Academic literature on the topic 'Mid-Brunhes event'

Abstract. The Mid-Brunhes Transition (MBT) began ∼ 430 ka with an increase in the amplitude of the 100 kyr climate cycles of the past 800 000 years. The MBT has been identified in ice-core records, which indicate interglaciations became warmer with higher atmospheric CO2 levels after the MBT, and benthic oxygen isotope (δ18O) records, which suggest that post-MBT interglaciations had higher sea levels and warmer temperatures than pre-MBT interglaciations. It remains unclear, however, whether the MBT was a globally synchronous phenomenon that included other components of the climate system. Here, we further characterize changes in the climate system across the MBT through statistical analyses of ice-core and δ18O records as well as sea-surface temperature, benthic carbon isotope, and dust accumulation records. Our results demonstrate that the MBT was a global event with a significant increase in climate variance in most components of the climate system assessed here. However, our results indicate that the onset of high-amplitude variability in temperature, atmospheric CO2, and sea level at ∼430 ka was preceded by changes in the carbon cycle, ice sheets, and monsoon strength during Marine Isotope Stage (MIS) 14 and MIS 13.

AbstractThis work presents a detailed, orbitally tuned biogenic silica record of continental paleoclimate change during the Brunhes chron. The Brunhes/Matuyama boundary lies within the warm isotopic stage 19 in Baikal, and the boundaries between eight lithological cycles correspond to terminations in the marine oxygen isotope record. The high amplitude and resolution of climatically driven changes in BioSi content in Lake Baikal sediments permits tuning of almost every precessional cycle during the Brunhes and reveals the structure of interglacial stages. For example, the last three interglacial stages (MIS 5, 7, and 9) clearly consist of five substages (a, b, c, d, e) corresponding to precessional insolation peaks. Abrupt and intense regional glaciations in Siberia during substages 5d and 7d were driven by extreme insolation minima. During substage 9d cooling was more gradual in response to more moderate forcing. The impact of strong glaciation is also observed in the middle of stage 15, where full glacial conditions appear to have lasted for over 30,000 yr during substages 15d, 15c, and 15b. Marine oxygen isotopic stage 11 appears to be the warmest period during the Brunhes in the Lake Baikal record, with at least three substages.A new hypothesis is presented regarding the response of the Lake Baikal BioSi record to insolation forcing. Based on the mechanism controlling modern diatom blooms, biogenic silica production is hypothesized to be dependent on changes in the heat balance of the lake and consequently on changes in the thermal structure of the water column. This mechanism is also sensitive to short-term sub-Milankovich cooling events, such as the mid-Eemian cooling, the Montaigu event during substage 5c, and a cooling which appears to be analogous to the Montaigu event during substage 9c. The continuity of the Lake Baikal paleoclimate record, its sensitivity to orbital forcing, and its high resolution make it an excellent candidate for a new “paleoclimatic stratotype” section for continental Asia.

