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 Inferring Ocean Circulation During the Last Glacial Maximum and Last Deglaciation Using Data and Models written by Dan Amrhein and published by . This book was released on 2016 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the Last Glacial Maximum (LGM, ~ 20,000 years ago) air temperatures warmed, sea level rose roughly 130 meters, and atmospheric concentrations of carbon dioxide increased. This thesis combines global models and paleoceanographic observations to constrain the ocean’s role in storing and transporting heat, salt, and other tracers during this time, with implications for understanding how the modern ocean works and how it might change in the future. • By combining a kinematic ocean model with “upstream” and “downstream” deglacial oxygen isotope time series from benthic and planktonic foraminifera, I show that the data are in agreement with the modern circulation, quantify their power to infer circulation changes, and propose new data locations. • An ocean general circulation model (the MITgcm) constrained to fit LGM sea surface temperature proxy observations reveals colder ocean temperatures, greater sea ice extent, and changes in ocean mixed layer depth, and suggests that some features in the data are not robust. • A sensitivity analysis in the MITgcm demonstrates that changes in winds or in ocean turbulent transport can explain the hypothesis that the boundary between deep Atlantic waters originating from Northern and Southern Hemispheres was shallower at the LGM than it is today.

Download or read book Ocean Circulation and Climate written by Stefan Rahmstorf and published by Elsevier Inc. Chapters. This book was released on 2013-10-22 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: The oceans play a crucial role in the Earth’s climate system due largely to their ability to store and transport heat. The instrumental record, spanning an order of magnitude of 100 years, is short compared with some of the important timescales of climate variability. To understand the oceans’ role in these long-term changes, proxy data from sediments, ice cores, and corals must be used. Using these proxy data, we examine the evidence for past ocean circulation and sea-level changes before instrumental oceanographic measurements began. We discuss what paleoclimatic data can tell us about past ocean states and what can be learned from ocean and climate models. Particular foci of the chapter are the ocean circulation and sea-level changes during the Quaternary and the Cretaceous, two particularly interesting periods in Earth’s history. The Quaternary covers the past 2.5 million years and is characterized by periodic glaciations, while the Cretaceous, reaching back around 100 million years, had a warm greenhouse climate with a weak temperature gradient between the tropics and the poles.

Download or read book MARGO written by M. Kucera and published by Elsevier. This book was released on 2006-04-10 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: MARGO - Multiproxy Approach for the Reconstruction of the Glacial Ocean surface summarizes the results of the MARGO international working group, with the aim to develop an updated and harmonised reconstruction of sea surface temperatures and sea-ice extent of the Last Glacial Maximum oceans. The MARGO approach differs from previous efforts by developing and consistently applying measures of various aspects of reconstruction reliability, and by combining faunal and geochemical proxies. In 14 papers, the volume provides a comprehensive review of earlier work and a series of new, proxy-specific reconstructions based on census counts of planktonic foraminifera, diatoms, radiolaria and dinoflagellate cysts as well as on Mg/Ca measurements in planktonic foraminifera. The approach of harmonising the calibration and application of different proxies is described in detail, various paleothermometry techniques and their results are compared and the challenge of treating sparsely sampled data as the basis for ocean circulation models is addressed. The use of stable oxygen isotope composition of foraminiferal shells as a proxy for past sea water composition is comprehensively reassessed, and a new approach to the transfer function paleothermometer is presented. This volume represents a landmark contribution to the understanding of ice-age oceanography as well as the proxies used to reconstruct past ocean states. The results will form the basis for forcing and validation of ocean circulation models. New regional reconstructions of Last Glacial Maximum ocean temperatures and sea ice cover Compilation of new calibration and fossil datasets as well as documentation of techniques and approaches to paleoenvironmental reconstructions Comparison of techniques, proxies and modelling approaches

Download or read book The Oceans and Rapid Climate Change written by Dan Seidov and published by John Wiley & Sons. This book was released on 2001-01-09 with total page 306 pages. Available in PDF, EPUB and Kindle. Book excerpt: Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 126. Until a few decades ago, scientists generally believed that significant large-scale past global and regional climate changes occurred at a gradual pace within a time scale of many centuries or millennia. A secondary assumption followed: climate change was scarcely perceptible during a human lifetime. Recent paleoclimatic studies, however, have proven otherwise: that global climate can change extremely rapidly. In fact, there is good evidence that in the past at least regional mean annual temperatures changed by several degrees Celsius on a time scale of several centuries to several decades.

