CL1.1.3

Examination of the palaeoclimate record of the last 800 kyr has revealed a large diversity among interglacials in terms of their duration, structure and intensity.  Interglacials may be classified as either short (mean duration 13 kyr) or long (mean duration 28 kyr).  The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks: the longest interglacials are characterized by the obliquity peak lagging the first precession minimum by 10±2 kyr and leading the second precession minimum by a similar amount; thus the first boreal summer insolation minimum occurs at the time of maximum obliquity, which overrides the increase in precession and prevents glacial inception associated with a decline in summer insolation.  The phasing of precession and obliquity also determines the structure of an interglacial, leading to two main categories: (1) shorter interglacials characterized by rapid deglaciation and an early temperature optimum, usually followed by a decline; and (2) longer interglacials characterized by protracted deglaciation and the persistence of interglacial values over two insolation peaks, with the interglacial peak occurring in the second insolation maximum.  With respect to intensity, a broad feature is that interglacials before the Mid-Brunhes Event (MBE; 430 ka) appear weaker (cooler, higher δ¹⁸O_benthic, atmospheric CO₂ lower than pre-industrial concentrations).  The strongest interglacials occurred after the MBE, although MIS7e and MIS7c-a are closer in intensity to pre-MBE interglacials.  Of particular interest is MIS 11c, one of the most unusual Quaternary interglacials.  Its features include: (i) a high sea-level highstand attained under modest insolation forcing; (ii) a long duration extending over two insolation peaks; (iii) persistence of relatively stable atmospheric CO₂ concentrations, remaining in the range 270-282 ppm for a 24 kyr period; and (iv) a decoupling between high CO₂ and high sea level in the early part of the interglacial that is unique in the last 800 kyr.  Although some of these features are also encountered in other interglacials, their combination with strong interglacial intensity is unique to MIS 11c and appears to be a function of the high CO₂concentrations from the beginning of the interglacial.

How to cite: Tzedakis, C., Hodell, D., Nehrbass-Ahles, C., and Wolff, E.: All interglacials are different, but some are more different than others, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2443, https://doi.org/10.5194/egusphere-egu22-2443, 2022.

Interglacials older than 450,000 years ago (ka) are still poorly documented at regional and global scale limiting our knowledge of the wide range of their potential variability and the understanding of the causes of such diversity. Here we present δ¹⁸O benthic foraminifera measurements along with sea surface temperature reconstructions and pollen data from IODP site U1385, collected during Expedition 339 « Mediterranean Outflow » on the southwestern Iberian margin, for the Early-Middle Pleistocene interglacials MIS 19, 17, 15 and 13 (~800 to 400 ka). The recorded vegetation and climate changes on land have been directly compared with changes in the eastern North Atlantic subtropical gyre and the global ice volume. This comparison reveals a different structure in the evolution of the Mediterranean forest during these interglacials. The highest forest development occurred during MIS 19e and 15e but in the middle part of MIS 13 (MIS 13c). In contrast with MIS 19, 15 and 13 marked by three more or less similar Mediterranean forest expansions, MIS 17 was characterised by one strong expansion in its middle part (MIS 17c), the strongest of the last 800,000 years, occurring just before the end of the Middle Pleistocene Transition, i.e. the establishment of the strong 100-kyr glacial cycles at ~700 ka.  The duration of the first forested phase was also variable depending on the interglacial with a length of ~12,000 years during MIS 19e and 15e, ~9,000 years for MIS 13c and as long as 16,000 years for MIS 17c. Interestingly, two Mediterranean forest expansions are recorded during two phases of ice growth, MIS 19b and 15b, indicating once more the decoupling between the evolution of global ice volume and the southern European environments. The comparison of the U1385 pollen record, located below 40°N, with sequences above 40°N, for example the Lake Orhid pollen record, shows that the structure and magnitude of the interglacials are different below and above this latitude. At Montalbano Jonico, southern Italy at 40°N, the forest expansion is also very strong (80%) during MIS 17 contrasting with the limited development in Lake Orhid. At this site, MIS 19 is further marked by a strong forest development contrasting with the limited expansion of the Mediterranean forest in SW Iberia.

