Climatic Control of Riverine and Seawater Uranium-Isotope Ratios

• Published in: Science (American Association for the Advancement of Science) Vol. 305; no. 5685; pp. 851 - 854
• Main Authors: Robinson, Laura F., Henderson, Gideon M., Hall, Lisa, Matthews, Iain
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 06.08.2004; The American Association for the Advancement of Science
• Subjects: Brackish; Chemistry; Climate change; Climate models; Cooling; Corals; Earth; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Groundwater; Hydrology; Hydrology. Hydrogeology; Isotopes; Marine; Marine and continental quaternary; Marine geology; Mechanical weathering; Organic Chemistry; Paleoclimatology; Rain; Rivers; Sea water; Seawater; Speleothems; Surficial geology; Topography; Uranium; Water; Weathering; New Zealand; South Island; New Zealand, South I; glaciers; physical weathering; Weichselian; Australasia; speleothems; upper Quaternary; paleoclimate; U-238/U-234; climate modification; hydrochemistry; isotopes; Cenozoic; climate cooling; Younger Dryas; sea water; rivers; models; rainfall; corals; atmospheric precipitation; Quaternary; weathering; climate; upper Pleistocene; glaciation; ocean; interpretation; uranium; Invertebrata; Phanerozoic; invertebrates; Pleistocene; climatic controls
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1099673

The large variation in the ratio of uranium-234 to uranium-238 ($^{234}U/^{238}U$) in rivers is not well understood, but may provide information about past weathering and rainfall and is important because it controls seawater ($^{234}U/^{238}U$). Here, we demonstrate the importance of physical weathering and rainfall for ($^{234}U/^{238}U$), using rivers from South Island, New Zealand. These data allow interpretation of an existing speleothem ($^{234}U/^{238}U$) 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 ($^{234}U/^{238}U$) during glacial cycles indicates that rejection of corals based on modern $(^{234}U/^{238}U) \pm <0.01$ is not merited and may reject the highest quality ages.