Journal articles: 'Mid-Brunhes event'

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Holden, P. B., N. R. Edwards, E. W. Wolff, P. J. Valdes, and J. S. Singarayer. "The Mid-Brunhes Event and West Antarctic ice sheet stability." Journal of Quaternary Science 26, no. 5 (June 13, 2011): 474–77. http://dx.doi.org/10.1002/jqs.1525.

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Blain, H. A., G. Cuenca-Bescos, I. Lozano-Fernandez, J. M. Lopez-Garcia, A. Olle, J. Rosell, and J. Rodriguez. "Investigating the Mid-Brunhes Event in the Spanish terrestrial sequence." Geology 40, no. 11 (August 22, 2012): 1051–54. http://dx.doi.org/10.1130/g33427.1.

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Barth, Aaron M., Peter U. Clark, Nicholas S. Bill, Feng He, and Nicklas G. Pisias. "Climate evolution across the Mid-Brunhes Transition." Climate of the Past 14, no. 12 (December 21, 2018): 2071–87. http://dx.doi.org/10.5194/cp-14-2071-2018.

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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.

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Xu, Xinwen, Xiaoke Qiang, Sheng Hu, Hui Zhao, Chaofeng Fu, and Qing Zhao. "Records of the Mid-Brunhes Event in Chinese loess-paleosol sequences." Palaeogeography, Palaeoclimatology, Palaeoecology 543 (April 2020): 109596. http://dx.doi.org/10.1016/j.palaeo.2020.109596.

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Wang, Pinxian, Jun Tian, Xinrong Cheng, Chuanlian Liu, and Jian Xu. "Carbon reservoir changes preceded major ice-sheet expansion at the mid-Brunhes event." Geology 31, no. 3 (2003): 239. http://dx.doi.org/10.1130/0091-7613(2003)031<0239:crcpmi>2.0.co;2.

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JANSEN, J. H. F., A. KUIJPERS, and S. R. TROELSTRA. "A Mid-Brunhes Climatic Event: Long-Term Changes in Global Atmosphere and Ocean Circulation." Science 232, no. 4750 (May 2, 1986): 619–22. http://dx.doi.org/10.1126/science.232.4750.619.

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Yin, Q. Z., and A. Berger. "Insolation and CO2 contribution to the interglacial climate before and after the Mid-Brunhes Event." Nature Geoscience 3, no. 4 (March 7, 2010): 243–46. http://dx.doi.org/10.1038/ngeo771.

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Prokopenko, Alexander A., Eugene B. Karabanov, Douglas F. Williams, Mikhail I. Kuzmin, Nicholas J. Shackleton, Simon J. Crowhurst, John A. Peck, Alexander N. Gvozdkov, and John W. King. "Biogenic Silica Record of the Lake Baikal Response to Climatic Forcing during the Brunhes." Quaternary Research 55, no. 2 (March 2001): 123–32. http://dx.doi.org/10.1006/qres.2000.2212.

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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.

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Leonhardt, Adriana, Felipe A. L. Toledo, and João Carlos Coimbra. "The Mid-Brunhes event in the southwestern Atlantic Ocean: coccolithophore assemblages during the Mis 11-9." REVISTA BRASILEIRA DE PALEONTOLOGIA 18, no. 3 (December 22, 2015): 343–54. http://dx.doi.org/10.4072/rbp.2015.3.01.

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Candy, I., G. R. Coope, J. R. Lee, S. A. Parfitt, R. C. Preece, J. Rose, and D. C. Schreve. "Pronounced warmth during early Middle Pleistocene interglacials: Investigating the Mid-Brunhes Event in the British terrestrial sequence." Earth-Science Reviews 103, no. 3-4 (December 2010): 183–96. http://dx.doi.org/10.1016/j.earscirev.2010.09.007.

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Haeberli, Marcel, Daniel Baggenstos, Jochen Schmitt, Markus Grimmer, Adrien Michel, Thomas Kellerhals, and Hubertus Fischer. "Snapshots of mean ocean temperature over the last 700 000 years using noble gases in the EPICA Dome C ice core." Climate of the Past 17, no. 2 (April 14, 2021): 843–67. http://dx.doi.org/10.5194/cp-17-843-2021.

