Bio-physical coupling and ocean dynamics in the central equatorial Indian Ocean during 2006 Indian Ocean Dipole

• Published in: Geophysical research letters Vol. 39; no. 14
• Main Authors: Prasanna Kumar, S., Divya David, T., Byju, P., Narvekar, J., Yoneyama, Kunio, Nakatani, Naoki, Ishida, Akio, Horii, Takanori, Masumoto, Yukio, Mizuno, Keisuke
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 28-07-2012; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: bio-physical coupling; Biological oceanography; Chemical oceanography; Dipoles; Earth sciences; Earth, ocean, space; equatorial Indian Ocean; Exact sciences and technology; Geophysics; Indian Ocean; Indian Ocean Dipole; Isotherms; Joining; Marine; Oceanography; Oceans; Onboard; Physical oceanography; Thermocline; Time series; Upper ocean; Wave propagation; Yanai wave; Indian Ocean; ISW, Equatorial Indian Ocean; ISW, Indian Ocean; advection; Short term; waves; shoals; Indian ocean dipole; high frequency; Surface layer; Time series; thermocline; chlorophyll; Ocean dynamics; isotherms; velocity; subsurface; nutrients; coupling; currents; propagation; periodicity; temperature; Gravity; shoaling
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2012GL052609

The high‐frequency time series data collected during 28th October to 21st November 2006 onboard R/V Mirai provided the first evidence of short‐term bio‐physical coupling in the central equatorial Indian Ocean (EIO). The predominant feature of the thermal structure was the down‐sloping of 28°C‐isotherm and up‐sloping of 14°C‐isotherm indicating deepening of surface‐layer and shoaling of lower‐thermocline respectively. Concomitant with the deepening of surface‐layer, nitracline and subsurface chlorophyll maximum (SCM) also deepened. From the prominent bi‐weekly periodicity in the 14°C‐isotherm and the upward phase propagation in the meridional current velocity, we infer that shoaling was the response of mixed Rossby‐Gravity (MRG) waves. Based on temperature and currents we propose that deepening of surface‐layer was caused by the eastward advection of warmer waters associated with the weakening of Indian Ocean Dipole (IOD). This made the upper ocean more nutrient‐depleted and biologically less‐productive, an indication that the central EIO is returning to its pre‐IOD condition.
Key Points
Reports hitherto unexplored bio‐physical coupling by Yanai wave at EIO
Proposed a new mechanism to explain observed deepening of the upper ocean
High‐resolution physical and biogeochemical data in the EIO is nonexistent