 |
| Titel |
Hydrothermal Fluxes at the Mid-Atlantic Ridge, 5°S |
| VerfasserIn |
Christian Mertens, Maren Walter, Janna Köhler, Jürgen Sültenfuß, Monika Rhein |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046434
|
|
|
|
|
|
| Zusammenfassung |
| The growing number of known hydrothermal vent sites has lead to an increasing recognition
of the quantitative importance of hydrothermally derived materials in the large scale ocean
circulation due to their possible impact on the ocean carbon cycle. The basin wide
spreading of primordial helium measured during the WOCE era revealed intense
hydrothermal venting in the South Atlantic, but it was not until 2005 that the first vent
fields were located after intense surveys along the Mid-Atlantic Ridge. Before these
surveys no hydrothermal fields were known in the Atlantic between 12- N and the
Southern Ocean, thus leaving a large gap in the biogeography of hydrothermal vent
fauna.
One of the newly discovered sites is located in a relatively short segment of the rift valley
at 5- S. It consists of three known high temperature fields: Turtle Pits, Comfortless Cove, and
Red Lion, as well as several areas were diffuse venting was found. Hydrographic
measurements were carried out at the Turtle Pits vent site during three cruises: Meteor cruise
68/1 in May 2006, a cruise with the french vessel L’Atalante in January 2008, and Meteor
cruise 78/2 in April/May 2009. The data collected during these cruises are vertical
profiles and towed sections of temperature, salinity, and turbidity, direct velocity
measurements with lowered ADCP, as well as water samples for Helium isotope
analysis.
The hydrography at the vent sites is largely determined by the location of the sites
in relation to the surrounding rift valley. The vents are situated in the center of
the valley at a topographic sill. The water column plumes of the vent fields are
clearly visible by strong signals in turbidity and temperature anomalies, and show a
maximum rise height of more than 200Â m, which does not exceed the height of the side
walls of the graben. The currents in the rift valley are predominantly northward; the
difference in stratification between upstream and downstream conditions and observed
Froude Numbers around one indicate a hydraulically controlled flow across the sill.
Turbulent mixing as evident in the frequent occurrence of overturns causes a vertical
transport of hydrothermal material downstream of the sill. Analysis of mixing from
finescale measurements indicates the possible importance of the mixing for the
transport of hydrothermal material into the upper water column above the ridge
crest.
Combining the observed throughflow with the helium distribution in the rift valley leads
to estimates of the power emission about 10 times larger than estimates using the rise height
of the plume. This may indicate an underestimation because of plume bending by the
background current. On the other hand the large emissions of helium may indicate a
considerable contribution of diffuse venting. |
|
|
|
|
|
|