TY  - JOUR
A1  - Brooke, Sam A. S.
A1  - Whittaker, Alexander C.
A1  - Armitage, John J.
A1  - Watkins, Stephen E.
A1  - D'Arcy, Mitchell
T1  - Quantifying sediment transport dynamics on alluvial fans from spatial and temporal changes in Grain Size, Death Valley, California
JF  - Journal of geophysical research : Earth surface
N2  - How information about sediment transport processes is transmitted to the sedimentary record remains a complex problem for the interpretation of fluvial stratigraphy. Alluvial fan deposits represent the condensed archive of sediment transport, which is at least partly controlled by tectonics and climate. For three coupled catchment-fan systems in northern Death Valley, California, we measure grain size across 12 well-preserved Holocene and late-Pleistocene surfaces, mapped in detail from field observations and remote sensing. Our results show that fan surfaces correlated to the late Pleistocene are, on average, 30-50% coarser than active or Holocene fan surfaces. We adopt a self-similar form of grain size distribution based on the observed stability of the ratio between mean grain size and standard deviation downstream. Using statistical analysis, we show that fan surface grain size distributions are self-similar. We derive a relative mobility function using our self-similar grain size distributions, which describes the relative probability of a given grain size being transported. We show that the largest mobile grain sizes are between 20 and 35mm, a value that varies over time and is clearly lower in the Holocene than in the Pleistocene; a change we suggest is due to a drier climate in the Holocene. These results support recent findings that alluvial fan sedimentology can record past environmental change and that these landscapes are potentially sensitive to climatic change over a glacial-interglacial cycle. We demonstrate that the self-similarity methodology offers a means to explore changes in relative mobility of grain sizes from preserved fluvial deposits. Plain Language Summary A key challenge in Earth Science is understanding how landscapes respond to climate. It may be possible to observe measurable differences in certain landscapes settings such as alluvial fans in desert regions. Alluvial fans are believed to be effective recorders of climate, representing a cumulative store of material transported downstream by rainfall-sensitive river systems. In northern Death Valley, California, we measure at high resolution grain size on three alluvial fans with surfaces that date from the Holocene and the arid climate of today to the 20-40% wetter late-Pleistocene epoch. We find that older late-Pleistocene surfaces are coarser on average than surfaces deposited during the modern and Holocene dry period, suggesting a changing sediment transport regime potentially in response to precipitation. We also show that measured grain size distributions within and between surfaces can be successfully normalized based on the decay in mean grain size and variance downstream, exhibiting a self-similar pattern. Finally, we employ a grain size relative mobility model using our field data to establish which grain sizes are likely to be in transport or locked in the substrate. This model predicts that during the wetter late-Pleistocene mobile grain sizes are up to 40% larger than during the Holocene.
KW  - alluvial fans
KW  - grain size
KW  - sediment transport
KW  - self-similarity
KW  - fluvial geomorphology
KW  - Death Valley
Y1  - 2018
U6  - https://doi.org/10.1029/2018JF004622
SN  - 2169-9003
SN  - 2169-9011
VL  - 123
IS  - 8
SP  - 2039
EP  - 2067
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Gottwald, Georg A.
A1  - Mitchell, Lewis
A1  - Reich, Sebastian
T1  - Controlling overestimation of error covariance in ensemble kalman filters with sparse observations a variance-limiting kalman filter
JF  - Monthly weather review
N2  - The problem of an ensemble Kalman filter when only partial observations are available is considered. In particular, the situation is investigated where the observational space consists of variables that are directly observable with known observational error, and of variables of which only their climatic variance and mean are given. To limit the variance of the latter poorly resolved variables a variance-limiting Kalman filter (VLKF) is derived in a variational setting. The VLKF for a simple linear toy model is analyzed and its range of optimal performance is determined. The VLKF is explored in an ensemble transform setting for the Lorenz-96 system, and it is shown that incorporating the information of the variance of some unobservable variables can improve the skill and also increase the stability of the data assimilation procedure.
