Climate of The Past最新文献

{"title":"Climate influences on sea salt variability at Mount Brown South, East Antarctica","authors":"Helen J. Shea, Ailie Gallant, Ariaan Purich, Tessa R. Vance","doi":"10.5194/egusphere-2024-2660","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2660","url":null,"abstract":"<strong>Abstract.</strong> The Mount Brown South (MBS) ice core in East Antarctica (69° S, 86° E) has produced records of sea salt concentration and snow accumulation for examining past climate. In a previous study, the sea salt concentration, but not snow accumulation, showed a significant, positive relationship with the El Niño-Southern Oscillation (ENSO) from June to November. Here, we use observations and reanalysis data to provide insights into the mechanisms modulating this previously identified relationship for the austral winter season (June-August). A teleconnection between the tropical Pacific and high-latitude winds in the vicinity of MBS is identified. Specifically, El Niño events are related to strengthened westerly winds ∼60° S, leading to more local sea ice via anomalous Ekman transport in an area to the northeast of the MBS site. Impacts from La Niña are less obvious, showing that there is a non-linear component to this relationship. MBS is a wet deposition site, and we show that sea salt is likely transported from northeast of MBS via synoptic-scale storms that accompany high precipitation events. These storms and their associated precipitation, show no substantial differences between years of high and low sea salt concentration, so we suggest it is the source of sea salt that differs, rather than the transport mechanism. El Niño-associated strengthened westerly winds in the MBS region could enhance sea salt availability by increasing ocean aerosol spray and/or by increasing sea ice formation, both of which can act as sources of sea salt. This may explain why sea salt concentration, rather than snow accumulation, is most closely related to ENSO variability in the ice core record. Identifying the mechanisms modulating key variables such as sea salts and snow accumulation at ice core sites provides further insights into what these valuable records can decipher about climate variability in the pre-instrumental period.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"10 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254018","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pattern scaling of simulated vegetation change in North Africa during glacial cycles","authors":"Mateo Duque-Villegas, Martin Claussen, Thomas Kleinen, Jürgen Bader, Christian H. Reick","doi":"10.5194/cp-2024-61","DOIUrl":"https://doi.org/10.5194/cp-2024-61","url":null,"abstract":"<strong>Abstract.</strong> Over the last hundreds of millennia natural rhythms in Earth's astronomical motions triggered large-scale climate changes and led periodically to humid conditions in much of North Africa. Known as African humid periods (AHPs), such times sustained river networks, vegetation, wildlife and prehistoric settlements. Mechanisms, extent and timing of the changes still cannot be completely outlined. Although AHPs along glacial cycles are recognizable in long marine sediment records, the related land cover changes are difficult to reconstruct due to scarcity of proxy data over the continent. Moreover, most available information covers only the latest AHP during the Holocene. Here we use a comprehensive Earth system model to look at additional, much earlier, possible cases of AHPs. We simulate the full last glacial cycle, aiming to reproduce the last four AHPs as seen in available proxies. The simulated AHPs seem in broad agreement with geological records, especially in terms of timing and relative strength. We focus on the simulated vegetation coverage in North Africa and we detect a dominant change pattern that seems to scale linearly with known climate forcing variables. We use such scaling to approximate North African vegetation fractions over the last eight glacial cycles. Although the simple linear estimation is based on a single mode of vegetation variability (that explains about 70 % of the variance), it helps to discuss some broad-scale spatial features that had been only considered for the Holocene AHP. Extending the climate simulation several millennia into the future reveals that such pattern scaling breaks when greenhouse gases become a stronger climate change driver.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"18 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Southern Ocean marine ice record of the early historical, circum-Antarctic voyages of Cook and Bellingshausen","authors":"Grant R. Bigg","doi":"10.5194/cp-20-2045-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2045-2024","url":null,"abstract":"Abstract. The circumnavigations of Cook (second voyage, 1772–1775) and Bellingshausen (1819–1821) were attempts to find any great southern land mass poleward of ∼ 50° S and consequently involved sailing for three or two summers, respectively, in polar latitudes around Antarctica. Extensive sea ice eventually blocked each voyage's southern probes, although Bellingshausen, unknowingly at the time, saw the Antarctic continent. However, these attempts meant sea ice and iceberg records from the early historical period were collected nearly simultaneously from around much of Antarctica. Here, these records are extracted from journals, analysed, and compared to each other and the modern satellite record of both forms of marine ice. They generally show an early historical period with a more northerly record of both forms of marine ice than normal for today, but to a geographically varying degree. However, the early historical period in the Pacific sector of the Southern Ocean saw marine ice generally within the range of modern observations for the same time of year, but the Weddell Sea and Indian Ocean marine ice, particularly on Cook's voyage, then extended several degrees further north than in today's extreme ice years.