AT37-12 Sievert "In situ Rates"

Ship

Vehicles

Cruise Party

Departure: Apr 24, 2017

Arrival: May 14, 2017

Operations Area

Science Objectives

Knowledge of the in situ metabolism of microorganisms carrying out CO₂-fixation at deep-sea hydrothermal vents is very limited. Particularly lacking are studies measuring rates of autotrophic carbon fixation in situ, which is a measurement ultimately needed to constrain production in these ecosystems. Although recent data suggests that nitrate reduction either to N₂ (denitrification) or to NH₄⁺ (dissimilatory reduction of nitrate to ammonium, DNRA) might be responsible for a significant fraction of chemoautotrophic production, NO₃^--reduction rates have never been measured in situ at hydrothermal vents. We hypothesize that chemoautrophic growth is strongly coupled to nitrate respiration in vent microbial communities. As part of this cruise, we are going to use a recently developed robotic micro-laboratory (Vent-SID) to measure rates of chemoautotrophic production and to determine the relative importance of oxygen and nitrate in driving chemosynthesis at hydrothermal vents at both in situ pressures and temperatures and to tackle the following currently unresolved science objectives: 1) obtain in situ rates of chemoautotrophic carbon fixation, 2) obtain in situ nitrate reduction rate measurements, and 3) directly correlate the measurement of these processes with the expression of key genes involved in carbon and energy metabolism. 

Science Activities

The cruise has 12 dives with DSV Alvin, to allow time for deployment and collection of experiments and for sampling of discrete vents along the axis of the 9°46’N to 9°53’N segment of the East Pacific Rise (EPR). We will focus our activities at Crab Spa, a diffuse flow vent site near Tica, and deploy experiments and sampling equipment, including the Vent-SID and a large volume pump (LVP). During the course of the cruise we will perform several deployments of the Vent-TSSID, as well as collect biomass from fluids and biofilms (deployment/recover experimental microbial colonizers) by utilizing the LVP. Both the Vent-SID and the LVP will be deployed as an elevator. It is planned to deploy the instruments and bring them close to the deployment site the night before a dive, and then to position the instruments at the site with Alvin the next day. Alvin will be releasing the instrument either on the same dive or any subsequent dive, after which the instrument will be picked up at the surface. Furthermore, we will carry out additional opportunistic sampling of other diffuse-flow vents. Fluid samples for chemical analyses will be collected at each deployment site using isobaric gas-tight samplers, which will also be used to sample fluids from the focus site for the shipboard incubations. Finally, we will deploy/recover experimental microbial colonizers to collect microbial biofilms, as well as collect Riftia for subsequent ‘omic analyses. We are also planning to perform several water casts at night, using the CTD/Niskin rosette on board Atlantis. 

Additional Info

Stations:

Supporting documentation:

From the Chief Mate

Q: “It sounds like night ops would consist of deploying and recovering elevators (maybe 1 per night) and CTD's.  Are there any other night operations planned, and if so, what ship's equipment would they use?”

A: No other night ops planned. For the CTD we might move away a couple of hours from the dive site. We probably will have night ops every night, but probably not elevators every night. 

A: It will be very similar to previous cruises, especially AT26-23, during which we used the Vent-SID.

Shipboard Equipment

Shipboard Communication

CTD/Water Sampling

Critical CTD Sensors

Sample Storage

Navigation

Navigation

Winches

Wire use and application

Standard Oceanographic Cables

Portable Vans

Specialized Deck Equipment

Over the Side Equipment

Special Requirements

Additional Cruise Items/Activities

Hazardous Material

Radioactive Material

Additional Information

Sievert/Taylor/Rich/White: we will be perfoming water casts using the ship-board CTD/Rosette system, we will also deploy elevators the night before an Alvin dive

Site Survey

Navigation

Vehicle Equipment

Elevators

Science Supplied Equipment

1. We will be using chemical in situ sensors developed by Nadine LeBris, these are self-contained units that have been frequently used with Alvin (last time on AT15-38)

3. A McLane in situ large volume pump is going to be deployed as an elevator. Alvin will need to move the pump to the deployment site and also release it after filtration is finished (6-8 hours)

4. Vent-SID: This is a newly developed isntrument that has been used with Alvin during AT26-23. The pressure senstive components have been pressure tested according to Alvin specificications. Fred Thwaites, who is the main engineer of the instrument, has been in touch with Alvin group, and so has Steve Faluotico, who is implementing an ICL to communicate to the instrument from the sphere.

The LVP and Vent-SID are independent units. They will be moved by Alvin and positioned at the sampling site. 

Hazardous Material

Additional Information

Checklist

Checklist