ice is the part of the ice core that is actually examined by scientists.
ice is the part of the ice core that is actually examined by scientists.
what part of the ice core is actually examined by scientists?
ice
Na
Na
the isotopic composition of ice cores from continental ice sheets and alpine glaciers have been developed as temperature proxies since the 1950s. samuel epstein was one of the first to demonstrate the applicability of this proxy by measuring oxygen isotopes in antarctic snow, and also pointed out complications in the stable isotope-temperature correlation caused by the history of the air masses from which the snow formed. ice cores in greenland and antarctica can be thousands of meters thick and record snow isotopic composition of the past few glacial-interglacial cycles. ice cores can be dated by layer counting on the top and ice flow modeling at depth, with additional age constraints from volcanic ash. cores from greenland and antarctica can be aligned in age at high-resolution by comparing globally well-mixed trace gas (e.g. ch) concentrations in the air bubbles trapped in the cores. some of the first ice core records from greenland and antarctica with age estimates go back to the last 100,000 years, and showed a depletion in δd and δo in the last ice age. the ice core record has since been extended to the last 800,000 years in antarctica, and at least 250,000 years in greenland. one of the best δd-based ice core temperature records is from the vostok ice core in antarctica, which goes back to 420,000 years. the δd-temperature (of the inversion layer where snow forms) conversion in east antarctica based on modern spatial gradient of δd (9‰/°c) is δt=(δδd-8δδo)/9, which takes into account variations in seawater isotopic composition caused by global ice volume changes. it should be noted that many local effects can influence ice δd in addition to temperature. these effects include moisture origin and transport pathways, evaporation conditions and precipitation seasonality, which can be accounted for in more complicated models. nevertheless, the vostok ice core record shows some very important results: (1) a consistent δd depletion of ~70‰ during the last four glacial periods compared to interglacial times, corresponding to a cooling of 8 °c in antarctica; (2) a consistent drop of atmospheric co concentration by 100 ppmv and ch drop by ~300 ppbv during glacial times relative to interglacials, suggesting a role of greenhouse gases in regulating global climate; (3) antarctic air temperature and greenhouse gas concentration changes precede global ice volume and greenland air temperature changes during glacial terminations, and greenhouse gases may be an amplifier of insolation forcing during glacial-interglacial cycles. greenland ice core isotope records, in addition to showing glacial-interglacial cycles, also shows millennial-scale climate oscillations that may reflect reorganization in ocean circulation caused by ice melt charges. there have also been ice core records generated in alpine glacials on different continents. a record from the andes mountains in peru shows a temperature decrease of 5-6 °c in the tropics during the last ice age. a record from the tibetan plateau shows a similar isotope shift and cooling during the last ice age. other existing alpine glacial isotope records include mount kilimanjaro in tanzania, mount altai and west belukha plateau in russia, mount logan in canada, the fremont glacier in wyoming, usa, and the illimani ice core in bolivia, most of which cover an interval of the holocene epoch.
hydrogen isotope biogeochemistry