Jenson V. George

Variability of fronts, fresh water input and chlorophyll in the Indian Ocean sector of the Southern Ocean

The aim of this study was to understand the variability in the fronts and water masses, and the effect of melt water on the concentration of chlorophyll (Chl a) in the Indian Ocean sector of the Southern Ocean using hydrographic data collected during the austral summer (February 2010 and 2011). The Southern Subtropical Front (SSTF) and Northern Sub Antarctic Front (SAF1) were found to be further south at 57°30′E than at 47–48°E. This southward shift of the fronts was consistent with the southward meandering (c. 2°) of the Antarctic Circumpolar Current (ACC) core from the western section to the eastern section, which could have been caused by the bottom topography. The intrusion of water masses also differed between the western and eastern transects of the study region as a result of the meandering of the ACC core. Fresh water layer thickness relative to the winter water in 2011 was more compared to that during 2010. This could have been due to the larger amount of sea ice that was present in the winter of 2010, which subsequently melted, resulting in the advection of melt water from the south and west of the study region. In situ observations and satellite data detected a high Chl a concentration (c. 0.38 mg m−3) south of the Northern Polar Front (PF1) in 2011, which was caused by this melt water.

BoBBLE (Bay of Bengal Boundary Layer Experiment): Ocean-atmosphere interaction and its impact on the South Asian monsoon

AbstractThe Bay of Bengal (BoB) plays a fundamental role in controlling the weather systems that make up the South Asian summer monsoon system. In particular, the southern BoB has cooler sea surface temperatures (SST) that influence ocean–atmosphere interaction and impact the monsoon. Compared to the southeastern BoB, the southwestern BoB is cooler, more saline, receives much less rain, and is influenced by the summer monsoon current (SMC). To examine the impact of these features on the monsoon, the BoB Boundary Layer Experiment (BoBBLE) was jointly undertaken by India and the United Kingdom during June–July 2016. Physical and biogeochemical observations were made using a conductivity–temperature–depth (CTD) profiler, five ocean gliders, an Oceanscience Underway CTD (uCTD), a vertical microstructure profiler (VMP), two acoustic Doppler current profilers (ADCPs), Argo floats, drifting buoys, meteorological sensors, and upper-air radiosonde balloons. The observations were made along a zonal section at 8°N b...AbstractThe Bay of Bengal (BoB) plays a fundamental role in controlling the weather systems that make up the South Asian summer monsoon system. In particular, the southern BoB has cooler sea surfac...

Seasonal Surface Chlorophyll a Variability in the Seychelles–Chagos Thermocline Ridge

Seychelles–Chagos Thermocline Ridge (SCTR, 5– 10S, 50–75E) in the southwestern tropical Indian Ocean is a unique area that experiences year-round upwelling. This is a response to the upward Ekman pumping prevalent in the region. Satellite data, model data and objectively analysed Argo temperature/ salinity data have been used to study the seasonal surface chlorophyll a (chl a) variability in SCTR. Variability of surface chl a concentration in SCTR showed a weak semiannual signature. The western part of SCTR (WSCTR, 50–62E) is characterized by higher chl a concentration than the eastern part (ESCTR, 63–75E). Average chl a concentration in WSCTR/ESCTR showed a primary peak in July– August (~0.26/~0.16 mg/m) and a secondary peak in January (~0.14/~0.12 mg/m). Minimum chl a concentration (~0.12/~0.1 mg/m) was observed during March– April and December–January. The high amplitude of chl a variability observed during July–August is associated with weak stratification and deep mixed layer depth (MLD). Deep MLD reaching to nutrient-rich thermocline entrains nutrients to the surface and thereby increases the surface chl a concentration. However, the low surface chl a concentration is a result of shallow MLD in the region. The deep MLD (30–40 m) observed during June–October is dominated by wind mixing and supported by buoyancy mixing. Shallow MLD (<30 m) observed during rest of the year is due to weak wind mixing and high surface buoyancy. The high surface buoyancy is a manifestation of ocean surface warming and presence of low saline surface waters in the SCTR region.