PP21A-1364 0800h
Signal-to-Noise Ratios and Climate Records from the Eclipse Icefield Ice Cores
The Arctic represents one of the key regions on Earth in our efforts to document and understand global change. The St. Elias mountain range in the southwestern Yukon Territory has recently been the focus of an international ice core research effort. Here we report on the signal-to-noise ratios and climate signals preserved in the major ion and stable isotope records from three cores recovered from the Eclipse Icefield (3107 m asl). The high snow accumulation rate (1.4 m water equivalent per year) allows for the development of seasonally to annual resolved records. Signal-to-noise ratios are calculated via statistical analysis of the glaciochemical records from the three different cores on seasonal and annual time frames. Our results indicate that stable isotopes and chemical species with gaseous precursors (e.g., sulfate, nitrate, and ammonium) show less glaciochemical variability at Eclipse compared to those species associated with particles. (e.g., calcium, magnesium, and sodium). We also provide a reconstruction of climatic variability in the region over the past 500 years via analysis of the stable isotope and major ion records.
PP21A-1365 0800h
An Ice Core Melter System for Continuous Major and Trace Chemical Analyses of a New Mt. Logan Summit Ice Core
The ice core melter system at the University of Maine Climate Change Institute has been recently modified and updated to allow high-resolution ($ < $1-2 cm ice/sample), continuous and coregistered sampling of ice cores, most notably the 2001 Mt. Logan summit ice core (187 m to bedrock), for analyses of 34 trace elements (Sr, Cd, Sb, Cs, Ba, Pb, Bi, U, As, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, REE suite) by inductively coupled plasma mass spectrometry (ICP-MS), 8 major ions (Na$^{+}$, Ca$^{2+}$, Mg$^{2+}$, K$^{+}$, Cl$^{-}$, SO$_{4}$$^{2-}$, NO$_{3}$$^{-}$, MSA) by ion chromatography (IC), stable water isotopes ($\delta$$^{18}$O, $\delta$D, {\it d}) and volcanic tephra. The UMaine continuous melter (UMCoM) system is housed in a dedicated clean room with HEPA filtered air. Standard clean room procedures are employed during melting. A Wagenbach-style continuous melter system has been modified to include a pure Nickel melthead that can be easily dismantled for thorough cleaning. The system allows melting of both ice and firn without wicking of the meltwater into unmelted core. Contrary to ice core melter systems in which the meltwater is directly channeled to online instruments for continuous flow analyses, the UMCoM system collects discrete samples for each chemical analysis under ultraclean conditions. Meltwater from the pristine innermost section of the ice core is split between one fraction collector that accumulates ICP-MS samples in acid pre-cleaned polypropylene vials under a class-100 HEPA clean bench, and a second fraction collector that accumulates IC samples. A third fraction collector accumulates isotope and tephra samples from the potentially contaminated outer portion of the core. This method is advantageous because an archive of each sample remains for subsequent analyses (including trace element isotope ratios), and ICP-MS analytes are scanned for longer intervals and in replicate. Method detection limits, calculated from de-ionized water blanks passed through the entire UMCoM system, are below 10% of average Mt. Logan values. A strong correlation (R$^{2}$$ > $0.9) between Ca and S concentrations measured on different fractions of the same sample by IC and ICP-MS validates sample coregistration. Preliminary analyses of data from the 2001 Mt. Logan summit ice core confirm subannual resolution sampling and annual scale variability of major and trace elements. Accumulation rate models and isotope data suggest that annual resolution will be possible to 1000-2000 y.b.p., with multi-annual to centennial resolution for the remainder of the Holocene and possibly including the last deglaciation. Dust proxy elements, including REEs, strongly co-vary in time-series and reveal concentration ratio fluctuations interpreted as source region changes. Volcanic eruptions are characterized by elevated concentrations of S, SO$_{4}$$^{2-}$, Cu, Sb, Zn and other trace elements. Concentrations of potential anthropogenic contaminants are also discussed.
PP21A-1366 0800h
Mount Logan Ice Core Evidence For Changes In The Hadley And Walker Circulations Following The End Of The Little Ice Age
The Hadley and Walker circulations dominate the climate of the tropics and contribute to extra-tropical climate variability through the forcing of planetary waves that result in the long-range correlation of atmospheric circulation patterns known as teleconnections. Previous work showed that an annually resolved 301-year ice core record of annual snow accumulation from a high elevation site on Mount Logan in northwestern North America contains an expression of one such teleconnection, the Pacific North America (PNA) pattern. Here we show that this record contains a related signal associated with the regional Hadley and Walker circulations in the Pacific. We argue that the positive trend in snow accumulation in the ice core that started in the middle of the 19th century is a reflection of changes in the intensities of these circulations that has been ongoing since the end of the Little Ice Age. This change may also be associated with the observed jump in $\delta^{18}$O that occurred in the ice core as well as in a number of widely spaced tropical coral records around the same time.
