scholarly journals Uneven spatial sampling distorts reconstructions of Phanerozoic seawater temperature

Geology ◽  
2021 ◽  
Author(s):  
Lewis A. Jones ◽  
Kilian Eichenseer
Keyword(s):  
Spatial Distribution ◽  
Global Climate ◽  
Seawater Temperature ◽  
Spatial Sampling ◽  
Deep Time ◽  
Proxy Records ◽  
Spatial Coverage ◽  
Reconstructed Temperature ◽  
Gradient Based ◽  
Cooling Trend

Paleotemperature proxy records are widely used to reconstruct the global climate throughout the Phanerozoic and to test macroevolutionary hypotheses. However, the spatial distribution of these records varies through time. This is problematic because heat is unevenly distributed across Earth’s surface. Consequently, heterogeneous spatial sampling of proxy data has the potential to bias reconstructed temperature curves. We evaluated the spatiotemporal evolution of sampling using a compilation of Phanerozoic δ18O data. We tested the influence of variable spatial coverage on global estimates of paleotemperature by sampling a steep “modern-type” latitudinal temperature gradient and a flattened “Eocene-type” gradient, based on the spatial distribution of δ18O samples. We show that global paleotemperature is overestimated in ~70% of Phanerozoic stages. Perceived climatic trends for some intervals might be artifactually induced by shifts in paleolatitudinal sampling, with equatorward shifts in sampling concurring with warming trends, and poleward shifts concurring with cooling trends. Yet, the magnitude of some climatic perturbations might also be underestimated. For example, the observed Ordovician cooling trend may be underestimated due to an equatorward shift in sampling. Our findings suggest that while proxy records are vital for reconstructing Earth’s paleotemperature in deep time, consideration of the spatial nature of these data is crucial to improving these reconstructions.

scholarly journals Tree-ring based reconstruction of mean maximum temperatures since AD 1829

2013 ◽  
Vol 89 (02) ◽  
pp. 184-191 ◽  
Author(s):  
Zhongjie Shi ◽  
Jixi Gao ◽  
Xiaohui Yang ◽  
Zhiqing Jia ◽  
Hao Guo ◽  
...  
Keyword(s):  
High Temperature ◽  
Tree Ring ◽  
Global Climate ◽  
Northern China ◽  
Warming Trend ◽  
Reconstructed Temperature ◽  
Maximum Temperatures ◽  
Temperature Levels ◽  
June July ◽  
Climate Events

The correlation between tree-ring widths and climate was developed using Pinus sylvestris var. mongolica after which mean maximum temperatures of June–July since 1829 were reconstructed. Results show that the transfer function of temperature explains more than 40% of the variance and that the reconstruction sequence was consistent with several reconstructed temperature variations in the region. Over the past 181 years, climate in the region has undergone eight distinct low temperature and eight high temperature periods. A high temperature period in the 1920s to 1930s is consistent with a drought that occurred in most regions of northern China. Periods of drought in the 1870s were also identified. There was no significant increase or decrease in mean maximum June–July temperatures over the last 181 years, although since the 1950s temperatures have increased gradually. A warming trend has become more pronounced since the early 1990s but temperature levels are not significantly higher than those of the 1850s. A multi-taper spectral analysis shows that there are significant periodicities of 2.4, 2.8, 4.9, 5.1 and 21.3 years in the sequence of reconstructed temperatures. Temperatures were also affected by global climate events and solar activity.

Early Eocene simulations with three different palaeogeographic conditions

2021 ◽  
Author(s):  
Zijian Zhang ◽  
Zhongshi Zhang ◽  
Zhengtang Guo
Keyword(s):  
Early Eocene ◽  
Model Intercomparison ◽  
Warm Climate ◽  
Time Model ◽  
Deep Time ◽  
Climate Proxy ◽  
Proxy Records ◽  
Intercomparison Project ◽  
Series Of Experiments ◽  
Very High

<p>The early Eocene is a warm period with a very high atmosphere CO<sub>2</sub> level in the Cenozoic. It  provides a good reference for our future climate under the Representative Concentration Pathway 8.5 scenario. Therefore, the early Eocene climate has received many attentions in  modeling studies, for example, the Deep-Time Model Intercomparison Project (DeepMIP). However, the early Eocene palaeogeographic conditions show remarkable contrasts to the present conditions. Meanwhile, there are a few different reconstructions for the early Eocene palaeogeography, which may cause further model spreads in simulating the early Eocene warm climate. Here, we present a series of experiments carried out with the NorESM1-F, under the framework of DeepMIP. In these experiments, we consider three different palaeogeographic reconstructions for the early Eocene. We also compare our simulations with climate proxy records, to validate which palaeogeographic reconstructions can reproduce simulations that agree better with the climate proxy records.</p>

scholarly journals Fossil crocodilian distributions, Upper Cretaceous to present: implications for paleoclimate

