Collaborative Research: A 700-Year Tephrochronology of the Law Dome Ice Core, East Antarctica

This award supports a project to analyze samples from the Law Dome ice core for volcanic tephra. The Law Dome ice core is the best-dated ice core from East Antarctica and contains a detailed record of climate and atmospheric chemistry over at least the last 700 years. Several global volcanic eruptions appear to be recorded in the Law Dome core, including the well known Tambora 1815 and Unknown 1809 events, as well as the Huaynaputina 1600 and Ruiz 1595 events. To verify the source eruptions responsible for these signals, as well as to differentiate between local Antarctic and southern hemisphere eruptions, a continuous scan for volcanic glass at an annual resolution will be done on the last 700 years of the Law Dome ice core. Sub-annual tephra analyses will be done in the sections containing the largest acid signals in the core. To better evaluate the climatic impact of large equatorial eruptions from ice cores, it is necessary to isolate local eruptions and their associated glaciochemical signal from that of these more distant sources. The identification of local eruptions in the Law Dome core will improve upon the existing chronology of Antarctic volcanism over the last 700 years through the presence of volcanic glass in conjunction with the results from this same type of study on the Siple Dome ice core

Highly Detailed Reconstructions of New England Weather over the Past Few Centuries and Their Climatic Implications

This award will enable researchers to reconstruct daily weather conditions for New England over the past 300 years by compiling and analyzing written archives such as diaries, journals, agricultural records, and marine logs. These archives will be used to reconstruct daily weather maps that will be compared with recent climatic conditions. New England has a large number of lengthy weather archives and is a region sensitive to changing climatic conditions. The region is influenced by storm tracks and upper-air disturbances that impact the Canadian High, Icelandic Low and the Bermuda-Azores High from year-to-year.Obtaining highly detailed and lengthy records of past climatic variability at the regional scale is important to better inform society about the range of climatic change in the lives of individuals. It is also important to develop records of past climatic conditions with daily resolution to evaluate how the number and magnitude of extreme climatic events (i.e., nor\u27Easters, hurricanes, tornadoes, and ice storms) have changed with time. It is these extreme events that can greatly affect individuals and communities.The use of the 300-year record from New England and the reconstruction of synoptic conditions helps to infer differences in seasonality between cold years, warm years, and more common (i.e., normal) years during the Little Ice Age. Instrumental records over approximately the last 100 years provide time series for the evaluation of recent changes that may be representative of anthropogenically-induced conditions. Daily weather conditions will be compiled in electronic format and placed on the World Wide Web. These data will be available to the general public, including schools, to use when evaluating changes in climate

Characteristics of modern atmospheric dust deposition in snow on the Penny Ice Cap, Baffin Island, Arctic Canada

We evaluated the concentration, size and distribution of insoluble dust microparticles in snowpits on the Penny Ice Cap (PIC), Baffin Island, to define (1) the characteristics of modern atmospheric dust deposition at the site, (2) the relative contributions of proximal and distal dust sources, and (3) the effects of summer melting on depositional signals in snow. The mean concentration (143 mg kg−1), flux (4.8 mg cm2 yr−1) and diameter (2.3 mm) of dust deposited on the PIC are similar to those observed in remote Arctic sites such as central Greenland, implying that dust is primarily supplied through long-range transport from far-removed source regions (at least 102–103 km distant). There is evidence for two seasonal maxima of dust deposition, one in late winter-early spring and one in late summer-early fall, although seasonal signals can not always be resolved in the snowpack due to some post-depositional particle migration with summer melt. However, ice layers appear to limit the mobility of particles, thereby preserving valuable paleoclimatic information in the PIC ice core dust record at a multi-annual to decadal temporal resolution

Late Pleistocene Age of the Type Temple Lake Moraine, Wind River Range, Wyoming, U.S.A.