PP21A-1367 0800h
Seasonal Variations In Density Profiles And Densification Process At Mts. Logan And Wrangell
Detailed density measurements were carried out for ice cores which were drilled at Mt. Logan (60$\deg$35'20"N, 140$\deg$36'15"W; 4135m a.s.l.; Shiraiwa et al., 2003) and Mt. Wrangell (62$\deg$00'N, 140$\deg$03'W; 4100m a.s.l.; Shiraiwa et al., 2004). The detailed density profiles show periodic fluctuations which seem to indicate seasonal cycles. In Mt. Logan, the number of annual layers which are estimated from the density profile agrees well with that estimated from the oxygen isotope data (Goto-Azuma et al., 2003) and the age of the ice core estimated from tritium peaks. On the other hand, in Mt. Wrangell, the number of annual layers from the density profile is quite different from that of the hydrogen isotope profile. The accumulation time series reconstructed from the density profile in Mt. Wrangell shows significant correlations with precipitation data of weather stations that locate near Mt. Wrangell. Accumulation rate and mean annual temperature at both sites are estimated to be almost the same (Benson & Motyka, 1978; Shiraiwa et al., 2003; Goto-Azuma et al., 2003; Shiraiwa et al., 2004). However, their firn/ice transition depths (Mt. Logan: 50m, Mt. Wrangell: 90m) are considerably different. This difference cannot be explained only from the difference in initial densities. Densification rate in Mt. Logan is higher than in Mt. Wrangell, i.e. compactive viscosity coefficient calculated from depth-density profile in Mt. Wrangell is more than double of the value in Mt. Logan.
PP21A-1368 0800h
Climatic Seesaws Across The North Pacific As Revealed By High-Mountain Ice Cores Drilled At Kamchatka And Wrangell-St. Elias Mountains
We drilled ca. 210-m deep ice cores at Mt. Ushkovsky (Kamchatka: 1998), King Col of Mt. Logan (2002) and Mt. Wrangell (2004). Thanks to the high accumulation rates up to 2 m per year in these mountains, the ice cores are expected to unveil the climate and atmospheric changes in the northern North Pacific during the last several centuries. The reconstructed annual accumulation rates time-series of Mt. Ushkovsky showed, for example, decadal to interdecadal oscillations which were closely correlated to the Pacific Decadal Oscillations (PDO). Comparison between the reconstructed accumulation rates between the Ushkovsky and our two ice cores from Wrangell-St. Elias mountains suggests that the PDO played an important role in determining the precipitation at both side of the northern North Pacific: positive PDO supplied high precipitation in the Pacific North America and the negative PDO did high in Kamchatka during the last two centuries. Beside the significance of the climate proxy signals, the physical properties of the ice cores and the related glaciological features at the three mountains provided unique feature of glaciers developing on high mountains with complicated topographies and high accumulation rates. It was shown that careful treatment of dynamic behavior in these high mountain glaciers are indispensable for the precise reconstruction of past accumulation time-series.
PP21A-1369 0800h
The White River Ash: New Evidence From the Bona-Churchill Ice Core Record
The White River Ash (WRA) is a well-documented bi-lobate Plinian deposit covering as much as 540,000 square km of the Yukon Territory, Canada and adjoining eastern Alaska. Recent studies have identified the source of the ash as Mount Churchill in the St. Elias Mountains of southeastern Alaska by comparing pumice deposits from the summit area of Mount Churchill with more distal pumice deposits of the WRA (e.g. {\it McGimsey et al., 1990; Richter et al., 1995}). In spring 2002 a team from The Ohio State University's (OSU) Byrd Polar Research Center recovered a 460-m long ice core drilled to bedrock in the col (elevation 4420 masl) between Mount Churchill and Mount Bona (4 km southwest) to reconstruct a proxy climate history for the region. This core is also ideal to assess whether Mount Churchill is the source of the WRA. No evidence of a visible ash layer was encountered during drilling. Borehole temperatures of -24 degrees C at 10m depth and -19.8 degrees C at the ice-bedrock interface indicate the glacier is frozen to its bed. After being returned frozen to OSU the core was cut into 12,162 samples that were analyzed for stable isotopic ratios, insoluble particles and soluble chemistry. A preliminary time scale was developed using annual variations in oxygen isotopes, dust and calcium concentrations, beta-radioactivity (bomb horizons) and well-documented historic volcanic eruptions. The $\sim$1500 year long record shows elevated sulfate values at $\sim$803AD possibly associated with the second of two eruptions in the past 2000 years that produced the eastern lobe of the WRA deposit. The paleoclimate records appear to be stratigraphically continuous and show no evidence of a depositional hiatus. The absence of an ash layer in the core suggests that the WRA deposit requires further investigation, and the source and age of the WRA will be addressed.
