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Hydrothermal Vents

  The Kick’em Jenny crater is about 350 m in diameter and 80 m deep. In its northwestern part there is an elongate inner crater, about 100 m wide and up to 20 m deep. The ROV dives in 2003 show that on the floor, slopes and rims of the inner crater there are literally hundreds of hydrothermal vents. These vents are sites where hot water and gases are issuing from fissure or holes in the crater floor, and they are the hosts of a variety of organisms, as explained in the Biology section of his web site.

 

Video clip of active vent

 

We used a thermocouple on the ROV to measure temperatures up to 78oC in the vent fluids. However, other evidence indicates that much higher temperatures exist just below the surface. When a plastic core tube composed of cellulose-acetyl-butyrate was pushed into the sediment near the one of the vents, the base of the tube melted at a depth of about 20 cm below the surface (Figure 1). The melting point of this plastic is about 270oC, thus indicating temperatures of several hundreds of degrees in the crater floor, below the thin sediment cover.

 

Figure 2

Figure 1: Melted core tube

 

Boiling Point of Seawater

Is the water boiling in the hydrothermal vents on the floor of the Kick’em Jenny crater? The temperature at which seawater boils depends on the pressure, i.e. the water depth. Pressure in the ocean increases by one atmosphere (0.101325 MPa ) for each ten meters of depth. For example, in a pressure cooker, where the safety valve is normally set for double the normal atmospheric pressure (two atmospheres), the boiling point is 121oC. The figure shows the change in the boiling point of seawater as a function of depth in the ocean. The Kick’em Jenny crater floor, where the hydrothermal vents are observed, is in the depth range of about 240 to 260 m below sea level. At that depth the boiling point of seawater is in the range of about 230o to 240oC (Figure 2). The evidence of the melting plastic tube (at about 270oC) suggests that the floor of the crater, a few cm below the sediment surface, is at a temperature close to that of boiling

 

Figure 3

Figure 2: Temperature/depth plot


The Gas Bubbles

  Most of the Kick’em Jenny hydrothermal vents show extensive gas escape, with steady trails of bubbles rising through the water column. Often the streaming of gas was so great that the ocean surrounding the vetns looked like a bubbling glass of champagne. We do not know the nature of this gas, but it is likely to include carbon dioxide, methane, steam (from boiling of water at greater depth) and sulfur gases. Water samples taken at the vents had a noticeable smell of hydrogen sulfide when they wer examined on board the ship.

 

video clip of a bubbling vent