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 Ice Drift Ocean Circulation and Climate Change written by Jens Bischof and published by Springer Science & Business Media. This book was released on 2000-11 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: The issue of global warming and climate change is of continuous concern. Since the 1970s, it bas been shown that the pack-ice around the Arctic Ocean is thinning, the margin of permafrost is moving north and the vegetation in the high northern parts of the world is changing (the 'greening' of the Arctic). But are these changes the result of human activity or simply regular variations of the Earth's climate system? Over thousands of years, a continuous archive of iceberg and sea ice drift bas formed in the deep-sea sediments, revealing the place of the ice's origin and allowing a reconstruction of the surface currents and the climate of the past. However, the drift of floating ice from one place to another is not just a passive record of past ocean circulation. It actively influences and changes the surface ocean circulation, thus having a profound effect on climate change. Ice Drift, Ocean Circulation and Climate Change is the first book to focus on the interactions between ice, the ocean and the atmosphere and to describe how these three components of the climate system influence each other. It makes clear the positive contribution of paleoclimatology and paleoceanography and should be read by anyone concerned with global warming and climate change.

Download or read book Understanding Antarctic Circumpolar Current Transport at the LGM Using an Isotope enabled Ocean Model written by Lingwei Li and published by . This book was released on 2019 with total page 43 pages. Available in PDF, EPUB and Kindle. Book excerpt: Changes in the Antarctic Circumpolar Current (ACC) transport during the last deglaciation cycle are thought to have played an important role on global climate variability. A better understanding of ACC transport at the Last Glacial Maximum (LGM) would allow better assessment of ACC dynamics and past global-scale climatic variations. However, estimates of ACC transport vary widely among some LGM coupled ocean-atmosphere climate model simulations and proxy studies. As the ACC is in the thermal wind balance, oxygen isotopic ratios (d18O) in the foraminifera (d18Oc) are often used as a proxy to reconstruct past density variation and thus ACC transport. Here we test the ACC transport and its dynamics at the LGM (20 ka) in a transient simulation of the last deglaciation with the CESM (C-iTRACE) and examine the ability of the d18Oc gradient to reconstruct the density gradient to estimate LGM ACC transport. The model simulation suggests that the ACC transport was approximately 60% greater at the LGM (227 Sv) compared with that of today (145 Sv), which mainly results from the baroclinic transport. Furthermore, the d18Oc gradient at the LGM over the Southern Ocean tends to underestimate the LGM density gradient because the d18Oc gradient results primarily from temperature changes but the density gradient is highly affected by salinity changes due to sea ice formation. Therefore, although d18Oc gradient is a powerful tool to reconstruct past density, it likely underestimates the Southern Ocean density gradient at the LGM and it hence to underestimate the ACC transport.

Download or read book A High Resolution Record of Ocean Circulation During the Last Glacial Cycle from Neodymium Isotopes written by Alexander Piotrowski and published by . This book was released on 2005 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Compilation of Deglacial Benthic Stable Carbon Isotope Data for Reconstructing Ocean Circulation Change Terrestrial Biosphere Change and 3D Visualizations written by Carlye D. Peterson and published by . This book was released on 2016 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt: Can 3D visualizations improve undergraduate students' understanding of fundamental Earth science concepts like plate tectonics? Our simple 3D Atlantic seafloor movie helps non-STEM students more than STEM students understand what the seafloor looks like and how ocean basins are formed. Simple 3D visualizations potentially benefit novice science students and closes the gap between STEM and non-STEM students' scores.

