Category: General Article
Wednesay, August 19, 2015
Submitted by Rachel Teasdale
Summary: The weather is keeping us from launching Jason and Sentry again today, so we did a midnight CTD launch and are continuing to recover and deploy seafloor instruments (OBHs – ocean bottom hydrophones and BPRs – bottom pressure recorders). We’ll do another CTD tow-yo later this evening.
As noted in previous entries, the winds have picked up and the seas have been rough, which continues to prevent the launch of the ROV Jason and AUV Sentry. Vehicle launches and recoveries require the Sentry- and Jason- group team members and numerous ship’s crew to work on the deck of the ship as cranes lift vehicles overhead while the ship is heaved up and down with the waves. In bad weather, the vehicles could potentially swing and collide with the ship, other equipment or personnel. The waves do not affect the AUV Sentry while it is in the sea, but it must be recovered within the lifespan of the batteries, so launches must be made when the window of weather is certain to allow a timely and safe recovery. The ROV Jason and Medea are tethered to the ship with a fiber-optic cable so can remain submerged for long periods of time, but large motions of the ship can cause the cable to yank on Medea which could damage the cable. Thus, the potential for damage or injury makes it not possible to use these vehicles during heavy weather.
One of Chief Scientist Bill Chadwick’s many responsibilities is scheduling the individual activities of the cruise, including each of the ROV Jason and AUV Sentry dives, installation and recovery of instruments, and CTD casts. Chadwick is revising the cruise plan to maximize the research that can be accomplished during the cruise in spite of the weather. In lieu of vehicle dives, the science plan during the last few days has been altered from predominantly dive-focused work, to activities that focus on other aspects of the cruise plan. The last few days we have been able to launch and recover OBH and BPR instruments that are used in the geophysical monitoring of Axial Seamount.
We have also been able to complete two CTD casts and will complete another tow-yo tonight to collect water samples and measure water Conductivity, Temperature and Depth. The previously described CTD tow-yo (August 17 Blog) was used to explore the water above the still- cooling lava flows erupted in the North Rift Zone in April 2015. In contrast, last night the CTD was cast vertically over known hydrothermal vents in the caldera that have been previously sampled. This time-series will allow the science team to look for changes due to the 2015 eruption in order to better understand how plumes change chemically, physically and in their biological diversity. After these CTD casts, the chemistry and biochemistry groups are busy processing samples once the water is back on board and with preparations for the next CTD cast.
Microbiologist Chris Algar has been collecting CTD water samples and will measure the activity of the microbe communities that live in the vents. Unlike humans who breathe oxygen (O2), autotrophic vent microbes respire hydrogen (H2) that is concentrated in vent fluids, producing methane (CH4) as a byproduct. The vent microbes incorporate carbon dioxide (CO2) to make their biomass, so to compare the activity of the vent microbes Chris measures the rate at which CO2 is taken up at each vent site and can also compare that activity with the carbon uptake in non-vent sea water. Ultimately, Chris’ work can be used to help quantify the role that microbe communities in vent fluids play in the ocean’s carbon cycle.
While waiting for ROV Jason and AUV Sentry dives to resume, scientists who rely on Jason samples and AUV Sentry data keep busy with projects on board. Microbiologist Jim Holden of University of Massachusetts, Amherst uses samples collected by Jason to identify and characterize the microbes inside the hydrothermal vents. He and his graduate student Begüm Topçuoğlu collected samples during the first Jason dive (August 16-17), which have been processed and are now frozen, ready for use in experiments back in their lab. For now, Jim is working on a journal article for publication, but he is eager for Jason dives to resume so more samples can be collected in a new experimental “incubator” (see upcoming blog for more!). Similarly, marine geologist Jenny Paduan has processed the 2015 lava flow rock samples collected during the first dive (see First Jason Dive blog) to prepare them for later chemical analyses. Jenny is looking forward to collecting and examining more 2015 lava samples during upcoming dives.
Engineer Zach Berkowitz is busy fine-tuning upgraded vehicle systems for the next deployment of AUV Sentry and Stefano Suman is testing a new data processing technique for the sonar data collected by AUV Sentry on August 16 to compare new and existing methods for creating the seafloor maps. Justin Fujii and Loral O’Hara are looking ahead and developing launch and recovery methods for a future cruise.
Photos and video courtesy of the 2015 Axial Team.