The type Temple Lake moraine lies about 3 km beyond and roughly 120 m lower than the modern glacier margin and the Gannett Peak (Little Ice Age) moraines deposited in the last few centuries. Because numerous glacial deposits throughout the western United States have been correlated to the Temple Lake moraine its age is important. We retrieved two sediment cores up to six meters long from Rapid Lake, outside the outer type Temple Lake moraine. The 383-413 cm depth dates 11,770 ± 710 yrs (GX-11,772), which we believe reflects the time when silt flux into Rapid Lake was abruptly reduced by the formation of a new sediment trap at Miller Lake as the valley glacier receded from its position at the outer Temple Lake moraine. A radiocarbon date of 11,400 ± 630 yrs BP (GX-12,719) obtained from the lower basin of Temple Lake, inside the inner type Temple Lake moraine, supports this interpretation. Sediments from Miller Lake, inside the outer Temple Lake moraine, that date 8300 ± 475 yrs BP (GX-12,277) are probably well above the bottom of the lake sediment sequence and possibly thousands of years younger than the moraine. We feel that the type Temple Lake moraine dates about 12,000 yrs BP, thus is Late Pleistocene in age. This interpretation is supported by maximum percentages of organic detritus in lake sediments between 10,000 and 8,000 yrs BP, and challenges BEGET's (1983) suggestion that the type Temple Lake moraine is early Holocene in age, a period he calls "Mesogiaciation".La moraine de référence de Temple Lake repose à environ 3 km au-delà (approximativement 120 m plus bas) de la marge glaciaire moderne et des moraines de Gannett Peak (Petit Âge glaciaire) mises en place au cours des derniers siècles. Il est d'autant plus important de connaître l'âge de cette moraine que plusieurs dépôts glaciaires à travers l'ouest des États-Unis lui sont associés. On a recueilli deux carottes de sédiments jusqu'à 6 m de long du Rapid Lake, à l'extérieur de la moraine externe de référence de Temple Lake. La datation de 11 770 ± 710 BP (GX-11,772), enregistrée à 383-413 cm de profondeur, pourrait représenter le moment où le flux limoneux dans le Rapid Lake a grandement été réduit en raison de la formation d'un piège à sédiments au Miller Lake alors que le glacier de vallée se retirait de la moraine externe de Temple Lake. La datation au radiocarbone de 11 400 ± 630 BP (GX-12,719) recueillie dans le bassin inférieur du Temple Lake, à l'intérieur même de la moraine interne, corrobore l'interprétation ci-dessus. Les sédiments du Miller Lake, à l'intérieur de la moraine externe de référence de Temple Lake, qui datent de 8300 ± 475 BP (GX-12,277), se situent probablement bien au-dessus de la base de la séquence de sédiments lacustres et sont vraisemblablement des milliers d'années plus jeunes que la moraine. Les auteurs croient que la moraine de référence de Temple Lake date d'environ 12 000 BP, donc du Pleistocene. La mesure de pourcentages maximaux, entre 10 000 et 8000 BP, de débris organiques dans les sédiments lacustres confirme cette interprétation et permet de rejeter l'hypothèse de BEGET (1983) selon laquelle la moraine de Temple Lake daterait du début de l'Holocène, période qu'il appelle « Mésoglaciation »

Examination of the 500,000-Year Climate Record in Ice at Mt. Moulton, West Antarctica

This project was a pilot project to determine if the ice on Mt. Moulton provides a reliable record of past climatic conditions. The area of study is a several hundred-meter section of blue ice (Trench A) that spans the time period from approximately the early Holocene to over 492k years ago. Dating control is obtained through radiometrically-dated tephra layers (i.e., air fall deposits) within the section (Figure 1) originating from the adjacent Mt. Berlin. Fieldwork during the 1999-2000 field season included the trenching of the complete section with electric chain saws mounted on a wheeled frame. Blocks were extracted and cut-down to sample a continuous section from the 50-cm depth. Several overlapping trenches, some completed to a depth of 1 meter, were sampled to test the validity of sampling at the 50-cm depth. Individuals from New Mexico Tech, collaborators in the project, developed a detailed map of visible tephra layers using a GPS and collected additional tephra samples with the goal of dating layers not presently dated and for refining existing ages. Once samples were brought back to the lab, a glaciochemistry time series was developed for comparison with other such records from Antarctica as well as from Greenland ice cores. Through the use of an ion chromatograph, concentrations of the major ions found in the atmosphere are determined. The suite of chemical species measured includes Na2+, Ca2+, Mg2+, K+, NH4+, Cl-, SO42-, and NO3-. One sample per 20 cm of ice was analyzed over the last ~150k to obtain a coarsely-resolved record to test the reliability of the record. Figure 1 shows the relationship between the Na2+ time series and the location of the dated tephra layers, thus the age model developed for Trench A. A similarity in broad trends would suggest that Mt. Moulton ice contains a valid paleoclimatic record thereby warranting more detailed (i.e., a much higher resolution) sampling and analyses than done in this study. As this was a pilot project the only presentations made were at meetings of the U.S. Ice Core Working Group and at meetings for the Siple Dome ice-coring project

