scholarly journals Sources of holocene variability of oxygen isotopes in paleoclimate archives

2009 ◽  
Vol 5 (2) ◽  
pp. 1133-1162 ◽  
Author(s):  
A. N. LeGrande ◽  
G. A. Schmidt
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ice Cores ◽  
Ocean General Circulation Model ◽  
Ocean Basin ◽  
Water Vapor Transport ◽  
Water Isotopes ◽  
Water Isotope

Abstract. Variability in water isotopes has been captured in numerous archives and used to infer climate change. Here we examine water isotope variability over the course of the Holocene using the water-isotope enabled, coupled atmosphere-ocean general circulation model, GISS ModelE-R. Eight Holocene time slices, mostly 1000 years apart are simulated using estimated changes in orbital configuration, greenhouse gases, and ice sheet extent. We find that water isotopes in the model match well with those captured in proxy climate archives in ice cores, ocean sediment cores, and speleothems. The climate changes associated with the water isotope changes, however, are more complex than simple modern analog interpretations. In particular, water isotope variability in Asian speleothems is linked to alterations in landward water vapor transport, not local precipitation, and ice sheet changes over North America lead to masking of temperature signals in Summit, Greenland. Salinity-seawater isotope variability is complicated by inter-ocean basin exchanges of water vapor. Water isotopes do reflect variability in the hydrologic cycle, but are better interpreted in terms of regional changes rather than local climate variables.

scholarly journals Sources of Holocene variability of oxygen isotopes in paleoclimate archives

2009 ◽  
Vol 5 (3) ◽  
pp. 441-455 ◽  
Author(s):  
A. N. LeGrande ◽  
G. A. Schmidt
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Climate Changes ◽  
Hydrological Cycle ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ice Cores ◽  
Water Vapor Transport ◽  
Water Isotopes ◽  
Water Isotope

Abstract. Variability in water isotopes has been captured in numerous archives and used to infer past climate changes. Here we examine water isotope variability over the course of the Holocene using the water-isotope enabled, coupled atmosphere-ocean general circulation model, GISS ModelE-R. Eight Holocene time slices, ~1000 years apart are simulated and driven by estimated changes in orbital configuration, greenhouse gases, and ice sheet extent. We find that simulated water isotope archives match well with those seen in ice cores, ocean sediment cores, and speleothems. The climate changes associated with the water isotope changes, however, are more complex than simple modern spatial slope interpretations might suggest. In particular, water isotope variability in Asian speleothems is linked to alterations in landward water vapor transport, not local precipitation, and ice sheet changes over North America lead to the masking of temperature signals in Summit, Greenland. Salinity-seawater isotope variability is complicated by inter-ocean basin exchanges of water vapor. Water isotopes do reflect variability in the hydrology, but are better interpreted in terms of regional hydrological cycle changes rather than as indicators of local climate.

scholarly journals Seasonality of moisture supplies to precipitation over the Third Pole: a stable water isotopic perspective

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Xiaoxin Yang ◽  
Tandong Yao
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Potential Effect ◽  
Water Vapor Transport ◽  
The Tibetan Plateau ◽  
Physical Processes ◽  
Large Scale Atmospheric Circulation

Abstract This study integrated isotopic composition in precipitation at 50 stations on and around the Tibetan Plateau (TP) and demonstrated the distinct seasonality of isotopic composition in precipitation across the study period. The potential effect of water vapor isotopes on precipitation isotopes is studied by comparing the station precipitation data with extensive isotopic patterns in atmospheric water vapor, revealing the close linkage between the two. The analysis of contemporary water vapor transport and potential helps confirm the different mechanisms behind precipitation isotopic compositions in different areas, as the southern TP is more closely related to large-scale atmospheric circulation such as local Hadley and summer monsoon circulations during other seasons than winter, while the northern TP is subject to the westerly prevalence and advective moisture supply and precipitation processes. The new data presented in this manuscript also enrich the current dataset for the study of precipitation isotopes in this region and together provide a valuable database for verification of the isotope-integrated general circulation model and explanation of related physical processes.

scholarly journals The Response of Ice Shelf Basal Melting to Variations in Ocean Temperature

