ALBERT

Description: Nature Geoscience 9, 375 (2016). doi:10.1038/ngeo2688 Authors: David C. Lang, Ian Bailey, Paul A. Wilson, Thomas B. Chalk, Gavin L. Foster & Marcus Gutjahr The circulation and internal structure of the oceans exert a strong influence on Earth’s climate because they control latitudinal heat transport and the segregation of carbon between the atmosphere and the abyss. Circulation change, particularly in the Atlantic Ocean, is widely suggested to have been instrumental in the intensification of Northern Hemisphere glaciation when large ice sheets first developed on North America and Eurasia during the late Pliocene, approximately 2.7 million years ago. Yet the mechanistic link and cause/effect relationship between ocean circulation and glaciation are debated. Here we present new records of North Atlantic Ocean structure using the carbon and neodymium isotopic composition of marine sediments recording deep water for both the Last Glacial to Holocene (35–5 thousand years ago) and the late Pliocene to earliest Pleistocene (3.3–2.4 million years ago). Our data show no secular change. Instead we document major southern-sourced water incursions into the deep North Atlantic during prominent glacials from 2.7 million years ago. Our results suggest that Atlantic circulation acts as a positive feedback rather than as an underlying cause of late Pliocene Northern Hemisphere glaciation. We propose that, once surface Southern Ocean stratification and/or extensive sea-ice cover was established, cold-stage expansions of southern-sourced water such as those documented here enhanced carbon dioxide storage in the deep ocean, helping to increase the amplitude of glacial cycles.

Description: The wetness of a watershed determines its response to precipitation, leading to variability in flood generation. The importance of total water storage - which includes snow, surface water, soil moisture and groundwater - for the predisposition of a region to flooding is less clear, in part because such comprehensive observations are rarely available. Here we demonstrate that basin-scale estimates of water storage derived from satellite observations of time-variable gravity can be used to characterize regional flood potential and may ultimately result in longer lead times in flood warnings. We use a case study of the catastrophic 2011 Missouri River floods to establish a relationship between river discharge, as measured by gauge stations, and basin-wide water storage, as measured remotely by NASA's Gravity Recovery and Climate Experiment (GRACE) mission. Applying a time-lagged autoregressive model of river discharge, we show that the inclusion of GRACE-based total water storage information allows us to assess the predisposition of a river basin to flooding as much as 5-11 months in advance. Additional case studies of flood events in the Columbia River and Indus River basins further illustrate that longer lead-time flood prediction requires accurate information on the complete hydrologic state of a river basin. © 2014 Macmillan Publishers Limited.

Description: The circulation and internal structure of the oceans exert a strong influence on Earth's climate because they control latitudinal heat transport and the segregation of carbon between the atmosphere and the abyss. Circulation change, particularly in the Atlantic Ocean, is widely suggested to have been instrumental in the intensification of Northern Hemisphere glaciation when large ice sheets first developed on North America and Eurasia during the late Pliocene, approximately 2.7 million years ago. Yet the mechanistic link and cause/effect relationship between ocean circulation and glaciation are debated. Here we present new records of North Atlantic Ocean structure using the carbon and neodymium isotopic composition of marine sediments recording deep water for both the Last Glacial to Holocene (35-5 thousand years ago) and the late Pliocene to earliest Pleistocene (3.3-2.4 million years ago). Our data show no secular change. Instead we document major southern-sourced water incursions into the deep North Atlantic during prominent glacials from 2.7 million years ago. Our results suggest that Atlantic circulation acts as a positive feedback rather than as an underlying cause of late Pliocene Northern Hemisphere glaciation. We propose that, once surface Southern Ocean stratification and/or extensive sea-ice cover was established, cold-stage expansions of southern-sourced water such as those documented here enhanced carbon dioxide storage in the deep ocean, helping to increase the amplitude of glacial cycles. © 2016 Macmillan Publishers Limited. All rights reserved.