images of very glassy, recently-erupted lava flows overlapping older flows. In many areas abundant cracks in the lava surface and areas of the flow are covered with what resembles microbial films and floc- some apparently venting warm to hot water. The TowCam track passed over the vicinity of many previously deployed experiments and markers located at over 10 known sites of high and low-temperature activity; none of these are visible in the better than ~80% coverage (on a linear basis) of the photos and the imaged swath was essentially devoid of macrofauna. Temperature anomalies 5 meters above the bottom detected with TowCam corresponded well geographically with known sites of venting, including the Tube Worm Pillar, Ty Vent, Bio9 Vent, Tica Vent, and Q Vent. Two snow-blower-like vents were observed, but these areas of high hydrothermal flux, flow and potential microbial floc were not considered as intense or abundant as in April 1991. Science team members on board who are very familiar with the details of the areas geology and biology from Alvin diving, are convinced that the character of the seafloor has changed dramatically from previous visits. Based on the detailed bottom depth profile acquired by TowCam the seafloor along the track is consistently at~ 2496-2500 m depth. There is some indication that the former 5-8 m deep trough may been have filled in by the new flow, although more observations are needed, especially across axis traverses.

During efforts to survey in and range on OBSs currently deployed in the area, we have found no changes in the position or operating status of the OBSs since April when the Knorr attempted to communicate with them.

10 May 2006

1600 hrs
Lat: 14° 14' N
Lon: 106° 57' W
Compass bearing: 152°

ETA at EPR site: 1900 23:59 5/10/06

Excitement is building as the R/V New Horizon and the science team are now within 24 hours of reaching the 9°N EPR ISS and the initiation of sampling. Fair weather, calm seas, and a lengthy transit time have allowed the team to spend the past five days preparing and testing equipment and sampling protocols.

At this point, the team is anxious and ready to begin sampling as soon as the ship arrives on site. The first order of business will be to conduct a Tow Yo CTD transect along the ridge axis in search of water column anomalies that would indicate increased venting and/or eruptions. Data from this effort (including temperature, turbidity, electrochemistry and seawater samples) will then be extended with a TowCam seafloor camera tow along the same transect, and this sequence will likely be repeated and refined based on the data acquired. As areas of interest are defined, more detailed water column sampling, camera tows and rock dredging will be conducted using a rosette with CTD, optical and water collection capabilities. Efforts will also be made using the TowCam to locate previously deployed OBS sensors that are non-responsive and whose position may have changed since deployment.