Download or read book Deciphering the Deglacial Evolution of Water Isotope and Climate in the Northern Hemisphere written by Chengfei He and published by . This book was released on 2021 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: To decipher the evolution of water isotope and climate in the last deglaciation, an isotope-enabled Transient Climate Experiment (iTRACE) of global climate and water isotopes in a state-of-the-art isotope-enabled Earth system model is conducted. The iTRACE successfully reproduces the oxygen-isotope evolutions across the pan-Asia and Greenland in the last deglaciation.

Download or read book Understanding the Deglacial Evolution of Deep Atlantic Water Masses in an Isotope enabled Ocean Model written by Jiaxu Zhang and published by . This book was released on 2016 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Abrupt Deglacial Climate Changes in the North Pacific and Implications for Climate Tipping Points written by Summer Kate Praetorius and published by . This book was released on 2014 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Paleoclimate archives have revealed abrupt climate events that are superimposed on more gradual climate changes throughout the last glacial and deglacial periods. The underlying causes of such rapid climate changes are still poorly understood, but the strong expression of these events in northern hemisphere records likely points to climatic mechanisms of a northern origin. A leading hypothesis for the trigger of these climate fluctuations has been changes in the strength of the Atlantic meridional overturning circulation (AMOC). However, the very rapid nature of some of the observed climate transitions (3-50 years) suggests a potential role for abrupt shifts in atmospheric circulation or nonlinear feedbacks within the climate system. Understanding the relative timing and magnitude of these events in different regions of the globe will help to identify the sources and possible amplifying mechanisms that have led to abrupt climate changes in the past, which will provide insight and constraints on the potential for abrupt climate changes in the future. This dissertation seeks to characterize climate changes occurring in the Northeast Pacific during the last deglaciation, a time period that encompasses the dynamic transition between the last ice age and the modern day interglacial period. So far, high-resolution records with precise chronologies from the North Pacific have been sparse, and paleoclimate models and proxy reconstructions disagree about the deglacial climate changes that are both predicted and observed to have occurred in this region. Marine sediment records from the Gulf of Alaska (GOA) have exceptionally high resolution (~1 cm/yr), making it possible to reconstruct climate changes in unprecedented detail for the North Pacific region. We establish new multi-decadal scale records of surface ocean variability using planktonic oxygen isotopes and sea-surface temperature (SST) estimates based on the alkenone U3--[superscript K'] unsaturation index, as well as regional records of ice-rafting and deglacial volcanic activity sourced from the Mt. Edgecumbe volcanic field (MEVF). The age models for these records are constrained by high-precision radiocarbon dating, tephra correlation, and "tuning" to the decadal-scale North Greenland Ice Core Project (NGRIP) oxygen isotope record. We combine new and previously published data from a depth transect of marine sites in the GOA and Northeast Pacific to place surface ocean changes in context of oceanic variability throughout the water column. These reconstructions are then used to evaluate three fundamental questions: 1) what are the timing and patterns of deglacial climate changes in the North Pacific relative to other regions, 2) what are the potential forcing mechanisms for deglacial climate variability in this region, and 3) how does the subsurface ocean respond to and influence abrupt climate change. In chapter two, we compare the timing and patterns of climate changes occurring between the North Pacific and North Atlantic regions. A major debate in the paleoclimate literature has been whether these regions operate in a synchronized or seesaw like mode. We compare the high resolution GOA and NGRIP oxygen isotope records as proxies for local temperature, and find that both synchronous and asynchronous climate patterns occur between regions throughout the past 18,000 years. The most abrupt climate transitions are preceded/accompanied by synchronous behavior, whereas times of relative climate stability exhibit asynchronous or anticorrelated (seesaw) patterns. This implies that coupling of North Pacific and North Atlantic heat transport could act as an amplifying mechanism in abrupt northern hemisphere climate change, whereas opposing oceanic regimes could act to balance northern hemisphere heat transport, and thus promote climate stability. In chapter three, we examine the timing between regional deglaciation and volcanism to evaluate potential feedbacks between climate and volcanic activity. Although volcanic eruptions have been observed to contribute to abrupt climate fluctuations with global effects in historical times, the role of volcanic forcing in climate variability of the more distant past (prior to the Holocene) has been neglected due to the very short-time scales in which volcanic events occur, and the difficulty of obtaining records with high enough resolution to capture these events and their associated climate effects. We evaluate the source and timing of a sequence of 23 tephra layers preserved in high-accumulation rate sediment cores proximal to the MEVF, and examine the regional climate response to this volcanic activity through comparison with reconstructions of sea surface temperatures, oxygen isotopes, and the [delta]18O of seawater. We find that the onset of enhanced volcanic activity coincides with abrupt warming at the onset of the Bølling Allerød, regional retreat of glaciers, and a period of rapid vertical land motion predicted from a model of regional isostatic rebound. These finding support the hypothesis that deglaciation may promote volcanism by removing crustal loading. The records of sea surface variability show large fluctuations during the episode of intense volcanic activity, suggesting that deglacial volcanic activity may not only respond to climate, but may also contribute to climate variance during the deglacial interval. In Chapter four, we examine the oceanographic changes that lead to two episodes of hypoxia in the GOA that lasted for millennia during the deglaciation. Similar hypoxic events have been documented across the North Pacific, indicating a widespread expansion of the oxygen minimum zone (OMZ) during the Bølling Allerød and early Holocene warm periods. These episodes have been linked to enhanced export productivity in many sites, however, the driving mechanisms for enhanced productivity and ocean deoxygenation remain elusive. Our alkenone temperature reconstructions reveal two abrupt warmings of 4-5°C that precisely coincide with the onset of increased export productivity and a sudden shift to hypoxic conditions, suggesting a strong link between ocean warming, marine productivity, and deoxygenation. Oxygen isotopes throughout the water column indicate that a transient subsurface warming of ~2°C might have accompanied the first hypoxic event during the BA. We propose that abrupt ocean warming lead to an expansion of the North Pacific OMZ through a reduction in oxygen solubility, enhanced thermal stratification, and a stimulation of marine productivity through the stabilization of the euphotic zone (related to stratification), combined with enhanced nutrient input from remobilization of iron in hypoxic shelf sediments. These studies indicate that large surface and subsurface ocean changes occurred in the North Pacific during the last deglaciation, with the potential for important feedbacks on global climate.

