Modellierung der globalen biogeochemischen Stoffverteilung im glazialen Ozean: Ein Modell-Datenvergleich

Abstract

:br:In this work, a numeric three-dimensional biogeochemical model of the global carbon-cycle (HAMOCC2) was coupled to an ocean general circulation model (LSG) to explore the :img:=delta.gif:/img::sup:13:/sup:C distribution in the glacial Atlantic. In addition to the model comparison of the present-day (pre-industrial) distribution of the components of the marine carbon system with observations (GEOSECS), three model experiments for the Last Glacial Maximum (LGM) were carried out. For the present-day ocean, adequate correlations between model and observations were obtained. However, deviations occurred in the isotopes pattern of :img:=delta1.gif:/img::sup:14:/sup:C and :img:=delta.gif:/img::sup:13:/sup:C, which are primary due to problems of modelling the North Atlantic Deep Water (NADW). On the other side, uncertainties in the observed :img:=delta.gif:/img::sup:13:/sup:C values should be also taken into account. The simulated glacial :img:=delta.gif:/img::sup:13:/sup:C pattern was compared with a new data set of benthic carbon isotopes of the Western and Eastern Atlantic from the Last Glacial Maximum (21,000 -- 23,500 calendar years before present). The model output fits the :img:=delta.gif:/img::sup:13:/sup:C distribution derived from sediment samples, when the glacial export of NADW to the Southern Ocean was reduced by 50 % and the inflow of glacial Antarctic Bottom Water (AABW) was held constant. Usually, the modeled :img:=delta.gif:/img::sup:13:/sup:C pattern matched the paleodata within a range of ±0.2 per mil. No additional increase of the nutrient inventory of the deep ocean was necessary to reproduce the paleodata. Hence it is concluded that a significant increase in biological pumping during glacials may not be necessary to explain the reconstructed :img:=delta.gif:/img::sup:13:/sup:C distribution in this region. The results are discussed with respect to other scenarios for the decrease of global atmospheric carbon dioxide.