scholarly journals Climate and marine biogeochemistry during the Holocene from transient model simulations

2018 ◽  
Vol 15 (10) ◽  
pp. 3243-3266 ◽  
Author(s):  
Joachim Segschneider ◽  
Birgit Schneider ◽  
Vyacheslav Khon
Keyword(s):  
Late Holocene ◽  
Large Scale ◽  
Model Simulation ◽  
Holocene Climate ◽  
Model Simulations ◽  
The Holocene ◽  
The Pacific ◽  
Marine Biogeochemistry ◽  
Global Mean ◽  
Atmospheric Pco2

Abstract. Climate and marine biogeochemistry changes over the Holocene are investigated based on transient global climate and biogeochemistry model simulations over the last 9500 years. The simulations are forced by accelerated and non-accelerated orbital parameters, respectively, and atmospheric pCO2, CH4, and N2O. The analysis focusses on key climatic parameters of relevance to the marine biogeochemistry, and on the physical and biogeochemical processes that drive atmosphere–ocean carbon fluxes and changes in the oxygen minimum zones (OMZs). The simulated global mean ocean temperature is characterized by a mid-Holocene cooling and a late Holocene warming, a common feature among Holocene climate simulations which, however, contradicts a proxy-derived mid-Holocene climate optimum. As the most significant result, and only in the non-accelerated simulation, we find a substantial increase in volume of the OMZ in the eastern equatorial Pacific (EEP) continuing into the late Holocene. The concurrent increase in apparent oxygen utilization (AOU) and age of the water mass within the EEP OMZ can be attributed to a weakening of the deep northward inflow into the Pacific. This results in a large-scale mid-to-late Holocene increase in AOU in most of the Pacific and hence the source regions of the EEP OMZ waters. The simulated expansion of the EEP OMZ raises the question of whether the deoxygenation that has been observed over the last 5 decades could be a – perhaps accelerated – continuation of an orbitally driven decline in oxygen. Changes in global mean biological production and export of detritus remain of the order of 10 %, with generally lower values in the mid-Holocene. The simulated atmosphere–ocean CO2 flux would result in atmospheric pCO2 changes of similar magnitudes to those observed for the Holocene, but with different timing. More technically, as the increase in EEP OMZ volume can only be simulated with the non-accelerated model simulation, non-accelerated model simulations are required for an analysis of the marine biogeochemistry in the Holocene. Notably, the long control experiment also displays similar magnitude variability to the transient experiment for some parameters. This indicates that also long control runs are required when investigating Holocene climate and marine biogeochemistry, and that some of the Holocene variations could be attributed to internal variability of the atmosphere–ocean system.

scholarly journals Climate and marine biogeochemistry during the Holocene from transient model simulations

2018 ◽  
Author(s):  
Joachim Segschneider ◽  
Birgit Schneider ◽  
Vyacheslav Khon
Keyword(s):  
Late Holocene ◽  
Large Scale ◽  
Water Mass ◽  
Model Simulation ◽  
Anthropogenic Forcing ◽  
Model Simulations ◽  
The Holocene ◽  
Marine Biogeochemistry ◽  
Ocean Atmosphere ◽  
Atmospheric Pco2

