Modeling dust emission response to North Atlantic millennial-scale climate variations from the perspective of East European MIS 3 loess deposits

Abstract

European loess sequences of the Marine Isotope Stage 3 (~60–25 kyr BP) show periods of strong dust accumulation alternating with episodes of reduced sedimentation, favoring soil development. In the western part of the loess belt centered around 50° N, these variations appear to have been related to the North Atlantic rapid climate changes: the Dansgaard–Oeschger (DO) and Heinrich (H) events. It has been recently suggested that the North Atlantic climate signal can be detected further east, in loess deposits from Stayky (50°05.65' N, 30°53.92' E), Ukraine. Here we use climate and dust emission modeling to investigate this data interpretation. We focus on the areas north and northeast of the Carpathians, where loess deposits can be found, and the corresponding main dust sources must have been located as well. The simulations were performed with the LMDZ atmospheric general circulation model and the ORCHIDEE land surface model. They represent a reference "Greenland stadial" state and two perturbations, seen as sensitivity tests with respect to changes in the North Atlantic surface conditions between 30° and 63° N: a "Greenland interstadial" and an "H event". The main source for the loess deposits in the studied area is identified as a dust deflation band, with two very active spots located west-northwest from our reference site. Emissions only occur between February and June. Differences from one deflation spot to another, and from one climate state to another, are explained by analyzing the relevant meteorological and surface variables. Over most of the source region, the annual emission fluxes in the "interstadial" experiment are 30 to 50% lower than the "stadial" values; they would only be about 20% lower if the inhibition of dust uplift by the vegetation were not taken into account. Assuming that lower emissions result in reduced dust deposition leads us to the conclusion that the loess–paleosol stratigraphic succession in the Stayky area reflects indeed North Atlantic millennial variations. In the main deflation areas of Western Europe, the vegetation effect alone determined most of the (~50% on average) stadial–interstadial flux differences. Even if its impact in Eastern Europe is less pronounced, this effect remains a key factor in modulating aeolian emissions at the millennial timescale. Conditions favorable to initiating particularly strong dust storms within a few hundred kilometers upwind from our reference site, simulated in the month of April of the H event experiment, support the correlation of H events with peaks in grain size index in some very detailed loess profiles, indicating increased coarse sedimentation

A map of Pleistocene aeolian deposits in Western Europe, with special emphasis on France

“…The resulting map is now widely used in research dealing with Pleistocene aeolian activity (e.g. Muhs, 2013;Sima et al, 2013). Traditional mapping, however, faces the difficulty of precise delineation of the deposits in the field mainly because of the lack of available cross-sections, the small extent of the outcrops and of local reworking of the deposits.…”

Eurasian contribution to the last glacial dust cycle: how are loess sequences built?

“…4). Therefore, as meridional circulation prevailed at least in eastern Asia due to the monsoonal system, aridity could have been reduced during the favorable season (around April, with some variation and delay, depending on the GSs or Heinrich stadials (HS) as observed in eastern Europe by Sima et al, 2013) of dust emission of these short intervals (Sun et al, 2012). A recent study of the decline of the snow cover over northeastern Russia, southwestern Asia, northern India, and the Tibetan Plateau reports that the snow cover decline creates favorable dynamical conditions for strong winds over the Arabian Sea and thus favoring a stronger summer monsoon (Goes et al, 2005).…”

“…1). The influence of the westerlies and the position of the polar jet stream were constrained by the variation in the extension of the sea ice during the last glacial interval (Sima et al, 2009(Sima et al, , 2013. Furthermore, the presence of ice sheets over Great Britain and Scandinavia, and an ice cap over the Alps enhanced the zonal circulation that reflects the location of the thickest loess deposits (Fig.…”

Major dust events in Europe during marine isotope stage 5 (130–74 ka): a climatic interpretation of the "markers"

“…These are precisely the seasons that Sima et al (2009Sima et al ( , 2013 recognized as the most favorable for dust emission under stadial conditions. Polar air outbreaks are thus a likely mechanism for the dust events we wish to explain herein, since they are associated with rapid low-level airstreams.…”

“…The modeling experiments of Sima et al (2009Sima et al ( , 2013) on dust emission for stadial conditions in western Europe show that ground surface conditions are most favorable in spring for both the emission and transport of fine-grained material. These favorable conditions arise after harsher winter conditions and before the start of the development of the vegetation, later in the season; the optimal time for dust emission and transport is slightly shifted towards early summer during Heinrich events.…”