Drivers of the evolution and amplitude of African Humid Periods

During orbital precession minima, the Sahara was humid and more vegetated, providing potential corridors for Hominins migration. Uncertainties remain over the climatic processes controlling the initiation, demise and amplitude of these African Humid Periods. Here we study these processes using a series of transient simulations of the penultimate deglaciation and Last Interglacial period, and compare the results with a transient simulation of the last deglaciation and Holocene. We find that the strengthening of the Atlantic Meridional Overturning Circulation at the end of deglacial millennial-scale events exerts a dominant control on the abrupt initiation of African Humid Periods as the Atlantic Meridional Overturning Circulation modulates the position of the Intertropical Convergence Zone. In addition, residual Northern Hemispheric ice-sheets can delay the peak of the African Humid Period. Through its impact on Northern Hemispheric ice-sheets disintegration and thus Atlantic Meridional Overturning Circulation, the larger rate of insolation increase during the penultimate compared to the last deglaciation can explain the earlier and more abrupt onset of the African Humid Period during the Last Interglacial period. Finally, we show that the mean climate state modulates precipitation variability, with higher variability under wetter background conditions.

Drivers of the evolution and amplitude of African Humid Periods

During orbital precession minima, the Sahara was humid and hosted tropical plant species thus providing a corridor for Hominins migration. Uncertainties remain over the climatic processes controlling the initiation, demise and amplitude of these African Humid Periods (AHPs). Here we present transient simulations of the penultimate deglaciation and Last Interglacial period (LIG), and compare them to transient simulations of the last deglaciation and Holocene. We find that the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) at the end of the deglacial millennial-scale events exerts a dominant control on the abrupt initiation of AHPs, as the AMOC modulates the position of the Intertropical Convergence Zone (ITCZ). In addition, residual Northern Hemispheric (NH) ice-sheets can delay the AHP peak. Through its impact on NH ice-sheets disintegration and thus AMOC variations, the larger rate of insolation increase during the penultimate compared to the last deglaciation can explain the earlier and more abrupt LIG AHP onset. Finally, we show that the background climate state modulates precipitation variability with higher variability under wetter background conditions.

Origin and Paleoenvironmental Significance of the Old Red Sand Along the Southeast Coast of China

The “Old Red Sand” (ORS) along the southeast coast of China is of significant paleoclimatic and paleoenvironmental significance. However, its provenance remains controversial. In this study, grain size characteristics and quartz grain surface microtextures were analyzed to study the origin and paleoenvironmental significance of the ORS, the results show that the grain size of the ORS show typical aeolian features, the quartz grain surface microtextures of the ORS show both aeolian features and subaqueous environments characteristics. Combined with the latest OSL dating data, we suggest that the ORS was coastal aeolian sand dunes developed since the last interglacial period. The formation of the ORS was restricted jointly by climate changes of the coastal area and the distance from the shoreline that resulted from sea level changes.

Eemian and early Weichselian environmental changes at the Jałówka site, NE Poland, and their correlation with marine and ice records

Vegetation changes were documented across the last interglacial period (MIS 5e, Eemian) and continuing through the older part of the last glacial period (MIS 5d–a, early Weichselian). This study was based on pollen data collected at the Jałówka site, NE Poland. Two cold oscillations appeared within warm periods during this stage of the upper Pleistocene. The older oscillation was the temporary intra–interglacial cooling at the end of the Eemian. The younger one was the intra–interstadial cooling that occurred within the oldest interstadial of the early Weichselian (MIS 5c, Brørup). This last event corresponds well to the stadial separating both the Amersfoort and Brørup sensu stricto interstadials in the Netherlands and to the Montaigu event as recognized in France. The development of a pollen sequence allows speculation as to potential correlations with Greenland ice cores and marine records. We suggest that the Eemian in NE Poland may comprise not only MIS 5e, but also a part of MIS 5d. This supposition could shed light on potential for non-synchrony in upper boundaries of the MIS 5e and terrestrial Eemian in Europe. We await the development of more precise independent dating controls to validate our theory more assiduously.

Lower oceanic <i>δ</i>¹³C during the last interglacial period compared to the Holocene

The last time in Earth's history when high latitudes were warmer than during pre-industrial times was the last interglacial period (LIG, 129–116 ka BP). Since the LIG is the most recent and best documented interglacial, it can provide insights into climate processes in a warmer world. However, some key features of the LIG are not well constrained, notably the oceanic circulation and the global carbon cycle. Here, we use a new database of LIG benthic δ13C to investigate these two aspects. We find that the oceanic mean δ13C was ∼ 0.2 ‰ lower during the LIG (here defined as 125–120 ka BP) when compared to the Holocene (7–2 ka BP). A lower terrestrial carbon content at the LIG than during the Holocene could have led to both lower oceanic δ13C and atmospheric δ13CO2 as observed in paleo-records. However, given the multi-millennial timescale, the lower oceanic δ13C most likely reflects a long-term imbalance between weathering and burial of carbon. The δ13C distribution in the Atlantic Ocean suggests no significant difference in the latitudinal and depth extent of North Atlantic Deep Water (NADW) between the LIG and the Holocene. Furthermore, the data suggest that the multi-millennial mean NADW transport was similar between these two time periods.

Genesis, Evolution, and Genetic Diversity of the Hexaploid, Narrow Endemic Centaurea tentudaica

Within the genus Centaurea L., polyploidy is very common, and it is believed that, as to all angiosperms, it was key in the history of its diversification and evolution. Centaurea tentudaica is a hexaploid from subsect. Chamaecyanus of unknown origin. In this study, we examined the possible autopolyploid or allopolyploid origin using allozymes and sequences of three molecular markers: nuclear-ribosomic region ETS, and low-copy genes AGT1 and PgiC. We also included three species geographically and morphologically close to C. tentudaica: C. amblensis, C. galianoi, and C. ornata. Neighbor-Net and Bayesian analyses show a close relationship between C. amblensis and C. tentudaica and no relationship to any of the other species, which suggest that C. tentudaica is an autopolyploid of C. amblensis. Allozyme banding pattern also supports the autopolyploidy hypothesis and shows high levels of genetic diversity in the polyploid, which could suggest multiple origins by recurrent crosses of tetraploid and diploid cytotypes of C. amblensis. Environmental niche modeling was used to analyze the distribution of the possible parental species during the present, Last Glacial Maximum (LGM), Last Interglacial Period (LIG), and Penultimate Glacial Maximum (PGM) environmental conditions. Supporting the molecular suggestions that C. tentudaica originated from C. amblensis, environmental niche modeling confirms that past distribution of C. amblensis overlapped with the distribution of C. tentudaica.