The Hawaiian PLUME Project: A Seismic Imaging Dataset Provides Glimpses into Ocean and Atmosphere Processes
The Hawaiian PLUME (Plume-Lithosphere Undersea Mantle Experiment) project operated a two-stage network of broadband ocean-bottom and land seismometers from early 2005 through May 2007. With an aperture exceeding 1000 km, the network included 10 land sites and nearly 70 ocean bottom sites (Laske et al., 2009). Most of the land and ocean bottom stations were equipped with 3-component broadband seismometers. In addition, the ocean bottom sites were also equipped with a Cox-Webb differential pressure gauge. The deployment of broadband instruments allowed us to apply a wide range of seismic analysis tools to determine seismic properties of the crust and mantle beneath the Hawaiian islands and its surrounding bathymetric swell. Body wave tomography conclusively imaged a complex low velocity anomaly that penetrates deep into the lower mantle (Wolfe et al., 2009), supporting the idea that Hawaii's extensive volcanism is fed by a deep-rooted mantle plume. The analysis of surface waves reveals a profoundly altered lithosphere beneath the island of Hawaii. The low shear velocity anomaly found at the base of the lithosphere continues into the asthenosphere but shifts westward, documenting an asymmetry in shallow mantle structure that mirrors some of the asymmetry of the bathymetric swell. Owing to the fact that PLUME made use of broadband instruments, the rich dataset from this experiment allowed us to also study patterns in seismicity around Hawaii. Using high-pass filtered records from the PLUME OBS networks we detected numerous off-shore events that were not detected by the monitoring networks on the Hawaiian islands (mainly the island of Hawaii). This gives new insight into seismic activity in some source regions and helps to refine seismic risk estimation for some high-population areas. Our network also produced excellent pressure recording of the somewhat enigmatic tsunami caused by the magnitude 8.3 15 November 2006 Kuril islands earthquake. This tsunami was relatively small when it reached Japan, and it caused no significant damage. After crossing the North Pacific ocean, it reached a height of over 1.5 m in Crescent City, CA and caused damage to the docks there estimated at nearly $2 million. This tsunami was recorded best on our DPGs but some horizontal seismometer components also show a signal. Finally, the PLUME instruments also recorded the journey of 2006 Hurricane Ioke. This long-lived category 5 hurricane was the largest recorded hurricane to form in the Central Pacific ocean. Unlike 2005 Hurricane Katrina, which released the most seismic energy when it made landfall as a weakened hurricane, the seismic energy release of Hurricane Ioke peaked when it reached the strongest state in the atmosphere. References: Laske, G., Collins, J.A., Wolfe, C.J., Solomon, S.C., Detrick, R.S., Orcutt, J.A., Bercovici, D. and Hauri, E.H., 2009. Probing The Hawaiian Hot Spot With New Ocean Bottom Instruments, EOS Trans. AGU, 90, 362-363. Wolfe, C.J., Solomon, S.C., Laske, G., Collins, J.A., Detrick, R.S., Orcutt, J.A., Bercovici, D. and Hauri, E.H., 2009. Mantle Shear-Wave Velocity Structure Beneath the Hawaiian Hot Spot. Science, 326, 1388-1390.
NH13B-1148 Poster [WITHDRAWN]
What Is the Atmosphere's Effect on Earth's Surface Temperature?
It is frequently stated in textbooks and scholarly articles that the surface temperature of Earth is 33C warmer than it would be without the atmosphere and that this difference is due to the greenhouse effect. In this invited talk, based on my recent AGU Forum piece (Zeng, 13 April 2010, Eos, Vol. 91, No. 15), I will first use observational data to show that the atmosphere effect leads to warming of only 20°C. This new conclusion requires a revision to all of the relevant literature in K-12, undergraduate, and graduate education material and to science papers and reports. New results from the analysis of IPCC simulations will also be presented. Furthermore, the possibility of linking IPCC models' atmosphere greenhouse effect in the 20th Century to the warming in the 21st Century will be explored.
Biological Extreme Events - Past, Present, and Future
Biological extreme events span wide ranges temporally and spatially and in type - population dieoffs, extinctions, ecological reorganizations, changes in biogeochemical fluxes, and more. Driving variables consist in meteorology, tectonics, orbital changes, anthropogenic changes (land-use change, species introductions, reactive N injection into the biosphere), and evolution (esp. of diseases). However, the mapping of extremes in the drivers onto biological extremes as organismal responses is complex, as laid out originally in the theoretical framework of Gutschick and BassiriRad (New Phytologist  100:21-42). Responses are nonlinear and dependent on (mostly unknown and) complex temporal sequences - often of multiple environmental variables. The responses are species- and genotype specific. I review extreme events over from past to present over wide temporal scales, while noting that they are not wholly informative of responses to the current and near-future drivers for at least two reasons: 1) the current combination of numerous environmental extremes - changes in CO2, temperature, precipitation, reactive N, land fragmentation, O3, etc. -is unprecedented in scope, and 2) adaptive genetic variation for organismal responses is constrained by poorly-characterized genetic structures (in organisms and populations) and by loss of genetic variation by genetic drift over long periods. We may expect radical reorganizations of ecosystem and biogeochemical functions. These changes include many ecosystem services in flood control, crop pollination and insect/disease control, C-water-mineral cycling, and more, as well as direct effects on human health. Predictions of such changes will necessarily be very weak in the critical next few decades, given the great deal of observation, experimentation, and theory construction that will be necessary, on both organisms and drivers. To make the research efforts most effective will require extensive, insightful planning, beginning immediately.
Massive dieoff of conifers in the US Southwest, an extreme event driven by a remarkably uncommon co-occurrence of high temperature, drought, and long active season for insects
The potential influence of thaw slumps and sea-level rise on the Arctic carbon cycle (Invited)
Potential soil carbon stores in the Arctic are estimated to be second only in size to that of the oceans. The majority of this carbon lies within permafrost dominated regions and is presently stored in frozen soils in the shallow subsurface (the upper 3 meters). Considerable attention and research is presently focused on how climate warming-induced thawing of permafrost and deepening of the seasonally thawed upper layer of the permafrost may alter the carbon cycle across the Arctic and globally. Less studied, however, many natural hazards have the potential to influence the Arctic carbon cycle due to their alteration of the landsurface. The temperature dependence and the influence of hydrology on Arctic landsurface processes make the occurrence of many natural hazards in the Arctic critically dependent on interactions between the landsurface, atmosphere, and oceans. Here we explore the potential role of two natural hazards in the Arctic carbon cycle: deep, retrogressive thaw slumps; and sea-level rise. Retrogressive thaw slumps are deep landslide features hypothesized to be initially triggered by the melting of bodies of ice contained within frozen sediments. Once triggered continued thawing of frozen soils and melting of buried ice along the failure face of the slide drives retreat of the slump headwall. Along the Selawik River in northwest Alaska a thaw slump triggered in 2004 has retreated approximately 300 m into a high river bluff and liberated more than a half million cubic meters of ice and sediment. The slump failure has mobilized both shallow soil carbon and much older carbon previously buried within the glacial deposits but now exposed in the actively retreating slump face. An unknown fraction of the carbon contained within slump sediments may be released directly to the atmosphere by oxidation or microbially mediated transformations. The remaining carbon is physically transported first onto the slump floor and then into the Selawik River. Once in the river the carbon may be deposited on the river bed, redistributed onto the floodplain or into bordering lakes by flood pulses, and ultimately delivered to coastal oceans. At the downstream end of many Arctic river systems global climate change has the potential to dramatically alter carbon cycle dynamics. Some current predictions suggest that sea-levels may rise up to a meter over the course of this century. In the Arctic, such a rise would inundate significant portions of many low lying deltas. Flooding by seawater of carbon-rich permafrost has the potential to alter the rate of permafrost thawing and carbon release in these regions. In order to better constrain these rates we apply a numerical model of permafrost dynamics to explore how such low lying areas may respond to varying amounts of inundation by seawater.
Climate-induced tree mortality: earth system consequences for carbon, energy, and water exchanges
One of the greatest uncertainties in global environmental change is predicting changes in feedbacks between the biosphere and atmosphere that could present hazards to current earth system function. Terrestrial ecosystems, and in particular forests, exert strong controls on the global carbon cycle and influence regional hydrology and climatology directly through water and surface energy budgets. Widespread, rapid, drought- and infestation-triggered tree mortality is now emerging as a phenomenon affecting forests globally and may be linked to increasing temperatures and drought frequency and severity. We demonstrate the link between climate-sensitive tree mortality and risks of altered earth system function though carbon, water, and energy exchange. Tree mortality causes a loss of carbon stocks from an ecosystem and a reduction sequestration capacity. Recent research has shown that the 2000s pinyon pine die-off in the southwest US caused the loss of 4.6 Tg of aboveground carbon stocks from the region in 5 years, far exceeding carbon loss from other disturbances. Widespread tree mortality in British Columbia resulted in the loss of 270 Tg of carbon, shifting affected forestland from a carbon sink to a source, and influenced Canadian forest policy on carbon stocks. Tree mortality, as an immediate loss of live tree cover, directly alters albedo, near-ground solar radiation, and the relative contributions of evaporation and transpiration to total evapotranspiration. Near-ground solar radiation, an important ecosystem trait affecting soil heating and water availability, increased regionally following the pinyon pine die-off. Conversely, forest canopy loss with tree mortality, is expected to increase regional albedo, especially for forests which experience winter snow cover, potentially offsetting the climate forcing of terrestrial carbon releases to the atmosphere. Initial hydrological response to die-off is likely a reduction in evapotranspiration, which can increase subsurface flow, runoff, groundwater recharge, and streamflow. Under some circumstances there may also be increased flood risks. We hypothesized thresholds of mean annual precipitation and canopy cover reduction identified from the forest harvesting literature as minima that must be exceeded for die-off to noticeably affect hydrologic processes. We note exceptions to these thresholds when snowmelt dominates the watershed hydrology and when mortality affects a single species with a unique hydrologic role. Management options for mitigating die-off effects on ecosystem and earth system processes and implementing post-die-off restoration will likely be limited and costly, requiring ecological and societal adaptation in many areas. As such, climate-induced tree mortality poses a significant risk to the current earth system function through altered exchanges of carbon, energy, and water between the land surface and atmosphere.
Recent SST trends and Flood Disasters in Brazil
We analyzed recent variations in the sea surface temperature (SST) anomalies of Pacific and Atlantic Oceans to understand their roles in extreme discharge of Amazon River Basin. In general, higher than monthly average discharge appears when La Niña condition forms and lower than monthly average discharge appears when El Niño condition forms. We also investigated the relationship between SST anomalies and recent floods in Brazil during the period of 1980-2010. Most severe floods (e.g. 2003 and 2010 Rio de Janeiro-São Paulo Flood) in austral summer occurred when El Niño Modoki appears in the Pacific Ocean. In addition, warm waters in tropical South Atlantic Ocean between American and African Coast also helped the moisture convergence to the affected region. Floods in some other locations (for example, Itaipava flood occurred in Maranhao State in 2008) occurred when a La Niña Modoki appeared in Pacific Ocean. These flood disasters in Brazil associated with climate phenomena may increase due to warmer SST trend under the global warming stress.