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- Title
- Crevasse Splays Versus Avulsions: A Recipe For Land Building With Levee Breaches.
- Creator
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Nienhuis, Jaap H., Tornqvist, Torbjorn E., Esposito, Christopher R.
- Abstract/Description
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Natural-levee breaches can not only initiate an avulsion but also, under the right circumstances, lead to crevasse splay formation and overbank sedimentation. The formative conditions for crevasse splays are not well understood, yet such river sediment diversions form an integral part of billion-dollar coastal restoration projects. Here we use Delft3D to investigate the influence of vegetation and soil consolidation on the evolution of a natural-levee breach. Model simulations show that...
Show moreNatural-levee breaches can not only initiate an avulsion but also, under the right circumstances, lead to crevasse splay formation and overbank sedimentation. The formative conditions for crevasse splays are not well understood, yet such river sediment diversions form an integral part of billion-dollar coastal restoration projects. Here we use Delft3D to investigate the influence of vegetation and soil consolidation on the evolution of a natural-levee breach. Model simulations show that crevasse splays heal because floodplain aggradation reduces the water surface slope, decreasing water discharge into the flood basin. Easily erodible and unvegetated floodplains increase the likelihood for channel avulsions. Denser vegetation and less potential for soil consolidation result in small crevasse splays that are not only efficient sediment traps but also short-lived. Successful crevasse splays that generate the largest land area gain for the imported sediment require a delicate balance between water and sediment discharge, vegetation root strength, and soil consolidation.
Show less - Date Issued
- 2018-05-16
- Identifier
- FSU_libsubv1_wos_000434111700035, 10.1029/2018GL077933
- Format
- Citation
- Title
- Warming And Inhibition Of Salinization At The Ocean's Surface By Cyanobacteria.
- Creator
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Wurl, O., Bird, K., Cunliffe, M., Landing, W. M., Miller, U., Mustaffa, N. I. H., Ribas-Ribas, M., Witte, C., Zappa, C. J.
- Abstract/Description
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This paper describes high-resolution in situ observations of temperature and, for the first time, of salinity in the uppermost skin layer of the ocean, including the influence of large surface blooms of cyanobacteria on those skin properties. In the presence of the blooms, large anomalies of skin temperature and salinity of 0.95 degrees C and -0.49 practical salinity unit were found, but a substantially cooler (-0.22 degrees C) and saltier skin layer (0.19 practical salinity unit) was found...
Show moreThis paper describes high-resolution in situ observations of temperature and, for the first time, of salinity in the uppermost skin layer of the ocean, including the influence of large surface blooms of cyanobacteria on those skin properties. In the presence of the blooms, large anomalies of skin temperature and salinity of 0.95 degrees C and -0.49 practical salinity unit were found, but a substantially cooler (-0.22 degrees C) and saltier skin layer (0.19 practical salinity unit) was found in the absence of surface blooms. The results suggest that biologically controlled warming and inhibition of salinization of the ocean's surface occur. Less saline skin layers form during precipitation, but our observations also show that surface blooms of Trichodesmium sp. inhibit evaporation decreasing the salinity at the ocean's surface. This study has important implications in the assessment of precipitation over the ocean using remotely sensed salinity, but also for a better understanding of heat exchange and the hydrologic cycle on a regional scale. Plain Language Summary We provide high-resolution in situ observations of large cyanobacterial blooms floating in a biofilm-like microlayer on the ocean's surface. Our observations show biologically controlled warming and freshening of the surface by the surface blooms that are essential in understanding global heat exchange and the hydrologic cycle. Our study describes a new phenomenon to force "apparent" freshening of the sea surfacein the literature assumed to occur only by precipitation. It further challenges the development of algorithms and validation of remotely sensed temperature and salinity from space. Our finding of active microbial communities in the sea surface microlayer highlights the sea surface as another environment for extreme habitats and microbial adaptation. Our discovery of their influence on satellite observations of sea surface temperature and salinity is fundamental for future research in remote sensing, marine microbiology, air-sea interaction, and climate regulation.
Show less - Date Issued
- 2018-05-16
- Identifier
- FSU_libsubv1_wos_000434111700053, 10.1029/2018GL077946
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- Citation
- Title
- Population And Energy Elasticity Of Tornado Casualties.
- Creator
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Fricker, Tyler, Elsner, James B., Jagger, Thomas H.
