Bottoms-Up Additions of Iron
Through Seafloor Vents?

Charlie Paull

The area off the northwestern edge of Monterey Bay, targeted for the 2000 Iron Regulation Experiment, was selected on the basis of its upwelling characteristics. However, to understand the results of the proposed experiment, all locally significant iron sources should be identified. This field area coincides with the San Gregorio Fault Zone. Remote sensing studies of the San Gregorio Fault Zone (Mullins and Nagel 1982) have identified this area as being associated with gas and, perhaps, fluid discharge that is adequate to produce acoustically detectable water-column plumes. If these identifications are correct, copious volumes of gas and fluid are discharging though this fault zone into the overlying water column. Because reduced ground water is typically six orders of magnitude richer in iron than open ocean waters, the possibility that seafloor venting is another source of iron needs to be factored into this experiment. 

AUV surveys in this area provided data to help establish whether these acoustical plumes are, in fact, associated with seafloor venting. If vent-related water-column anomalies are found, their potential importance to the iron budget can be assessed. Moreover, locating sites of concentrated gas venting is of great value for other ongoing MBARI studies. To perform this assessment, the AUVs will need to carry only a methane sensor and a flourometer. MBARI's existing METS sensor and a commercially available flourometer will be adequate for this purpose.

Mullins, Henry T. and Nagel, David K. (1982). "Evidence for shallow hydrocarbons offshore northern Santa Cruz County, California", American Association of Petroleum Geologists Bulletin, 66:8, pp.1130-1140.

Data Index Aircraft AUV CODAR
Drifters Moorings Satellites Ships