1992 ◽  
Vol 6 ◽  
pp. 198-198
Author(s):  
Paul Markwick
Keyword(s):  
Late Cretaceous ◽  
Middle Eocene ◽  
Global Climate ◽  
A Priori ◽  
Tropical Regions ◽  
Cooling Trend ◽  
Geologic Record ◽  
Continental Interior ◽  
Different Levels ◽  
Limited Scope

The present day distribution of crocodilians appears to be climatically controlled, at least in part, with the group restricted to tropical through sub-tropical regions. Studies have shown that although crocodiles may be able to withstand sub-zero temperatures they can do so for only limited periods. By analogy the presence of fossil crocodilians in the geologic record has been interpretated as indicating warmth. However previous studies have generally been of limited scope. This study uses global paleodistributions of the crocodilians to map gross global climate for the last 100 million years.A comprehensive database of published occurrences of fossil crocodilians from the late Cretaceous to the Present has been constructed. Taphonomic and collection biases have been addressed using ‘control groups', these are respectively the Testudines and the vertebrates in general. Problems of taxonomic inconsistency have been dealt with by ‘accepting’ a standard published taxonomic scheme (Carroll, 1988). Geographic and temporal uncertainties and imprecisions are coded on the database to facilitate sorting; this allows the analyses to be run at different levels of precision and provides an opportunity to understand the way biogeographic and hence paleoclimatic interpretations may be influenced by both the nature of the geologic record itself and by a priori decisions made by the worker. The database also includes lithologic, stratigraphic and environmental information on some 3300 localities and includes specimen information for the taxa entered (>14000 separate entries assembled from 1000 references).Preliminary analyses of paleolatitudinally reconstructed localities reveals the following trends: an overall equatorward movement of the poleward limit of the crocodiles from the late Cretaceous to the present; this is punctuated by an abrupt equatorward excursion of almost 10° during the Oligocene and another of similar magnitude at the end of the Miocene, with an apparent Miocene ‘recovery’ in between (this trend is shown most clearly by the families Alligatoridae and Crocodylidae). At the suborder level the Mesosuchians (excluding the Sebecidae) show a distinct equatorial shift from the Campanian through to the middle Eocene when they disappear; inclusion of the Sebecidae in the Mesosuchia gives rise to a sudden poleward expansion in the middle Eocene of some 20° paleolatitude. Map reconstructions, especially for North America, reveal an eastward shift of crocodilian localities as the Tertiary progresses, perhaps due in part to a taphonomic artifact, viz., the migration of the locus of sedimentation. With the late Miocene the crocodilians disappeared completely from the continental interior record, a transition which seems tied to increased aridity (as indicated by the development of caliches in many areas) and increased seasonality of temperature. This pattern is also seen in the southern ‘U.S.S.R’.The distributions of the Crocodylia through time therefore reflect and support established views concerning late Cretaceous through Tertiary climate with a general cooling trend from the late Cretaceous to the present punctuated by abrupt coolings in the Oligocene and around the Miocene-Pliocene boundary.

Reconstructing the distribution of surface mass balance over East Antarctica (DML) from 1850 to present day

2020 ◽  
Author(s):  
Nicolas Ghilain ◽  
Stéphane Vannitsem ◽  
Quentin Dalaiden ◽  
Hugues Goosse
Keyword(s):  
Spatial Distribution ◽  
Mass Balance ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Ice Cores ◽  
Global Climate Models ◽  
East Antarctica ◽  
Surface Mass Balance ◽  
Surface Mass

<p>Over recent decades, the Antarctic Ice Sheet has witnessed large spatial variations at its surface through the surface mass balance (SMB). Since the complex Antarctic topography, working at high resolution is crucial to represent accurately the dynamics of SMB. While ice cores provide a mean to infer the SMB over centuries, the view is very spatially constrained. Global Climate models estimate the spatial distribution of SMB over centuries, but with a too coarse resolution with regards to the large variations due to local orographic effects. We have therefore explored a methodology to statistically downscale the SMB components from the climate model historical simulations (1850-present day). An analogue method is set up over a period of 30 years with the ERA-Interim reanalysis (1979-2010 AD) and associated with SMB components from the Regional Atmospheric Climate Model (RACMO) at 5 km spatial resolution over Dronning Maud in East Antarctica. The same method is then applied to the period from 1850 to present days using an ensemble of 10 simulations from the CESM2 model. This method enables to derive a spatial distribution of SMB. In addition, the changes in precipitation delivery mechanisms can be unveiled.</p>

scholarly journals The influence of non-stationary ENSO teleconnections on reconstructions of paleoclimate using a pseudoproxy framework

