Seasonal dissolved rare earth element dynamics of the Amazon River main stem, its tributaries, and the Curuai floodplain

[1] We present a comprehensive dissolved rare earth element (REE) data set for the Amazon River and its main tributaries, Rio Negro, Solimoes, and Madeira, as well as the Curuai floodplain. The two-year time series show that REE vary seasonally with discharge in each of the tributaries, and indicate a hydrologically dominated control. Upper crust normalized REE patterns are relatively constant throughout the year, with Ce/Ce* anomalies being positively related to discharge. We propose revised annual dissolved REE fluxes to the surface Atlantic Ocean based on an integration of the seasonal data. For Nd (< 0.22 mu m) this results in an average flux of 607 +/- 43 T/yr, which is at least 1.6 times larger than the previous estimate of 374 T/yr (< 0.45 mu m) based on low water stage data. Moreover, during the high water season the maximum Nd flux measures 1277 t. yr(-1), constituting 30% of the required flux to the Atlantic Ocean (Tachikawa et al., 2003). Consequently, a smaller contribution of Nd from atmospheric and river particle desorption is required than was previously suggested. A mass balance of Amazon tributaries and observed fluxes at Obidos indicates that dissolved LREE behave quasi-conservatively. Conversely, the HREE mass balance presents a deficit during the high water stages, which could be related to the passage of water through the floodplain system accompanied by solid/dissolved phase transfer.