U33A-0001
Changes in Maximum Discharge From a new River Flow Dataset for the Eurasian pan- Arctic
There is a growing body of evidence pointing to significant environmental change in the north polar region and in particular in the Eurasian pan-Arctic. These changes are important not only as potential signals of global climate change, but also through their feedbacks to the global climate and hydrological systems and to their impacts upon humans. Many of the recent estimates of hydrological change based on annual, seasonal or monthly discharge data available from R-ArcticNet reported the significant increase in discharge across northern Eurasia. However, ''river discharge is increasing in Arctic Russian rivers'' does not adequately characterize regional or seasonal patterns in terrestrial runoff production. A significant improvement in the interpretations of the physical processes underlying decadal trends in monthly and annual discharge values is through study of daily discharge time-series. This work was focused on an analysis of maximum daily discharge based on new data set for 134 Russian gauges in the Eurasian pan-Arctic with drainage areas from 1000 to 50 000 km$^{2}$. These river discharge stations, spread across the Russian pan-Arctic drainage system, were chosen for their long time series and minimal human impact. We investigate trends in magnitude and timing of daily annual and spring discharge maximums as well as analyze their spatial distributions and discuss the possible causes of the observed changes.
U33A-0002
Eocene History of the Arctic Ocean Basin From Nd-Sr Isotopes in Fossil Fish Debris
Early to Mid Eocene sediments recovered by IODP Expedition 302 (ACEX) from Lomonosov Ridge ($88\deg$N), Arctic Ocean Basin, are concentrated in fossil fish debris. Anoxic conditions in bottom waters produced organic- rich deposits preserving abundant fish scales, teeth and bone fragments. Nd and Sr isotopes measured from pre-cleaned fish debris are indirect indicators of bottom and near-surface water compositions, respectively, and can be used to reconstruct a history of water column structure and circulation in the early Arctic Ocean. Data obtained so far indicate that the fish species analyzed likely metabolized Sr in a brackish water environment (salinities well below seawater), consistent with radiogenic $^{87}$Sr/$^{86}$Sr values (~0.7079 to 0.7087) that plot above the Eocene global seawater Sr curve ( < 0.7078). Nd isotopes (incorporated post-mortem) indicate bottom water $\Epsilon$Nd of -6 to -8, becoming less radiogenic after 49 Ma. These values are more radiogenic than North Atlantic or modern Arctic Ocean Nd (< -10), but could indicate some deep water exchange with either Pacific or Tethyan water masses. The data represent a ~7 m.y. interval (44 to 51 Ma) that commences near a significant sea level drop (~49.5 Ma), followed by cooling temperatures. The first appearance of ice rafted debris occurs in these cores at approximately 45 Ma. While the Sr isotopic data (n = 20) almost certainly reflect local inputs from Arctic Basin continental/riverine sources, the Nd data are more difficult to interpret with the small data set (n = 10). They could also turn out to reflect more local continental sources, as has been suggested for the Pleistocene Arctic Ocean Nd. The Sr data appear to be consistent thus far with a restricted basin-wide circulation, indicative of a poorly mixed ocean and a highly stratified water column. A stable, �fresh� water upper layer was likely a pervasive feature that helped concentrate nutrients during enhanced continental runoff. Based on Sr isotopes, oxygen isotopes and paleontological observations, this brackish lens could have involved a mixture of 50-80% river input, with correspondingly smaller amounts of seawater component, possibly accompanied by enhanced evaporation.
U33A-0003
ACEX Grain Size Analyses, Revealing Arctic Paleo-Ice Environments
Summer 2004 hosted an unprecedented event in Arctic research; the successful coring of Arctic sediments to obtain a paleo-climate record that extends through the Cenozoic Era. Low resolution grain size analyses of samples taken during the Arctic Coring Expedition (ACEX) reveal five ice rafted debris (IRD) relationships, which we hypothesize to correspond to five distinct Arctic paleo-ice environments. This study defines IRD as the percentage of terrigenous grains > 63 $\mu$m. IRD is comprised of both sea-ice rafted debris (SIRD) and iceberg rafted debris (IBRD). IBRD is defined as the percentage of terrigenous grains > 250 $\mu$m (modified from Bischof, 2000). Grain size analyses were completed using a Malvern Mastersizer 2000. The five relationships and their corresponding environments are: 1) high IRD percentage and high iceberg rafted debris (IBRD) percentage, reflecting a vastly glaciated environment, 2) low IRD percentage and low IBRD percentage, indicating a possibly seasonally cold environment with little permanent ice, 3) high IRD percentage and low IBRD percentage, an indication of a sea-ice dominated environment, 4) low IRD percentage and high IBRD percentage, indicative of conditions of considerable iceberg expulsion and low sea-ice production, and 5) No IRD present, corresponding to a warm ice-free Arctic climate. The earliest indication of IRD in the ACEX record occurs in the Eocene, a time much older than the intensification of Northern Hemisphere glaciation of ~ 3 Ma. Throughout the Neogene, IRD remains an important component of the sedimentary record. Differentiating modes of IRD in terms of SIRD and IBRD is an important step in reconstructing Arctic paleo-environment.