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"313 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Environmental controls of rapid terrestrial organic matter mobilization to the western Laptev Sea since the last deglaciation","authors":"Tsai-Wen Lin, Tommaso Tesi, Jens Hefter, Hendrik Grotheer, Jutta Wollenburg, Florian Adolphi, Henning Bauch, Alessio Nogarotto, Juliane Müller, Gesine Mollenhauer","doi":"10.5194/cp-2024-60","DOIUrl":"https://doi.org/10.5194/cp-2024-60","url":null,"abstract":"<strong>Abstract.</strong> Arctic permafrost stores vast amounts of terrestrial organic matter (terrOM). Under warming climate conditions, Arctic permafrost thaws, releasing aged carbon and potentially impacting the modern carbon cycle. We investigated the characteristics of terrestrial biomarkers, including <em>n</em>-alkanes, fatty acids, and lignin phenols, in marine sediment cores to understand how the sources of terrOM transported to the ocean change in response to varying environmental conditions such as sea-level rise, sea ice coverage, inland climate warming, and freshwater input. We examined two sediment records from the western Laptev Sea (PS51/154 and PS51/159) covering the past 17.8 kyr. Our analyses reveal three periods with high mass accumulation rates (MARs) of terrestrial biomarkers, from 14.1 to 13.2, 11.6 to 10.9, and 10.9 to 9.5 kyr BP. These MAR peaks revealed distinct terrOM sources, likely in response to changes in shelf topography, rates of sea-level rise, and inland warming. By comparing periods of high terrOM MAR in the Laptev Sea with published records from other Arctic marginal seas, we suggest that enhanced coastal erosion driven by rapid sea-level rise during meltwater pulse 1A (mwp-1A) triggered elevated terrOM MAR across the Arctic. Additional terrOM MAR peaks coincided with periods of enhanced inland warming, prolonged ice-free conditions, and freshwater flooding, which varied between regions. Our results highlight regional environmental controls on terrOM sources, which can either facilitate or preclude regional terrOM fluxes in addition to global controls.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"17 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Simulated ocean oxygenation during the interglacials MIS 5e and MIS 9e","authors":"Bartholomé Duboc, Katrin J. Meissner, Laurie Menviel, Nicholas K. H. Yeung, Babette Hoogakker, Tilo Ziehn, Matthew Chamberlain","doi":"10.5194/egusphere-2024-2675","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2675","url":null,"abstract":"<strong>Abstract.</strong> Recent studies investigating future warming scenarios have shown that the ocean oxygen content will continue to decrease over the coming century due to ocean warming and changes in oceanic circulation. However, significant uncertainties remain regarding the magnitude and patterns of future ocean deoxygenation. Here, we simulate ocean oxygenation with the ACCESS ESM1.5 model during two past interglacials that were warmer than the preindustrial climate, the Last Interglacial (Marine Isotope Stage (MIS) 5e, ~ 129–115 ka) and MIS 9e (~ 336–321 ka). While orbital parameters were similar during MIS 5e and MIS 9e, with lower precession, higher eccentricity and higher obliquity than pre-industrial, greenhouse gas radiative forcing was highest during MIS 9e. We find that the global ocean is overall less oxygenated in the MIS 5e and MIS 9e simulations compared to the preindustrial control run and that oxygen concentrations are more sensitive to changes in the distribution of incoming solar radiation than to differences in greenhouse gas concentrations. Large regions in the Mediterranean Sea are hypoxic in the MIS 5e simulation, and to a lesser extent in the MIS 9e simulation, due to an intensification and expansion of the African Monsoon, enhanced river run-off and resulting freshening of surface waters and stratification. Upwelling zones off the coast of North America and North Africa are weaker in both simulations compared to the preindustrial control run, leading to less primary productivity and export production. Antarctic Bottom Water is less oxygenated, while North Atlantic Deep Water and the North Pacific Ocean at intermediate depths are higher in oxygen content. All changes in oxygen concentrations are primarily caused by changes in ocean circulation and export production and secondarily by changes in temperature and solubility.