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  • 1
    Online Resource
    Online Resource
    A 700 year record of Southern Hemisphere extratropical climate variability
    International Glaciological Society ; 2004
    In:  Annals of Glaciology Vol. 39 ( 2004), p. 127-132
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 39 ( 2004), p. 127-132
    Abstract: Annually dated ice cores from West and East Antarctica provide proxies for past changes in atmospheric circulation over Antarctica and portions of the Southern Ocean, temperature in coastal West and East Antarctica, and the frequency of South Polar penetration of El Niño events. During the period AD 1700–1850, atmospheric circulation over the Antarctic and at least portions of the Southern Hemisphere underwent a mode switch departing from the out-of-phase alternation of multi-decadal long phases of EOF1 and EOF2 modes of the 850 hPa field over the Southern Hemisphere (as defined in the recent record by Thompson and Wallace, 2000; Thompson and Solomon, 2002) that characterizes the remainder of the 700 year long record. From AD 1700 to 1850, lower-tropospheric circulation was replaced by in-phase behavior of the Amundsen Sea Low component of EOF2 and the East Antarctic High component of EOF1. During the first phase of the mode switch, both West and East Antarctic temperatures declined, potentially in response to the increased extent of sea ice surrounding both regions. At the end of the mode switch, West Antarctic coastal temperatures rose and East Antarctic coastal temperatures fell, respectively, to their second highest and lowest of the record. Polar penetration of El Niño events increased during the mode switch. The onset of the AD 1700–1850 mode switch coincides with the extreme state of the Maunder Minimum in solar variability. Late 20th-century West Antarctic coastal temperatures are the highest in the record period, and East Antarctic coastal temperatures close to the lowest. Since AD 1700, extratropical regions of the Southern Hemisphere have experienced significant climate variability coincident with changes in both solar variability and greenhouse gases.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756404781814249
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2004
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  • 2
    Online Resource
    Online Resource
    Features of meteorological events preserved in a high-resolution Law Dome (East Antarctica) snow pit
    International Glaciological Society ; 2002
    In:  Annals of Glaciology Vol. 35 ( 2002), p. 463-470
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 35 ( 2002), p. 463-470
    Abstract: Snow-pit and shallow firn-core records of oxygen isotope ratios (δ 18 O) and trace ion species were generated at a high-accumulation site on Law Dome, East Antarctica. Concordance between accumulation events identified in records up to 7.7 km a part confirms that the observed glaciochemical variations are the result of regional rather than local surface effects. This allows calibration of the snow-pit records with measured meteorological parameters. Net accumulation periods that comprise the snow-pit record are identified using hourly snow-accumulation measurements from a co-located automatic weather station (AWS). Particular focus is given to three net accumulation periods preserved during austral summer 1999/2000 that correspond to the top 0.5 m of the snow pit. Local meteorological conditions recorded during the summer accumulation periods by the AWS are combined with regional and synoptic-scale meteorology derived from Casey station (110 km away) and Advanced Very High Resolution Radiometer satellite imagery to identify potential source regions for chemical signals preserved in summer snow at Law Dome.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756402781816780
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2002
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  • 3
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    Online Resource
    High‐precision dating of volcanic events (A.D. 1301–1995) using ice cores from Law Dome, Antarctica
    American Geophysical Union (AGU) ; 2001
    In:  Journal of Geophysical Research: Atmospheres Vol. 106, No. D22 ( 2001-11-27), p. 28089-28095
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 106, No. D22 ( 2001-11-27), p. 28089-28095
    Abstract: A record of volcanic activity over the period A.D. 1301–1995 has been extracted from three Law Dome ice cores (East Antarctica). The record dating is unambiguous at the annual level from A.D. 1807 to 1995 and has an uncertainty of ±1 year at A.D. 1301. Signals from 20 eruptions are preserved in the record, including those of two unknown eruptions with acid deposition beginning in A.D. 1810.8 and A.D. 1685.8. The beginning of the ice core signal from the A.D. 1815 Tambora eruption is observed in the austral summer of A.D. 1816/1817. The mean observed stratospheric transport and deposition time to Law Dome from the eruption site is 1.5 years (σ = 0.6 years) from 11 well‐dated eruptions. The largest eruption observed in the Law Dome record has its maximum in A.D. 1460 with volcanic sulfate deposition beginning in the austral winter of A.D. 1459. This event is also observed in other ice core records and is attributed to the volcano Kuwae, with an eruption date in the range A.D. 1455.9–1459.9 if all sources of error are considered. This is at least three years later than the date previously ascribed by dendrochronological and historical studies.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2001JD000330
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2001
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  • 4
    Online Resource
    Online Resource
    Antarctic volcanic flux ratios from Law Dome ice cores
    International Glaciological Society ; 2002
    In:  Annals of Glaciology Vol. 35 ( 2002), p. 329-332
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 35 ( 2002), p. 329-332
    Abstract: Explosive volcanic eruptions can inject large quantities of sulphur dioxide into the stratosphere. the aerosols that result from oxidation of the sulphur dioxide can produce significant cooling of the troposphere by reflecting or absorbing solar radiation. It is possible to obtain an estimate of the relative stratospheric sulphur aerosol concentration produced by different volcanoes by comparing sulphuric acid fluxes determined by analysis of polar ice cores. Here,we use a non-sea-salt sulphate time series derived from three well-dated Law Dome ice cores to investigate sulphuric acid flux ratios for major eruptions over the period AD 1301–1995. We use additional data from other cores to investigate systematic spatial variability in the ratios. Only for the Kuwae eruption (Law Dome ice date AD 1459.5) was the H 2 SO 4 flux larger than that deposited by Tambora (Law Dome ice date AD 1816.7).