U33A-0004
Solar Arctic Connection on Multidecadal to Centennial Timescales: Empirical Evidence and Mechanistic Explanation
In Soon (2005), the variable total solar irradiance series of Hoyt and Schatten (1993) has been shown to be able to explain, rather surprisingly, well over 75%\ of the variance for the decadally-smoothed Arctic-wide surface air temperature of Polyakov et al. (2003) over the past 130 years or so. Detailed examination and reconstruction of the seasonal pattern of Arctic temperature records, based on inverse wavelet transform, support a solar-Arctic physical connection. In this paper, I will provide additional empirical evidence for this physical connection both through several newly published, high-resolution paleo-proxy records and through reliable climate modeling outputs, and sketch a mechanistic explanation, involving the variable strength of the Atlantic meridional overturning circulation, the shift and modulation of the Inter-tropical Convergence Zone (ITCZ) rainbelt, and perhaps the intensity of the wind-driven subtropical and subpolar gyre circulation, while taking full advantage of the decomposition of solar insolation forcing into its symmetric and antisymmetric components proposed earlier by Bin Wang (1994), in order to better spell out the physical reality of this connection. The latter unique perspective is to offer a better interpretation and synthesis framework that would allow, in dynamical systems theory, a more natural correspondence with the decomposition of multidecadal and centennial climate variability into wind-driven and the thermohaline circulation modes with large-scale zonal (east-west) and meridional (north-south) symmetries or asymmetries (Dijkstra 2006). The ultimate goal of my scientific research, though, is to gain sufficient mechanistic details so that the proposed solar Arctic climate connection on multidecadal to centennial timescales can be confirmed or falsified. A differentiation of this total solar irradiance forcing proposal on the focused timescale from the related decadal-scale solar UV irradiance forcing will also be emphasized. A further incentive to expand this physical connection to even longer millennial-scale variability is motivated by the recent results shown by Braun et al. (2005). References Braun and colleagues (2005) Nature, vol. 438, 208-211.\Dijkstra (2006) J Physical Oceanography, vol. 36, 286-299.\Hoyt and Schatten (1993) JGR, vol. 98 (A11), 18895- 18906.\Polyakov and colleagues (2003) J Climate, vol. 16, 2067-2077.\Soon (2005) GRL, vol. 32, 2005GL023429.\Wang (1994) J Climate, vol. 7, 1926-1942.
U33A-0005
Parameterizing Arctic sea-ice melt pond characteristics for radiation budgets and climate modeling
Solar heating in the Arctic atmosphere-ice-ocean system plays a key role in the recently observed decline of the Arctic sea-ice cover and is key to ice-albedo feedback. The summertime absorption and transmission of shortwave radiation by Arctic sea ice is strongly affected by the areal extent and optical properties of melt ponds. As part of an effort to arrive at an integrated assessment of the disposition of solar radiation in the Arctic atmosphere-ice-ocean system, we have examined the spatial and temporal evolution of melt ponds as a function of ice type and melt-season stage based on a combination of field measurements, a pond-hydrology model and remote sensing. Previous work has shown that the pond distribution is largely controlled by meltwater production at the ice surface, surface topography and the permeability of the underlying ice. Here, as a first step, meltwater production is parameterized as a simple function of initial snow depth, seasonal melt progression and latitude, with a focus on the impact of variations in surface topography and permeability on pond evolution. Ice permeability has been derived from an empirical porosity-permeability model, with temperature and salinity profiles determined by ice type and melt stage. We distinguish between four different ice types with different ponding characteristics: level and rough first-year and multi-year ice, respectively. Data on the surface topography and summary statistics of surface elevation or effective hydraulic head have been obtained from a range of field measurements in different sectors of the Arctic, employing both ground-based and airborne techniques. In summer, the evolution of ice surface topography is largely controlled by ablation processes and it is mostly the pooling and flow of surface meltwater during the first third to one half of the melt season that determine the ponds' distribution during the stagnant, latter stages of melt. In order to assess variations in pond evolution, the timing of onset and termination of melt have been derived from QuikScat Scatterometer data (determined through analysis of diurnal backscatter variations) for selected locations within the Arctic Ocean between 1999 and 2005. In conjunction with determinations of the ice and pond optical properties, the impact of ponds on total absorption of shortwave radiation by the ice-ocean system is assessed.
U33A-0006
Difference in Seasonal Variation of net Precipitation between the Arctic and Antarctic Regions
The difference in the climatological seasonal variation of the net precipitation (precipitation minus evaporation) between the Arctic and the Antarctic was evaluated using ECMWF reanalysis data. Evaluated for simplified polar caps (the regions poleward of 70N and 67.5S), over the Arctic, the net precipitation is large in the boreal summer, while, over the Antarctic, it is large in the austral winter. The net precipitation depends strongly on the poleward transient moisture flux into the region, which is affected by both the meridional moisture gradient and eddy activity. Thus, the seasonal variation of the poleward transient moisture flux is determined by the relative amplitude of the moisture and eddy factors, that is, by the ratio of the amplitude of the seasonal variation to the annual mean. While both regions have similar relative amplitudes of the eddy factor, the moisture factor in the Arctic is much larger than in the Antarctic. The moisture factor explains the difference in the seasonal variation of the net precipitation.
U33A-0007
Remotely Sensed Variations of Pan-Arctic Terrestrial Vegetation Productivity from 1982- 2005
We applied the MOD17A2 production efficiency model (PEM) using AVHRR Pathfinder (PAL) and MODIS LAI/FPAR time series, and corrected NCEP reanalysis daily surface meteorology to assess terrestrial NPP for the pan- Arctic basin and Alaska from 1982 to 2005. We applied a `moving window' correction of the NCEP reanalysis time series using observed daily minimum and mean surface air temperatures and dew points from 5,874 surface weather stations distributed across the region. We conducted a pixel-wise integration of the AVHRR and MODIS time series by empirical adjustment of the AVHRR record using land cover specific regressions of overlapping NPP results for 2000. Annual NPP for the domain showed a significant, positive productivity trend of 0.2% per year (P=0.01) from 1982 to 1997 followed by a significant productivity decline of 0.8% per year (P=0.035) after 1997. The annual onset of the growing season defined by the timing of the spring drawdown of atmospheric CO2 from NOAA CMDL high latitude (>50$^{circ}$N) stations was highly correlated (r = -0.510; P = 0.013) with annual anomalies of regional average NPP for the study domain before 2000, while this correlation was reduced (r = -0.148, P = 0.29) after 2000. The satellite derived NPP anomalies were also highly correlated (r = 0.62, P = 0.01) with stand-level observations of boreal Aspen growth anomalies for 72 stands across west-central Canada. These results indicate that low temperature constraints on vegetation productivity are decreasing (P < 0.001), particularly for Eurasia, whereas increasing moisture stress (P = 0.069), especially after 2000, is offsetting the potential benefits of longer growing seasons and resulting in a recent, widespread productivity decline.
