Abstract
Abstract. The last glacial period has been punctuated by two types of abrupt climatic events, the Dansgaard–Oeschger (DO) and Heinrich (HE) events. These events, recorded in Greenland ice and in marine sediments, involved changes in the Atlantic Meridional Overturning Circulation (AMOC) and led to major changes in the terrestrial biosphere. Here we use the dynamical global vegetation model ORCHIDEE to simulate the response of vegetation to abrupt changes in the AMOC strength. We force ORCHIDEE offline with outputs from the IPSL_CM4 general circulation model, in which the AMOC is forced to change by adding freshwater fluxes in the North Atlantic. We investigate the impact of a collapse and recovery of the AMOC, at different rates, and focus on Western Europe, where many pollen records are available for comparison. The impact of an AMOC collapse on the European mean temperatures and precipitations simulated by the GCM is relatively small but sufficient to drive an important regression of forests and expansion of grasses in ORCHIDEE, in qualitative agreement with pollen data for an HE event. On the contrary, a run with a rapid shift of the AMOC to a hyperactive state of 30 Sv, mimicking the warming phase of a DO event, does not exhibit a strong impact on the European vegetation compared to the glacial control state. For our model, simulating the impact of an HE event thus appears easier than simulating the abrupt transition towards the interstadial phase of a DO. For both a collapse or a recovery of the AMOC, the vegetation starts to respond to climatic changes immediately but reaches equilibrium about 200 yr after the climate equilibrates, suggesting a possible bias in the climatic reconstructions based on pollen records, which assume equilibrium between climate and vegetation. However, our study does not take into account vegetation feedbacks on the atmosphere.
Highlights
Hydrology and The last glacial period (E10a–9r0thkySBPy)shtaesmbeen punctuated bOyestcwhogetry(pDeOs )oefvaebnrtusp(tDcalnismgaataiSrcdccehiteaanln.g,ce1s9e, 9st3h)eaDndanHsegianarridc–h events (Heinrich, 1988)
We focus on the timing of the response of vegetation compared to the timing of the Atlantic Meridional Overturning Circulation (AMOC) evolution and analyse the specific response of the different plant functional types (PFTs) simulated in ORCHIDEE, in order to investigate their different sensitivities to the simulated abrupt climate changes
The main issues that we wanted to investigate in the present paper were: is the European glacial vegetation simulated by ORCHIDEE sensitive to AMOC changes? Can the model simulate vegetation changes in agreement with changes inferred from pollen data for Heinrich events (HE) or DO events? What is the timing of the vegetation evolution?
Summary
Hydrology and The last glacial period (E10a–9r0thkySBPy)shtaesmbeen punctuated bOyestcwhogetry(pDeOs )oefvaebnrtusp(tDcalnismgaataiSrcdccehiteaanln.g,ce1s9e, 9st3h)eaDndanHsegianarridc–h events (Heinrich, 1988). We investigate the impact of a collapse and recovery of the AMOC, at different rates, and focus on Western Europe, where many pollen an initial abrupt warming of up to 8 to 16 ◦C over Greenland in a few decades (Johnsen et al, 1992, 1995; Landais et al., 2004; Wolff et al, 20O10c),efaolnlowSedcibeynacwearm phase A run with a rapid shift of the AMOC to a hyperactive massive iceberg discharges from the Laurentide ice sheet in the North Atlantic, occurringSevoerlyid tEo a7 krythand recorded in marine sediment cores by the presence of ice-rafted detritus state of 30 Sv, mimicking the warming phase of a DO event, does not exhibit a strong impact on the European vegetation (Heinrich, 1988; Bond and Lotti, 1995). For our model, simulating the impact of an HE event appears easier than simulating the abrupt transition towards the interstadial phase of et al, 2001; Schulz, 2002), the significance of this preenricoedaiccittuyalilsydceabnanteodtTbaehnddeissotCimngreuyaioushtsheodprsfhrcoelmarimea rtahnadtothmeorceccuurr--
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have