Abstract
Among the 100 kyr climatic cycles of the late Pleistocene, Termination V (TV, ~[404-433] kyr BP), the fifth last deglaciation, stands out for its minimum in astronomical forcing associated paradoxically with maxima in sea level, Antarctic temperature and atmospheric CO2 concentration. However, the driving mechanisms explaining TV remain only partially understood. For instance, climate models cannot fully represent the atmospheric CO2 variation observed in paleoclimate data. Aside from essential oceanic circulation processes, there is increasing evidence that terrestrial biosphere may have played a key role in the global carbon cycle. This study proposes a three-step integrated approach, combining regional and global vegetation records with modeling results, to unveil the evolution of terrestrial biosphere and its contribution to the carbon cycle during TV. First, we provide a new high resolution (~700 years) deep-sea pollen record from the Gulf of Cadiz (Site U1386, 36°49.680 N; 7°45.320 W) for TV, which shows a moderate expansion of the Mediterranean forest. We then construct the first global forest pollen database for this period. Our compilation features distinct evolutions for different types of forest, highlighting a strong development of temperate and boreal forest which may have delayed the atmospheric CO2 increase during TV. Finally, the direct comparison of global simulated forests (iLOVECLIM model) to our pollen database reveals consistent forest evolutions despite model biases, thereby supporting a CO2 mitigation by high latitude forests of the northern hemisphere.
Highlights
IntroductionAmong the five major short-term carbon reservoirs of the climate system (ocean, atmosphere, terrestrial biosphere, surface sediments, permafrost), terrestrial biosphere (including vegetation and soils) is considered as an essential component of current 30 anthropogenic climate change mitigation strategies (Harris, et al, 2021, Shukla, et al, 2019)
Among the five major short-term carbon reservoirs of the climate system, terrestrial biosphere is considered as an essential component of current 30 anthropogenic climate change mitigation strategies (Harris, et al, 2021, Shukla, et al, 2019)
The large proportion of Pioneer taxa and low Mediterranean Forest (MF) further confirms that climate conditions were too harsh for large temperate trees to grow, leaving a shrub-dominated land cover
Summary
Among the five major short-term carbon reservoirs of the climate system (ocean, atmosphere, terrestrial biosphere, surface sediments, permafrost), terrestrial biosphere (including vegetation and soils) is considered as an essential component of current 30 anthropogenic climate change mitigation strategies (Harris, et al, 2021, Shukla, et al, 2019). Natural land sinks are marked by large internal climate variability resulting in uncertainties on the global carbon budget (Loughran, et al 2021). This respect, the study of past climate changes and associated terrestrial biosphere responses remains crucial to reduce uncertainty related to Earth’s sensitivity to climate forcings (Overpeck et al, 2003; Masson-Delmotte et al, 2021). Paleoenvironmental research allows us to investigate terrestrial biosphere feedbacks on the climate on multi-millennial 35 timescales (Overpeck et al, 2003). While extensive studies cover the last glacial cycle (Hoogakker et al 2016) and the Holocene (Bartlein et al 2010), there are no global descriptions of terrestrial biosphere for older periods of the Quaternary marked by different climatic boundary conditions
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