Download or read book Ocean Temperature Variability During the Late Pleistocene written by Jeremy Scott Hoffman and published by . This book was released on 2016 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation explores one overarching question relevant to the paleoclimate of the latest Pleistocene glacial cycle (approximately the last 130,000 years): “How did spatial and temporal evolution of ocean temperature, both at the surface and interior, relate to other parts of the climate system in the late Pleistocene?” Results from three studies are presented that seek to address longstanding questions in paleoceanography and paleoclimatology for the late Pleistocene using a combination of novel and accepted statistical and geochemical analysis techniques and leveraging comparisons with available global climate model data. The last interglaciation (LIG; ~129-116 ka) was the most recent period in Earth’s history with higher-than-present global sea level (≥6-9 m) under similar-to-preindustrial concentrations of atmospheric CO2. This suggests that additional feedbacks related to albedo, insolation, and ocean overturning circulation may have resulted in the apparent warming required to cause the higher sea level. Our understanding of how much warmer the LIG was relative to the present interglaciation remains uncertain, however, with current estimates suggesting that sea-surface temperatures (SSTs) were 0-2°C warmer than late-20th century average global temperatures. We present a global compilation of proxy-based annual SST spanning the LIG. Using Monte Carlo and Bayesian techniques to propagate uncertainties in age-model and proxy-based SST reconstructions, our results quantify the spatial timing, amplitude, and uncertainty in global and regional SST change during the LIG. Our conclusions suggest that the LIG surface ocean was indistinguishable from the average surface ocean temperatures observed for the last two decades (1995-2014). This may ultimately imply that the Earth is currently committed to ≥6-9m of equilibrium sea-level rise. Although the LIG is not an analogue for present and future climate change due to the large differences in seasonal orbital insolation and absence of anthropogenic greenhouse gas radiative forcing, it provides an opportunity to test the ability of global climate models to simulate the mechanisms and climate feedbacks responsible for the warmer climate and higher global mean sea level during the LIG. However, when forced only by LIG greenhouse gas concentrations and insolation changes, climate models suggest that the annual mean temperature response was not significantly different from preindustrial control simulations. We present the first multi-model and multiscenario ensemble of transient and equilibrium global climate modeling results spanning the LIG. We show, using a novel model-data comparison framework, that these scenario-specific model results exhibit regionally independent agreement with ocean basin-specific proxy-based SST stacks. This result ultimately implies structural uncertainties and/or misrepresentations of climate feedbacks in the existing suite of climate model simulations, or underestimations of additional proxy-based SST uncertainties. Our conclusions suggest a new target LIG time period for future model-data comparisons and highlight the need for higher resolution transient climate modeling of the LIG and its dependence on meltwater input to the high latitude oceans during the preceding deglaciation. Few discoveries have stimulated the paleoclimate community more so than Heinrich events. Nevertheless, the cause of Heinrich events, characterized by a large flux of icebergs sourced from the Hudson Strait Ice Stream into the North Atlantic, remains debated. Commonly attributed to internal ice-sheet instability, the occurrence of Heinrich events during the coldest intervals of the last glacial cycle instead suggests an external climate control. We expand on recent studies that have shown that incursions of warm subsurface waters into the intermediate depth North Atlantic Ocean destabilized an ice shelf fronting the Hudson Strait Ice Stream, causing a Heinrich event. We present new surface- and bottom-water stable isotope, trace metal, and sedimentary records from two cores taken along the Labrador margin that further support subsurface warming as a trigger of Hudson Strait Heinrich events. We further relate these changes to other sediment core records from the North Atlantic and transient deglacial climate modeling results to show that subsurface warming was ubiquitous across the intermediate North Atlantic during the early part of the last deglaciation and was most likely caused by a preceding reduction in the Atlantic Meridional Overturning Circulation.