Abstract. Climate and marine biogeochemistry changes over the Holocene are investigated based on transient global climate and biogeochemistry model simulations over the last 9,500 yr. The simulations are forced by accelerated and non-accelerated orbital parameters, respectively, and atmospheric pCO2. The analysis focusses on key climatic parameters of relevance to the marine biogeochemistry, on the processes that determine the strength of the carbon pumps that drive the ocean–atmosphere carbon flux, and on the oxygen minimum zones (OMZs) in the ocean. The most pronounced changes occur in the eastern equatorial Pacific (EEP) OMZ, and in the North Atlantic. Changes in global mean values of biological production and export of detritus remain modest, with generally lower values in the mid-Holocene. The simulated ocean–atmosphere CO2-flux is of the right order of magnitude to explain the observed atmospheric pCO2 evolution, but with different timing. As the most significant result, we find a substantial increase in volume of the OMZ in the EEP continuing into the late Holocene in the non-accelerated simulation. The concurrent increase of age of the water mass within the EEP OMZ suggests that this growth is driven by a slow down of the circulation in the interior of the deep Pacific. This results in large scale deoxygenation in the deeper Pacific and hence the source regions of the EEP OMZ waters from mid-to-late Holocene. The simulated expansion of the OMZ raises the question whether the currently observed deoxygenation is a continuation of the orbitally driven decline in oxygen, or if it is already a result of the occuring climate change from anthropogenic forcing as widely assumed. An additional explanation would be that the anthropogenic forcing amplifies the natural forcing. The increase in water mass age and EEP OMZ volume can only be simulated with the non-accelerated model simulation. The simulations thus demonstrate that non-accelerated experiments are required for an analysis of the marine biogeochemistry in the Holocene.

scholarly journals Global temperature modes shed light on the Holocene temperature conundrum

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jürgen Bader ◽  
Johann Jungclaus ◽  
Natalie Krivova ◽  
Stephan Lorenz ◽  
Amanda Maycock ◽  
...  
Keyword(s):  
Global Warming ◽  
Late Holocene ◽  
Model Simulation ◽  
Volcanic Eruptions ◽  
Arctic Sea Ice ◽  
Global Temperature ◽  
Mean Annual Temperature ◽  
Cooling Mode ◽  
The Holocene ◽  
Global Mean

Abstract Reconstructions of the global mean annual temperature evolution during the Holocene yield conflicting results. One temperature reconstruction shows global cooling during the late Holocene. The other reconstruction reveals global warming. Here we show that both a global warming mode and a cooling mode emerge when performing a spatio-temporal analysis of annual temperature variability during the Holocene using data from a transient climate model simulation. The warming mode is most pronounced in the tropics. The simulated cooling mode is determined by changes in the seasonal cycle of Arctic sea-ice that are forced by orbital variations and volcanic eruptions. The warming mode dominates in the mid-Holocene, whereas the cooling mode takes over in the late Holocene. The weighted sum of the two modes yields the simulated global temperature trend evolution. Our findings have strong implications for the interpretation of proxy data and the selection of proxy locations to compute global mean temperatures.

scholarly journals Computational cognitive neuroscience: Model fitting should not replace model simulation

2016 ◽  
Author(s):  
Stefano Palminteri ◽  
Valentin Wyart ◽  
Etienne Koechlin
Keyword(s):  
Decision Making ◽  
Cognitive Neuroscience ◽  
Large Scale ◽  
Model Comparison ◽  
Model Simulation ◽  
Model Fitting ◽  
Model Simulations ◽  
Model Based ◽  
Comparison Results ◽  
Future Work

AbstractCognitive neuroscience, especially in the fields of learning and decision-making, is witnessing the blossoming of computational model-based analyses. Several methodological and review papers have indicated how and why candidate models should be compared by trading off their ability to predict the data as a function of their complexity. However, the importance of simulating candidate models has been so far largely overlooked, which entails several drawbacks and leads to invalid conclusions. Here we argue that the analysis of model simulations is often necessary to support the specific claims about behavioral function that most of model-based studies make. We defend this argument both informally by providing a large-scale (N>300) review of recent studies, and formally by showing how model simulations are necessary to interpret model comparison results. Finally, we propose guidelines for future work, which combine model comparison and simulation.

scholarly journals North American Winter Dipole: Observed and Simulated Changes in Circulations

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 793 ◽  
Author(s):  
Yu-Tang Chien ◽  
S.-Y. Simon Wang ◽  
Yoshimitsu Chikamoto ◽  
Steve L. Voelker ◽  
Jonathan D. D. Meyer ◽  
...  
Keyword(s):  
North America ◽  
North American ◽  
Large Scale ◽  
Climate Model ◽  
Model Simulations ◽  
The North ◽  
Weather Events ◽  
The Pacific ◽  
Climate Model Simulations ◽  
Northwestern North America