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Abstract. Together with the latent heat stored in glacial ice sheets, the ocean heat uptake carries the lion's share of glacial–interglacial changes in the planetary heat content, but little direct information on the global mean ocean temperature (MOT) is available to constrain the ocean temperature response to glacial–interglacial climate perturbations. Using ratios of noble gases and molecular nitrogen trapped in the Antarctic EPICA Dome C ice core, we are able to reconstruct MOT for peak glacial and interglacial conditions during the last 700 000 years and explore the differences between these extrema. To this end, we have to correct the noble gas ratios for gas transport effects in the firn column and gas loss fractionation processes of the samples after ice core retrieval using the full elemental matrix of N2, Ar, Kr, and Xe in the ice and their individual isotopic ratios. The reconstructed MOT in peak glacials is consistently about 3.3 ± 0.4 ∘C cooler compared to the Holocene. Lukewarm interglacials before the Mid-Brunhes Event 450 kyr ago are characterized by 1.6 ± 0.4 ∘C lower MOT than the Holocene; thus, glacial–interglacial amplitudes were only about 50 % of those after the Mid-Brunhes Event, in line with the reduced radiative forcing by lower greenhouse gas concentrations and their Earth system feedbacks. Moreover, we find significantly increased MOTs at the onset of Marine Isotope Stage 5.5 and 9.3, which are coeval with CO2 and CH4 overshoots at that time. We link these CO2 and CH4 overshoots to a resumption of the Atlantic Meridional Overturning Circulation, which is also the starting point of the release of heat previously accumulated in the ocean during times of reduced overturning.

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Voelker, A. H. L., T. Rodrigues, R. Stein, J. Hefter, K. Billups, D. Oppo, J. McManus, and J. O. Grimalt. "Variations in mid-latitude North Atlantic surface water properties during the mid-Brunhes: Does Marine Isotope Stage 11 stand out?" Climate of the Past Discussions 5, no. 3 (June 3, 2009): 1553–607. http://dx.doi.org/10.5194/cpd-5-1553-2009.

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Abstract. New planktonic stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699) are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9–14 (300–540 ka). Together the study sites reflect western and eastern basin boundary currents as well as north to south transect sampling of subpolar and transitional water masses. Planktonic δ18O records indicate that during peak interglacial MIS 9 and 11 hydrographic conditions were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of which is slightly warmer. Enhanced subsurface northward heat flux in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktonic foraminifer species. MIS 13 was generally colder and more variable than the younger interglacials. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north-south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Drift as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. A strong Azores Current influence is seen especially during MIS 12, when SST dropped significantly only during the Heinrich-type ice-rafting event at the onset of Termination V. Given the subtropical overprint on Portuguese nearshore sites such as MD03-2699 and MD01-2443 caution needs to be taken to interpret their records as basin-wide climate signals.

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CANDY, IAN, and ERIN L. MCCLYMONT. "Interglacial intensity in the North Atlantic over the last 800 000 years: investigating the complexity of the mid-Brunhes Event." Journal of Quaternary Science 28, no. 4 (May 2013): 343–48. http://dx.doi.org/10.1002/jqs.2632.

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Dupont, Lydie M., Thibaut Caley, and Isla S. Castañeda. "Effects of atmospheric CO<sub>2</sub> variability of the past 800 kyr on the biomes of southeast Africa." Climate of the Past 15, no. 3 (June 19, 2019): 1083–97. http://dx.doi.org/10.5194/cp-15-1083-2019.

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Abstract. Very little is known about the impact of atmospheric carbon dioxide pressure (pCO2) on the shaping of biomes. The development of pCO2 throughout the Brunhes Chron may be considered a natural experiment to elucidate relationships between vegetation and pCO2. While the glacial periods show low to very low values (∼220 to ∼190 ppmv, respectively), the pCO2 levels of the interglacial periods vary from intermediate to relatively high (∼250 to more than 270 ppmv, respectively). To study the influence of pCO2 on the Pleistocene development of SE African vegetation, we used the pollen record of a marine core (MD96-2048) retrieved from Delagoa Bight south of the Limpopo River mouth in combination with stable isotopes and geochemical proxies. Applying endmember analysis, four pollen assemblages could be distinguished representing different biomes: heathland, mountain forest, shrubland and woodland. We find that the vegetation of the Limpopo River catchment and the coastal region of southern Mozambique is influenced not only by hydroclimate but also by temperature and atmospheric pCO2. Our results suggest that the extension of mountain forest occurred during those parts of the glacials when pCO2 and temperatures were moderate and that only during the colder periods when atmospheric pCO2 was low (less than 220 ppmv) open ericaceous vegetation including C4 sedges extended. The main development of woodlands in the area took place after the Mid-Brunhes Event (∼430 ka) when interglacial pCO2 levels regularly rose over 270 ppmv.

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Candy, Ian, and Montserrat Alonso-Garcia. "A 1 Ma sea surface temperature record from the North Atlantic and its implications for the early human occupation of Britain." Quaternary Research 90, no. 2 (August 17, 2018): 406–17. http://dx.doi.org/10.1017/qua.2018.62.

