Climatic control of riverine and Seawater uranium-isotope ratios

The large variation in the ratio of uranium-234 to uranium-238 (U-234/U-238) in rivers is not well understood, but may provide information about past weathering and rainfall and is important because it controls seawater (U-234/U-238). Here, we demonstrate the importance of physical weathering and rainfall for (U-234/U-238), using rivers from South Island, New Zealand. These data allow interpretation of an existing speleothem (U-234/U-238) record and suggest that New Zealand glacier advance 13,000 years ago was influenced by increased rainfall rather than by Younger Dryas-like cooling. A model of seawater (U-234/U-238) during glacial cycles indicates that rejection of corals based on modern (U-234/U-238) +/- < 0.01 is not merited and may reject the highest quality ages.