In recent years, a pair of large-scale circulation patterns consisting of an anomalous ridge over northwestern North America and trough over northeastern North America was found to accompany extreme winter weather events such as the 2013–2015 California drought and eastern U.S. cold outbreaks. Referred to as the North American winter dipole (NAWD), previous studies have found both a marked natural variability and a warming-induced amplification trend in the NAWD. In this study, we utilized multiple global reanalysis datasets and existing climate model simulations to examine the variability of the winter planetary wave patterns over North America and to better understand how it is likely to change in the future. We compared between pre- and post-1980 periods to identify changes to the circulation variations based on empirical analysis. It was found that the leading pattern of the winter planetary waves has changed, from the Pacific–North America (PNA) mode to a spatially shifted mode such as NAWD. Further, the potential influence of global warming on NAWD was examined using multiple climate model simulations.

Mongolian dryland paleoenvironment and paleoclimate issues : calibrations and applicability of GDGT and pollen reconstructions over the Late Holocene.

2021 ◽  
Author(s):  
Lucas Dugerdil ◽  
Sébastien Joannin ◽  
Odile Peyron ◽  
Isabelle Jouffroy-Bapicot ◽  
Boris Vannière ◽  
...  
Keyword(s):  
Late Holocene ◽  
Qaidam Basin ◽  
Calibration Method ◽  
Altai Mountains ◽  
Climate Trends ◽  
Holocene Climate ◽  
Independent Dataset ◽  
The Holocene ◽  
Surface Samples

<p>Our understanding of climate changes throughout the Holocene is hampered by representativeness in sedimentary archives. Potential production and preservation biases of the markers are identified by comparing these proxies with modern environments. It is important to conduct robust calibrations on each biome. These calibrations use large database dominated by forest samples. The Mongolian plateau is especially characterized by low annual precipitation and continental annual air temperature. The characterization of the climate system of this area is crucial for the understanding of Holocene Monsoon Oscillations. This study focuses on the calibration of proxy-climate relationships for pollen and glycerol dialkyl glycerol tetraethers (GDGTs) by comparing large published Eurasian calibrations with a set of 49 new surface samples (moss polster, soil and mud from temporary dry pond). These calibrations are then cross-validated by an independent dataset of top-core samples and applied to two Late Holocene paleosequences in the Altai mountains and the Qaidam basin. We show that: (1) preserved pollen assemblages are clearly imprinted on the extremities of the ecosystem range but mitigated and unclear on the ecotones; (2) for both proxies, inferred relationships depend on the geographical range covered by the calibration database as well as on the nature of samples; (3) even if local calibrations suffer from reduced amplitude of climatic parameter due to local homogeneity, they better reflect actual climate than the global ones by reducing the limits for saturation impact, (4) a bias in climatic reconstructions is induced by the over-parameterization of the models and (5) paleoclimate values reconstructed here are consistent with Mongolia-China Late Holocene climate trends, and validate the application of local calibrations for both pollen and GDGTs. We encourage the application of this surface calibration method to reconstruct paleoclimate and especially consolidate our understanding of the Holocene climate and environment variations in Arid Central Asia.</p>

Vegetation changes and associated climatic changes in the southern Altai Mountains within China during the Holocene

The Holocene ◽  
2016 ◽  
Vol 27 (5) ◽  
pp. 683-693 ◽  
Author(s):  
Zhaodong Feng ◽  
Aizhi Sun ◽  
Nurbayev Abdusalih ◽  
Min Ran ◽  
Alishir Kurban ◽  
...  
Keyword(s):  
Climatic Change ◽  
North Atlantic ◽  
Late Holocene ◽  
Mean Annual Precipitation ◽  
Mean Annual Temperature ◽  
Mountain Range ◽  
Altai Mountains ◽  
Pollen Data ◽  
The Holocene ◽  
The Pacific

