Sub-aerially Exposed Continental Shelves Since the Middle Pleistocene Climatic Transition and Antarctic ice Core Chemistry

The sharp increase in atmospheric carbon dioxide and methane recorded in the Vostok ice core (Petit et al., 1999) during the termination of glacial maximas may be attributed to the release of these two greenhouse gases from sub-aerially exposed continental shelves (Yim et al., 2002). Carbon dioxide is produced on both sub-aerially exposed siliciclastic-dominated shelves and carbonate-dominated shelves through acid-sulphate soil development and karstification respectively while methane is generated mainly through biogenic activity. The publication of chemical results over the past eight glacial cycles in the EPICA Dome C ice core by Wolff et al. (2006) is providing further supporting evidence. Measured concentrations of calcium, sodium, iron and sulphate in the EPICA Dome C ice core are higher during glacial periods than during interglacial periods. The preliminary conclusions drawn are: (1) The increase in calcium is consistent with the atmospheric depositional record of loess. (2) The increase in sodium is consistent with wind intensification. (3) The increase in iron which is inferred to reflect strongly changing Patagonian conditions (Wolff et al., 2006) is consistent with the sub-aerial exposure of the siliciclastic-dominated Argentinean continental shelf which is amongst the widest known. (4) The increase in sulphate is consistent with acid-sulphate soil development on sub-aerially exposed siliciclastic-dominated continental shelves particularly in tropical and subtropical regions. Studies on more sub-aerially exposed continental shelves since the Middle Pleistocene climatic transition are needed to further test these hypotheses. References Petit, J.R. and 18 co-authors (1999). Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399: 429-436. Wolff, E.W. and 27 co-authors (2006). Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles. Nature 440: 491-496. Yim, W.W.-S. and 4 co-authors (2002). Carbon flux during the last interglacial cycle in the inner continental shelf of the South China Sea off Hong Kong. Global and Planetary Change 33: 29-45.