Glacial thermohaline circulation states of the northern Atlantic: the compatibility of modelling and observations

Observational evidence from deep-sea cores suggests that the ocean circulat ion during the last glacial cycle was highly variable, at times occupying s tates very different from those found today. Modelling can be used to dynam ically constrain the possible circulation states compatible with observatio ns, thus guiding both understanding of past climate but also the geographic al and scientific thrust of future palaeoceanographic research. The Last Gl acial Maximum has been extensively studied and here, using carbon isotopes, among other variables, the most likely thermohaline state consistent with palaeoclimatic data is constructed. Past and new modelling efforts for the Last Glacial Maximum are then examined, to contrast questions resolvable by the modelling/data comparison with those that remain unanswered. This show s modelling evidence to confirm the prevailing view of intermediate-depth N orth Atlantic Deep Water being produced at the Last Glacial Maximum, in com bination with deep water production around Antarctica. The potential sites for this deep and intermediate water production are defined by the basic st ate of the thermohaline circulation. However, their relative importance is a function of small perturbations in the surface temperature and salinity f ields brought about by active coupling between the ocean and atmosphere. Re gions where these water masses may have been produced at the Last Glacial M aximum are suggested.