A global satellite survey of density plumes at river mouths and at other environments: Plume configurations, external controls, and implications for deep-water sedimentation

Abstract

The U. S. National Aeronautics and Space Administration (NASA) has archived thousands of satellite images of density plumes in its online publishing outlet called ‘Earth Observatory’ since 1999. Although these images are in the public domain, there has not been any systematic compilation of configurations of density plumes associated with various sedimentary environments and processes. This article, based on 45 case studies covering 21 major rivers (e.g., Amazon, Betsiboka, Congo [Zaire], Copper, Hugli [Ganges], Mackenzie, Mississippi, Niger, Nile, Rhone, Rio de la Plata, Yellow, Yangtze, Zambezi, etc.) and six different depositional environments (i.e., marine, lacustrine, estuarine, lagoon, bay, and reef), is the first attempt in illustrating natural variability of configurations of density plumes in modern environments. There are, at least, 24 configurations of density plumes. An important finding of this study is that density plumes are controlled by a plethora of 18 oceanographic, meteorological, and other external factors. Examples are: 1) Yellow River in China by tidal shear front and by a change in river course; 2) Yangtze River in China by shelf currents and vertical mixing by tides in winter months; 3) Rio de la Plata Estuary in Argentina and Uruguay by Ocean currents; 4) San Francisco Bay in California by tidal currents; 5) Gulf of Manner in the Indian Ocean by monsoonal currents; 6) Egypt in Red Sea by Eolian dust; 7) U.S. Atlantic margin by cyclones; 8) Sri Lanka by tsunamis; 9) Copper River in Alaska by high-gradient braid delta; 10) Lake Erie by seiche; 11) continental margin off Namibia by upwelling; 12) Bering Sea by phytoplankton; 13) the Great Bahama Bank in the Atlantic Ocean by fish activity; 14) Indonesia by volcanic activity; 15) Greenland by glacial melt; 16) South Pacific Ocean by coral reef; 17) Carolina continental Rise by pockmarks; and 18) Otsuchi Bay in Japan by internal bore. The prevailing trend in promoting a single type of river-flood triggered hyperpycnal flow is flawed because there are 16 types of hyperpycnal flows. River-flood derived hyperpycnal flows are muddy in texture and they occur close to the shoreline in inner shelf environments. Hyperpycnal flows are not viable transport mechanisms of sand and gravel across the shelf into the deep sea. The available field observations suggest that they do not form meter-thick sand layers in deep water settings. For the above reasons, river-flood triggered hyperpycnites are considered unsuitable for serving as petroleum reservoirs in deep-water environments until proven otherwise. Key words: NASA satellites, density plumes, river-mouth environments, controlling factors, hyperpycnal flows, submarine fans, deep-water reservoirs