U33A-0008
Early Middle Eocene Palaeoenvironments and Biostratigraphy of the Lomonosov Ridge: A Diatom and Chrysophyte Perspective
The Arctic Coring Expedition (ACEX), Integrated Ocean Drilling Program Leg 302 recovered sediment cores from the Lomonosov Ridge to >400 meters below seafloor (mbsf). Dark grey mud-bearing organic-rich laminated biosiliceous ooze, between ~200-300 mbsf in Holes M0002A and M0004A, are Middle Eocene in age and contain shallow water marine diatoms in good preservation with abundances on the order of 10$^{6}$-10$^{7}$ valves/gram. The highest levels of biogenic silica, and the best siliceous microfossil preservation, occur below 220 mbsf, corresponding to Lithostratigraphic Unit 2. The diatoms occur in conjunction with variable abundances of other marine to brackish siliceous microfossils (ebridians, silicoflagellates and endoskeletal dinoflagellates) as well as diverse assemblages of freshwater chrysophyte cysts and marine and terrestrial palynomorphs. There are clear and frequent changes in dominance between the main siliceous microfossil groups, reflecting of an extraordinary depositional environment where both shallow marine and freshwater influences prevailed. We quantify these changes for the diatoms and chrysophytes. While the cyclical nature of these inferred salinity changes is under investigation, we report here on the broad scale variation in biosiliceous components through the Middle Eocene focusing in particular on the diatom and chrysophyte changes. Our initial results highlight the potential for an integrated regional diatom biostratigraphy for the Middle Eocene of the Arctic and Barents Sea, and indicate basin-wide palaeo-environmental fluctuations on long and short timescales. This poster outlines the various lines of work we are currently exploring in more detail.
U33A-0009
International Study of Arctic Change - ISAC
The International Study of Arctic Change is a new science program launched by the International Arctic Science Committee (IASC) and the Arctic Ocean Sciences Board (AOSB). It is designed as a long-term, international, cross-disciplinary and pan-arctic program to document Arctic environmental changes. ISAC will take a system approach to facilitate expansion and deepening of our knowledge of the Arctic system and to document changes in the Arctic. ISAC is motivated by already documented changes large enough to affect the lives of native populations, other residents in the Arctic realm, as well as the ecosystem. Climate models suggest substantial future changes; these will have a profound impact on Humankind not only at high latitudes but potentially also at lower latitudes through climatic tele-connections. It is obvious that the distribution of marine sustainable resources will change, but to what degree and in what patterns is not possible to answer with certainty before reliable climate forecasting can be performed. It cannot be disregarded that poorly understood feedback mechanism might alter the system resulting in abrupt changes in climate. Whereas dealing with changes is challenging enough, the lack of predictability compounds the problem because it does not allow development of strategies to deal with the changed environment. Among the major products of ISAC will be contributions to scientific assessments that address present and future needs of impact assessments. Toward this end ISAC will engage in multidisciplinary observational, synthesis, and modelling activities responding to societal needs, science plans and priorities established by scientific community.
U33A-0010
New Data on the Stable Isotopes and Vertical Distribution of Benthic Foraminifers in the Western Barents Sea
Despite a wide use of benthic foraminifers in paleoceanographic and paleoclimatic studies, notably in the Arctic seas, their ecology is still poorly known. We studied the distribution of living (Rose Bengal stained) and dead benthic foraminifers, as well as oxygen and carbon isotope composition of monospecific samples in the upper 10 cm of sediment in six box corers retrieved from the Western Barents Sea and the West Spitsbergen shelf during cruise 63 of RV {\it Professor Shtokman}. Living specimens of five common infaunal species and {\it C. lobatulus}, generally considered as epifaunal species, penetrate down to 7-10 cm except for the West Spitsbergen shelf where the habitat depth of all six species is limited to the upper 3-7 cm. The highest species diversity and amount of living specimens per 50 cm$^{3}$ were found in the seasonally ice-free areas notably on the West Spitsbergen shelf and in the mouth of Isfjorden (Svalbard), areas characterized by very high primary production. In general, four species show higher abundance among living calcareous foraminifers as compared to the dead assemblages, whereas two species, {\it C. reniforme} and {\it I. norcrossi}, demonstrate an opposite behavior, i.e. are accumulated in the sediments. In most cases, the uppermost thin oxidized brownish layer of the sediment contains more living specimens and more fragile agglutinated foraminifers than olive-grey and grey (reduced) sediments below. If the latter two findings will be confirmed by further studies they may have important implications for paleoceanographic reconstructions as an evidence of a transformation of biocoenoses into thanathocoenoses in the Arctic seas. The epifunal species {\it C. lobatulus} demonstrate the heaviest (positive) carbon isotope values and the lowest oxygen isotope values as compared to all other species. Three infaunal species show relatively similar negative $\delta$$^{13}$ C values due to the microhabitat effect (i.e. oxidation of organic matter within the sediment). The heaviest oxygen isotope values are typical for {\it N.labradoricum} which is consistent with the previous studies. All species show heavier values in box-corers from the Persey Trough where the warm Atlantic water does not chill the sea floor unlike the other studied locations. Both $\delta$$^{18}$O and $\delta$ $^{13}$C measurements reveal different downcore trends with changing offsets between the species. This may be related to a vital effect of specific ontogenetic stages, but may also result from insufficient time resolution to obtain simultaneous data for all species.
