Amazon Shelf SEDiment Study (AmasSeds)


Funding Agency: NSF

Abstract:

Nittrouer, C.A., DeMaster, D.J., 1996. The Amazon shelf setting: tropical, energetic, and influenced by a large river. Continental Shelf Research, 16, 5/6, 553-573.

A Multidisciplinary Amazon Shelf SEDiment Study (AmasSeds) investigated the oceanic processes near the mouth of the Amazon River in order to understand the fate of its enormous discharge of water, solutes and particulates. In addition to receiving a large fluvial discharge, the continental shelf near the Amazon mouth is situated on the equator and experiences an extremely energetic physical regime. As such, it represents an end member in the spectrum of coastal marine settings, with regard to latitude, energy and discharge. The oceanic processes occurring on the Amazon shelf reflect these environmental characteristics.

A range of interdisciplinary interactions was observed on the Amazon shelf in response to its low latitude, among them: plume dynamics have little influence from Coriolis acceleration, riverine particles experience intense weathering conditions, high primary productivity occurs during all seasons, and shoreline sedimentation involves mangrove vegetation. The high energy conditions of the Amazon shelf result in: water motions dependent on suspended-sediment distributions, tracemetal adsorption controlled by seabed dynamics, severe restriction of macrobenthos, and deep physical reworking of sedimentary strata (to 1 m or more). The great discharge of fluvial materials (water, solutes, particulates) directly or indirectly causes three-dimensional estuarine-like processes and very high rates of primary productivity, sediment accumulation and carbon burial to occur on the shelf.

Although AmasSeds research can link a wide range of interdisciplinary oceanic processes to latitude, energetics or discharge, in many cases the observed process is strongly influenced by a coupling of these characteristics. For example, the dominance of Fe and Mn oxides in controlling redox reactions is a result of tropical weathering that concentrates the Fe and Mn and of intense seabed reworking that regularly reoxidizes these phases. Therefore, the importance of Fe and Mn oxides is a result of both latitude and energy considerations. A fourth characteristic of the Amazon system is its tectonic setting, which determines physiographic features such as drainage-basin size and shelf width. Low latitude and great discharge characterize all areas of the wet tropics; energy expenditure and tectonic setting vary with specific location. All four characteristics must be considered when extrapolating AmasSeds observations to other areas and attempting to predict or interpret oceanic processes.

Collaborators

University of Washington: Chuck Nittrouer

NCSU: Dave Demaster