- Abstract/Description
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Tornadoes are capable of catastrophic destruction and mass casualties, but there are yet no estimates of how sensitive the number of casualties are to changes in the number of people in harm's way or to changes in tornado energy. Here the relationship between tornado casualties (deaths and injuries), population, and energy dissipation is quantified using the economic concept of elasticity. Records of casualties from individual tornadoes over the period 2007-2015 are fit to a regression model....
Show moreTornadoes are capable of catastrophic destruction and mass casualties, but there are yet no estimates of how sensitive the number of casualties are to changes in the number of people in harm's way or to changes in tornado energy. Here the relationship between tornado casualties (deaths and injuries), population, and energy dissipation is quantified using the economic concept of elasticity. Records of casualties from individual tornadoes over the period 2007-2015 are fit to a regression model. The coefficient on the population term (population elasticity) indicates that a doubling in population increases the casualty rate by 21% [(17, 24)%, 95% credible interval]. The coefficient on the energy term (energy elasticity) indicates that a doubling in energy dissipation leads to a 33% [(30, 35)%, 95% credible interval] increase in the casualty rate. The difference in elasticity values show that on average, changes in energy dissipation have been relatively more important in explaining tornado casualties than changes in population. Assuming no changes in warning effectiveness or mitigation efforts, these elasticity estimates can be used to project changes in casualties given the known population trends and possible trends in tornado activity.
Show less - Date Issued
- 2017-04-28
- Identifier
- FSU_libsubv1_wos_000401847500058, 10.1002/2017GL073093
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- Citation
- Title
- Stationary mesoscale eddies, upgradient eddy fluxes, and the anisotropy of eddy diffusivity.
- Creator
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Lu, Jianhua, Wang, Fuchang, Liu, Hailong, Lin, Pengfei
- Abstract/Description
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The mesoscale eddies of which parameterization is needed in coarse-resolution ocean models include not only the transient eddies akin to baroclinic instability but also the stationary eddies associated with topography. By applying a modified Lorenz-type decomposition to the eddy-permitting Southern Ocean State Estimate, we show that the stationary mesoscale eddies contribute a significant part to the total eddy kinetic energy, eddy enstrophy, and the total eddy-induced isopycnal thickness and...
Show moreThe mesoscale eddies of which parameterization is needed in coarse-resolution ocean models include not only the transient eddies akin to baroclinic instability but also the stationary eddies associated with topography. By applying a modified Lorenz-type decomposition to the eddy-permitting Southern Ocean State Estimate, we show that the stationary mesoscale eddies contribute a significant part to the total eddy kinetic energy, eddy enstrophy, and the total eddy-induced isopycnal thickness and potential vorticity fluxes. We find that beneath middepth (about 1000 m) the upgradient eddy fluxes, or so-called "negative" eddy diffusivities, are mainly attributed to the stationary mesoscale eddies, whereas the remaining transient eddy diffusivity is positive, for which the Gent and McWilliams (1990) parameterization scheme applies well. A quantitative method of measuring the anisotropy of eddy diffusivity is presented. The effect of stationary mesoscale eddies is one of major sources responsible for the anisotropy of eddy diffusivity. We suggest that an independent parameterization scheme for stationary mesoscale eddies may be needed for coarse-resolution ocean models, although the transient eddies remain the predominant part of mesoscale eddies in the oceans.
Show less - Date Issued
- 2016-01-28
- Identifier
- FSU_libsubv1_wos_000372056400032, 10.1002/2015GL067384
- Format
- Citation
- Title
- Diagnosing United States hurricane landfall risk: An alternative to count-based methodologies.
- Creator
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Staehling, Erica M., Truchelut, Ryan E.
- Abstract/Description
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Assessing hurricane landfall risk is of immense public utility, yet extant methods of diagnosing annual tropical cyclone (TC) activity demonstrate no skill in diagnosing U.S. hurricane landfalls. Atlantic TC count itself has limited skill, explaining less than 20% of interannual variance in landfall incidence. Using extended landfall activity and reanalysis data sets, we employed empirical Poisson modeling to produce a landfall diagnostic index (LDI), incorporating spatially and temporally...