U33A-0011
Regional Trend Analysis of Satellite-Derived Snow Extent and Global Temperature Anomalies
The extent and variability of seasonal snow cover are important parameters in climate and hydrologic systems due to effects on energy and moisture budgets. Northern Hemisphere snow cover extent, comprising about 98 percent of global seasonal snow cover, is the largest single spatial component of the cryosphere, with a mean maximum extent of 47 million square kilometers (nearly 50 percent of the land surface area). During the past four decades, much important information on Northern Hemisphere snow extent has been provided by the NOAA weekly snow extent charts, derived from visible-band polar orbiting and geo-stationary satellite imagery. Since 1978, satellite passive microwave sensors have provided an independent source for snow monitoring, with the ability to penetrate clouds, provide data during darkness, and the potential to provide an index of snow water equivalent. We see both positive and negative trends in snow cover derived from these data sets, depending on region and time of year. We continue to search for attribution of these trends. We present regional trend analysis of both snow cover data sets, and comparisons with gridded temperature anomalies from the NASA GISS Surface Temperature Analysis data.
U33A-0012
Interactions and Feedbacks in the Changing Arctic Hydrologic System
Change in the Arctic climate system is dramatic and widespread. The exchange of freshwater in all its forms plays a leading role in the system, as its influence reaches far beyond the boundaries of the region, has strong ties to ecology and humans, and constitutes important links between the atmosphere, ocean, and terrestrial ecosystem. The manifestations of change in components of the hydrologic cycle are difficult to unravel, however, owing to the complex interactions among them as well as between the Arctic and lower latitudes. In this study we adopt a graphical approach to identify and understand the primary drivers of the system, particularly as they effect biological and human well- being, and explore how these interactions may change in a future Arctic with dramatically reduced permanent ice. Positive and negative feedbacks are identified by examining the connecting pathways of influence. Focusing only on those that affect the living components of the system (marine productivity, terrestrial plants, and humans), our preliminary analyses suggest: 1) The majority of feedbacks are positive, with the notable exception of those involving the exchange of freshwater in the unfrozen ocean, 2) All feedbacks in the terrestrial system that affect vegetation contain a weak link, 3) If the observed trajectory of change in the physical hydrologic system continues, feedbacks affecting living components will further augment terrestrial vegetation, marine productivity, and human well-being.
U33A-0013
Arctic Climate Change: Are Current Climate Models too Conservative?
Arctic Climate Change: Are Current Climate Models too Conservative? Julienne Stroeve, Marika Holland, Mark Serreze Climate models have long predicted that warming in the Arctic in response to greenhouse gas loading will be especially pronounced. This strong warming is closely related to loss of the sea ice cover. However, observed sea ice losses since 1979 have been stronger than those simulated by most of the models from the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). This begs the question: Is the observed sharp decline strongly influenced by natural processes that dominate the short observational sea ice record, or is there a reason to believe that the AR4 models are systematically under-representing the sensitivity of the Arctic sea ice cover to greenhouse gas loading? Using results from sea ice simulations from IPCC AR4, we computed multimodel ensemble mean ice extent for three different emission scenarios. Comparisons of model output using the SRES A1B model (CO2 of 720 ppm by 2100) with observations from satellite reveal that although most of the models climatological sea ice area is within 20 percent of the observational climatology, the Arctic sea ice is currently disappearing faster than the ensemble mean and faster than indicated by the range of ensemble members. From 1953-2005, a combination of satellite and in situ observations indicate the September sea ice has declined by -7.6 percent per decade. The multimodel ensemble mean from models that show climatological mean sea ice extents within 20 percent of the observations, suggest a much smaller rate of decline (-2.3 percent per decade). During the satellite era from 1979-2005, the rate of decline is -8.9 percent per decade, which is also significantly underestimated by the multimodel ensemble mean rate of -4.3 percent per decade. Although the latest results from the IPCC AR4 model simulations incorporate many improvements in physics, parameterizations and resolution, important processes are still missing in many of the AR4 models. One example is that most of the models do not parameterize the sub-grid scale ice thickness distribution which results in a weaker ice-albedo feedback. Questions also remain regarding the ability of climate models to represent changes in atmospheric modes of variability (e.g. NAO-like behavior) and changes in high latitude ocean conditions in response to a warming climate. The omission of such important processes could be one reason why the models are failing to track the current state of the Arctic sea ice. In addition, since there remains a large range of uncertainty in the climate models as indicated by the large standard deviation of the multimodel ensemble mean, future projections of when the Arctic will become ice free still contain a high amount of uncertainty.
U33A-0014
Intra-seasonal relationship between the Northern Hemisphere sea ice variability and the North Atlantic Oscillation
An intra-seasonal relationship, including a possible feedback, is investigated between the North Atlantic Oscillation (NAO) and a hemispheric-scale seesaw-like pattern dominant in sea ice variability over the wintertime Northern Hemisphere, with one polarity in the Bering and Labrador Seas and the other in the Okhotsk and Greenland- Barents Seas. Statistical analysis using observational data suggests that a particular phase of NAO and anomalous atmospheric circulation in the Pacific during early winter contribute toward the development of the midwinter hemispheric sea-ice seesaw. In contrast, the ice seesaw tends to damp the preexisting NAO signal during late winter, indicating a reversal of the phase relation between them. This NAO damping may be triggered by the Pacific sea-ice anomalies. Results from numerical experiments generally support this notion and further suggests a stationary Rossby wave train emanated from the North Pacific as a dynamical mechanism for damping the NAO signal.
