PP14A-01
Extreme Eutrophication and Anoxic Events in the Baltic Sea
The anoxic and reducing conditions in the deepest Baltic basins are today so extreme that there is nowhere else in the world that manganese sulfide minerals (both hexagonal and cubic MnS) are known to form and be preserved in sea-floor sediments. However, the same MnS mineralogy, reflecting similarly extreme reducing conditions, was also formed ca. 1500 C14-yrs ago in the Landsort Deep. Therefore, anthropogenic sources of nutrients are not necessarily the primary cause of modern eutrophication as is commonly assumed, and the reduction of these nutrient sources may not result in the desired impact on environmental conditions as many models would predict. Detailed element scans and thin-section studies using Markov-chain analyses have indicated cyclic variations on mm-, cm- and m-scales in both detrital and authigenic components, interpreted to relate to climatic or circulation changes. Carbon, sulfur and grain size vary together, suggesting the importance of organic matter for sulfur precipitation. In addition to favorable climatic and nutrient conditions, organic matter production is influenced by mixing processes and salinity changes that are associated with periodic inflow from the North Sea as part of the estuarine circulation that renews bottom water. We have calculated sedimentation rates and element fluxes. Detrital mineralogy was used to identify and partition sediment supply from idealized source types. Initially, the sediment contributions from glacial meltwater, sediment reworking and soil terrains have been modelled. Although human influence was much less 1500 C14- yrs ago, forest clearing and changed land use might have allowed greater erosion and nutrient supply. This is supported by an increased proportion of sediment supplied from soil terrains, but not supported by the slow total sedimentation rates (<0.4 mm yr) related to sapropel formation. Climatic influences and paleoceanographic dynamics are considered most important. Natural causes for rapid organic production, extreme eutrophication and anoxic precipitation of MnS minerals need to be better accounted for in models for eutrophication in the modern Baltic Sea.
PP14A-02
Multiple Equilibria and Hysteresis in a Zonally Averaged Moist, Cloudy, Convecting Atmosphere, with Implications for the Equator to Pole Temperature Difference abd Equable Climate Dynamics
Multiple climate equilibria and hysteresis are found in a simple zonally averaged two-level model of the atmosphere. The model contains highly simplified parameterizations for physical processes relating to the atmospheric component of the hydrological cycle and its radiative effects. These include convection, precipitation, diagnostically calculated clouds, and a longwave radiation scheme that explicitly depends on carbon dioxide, water vapor, and cloud fraction. Convection at midlatitudes and high latitudes is shown to represent a strong positive feedback on boundary layer temperatures there, due mainly to the radiative effect of clouds. This feedback leads to a climate solution with warm boundary layer temperatures and convection at high latitudes and an equator to pole temperature difference that is reduced by about 15$^\circ$C. Changes in high latitude local energy balance, not meridional heat transport, are responsible for the reduction in the equator to pole temperature difference and are caused by changes in cloud radiative forcing. The model settles into the mode with a reduced equator to pole temperature difference at high CO$_2$ levels and into a mode similar to the current climate at low CO$_2$ levels. At intermediate CO$_2$ levels both modes exist. The possible connection of the high CO$_2$ climate mode with the equable climates of the Cretaceous, Paleocene and Eocene is considered. Results are valid when the model is run at 30$^\circ$ latitude and 3$^\circ$ latitude meridional resolution and are robust to 25% changes in most model parameters.
PP14A-03
Impact of methane and hydrogen sulfide on atmospheric ozone at the Permian-Triassic boundary
We discuss model experiments valid for the Permian-Triassic boundary in which we explore the impact of changes in tropospheric methane concentration. For scenarios relevant to methane clathrate release, we consider surface methane concentration with values up to 5000 times its preindustrial concentration. We employ a comprehensive three-dimensional tropospheric-stratospheric model with chemistry that allows for the feedbacks between chemistry and climate. We show that stratospheric ozone starts collapsing for methane surface concentrations of the order of 1000 times their preindustrial concentration. At 5000 times, more than half of the total ozone column has disappeared. As the methane lifetime never reaches more than 50 years, this perturbation can only be short-lived. We show he addition of large hydrogen sulfide emissions (from an anoxic ocean) can provide the chemical sink for the hydroxyl radical (OH) and make the methane perturbation much more long-lived. However, the hydrogen sulfide itself does not seem to exert much influence on stratospheric ozone.