L’océan Indien est le lieu de processus atmosphériques et océaniques majeurs dont les répercussions en terme climatique peuvent être de grandes importances. Cette thèse se propose de documenter les forçages, les variabilités, les impacts et les interactions de la mousson Indo-asiatique et du courant des Aiguilles à l’échelle orbitale (incluant les conditions glaciaires-interglaciaires) au cours de la période Quaternaire.Si le maximum d’insolation (minimum de précession et maximum d’obliquité) initie les fortes moussons Indo-asiatiques, des forçages internes au système climatique jouent également un rôle majeur pour expliquer leur dynamique (fort vents et précipitations), en particulier le changement de volume de glace de l’hémisphère Nord et l’export de chaleur latente de l’océan Indien Sud. La prédominance de ces forçages internes est propre à la mousson Indo-asiatique et la distingue des moussons boréales Africaines. Ceci indique que le concept de mousson globale n’est pas valable à l’échelle orbitale.Concernant l’hémisphère Sud, les variations de température de surface du courant des Aiguilles exercent un contrôle important sur le climat Sud Africain (la végétation et les précipitations). Ce courant permet également le transfert plus ou moins important de chaleur et de sel vers l’océan Atlantique Sud par l’intermédiaire de la migration de la convergence subtropicale et des vents d’ouest associés. Ce mécanisme, contrôlé fortement par la dynamique des hautes latitudes Sud, affecte la circulation thermo-haline globale et constitue un acteur important des transitions glaciaires-interglaciaires et des changements de mode de variabilité climatique au cours du Quaternaire (Transition Mid-Pleistocène et évènement du Mid-Brunhes). Les changements induits dans le climat de l’Hémisphère Nord, et notamment le volume de glace, pourraient ensuite se répercuter sur la dynamique de la mousson. En revanche, l’effet des moussons sur le courant des Aiguilles parait mineur. Toutefois, les interactions entre la mousson Indo-asiatique, l’ENSO et les éventuels IOD (dipôles climatiques de l’océan Indien) pourraient affecter la dynamique du courant
The Indian Ocean is the place of major atmospheric and oceanic processes with large potential repercussions on the global climatic system. This thesis investigates forcing, variations, impacts and interactions of the Indo-Asian monsoon and of the Agulhas current at the orbital scale (including glacial-interglacial conditions) over the Quaternary period.Insolation maximum (precession minimum and obliquity maximum) initiates strong Indo-Asian monsoons, but processes internal to the climate system, in particular Northern Hemisphere (NH) ice volume changes and the latent heat export of the south Indian Ocean, play a major role to explain their dynamics (strongest winds and precipitation). The predominance of these internal forcings is a specificity of the Indo-Asian monsoon and distinguishes it from African boreal monsoons. This indicates that the concept of a global monsoon at the orbital scale is a misnomer.Concerning the Southern hemisphere, sea surface temperature variations of the Agulhas current exert an important control upon the South African climate (vegetation and precipitation). This current also participates to the transfer of heat and salt towards the South Atlantic Ocean whose intensity is mainly related to the migration of the subtropical convergence and associated westerlies winds. This mechanism, strongly controlled by high southern latitudes dynamics, affects the global overturning circulation and plays an important role for glacial-interglacial transitions and changes in modes of climate variability during the Quaternary (Mid-Pleistocene Transition and Mid-Brunhes event). Induced Northern hemisphere climate changes, in particular ice volume, could in turn influence monsoon dynamics. On the other hand, the effect of monsoons on the Agulhas current seems to be of minor importance. However, interactions between the Indo-Asian monsoon, ENSO and the possible IOD (Indian Ocean climatic Dipole) could affect the dynamic of the current

The characteristic glacial and interglacial cycles of the Pleistocene underwent a climatic transition at ~430 ka known as the Mid- Brunhes Event (MBE). Many studies, particularly from the Southern Hemisphere have noted that after this transition, the amplitude of the climatic cycles increased. Despite the indication of an MBE signal in many globally distributed paleoclimate records, the geographic extent of the climatic transition remains unknown and its presence in northern hemisphere and terrestrial records is debated. Lake El’gygytgyn is located in the far- east Russian Arctic and provides the longest, most continuous record of Arctic climate (3.6 Ma). This study examines organic biomarkers in the Lake El’gygytgyn sediment core to determine if the MBE is expressed in the terrestrial Arctic. The paleoclimate reconstruction spans the interval of 340- 730 ka at a resolution of ~3 ka. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are utilized to reconstruct temperature and plant leaf wax n-alkanes are used to examine vegetation changes. Statistical analysis of this, and other existing proxy data, indicates that a signal of the MBE is preserved in the Lake El’gygytgyn sediment record. BrGDGT temperature reconstructions suggest the terrestrial Arctic experienced both the warmest interglacials and coldest glacial periods after the MBE climatic transition. Arid glacial intervals and wetter interglacials are recorded by changes in the average chain length of n- alkanes, with wetter interglacials predominating after the MBE.