Download or read book Understanding the Last Glacial and Deglacial Ocean Circulation Using an Isotope enabled Ocean Model written by Sifan Gu and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ocean circulation during the last deglaciation can help to improve the understanding of the mechanisms underlying the ocean circulation. However, previous model-data comparisons suffer from indirect comparison because both reconstruction and climate model have uncertainties. To meet this challenge, my PhD work contributes to the isotope enabled Community Earth System Model (iCESM) project by developing a Neodymium (Nd) model and a Protactinium (231Pa) and Thorium (230Th) in the ocean model of CESM. With the isotope enabled ocean model (iPOP2), I investigated two scientific questions: (1) Deglacial AAIW in the Atlantic. AAIW plays important roles in the global climate system and the global ocean nutrient and carbon cycles. However, neodymium isotopic composition ([epsilon]Nd) reconstructions from different locations from the tropical Atlantic, have led to a debate on the relationship between northward penetration of AAIW into the tropical Atlantic and AMOC variability during the last deglaciation. Our results suggest a coherent response of AAIW and AMOC: when AMOC weakens, the northward penetration and transport of AAIW decreases while its depth and thickness increase. Moreover, the inconsistency among different tropical Atlantic [epsilon]Nd reconstructions is reconciled by considering their corresponding core locations and depths, which were influenced by different water masses in the past. (2) Using 18Oc to reconstruct AMOC. 18Oc gradient can be used to reconstruct density gradient, therefore the AMOC strength. 18Oc from the Florida Straits has been used to reconstruct AMOC evolution during the last deglaciation but the strength of Florida current can also be influenced by surface wind stress. Our model simulation suggests that in the western boundary, the Florida current strength is dominated by AMOC through the last deglaciation, instead of surface wind. However, in the South Atlantic, the basin-wide 18Oc contrast is decoupled from density contrast through the deglaciation in the upper ocean because of the deglacial density contrast change is dominated by salinity, which is caused by the deglacial change of AAIW. Our model suggests that 18Oc contrast across the western boundary is a good indicator for AMOC strength and 18Oc contrast across the whole basin only works for the North Atlantic.