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 Ocean Circulation and Climate written by John A. Church and published by Elsevier Inc. Chapters. This book was released on 2013-10-22 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ocean has the largest heat capacity in the climate system and as a result the ocean plays a critical role in the climate. Changes in ocean heat content dominate the Earth’s energy storage; and the ocean’s thermal expansion has been a major contributor to sea-level rise in the twentieth century and likely to be the largest contributor in the twenty-first century. The agreement between changes in ocean heat storage over recent decades and changes in the Earth’s radiative balance, within uncertainties, provides strong support for current understanding of anthropogenic climate change. As a result of improvements in observations and modeling of sea level and components contributing to sea-level change, there is now an improved explanation for twentieth century sea-level rise. Models project a continuing sea-level rise during the twenty-first century and beyond. However, a number of uncertainties remain in our understanding of the global mean and regional distribution of sea-level rise resulting from changes in ocean circulation and changes in the Earth’s gravitational field. Ocean-ice-sheet interactions are important for quantitatively estimating future ice-sheet contributions to sea-level rise.

Download or read book Holocene Ice Sheet Dynamics and Detrital Provenance Shifts Along the West Greenland Margin written by Lina Madaj and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the effect of Arctic Amplification the Arctic is currently warming at least twice as fast as the rest of the planet. Seasonal sea-ice extent has been alarmingly declining in the past decade. Glaciers and ice caps along the Greenland coast and in the Canadian Arctic have been losing mass on an accelerated rate during the past century. As the global climate system is a complex system connecting different regions via atmospheric transport, changes in Arctic climate patterns are affecting the climate and weather conditions in the lower latitudes. The Greenland Ice Sheet as well as glaciers and ice caps in the Canadian Arctic are the largest freshwater storages on the northern hemisphere and expected to be among the highest contributors to global sea level rise. Freshwater input through meltwater discharge is not only affecting sea level rise but further influencing deep water formation in the Labrador Sea and the subpolar North Atlantic and hence global ocean circulation and climate patterns. To be able to sufficiently predict future developments of the Greenland Ice Sheet with respect to mass loss and resulting impacts on the global climate, data from past climate and Greenland Ice Sheet extents are crucially important. The Holocene spanning the last period of the deglaciation after the Last Glacial Maximum culminating in the Holocene Thermal Maximum when atmospheric temperatures were warmer and glacier and ice-sheet extent smaller than today represents the closest analogue to current atmospheric warming and Greenland Ice Sheet mass loss. The wide west Greenland shelf of Baffin Bay and Labrador Sea hosts thick marine sediments archiving around ten thousand years of this past climate and ice-sheet history. Siliciclastic detrital material discharged into Baffin Bay and the Labrador Sea via meltwater and erosion can be separated from those sedimentary archives and traced back to its source region. Radiogenic isotopes (Sr, Nd, Pb) label the source regions of those sediments by fingerprinting the isotopic composition of the prevailing bedrock. Hence, they can be used as reliable provenance tracers. Retreating land-ice masses expose bedrock that before was not subject to erosion, influencing the isotopic signatures delivered into the surrounding ocean. Based on this theory, radiogenic isotopes can record changes in siliciclastic detrital sediment provenance and hence, indirectly trace ice-sheet dynamics. The overall aim of this thesis work is to reconstruct changes in detrital sediment provenance along the west Greenland shelf to gain new insights into Holocene Greenland Ice Sheet dynamics and ocean current-induced sediment transport. Sedimentary archives from three main research areas (eastern Labrador Sea, northeastern Baffin Bay, and Kane Basin, central Nares Strait) record obvious shifts in sediment provenance throughout the Holocene. Those shifts coincide with major regional climatic changes in the research area. Generally, all records reveal the local bedrock as the main source region of detrital material and distal-sourced material transported along the coast via the West Greenland Current as a secondary source. Although the proportion of distal sourced material appears to be small, changes in West Greenland Current strength have been recorded in the isotopic composition. In southwestern Greenland and the Labrador Sea radiogenic isotope records reveal a shift towards a higher proportion of the local Archean Block in the late Holocene caused by Neoglacial ice advance and a reduction in West Greenland Current speed delivering less material from southern most Greenland. Farther north in the Upernavik region, midwest Greenland coast, the isotopic composition marks a change with the transition from early to mid Holocene caused by increased West Greenland Current strength and the opening of Vaigat Strait which enabled erosion and transport of freshly exposed basalts from the Disko Bay area due to ice-sheet retreat. This basalt input is, however, not transported all the way to northernmost Melville Bay (northern Baffin Bay) where the detrital sediment composition is clearly dominated by contribution of the local Committee-Melville Belt without any significant provenance changes throughout the Holocene. Farthest north, the sedimentary record from Kane Basin records provenance shifts that confirm the opening of Nares Strait around 8.3 ka BP. This event is followed by an increased delivery of carbonate-rich detrital sediments from northern Ellesmere Island due to the newly established gateway of Arctic Ocean water transporting sediments from further north to the core location. Additionally determined mineralogical composition of the sedimentary records along the west Greenland coast supports the interpretation drawn from the radiogenic isotopic composition. Furthermore, it points out the additional value of radiogenic isotopes through variations only visible in isotopic composition but not in the mineralogical composition. Further comparison to other studies from the region based on different tracers confirms the reliability and sufficient application of radiogenic isotopes in provenance studies as well as the advantage of multi-proxy approaches in paleoclimatological studies. Overall, this study highlights the advantages and reliability of radiogenic isotopes in provenance studies with regards to reconstructions of ice-sheet dynamics. The combination of the three isotopic systems (Sr, Nd, Pb) enables source region determination with a higher probability compensating for overlapping signatures within individual isotopic systems. The transect of sedimentary records along the west Greenland coast identifies clearly distinguishable isotopic ranges for the different Greenland bedrock terrains, qualifying this approach for further high-resolution investigation in past Greenland Ice Sheet development.