PP21A-1370 0800h
Onset and Multiple Fluctuations of Holocene Glaciation in the Sierra Nevada, California
Multiple sediment cores from two paternoster tarns (First and Second lakes) in North Fork Big Pine Creek, Sierra Nevada, preserve the most detailed and complete record of Holocene glaciation yet recovered in the range; they indicate that the glacier was absent during the early Holocene, reformed in the late Holocene, and experienced several expansions and contractions, culminating with the Matthes maximum during the last $\sim$200 years. The lakes are fed by outwash from the Palisade Glacier, the largest ($\sim$1.3 km$^{2}$) and presumably longest-lived glacier in the Sierra Nevada, and capture essentially all of the rock flour produced by the glacier. Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes. Thus, the lakes have received continuous sedimentation since the retreat of the Tioga glacier ($\sim$15,000 yr B.P.), and therefore capture rock flour related to all subsequent advances. First and Second lakes occupy relatively deep bedrock basins at 3036 m and 3066 m asl., respectively. Third Lake, a shallow ($ < $3 m deep), moraine-dammed lake that lies directly above Second Lake, is the only lake between the Palisade Glacier and the lower lakes. As such, it captures the coarsest (sand/gravel bedload) outwash, but abundant suspended sediment (silt/clay) continues to the lower lakes. We cored the lakes using both Reasoner and Livingston corers, to sediment depths of up to $\sim$5 m. The deepest cores bottomed in coarse, inorganic sand and silt that we interpret as outwash or slopewash related to Tioga deglaciation. Magnetic susceptibility (MS) analyses of the sediment cores indicate that both lakes record multiple late-Holocene peaks in MS, with the most recent peak being the largest. They also retain outwash near the base related to the more extensive Recess Peak advance. MS peaks in Sierran lakes typically indicate greater abundances of clastic (vs. organic) sediment. The peaks in our cores thus imply 4-5 periods of increased flux of rock flour (outwash) from the upstream Palisade Glacier, most likely related to formation and expansions of the glacier in the late Holocene. The maximum peak at the top of the cores confirms the moraine record, which indicates that the maximum Holocene advance of Sierran glaciers occurred during the late Little Ice Age (last $\sim$200 yr) At least one tephra layer, possibly related to the Mono/Inyo dome complexes, occurs in the middle depths of the First Lake cores. Other narrow peaks in MS may also be associated with tephra deposits. Ongoing detailed analyses of the sediments, including AMS radiocarbon dating, visual and x-ray imaging, particle size analysis, organic content, tephrochronology, diatom assemblages, and palynology will constrain the timing and character of the environmental fluctuations related to the rock-flour flux. We will present results of these analyses at the meeting.
PP21A-1371 0800h
A Continental Shelf Sediment Transport Proxy Record of Decadal Atmospheric and Oceanographic Variability in Southern Alaska
The Gulf of Alaska (GOA) margin is a prime location to study and quantitatively model glacial climate and continental margin sedimentation. Coupled oceanographic and atmospheric processes control sediment transport and sedimentation patterns on the GOA continental shelf, and consequently contain a proxy record for regional climate variability. However, the specifics of this coupled relationship between climate and sediment transport have not been studied. In collaboration with the GOA-NEP GLOBEC program, gravity cores were taken at three sites of high sedimentation rates along the GOA margin in 2001 and 2003 representing proximal and distal shelf depocenters. Chronologies were established using Pb-210 and Cs-137 and sedimentation rates vary from 0.3 to 3 cm/yr, providing near-annual to decadal-scale resolution. High-spatial resolution grain-size analyses and multi-sensor core logging of bulk density and magnetic susceptibility were measured to recognize relationships between these three proxies of sediment transport in each core and between sites. The time series of these properties have been compared to oceanographic and atmospheric instrumental records--generally beginning in the early to middle 20th century--such as sea level pressure, temperature, significant wave height, and wind speed. The three measured properties positively correlate within each core and between each core, indicating that these are likely controlled by similar sediment transport processes, such as wave resuspension and bottom-current transport, at all three sites. Strong correlation on a decadal scale was found between the physical properties of the cores and the instrumental records of temperature and significant wave height, as well as variability in regional precipitation. Also, there is a marked increase in bulk density, magnetic susceptibility, and grain size values from the late 1970's onward, which corresponds to the timing of a shift from a negative to a positive regime in the Pacific Decadal Oscillation. These results suggest that temporal variability in grain size, bulk density, and magnetic susceptibility on Alaska's continental shelf are, in part, controlled by changes in wind speed, wind direction, and wave height.
