Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmpp33c1579h&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #PP33C-1579
Other
0724 Ice Cores (4932), 1030 Geochemical Cycles (0330), 1621 Cryospheric Change (0776), 3344 Paleoclimatology (0473, 4900), 8409 Atmospheric Effects (0370)
Scientific paper
Proportions of trace metals in Antarctic ice samples indicate that the type of volcanoes that dominated atmospheric emissions (or volcanic activity in general) changed, at about the middle Holocene, from relatively mafic, deep source volcanoes, to more silicic, shallower-source volcanoes. We base this inference on the ratio of the trace metal indium to other trace metals in ice deposited at known times in the past, and in the modern emissions of volcanoes of different types. Between climatic regimes, changes in load pressures on the earth's surface from the accumulation and removal of ice sheets, changes in sea level, and consequent tectonic adjustments, may influence volcanic activity, including both energetic eruptions and continuous degassing at vents. Content of the rare, volatile chalcophile trace metal indium varies in emissions of volcanoes of different type, being relatively abundant in emissions of basaltic hot-spot volcanoes, and lower from more silicic, shallow source volcanoes. There is meteoritic evidence that indium is partitioned to the interiors (stony mantles) of differentiated planets, and depleted in their crusts, and therefore this difference between volcano types is expected. In ice core samples from the Antarctic Taylor Dome site there is evidence that the concentrations of a suite of volatile trace metals are best accounted for by quiescent degassing of volcanoes, not by mineral dust or other. The proportions of indium in the suite of Taylor Dome ice samples change distinctively in the middle Holocene (between 7ka and 10ka), indicating a change to more silicic volcanism. It appears that there may be three distinct modes of volcanism dominant during the three time periods: mixed types of volcanoes active during the full glacial time, when some regions of land were heavily loaded with and depressed by ice sheets, and sea level was low; relatively ferromagnesian, deep-source volcanism dominant for several millenia after the rapid deglacierization and rapid sea level rise with which the Holocene began; and more silicic, shallower-source volcanism dominant during the subsequent millenia, after a certain amount of crustal adjustment to the changed conditions. As to the question of whether indium and other volatile trace metals in the ice in Antarctica originate specifically from Antarctic volcanoes, or whether they represent an integration of volcanoes from a wider area (viz. ocean island and other volcanoes of the southern hemisphere), the proportions and amounts of trace metals, as well as the isotopic proportions of lead (Pb), correspond well enough between the deposition of metals to the ice and the estimated worldwide source strength of degassing volcanoes.
Hinkley Todd
Matsumoto Akikazu
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