U33A-0015
Simulation of reservoir effects on streamflow seasonality for the Lena, Yenisey, and Ob' rivers
Since the 1930s, observed streamflow at the outlets of the Lena, Yenisey, and Ob' River basins has increased during the winter and spring. This has resulted in a shift in seasonality of the total river runoff discharged to the Arctic Ocean from the Eurasian Arctic. Potential causes of this shift include climate-induced agents of change (e.g. a shift in precipitation seasonality, an earlier snowmelt, and/or an increase in permafrost active layer depth combined with a delay in the freeze-up of the soil column), as well as direct anthropogenic effects, most obviously the storage and release of river runoff in reservoirs. Large reservoirs in these three river basins were constructed between the 1950s and the 1980s. Currently operating large reservoirs (exceeding 1 km3 in storage capacity) total one for the Lena, three for the Ob', and seven for the Yenisey (an eighth, the Boguchany reservoir, is still under construction). We describe a method to estimate the climatic versus reservoir-induced effects on streamflow seasonality, and we compare these estimates to those of prior studies. We simulate reservoir effects using a reservoir routing model coupled off-line to the Variable Infiltration Capacity (VIC) land surface hydrology model for the Lena, Yenisey and Ob' river basins. The simulation captures the main effects of reservoir operations, assuming that the primary purpose of each reservoir is to generate hydropower (i.e. reservoir releases are determined by maximizing hydropower production for each operational year). The potential of reservoirs to affect basin-average evaporation are also considered. We evaluate the simulations by comparing the output from the reservoir model to observed streamflow data. Furthermore, we compare the reservoir signature of our product to those of other products. The reservoir signatures are calculated by differencing the simulated streamflow hydrograph with reservoir effects from the simulated streamflow hydrograph without reservoir effects (for our product), and by differencing the observed streamflow hydrograph from the "naturalized" streamflow hydrograph (for estimates from previous work).
U33A-0016
The influence of the annual Arctic Oscillation on the negative correlation between Okhotsk sea ice and Amur River discharge
Newly obtained observational discharge data reveal the cause of a significant negative correlation between Amur River discharge and Okhotsk Sea ice at multiyear timescales. The annually integrated Arctic Oscillation (AO) influences both summer discharge and winter ice. Summer discharge is larger and winter ice is reduced during positive AO years. Annual AO also influences the annual horizontal moisture flux convergence in the river basin. When the annual AO is positive, the annual mean air temperatures are warm over Eurasia, particularly over the Amur River basin and the Okhotsk. Consequently, autumn SSTs are warmer in the Okhotsk Sea. The warmer autumn SSTs suppress ice formation during the following winter. Freshwater from the river is not the main control of multiyear ice variability. Consideration of the annual AO provides a new look at climate system persistence at multi-seasonal scales.
U33A-0017
Impact of global warming on seasonal variations of net precipitation in polar regions
We investigated the impact of global warming on seasonal variations of net precipitation in polar regions, comparing IPCC simulations with ECMWF reanalysis data (ERA40). IPCC simulations from 5 models (MRI, MIROC-hires, MIROC-medres, GISS and ECHAM) are used. To assess the impact of global warming, the difference between climate of the 20th Century experiment (20C3M) and 720 ppm stabilization experiment (SRES A1B) were estimated. All IPCC simulations are underestimated poleward moisture fluxes and amplitudes of seasonal variation are small in both polar regions. From these comparisons with ERA40, MIROC-medres and ECMAM are relatively reasonable for seasonal patterns of poleward moisture fluxes in polar regions. According to results from these two models, under global warming condition, meridional moisture flux into the Arctic is enhanced in boreal summer and that into the Antarctic is enhanced in late winter and spring. Recently, we found that the difference in the seasonal variation of the net precipitation between the Arctic and Antarctic regions can be explained by decomposing the transient moisture flux into the contributions due to the moisture effect and eddy activity effect (Oshima and Yamazaki, 2006, GRL). Based on this idea, it is found that the enhancement of moisture flux into polar regions is caused by the intensification of meridional moisture gradient.
U33A-0018
Global ocean wave intensity changes observed across decadal-scale time intervals using seismic background noise
Seismic background energy on Earth between roughly 6 and 25 s period, even in deep continental interiors, is dominated by a persistent ``microseism'' arising from energy transferred from ocean gravity waves to elastic Rayleigh waves. High-quality continuous digital records from the IRIS/USGS Global Seismographic Network (GSN) and its precursor networks now extend back over 15 years at the longest-operational sites. We examine using the microseism as a proxy for decadal-scale changes in storm wave intensity, a topic of considerable interest in the debate about how global change may influence oceanic storm frequency and intensity. Microseism power spectral density (PSD) is dominated by a primary peak centered near ~16 s that is generated by waves breaking on coastlines, and by a (generally much stronger) secondary peak centered near ~8 s that is generated by the half-period periodic variation of sea bottom pressure due to standing wave components of the ocean gravity wave field. We measure microseism intensities on decadal intervals, eliminating signals at similar periods arising from earthquakes by evaluating medians of large numbers of 1-hour PSDs over day- to months- long intervals. Integrated PSD median curves over relevant period ranges give representative microseism power levels. Microseism power time series from the GSN show secular changes in the roughness (storm-wave intensity) of Earth's oceans extending back as far as the late 1970's. Resulting time series for northern hemisphere stations clearly show very strong effects from northern Pacific winter storms, where PSD levels can increase by 2 orders of magnitude over summer levels (e.g., as observed at Kipapa, Oahu). We also see the effects of southern hemisphere storms during the austral winter and, in Antarctica, seasonal shielding effects that are attributable to the formation/disintegration of sea ice at southern hemisphere stations (e.g., at South Pole). El Nino-induced sea surface roughness changes are also visible at northern hemisphere stations, such as notably increased microseism levels during 1997-1998. These observations suggest that the microseism may provide a useful proxy record for evaluating the influence of climate variations on oceanic storminess.