PP14A-04
Preliminary Results of Geophysical and Geological Investigations in the Transition Zone between the Mendeleev Rise and adjacent Siberian Shelf
In 2005 integrated geological and geophysical investigations were carried in the transition zone between Mendeleev Rise and adjacent shelf of the East-Siberian Sea and Chuckchi Sea to create the tectonic model of the junction zone. Investigations included: deep seismic soundings (DSS with offsets up to 250 km), single seismic reflection observations from drifting ice; on-ice gravity measurements (by means of helicopters based on research vessel �Akademik Fedorov�) and geological sampling from vessel; aeromagnetic and aerogravity mapping within 100 km swath elongated along DSS seismic profile at a trackline spacing of about 10 km. The length of the main sublongitudinal seismic profile was 600 km, extending con-tinuously along the Mendeleev Rise and across its transition to the Siberian Shelf. The preliminary results of integrated analysis of mentioned above data add up to following: The top of the mantle is characterized by 7.7-7.9 km/s lateral changes of boundary velocity. The southern part of DSS profile crosses the deep-water prolongations of two shelf structures with N-W trend: North-Chuckchi Trough and North-Chuckchi Rise. The total thickness of crust of the first structure is about 25 km including 10 km of sediments. The second structure has the thickness of crust about 34-35 km including 5-6 km of sediments. The northern part of DSS profile goes along the crest of the Mendeleev Rise up to 79.2 N. The Earth's crust within the Rise is presented by two layers (upper and lower) recovered by sediments. The thickness of the lower crust with interval velocities of 6.7-7.0 km/s varies from 15 to17 km. The thick-ness of the upper crust with 6.0-6.45 km/s interval velocity runs up to 9 km and becomes commensu-rable with the lower crust. The sedimentary cover is subdivided into three sequences with interval velocities (from the top to the bottom) of 1.7-1.9 km/s, 3.1-3.3 km/s, and 4.2-4.5 km/s. The lower sequence occupies more than a half of the whole sedimentary cover both within the Mendeleev Rise and transition zone. The dredging of rock samples was successful only on the bottom scarps. The most part (70%) of psephytic samples is presented by sharp-edged fragments of sedimentary rocks (speckled sandstones, laminated siltstones, silty mudstones, black shales, weathered limestones). Existent magnetic and gravity databases are essentially improved based on results of new aero-magnetic and aerogravity surveys. A few preliminary schemes are constructed, namely: depth to basement and sediment distribution, based on results of depth to magnetic sources estimation; and main tectonic features. Transition zone between the Mendeleev Rise and adjacent Siberian Shelf is represented by ter- raced deepening of sea bottom and consists of a few troughs and rises. In spite of it the upper crust layer is traced in all parts of this zone. Its thickness varies from 5 km (in the North-Chuckchi Trough) to 10 km within the North-Chuckchi Rise. Results of preliminary interpretation show that the Mendeleev Rise is a continental structure. It could be a part of NE Eurasia margin submerged in Neogene time.
PP14A-05
Widespread Reduction in Coral Growth Rates on the Mesoamerican Reef Following the 1998 El Nino and Hurricane Mitch
Corals on the Mesoamerican Reef have been declining in health over the past few decades, and it is important to determine the cause, if conservation measures are to be effective. Cores from large {\it Montastrea spp.}, {\it Diploria strigosa}, and {\it Siderastrea siderea} corals were collected in two locations on the Belizean barrier reef: 34 from Frank's Caye, Sapodilla Cayes, in the southern section and 7 from Dog Flea Caye, Turneffe Atoll, in the northern section. Most of the precipitation in this area occurs in southern Belize and Guatemala, therefore the corals from the Sapodilla Cayes may be more heavily impacted by land-based runoff than those at Turneffe Atoll. In 9 of 10 {\it Montastrea} and 2 {\it Diploria} cores from the Sapodilla Cayes, as well as 2 of 4 Montastrea cores from Turneffe Atoll analyzed so far, extension rates were significantly depressed coincident with unusually dense calcification during ~ 1998 or 1999. In 6 of the {\it Montastrea} cores from the Sapodilla Cayes and 1 from Turneffe Atoll, partial mortality was also observed coincident with this anomalous band. The oxygen isotopic and Sr/Ca ratios of the coral skeleton will be used to constrain the timing of this event, based upon cycles in these proxies corresponding to seasonal sea surface temperature fluctuations. These measures will also be used to determine whether high sea surface temperatures are concurrent with the abnormal growth band, which is expected if the stress band formed due to temperature-induced bleaching associated with the 1998 El Nino event. Ba/Ca ratios will be used as a proxy for terrigenous runoff to test the hypothesis that large, sediment-laden runoff plumes that occurred during Hurricane Mitch were also contemporaneous with the coral growth disturbance. We hypothesize that high sea surface temperatures and extraordinarily large runoff plumes were responsible for stressing the Mesoamerican corals, causing a reduction in extension rates, the formation of dense �stress� bands, and widespread partial mortality.