Depletion of atmospheric nitrate and chloride as a consequence of the Toba Volcanic Eruption

Continuous measurements of SO42− and electrical conductivity (ECM) along the GISP2 ice core record the Toba mega‐eruption at a depth 2590.95 to 2091.25 m (71,000±5000 years ago). Major chemical species were analyzed at a resolution of 1 cm per sample for this section. An ∼6‐year long period with extremely high volcanic SO42− coincident with a 94% depletion of nitrate and 63% depletion of chloride is observed at the depth of the Toba horizon. Such a reduction of chloride in a volcanic layer preserved in an ice core has not been observed in any previous studies. The nearly complete depletion of nitrate (to 5 ppb) encountered at the Toba level is the lowest value in the entire ∼250,000 years of the GISP2 ice core record. We propose possible mechanisms to explain the depletion of nitrate and chloride resulting from this mega‐eruption

Potential atmospheric impact of the Toba Mega‐Eruption ∼71,000 years ago

An ∼6‐year long period of volcanic sulfate recorded in the GISP2 ice core about 71,100 ± 5000 years ago may provide detailed information on the atmospheric and climatic impact of the Toba mega‐eruption. Deposition of these aerosols occur at the beginning of an ∼1000‐year long stadial event, but not immediately before the longer glacial period beginning ∼67,500 years ago. Total stratospheric loading estimates over this ∼6‐year period range from 2200 to 4400 Mt of H2SO4 aerosols. The range in values is given to compensate for uncertainties in aerosol transport. Magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this ∼1000‐year cooling event

Preservation of glaciochemical time-series in snow and ice from the Penny Ice Cap, Baffin Island

A detailed investigation of major ion concentrations of snow and ice in the summit region of Penny Ice Cap (PIC) was performed to determine the effects of summer melt on the glaciochemical time-series. While ion migration due to meltwater percolation makes it difficult to confidently count annual layers in the glaciochemical profiles, time-series of these parameters do show good structure and a strong one year spectral component, suggesting that annual to biannual signals are preserved in PIC glaciochemical records

Volcanic aerosol records and tephrochronology of the Summit, Greenland, ice cores

The recently collected Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project ice cores from Summit, Greenland, provide lengthy and highly resolved records of the deposition of both the aerosol (H2SO4) and silicate (tephra) components of past volcanism. Both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism‐climate system. The continuous time series of volcanic SO42− for the last 110,000 years show a strong relationship between periods of increased volcanism and periods of climatic change. The greatest number of volcanic SO42− signals, many of very high magnitude, occur during and after the final stages of deglaciation (6000–17,000 years ago), possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins (sea level change). The increase in the number of volcanic SO42− signals at 27,000–36,000 and 79,000–85,000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation, respectively. A comparison of the electrical conductivity of the GISP2 core with that of the volcanic SO42− record for the Holocene indicates that only about half of the larger volcanic signals are coincident in the two records. Other volcanic acids besides H2SO4 and other SO42− sources can complicate the comparisons, although the threshold level picked to make such comparisons is especially critical. Tephra has been found in both cores with a composition similar to that originating from the Vatnaöldur eruption that produced the Settlement Layer in Iceland (mid‐A.D. 870s), from the Icelandic eruption that produced the Saksunarvatn ash (∼10,300 years ago), and from the Icelandic eruption(s) that produced the Z2 ash zone in North Atlantic marine cores (∼52,700 years ago). The presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras. The presence of both rhyolitic and basaltic shards in the Z2 ash in theGISP2 core and the composition of the basaltic grains lend support to multiple Icelandic sources (Torfajökull area and Katla) for the Z2 layer. Deposition of the Z2 layer occurs at the beginning of a stadial event, further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions