Interaction between seabed morphology and water mass in the South Eastern Arabian Sea: deductions of water mass flow

Abstract

Geomorphic analysis utilizing multibeam bathymetry and sediment profiler data along with conductivity, temperature and depth (CTD) measurements was undertaken to investigate morphological aspects of bottom current features that prevail in the area. The aim of the study was to deduce the prevailing water mass in the area and to infer interactions between water mass and seabed of South Eastern Arabian Sea. Morphological and bottom current features were identified and analysed. Based on morphological components and their structural orientation, deduction of flow pattern and direction of current flow in the area were attempted. Deconstructing structural aspects of typical bottom current features such as contourite drifts and scours reveal origin under influence of consistent exogenic bottom current having definitive flow pattern. Sub-surface seismic profiles were analysed to infer the presence of a consistently aggrading seafloor. The aspect distribution computed exhibits a prominent trend ranging between 200° and 275° indicating NNW-SSE orientation of erosive features which is usually synonymous with flow direction in the area. Backscatter intensity analysis undertaken for the area revealed seafloor with patches of loose to compact surface sediment distribution. Variation in reflection intensity level from surface sediments was utilized to demarcate zones that are susceptible in future to consistent turbulence-induced erosion. Temperature salinity (TS) diagram for values from CTD measurements was plotted overlaying isopycnals and the resulting plots tagged for various water masses that prevail in the Arabian Sea. Owing to the depth of the study area (~ 1800 m) and structural orientation of bottom current features, dominant oceanographic agent from TS plot was deduced to be the North Indian Deep Water (NIDW). Surface and sub-surface morphology of existing features were interpreted for influence of bottom current action. Geomorphic analysis of seabed is an efficient method to understand the flow pattern and of prevailing water masses and can be applied as passive indicators of bottom current flow. This approach of deducing flow pattern and intensity of water mass movement by analysing morphology of the undersea features can be effectively used globally especially in areas where adequate data and observations for deep water masses are scarce.