How to cite: Sanchez Goñi, M. F., Oliveira, D., Morales-Molino, C., Desprat, S., Polanco-Martinez, J. M., Hodell, D., Naughton, F., and Rodrigues, T.: The Early-Middle Pleistocene interglacials in the Iberian margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3148, https://doi.org/10.5194/egusphere-egu22-3148, 2022.

Numerous studies have been made on paleoclimate and paleovegetation reconstructions and simulations of the past interglacials. However, systematical analysis of the global patterns of the correlation between vegetation pattern and astronomical forcing as well as CO₂ between different interglacials is rare. Given the distinct differences in orbital configurations and climate/vegetation variations between MIS-11 and MIS-13, we performed two sets of transient simulations using LOVECLIM 1.3, one driven by insolation change only, and another one by changes in both insolation and CO₂. These simulations allow us to investigate the relative effect of astronomical forcing and CO₂ on global and regional vegetation changes during these two interglacials. Our results show that the effects of precession and obliquity on vegetation depend strongly on regions, and the simulated results are in good agreement with vegetation reconstructions at key regions. The vegetation response differs widely between MIS-11and MIS-13, which is mainly caused by the difference in their astronomical configurations, and the difference in CO₂ concentration between these two interglacials plays a minor role. In addition to the effect of precession and obliquity, our simulations are also able to capture the half precession signal (~ 10 ka) in the climate and vegetation changes in the tropical regions in response to the tropical insolation.

How to cite: Su, Q., Lyu, A., Wu, Z., and Yin, Q.: Diverse manifestations of the impact of astronomical forcing and CO2 on climate and vegetation changes during MIS-11 and MIS-13, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4354, https://doi.org/10.5194/egusphere-egu22-4354, 2022.

The climate system experienced several periodic oscillations over the last ca. 800 ka known as glacial-interglacial (G-IG) cycles. Disruptions of the global carbon cycle were evident on this time scale, promoting fluctuations in the atmospheric CO₂ concentration leading to global climate variability. In the more recent interglacials, both Antarctic temperatures and atmospheric CO₂ concentrations are significantly higher than in the previous “lukewarm interglacials” (ca. 800 – 430 ka) before the Mid-Brunhes Transition (MBT). Changes in the Atlantic Meridional Overturning Circulation (AMOC) and deepwater formation rate around Antarctica have been invoked to explain a 30 ppm increase in the atmospheric CO₂ ­during post-MBT interglacial periods. Deepwater variability is tightly coupled to the ventilation of CO₂ in the Southern Ocean by atmospheric and oceanic connections, contributing to carbon storage in the deep ocean and the atmospheric CO₂. Here, we present a new 770 ka benthic foraminifera δ¹³C record from sediment core GL-854 retrieved from the western South Atlantic (WSA) at 2200 m water depth. We compare our record with published δ¹³C data from the eastern margin to investigate the zonal gradient variability of the North Atlantic Deep Water (NADW) in the deep South Atlantic basin. WSA δ¹³C variability and absolute values strongly mimic the North Atlantic mid-depth record at the NADW formation region. This similarity is interpreted as NADW preferentially carrying a modified signal through the deep western boundary current towards the WSA (rather than towards the eastern margin) after the MBT. The δ¹³C gradient based on the difference between benthic foraminifera C. wuellerstorfi from both margins (Δδ¹³C_w-e) gradually increases after a transitional period between ca. 400 ka to 300 ka towards the Holocene. We suggest that the mechanism behind this long-term increasing trend on the Δδ¹³C_w-e record post-MBT is the result of enhanced production of North Component Water due to Agulhas Leakage intensification driven by reduced sea-ice extent after the MBT. Furthermore, reduced sea-ice extent decreases the Antarctic Bottom Water density and formation in the Southern Ocean, contributing to the deepening of the AMOC during post-MBT interglacial periods. Our interpretation proposes a framework connecting sea-ice and ocean-atmosphere dynamics to deepwater geometry within the South Atlantic basin, which ultimately contributed to the climate change observed across the MBT.

How to cite: Ballalai, J., Santos, T., Nascimento, R., Venancio, I., Piacsek, P., Dias, B., Belem, A., Costa, K., Vázquez Riveiros, N., and Albuquerque, A. L.: Increased zonal δ13C gradient in the deep South Atlantic after the Mid-Brunhes Transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8018, https://doi.org/10.5194/egusphere-egu22-8018, 2022.

