Hydrothermal plume anomalies along the Central Indian Ridge

Water column turbidity and temperature were investigated along the Central Indian Ridge (CIR) from 25°19′S to 23°48′S during a December 2005 cruise on board Chinese R/V DayangYihao. Measurements were made using NOAA’s MAPR (Miniature Autonomous Plume Recorder) sensors during CTD casts, TV grabber operations, and tow-yo profiles, yielding the following results on hydrothermal plume anomalies: (1) Strong hydrothermal turbidity and temperature anomalies were recorded over the previously discovered Kairei (25°19.2′S, 70°02.4′E) and Edmond (23°52.7′S, 69°35.8′E) vent fields, with the plume anomalies concentrated at depths of 2150–2300 m and 2700–2900 m, respectively. The maximum height of the turbidity anomalies near the Kairei vent field recorded in December 2005 was slightly below 2100 m, which is consistent with the plume depth measured in June 2001, indicating that the Kairei plume may have maintained its buoyancy flux in the intervening 4.5 years. (2) The water column beneath the Kairei plume has background anomalies of about 0.005ΔNTU, whereas no such background turbidity anomalies were observed below the Edmond hydrothermal plume. (3) No visible turbidity anomalies were detected from 24°42′S to 24°12′S including the Knorr Seamount. Thus 24°12′S marks the southern end of the hydrothermal plume. (4) Significant turbidity anomalies were observed at four individual sections from 24°12′S to 23°56′S at the depth of 2500–3000 m along the eastern rift valley wall. Whether the individual sections of anomalies are connected is still unknown due to the absence of data at the intervening gaps. If the four sections are connected with each other and are linked to the Edmond vent field farther to the north, the total along-axis length of the plume anomaly would be more than 37 km, implying a plume incidence value p _h of 0.38, greater than the predicted p _h of 0.21–0.25 based on the spreading rate of the Central Indian Ridge. Supported by WHOI Deep Ocean Exploration Institute and Cecil H. and Ida M. Green Technology Innovation Awards (J. Lin) and the Chinese Ocean Mineral Resources R&D Association (J. Chen)