The location of the Altai Mountains at the limits of both the Pacific and Atlantic influences implies that this mountain range is an important climatic boundary. Based on pollen data of 188 samples of a 390-cm core from Narenxia Peat in the southern Altai with a chronologic support of 11 accelerator mass spectrometry (AMS) dates, we reconstructed the Holocene climatic change at Narenxia Peat. The reconstruction revealed five stages of climatic change: a cold and dry latest deglacial (prior to ~11,500 cal. yr BP), a warm and wet early-Holocene (~11,500 to ~7000 cal. yr BP), a considerably cooled and dried middle Holocene (~7000 to ~4000 cal. yr BP), a resumed warm and wet late-Holocene (~4000 to ~1200 cal. yr BP), and a relatively cool and dry latest Holocene (past ~1200 years). The reconstructions of mean annual temperature (MAT) and mean annual precipitation (MAP) from Narenxia Peat well resemble the reconstructions of North Atlantic Oscillations (NAO) and El Niño–Southern Oscillations (ENSO). The resemblance implies that the Holocene millennial-scale changes in MAT and MAP in the Altai might have been causally associated with the variations in NAO and ENSO.

scholarly journals Long-term variations in Iceland–Scotland overflow strength during the Holocene

2013 ◽  
Vol 9 (2) ◽  
pp. 1627-1656 ◽  
Author(s):  
D. J. R. Thornalley ◽  
M. Blaschek ◽  
F. J. Davies ◽  
S. Praetorius ◽  
D. W. Oppo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Late Holocene ◽  
Deep Convection ◽  
Arctic Sea Ice ◽  
Global Ocean ◽  
Nordic Seas ◽  
Model Simulations ◽  
The Holocene ◽  
Arctic Sea

Abstract. The overflow of deep water from the Nordic Seas into the North Atlantic plays a critical role in global ocean circulation and climate. Approximately half of this overflow occurs via the Iceland–Scotland (I–S) overflow, yet the history of its strength throughout the Holocene (~0–11 700 yr ago, ka) is poorly constrained, with previous studies presenting apparently contradictory evidence regarding its long-term variability. Here, we provide a comprehensive reconstruction of I–S overflow strength throughout the Holocene using sediment grain size data from a depth transect of 13 cores from the Iceland basin. Our results reveal weaker I–S overflow during the early and late Holocene, with maximum overflow strength occurring at ~7 ka, the time of a regional climate thermal maximum. Climate model simulations suggest a shoaling of deep convection in the Nordic Seas during the early and late Holocene, consistent with our evidence for weaker I–S overflow during these intervals. Whereas the reduction in I–S overflow strength during the early Holocene likely resulted from melting remnant glacial ice-sheets, the decline throughout the last 7000 yr was caused by an orbitally-induced increase in the amount of Arctic sea-ice entering the Nordic Seas. Although the flux of Arctic sea-ice to the Nordic Seas is expected to decrease throughout the next century, model simulations predict that under high emissions scenarios, competing effects, such as warmer sea surface temperatures in the Nordic Seas, will result in reduced deep convection, likely driving a weaker I–S overflow.

Comparing temperature trends and variability over the Holocene in climate models of low and high complexity

2021 ◽  
Author(s):  
Christian Wirths ◽  
Elisa Ziegler ◽  
Matthew Toohey ◽  
Julie Christin Schindlbeck-Belo ◽  
Steffen Kutterolf ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Volcanic Eruptions ◽  
Arctic Sea Ice ◽  
Balance Model ◽  
Earth System ◽  
Holocene Climate ◽  
Model Simulations ◽  
The Holocene ◽  
Temperature Trends ◽  
Proxy Reconstructions