Interglacial intensity in past 800 kyr is characterized by a transition, about 430 kyr ago, between the older ones, which were relatively cool and low sea level, and the more recent ones, which were relatively warm and high sea level. This transition, as identified in Antarctic ice core and benthic calcite d¹⁸Oc records, corresponds to the so-called mid-Brunhes Transition (MBT). However, its origin and underlying dynamics remain elusive. Here we show, based on a start-of-art, stable water isotope enabled climate model, that additional ice volume to the present-day levels should be considered in order to reproduce the systematic enrichment in interglacial d¹⁸Oc before the MBT. This extra ice of ~18 e.s.l.m. likely exists in the Antarctic, which in turn weakens vertical mixing in Southern Ocean, potentially accounting for the low interglacial atmospheric CO₂ levels prior to the MBT. Our results further indicate that during MIS11c the unique climate background leads to extra Antarctic ice sheet melting, eventually giving rise to a systematic change in interglacial climate and hence accounting for the MBT.

How to cite: Zhang, X., Barker, S., Werner, M., Sun, Y., and Tzedakis, C.: Mid-Brunhes Transition caused by Antarctic ice sheet melting during MIS11c, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13443, https://doi.org/10.5194/egusphere-egu22-13443, 2022.

Marine oxygen isotope records and ice cores in Antarctica suggest that Marine Isotope Stage (MIS) 9, an interglacial occurring about 300 ka ago, is a strong interglacial and has the highest greenhouse gases (GHG) concentrations during the past 800 ka. Model results also show that MIS-9 is the warmest interglacial among the last nine ones as a result of both its high CO₂ concentration and its high summer insolation in the northern Hemisphere (NH). However, the China loess records show that the paleosol S3 that corresponds to MIS-9 is not necessarily strong as compared to some other paleosol units such as the S4 soil that was formed during MIS-11, suggesting relatively drier climate condition during MIS-9. By contrast, in Tajikistan of southern central Asia, the paleosol S3 is the most developed soil over the past 800 ka, indicating a relatively warm and humid climate conditions. The difference in the paleosol formation and the MIS-9 climate between monsoonal China and central Asia is intriguing. In this study, we combine loess records from monsoonal China and central Asia as well as climate simulation results to understand the spatial difference of the MIS-9 climate in particular in comparison with the climate of MIS-11. The individual and combined contributions of insolation and greenhouse gases are quantified through simulations with the LOVECLIM model and using the factor separation technique. Our results show that the simulated effective moisture conditions between northern China and southern central Asia are consistent with the loess records and field observation. Insolation leads to much more annual mean precipitation than GHG during MIS-9 in southern central Asia, explaining a much wetter MIS-9 there. By contrast, both insolation and GHG lead to more annual mean precipitation and evaporation during MIS-9 in northern China, leading to only a slight difference in the effective moisture between MIS-9 and MIS-11. In addition, compared to MIS-11, the larger obliquity and higher GHG concentration during MIS-9 lead to an anomalous atmospheric circulation pattern similar to negative phase of North Atlantic Oscillation (NAO), favoring precipitation increase in southern central Asia and therefore explain strong soil development in Tajikistan.

How to cite: Lu, H., Yin, Q., Wu, Z., Shi, F., Hao, Q., Xia, D., and Guo, Z.: Impacts of insolation and CO2 on the spatial differences of the MIS-9 and MIS-11 climate between monsoonal China and central Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13117, https://doi.org/10.5194/egusphere-egu22-13117, 2022.

Past interglacials allow investigating the climatic processes and associated feedbacks during warm periods, which are characterized by different combinations of climatic forcing such as solar radiation, GHGs, and ice sheets. Arctic warming amplification, a common phenomenon between past interglacials and present warming, has seasonality in its feedback mechanism, and detailed study of these internal feedbacks is still lacking despite its global impact. In this study, the simulation experiments under conditions close to the past interglacial periods (MIS1; Holocene, MIS5e; Last Interglacial, and MIS11) are conducted using a coupled atmosphere-ocean-vegetation model MIROC (4m) AOVGCM, particularly focusing on the role of ice sheets and Arctic sea ice. Climate responses to inputs and conditions are compared to examine the seasonal effects of atmosphere-ocean-ice feedbacks on Northern hemisphere high-latitudes temperature. Ice sheet distribution is set as a boundary condition in addition to the orbital elements, land cover, and GHGs to account the effect of remaining ice sheets at the timing of peak insolation. Feedback Analysis is also conducted to quantify the contribution of each feedback element to the surface temperature change. It is demonstrated that an inter-seasonal effect of air-sea-ice-vegetation feedbacks contributes to Arctic warming amplification, where heat gained in summer is used for sea ice melting and ocean absorption, and is released in autumn and winter, resulting in annual warming. This process is amplified when considering vegetation feedbacks and seen commonly in MIS1, 5e, and 11. In periods when ice sheets remain, Arctic sea ice keeps a high degree of concentration in summer, and annual mean temperatures at Northern high latitudes are lower than would be expected from insolation intensity. These results imply that the presence of Northern hemisphere ice sheet has a significant effect on Arctic climate response to insolation intensity by suppressing feedbacks that contribute to Arctic amplification through the reduced melt of summer sea ice.

