Syvitski James P. M.

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Syvitski
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James P. M.
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  • Preprint
    Sinking deltas due to human activities
    ( 2008-12-26) Syvitski, James P. M. ; Kettner, Albert J. ; Overeem, Irina ; Hutton, Eric W. H. ; Hannon, Mark T. ; Brakenridge, G. Robert ; Day, John W. ; Vorosmarty, Charles J. ; Saito, Yoshiki ; Giosan, Liviu ; Nicholls, Robert J.
    The world’s population living on low-lying deltas is increasingly vulnerable to flooding, whether from intense rainfall, rivers or from hurricane-induced storm surges. High-resolution SRTM and MODIS satellite data along with geo-referenced historical map analysis allows quantification of the extent of low-lying delta areas and the role of humans in contributing to their vulnerability. Thirty-three major deltas collectively include ~26,000 km2 of area below local mean sea level and ~96,000 km2 of vulnerable area below 2 m a.s.l. The vulnerable areas may increase by 50% under projected 21st Century eustatic sea level rise, a conservative estimate given the current trends in the reduction in sedimentary deposits forming on the surface of these deltas. Analysis of river sediment load and delta topographical data show that these densely populated, intensively farmed landforms, that often host key economic structures, have been destabilized by human-induced accelerated sediment compaction from water, oil and gas mining, by reduction of incoming sediment from upstream dams and reservoirs, and from floodplain engineering.
  • Article
    Global N removal by freshwater aquatic systems using a spatially distributed, within-basin approach
    (American Geophysical Union, 2008-06-20) Wollheim, Wilfred M. ; Vorosmarty, Charles J. ; Bouwman, A. F. ; Green, Pamela ; Harrison, John A. ; Linder, Ernst ; Peterson, Bruce J. ; Seitzinger, Sybil P. ; Syvitski, James P. M.
    We explored the role of aquatic systems in the global N cycle using a spatially distributed, within-basin, aquatic nitrogen (N) removal model, implemented within the Framework for Aquatic Modeling in the Earth System (FrAMES-N). The model predicts mean annual total N (TN) removal by small rivers (with drainage areas from 2.6–1000 km2), large rivers, lakes, and reservoirs, using a 30′ latitude × longitude river network to route and process material from continental source areas to the coastal zone. Mean annual aquatic TN removal (for the mid-1990s time period) is determined by the distributions of aquatic TN inputs, mean annual hydrological characteristics, and biological activity. Model-predicted TN concentrations at basin mouths corresponded well with observations (median relative error = −12%, interquartile range of relative error = 85%), an improvement over assumptions of uniform aquatic removal across basins. Removal by aquatic systems globally accounted for 14% of total N inputs to continental surfaces, but represented 53% of inputs to aquatic systems. Integrated aquatic removal was similar in small rivers (16.5% of inputs), large rivers (13.6%), and lakes (15.2%), while large reservoirs were less important (5.2%). Bias related to runoff suggests improvements are needed in nonpoint N input estimates and/or aquatic biological activity. The within-basin approach represented by FrAMES-N will improve understanding of the freshwater nutrient flux response to anthropogenic change at global scales.
  • Article
    Cyclone-driven deep sea injection of freshwater and heat by hyperpycnal flow in the subtropics
    (American Geophysical Union, 2010-11-04) Kao, Shuh-Ji ; Dai, Minhan ; Selvaraj, K. ; Zhai, W. ; Cai, Pinghe ; Chen, Shih-Nan ; Yang, J. Y. T. ; Liu, J. T. ; Liu, C. C. ; Syvitski, James P. M.
    The western tropical Pacific gives birth to 23 tropical cyclones annually, bringing torrential rainfall to mountainous islands across Oceania resulting in a global sediment production hotspot, in which many rivers have great hyperpycnal potential. By using a temperature (T) and salinity (S) profiler, we observed anomalously warm, low salinity turbid water at 3000–3700 m depths in seas ∼180 km off southwestern Taiwan immediately after Typhoon Morakot in 2009. This 250m-thick bottom-hugging water occupies ∼2400 km2, and contains 0.15% freshwater, suggesting a remarkably high fraction (6–10%) of event rainfall from southwestern Taiwan. These characteristics indicate the turbid water originated from shallow coastal waters via hyperpycnal flow. Apparently, sediment produced from the land during tropical cyclones open an “express gate” to convey heat and freshwater vertically to the deep ocean basin subsequently warming the deep water from the bottom up.