2008 ◽  
Vol 21 (11) ◽  
pp. 2558-2572 ◽  
Author(s):  
Paul R. Holland ◽  
Adrian Jenkins ◽  
David M. Holland
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Flow Speed ◽  
Ocean Warming ◽  
Ocean Temperature ◽  
Ice Shelf ◽  
Ice Shelves

Abstract A three-dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean-warming scenarios. The model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms. This occurs because the melt rate is proportional to the product of ocean flow speed and temperature in the mixed layer directly beneath the ice shelf, both of which are found to increase linearly with ocean warming. The behavior of this complex primitive equation model can be described surprisingly well with recourse to an idealized reduced system of equations, and it is shown that this system supports a melt rate response to warming that is generally quadratic in nature. This study confirms and unifies several previous examinations of the relation between melt rate and ocean temperature but disagrees with other results, particularly the claim that a single melt rate sensitivity to warming is universally valid. The hypothesized warming does not necessarily require a heat input to the ocean, as warmer waters (or larger volumes of “warm” water) may reach ice shelves purely through a shift in ocean circulation. Since ice shelves link the Antarctic Ice Sheet to the climate of the Southern Ocean, this finding of an above-linear rise in ice shelf mass loss as the ocean steadily warms is of significant importance to understanding ice sheet evolution and sea level rise.

scholarly journals Interannual Atmospheric Variability Affects Continental Ice Sheet Simulations on Millennial Time Scales

2008 ◽  
Vol 21 (22) ◽  
pp. 5976-5992 ◽  
Author(s):  
Michael S. Pritchard ◽  
Andrew B. G. Bush ◽  
Shawn J. Marshall
Keyword(s):  
North American ◽  
General Circulation ◽  
Southern Oscillation ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Equilibrium Geometry ◽  
Atmospheric Variability ◽  
Enso Teleconnections

Abstract To inform the ongoing development of earth system models that aim to incorporate interactive ice, the potential impact of interannual variability associated with synoptic variability and El Niño–Southern Oscillation (ENSO) at the Last Glacial Maximum (LGM) on the evolution of a large continental ice sheet is explored through a series of targeted numerical modeling experiments. Global and North American signatures of ENSO at the LGM are described based on a multidecadal paleoclimate simulation using an atmosphere–ocean general circulation model (AOGCM). Experiments in which a thermomechanical North American ice sheet model (ISM) was forced with persistent LGM ENSO composite anomaly maps derived from the AOGCM showed only modest ice sheet thickness sensitivity to ENSO teleconnections. In contrast, very high model sensitivity was found when North American climate variations were incorporated directly in the ISM as a looping interannual time series. Under this configuration, localized transient cold anomalies in the atmospheric record instigated substantial new ice formation through a dynamically mediated feedback at the ice sheet margin, altering the equilibrium geometry and resulting in a bulk 10% growth of the Laurentide ice sheet volume over 5 kyr.

scholarly journals Influence of Last Glacial Maximum boundary conditions on the global water isotope distribution in an atmospheric general circulation model

2013 ◽  
Vol 9 (2) ◽  
pp. 789-809 ◽  
Author(s):  
T. Tharammal ◽  
A. Paul ◽  
U. Merkel ◽  
D. Noone
Keyword(s):  
Boundary Conditions ◽  
Surface Temperature ◽  
General Circulation Model ◽  
Last Glacial Maximum ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Ice Sheet ◽  
Circulation Model ◽  
Atmospheric General Circulation ◽  
Water Isotope

Abstract. To understand the validity of δ18O proxy records as indicators of past temperature change, a series of experiments was conducted using an atmospheric general circulation model fitted with water isotope tracers (Community Atmosphere Model version 3.0, IsoCAM). A pre-industrial simulation was performed as the control experiment, as well as a simulation with all the boundary conditions set to Last Glacial Maximum (LGM) values. Results from the pre-industrial and LGM simulations were compared to experiments in which the influence of individual boundary conditions (greenhouse gases, ice sheet albedo and topography, sea surface temperature (SST), and orbital parameters) were changed each at a time to assess their individual impact. The experiments were designed in order to analyze the spatial variations of the oxygen isotopic composition of precipitation (δ18Oprecip) in response to individual climate factors. The change in topography (due to the change in land ice cover) played a significant role in reducing the surface temperature and δ18Oprecip over North America. Exposed shelf areas and the ice sheet albedo reduced the Northern Hemisphere surface temperature and δ18Oprecip further. A global mean cooling of 4.1 °C was simulated with combined LGM boundary conditions compared to the control simulation, which was in agreement with previous experiments using the fully coupled Community Climate System Model (CCSM3). Large reductions in δ18Oprecip over the LGM ice sheets were strongly linked to the temperature decrease over them. The SST and ice sheet topography changes were responsible for most of the changes in the climate and hence the δ18Oprecip distribution among the simulations.