How to cite: Hirose, L., Abe-Ouchi, A., Yoshimori, M., Chan, W.-L., O'ishi, R., and Obase, T.: Arctic Amplification through Inter-seasonal Feedback Effect in Past Interglacials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12943, https://doi.org/10.5194/egusphere-egu22-12943, 2022.

Understanding the sea ice variability and the mechanisms involved during warm periods of the Earth is essential for a better understanding of the sea ice changes at the present and in the future. Based on simulations with the model LOVECLIM, this study investigates the sea ice variations during the last nine interglacials and focuses on the inter-comparison between interglacials as well as their differences from the present and future. Our results show that, for the double CO₂ experiment and the Shared Socioeconomic Pathway (SSP)1-2.6, SSP2-4.5 and SSP5-8.5 scenario experiments, the global, Arctic and Southern Ocean sea ice areas simulated by LOVECLIM all fall in the range of the multi-model results from CMIP 6. In addition, the results show that the annual mean Arctic sea ice variation is primarily controlled by local summer insolation, while the annual mean Southern Ocean sea ice variation is more influenced by the CO₂ concentration but the effect of local summer insolation can’t be ignored. The lowest Arctic sea ice area results from the highest summer insolation at MIS-15, and the lowest Southern Ocean sea ice area at MIS-9 is explained by the highest CO₂ concentration and moderate local summer insolation. As compared to the present, the last nine interglacials all have much less sea ice in the Arctic annually and seasonally due to high summer insolation. They also have much less Arctic sea ice in summer than the double CO₂ experiment, which makes to some degree the interglacials possible analogues for the future in terms of the changes of sea ice. However, compared to the double CO₂ experiment, the interglacials all have much more sea ice in the Southern Ocean due to their much lower CO₂ concentration, which suggests the inappropriateness of considering the interglacials as analogues for the future in the Southern Ocean. Our results suggest that in the search for potential analogues of the present and future climate, the seasonal and regional climate variations should be considered.

Reference: Zhipeng Wu, Qiuzhen Yin, Zhengtang Guo, André Berger, 2022. Comparison of Arctic and Southern Ocean sea ice between the last nine interglacials and the future. Climate Dynamics, accepted.

How to cite: Wu, Z., Yin, Q., Guo, Z., and Berger, A.: Comparison of Arctic and Southern Ocean sea ice between the last nine interglacials and the future, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3087, https://doi.org/10.5194/egusphere-egu22-3087, 2022.

Marine Isotope Stage (MIS) 5, between about 130 and 70 ka BP, is a relatively long warm period characterized by climate oscillations consisting of three interstadials and two stadials. In this study, two sets of snapshot simulations by a step of 2 ka covering the whole MIS-5 period are performed with the model HadCM3 to investigate the relative impacts of insolation, CO₂ and Northern Hemisphere ice sheets on the internal variations within MIS-5 and spatial variations of the East Asian climate, including the East Asian summer monsoon (EASM) intensity. The first set of experiments are forced by varying insolation and GHGs (OrbGHG) and the second ones are forced by varying insolation, GHGs and ice sheets (OrbGHGIce). Results show that a similar trend with precession can be found in the simulated summer precipitation, temperature and EASM index in both OrbGHG and OrbGHGIce, indicating the dominant role of precession on the EASM. Within the range of CO₂ variability during MIS-5, the change of CO₂ causes similar degree of warming effect, but much lower degree of humidifying effect compared to insolation. Insolation and CO₂ change the precipitation through different dynamic and thermodynamic processes. Our results also show that the influence of ice sheets on temperature and precipitation is less important than the effect of insolation and it varies from regions and in time. The effect of ice sheets depends on background insolation and also the location, height and area of ice sheets. The simulated spatial-temporal variations of the EASM climate are compared with proxy records and the mechanisms involved are investigated. 

