Comparison and Synthesis of Sea‐Level and Deep‐Sea Temperature Variations Over the Past 40 Million Years
Eelco J. RohlingGavin L. FosterThomas M. GernonKatharine GrantDavid HeslopFiona HibbertAndrew P. RobertsJimin Yu
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Abstract Global ice volume (sea level) and deep‐sea temperature are key measures of Earth's climatic state. We synthesize evidence for multi‐centennial to millennial ice‐volume and deep‐sea temperature variations over the past 40 million years, which encompass the early glaciation of Antarctica at ∼34 million years ago (Ma), the end of the Middle Miocene Climate Optimum, and the descent into bipolar glaciation from ∼3.4 Ma. We compare different sea‐level and deep‐water temperature reconstructions to build a resource for validating long‐term numerical model‐based approaches. We present: (a) a new template synthesis of ice‐volume and deep‐sea temperature variations for the past 5.3 million years; (b) an extended template for the interval between 5.3 and 40 Ma; and (c) a discussion of uncertainties and limitations. We highlight key issues associated with glacial state changes in the geological record from 40 Ma to present that require attention in further research. These include offsets between calibration‐sensitive versus thermodynamically guided deep‐sea paleothermometry proxy measurements; a conundrum related to the magnitudes of sea‐level and deep‐sea temperature change at the Eocene‐Oligocene transition at 34 Ma; a discrepancy in deep‐sea temperature levels during the Middle Miocene; and a hitherto unquantified non‐linear reduction of glacial deep‐sea temperatures through the past 3.4 million years toward a near‐freezing deep‐sea temperature asymptote, while sea level stepped down in a more uniform manner. Uncertainties in proxy‐based reconstructions hinder further distinction of “reality” among reconstructions. It seems more promising to further narrow this using three‐dimensional ice‐sheet models with realistic ice‐climate‐ocean‐topography‐lithosphere coupling, as computational capacities improve.Keywords:
Paleoclimatology
The past decade saw a surge in interest in the role of the Tropics in paleoclimate changes. This was motivated by the emergence of outstanding questions in paleoclimate that pointed to a role for the Tropics in addition to advances in tropical climate dynamics. This article reviews these developments, starting from a historical perspective. Three properties of tropical dynamics are prominent in paleoclimate: the sensitivity of the tropical climate to change; the ability of the tropical climate to reorganize; and the ability of the tropical climate to project its influence globally. The El Niño-Southern Oscillation (ENSO) system exemplifies these properties, making ENSO particularly prominent in paleoclimate. Summaries of three paleoclimate cases in which the science developed over the past decade—mid-Holocene ENSO, abrupt climate change during the most recent glacial period, and the mid-Pliocene permanent El Niño scenario—illustrate how the tropical hypothesis worked its way into paleoclimate research. This review closes with a discussion of prevailing views of the Tropics in the paleoclimate changes.
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Foreword Introduction Marine Biotic Indicators of Paleoclimate Continental Biotic Indicators of Paleoclimate Marine Lithologic Indicators of Paleoclimate Continental Lithologic Indicators of Paleoclimate Integrating Marine and Continental Paleoclimatic Records Models Case Histories of Paleoclimatic Studies
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Changes in the study of paleoclimate during the past 50 years can be demarcated by three revolutions. Plate tectonics was a major ("Kuhnian") revolution. Two smaller, but nevertheless significant, revolutions were the ocean-drilling revolution and the climate-model revolution. The history of paleoclimate studies shows, in general, an evolution from geographically and/or temporally focused studies in the pre-plate tectonics era, to development of paleoclimate proxies and studies of global climate patterns, to predominantly global studies in connection with paleoclimate modeling; the revolutions have been responsible for some of the shifts in focus. In the most recent decade, new questions posed by...