Download or read book Deep Ocean Circulation and Continental Weathering Regimes During Climate Transitions last Deglaciation and Eocene Oligocene Using Sr Nd and Pb Isotopes in Sedimentary Archives written by Chandranath Basak and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Major climate change is frequently associated with readjustment of carbon sources and sinks. The ocean is a relatively large carbon sink that can exchange carbon with the atmosphere over geologically short time scales. Chemical weathering of continental silicate rocks also plays a key role in sequestering atmospheric carbon over geologically long time scale. Therefore, the interplay between physical and chemical continental weathering can have major implications for the long term carbon budget of the Earth.

Download or read book Collaborative Proposal Development of an Isotope Enabled CESM for Testing Abrupt Climate Changes written by and published by . This book was released on 2015 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have made significant landmarks in our proposed work in the last 4 years (3 years plus 1 year of no cost extension). We have developed the simulation capability of the major isotopes in CESM. In particular, we have completed the implementation of the stable water isotopes ([delta]18O, [delta]D) into the components for the atmosphere, ocean, land surface, runoff transport, sea ice, and coupler. In addition, the carbon isotopes (abiotic and biotic radiocarbon, [delta]13 C) have been implemented into the CESM ocean and land models, and long spinup simulations have been completed (Jahn et al., 2015). Furthermore, we have added abiotic Neodymium to the CESM ocean model as a tracer of ocean circulation, also measured by the proxy data community. Fullycoupled simulations with the stable water isotopes and ocean radiocarbon are currently being run for the preindustrial and also the Last Glacial Maximum. We have secured 19 million core-hours on the NWSC Yellowstone supercomputer for 12 months. Together with some CESM Paleoclimate Working Group CSL Yellowstone core hours, we are guaranteed sufficient computing for the spin-up experiments and deglaciation simulations for 21 to 15ka.

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.