Download or read book An Inverse Approach to Understanding Benthic Oxygen Isotope Records from the Last Deglaciation written by Daniel Edward Amrhein and published by . This book was released on 2014 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: Observations suggest that during the last deglaciation (roughly 20,000-10,000 years ago) the Earth warmed substantially, global sea level rose approximately 100 meters in response to melting ice sheets and glaciers, and atmospheric concentrations of carbon dioxide increased. This interval may provide an analog for the evolution of future climate. The ocean plays a key role in the modern climate system by storing and transporting heat, salt, and nutrients, but its role during the last deglaciation remains uncertain. Prominent signals of the last deglaciation in the ocean are a gradual warming and a decrease of the seawater oxygen isotope ratio 18O (a signature of melting land ice sheets). These changes do not occur uniformly in the ocean, but propagate like plumes of dye over hundreds and thousands of years, the aggregate results of turbulent advective and diffusive processes. Information about changing temperatures and oxygen isotopes is stored in the shells of benthic organisms recovered in ocean sediment cores. This thesis develops and applies an inverse framework for understanding deglacial oxygen isotope records derived from sediment cores in terms of the Green functions of ocean tracer transport and ocean mixed layer boundary conditions. Singular value decomposition is used to find a solution for global mixed layer tracer concentration histories that is constrained by eight last-deglacial sediment core records and a model of the modern ocean tracer transport. The solution reflects the resolving power of the data, which is highest at model surface locations associated with large rates of volume flux into the deep ocean. The limited data resolution is quantified and rationalized through analyses of simple models. The destruction of information contained in tracers is a generic feature of advective-diffusive systems. Quantifying limitations of tracer records is important for making and understanding inferences about the long-term evolution of the ocean.

Download or read book The Great Ice Age written by J.A. Chapman and published by Routledge. This book was released on 2005-06-21 with total page 381 pages. Available in PDF, EPUB and Kindle. Book excerpt: Documents and explains the natural climatic and ecological changes that have occurred during the past 2.6 million years. It also outlines the emergence and global impact of humans during this period.

Download or read book The Geologic Record of Climatic Change written by Thomas J. Crowley and published by . This book was released on 1982 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Oxygen Isotope Exchange and Transport in Deep Sea Sediments and Pore Fluids written by Daniel Paul Schrag and published by . This book was released on 1993 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Abrupt Climate Change written by National Research Council and published by National Academies Press. This book was released on 2002-04-23 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: The climate record for the past 100,000 years clearly indicates that the climate system has undergone periodic-and often extreme-shifts, sometimes in as little as a decade or less. The causes of abrupt climate changes have not been clearly established, but the triggering of events is likely to be the result of multiple natural processes. Abrupt climate changes of the magnitude seen in the past would have far-reaching implications for human society and ecosystems, including major impacts on energy consumption and water supply demands. Could such a change happen again? Are human activities exacerbating the likelihood of abrupt climate change? What are the potential societal consequences of such a change? Abrupt Climate Change: Inevitable Surprises looks at the current scientific evidence and theoretical understanding to describe what is currently known about abrupt climate change, including patterns and magnitudes, mechanisms, and probability of occurrence. It identifies critical knowledge gaps concerning the potential for future abrupt changes, including those aspects of change most important to society and economies, and outlines a research strategy to close those gaps. Based on the best and most current research available, this book surveys the history of climate change and makes a series of specific recommendations for the future.

Download or read book Polar Environments and Global Change written by Roger G. Barry and published by Cambridge University Press. This book was released on 2018-08-09 with total page 445 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surveys atmospheric, oceanic and cryospheric processes, present and past conditions, and changes in polar environments.

Download or read book Iberia Land of Glaciers written by Marc Oliva and published by Elsevier. This book was released on 2021-09-22 with total page 620 pages. Available in PDF, EPUB and Kindle. Book excerpt: Iberia, Land of Glaciers: How The Mountains Were Shaped By Glaciers discusses the impact of past glaciers in the current landscape of Iberia. Currently, there are only small glaciers in the highest peaks of the Pyrenees that are the legacy of the last cold period that ended at the end of the 19th century: The Little Ice Age. However, an accurate observation of the landscape of the highest peaks and adjacent valleys of the Iberian Peninsula reveals a past shaped by the successive passage of glaciers with hundreds of meters of ice, similar to what happens today in the Alps or Patagonia. Iberian glaciation has resulted in ice expansion through valleys that are now used by the road network and where important populations settle; in addition, large accumulations of sediments deposited by those glaciers are still unstable today and can trigger risks for mountain populations. Iberia, Land of Glaciers presents the impact of the glaciers in the landscape of mountains following a more educational perspective with examples of 21 Iberian massifs written by specialists from each of the areas. Assesses present-day Iberian Peninsula landscape trends by understanding the past behavior of glaciers Includes the latest findings of all the major Iberian mountains in a single book Includes quality, color figures to enhance understanding of glacier formations Provides a more educational and pedagogical perspective on glacial processes to reach an audience beyond academia