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Abstract Varied origins have the ability to construct the continental red beds, such as paleoclimate, provenance, drainage status, etc. Reconstructing paleoclimate is the key to investigate the origin. Thus, this paper outlines the normal distribution constrained method (NDCM) to reconstruct paleoclimate quantitatively and accurately during the lower fourth sub-member of Shahejie (Es4 x ) in the Bonan Sag, which is in low requirement of data and environmental conditions. Based on the NDCM, the paleoclimate is still in a long-term arid background as the potential evapotranspiration rates (PERs) are larger than 6 in the transgressive system tract (TST) and regressive system tract (RST) during the period of Es4 x . The decreasing PERs that range from 6.28 to 6.04, decreasing atmospheric temperature range from 14.37 to 13.95 °C and increasing mean precipitation of the wettest month and mean precipitation of the driest month indicate the paleoclimate is breaking away from the hot and arid background from TST to RST. Meanwhile, the paleoclimate fluctuation develops decreasing frequency and increasing amplitude which can be inferred from the increasing standard deviation (std), Th/K and Th/U curves. The hot and arid background is still the main origin of red color during the Es4 x . Moreover, the other origin may also develop since there is no clear law between red coloration and the developing location of sediments.
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Paleosols are an important tool in the paleoclimatic and paleoenvironmental interpretation of continental deposits and can provide a high‐resolution proxy for paleoclimate. Results from geochemical climofunctions applied to Early Miocene strata exposed in the Ebro Basin, Spain, demonstrate that mean annual precipitation was the dominant control on paleosol type and indicate that the paleoclimate was considerably wetter during the Early Miocene, by up to 1150 mm yr−1, in comparison to modern values, placing it in a subhumid climatic regime rather than an arid‐semiarid regime as previously suggested by sedimentological and paleontological approaches. By making comparisons with published data on paleoclimate during the Early Miocene, this article stresses the importance of regional climatic changes in global paleoclimatic interpretation.
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Upper Triassic Xujiahe Formation in Sichuan Basin is the principal producing formation.Six members of Xujiahe Formation form sandwich-like sedimentation structure with interbeded sandstone and mudstone.In order to discuss the contribution of paleoclimate on this kind of sedimentation structure,three commonly-used methods of restoring paleoclimate,namely sporopollen,elements and GR-ray logging were used to restore the paleoclimate of the time when each member of Xujiahe Formation was deposited.78 genera of sporopollen were found in the samples of Xujiahe Formation,forming the sporopollen combination of Dictyophyllidites-Concavisporites-Cycadopites.The combination indicates warm and humid climate in tropic and/or subtropic zone.The ratio of Ca/Mg has a positive correlation with paleotemperature while the ratio of Sr/Ba has a negative correlation with salinity(paleomoisture).The Gamma Ray can also illustrate the change of paleoclimate.The high GR data indicate humid climate,and vice versa.The proofs from sporopollen provided the climate background,and the other two methods described the details of paleoclimate. Combined all the three methods,we can find that the paleoclimate when Xujiahe Formation was sediment belongs to warm-humid tropics-subtropics zone.Paleoclimate when T3 x 1,T 3 x3and T3 x 5were formed showed hot and humid.In the meantime,when T 3x 2,T 3x 4 and T3 x 6 were formed it was warm and relatively dry.The climate of T3 x 5 was outstanding hot and humid,while the temperature and moisture of T 3x 2 was lowest.Controlled by the regular changes of paleoclimate,even numbered members were dominated by mudstone,and odd numbered members were dominated by sandstones.This kind of sandwich-like sedimentation structure formed by alternating layers of mudstone and sandstone provided favorite conditions for the formation of hydrocarbon reservoirs.
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Long-term continuous deposits and well-preserved thick loess sections are natural archives for the reconstruction of global climate change. However, the loess sections are often discontinuous owing to soil erosions and accumulations. This study aimed at reconstructing long-term continuous paleoclimatic records by integrating the target sections of two typical loess sequences in northeast (NE) China. One section, the Dajiugang (DJG) section, was investigated and sampled, and the Sanbahuo (SBH) section was used as the target for integrating and reconstructing the paleoclimate. Sedimentary, pedogenesis, and luminescence dating analyses were conducted to analyze the potentials for reconstructing the paleoclimate by integrating two typical loess sections. The results indicated that the paleoclimate records derived from the DJG section can be used to reconstruct the continuous paleoclimate of NE China by integrating them with the SBH section. The paleoclimate information inferred from the DJG section could impute paleoclimate data from 71 to 11.7 ka, which were missing in the SBH section. The paleoclimate of NE China generally consisted of three periods from 71 to 11.7 ka: cold and dry from 29 to 11.7 ka, alternately cold and warm from 57 to 29 ka, and warm and wet to cold and dry from 71 to 57 ka. Integrating the target loess sections can contribute to reconstructing regional long-term continuous paleoclimate records where discontinuous loess sequences occurred.
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