Differential bleaching of corals based on El Niño type and intensity in the Andaman Sea, southeast Bay of Bengal.

The Andaman coral reef region experienced mass bleaching events during 1998 and 2010. The purpose of this study is to investigate the role of the El Niño in the coral reef bleaching events of the Andaman region. Both Niño 3.4 and 3 indices were examined to find out the relationship between the mass bleaching events and El Niño, and correlated with sea surface temperature (SST) anomalies in the Andaman Sea. The result shows that abnormal warming and mass bleaching events in the Andaman Sea were seen only during strong El Niño years of 1997-1998 and 2009-2010. The Andaman Sea SST was more elevated and associated with El Niño Modoki (central Pacific El Niño) than conventional El Niño (eastern Pacific El Niño) occurrences. It is suggested that the development of hot spot patterns around the Andaman Islands during May 1998 and April-May 2010 may be attributed to zonal shifts in the Walker circulation driven by El Niño during the corresponding period.

Residual fluxes of water and nutrient transport through the main inlet of a tropical estuary, Cochin estuary, West Coast, India.

Determining robust values for estuarine material fluxes has been a complex task and an interdisciplinary research challenge. With the advent of acoustic Doppler profilers (ADPs) having bottom-track capability and which provides three-dimensional current velocity profiles, more accurate estimation of cross-sectional fluxes is far accomplished in unsteady and bidirectional flow conditions of estuaries. This paper reports for the first time the discharge measurements conducted across Cochin inlet using ADP to examine the spring-neap variability in residual fluxes of water and nutrients during dry season. Cross-sectional current velocity profiles and salinity profiles were captured using ADP and conductivity temperature depth (CTD) instrumentation. Samples of surface and bottom water were also collected at 3-h intervals. The results indicated that there is a distinct transition from the neap to spring tides related to flow and salinity structure. The neap tide was partially mixed with large diurnal inequalities whereas the spring tide was well-mixed with symmetric tides. During ebb, an increase in the concentrations of nitrate, nitrite, phosphate, and silicate was noticed indicating upstream sources for their inputs. In contrast, elevated levels of ammonia were found in the estuary throughout the period of observation. There was net residual outflow during both tides, and the computed residual water fluxes of neap doubled that of spring. The strong ebb currents and the increased nutrient concentrations during ebb resulted in the export of all nutrients (except ammonia during spring) into the sea. The findings of this study highlight the consequences of anthropogenic interventions in the estuary and their effects on the fluxes of ecologically relevant substances.

Mesoscale process-induced variation of the West India Coastal Current during the winter monsoon.

This manuscript presents the analysis of current meter records at Kollam and Kannur along the 20-m isobaths during November-December 2005. Currents in the coastal waters are strongly influenced by winds (both local and remote forcing), tides, propagation of coastal Kelvin and Rossby waves, etc. We hypothesize that the mesoscale (spatial scales of 10-500 km and temporal scale of 10-100 days) features in ocean are also competent to alter the characteristics of coastal currents to a large extent. Analysis of sea level anomaly from the merged altimeter data reveals the existence of a large anticyclonic eddy in the southeastern Arabian Sea during the winter monsoon. The eddy moves westward with an average speed of ∼15 km day(-1) corresponding to an increase in sea level amplitude up to 28 cm. Off southwest India, the poleward flow is along the western flank of this anticyclonic eddy and the geostrophic current completes the circulation around the eddy. The eastward component of the geostrophic current at the northern edge of the eddy is bifurcated at ∼9° N: one flowing towards north and the other towards south. Current meter records at station Kollam revealed a dominant southward current due to the bifurcated southward component. The bifurcated northward component coalesced with the poleward flow along the western flank of the anticyclonic eddy. At Kannur, a poleward flow along the coast is responsible for a predominant northward trend in the observed current pattern during the initial phase of observation. A reversal in the current direction is caused by the southward-flowing geostrophic current along the eastern flank of the subsequent anticyclonic eddy centered at 73.5° E and 13° N. The stations were located at the eastern periphery of these anticyclonic eddies, where the mesoscale features overwhelm the seasonal characteristics of the West India Coastal Current (WICC).

An appraisal of biological responses and network of environmental interactions in non-mining and mining impacted coastal waters.

The coastal waters of Goa and Ratnagiri lying on the West coast of India are influenced by terrestrial influx. However, Goa is influenced anthropogenically by iron-ore mining, while Ratnagiri is influenced by deposition of heavy minerals containing iron brought from the hinterlands. We hypothesize that there could be a shift in biological response along with changes in network of interactions between environmental and biological variables in these mining and non-mining impacted regions, lying 160 nmi apart. Biological and environmental parameters were analyzed during pre-monsoon season. Except silicates, the measured parameters were higher at Goa and related significantly, suggesting bacteria centric, detritus-driven region. At Ratnagiri, phytoplankton biomass related positively with silicate suggesting a region dominated by primary producers. This dominance perhaps got reflected as a higher tertiary yield. Thus, even though the regions are geographically proximate, the different biological response could be attributed to the differences in the web of interactions between the measured variables.