How to cite: Lyu, A. and Yin, Q.: The spatial-temporal patterns of East Asian climate in response to insolation, CO2 and ice sheets during MIS-5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2635, https://doi.org/10.5194/egusphere-egu22-2635, 2022.

The North Atlantic Oscillation (NAO) is currently the main mode of winter atmospheric variability in the extratropical Northern Hemisphere. It represents the fluctuation of the meridional sea-level pressure gradient in the North Atlantic, with high and low phases defined by high and low pressure gradients, respectively. High (or low) NAO phases are associated with wet and warm (or dry and cold) weather conditions in Northern Europe. In mid latitude regions such as the Mediterranean, this relationship is inverse, producing dry and cold (or wet and warm) conditions. Whether or not the average state of the NAO may have shifted in the past is much debated, with major implications for the understanding of past regional climate. Using a climate model, Felis et al. (2004) showed that the average state of the NAO during the Last Interglacial (130-115 ka BP) was significantly higher than during the pre-industrial period, with a high plateau from ~126 to 118 ka BP. However, proxy-based reconstructions of temperature and rainfall are needed to support this. Here, we use a new method, Brillouin spectroscopy on halite fluid inclusions, to reconstruct the evolution of temperature and hydrology in the Dead Sea, southern Levant, throughout the Last Interglacial. We find lower than modern Dead Sea temperatures and a lowering freshwater influx throughout the last interglacial. Using climate data from the recent decades, we demonstrate that the temperature of the Dead Sea hypolimnion mainly depends on winter air temperature, which is itself anti-correlated with the NAO. We also demonstrate that, during years of very high NAO, rainfall is drastically reduced in the lake catchment. In light of our analysis of modern climate data, the reconstructed cold and dry conditions in the Dead Sea area is consistent with the modelled higher NAO conditions.

How to cite: Guillerm, E., Gardien, V., Brall, N., Ariztegui, D., Schwab, M., Neugebauer, I., Waldmann, N., Lach, A., and Caupin, F.: Higher state of the North Atlantic Oscillation during the Last Interglacial (130-115 ka BP): evidence from temperature and hydrology in the Dead Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10148, https://doi.org/10.5194/egusphere-egu22-10148, 2022.

Investigating climate models responses and feedbacks under warmer climates is useful in building confidence in future climate projections. Here we focus on the summer sea ice in the Arctic during the Last Interglacial period (LIG), when the Arctic was warmer than the Pre-Industrial period (PI) by around 4.5 ± 1.7 K. Given that it is difficult to ascertain the state of Arctic sea ice from marine core proxies of sea ice state, we focus instead on summer surface air temperature (SSAT) in CMIP6-PMIP4 simulations and compare these with equivalent proxy data. All 12 models we have analysed show both warmer SSAT and a reduction in summer sea ice in the LIG compared to the PI, with an average warming of +3.6K and an average 52% decrease in minimum sea ice area.

We find that model-observation differences in LIG SSAT are linearly related to the percentage loss of summer Arctic sea ice. However this general finding does not fit the CNRM model result, which is an outlier. This simulation captures the observed pattern of SSAT, without being close to ice-free. However peculiarities in the CNRM set-up (forcing and sea ice model tuning) means it is unclear what can be drawn from this one result. CNRM aside, models tend to yield more accurate LIG SSAT changes when they are closer to an ice-free state in summer. The models which feature sea ice losses larger than the multi-model-mean sea ice loss, tend to have the smallest model-observation SSAT errors. The results of this study provides caveated support to the argument that Arctic could have been ice-free during LIG summers. That said, a careful examination of the SSAT dataset would also be value to the LIG community, given that these results are dependent on the LIG SSAT observational dataset.

How to cite: Sivankutty, R., Sime, L., Malmierca Vallet, I., and de Boer, A.: Summer Arctic temperatures in PMIP4 Last Interglacial simulations and their link to Arctic sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12679, https://doi.org/10.5194/egusphere-egu22-12679, 2022.