Y1  - 2011
U6  - https://doi.org/10.1175/2011MWR3557.1
SN  - 0027-0644
VL  - 139
IS  - 8
SP  - 2650
EP  - 2667
PB  - American Meteorological Soc.
CY  - Boston
ER  - 
TY  - JOUR
A1  - Tiscareno, Matthew S.
A1  - Mitchell, Colin J.
A1  - Murray, Carl D.
A1  - Di Nino, Daiana
A1  - Hedman, Matthew M.
A1  - Schmidt, Jürgen
A1  - Burns, Joseph A.
A1  - Cuzzi, Jeffrey N.
A1  - Porco, Carolyn C.
A1  - Beurle, Kevin
A1  - Evans, Michael W.
T1  - Observations of Ejecta clouds produced by impacts onto Saturn's rings
JF  - Science
N2  - We report observations of dusty clouds in Saturn's rings, which we interpret as resulting from impacts onto the rings that occurred between 1 and 50 hours before the clouds were observed. The largest of these clouds was observed twice; its brightness and cant angle evolved in a manner consistent with this hypothesis. Several arguments suggest that these clouds cannot be due to the primary impact of one solid meteoroid onto the rings, but rather are due to the impact of a compact stream of Saturn-orbiting material derived from previous breakup of a meteoroid. The responsible interplanetary meteoroids were initially between 1 centimeter and several meters in size, and their influx rate is consistent with the sparse prior knowledge of smaller meteoroids in the outer solar system.
Y1  - 2013
U6  - https://doi.org/10.1126/science.1233524
SN  - 0036-8075
VL  - 340
IS  - 6131
SP  - 460
EP  - 464
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Jones, Geraint H.
A1  - Arridge, Christopher S.
A1  - Coates, Andrew J.
A1  - Lewis, Gethyn R.
A1  - Kanani, Sheila
A1  - Wellbrock, Anne
A1  - Young, David T.
A1  - Crary, Frank J.
A1  - Tokar, Robert L.
A1  - Wilson, R. J.
A1  - Hill, Thomas W.
A1  - Johnson, Robert E.
A1  - Mitchell, Donald G.
A1  - Schmidt, Jürgen
A1  - Kempf, Sascha
A1  - Beckmann, Uwe
A1  - Russell, Christopher T.
A1  - Jia, Y. D.
A1  - Dougherty, Michele K.
A1  - Waite, J. Hunter
A1  - Magee, Brian A.
T1  - Fine jet structure of electrically charged grains in Enceladus' plume
N2  - By traversing the plume erupting from high southern latitudes on Saturn's moon Enceladus, Cassini orbiter instruments can directly sample the material therein. Cassini Plasma Spectrometer, CAPS, data show that a major plume component comprises previously-undetected particles of nanometer scales and larger that bridge the mass gap between previously observed gaseous species and solid icy grains. This population is electrically charged both negative and positive, indicating that subsurface triboelectric charging, i.e., contact electrification of condensed plume material may occur through mutual collisions within vents. The electric field of Saturn's magnetosphere controls the jets' morphologies, separating particles according to mass and charge. Fine-scale structuring of these particles' spatial distribution correlates with discrete plume jets' sources, and reveals locations of other possible active regions. The observed plume population likely forms a major component of high velocity nanometer particle streams detected outside Saturn's magnetosphere.
Y1  - 2009
UR  - http://www.agu.org/journals/gl/
U6  - https://doi.org/10.1029/2009gl038284
SN  - 0094-8276
ER  - 
TY  - JOUR
A1  - De Frenne, Pieter
A1  - Rodriguez-Sanchez, Francisco
A1  - Coomes, David Anthony
A1  - Bäten, Lander
A1  - Versträten, Gorik
A1  - Vellend, Mark
A1  - Bernhardt-Römermann, Markus
A1  - Brown, Carissa D.
A1  - Brunet, Jörg
A1  - Cornelis, Johnny
A1  - Decocq, Guillaume M.
A1  - Dierschke, Hartmut
A1  - Eriksson, Ove
A1  - Gilliam, Frank S.
A1  - Hedl, Radim
A1  - Heinken, Thilo
A1  - Hermy, Martin
A1  - Hommel, Patrick
A1  - Jenkins, Michael A.
A1  - Kelly, Daniel L.
A1  - Kirby, Keith J.
A1  - Mitchell, Fraser J. G.
A1  - Naaf, Tobias
A1  - Newman, Miles
A1  - Peterken, George
A1  - Petrik, Petr
A1  - Schultz, Jan
A1  - Sonnier, Gregory
A1  - Van Calster, Hans
A1  - Waller, Donald M.
A1  - Walther, Gian-Reto
A1  - White, Peter S.
A1  - Woods, Kerry D.
A1  - Wulf, Monika
A1  - Graae, Bente Jessen
A1  - Verheyen, Kris
T1  - Microclimate moderates plant responses to macroclimate warming
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - Recent global warming is acting across marine, freshwater, and terrestrial ecosystems to favor species adapted to warmer conditions and/or reduce the abundance of cold-adapted organisms (i.e., "thermophilization" of communities). Lack of community responses to increased temperature, however, has also been reported for several taxa and regions, suggesting that "climatic lags" may be frequent. Here we show that microclimatic effects brought about by forest canopy closure can buffer biotic responses to macroclimate warming, thus explaining an apparent climatic lag. Using data from 1,409 vegetation plots in European and North American temperate forests, each surveyed at least twice over an interval of 12-67 y, we document significant thermophilization of ground-layer plant communities. These changes reflect concurrent declines in species adapted to cooler conditions and increases in species adapted to warmer conditions. However, thermophilization, particularly the increase of warm-adapted species, is attenuated in forests whose canopies have become denser, probably reflecting cooler growing-season ground temperatures via increased shading. As standing stocks of trees have increased in many temperate forests in recent decades, local microclimatic effects may commonly be moderating the impacts of macroclimate warming on forest understories. Conversely, increases in harvesting woody biomass-e.g., for bioenergy-may open forest canopies and accelerate thermophilization of temperate forest biodiversity.
KW  - climate change
KW  - forest management
KW  - understory
KW  - climatic debt
KW  - range shifts
Y1  - 2013
U6  - https://doi.org/10.1073/pnas.1311190110
SN  - 0027-8424
VL  - 110
IS  - 46
SP  - 18561
EP  - 18565
PB  - National Acad. of Sciences
CY  - Washington
ER  - 
TY  - JOUR
A1  - Hochrein, Lena
A1  - Mitchell, Leslie A.
A1  - Schulz, Karina
A1  - Messerschmidt, Katrin
A1  - Müller-Röber, Bernd
T1  - L-SCRaMbLE as a tool for light-controlled Cre-mediated recombination in yeast
JF  - Nature Communications
N2  - The synthetic yeast genome constructed by the International Synthetic Yeast Sc2.0 consortium adds thousands of loxPsym recombination sites to all 16 redesigned chromosomes, allowing the shuffling of Sc2.0 chromosome parts by the Cre-loxP recombination system thereby enabling genome evolution experiments. Here, we present L-SCRaMbLE, a lightcontrolled Cre recombinase for use in the yeast Saccharomyces cerevisiae. L-SCRaMbLE allows tight regulation of recombinase activity with up to 179-fold induction upon exposure to red light. The extent of recombination depends on induction time and concentration of the chromophore phycocyanobilin (PCB), which can be easily adjusted. The tool presented here provides improved recombination control over the previously reported estradiol-dependent SCRaMbLE induction system, mediating a larger variety of possible recombination events in SCRaMbLE-ing a reporter plasmid. Thereby, L-SCRaMbLE boosts the potential for further customization and provides a facile application for use in the S. cerevisiae genome reengineering project Sc2.0 or in other recombination-based systems.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-017-02208-6
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  -