PP21A-1372 0800h
A High-Resolution Record of Holocene Climate Variability from a Western Canadian Coastal Inlet
Conditions within the Pacific Ocean have a major effect on the climate of northwestern North America. High resolution records of present and past northeast Pacific climate are revealed in our multi-disciplinary study of annually laminated marine sediments from anoxic coastal inlets of British Columbia. Past climate conditions for the entire Holocene are recorded in the sediment record contained in a 40 meter, annually laminated marine sediment core taken in Effingham Inlet, on the west coast of Vancouver Island, British Columbia, from the French ship the Marion Dufresne, as part of the international IMAGES program. By combining our eight year continuous instrument record of modern coastal ocean dynamics and climate with high-resolution analysis of depositional processes, we have been able to develop proxy measurements of past climatic and oceanographic changes on annual to millennial time scales. Results indicate that regional climate has oscillated on a variety of time scales throughout the Holocene. At times, climatic change has been dramatically rapid. We are also developing digital methods for statistical time-series analyses of physical sediment properties through the Holocene in order to obtain a more objective quantitative approach for detecting cyclicity in our data. Results of the time series analysis of lamination thickness reveals statistically significant spectral peaks of climate scale variability at established decadal to century time scales. These in turn may be related to solar cycles and quasi-cyclical ocean processes such as the Pacific Decadal Oscillation. However, the annually laminated time series are periodically interrupted by massive mud intervals which are related to bottom currents and at times paleo-seismic events, illustrating the need for a full understanding of modern oceanographic and sedimentation processes, so an accurate proxy record of past climate can be established.
PP21A-1373 0800h
A High-Resolution Mid- to Late-Holocene Sea-Surface Temperature Record from the Subtropics, Baja California, Mexico
San Lazaro basin provides a unique environment in which to study paleoclimate because it lies at the intersection of the cooler California Current that originates to the north and the warmer Pacific tropical current that originates to the south. Studies in this basin will provide insight into the varying strength of these currents at decadal and centennial resolutions. In addition, the present-day basin is suboxic ($ < $3 uM/kg), and laminations throughout the top $\sim$6 m of ocean floor sediments indicate that it may have been suboxic for the past $\sim$6.5 ky. Suboxia is advantageous in the study of high-resolution paleoclimate records, as lower levels of oxygen inhibit the activity of sediment-disturbing organisms that might smooth climate records. We will present parts of a new decadal-resolution sea-surface temperature (SST) record from San Lazaro (AKA Soledad) basin, Baja California, Mexico. We estimate SST using Mg/Ca and d18O data measured on surface-dwelling planktonic foraminifera Globigerinoides ruber and Globigerina bulloides from ocean-sediment giant box core MD02-2506C2. This 4.6-m core exhibits an $\sim$0.8 mm/yr sedimentation rate (van Geen et al., 2003) and represents the period $\sim$5,000 to $\sim$500 years BP. We sampled the core at 1-cm continuous (i.e., approximately decadal) resolution. Preliminary results indicate that Mg/Ca values for G. ruber range between 2.3 and 3.3 mmol/mol ($\sim$20 and $\sim$24 deg C), with higher values characteristic of the mid-Holocene. Annual sea-surface temperatures for the period 1950 to 1990 ranged between $\sim$19 and $\sim$23 deg C (CalCOFI, COADS), suggesting that mid- to late-Holocene SST values were $\sim$1 deg C higher than the those of the last half century. We will compare our SST proxy results with d18O records from Santa Barbara basin (e.g., Kennett and Kennett, 2000); tree-ring records from Baja California (Bullock, 2003) and Southern California (De Nava et al., 1999); and pluvial (Davis, 2003) and packrat midden (Clark and Sankey, 1999) records from Baja California.