U.S. Environmental Protection Agency
EPA Science Advisory Board
Background Information


Document NameOn the seasonal correlation of surface particle fields with wind stress and Mississippi discharge in the northern Gulf of Mexico,
Document AuthorSalisbury, J. E.
Campbell, J.W.
Linder, E.
Meeker, L.D.
Muller-Karger, F.E.
Vorosmarty, C.J.
Short DescriptionDeep-Sea Research Part Ii-Topical Studies in Oceanography, 51, 1187-1203.
CategorySubgroup 1: Characterization of the Cause(s) of Hypoxia
Publication Year2004
Text:

Abstract: Spatio-temporal correlation analyses were performed on time series of daily freshwater discharge, wind fields, and SeaWiFS-derived surface particle concentrations in the northern Gulf of Mexico. The influences of discharge and winds on surface particle concentrations were investigated by mapping temporal correlation coefficients at each pixel for the whole time series (1997-2000) and for each season during 1999 and 2000. Maps of the correlation between suspended particulate matter concentration (SPM) and river discharge suggest regions that are fluvially influenced. The particulate matter may be sediments carried by the river plume or biogenic particles (e.g., detritus) stimulated by the river discharge. The algorithm used to estimate SPM concentrations does not differentiate between sediment and detritus. Maps of the correlation between wind stress and SPM suggest regions where wind mixing accounts for particulate resuspension and subsequent transport. Regions of significant positive wind-SPM correlation were independent, and often spatially separated, from regions of strong positive discharge-SPM correlation. Thus, the influences of winds and discharge on particle distributions can be investigated independently. Regions of high wind-SPM correlation were associated with shallow shelf areas, as correlation contours generally followed the bathymetric contours, and expanded in size under offshore wind regimes. These areas exhibited less spatial and temporal variability than the regions of high discharge-SPM correlation associated with the Mississippi-Atchafalaya river system. There was no apparent relationship between the magnitude of Mississippi- Atchafalaya discharge and the spatial extent of the region of high discharge-SPM correlation during seasonal analyses. Instead, the spatial extent and orientation of the discharge-SPM correlation field appeared to be a function of winds (both their direction and speed) and the buoyancy of the plume.