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756402781816771
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2002
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  • 5
    Online Resource
    Online Resource
    Ice Core Evidence for Antarctic Sea Ice Decline Since the 1950s
    American Association for the Advancement of Science (AAAS) ; 2003
    In:  Science Vol. 302, No. 5648 ( 2003-11-14), p. 1203-1206
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 302, No. 5648 ( 2003-11-14), p. 1203-1206
    Abstract: The instrumental record of Antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal Antarctica. Here we report a significant correlation ( P 〈 0.002) between methanesulphonic acid (MSA) concentrations from a Law Dome ice core and 22 years of satellite-derived sea ice extent (SIE) for the 80°E to 140°E sector. Applying this instrumental calibration to longer term MSA data (1841 to 1995 A.D.) suggests that there has been a 20% decline in SIE since about 1950. The decline is not uniform, showing large cyclical variations, with periods of about 11 years, that confuse trend detection over the relatively short satellite era.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1087888
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2003
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  • 6
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    Dimethyl sulfide in the Southern Ocean: Seasonality and flux
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Atmospheres Vol. 105, No. D16 ( 2000-08-27), p. 20451-20459
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 105, No. D16 ( 2000-08-27), p. 20451-20459
    Abstract: The first flux estimate of dimethyl sulfide (DMS) from the Australian sector of the Southern Ocean (63°E to 162°E) has been calculated from seven voyages, which span spring and summer seasons from 1991 to 1995. Increases in seawater DMS and its precursor, dimethyl sulfoniopropionate (DMSP) generally occurred in Southern Ocean surface waters during the transition from spring to summer. DMS flux from the Subantarctic Zone (SAZ), Antarctic Zone (AZ), and Seasonal Ice Zone (SIZ) ranged from 1.7 to 49 μmol/m 2 /d with a mean value of 9.4 μmol/m 2 d. These flux calculations are believed to be underestimates, and do not include potential contributions from sea ice. Very high levels of DMSP in sea ice suggest that the SIZ may be a source of DMS to the atmosphere. The different types of vertical DMSP profiles found in sea ice possibly reflect the type of algal assemblage present and the age of the sea ice. Without considering contributions of DMS from sea ice, the overall Southern Ocean DMS emission estimate from this work was 139 Gmol S/yr. The emission estimate for the Antarctic region alone (AZ and SIZ) was 85 Gmol S/yr. This represents 17% of the global emission estimate, from 6% of the ocean surface area. This emission estimate is almost double that of an earlier estimate by Berresheim [1987] of 48 Gmol S/yr, and is likely to be higher when the amount released from the sea ice surrounding Antarctica is more accurately characterized.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2000JD900176
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2000
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    detail.hit.zdb_id: 2220777-6
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    SSG: 16,13
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  • 7
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    Online Resource
    Deglacial and Holocene changes in accumulation at Law Dome, East Antarctica
    International Glaciological Society ; 2004
    In:  Annals of Glaciology Vol. 39 ( 2004), p. 359-365
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 39 ( 2004), p. 359-365
    Abstract: Dating constraints have been combined with an ice-flow model to estimate surface accumulation rates at Law Dome, East Antarctica, to approximately 80 kyr BP. Results indicate that the present high-accumulation regime (~0.7ma –1 ice equivalent) was established some time after ~7 kyr BP, following an increase of approximately 80% from early to mid-Holocene. The accumulation rate at the Last Glacial Maximum is estimated at less than ~10% of the modern value. The record reveals an approximately linear dependence between temperature (inferred from isotope ratio) and accumulation rate through the glacial period. This dependence breaks down in the early Holocene, and this is interpreted as a change to a mode in which moisture-transport changes have a stronger influence on accumulation than temperature (via absolute humidity). The changes in accumulation, including the large change in the early to mid-Holocene, are accompanied by changes in sea-salt concentrations which support the hypothesis that Law Dome climate has shifted from a glacial climate, more like that of the present-day Antarctic Plateau, to its current Antarctic maritime climate. The change between these two modes occurred progressively through the early Holocene, possibly reflecting insolation-driven changes in atmospheric moisture content and circulation.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756404781814221
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2004
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    SSG: 14
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  • 8
