H54A-01 INVITED 16:00h
Climate and Climate Variability as Input to Surface Dynamic Models
An important way to investigate the interwoven complexity of earth surface processes is through the judicious application of surface dynamic models. Community-developed models (e.g. HydroTrend, SedFlux) are continuously upgraded in their representation of biophysical processes. Their general use, however, often depend on the availability of appropriate numerical boundary conditions, such as the time dependency of spatial climatic factors (e.g. wind-wave, rainfall, temperature), and geomorphic basin properties (e.g. DEM, geology, distribution of ice-fields and lakes). In an effort to aid the penetration of these models into the surface dynamics community, we have investigated the utility of global climate and biophysical data sets. We have conducted an analysis of the gridded temperature and precipitation data (1970-1999) released by NOAA/NCDC and GHCN/U. Delaware, the gridded global discharge data from GRDC and U. New Hampshire (1960-1994), and the gridded wind-wave data (1997-2004) from NOAA's World Wavewatch III. Our presentation highlights the time-sequencing of this data and the use of the coefficient of variation as an aid to understanding within month, between month and between year temporal climate variability. In conjunction with daily global satellite imaging (MODIS), earth scientists can presently "witness" how climate manifests itself across landscapes, and thus develop a fuller appreciation of the impact of climate on surface dynamics (fires, river floods, sediment plumes, resuspension events, landslides). In addition to climate forcings, an increasing domination of the terrestrial water cycle, through diverse activities such as irrigation, diversion, and impoundment, will embed its impact into these dynamics. Future earth-surface modeling must take these factors into account.
H54A-02 16:15h
Climate Controls on Sediment Discharge in Selected Fluvial Systems in Indonesia
Sediment discharge was evaluated in selected rivers in Indonesia where catchment basin size, relief, and gradient are somewhat similar, but where tectonic setting, bedrock lithology, and atmospheric circulation and rainfall, are variables. Rivers were studied in humid to perhumid regions where the Intertropical Convergence Zone (ITCZ) is relatively stable and rainfall exceeds evapotranspiration for all or most months of the year (Sumatra, Borneo, Seram, and Irian Jaya). In contrast, fluvial sediment discharge was evaluated in rivers in Timor where 85 percent of all rainfall occurs during a four-month rainy season (dry subhumid climate) in response to the passage of the ITCZ. Stream sampling was conducted for solid suspended sediment concentrations, solute concentrations, and pH. In addition, the nature of stream channels (meandering or braided), streambed materials, the degree and source of estuarine fill, the degree of delta formation, and the nature of coastlines were used to evaluate fluvial sediment discharge. Very low sediment concentrations (10 mg/l suspended and 10mg/l solute) in rivers in the perhumid to humid regions are indicative of a very low fluvial sediment discharge. The absence of fluvially derived bed loads, river mouth deltas, the lack of fluvial fill of estuaries, and mud-dominated coastal zones are consistent with this observation. In contrast, very high sediment concentrations (2100 mg/l suspended and 340 mg/l dissolved) during rainy season discharge in dry-subhumid regions (Timor) are indicative of very high sediment discharge in dry subhumid climates. Coarse-grained braided streams, the complete fluvial fill of estuaries, the formation of river-mouth deltas, cobbles transported to the coast, and coarse-grained beaches are consistent with this observation. All factors indicate that fluvial sediment discharge is exceedingly low in humid and perhumid areas where denudation is dominated by chemical weathering, whereas fluvial sediment discharge is exceedingly high in relatively dry seasonal climates where denudation appears to be primarily controlled by both chemical and mechanical processes. The dominant variable affecting fluvial sediment discharge among the islands of Indonesia, therefore, appears to be the degree of seasonality in rainfall regardless of tectonic setting.
H54A-03 16:30h
Tropical intraseasonal variabilitiy and extreme flooding in California: The New Year's 1997 Floods
Recent studies have linked California wintertime floods to tropical intraseasonal variability. Statistically significant links have been established between the Madden-Julian Oscillation (MJO) and extreme precipitation events in California. The anamolous moisture transport associated with these events is often referred to as the "Pineapple Express" because much of the moisture flows over the Hawaiian Islands en route to the West Coast. The destructive floods that affected much of California during January 1997 were an example of a Pineapple Express type system. We present a meteorological case study of this event using numerical simulations computed with the Fifth Generation PSU/NCAR Mesoscale Model (MM5). Our results indicate that the topography of the Sierra Nevada and Coast Ranges exerted primary control over the localization of extreme rainfall and the associated geomorphic effects. Moisture-laden winds were able to flow over mountainous topography and release copious rainfall over the northern Coast Ranges and northern Sierra Nevada, while drier winds were deflected by topography and acted to enhance rainfall in the northern Sierras by changing the effective topography of the western Sierra Nevada foothills. The strong coupling between topography and extreme rainfall in this case suggests a range of potentially important feedbacks that may have shaped California's landscape.
H54A-04 16:45h
ENSO-Orchestrated Particle Supply, Deposition, and Carbon Sequestration in Amazonian River Basins by Erosion-Sedimentation Processes
Application of a new geochronological method quantifies century-scale floodplain sedimentation rates across a pristine 720,000 km$^{2}$ basin in northern Bolivia, covering the principal sediment and water sources for the Madeira River, the largest sediment source for the Amazon. Large, rapid-rise, cold-phase ENSO floods account for the preponderance of sediment accumulation and dominate sediment discharge from Andean tributaries into the large rivers of the Amazonian lowland. Discharge data indicate considerable inter-annual variation of sediment supply from the Andes, resulting from the interaction of Andean erosion and the dynamics of extreme climate. Transient, ENSO-driven processes therefore control both the formation of floodplains and sedimentary strata within the Bolivian foreland, and also modulate the efflux, transport, floodplain storage, exchange due to channel migration, and downstream delivery of sediment and associated carbon (entrained coarse material and sorbed molecules), nutrients, and pollutants to the Amazon main stem. Such infrequent, extreme mechanisms of sediment and carbon transport suggest that a three-step process could represent a major carbon sink in Amazonian foreland basins: 1) extensive Andean hillslope failure and channel migration during large La Niña associated storms mobilizes vast quantities of fresh organic matter and sediment with low organic carbon (OC) content; 2) within the river, mineral surfaces acquire normal OC loadings via sorption as they are rapidly evacuated from the mountainous source basins to adjacent foreland depocenters; and 3) deposited sediments preserve "fresh" carbon within organo-mineral complexes and by deep burial in point bars and "crevasse-splay" deposits that have little potential for exchange with the biosphere and atmosphere. Calculations and new measurements suggest that this process could sequester 250-500 Mtonnes of carbon per event in the Amazonian foreland and regulate the supply of particulate OC to the lower Amazon. Extrapolated globally, this hypothesis could account for a significant fraction of the "missing carbon sink" and the atmospheric carbon dioxide anomalies typically observed during cold-phase ENSO.
H54A-05 17:00h
GeoSystems: Probing Climate and Linked Systems of Earth's Deep-Time Dark Ages
GeoSystems is a developing community-based initiative that focuses on the importance of the deep-time perspective for understanding the complexities of Earth's atmosphere, hydrosphere, biosphere and surficial lithosphere using climate as the focus. Earth's climate operates on a continuum of temporal, spatial and parametric scales. The deep-time geologic record preserves the results of multiple large-scale experiments in climate and broader environmental change, many of which are far more extreme than those archived in instrumental, historical, or Quaternary records, but are potentially repeatable on human time scales. Indeed, aspects of our modern climate are now returning to a state last known from "deep" time. Understanding the ranges, rates, and processes responsible for these "alternative Earth" extremes in global systems behavior is critical for developing a holistic knowledge of our planet's climate system and constraining predictions of future scenarios. Processes such as extinction and evolution of species, orogenic and magmatic events, sea-level change, and the like operate over a variety of time scales and are complexly entwined with climatic trends, many of which also operate over a variety of time scales and must be viewed within the context of the deep-time perspective. Recent research on Earth's climate and linked systems behavior in deep time is shattering previous preconceptions and interpretations by reconstructing, with increasing rigor and resolution, key parameters such as atmospheric CO2, sea-surface temperatures, rates and modes of ocean circulation, ocean state (anoxia, nutrient status, biological productivity), winds, seasonality, and even diurnal terrestrial temperatures from records dating from millions of years in the past. Beyond this, these same records are simultaneously teaching us how the climate system interacted with Earth's biosphere, lithosphere, and hydrosphere in ways previously unimagined.
http://geosystems.ou.edu
H54A-06 17:15h
Vegetation-Precipitation Interactions Drive Paleoenvironmental Evolution
In studies of climate effects on the sedimentary record, vegetation is often relegated to the role of proxy data. However, modern environmental distributions reflect strong feedbacks among vegetation communities, precipitation, and temperature that can reinforce secular climate changes. These feedbacks are strong enough to dry out tropical rainforests, green deserts, or warm high latitudes. Four distinct phases in the evolution of land plants have progressively altered the global distribution of precipitation and smoothed the climatic gradient between continent interiors and coastal margins. Each phase of land-plant evolution and its attendant climate effects have influenced sedimentary systems by modifying the relationship between climate and sediment yield. The phases are: 1) pre-Devonian, 2) Devonian-Cretaceous, 3) Cretaceous-Oligocene, 4) post-Oligocene. In the pre-Devonian, before widespread land-plant cover, precipitation patterns depended solely on latitude, the distribution of continents and oceans, and the consequent atmospheric circulation patterns. The known spatial distribution of evaporite deposits and the characteristics of fluvial systems at this time reflect how dissimilar this environment is to today. The Devonian-Cretaceous phase saw the rise and diversification of most major land-plant groups. However, these arid-intolerant floras were concentrated in high-humidity lowlands and coastal margins. Low-density vegetative cover in uplands and continental interiors was reinforced by a positive feedback among increased temperature, decreased moisture and decreased vegetation density. The climatic gradient from continental interior to coastal margin was at a maximum during this period. Continent-interior to coastal climatic gradients became less pronounced in the Cretaceous to Oligocene with the advent of arid-tolerant herbaceous angiosperms that increased the vegetative cover in dry uplands. A positive feedback among increased vegetative cover, increased moisture retention and decreased temperatures ameliorated the climatic extremes of continental interiors, enhancing chemical weathering, retarding sediment fluxes, and increasing the dissolved load of streams. The increased vegetative cover on uplands also stabilized sediment yields and increased the formation of finer-grained sediments in any given paleogeographic setting. The post-Oligocene period spans the evolution of grasslands, tundra and taiga environments, which further expanded the vegetative cover of terrestrial environments. As the nature of vegetation has changed during the Phanerozoic, the nature of the interactions between vegetation, paleoenvironments, and sediment yield has also evolved. These changes dramatically affect what paleoenvironmental conditions are predictable for the past, our understanding of ancient sediment yields, and the relationship between climate and continental depositional systems.
H54A-07 17:30h
Linked Sea Level and Climate Change at the Scale of Third-Order Stratigraphic Sequences During the Late Paleozoic
Deposition of the Permian Cutler Group in and around the Paradox basin, at tropical (approximately 0 to 10 degrees north) paleolatitudes, was influenced by linked changes in sea-level and local climate at a variety of temporal scales. At the scale of 3rd-order depositional sequences (1 to 10 m.y.), relatively wet sub-humid to semiarid conditions were associated with sea-level highstands, and semiarid to arid conditions were associated with sea-level lowstands. Linked cycles of local climate and sea-level change previously identified within the Cutler Group occur at the scale of 4th- and 5th-order depositional sequences (0.01 to 1 m.y.). These shorter-term, higher-frequency cycles are superimposed on the longer-term, 3rd-order-scale cycles described here. The Paradox basin was a foreland basin located between the southwest side of the Uncompahgre uplift of the Ancestral Rocky Mountains and the western shoreline of Pangea. The Cutler Group consists primarily of clastic sedimentary rocks derived from two distinct source areas: the Uncompahgre uplift located to the northeast of the Paradox basin, and the marine shelf located to the west. When sea level was high and the climate was sub-humid to semiarid, Uncompahgre-derived feldspar- and mica-rich sand and mud was transported across much of the Paradox basin and deposited in extensive low-gradient fluvial channels, floodplains, and tidal mudflats. At the same time, limestones and quartz-rich sands were deposited on the marine shelf. When sea level was low and the climate was semiarid to arid, clastic influx from the Uncompahgre was reduced. At the same time subaerially exposed shelf sediments were reworked and transported southeastward into the Paradox basin by onshore winds, where they were deposited as eolian dunes and sandsheets. The unique positioning of the Paradox basin at tropical latitudes, between the tectonically active Uncompahgre uplift and the passive margin of Pangea during the waning stages of late Paleozoic, high-latitude, southern-hemisphere glaciation resulted in ideal conditions for preservation of a long-term record of linked cycles of local climate and sea-level change at a variety of scales.
H54A-08 INVITED 17:45h
Recording of Climatic Signals in Physical Stratigraphy: Experimental Results
We review results from experimental stratigraphy studies that bear on interpreting physical-sedimentary climate records. Superposition of base-level cycles driven at comparable but distinct frequencies, such as those associated with climatic glacioeustatic cycles, leads to ambiguously superposed major stratal surfaces. High-frequency cycles grouped on the falling limbs of lower-frequency tend to be highly amalgamated while those on rising limbs are relatively distinct. Preserved erosional "valleys" are highly composite surfaces representing, in some cases, multiple base-level cycles as well as autogenic scour events within a single cycle. One problem in interpreting paleoclimate from preserved physical-sedimentary signals is the interference between relatively high-frequency climatic signals and internally generated (autogenic) signals. In channelized flow systems these autogenic signals, mainly associated with sediment storage and release, have time scales ranging from very short to at least a few thousand years. The upper limit for autogenic variability in terms of time and space scales is not known at present. Experimental data suggest the possibility of long-period cycles involving changes in the overall organization of the channel system. A key feature of autogenic variability is that it cannot be thought of as "noise" that passively masks climatic and other external signals. Rather, autogenic variation actively smears externally forced signals falling within the autogenic frequency range. In some respects the process is analogous to turbulent mixing in fluids. Depending on amplitude, frequency, and location relative to the sampling site, high-frequency climatic signals may be "mixed" to the point of being undetectable.