Estuarine forcing of a river plume by river flow and tides

Abstract

[1] Estuarine forcing of a river plume by river discharge and tides is examined with a novel data set capable of characterizing semidiurnal to annual time scales. An instrumented ferry made high-resolution salinity measurements as it crossed the Fraser River plume, British Columbia, Canada, eight times per day over the years [2003][2004][2005][2006]. The relative contribution of different forcing factors in controlling the river plume salinity and surface area is examined over the full range of time scales. A Lomb-Scargle periodogram of the plume salinity shows energy concentrated in the semidiurnal and diurnal tidal bands. Diurnal lines contain more energy relative to semidiurnal lines than the respective tidal constituents would suggest. At fortnightly frequencies, local maxima in plume salinity coincide with periods of maxima in daily tidal height, with no phase shift. Thus the estuary adjusts quickly to changes in forcing. The effectiveness of tides in setting the plume salinity is a function of river discharge and is greatest when the river discharge is high and minimal when the river discharge is low. Tidal effects are superimposed onto the longperiod river discharge cycle. At time scales of 25 days or longer, the mean river plume salinity decreases quasi-linearly with increasing river discharge, but the change in salinity with river discharge is instantaneous to within the sampling resolution. Plume surface area increases with river discharge, from 200-500 km 2 at low river flow to 1000-1500 km 2 at high river flow. The magnitude of the surface area is predicted well by scaling the mouth deformation radius.Citation: Halverson, M. J., and R. Pawlowicz (2008), Estuarine forcing of a river plume by river flow and tides,

Hydrologic controls on coastal suspended sediment plumes around the Greenland Ice Sheet

“…Also, other physical factors besides terrestrial runoff influence plume dynamics in the short term, including tides and wind (e.g. Dowdeswell and Cromack, 1991;Whitney and Garvine, 2005;Halverson and Pawlowicz, 2008). Detecting short-term (days to ∼1 week) variations in terrestrial runoff from sediment plumes remains challenging from a satellite remote sensing approach.…”

“…The area and length of buoyant plumes have also been measured as a proxy for hydrologic outflows from the land surface to ocean (e.g. Thomas and Weatherbee, 2006;Halverson and Pawlowicz, 2008;Lihan et al, 2008;Chu et al, 2009;McGrath et al, 2010).…”

“…For marine-terminating outlet glaciers, sediment export to the ocean is dominated by the distinctly different mechanisms of iceberg rafting and/or en-and sub-glacially transported meltwater runoff (Andrews et al, 1994). In both environments, as plumes move farther downstream, sediment distribution and settling rates are further influenced by tides (Castaing and Allen, 1981;Bowers et al, 1998;Halverson and Pawlowicz, 2008), wind (Stumpf et al, 1993;Whitney and Garvine, 2005), and sea ice (Hasholt, 1996).…”

Sediment plumes as a proxy for local ice-sheet runoff in Kangerlussuaq Fjord, West Greenland

“…The tidal influence is often modulated by river discharge, such that during periods of high flow the estuarine stratification is too strong for the tides to produce enough shear to mix layers (Halverson and Pawlowicz, 2008). At the head of a fjord, the tide is primarily a standing wave and thus produces little residual flow, reducing the impact on the plume (Syvitski and others, 1987).…”

“…Alternatively, measurements of plume area, length and mean reflectance have been used to elucidate river discharge and coastal currents (Nezlin and DiGiacomo, 2005;Thomas and Weatherbee, 2006;Halverson and Pawlowicz, 2008;Lihan and others, 2008). Lihan and others (2008) showed a strong correlation between discharge of the Tokachi river, Japan, and plume area during the AprilOctober season from 1998 to 2002, using a 1 day time lag (r 2 = 0.40-0.66).…”