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"240 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Contrasting responses of summer precipitation to orbital forcing in Japan and China over the past 450 kyr","authors":"Taiga Matsushita, Mariko Harada, Hiroaki Ueda, Takeshi Nakagawa, Yoshimi Kubota, Yoshiaki Suzuki, Youichi Kamae","doi":"10.5194/cp-20-2017-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2017-2024","url":null,"abstract":"Abstract. Understanding orbital-scale changes in East Asian summer monsoon (EASM) precipitation is a fundamental issue in paleoclimate research as it helps assess the response of the East Asian monsoon to different climatic forcings, such as insolation, ice volume, and greenhouse gases. However, due to inconsistencies between different proxies, the fundamental driving force for EASM variability remains controversial. The present study simulated the global climate under given insolation changes over the past 450 kyr using a climate model, version 2.3 of the Meteorological Research Institute's Coupled General Circulation Model (MRI-CGCM2.3). Changes in summer insolation over East Asia resulted in distinct climatic responses in China and Japan: an increase in summer insolation led to increased summer precipitation in China and decreased summer precipitation in Japan. Composite analyses of simulated climate under strong boreal-summer insolation suggest that warming of the Indian Ocean occurs under intense insolation, resulting in the intensification of the North Pacific subtropical high (sub-high). The northern shift in the monsoon front, associated with the intensified sub-high, leads to an increase in rainfall in the coastal area of China. In contrast, the intensity of the EASM around Japan is affected by the strength of the North Pacific High. Under strong insolation, the increase in thermal contrast between the North American continent and the North Pacific Ocean intensifies the North Pacific High, decreasing summer precipitation around Japan. Thus, strong regional differences in the effects of solar-insolation variability on summer precipitation in East Asia exist due to interactions with different ocean basins.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"13 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New estimates of sulfate diffusion rates in the EPICA Dome C ice core","authors":"Rachael H. Rhodes, Yvan Bollet-Quivogne, Piers Barnes, Mirko Severi, Eric W. Wolff","doi":"10.5194/cp-20-2031-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2031-2024","url":null,"abstract":"Abstract. To extract climatically relevant chemical signals from the deepest, oldest Antarctic ice, we must first investigate the degree to which chemical ions diffuse within solid ice. Volcanic sulfate peaks are an ideal target for such an investigation because they are high-amplitude, short-duration (∼3 years) events with a quasi-uniform structure. Here we present an analysis of the EPICA Dome C sulfate record over the last 450 kyr. We identify volcanic peaks and isolate them from the non-sea-salt sulfate background to reveal the effects of diffusion: amplitude damping and broadening of peaks in the time domain with increasing depth and age. Sulfate peak shape is also altered by the thinning of ice layers with depth that results from ice flow. Both processes must be simulated to derive effective diffusion rates. This is achieved by running a forward model to diffuse idealised sulfate peaks at different rates while also accounting for ice thinning. Our simulations suggest a median effective diffusion rate of sulfate ions of 2.4±1.7×10-7 m2 yr−1 in Holocene ice, slightly faster than suggested by previous work. The effective diffusion rate observed in deeper ice is significantly lower, and Holocene ice shows the highest rate of the last 450 kyr. Beyond the Holocene, there is no systematic difference between the effective diffusion rates of glacial and interglacial periods despite variations in soluble ion concentrations, dust loading, and ice grain radii. Effective diffusion rates for 40 to 200 ka are relatively constant and of the order 1×10-8 m2 yr−1. Our results suggest that the diffusion of sulfate ions within volcanic peaks is relatively fast initially, perhaps through an interconnected vein network, but slows significantly after 40 kyr. In the absence of clear evidence for a controlling influence of temperature on sulfate diffusivity with depth and age, we hypothesise that the rapid decrease in effective diffusion rate from the time of deposition to ice of 50 ka age may be due to a switch in the mechanism of diffusion resulting from the changing location of sulfate ions within the ice microstructure and/or interconnectedness of veins and grain boundaries.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"16 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Glacial AMOC shoaling despite vigorous tidal dissipation: vertical stratification matters","authors":"Yugeng Chen, Pengyang Song, Xianyao Chen, Gerrit Lohmann","doi":"10.5194/cp-20-2001-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2001-2024","url":null,"abstract":"Abstract. During the Last Glacial Maximum (LGM), tidal dissipation was about 3-fold higher than today, which could have led to a considerable increase in vertical mixing. This increase might have enhanced the glacial Atlantic Meridional Overturning Circulation (AMOC), contradicting the shoaled AMOC indicated by paleoproxies. Here, we conduct ocean model simulations to investigate the impact of background climate conditions and tidal mixing on the AMOC during the LGM. We successfully reproduce the stratified ocean characteristics of the LGM by accurately simulating the elevated salinity of the deep sea and the rapid temperature decrease in the ocean's upper layers. Our findings indicate that the shoaled glacial AMOC is mainly due to strong glacial-ocean stratification, regardless of enhanced tidal dissipation. However, glacial tidal dissipation plays a critical role in the intensification of Antarctic Bottom Water (AABW) during the LGM. Given the critical role of the AMOC in (de-)glacial climate evolution, our results highlight the complex interactions of ocean stratification and tidal dissipation that have been neglected so far.