<div> <p>Modeled and observed temperature trends over the Holocene disagree. Proxy reconstructions suggest global cooling during the late Holocene. Model simulations, on the other hand, show a warming trend for the entire Holocene, a contradiction known as the Holocene temperature conundrum.  </p> </div><div> <p>A recent study by Bader et. al. (2020) introduced a new approach to the question by proposing the coexistence of a cooling and warming climate mode. While the warming mode is proposed to be related to changes in greenhouse gas concentrations, the physical process behind the cooling mode might be a change in the seasonal cycle of Arctic sea-ice. It’s unclear to what extent this process is responsible for the observed climate response. Depending on their strength and location these modes have strong implications for proxy data interpretation and location selection when calculating global mean temperatures.   </p> </div><div> <p>Here, we investigate if similar modes and temperature trends can be found in models of different complexity. Therefore, we use a 2D Energy Balance Model (EBM), with solar, volcanic, ice-sheet and greenhouse gas forcing, for transient simulations of the Holocene climate. We analyze these Holocene climate simulations in terms of global and regional temperature trends, modes and variability patterns. We conduct sensitivity tests to examine the influence of the forcings on those trends and modes. In particular, we are interested in the influence of volcanic eruptions on the Holocene climate. Furthermore, we compare our model results with temperature reconstructions and simulations from Earth System Models.    </p> </div><div> <p>Altogether, we comprehensively analyze Holocene climate as simulated by a conceptual EBM, a state-of-the-art Earth System Model and proxy reconstructions. The results provide insight into whether models of different complexity produce similar modes and trends and whether these occur due to climate forcing rather than internal processes of the earth system. Finally, we will provide a better understanding of Holocene cooling and warming and the interpretation of differences between Holocene temperature proxy reconstructions and climate model simulations.    </p> </div><div> <p> </p> </div><div> <p>References:  <br>Bader, J., Jungclaus, J., Krivova, N. et al. Global temperature modes shed light on the Holocene temperature conundrum. Nat Commun 11, 4726 (2020). https://doi.org/10.1038/s41467-020-18478-6 </p> </div>

scholarly journals Multivariate Empirical Orthogonal Function analysis of the upper thermocline structure of the Mediterranean Sea from observations and model simulations

2003 ◽  
Vol 21 (1) ◽  
pp. 167-187 ◽  
Author(s):  
S. Sparnocchia ◽  
N. Pinardi ◽  
E. Demirov
Keyword(s):  
Mediterranean Sea ◽  
Large Scale ◽  
Vertical Structure ◽  
Model Simulation ◽  
Function Analysis ◽  
Original Data ◽  
Empirical Orthogonal Functions ◽  
Data Set ◽  
Model Simulations ◽  
The Mediterranean

Abstract. Multivariate vertical Empirical Orthogonal Functions (EOF) are calculated for the entire Mediterranean Sea both from observations and model simulations, in order to find the optimal number of vertical modes to represent the upper thermocline vertical structure. For the first time, we show that the large-scale Mediterranean thermohaline vertical structure can be represented by a limited number of vertical multivariate EOFs, and that the "optimal set" can be selected on the basis of general principles. In particular, the EOFs are calculated for the combined temperature and salinity statistics, dividing the Mediterranean Sea into 9 regions and grouping the data seasonally. The criterion used to establish whether a reduced set of EOFs is optimal is based on the analysis of the root mean square residual error between the original data and the profiles reconstructed by the reduced set of EOFs. It was found that the number of EOFs needed to capture the variability contained in the original data changes with geographical region and seasons. In particular, winter data require a smaller number of modes (4–8, depending on the region) than the other seasons (8–9 in summer). Moreover, western Mediterranean regions require more modes than the eastern Mediterranean ones, but this result may depend on the data scarcity in the latter regions. The EOFs computed from the in situ data set are compared to those calculated using data obtained from a model simulation. The main results of this exercise are that the two groups of modes are not strictly comparable but their ability to reproduce observations is the same. Thus, they may be thought of as equivalent sets of basis functions, upon which to project the thermohaline variability of the basin. Key words. Oceanography: general (water masses) – Oceanography: physical (hydrography; instruments and techniques)

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