Download or read book The Deglacial Evolution of North Atlantic Surface Circulation and Climate Reconstructed Using Diatom Assemblages written by Jordan Eastwood and published by . This book was released on 2014 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Marine Isotope Stage 3 in Southern South America 60 KA B P 30 KA B P written by Germán Mariano Gasparini and published by Springer. This book was released on 2016-07-26 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents isotope data reflecting changes in temperature derived from core samples in South America. Marine Isotope Stage (MIS) is examined in detail with respect to Stage 3. With over 20 chapters, this detailed treatise discusses high climatic variability, paleoclimatic events, Dansgaard-Oeschger cycles, continental vertebrates, sea level changes, vegetation and climate changes based on pollen records, and the non-Amazon landscape and fauna from 65 to 20 ka B.P. The book also looks at the earth’s magnetic field and climate change during MIS 3 and MIS 5 and presents a comparison between both stages with respect to marine deposits in Uruguay. With case studies drawn from Brazil, Argentina and Uruguay this book presents research from the some of the worlds experts in this field.

Download or read book Regional Atmospheric Modelling of the Stable Water Istope Cycle written by Kristof Sturm and published by . This book was released on 2005 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: Climate change has recently become a major concerning among scientists and the general public. A better knowledge of past climates helps forecasting the future evolution of climate. Stable water isotopes stand as an outstanding paleo-climate proxy. Physical properties of heavy stable water isotopes (H182 O; HDO) cause fractionation processes related to temperature and degree of distillation. If the isotopic signal is correctly inverted, past climate change can be inferred from isotopic archives. Andean ice-cores offer a unique records of tropical climate and its variability through time. However, the interpretation of the isotopic signal is difficult because of complex atmospheric dynamic over South America. For this purpose, we developed a module handling the stable water isotope fractionation processes within the regional circulation model REMO and applied it to South America. The manuscript outlines the major milestones of the present PhD. We first introduce the research topic in the wider scope of climate change; the description of the stable water isotope enabled regional circulation model REMOiso; an initial validation of REMOiso over Europe; an investigation of the seasonal variations of precipitation, atmospheric circulation and isotopic signal over South America; and at last the recording of the south American monsoon system (SAMS) by stable water isotope diagnostics.

Download or read book Characterisation of Rapid Climate Changes Through Isotope Analyses of Ice and Entrapped Air in the NEEM Ice Core written by Myriam Guillevic and published by . This book was released on 2013 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: The analyses of ice drilled in the Greenland ice sheet have revealed the occurrence of rapid climatic instabilities during the last glacial period, known as Dansgaard-Oeschger (DO) events. The imprint of DO events is also recorded at mid to low latitudes in different archives of the northern hemisphere. A detailed multiproxies study of the sequence of these rapid instabilities is essential for understanding the climate mechanisms at play. In this thesis, we combine water isotopes (d18O, d-excess and 17Oexcess) and air in Greenland ic cores (markers of temperature changes d15N, of land productivity d18Oatm, and also concentration and isotopic composition of methane) to quantify regional temperature changes in Greenland, to characterize the reorganization of the hydrological cycle and to better understand the role of the biosphere in climate feedbacks and the sequences of climatic events. Finally, we develop a multiproxies approach to identify in polar ice cores the fingerprint of Heinrich events (layers of ice rafted debris in North Atlantic marine cores, deposited by icebergs melt, caused by the collapse of Northern hemisphere ice sheets). Most of the new data presented in this thesis were obtained from the NEEM ice core, NW Greenland, drilled in 2008-2011 in the frame of an international project led by the Centre for Ice an Climate, Denmark.

