Stable-isotope (H, O, and Si) evidence for seasonal variations in hydrology and Si cycling from modern waters in the Nile Basin: implications for interpreting the Quaternary record

► Large seasonal shifts in δ2H and δ18O reflect changes in water balance. ► Upper limit of δ30Si values for dissolved Si in natural waters is increased by 1‰. ► Progressive downstream enrichment in δ30Si represents Si uptake by aquatic ecosystems. ► δ30Si values are enriched in dry season due to biological demand exceeding DSi supply. ► DSi flux to the oceans can be expected to vary on a glacial/interglacial time scale.