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"14 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Can we reliably reconstruct the mid-Pliocene Warm Period with sparse data and uncertain models?","authors":"James D. Annan, Julia C. Hargreaves, Thorsten Mauritsen, Erin McClymont, Sze Ling Ho","doi":"10.5194/cp-20-1989-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1989-2024","url":null,"abstract":"Abstract. We present a reconstruction of the surface climate of the mid-Pliocene Warm Period (mPWP), specifically Marine Isotope Stage (MIS) KM5c or 3.205 Ma. We combine the ensemble of climate model simulations, which contributed to the Pliocene Model Intercomparison Project (PlioMIP), with compilations of proxy data analyses of sea surface temperature (SST). The different data sets we considered are all sparse with high uncertainty, and the best estimate of annual global mean surface air temperature (SAT) anomaly varies from 2.1 up to 4.8 °C depending on the data source. We argue that the latest PlioVAR analysis of alkenone data is likely more reliable than other data sets we consider, and using this data set yields an SAT anomaly of 3.9±1.1 °C, with a value of 2.8±0.9 °C for SST (all uncertainties are quoted at 1 standard deviation). However, depending on the application, it may be advisable to consider the broader range arising from the various data sets to account for structural uncertainty. The regional-scale information in the reconstruction may not be reliable as it is largely based on the patterns simulated by the models.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"51 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190491","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The climate and vegetation of Europe, northern Africa, and the Middle East during the Last Glacial Maximum (21 000 yr BP) based on pollen data","authors":"Basil A. S. Davis, Marc Fasel, Jed O. Kaplan, Emmanuele Russo, Ariane Burke","doi":"10.5194/cp-20-1939-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1939-2024","url":null,"abstract":"Abstract. Pollen data represent one of the most widely available and spatially resolved sources of information about the past land cover and climate of the Last Glacial Maximum (LGM; 21 000 yr BP). Previous pollen data compilations for Europe, the Mediterranean, and the Middle East, however, have been limited by small numbers of sites and poor dating control. Here we present a new compilation of pollen data from the region that improves on both the number of sites (63) and the quality of the chronological control. Data were sourced from both public data archives and published (digitized) diagrams. The analysis is presented based on a standardized pollen taxonomy and sum, with maps shown for the major pollen taxa and biomes and the total arboreal pollen (AP), and on quantitative reconstructions of forest cover and of winter, summer, and annual temperatures and precipitation. The reconstructions are based on the modern analogue technique (MAT) adapted using plant functional type (PFT) scores and with a modern pollen dataset taken from the latest Eurasian Modern Pollen Database (EMPD) (∼8000 samples). A site-by-site comparison of the MAT and the inverse modelling method shows little or no significant difference between the methods for the LGM, indicating that the presence of low-CO2 conditions and no modern analogue during the LGM does not appear to have had a major effect on MAT transfer function performance. Previous pollen-based climate reconstructions using modern pollen datasets show a much colder and drier climate for the LGM than both inverse modelling and climate model simulations do, but our new results suggest much greater agreement. Differences between our latest MAT reconstruction and those in earlier studies can largely be attributed to bias in the small modern dataset previously used and to differences in the method itself (Brewer et al., 2008; Salonen et al., 2019). We also find that quantitative forest cover reconstructions show more forest than previously suggested by biome reconstructions but less forest than suggested by simply the percentage of arboreal pollen, although uncertainties remain large. Overall, we find that LGM climatic cooling and drying were significantly greater in winter than in summer but with large site-to-site variance that emphasizes the importance of topography and other local factors in controlling the climate and vegetation of the LGM.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"9 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}