scholarly journals Global-Scale Energy and Freshwater Balance in Glacial Climate: A Comparison of Three PMIP2 LGM Simulations

2008 ◽  
Vol 21 (19) ◽  
pp. 5008-5033 ◽  
Author(s):  
Shigenori Murakami ◽  
Rumi Ohgaito ◽  
Ayako Abe-Ouchi ◽  
Michel Crucifix ◽  
Bette L. Otto-Bliesner
Keyword(s):  
Water Vapor ◽  
Heat Transport ◽  
General Circulation ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Water Vapor Transport ◽  
Second Phase ◽  
Low Latitudes ◽  
Freshwater Balance

Abstract Three coupled atmosphere–ocean general circulation model (AOGCM) simulations of the Last Glacial Maximum (LGM: about 21 000 yr before present), conducted under the protocol of the second phase of the Paleoclimate Modelling Intercomparison Project (PMIP2), have been analyzed from a viewpoint of large-scale energy and freshwater balance. Atmospheric latent heat (LH) transport decreases at most latitudes due to reduced water vapor content in the lower troposphere, and dry static energy (DSE) transport in northern midlatitudes increases and changes the intensity contrast between the Pacific and Atlantic regions due to enhanced stationary waves over the North American ice sheets. In low latitudes, even with an intensified Hadley circulation in the Northern Hemisphere (NH), reduced DSE transport by the mean zonal circulation as well as a reduced equatorward LH transport is observed. The oceanic heat transport at NH midlatitudes increases owing to intensified subpolar gyres, and the Atlantic heat transport at low latitudes increases in all models whether or not meridional overturning circulation (MOC) intensifies. As a result, total poleward energy transport at the LGM increases in NH mid- and low latitudes in all models. Oceanic freshwater transport decreases, compensating for the response of the atmospheric water vapor transport. These responses in the atmosphere and ocean make the northern North Atlantic Ocean cold and relatively fresh, and the Southern Ocean relatively warm and saline. This is a common and robust feature in all models. The resultant ocean densities and ocean MOC response, however, show model dependency.

scholarly journals Greenland Ice Sheet influence on Last Interglacial climate: global sensitivity studies performed with an atmosphere–ocean general circulation model

2015 ◽  
Vol 11 (2) ◽  
pp. 933-995 ◽  
Author(s):  
M. Pfeiffer ◽  
G. Lohmann
Keyword(s):  
General Circulation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
High Latitudes ◽  
Last Interglacial ◽  
Proxy Records ◽  
Sensitivity Studies ◽  
The Impact

Abstract. During the Last Interglacial (LIG, 130–115 kiloyear before present), the northern high latitudes experienced higher temperatures than those of the late Holocene with a notably lower Greenland Ice Sheet (GIS). However, the impact of a reduced GIS on the global climate has not yet been well constrained. In this study, we quantify the contribution of the GIS to LIG warmth by performing various sensitivity studies, employing the Community Earth System Models (COSMOS), with a focus on height and extent of the GIS. In order to asses the effects of insolation changes over time and for a comparison of LIG climate with the current interglacial, we perform transient simulations covering the whole LIG and Holocene. We analyze surface air temperature (SAT) and separate the contribution of different forcings to LIG warmth. The strong Northern Hemisphere warming is mainly caused by increased summer insolation. Reducing the height and extent of the GIS leads to a warming of several degrees Celcius in the northern and southern high latitudes during local winter. In order to evaluate the performance of our LIG simulations, we additionally compare the simulated SAT anomalies with marine and terrestrial proxy-based LIG temperature anomalies. Our model results are in good agreement with proxy records with respect to the pattern, but underestimate the reconstructed temperatures. We are able to reduce the mismatch between model and data by taking into account the potential seasonal bias of the proxy record and the uncertainties in the dating of the proxy records for the LIG thermal maximum. The seasonal bias and the uncertainty of the timing are estimated from our own transient model simulations. We note however that our LIG simulations are not able to reproduce the full magnitude of temperature changes indicated by the proxies, suggesting a potential misinterpretation of the proxy records or deficits of our model.

