Loading in 2 Seconds...
Loading in 2 Seconds...
Southwestern Atlantic Ocean Margin Workshop Montevideo, Uruguay 16-22 November 2008. Submarine Groundwater Discharge into the ocean off Mangueira Lagoon via 222 Rn and Ra isotopes: Preliminary findings and perspectives . Isaac R. Santos ; William Burnett
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Southwestern Atlantic Ocean Margin Workshop Montevideo, Uruguay 16-22 November 2008 Submarine Groundwater Discharge into the ocean off Mangueira Lagoon via 222Rn and Ra isotopes: Preliminary findings and perspectives Isaac R. Santos; William Burnett Department of Oceanography, Florida State University, Tallahassee, FL, USA Felipe Niencheski; Karina Attisano; Carlos Andrade; Idel Milani Department of Chemistry, Fundação Universidade do Rio Grande, Rio Grande, Brazil
Outline • Area background • Tracing SGD via 222Rn and radium isotopes • Is the La Plata River Paleocanal a preferential SGD pathway?
Brazil - SGD Fe inputs ~10% of atmospheric Fe inputs into the entire South Atlantic (Windom et al., 2006) Patos Mirim • Higher SGD than North of Patos Lagoon? • Mangueira Lagoon level is higher than • Patos Lagoon level • Lagoon closer to the ocean • Sediments more permeable (shell deposits) Mangueira
Alongshore distribution of silicate (10 m depth) - Patos Lagoon and La Plata River are the obvious nutrient sources • No N-S trends suggest an additional source – • Widespread, diffuse SGD? Silicate in mM data from Attisano, Niencheski, et al., 2008
222Rn as a SGD tracer Platform with a continuous Rn monitor system Push-point piezometer for groundwater sampling Non-steady state box model Assume wave action was constant during deployment
222Rn time series Concheiros Hermenegildo • Background 226Ra: ~70 dpm/m3 • Excess radon in spite of breaking waves • Modeled SGD rates 2.22.4 cm/day
- Some enriched 223Ra and 224Ra samples in the south - Are the shell deposits a preferential flow path? Radium along-shore transect • Fresher seawater in the winter • No seasonal radium changes Concentrations in dpm/100L
Radium in beach groundwater C*gw Modeling SGD from radium isotopes Seawater residence time (t) : Advection rates:
Estimated SGD inputs (cm/day) Overall averages: 3.1 cm/day Area: 220 km long; 10 km wide Total SGD into the area: ~800 m3/s Patos Lagoon Flux: ~2400 m3/s Is SGD a new source of nutrients (fresh SGD) or purely a recycling mechanism (saline SGD)?
Offshore radium transect • Onshore radium source, likely SGD • Mixing coefficients >3000 m2/s (too high!). • Violates assumption of no inputs offshore? • Peak at ~100 km indicates an additional source or advection of nearshore waters
La Plata paleocanal • 70 km long • 20 km wide • - 30 m deep Campos et al., 2007.
Silicate in bottom waters - SGD or sub-Antarctic water advection onto the shelf? mM Paleocanal slope
Summary 1) Radium is the preferred SGD tracer as we cannot model how waves influence radon evasion 2) SGD is potentially a major source of water and nutrients to the Albardão area and the entire SWAOM margin 3) Shell deposits and the La Plata River Paleocanal may represent a preferential flow path for SGD