U33A-0019
The Middle Eocene Paleoceanography of the Arctic Ocean Based on Silicoflagellates and Ebridians
The early middle Eocene Arctic samples, which were obtained by IODP Expedition 302 (ACEX), were studied for the siliceous microfossils of silicoflagellates and ebridians in order to decipher the paleoceanographic changes of the upper water column. The presence of low salinity waters in the Eocene Arctic is suggested from the co- occurrence of freshwater and blackish water microfossils. Changes of characteristic assemblages with age are probably due to the habitat modulation governed by the extent of mixing of significantly different water masses between the low salinity waters derived from the Arctic region and relatively high salinity waters supplied from the outside of the semi-closed paleo-Arctic basin. The freshwater is attributed to the rainfall and river influx during the rainy Eocene Arctic summers. According to the basin to basin fractionation model of Berger (1970), the Eocene Arctic Ocean probably corresponds to an estuarine type, which includes the Black Sea or the Baltic Sea today. The significantly high abundance of ebridians may reflect the presence of H$_{2}$S boundary within the euphotic layer based on the extant ebridian ecology of Hermesinum adriaticum with symbiotic algae, which is present in the Black Sea today.
U33A-0020
Paleoceanography of the Eocene Central Arctic Basin Based on Geochemical Measurements of Biogenic Matter
The IODP Leg 302 Arctic Coring Expedition retrieved approximately 120 m long continuous Eocene section from the Lomonosov Ridge in the central Arctic for the first time. The Eocene section is lithologically classified into Unit 2 with the assigned age of ~49-44Ma below and Unit 1/6 with 44Ma above the unit boundary. Unit 2 consists of very dark gray mud bearing siliceous ooze and Unit 1/6 consists of very dark gray silty clay to clayey silt. Biogenic opal (293 samples), organic carbon, nitrogen, and sulfur (150 samples) were measured. The sample resolutions are approximately 16 kyrs for Unit 2 and 8 kyrs interval for Unit 1/6, respectively. In Unit 2 biogenic opal ranged from 40 to 70% whereas in Unit 1/6, it decreased down to 10-20%, except for a peak of 37% at approximately 203 mbsf. Organic carbon consistently showed high values such as 1.4-5.7% both in Units 2 and 1/6. C/N ratios ranged from 15 to 20. Sulfur values ranged 2.6-7.7% in Unit 2 and it significantly increased to 4.0- 19.4% in Unit 1/6. Based on the presence of abundant framboidal pyrites and the observed extremely low C/S ratios of < 1.2 clearly indicate that the basin was under euxinic marine condition with sluggish bottom water circulation. Siliceous plankton mainly contributed to the biological productivity from 250 to 220 mbsf in Unit 2 and from 216 to 207 mbsf in Unit 1/6, judging from positive correlations of biogenic opal vs %organic carbon. In other parts of the section such a positive correlation was not seen, implying something else other than siliceous plankton mainly contributed the total productivity. From Unit 2 to Unit 1/6, three rather drastic environmental changes are suggested: decrease of siliceous plankton productivity, increase of sulfate availability, and intensification of the euxinic conditions. In Unit 1/6 where sulfur values significantly increased, an increase of marine water inflow from the North Atlantic suggested by a study on silicofragellates assemblages. The marine water inflow appears to explain the raised dissolved sulfate concentration, resulting more pyrite formation. The conclusions derived from other microfossil studies are also conformable with the results of this study; they are: the Eocene conditions were interpreted as brackish water, fresh water at the top, marine water lying subsurface, eutrophic, relatively shallow, sluggish bottom water circulation, and occasional pelagic water invasions at least in the upper layer.
U33A-0021
Deglaciation of the Last North European Ice Sheet: Responses From Marine Sedimentary Records
Multiproxy sediment core records and high-frequency seismic profiles from Baltic, Norwegian, and Barents seas reveal a lithostratigraphic/seismostratigraphic sequence of glaciomarine (glaciolacustrine) deposits of the last deglaciation. The complete Late Weichselian glaciation to Recent sedimentary sequence recovered by core ASV- 880 from the Franz-Victoria Trough includes four lithostratigraphic units: (IV) coarse-grained glacial till of LGM with almost fresh pore water, (III) proximal glaciomarine diamicton of the initial deglaciation with abundant IRD and saline pore water; (II) distal glaciomarine laminated mud of the late deglaciation, with scarce, but sporadically rich foraminiferal assemblages; (I) Holocene marine facies. The sequence is recovered by numerous cores and can be traced by seismic records from shelf depressions throughout the Barents Sea. However, the unit boundaries are diachronous depending on the progressive glacier retreat from the west and north to the east controlled by the surface and subsurface Atlantic water inflow The deglaciation of the Barents Sea started about 17 ka and the initial deglaciation phase (Unit III) followed the rapidly retreating ice edge up to 15-12 ka, when the ice sheet disappeared from the open Barents Sea and proximal glaciomarine facies were replaced with distal ones characterized by laminated sediments deposited from low-density gravity flows. The late deglaciation unit II is thicker (up to 20 m) in the southern Barents Sea, and less than 1m thick in its central part. Core PSh-5159 from the Ingeyajupet deep (SW Barents Sea) recovered 4 m of mud with sand laminae likely corresponding to distal glaciomarine facies, although its lower part was deposited prior to 14 cal. Ka BP, when Unit III accumulated in northern areas. Foraminiferal assemblages, IRD, and delta 18O record suggest climate changes during the deglaciation. The deglaciation sequence of the Barents Sea correlates with that from the Baltic Sea, where proximal glaciolacustrine (?) facies between the glacial till below and laminated (varved) clay of the Baltic Ice Lake (BIL) above correspond to units IV through II of the Barents Sea. The Baltic Sea deglaciation started at about 17 ka in the west. A major part of the Baltic Sea became ice-free to 13-12.5 ka, and distal glaciolacustrine varved clay facies accumulated in the BIL. The south-eastern ice sheet edge began to retreat about 17 ka supplying Volga River with meltwater that resulted in rapid Caspian and Black Sea level rise.