Show moreAssessing hurricane landfall risk is of immense public utility, yet extant methods of diagnosing annual tropical cyclone (TC) activity demonstrate no skill in diagnosing U.S. hurricane landfalls. Atlantic TC count itself has limited skill, explaining less than 20% of interannual variance in landfall incidence. Using extended landfall activity and reanalysis data sets, we employed empirical Poisson modeling to produce a landfall diagnostic index (LDI), incorporating spatially and temporally averaged upper level divergence, relative sea surface temperature, meridional wind, and zonal shear vorticity. LDI captures 31% of interannual variability of U.S. hurricane landfalls and offers physical insight into why indices that successfully capture TC activity fail to diagnose landfalls: there is inherent tension between conditions likely to steer hurricanes toward the U.S. and conditions favorable for TC development. Given this tension, attempting to diagnose, predict, or understand TC count is inadequate for quantifying societal impacts due to landfalling hurricanes.
Show less - Date Issued
- 2016-08-28
- Identifier
- FSU_libsubv1_wos_000384443800056, 10.1002/2016GL070117
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- Citation
- Title
- Characterizing the onset and demise of the Indian summer monsoon.
- Creator
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Noska, Ryne, Misra, Vasubandhu
- Abstract/Description
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An objective index of the onset and demise of the Indian summer monsoon (ISM) is introduced. This index has the advantage of simplicity by using only one variable, which is the spatially averaged all-India rainfall, a reliably observed quantity for more than a century. The proposed onset index is shown to be insensitive to all historic false onsets. By definition, now the seasonal mean rainfall anomalies become a function of variations in onset and demise dates, rendering their monitoring to...
Show moreAn objective index of the onset and demise of the Indian summer monsoon (ISM) is introduced. This index has the advantage of simplicity by using only one variable, which is the spatially averaged all-India rainfall, a reliably observed quantity for more than a century. The proposed onset index is shown to be insensitive to all historic false onsets. By definition, now the seasonal mean rainfall anomalies become a function of variations in onset and demise dates, rendering their monitoring to be very meaningful. This new index provides a comprehensive representation of the seasonal evolution of the ISM by capturing the corresponding changes in large-scale dynamic and thermodynamic variables. We also show that the interannual variability of the onset date of the ISM is associated with El Nino-Southern Oscillation (ENSO) with early (late) onsets preceded by cold (warm) ENSO.
Show less - Date Issued
- 2016-05-16
- Identifier
- FSU_libsubv1_wos_000378339200057, 10.1002/2016GL068409
- Format
- Citation
- Title
- Recent historically low global tropical cyclone activity.
- Creator
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Maue, Ryan Nicholas
- Abstract/Description
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Tropical cyclone accumulated cyclone energy (ACE) has exhibited strikingly large global interannual variability during the past 40-years. In the pentad since 2006, Northern Hemisphere and global tropical cyclone ACE has decreased dramatically to the lowest levels since the late 1970s. Additionally, the global frequency of tropical cyclones has reached a historical low. Here evidence is presented demonstrating that considerable variability in tropical cyclone ACE is associated with the...
Show moreTropical cyclone accumulated cyclone energy (ACE) has exhibited strikingly large global interannual variability during the past 40-years. In the pentad since 2006, Northern Hemisphere and global tropical cyclone ACE has decreased dramatically to the lowest levels since the late 1970s. Additionally, the global frequency of tropical cyclones has reached a historical low. Here evidence is presented demonstrating that considerable variability in tropical cyclone ACE is associated with the evolution of the character of observed large-scale climate mechanisms including the El Niño Southern Oscillation and Pacific Decadal Oscillation. In contrast to record quiet North Pacific tropical cyclone activity in 2010, the North Atlantic basin remained very active by contributing almost one-third of the overall calendar year global ACE.
Show less - Date Issued
- 2011
- Identifier
- FSU_migr_coaps_pubs-0039, 10.1029/2011GL047711
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- Citation
- Title
- Riverine dissolved lithium isotopic signatures in low-relief central Africa and their link to weathering regimes.
- Creator
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Henchiri, Soufian, Gaillardet, Jerome, Dellinger, Mathieu, Bouchez, Julien, Spencer, Robert G. M.
- Abstract/Description
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The isotopic composition of dissolved lithium (delta Li-7) near the Congo River mouth varied from 14% to 22% in 2010 and was negatively correlated to discharge. From the relationship between dissolved delta Li-7 and strontium isotopes, we suggest that this large variation is due to mixing of waters from two contrasting continental weathering regimes. One end-member (high delta Li-7 approximate to 25%) represents waters sourced from active lateritic soils covering the periphery of the basin ...