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AbstractThe British Quaternary sequence has an exceptionally rich record of Palaeolithic archaeology up to 1 Ma. In this study, we reinvestigate foraminifera-based sea surface temperature (SST) reconstructions from the two marine core records (Ocean Drilling Program Site 980 and M23414) that are most relevant to the climatic history of the British Isles, consequently allowing the evolution of SST over the past 1 Ma to be studied. This is then compared with long-term changes with the British archaeological record in order to understand in greater detail the changing patterns of climatic forcing and the major climatic transitions that were the background environmental drivers against which patterns of early human occupation occurred. These include the mid-Pleistocene revolution, the mid-Brunhes event, and changing patterns of isotopic substage complexity. Significantly, however, the SST record indicates that the Marine Oxygen Isotope Stage 15–13 interval was characterised by the most prolonged period of consistently warm conditions of the entire 1 Ma interval in the northeast Atlantic. This unique climatic period correlates with the first major proliferation of archaeological sites in northwest Europe. The article concludes by discussing the significance of these climatic shifts for our understanding of early human occupation in this region.

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Huang, Huai‐Hsuan M., Moriaki Yasuhara, Hokuto Iwatani, Carlos A. Alvarez Zarikian, Maria‐Angela Bassetti, and Takuya Sagawa. "Benthic Biotic Response to Climate Changes Over the Last 700,000 Years in a Deep Marginal Sea: Impacts of Deoxygenation and the Mid‐Brunhes Event." Paleoceanography and Paleoclimatology 33, no. 7 (July 2018): 766–77. http://dx.doi.org/10.1029/2018pa003343.

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Huang, Huai-Hsuan May, Moriaki Yasuhara, Hokuto Iwatani, Tatsuhiko Yamaguchi, Katsura Yamada, and Briony Mamo. "Deep-sea ostracod faunal dynamics in a marginal sea: biotic response to oxygen variability and mid-Pleistocene global changes." Paleobiology 45, no. 1 (November 23, 2018): 85–97. http://dx.doi.org/10.1017/pab.2018.37.

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AbstractDeep-sea benthic ostracod assemblages covering the last 2 Myr were investigated in Integrated Ocean Drilling Program Site U1426 (at 903 m water depth) in the southern Sea of Japan. Results show that (1) orbital-scale faunal variability has been influenced by eustatic sea-level fluctuations and oxygen variability and (2) secular-scale faunal transitions are likely associated with the mid-Brunhes event (MBE, ~0.43 Ma) and the onset of the Tsushima Warm Current (TWC, ~1.7 Ma).Krithe,Robertsonites, andAcanthocythereisare the three most abundant genera throughout the core, accounting for 78.5% of total specimens. Multiple-regression tree analysis indicated that the TWC, the MBE, and oxygen content are the significant controlling factors of ostracod dominance. Changes in assemblages exhibit decline and recovery patterns corresponding to orbital-scale cyclicity of sea-level changes. In the Sea of Japan marginal ocean setting, this cyclicity shows a close relationship with bottom-water oxygen variability since the onset of the TWC influx. The MBE amplified the influence of the TWC and oxygen variability to the deep-sea ecosystem through larger sea-level fluctuations.Acanthocythereis dunelmensis, a circumpolar species, dominates before the TWC onset. After the TWC onset and during the mid-Pleistocene transition (MPT, ~1.2–0.7 Ma)Krithespp., known for their low-oxygen tolerance, substantially increase under moderate oxygen depletion. At the end of the MPT,Krithedominance diminishes and is replaced byRobertsonites hanaiiandPropontocyprisspp. after the MBE. The post-MBE assemblage, characterized byR. hanaii, suggests a slightly warmer environment under the development of the TWC. In addition, the post-MBE high-amplitude climate system may have caused the increased abundance of active-swimmingPropontocyprisspp. due to their superior migration ability. Benthic ecosystems in marginal seas are sensitive and vulnerable to both short- and long-term climatic changes, and the MBE is suggested to be a global biotic event affecting benthic ecosystems substantially.

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Chuey, John M., David K. Rea, and Nicklas G. Pisias. "Late Pleistocene Paleoclimatology of the Central Equatorial Pacific: A Quantitative Record of Eolian and Carbonate Deposition." Quaternary Research 28, no. 3 (November 1987): 323–39. http://dx.doi.org/10.1016/0033-5894(87)90001-9.