U33A-0022
Late Pleistocene Variations in the Water Current and Ice Rafting Transportations of Organic Matter in the Central Arctic Ocean (ACEX Hole M0004C)
Little is known about the source of organic matter and the response of sedimentary organic matter composition to glacial-interglacial changes in the central Arctic Ocean. Here we have generated late Pleistocene records of biomarkers and ice rafted debris (IRD) from IODP-Arctic Coring Expedition (ACEX) Hole M0004C to understand the glacial-interglacial changes of mass transportation in the Arctic Ocean. Major biomarkers detected in Hole M0004C were long-chain n-alkanes, n-fatty acids and n-alkan-1-ols, derived from fresh higher plants, and gem-alkanes (branched aliphatic alkanes with a quaternary substituted carbon atom), derived from unknown source. Minor biomarkers were oleanenes of angiosperm origin, unsaturated fatty acids, bacteria-derived anteiso- and iso-fatty acids, various hydroxy acids, formed by hydroxylation of n-fatty acids by aerobic bacteria, cholesterol and sitosterol, and hopanes, formed by diagenetic alteration of bacterial biohopanoids. There was no concrete evidence for in situ production of phytoplanktons. The concentrations of these biomarkers varied with IRD number variation. During periods of abundant IRD, diagenetic hopanes were abundant, suggesting that clastic materials were supplied by ice rafting. During periods of scarce IRD, the other biomarkers such as long-chain compounds were abundant, suggesting that the riverine discharge was enhanced. The IRD and biomarker variations were synchronized with the eastward expansion of the Fennoscandinavian Ice Sheet to northen Siberia, suggesting that the ice cover of northen Siberia is critical in switching mass transportation mechanisms in the Arctic Ocean.
U33A-0023
Arctic-ice history and its related sedimentary regimes in the central Arctic Ocean: IODP Expedition 302�|Arctic Coring Expedition: ACEX by new non-destructive 2-D XRF and transmission X-Ray sediment-scanning techniques, TATSCAN
Until the recent when the Integrated Ocean Drilling Program (IODP) Expedition 302 has conducted a deep sea drilling at the central Arctic Ocean, the past Arctic-ice history has been a mystery of the Cenozoic icehouse Earth system. The IODP- Arctic Coring Expedition (ACEX) has successfully recovered over 400m sediment records (about 0 to 55 Ma) on the Lomonosov Ridge in 2004 (Moran et al., 2006). In order to reconstruct and reveal the ice history in the central Arctic Ocean, we conducted new non-destructive sediment core scanning techniques, TATSCAN, that is a code name of developing original instruments for non- destructive sediment scanning and imaging in range of millimeter and micrometer scale. In the recent, we have newly developed non-destructive energy dispersive type X-ray Fluorescence (XRF) scanner, TATSCAN-F2, for 2- dimensional elemental imaging of the surface of sediment with 1mm- or 1cm- measuring diamter in the length of up to 150 cm. The TATSCAN-X is another non-destructive scanning technique by using transmission X-ray, which can detect and identify discrete shapes such like isolated granule and pebble in the sediment core. The number of ice-rafted debris (IRD) that was defined as discrete grains more than 1mm in diameter in the X- ray imaging, was direct information of the past Arctic ice recorded in the sediment. IRD increased 1.6 – 1.75 Ma and 0.0 - 0.8 Ma. During 0.8 Ma, especially, IRD significantly became 2 to 4 time richer than previous duration. IRD increased in the glacial and decreased in the interglacial. The IRD variation was consistent with biomarkers in the sediment core. The increase of IRD corresponds to high amount of diagenetic hopanes and to low concentration of other biomarkers such as long-chain organic compounds derived from fresh higher plant, which was mainly supplying by river discharge. The variation of the IRD should be related to expansion of northern Siberian ice-sheet to the Arctic during the cold durations. High-resolution manganese (Mn) variation corresponding to brownish colored sediment interval was detected by TATSCAN-F2 scanner. It increased in the intervals of with no and less IRD concentration, corresponding to the warm duration. The possible source of Mn in the sediment is transportation of source material such as river draining peat from northern Siberia and/or enhanced Mn-precipitation by active water circulation.
U33A-0024
Interdecadal Modulations and Seasonal Dependence of the Icelandic and Aleutian Lows: Their Inter-Basin Link and Impacts on High-Latitude Climate
The Icelandic and Aleutian lows (IL and AL, respectively) are wintertime semipermanent low-pressure systems over the North Atlantic and North Pacific, respectively. The interannual and intraseasonal IL and AL variability are closely related to the North Atlantic Oscillation (NAO) and Pacific-North American (PNA) pattern. Wintertime weather conditions in mid- to high-latitudes can be strongly influenced by variability of the two low pressure systems on multi-timescales. It has been found that an interannual seesaw-like oscillation exists between the AL and IL intensities (the AL-IL seesaw, AIS). The associated anomalies in surface air temperature (SAT) for the strong IL and weak AL are characterized as warmer conditions over the northern Europe, the southeastern US and the Far East, and colder conditions on the northern part of the North America and the Middle East. Since the seesaw formation is triggered by eastward propagation of stationary Rossby wave trains from the North Pacific into the North Atlantic, this upper-tropospheric downstream influence could be a basis for predicting climatic conditions in the Euro-Atlantic sector a month ahead. It is also known that the pronounced wintertime warming trend over landmasses observed in the recent decades is associated with concomitant deepening of the AL and IL intensities, a pattern akin to the �gCold Ocean Warm Land�h (COWL) pattern, which is the opposite sense to the AIS. The associated SAT anomalies strongly reflect the recent weakening of a land-ocean contrast especially in high latitudes, suggestive of strong climatic impacts on the polar regions for the recent decades. Interestingly, these respective out-of-phase and in-phase relationships between the IL and AL can be identified as the two leading EOF modes of variability in the upper troposphere for the recent 50 or more winter seasons. Actually, interannual variability and long-term changes and �gactiveness�h of the AIS and COWL for the last half century are essentially extracted in the two leading modes, which reflects the corresponding modulations in the strength of dynamical linkage between the North Pacific and North Atlantic in the upper troposphere. Further investigation based on more than hundred-year surface observational data set for the sea-level pressure and SAT shows that the AIS underwent multidecadal modulations and seasonal dependence during the 20th century. It was weak in the mid-1950s through the mid-1960s, while it was particularly strong during the preceding period from the 1920s to the 1940s with its impact on surface temperatures as extensive as in the recent period, although its maturity was in January. The COWL-related spatial structures and amplitudes have been also multidecadally modulated during the last century, which were not necessarily associated with the global warming trend, especially in the first half of the last century.