Antarctic Uncertainty: Learning more about past ice sheet shapes with Bayesian methods

2020 ◽  
Author(s):  
Fiona Turner ◽  
Richard Wilkinson ◽  
Caitlin Buck ◽  
Julie M. Jones ◽  
Louise Sime
Keyword(s):  
Bayesian Methods ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Paired Data ◽  
Antarctic Ice Sheet ◽  
The Antarctic ◽  
The Relationship ◽  
Water Isotope

<p>Understanding the effect warming has on ice sheets is vital for accurate projections of climate change. A better understanding of how the Antarctic ice sheets have changed size and shape in the past would allow us to improve our predictions of how they may adapt in the future; this is of particular relevance in predicting future global sea level changes. This research makes use of previous reconstructions of the ice sheets, ice core data and Bayesian methods to create a model of the Antarctic ice sheet at the Last Glacial Maximum (LGM). We do this by finding the relationship between the ice sheet shape and water isotope values. </p><p>We developed a prior model which describes the variation between a set of ice sheet reconstructions at the LGM. A set of ice sheet shapes formed using this model was determined by a consultation with experts and run through the general circulation model HadCM3, providing us with paired data sets of ice sheet shapes and water isotope estimates. The relationship between ice sheet shape and water isotopes is explored using a Gaussian process emulator of HadCM3, building a statistical distribution describing the shape of the ice sheets given the isotope values outputted by the climate model. We then use MCMC to sample from the posterior distribution of the ice sheet shape and attempt to find a shape that creates isotopic values matching as closely as possible to the observations collected from ice cores. This allows us to quantify the uncertainty in the shape and incorporate expert beliefs about the Antarctic ice sheet during this time period. Our results suggests that there may have been a thicker West Antarctic ice sheet at the LGM than previously estimated.</p>

scholarly journals Influence of LGM boundary conditions on the global water isotope distribution in an atmospheric general circulation model

2012 ◽  
Vol 8 (2) ◽  
pp. 1319-1368 ◽  
Author(s):  
T. Tharammal ◽  
A. Paul ◽  
U. Merkel ◽  
D. Noone
Keyword(s):  
Boundary Conditions ◽  
Surface Temperature ◽  
General Circulation Model ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Ice Sheet ◽  
Circulation Model ◽  
Climate System Model ◽  
Atmospheric General Circulation ◽  
Water Isotope

Abstract. A series of experiments was conducted using a water isotope tracers-enabled atmospheric general circulation model (Community Atmosphere Model version 3.0, CAM3.0-Iso), by changing the individual boundary conditions (greenhouse gases, ice sheet albedo and topography, sea-surface temperature) each at a time to Last Glacial Maximum (LGM) values. In addition, a combined simulation with all the boundary conditions being set to LGM values was carried out. A pre-industrial (PI) simulation with boundary conditions taken according to the PMIP2 (Paleoclimate Modelling Intercomparison Project) protocol was performed as the control experiment. The experiments were designed in order to analyze the temporal and spatial variations of the oxygen isotopic composition of precipitation (δ18Oprecip) in response to individual climate factors. The change in topography (due to the change in land-ice cover) played a significant role in reducing the surface temperature and δ18Oprecip over North America. Exposed shelf areas and the ice sheet albedo reduced the Northern Hemisphere surface temperature and δ18Oprecip further. A global mean cooling of 4.1 °C was simulated with combined LGM boundary conditions compared to the control simulation, which was in agreement with previous experiments using the fully coupled Community Climate System Model (CCSM3). Large reductions in δ18Oprecip over the LGM ice sheets were highly correlated with the temperature decrease over them. The SST and ice sheet topography changes were found to be responsible for most of the changes in the climate and hence the δ18Oprecip distribution among the simulations.

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