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AbstractDetailed records of δ18O, δ13C, percentage and mass accumulation rate of CaCO3, and eolian percentage, mass accumulation rate, and grainsize generated for core RC11-210 from the equatorial Pacific reveal the timing of paleoclimatic events over the past 950,000 yr. The CaCO3 percentage record shows the standard Pacific correlation of high CaCO3 content with glacial periods, but displays a marked change of character about 490,000 yr ago with older stages showing much less variability. The carbonate mass flux record, however, does not show such a noticeable change. Sedimentation rates vary from about 0.5 to 3.0 cm/1000 yr and, during the past 490,000 yr, sections with enhanced sedimentation rates correspond to periods of high CaCO3 percentage. Eolian mass accumulation rates, an indication of the aridity of the source region, are usually higher during glacial times. Eolian grainsize, an indication of the intensity of atmospheric circulation, generally fluctuates at a higher frequency than the 100,000-yr glacial cycle. The mid-Brunhes climatic event centered at 300,000 yr ago appears as a 50,000-yr interval of low intensity and reduced variability of atmospheric circulation. Furthermore, the nature of this entire record changes then, with the younger portion indicating less variation in wind intensity than the older part of the record. The late Matuyama increase in amplitude of paleoclimatic signals begins 875,000 yr ago in the eolian record, 25,000 yr before the δ18O and CaCO3 percentage amplitude increases about 850,000 yr ago.

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Kender, Sev, Adeyinka Aturamu, Jan Zalasiewicz, Michael A. Kaminski, and Mark Williams. "Benthic foraminifera indicate Glacial North Pacific Intermediate Water and reduced primary productivity over Bowers Ridge, Bering Sea, since the Mid-Brunhes Transition." Journal of Micropalaeontology 38, no. 2 (December 3, 2019): 177–87. http://dx.doi.org/10.5194/jm-38-177-2019.

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Abstract. The Mid-Brunhes Transition (MBT) saw an increase in the amplitude of glacial cycles expressed in ice core and deep ocean records from about 400 ka, but its influence on high-latitude climates is not fully understood. The Arctic Ocean is thought to have warmed and exhibited reduced sea ice, but little is known of sea ice marginal locations such as the Bering Sea. The Bering Sea is the link between the Arctic and Pacific Ocean and is an area of high productivity and CO2 ventilation; it hosts a pronounced oxygen minimum zone (OMZ) and is thought to be the location of Glacial North Pacific Intermediate Water (GNPIW) formation in the Pleistocene. To understand palaeoceanographic change in the region, we analysed benthic foraminiferal faunas from Bowers Ridge (Site U1342, 800 m of water depth) over the past 600 kyr, as they are uniquely well preserved and sensitive to changes in deep and surface ocean conditions. We identified and imaged 71 taxa and provide a full taxonomy. Foraminiferal preservation is markedly higher during glacials, indicating the presence of less corrosive GNPIW. The most abundant species are Bulimina exilis, Takayanagia delicata, Alabaminella weddellensis, Gyroidina sp. 2, Cassidulina laevigata, Islandiella norcrossi, and Uvigerina bifurcata, consistent with broadly high net primary production throughout the last 600 kyr. Correspondence analysis shows that the most significant Assemblage 1 comprises B. exilis, T. delicata, Bolivina spissa, and Brizalina, which occur sporadically within intervals of laminated, biogenic-rich sediment, mostly during glacials and also some deglacials, and are interpreted as indicating very high productivity. Other assemblages contain the phytodetritivore species A. weddellensis, I. norcrossi, and C. laevigata, indicative of seasonal phytoplankton blooms. Before the MBT, more numerous intervals of the very high-productivity Assemblage 1 and A. weddellensis occur, which we suggest reflect a time of more sea-ice-related seasonal stratification and ice edge blooms. Our inference of a decrease in sea ice meltwater stratification influence in the central Bering Sea after the MBT is consistent with records showing that the Arctic and Pacific Ocean warmed during glacials and suggests that high-latitude productivity and sea ice changes were an important feature of this climate event.

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Wang, PinXian, QianYu Li, Jun Tian, ZhiMin Jian, ChuanLian Liu, Li Li, and WenTao Ma. "Long-term cycles in the carbon reservoir of the Quaternary ocean: a perspective from the South China Sea." National Science Review 1, no. 1 (December 31, 2013): 119–43. http://dx.doi.org/10.1093/nsr/nwt028.