U33A-0025
Halogens in the Dry Valleys Lakes, Antarctica: dynamic cycling between water, sediment, and cryogenic evaporites
Many of the McMurdo Dry Valleys lakes of Antarctica exhibit saline to hypersaline bottom waters whose chemistry is distinct from that of sea water. The source and relative abundance of dissolved Cl, Br, and I in these unusual waters has been modified by several potential processes including: seawater incursions, water-rock interactions, microbial scavenging, glacial melting and precipitation, and atmospheric deposition. Since all of these processes are affected by both long-term and short-term climate change, lake waters and the salts that are deposited around them provide sensitive indicators of lake dessication and refilling in the past.\\ We present elemental analyses, not only of the lake water, but also of bottom sediments and cryogenic evaporites recovered from the Dry Valleys. XRD analyses indicate that gypsum and antarcticite are precipitated around saline lakes presently situated more than 40 km from the ocean (Vanda, Don Juan, Joyce), while mirabilite is found near small pools in the Garwood Valley, only a few km from the ocean. Lake water enrichments in Ca and Cl, relative to Na suggest that either dissolution of gypsum and antarcticite has occurred in Don Juan Pond and Lake Vanda, or that these two small bodies of water previously lost sodium to mirabilite formation. Lakes Fryxell and Joyce, as well as waters in Garwood Valley show nearâ€â€�sea water ratios. \\ Dissolved iodine, and to a lesser extent bromine, are commonly associated with diagenesis of marine organic matter in regions of high productivity, so it is surprising that the Dry Valleys lake waters are enriched in these two elements. These enrichments are also apparent in pore fluids of shallow sediments on the lake bottoms. In addition, the sediments themselves are highly enriched in iodine in the upper 5 cm (up to 77 ppm). This is likely due to remobilization of dissolved iodide, which is mobile in reduced form, but becomes fixed as adsorbed or organic iodine upon diffusing into shallow oxic sediments. Temporal changes in ice cover, and oxidation state of the deeper lake waters may be reflected in the efficiency by which dissolved iodide is released from these deep sediments and diffuses up through the water column.\\
U33A-0026
Pan-Arctic Temperatization: A Preliminary Study of Future Climate Impacts on Agriculture Opportunities in the Pan-Arctic Drainage System
With increased population and predicted temperature increases in the next century between 2 and 4 degrees Celsius; questions have arisen about what effects global warming may have on water availability and food security and water availability. A preliminary investigation was conducted on changing agriculture opportunities in the pan-Arctic drainage system caused by global warming. Temperature and precipitation predictions from the HadleyCM3 model based on IPCC scenarios were used. Average growing degree days and precipitation were compared for the contemporary time period and end of the century. Based on only temperature requirements potential cropland area with enough growing degree days to support crop growth in the Pan-Arctic doubled by 2080. However, Soil physical and chemical properties greatly reduce potential crop growing area estimates especially in Western Canada. Water limits further constrain potential crop growth area estimates and could reduce areas under current cultivation. Although increased temperatures may increase potential crop growth and productivity in the Pan-Arctic, increasing water demands and drying conditions may actually lead to a decline in productivity in some areas.
U33A-0027
Acceleration of the Arctic Water Cycle: evidence from the Lena Basin, Siberia
Strong positive climate feedbacks cause much of the Arctic to warm faster than the global average (IPCC, 2001; ACIA, 2004). The global hydrologic cycle is expected to accelerate in a warmer world because a warmer atmosphere can hold more water vapor. However, an important question that has not been adequately addressed is whether thawing of permafrost and deepening of the soil's active layer, which pulls moisture away from the surface into deeper reservoirs, will lead to a wetter or dryer Arctic climate (V�r�smarty et al., 2001). There is an apparent paradox in the Arctic between increasing annual precipitation trends (ACIA, 2004), increasing occurrence of forest fires (Kasischke et al., 1999; Korovin and Zukkert 2003), and the drying of surface lakes (Smith et al., 2005). Our investigation of hydroclimatological change in the Lena basin (Russia) points to an increasingly wet Arctic. Though much of the near-surface air temperature (SAT) warming is occurring when the ground is covered by snow, increases in frozen precipitation are also contributing to warmer soil temperatures by increasing soil insulation. A deeper active layer caused by spring and summer warming holds more soil moisture and is leading to increasing potential evapotranspiration (shown in the model), increasing hydrologic baseflow (modeled and observed), and increasing summer nighttime cloudiness (observed). Changes in summer cloud types are suppressing warming during the days, but warming the nights significantly even during the polar day (Groisman et al. 1996). Earlier onset of snow cover in autumn traps the spring and summer warming, a trend that leads to further deepening of the active layer. These observed and modeled feedbacks describe an Arctic hydroclimatological regime in which water storage and flow has increased and moved from the surface to the subsurface.