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    Online Resource
    Ultra-high-resolution seasonality of trace-ion species and oxygen isotope ratios in Antarctic firn over four annual cycles
    International Glaciological Society ; 2004
    In:  Annals of Glaciology Vol. 39 ( 2004), p. 34-40
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 39 ( 2004), p. 34-40
    Abstract: Ultra-high-resolution firn-core records covering four annual cycles of oxygen isotope ratios (Δ 18 O) and trace-ion species were generated from a high-accumulation site on Law Dome, East Antarctica. Event-scale dating of the records was established using hourly snow accumulation measurements from a co-located automatic weather station (AWS). These net accumulation events were used to examine the seasonal timing of Δ 18 O and a suite of trace-ion species including marine biogenic sulphur compounds (methanesulphonic acid (MSA), non-sea salt sulphate), nitrate and major sea-salt species (sodium, chloride, magnesium). The ultra-high-resolution nature of this study and independent dating scale provide an opportunity to examine exact timings in the seasonality of each species. The traditional summer-maximum species of Δ 18 O and MSA show consistent relative phasing during midsummer over the four annual cycles. Nitrate shows an erratic seasonal cycle with a general trend characterized by narrow peaks during spring and early summer, preceding the mid-summer peaks in Δ 18 O and MSA. Non-sea-salt sulphate cycles indicate similar characteristics to MSA signals during summer, but are more comparable to nitrate signals during spring, autumn and winter. This suggests the summer non-sea-salt sulphate signal is driven by biological activity, although this species appears to be linked with nitrate signals outside the summer season. Finally, the sea-salt species indicate a seasonal cycle characterized by maximum concentrations during spring, winter and autumn. Event-scale dating of the firn-core records allows direct comparisons between the seasonal cycles and meteorological conditions. Contemporaneous local air-temperature measurements are compared with the high-resolution Δ 18 O record. This allows a detailed investigation of the relationship between site temperature and Δ 18 O signals in the ice core.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756404781814609
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2004
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    SSG: 14
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  • 9
    Online Resource
    Online Resource
    Methanesulphonic acid movement in solid ice cores
    International Glaciological Society ; 2004
    In:  Annals of Glaciology Vol. 39 ( 2004), p. 540-544
    Details
    In: Annals of Glaciology, International Glaciological Society, Vol. 39 ( 2004), p. 540-544
    Abstract: Methanesulphonic acid (MSA) is an important trace-ion constituent in ice cores, with connections to biological activity and sea-ice distribution. Post-depositional movement of MSA has been documented in firn, and this study investigates movement in solid ice by measuring variations in MSA distribution across several horizontal sections from an ice core after 14.5 years storage. The core used is from below the bubble close-off depth at Dome Summit South, Law Dome, East Antarctica. MSA concentration was studied at 3 and 0.5 cm resolution across the core widths. Its distribution was uniform through the core centres, but the outer 3 cm showed gradients in concentrations down to less than half of the central value at the core edge. This effect is consistent with diffusion to the surrounding air during its 14.5 year storage. The diffusion coefficient is calculated to be 2 ×10 –13 m 2 s –1 , and the implications for the diffusion mechanism are discussed.
    Type of Medium: Online Resource
    ISSN: 0260-3055 , 1727-5644
    URL: Article
    DOI: 10.3189/172756404781814645
    Language: English
    Publisher: International Glaciological Society
    Publication Date: 2004
    detail.hit.zdb_id: 2122400-6
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  • 10
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    Ice‐core evidence for a small solar‐source of atmospheric nitrate
    American Geophysical Union (AGU) ; 2001
    In:  Geophysical Research Letters Vol. 28, No. 10 ( 2001-05-15), p. 1953-1956
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 28, No. 10 ( 2001-05-15), p. 1953-1956
    Abstract: A precision‐dated ice‐core nitrate record from Law Dome, coastal East Antarctica is compared to the timing of known solar proton events and geomagnetic storms over the period 1888 to 1995. We find statistical evidence for a significant ( P 〈 0.03) but small elevation in mean nitrate concentrations following the solar events (∼11% over the 12 months beginning 3 months post‐event). While some solar events are identifiable in the nitrate record, most are not distinguishable from the background noisy signal (which has numerous large peaks), and some solar events show no nitrate elevation above even mean levels.
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2000GL012207
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2001
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    SSG: 16,13
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