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Abstract In recent years, long-term, high-resolution records from the deep sea and ice-cores have offered new research opportunities for Quaternary science. Paleoclimate studies are no longer restricted to individual glacial cycles, but extend to long-term (≥105 yr) processes across those cycles. Ocean Drilling Program Leg 184 of the South China Sea in 1999 uncovered well-preserved sediment sections, in which three long-term cycles in Pleistocene carbon isotope (δ13C) sequence have been found and demonstrated to be common in the global ocean. Subsequent discoveries confirm the existence of long-term processes of 105 yr in both the hydrologic (ice-sheet changes) and carbon (biogeochemical changes) cycles, posing the question whether the two processes are related. The present review shows that the long-eccentricity cycles prevail throughout the δ13C and other biogeochemical records in geologic history, and 400-kyr cycles in the oceanic δ13C sequence before the Quaternary can be hypothetically explained by changes in ratio between particulate and dissolved organic carbon (POC/DOC) in the ocean, depending on the monsoon-controlled nutrient supply. This is a ‘DOC hypothesis’. However, ocean restructuring at 1.6 Ma marked by the isolation of a sluggish abyss under the Southern Ocean has obscured the long-eccentricity 400-kyr signal in oceanic δ13C. The last million-year period has experienced two major changes in the climate regime, namely the mid-Pleistocene transition (MPT) centered at 0.9 Ma and the mid-Brunhes event (MBE) around 0.4 Ma. The MPT and MBE were preluded by δ13C maxima-III (δ13Cmax-III) ∼ 1.0 Ma and δ13Cmax-II ∼ 0.5 Ma, respectively. Together with similar hydroclimatic phenomena over corresponding glacial cycles, the two groups of hydrologic and biogeochemical events appear to have been driven largely by oceanographic changes in the Southern Ocean. Therefore, we interpret that the long-term biogeochemical processes originating from the Southern Ocean must have played a crucial role in Quaternary ice-sheet waxing and waning.

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Owen, R. Bernhart, Veronica M. Muiruri, Tim K. Lowenstein, Robin W. Renaut, Nathan Rabideaux, Shangde Luo, Alan L. Deino, et al. "Progressive aridification in East Africa over the last half million years and implications for human evolution." Proceedings of the National Academy of Sciences 115, no. 44 (October 8, 2018): 11174–79. http://dx.doi.org/10.1073/pnas.1801357115.

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Evidence for Quaternary climate change in East Africa has been derived from outcrops on land and lake cores and from marine dust, leaf wax, and pollen records. These data have previously been used to evaluate the impact of climate change on hominin evolution, but correlations have proved to be difficult, given poor data continuity and the great distances between marine cores and terrestrial basins where fossil evidence is located. Here, we present continental coring evidence for progressive aridification since about 575 thousand years before present (ka), based on Lake Magadi (Kenya) sediments. This long-term drying trend was interrupted by many wet–dry cycles, with the greatest variability developing during times of high eccentricity-modulated precession. Intense aridification apparent in the Magadi record took place between 525 and 400 ka, with relatively persistent arid conditions after 350 ka and through to the present. Arid conditions in the Magadi Basin coincide with the Mid-Brunhes Event and overlap with mammalian extinctions in the South Kenya Rift between 500 and 400 ka. The 525 to 400 ka arid phase developed in the South Kenya Rift between the period when the last Acheulean tools are reported (at about 500 ka) and before the appearance of Middle Stone Age artifacts (by about 320 ka). Our data suggest that increasing Middle- to Late-Pleistocene aridification and environmental variability may have been drivers in the physical and cultural evolution of Homo sapiens in East Africa.

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Bouttes, Nathaelle, Didier Swingedouw, Didier M. Roche, Maria F. Sanchez-Goni, and Xavier Crosta. "Response of the carbon cycle in an intermediate complexity model to the different climate configurations of the last nine interglacials." Climate of the Past 14, no. 2 (March 2, 2018): 239–53. http://dx.doi.org/10.5194/cp-14-239-2018.

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Abstract. Atmospheric CO2 levels during interglacials prior to the Mid-Brunhes Event (MBE, ∼ 430 ka BP) were around 40 ppm lower than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to different external forcings before and after the MBE, might have increased the ocean carbon storage in pre-MBE interglacials, thus lowering atmospheric CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings, ice sheet configurations and atmospheric CO2 concentrations over the last nine interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few parts per million. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 levels are lower during these pre-MBE simulated interglacials including all these effects, but the magnitude is still far too small. These results suggest a possible misrepresentation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, to fully account for the lower atmospheric CO2 concentrations during pre-MBE interglacials.

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Cronin, T. M., G. S. Dwyer, E. K. Caverly, J. Farmer, L. H. DeNinno, J. Rodriguez-Lazaro, and L. Gemery. "Enhanced Arctic Amplification Began at the Mid-Brunhes Event ~400,000 years ago." Scientific Reports 7, no. 1 (November 3, 2017). http://dx.doi.org/10.1038/s41598-017-13821-2.

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Journal articles on the topic 'Mid-Brunhes event'

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