PP14A-06
Validation of Chironomid-Inferred Temperature Reconstructions in Iceland: The Potential for Reconstructing Quantitative Changes in Holocene Climate.
Since 1990 a number of chironomid-temperature inference models have been developed allowing the production of quantitative reconstructions of past climate. Whilst much recent work investigating the use of chironomids as a quantitative palaeoclimatic proxy has been carried out in the northern hemisphere, very little has been undertaken in Iceland, a key area in which to study past and present climatic changes. There is currently a lack of terrestrially-derived climatic reconstructions from Iceland, and the analysis of subfossil chironomid remains, combined with the recent development of an Icelandic chironomid-mean July air temperature inference model (Langdon, unpub.), offers an excellent opportunity to produce high-resolution quantitative palaeoclimatic reconstructions from this climatically sensitive area. An attempt to validate the chironomid-inferred temperature reconstructions against instrumental meteorological data showed that although errors associated with the inferred temperatures are larger than the magnitude of recent climate variability, the trends and patterns produced by the chironomid-based temperature reconstructions were similar to those of the meteorological data. Application of the transfer function to early Holocene lacustrine sediments produced a greater magnitude of variation within the chironomid-inferred temperatures. The palaeoclimatic reconstruction corresponds well with changes seen in other records, both from marine and ice cores. The results from this work suggest that subfossil chironomids can provide a reliable estimate of July air temperatures, especially temperature trends, even if the error terms still tend to overlap with the magnitude of recent Holocene temperature changes. They are however best used as part of a multi-proxy, multi-site study where other proxies are able to support the relatively subtle changes inferred based on analysis of the subfossil chironomids.
PP14A-07
Cosmogenic Chlorine-36 Dating of Shoreline Deposits in Panamint Valley, CA
Panamint Valley, California, held the fifth in a chain of six lakes that formed by overflow of the Owens River during Pleistocene pluvial episodes in the southwestern Great Basin. The chronology of filling events in Panamint Valley is of particular interest because it filled only during unusually wet conditions in the Pleistocene. We sampled two accretionary beach features, gravel lacustrine bars, for cosmogenic chlorine-36 profile dating. One site was on the east side of the valley at 627m and one was near the southwest end at 616m. These beach features represent the most prominent shorelines at the elevation of the outlet channel to Death Valley (603m), thus they represent the last time the climate was wet enough to fill Panamint Valley. The profile on the east side of the valley yielded a profile age of 62 +17/-21 ka and that on the west side an age of 91 +22/-26 ka. These results indicate that the last overflow of Panamint Valley was during marine oxygen isotope stage (MIS) 4 or 5. These ages may indicate two separate overflow events, but more likely represent statistical variation of results from landforms created simultaneously. Core records from Owens Lake (upstream) suggest brief periods of wetness during MIS 4 and 5, but there is little evidence of extreme wetness in Death Valley (downstream) during these times. Unlike Lahontan, the paleo-Owens system did not fill to maximum extent during the Last Glacial Maximum.
PP14A-08
Application of BI (Bioturbation Index) Log in Interpreting Sedimentary Record
Various BI (bioturbation index) schemes have been developed since early 60's to semi-quantitatively measure the degree of bioturbation in sediments. Although BI scheme has been used as a paleo-oxygen proxy in fine- grained basinal strata, its wider application remained under-explored. Like geophysical wireline logs, a continuous line curve of BI can be plotted against the thickness of a sedimentary succession. This �BI log' characterizing the variation of bioturbation intensity down to the bed/lamina-scale can be generated in outcrops, and from cores and FMI (formation micro-imager) logs. The application of BI log in interpreting sedimentary record is diverse. Five basic trends of BI log (uniform and low, uniform and high, non-uniform, upward- decreasing, and upward-increasing) can be recognized, each indicating a distinct paleo-environmental condition, either persistent or changing, for trace makers. These trends can be used as proxies for sedimentation rate, dominant energy (wave, tide, and river), and/or paleoclimate (oxygen, salinity, temperature, and organic carbon). For example, BI logs of shallow marine and transitional strata show distinct trends depending on the relative influence of rivers, waves, storms, and tides. Characteristic deflections of BI log across lithostratigraphic boundaries, key sequence stratigraphic surfaces, and across depositional systems are observed. BI log can also be used relatively as an indicator of reservoir property (porosity and permeability), particularly for �tight' reservoirs. When co-interpreted with other ichnological, sedimentological and geochemical data, BI log can be a powerful tool in various disciplines, such as sedimentology, paleoclimatology, stratigraphy, and petroleum geology.