Accounting for a realistic river routing and the presence of a proglacial lake at the Last Glacial Maximum

Accounting for changes in river routing and the presence of a proglacial lake at the Last Glacial Maximum (LGM) is a major step to more accurately depict the atmospheric and oceanic dynamics at that time and to establish a base state of the climate prior to deglaciation. This work is also necessary to better consider potential climate changes through sudden fresh-water discharges which took place in glacial conditions. Such changes, induced by the presence of large ice sheets which modify the river routing over mid to high latitudes of the North hemisphere have never been taken yet into account in simulations of the LGM climate. We have studied the impact of those changes in the LMDz Atmospheric General Circulation Model (AGCM), with a focus on the Arctic and North Atlantic basins. We first show that the extent of the ICE-5G Fennoscandian ice sheet implies the existence of a proglacial lake in which the Ob and Yenissei Rivers pour. Despite this change, we show that hydrology of the Arctic Ocean is not drastically modified, since the lake implies strong evaporation followed by strong precipitation in the nearby river basins, thus compensating the missing discharges of the Ob and Yenessei Rivers. On the contrary, the simulation shows that in the North Atlantic sector, the drastic runoff reduction at high latitudes (northward of 54°N), partly at the expense of the more southern sector (28°-54°N) through river routing changes, leads to a salinity dipole. Nonetheless, this feature may not be large enough to drastically change the glacial ocean circulation simulated at LGM when not considering the river routing modifications. From that stage, the next step is to disturb the simulation from `glacial equilibrium' by fresh water input.