Show moreThe isotopic composition of dissolved lithium (delta Li-7) near the Congo River mouth varied from 14% to 22% in 2010 and was negatively correlated to discharge. From the relationship between dissolved delta Li-7 and strontium isotopes, we suggest that this large variation is due to mixing of waters from two contrasting continental weathering regimes. One end-member (high delta Li-7 approximate to 25%) represents waters sourced from active lateritic soils covering the periphery of the basin (Li highly sequestered into secondary mineral products) and another representing blackwater rivers (low delta Li-7 approximate to 5.7%) derived from the swampy central depression where high organic matter content in water leads to congruent dissolution of the Tertiary sedimentary bedrock. This suggests that the lithium isotopic signature of tropical low-relief surfaces is not unique and traces the long-term, large-scale vertical motions of the continental crust that control geomorphological settings. This evolution should be recorded in the oceanic secular delta Li-7 curve.
Show less - Date Issued
- 2016-05-16
- Identifier
- FSU_libsubv1_wos_000378339200038, 10.1002/2016GL067711
- Format
- Citation
- Title
- Subinertial canyon resonance.
- Creator
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Clarke, Allan J., Van Gorder, Stephen
- Abstract/Description
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Near the bottom of a narrow canyon currents that oscillate back and forth along the bottom slope h(x) in a stratified ocean of buoyancy frequency N do so with a natural internal gravitational frequency Nh(x). From May 2012 to May 2013 Acoustic Doppler Current Profiler measurements were made at 715 m depth in the deep narrow part of the DeSoto Canyon south of Pensacola, Florida, in water with 2 pi/Nh(x) approximate to 2.5 days. Above the canyon the flow follows the large-scale isobaths, but...
Show moreNear the bottom of a narrow canyon currents that oscillate back and forth along the bottom slope h(x) in a stratified ocean of buoyancy frequency N do so with a natural internal gravitational frequency Nh(x). From May 2012 to May 2013 Acoustic Doppler Current Profiler measurements were made at 715 m depth in the deep narrow part of the DeSoto Canyon south of Pensacola, Florida, in water with 2 pi/Nh(x) approximate to 2.5 days. Above the canyon the flow follows the large-scale isobaths, but beneath the canyon rim the current oscillates along the canyon axis with 2-3 day periodicity, and is much stronger than and uncorrelated with the overlying flow. A simple theoretical model explains the resonant response. Published observations from the Hudson and Gully canyons suggest that the strong subinertial current oscillations observed in these canyons occur close to the relevant local frequency Nh(x), consistent with the proposed simple model physics.
Show less - Date Issued
- 2016-04-28
- Identifier
- FSU_libsubv1_wos_000378338800032, 10.1002/2016GL068258
- Format
- Citation
- Title
- Estimates of vertical turbulent mixing used to determine a vertical gradient in net and gross oxygen production in the oligotrophic South Pacific Gyre.
- Creator
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Haskell, W. Z., Prokopenko, M. G., Stanley, R. H. R., Knapp, A. N.
- Abstract/Description
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Mixed layer (ML) gross (GOP) and net (NOP) oxygen production rates based on in situ mass balances of triple oxygen isotopes (TOI) and O-2/Ar are influenced by vertical transport from below, a term traditionally difficult to constrain. Here we present a new approach to estimate vertical eddy diffusivity (K-z) based on density gradients in the upper thermocline and wind speed-based rates of turbulent shear at the ML depth. As an example, we use this K-z, verified by an independent Be-7-based...
Show moreMixed layer (ML) gross (GOP) and net (NOP) oxygen production rates based on in situ mass balances of triple oxygen isotopes (TOI) and O-2/Ar are influenced by vertical transport from below, a term traditionally difficult to constrain. Here we present a new approach to estimate vertical eddy diffusivity (K-z) based on density gradients in the upper thermocline and wind speed-based rates of turbulent shear at the ML depth. As an example, we use this K-z, verified by an independent Be-7-based estimate, in an O-2/TOI budget at a site in the oligotrophic South Pacific Gyre. NOP equaled 0.310.16mmolm(-2)d(-1) in the ML (similar to 55-65m depth) and 1.20.4mmolm(-2)d(-1) (80%) beneath the ML, while GOP equaled 7427mmolm(-2)d(-1) (86%) in the ML and 124mmolm(-2)d(-1) (14%) below, revealing a vertical gradient in production rates unquantifiable without the K-z estimate.
Show less - Date Issued
- 2016-07-28
- Identifier
- FSU_libsubv1_wos_000383290200037, 10.1002/2016GL069523
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- Citation