Download or read book Investigating Paleoclimate Questions Using an Isotope enabled Earth System Model written by Jiang Zhu and published by . This book was released on 2017 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: Paleoclimate reconstructions can help us learn the evolution of climate mean state and variability in the past, understand mechanisms for climate change, and test the climate models that are extensively used for future climate projections. However, reconstructions have one major disadvantage that usually they are measurements of proxy variables (e.g., oxygen isotopes in calcium shells of foraminifera) instead of climate state variables (e.g., ocean temperature), which are directly simulated in traditional coupled climate models. This require that the model-data comparisons are indirect in paleoclimate studies and making it extremely difficult to address model-data discrepancies, especially when both models and reconstructions are subject to substantial biases and uncertainties. To overcome this obstacle, my PhD work involves developing a fully coupled water isotope-enabled Community Earth System Model (iCESM) in collaboration with other scientists. The physical climate of the iCESM is one of the best state-of-the-art fully coupled earth system models. In addition to the regular hydrologic cycle, iCESM can explicitly simulate the transport and transformation of water isotopes (e.g., H218O) in its components--the atmosphere, land, ocean, sea ice and river runoff. The iCESM can well-reproduce the major features of water isotopes in observations, including the tropical amount effect and high latitude temperature effect, as well as the continental and altitude effects in precipitation-d18Op in present day observations. The simulated d18O in seawater (d18Ow) also closely resemble the pattern in observations. Moreover, a simulation of the LGM (21,000 ka before present) shows that the model is able to simulate the glacial-interglacial changes of d18Op in ice cores, d18Ow in porefluid reconstructions, and d18Oc in ocean sediments, suggesting the model is suited for paleoclimate studies. With the water-isotope capability of the iCESM, I have investigated the following scientific questions: (1) How and why the water isotope-temperature relationship in Greenland ice cores varies during abrupt climate changes; (2) Whether the El Niño-Southern Oscillation (ENSO) was stronger or weaker at the LGM than the present day. (1) Isotope-temperature relationship. For more than 50 years, water isotope values (e.g., d18O) in ice cores have provided a tremendous amount of information about the Earth climate history during the late Quaternary. Initially based on a "modern analogue method", d18O changes in ice cores were directly interpreted as variations in local temperature, which was challenged later by independent reconstructions. Although it is now becoming clear that the temporal d18O-temperature relationship could vary both spatially and temporally in ice-core records, how the temporal slope could vary during abrupt climate changes and what is causing these changes still remain unclear. In my PhD study, I have quantitatively studied the changes in d18O-temperature relationship over Greenland in response to varied climatic forcings using the iCESM. I found that the temporal slope in Greenland increases significantly with the amount of meltwater discharged into the northern North Atlantic Ocean, due to the reduced moisture from the nearby oceans and the tracer effect from depleted meltwater (e.g., about -30 ‰). Otherwise, the d18O-temperature relationships (spatial and temporal) are relatively stable in response to greenhouse gas (GHG), ice sheets and mid-Holocene orbital forcing. It is also found that part of the d18O signal in ice cores during meltwater events can be simply attributed to the tracer effect--the propagation of depleted meltwater in the hydrological cycle--instead of any changes in the climate state. These important findings imply that abrupt temperature changes during meltwater events previously inferred from ice cores could have been significantly overestimated. (2) ENSO variability at the LGM. Despite its paramount importance in climate system, the response of ENSO to anthropogenic global warming is still inconclusive in recent climate models. Studying the ENSO strength in the past can serve as a testbed for these climate models used for future projections and provide us the opportunity to investigate possible relationships between ENSO variability and the mean climate states. But, the ENSO strength at the LGM is inconclusive both in current climate models and paleoclimate reconstructions, including those records using the individual foraminifera analysis (IFA) in the eastern equatorial Pacific (EEP). Here, for the first time, I have directly compared modeled water isotopes in the iCESM with the IFA records. Synthesizing evidence from both models and reconstructions, it is found that ENSO at the LGM is most likely weaker than that of the preindustrial, because of the weakened Bjerknes feedbacks. The iCESM suggests that total variance of the IFA records may only reflect changes in the annual cycle instead of ENSO variability as previously assumed. Furthermore, the interpretation of subsurface IFA records can be substantially complicated by the habitat depth of thermocline-dwelling foraminifera and their vertical migration with a temporally varying thermocline. The model suggests an inverse relationship between ENSO variability and zonal SST gradient, thermocline depth and surface winds in equatorial Pacific, consistent with previous theoretical or observation based studies. Results indicate that ENSO variability could be stronger in response to the future anthropogenic global warming.

Download or read book Antarctic Climate Evolution written by Fabio Florindo and published by Elsevier. This book was released on 2008-10-10 with total page 606 pages. Available in PDF, EPUB and Kindle. Book excerpt: Antarctic Climate Evolution is the first book dedicated to furthering knowledge on the evolution of the world's largest ice sheet over its ~34 million year history. This volume provides the latest information on subjects ranging from terrestrial and marine geology to sedimentology and glacier geophysics. - An overview of Antarctic climate change, analyzing historical, present-day and future developments - Contributions from leading experts and scholars from around the world - Informs and updates climate change scientists and experts in related areas of study