Stratification and mixing in large floodplain lakes along the lower Amazon River

Abstract Large, shallow lakes are common in the extensive floodplainsthroughout the tropics. To determine controls on their mixing dynamics, we instrumented 5 stations in two shallow, connected tropical lakes on the lower Amazon floodplainwith meteorological and temperature sensors. A tight relation between changes in thermal structure and L MO / h (the ratio of the Monin-Obukhov lengthscale to the depth of the actively mixing layer) indicates the sensitivity of thermal structure to wind speed relative to heating and cooling. Four regimes led to variations in mixing: (i) high solar radiation with light winds in the mid-morning to early afternoon resulted in shallow stratification, 0  MO / h MO / h  > 1; (iii) by late afternoon, buoyancy flux became negative and L MO / h u ∗ W and w ∗ both >0.06 m s −1 , mixing from wind and cooling co-occurred; and (iv) convection dominated mixing on nights with light winds, −1  MO / h