2015 ◽  
Vol 11 (4) ◽  
pp. 3853-3895 ◽  
Author(s):  
R. Batehup ◽  
S. McGregor ◽  
A. J. E. Gallant
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Southern Oscillation ◽  
Global Climate ◽  
Global Climate Model ◽  
Proxy Records ◽  
Enso Teleconnections ◽  
Reconstruction Methods ◽  
Paleoclimate Records ◽  
Proxy Reconstructions

Abstract. Reconstructions of the El Niño-Southern Oscillation (ENSO) ideally require high-quality, annually-resolved and long-running paleoclimate proxy records in the eastern tropical Pacific Ocean, located in ENSO's centre-of-action. However, to date, the paleoclimate records that have been extracted in the region are short or temporally and spatially sporadic, limiting the information that can be provided by these reconstructions. Consequently, most ENSO reconstructions exploit the downstream influences of ENSO on remote locations, known as teleconnections, where longer records from paleoclimate proxies exist. However, using teleconnections to reconstruct ENSO relies on the assumption that the relationship between ENSO and the remote location is stationary in time. Increasing evidence from observations and climate models suggests that some teleconnections are, in fact, non-stationary, potentially threatening the validity of those paleoclimate reconstructions that exploit teleconnections. This study examines the implications of non-stationary teleconnections on modern multi-proxy reconstructions of ENSO. The sensitivity of the reconstructions to non-stationary teleconnections were tested using a suite of idealized pseudoproxy experiments that employed output from a fully coupled global climate model. Reconstructions of the variance in the Niño 3.4 index, representing ENSO variability, were generated using four different methods to which surface temperature data from the GFDL CM2.1 was applied as a pseudoproxy. As well as sensitivity of the reconstruction to the method, the experiments tested the sensitivity of the reconstruction to the number of non-stationary pseudoproxies and the location of these proxies. ENSO reconstructions in the pseudoproxy experiments were not sensitive to non-stationary teleconnections when global, uniformly-spaced networks of a minimum of approximately 20 proxies were employed. Neglecting proxies from ENSO's center-of-action still produced skillful reconstructions, but the chance of generating a skillful reconstruction decreased. Reconstruction methods that utilized raw time series were the most sensitive to non-stationary teleconnections, while calculating the running variance of pseudoproxies first, appeared to improve the robustness of the resulting reconstructions. The results suggest that caution should be taken when developing reconstructions using proxies from a single teleconnected region, or those that use less than 20 source proxies.

scholarly journals A spectral approach to estimating the timescale-dependent uncertainty of paleoclimate records – Part 2: Application and interpretation

2021 ◽  
Vol 17 (2) ◽  
pp. 825-841
Author(s):  
Andrew M. Dolman ◽  
Torben Kunz ◽  
Jeroen Groeneveld ◽  
Thomas Laepple
Keyword(s):  
Error Estimates ◽  
Marine Sediment ◽  
Sediment Cores ◽  
Theoretical Framework ◽  
New Approach ◽  
Past Climate ◽  
Proxy Records ◽  
Spatial Coverage ◽  
Paleoclimate Records ◽  
Earth’S Climate

Abstract. Proxy climate records are an invaluable source of information about the earth's climate prior to the instrumental record. The temporal and spatial coverage of records continues to increase; however, these records of past climate are associated with significant uncertainties due to non-climate processes that influence the recorded and measured proxy values. Generally, these uncertainties are timescale dependent and correlated in time. Accounting for structure in the errors is essential for providing realistic error estimates for smoothed or stacked records, detecting anomalies, and identifying trends, but this structure is seldom accounted for. In the first of these companion articles, we outlined a theoretical framework for handling proxy uncertainties by deriving the power spectrum of proxy error components from which it is possible to obtain timescale-dependent error estimates. Here in Part 2, we demonstrate the practical application of this theoretical framework using the example of marine sediment cores. We consider how to obtain estimates for the required parameters and give examples of the application of this approach for typical marine sediment proxy records. Our new approach of estimating and providing timescale-dependent proxy errors overcomes the limitations of simplistic single-value error estimates. We aim to provide the conceptual basis for a more quantitative use of paleo-records for applications such as model–data comparison, regional and global synthesis of past climate states, and data assimilation.

scholarly journals Comparing Seawater Temperature Proxy Records for the Past 90 Myrs From the Shallow Shelf Record Bass River, New Jersey

2019 ◽  
Vol 34 (4) ◽  
pp. 455-475 ◽  
Author(s):  
M. W. Bar ◽  
L. J. Nooijer ◽  
S. Schouten ◽  
M. Ziegler ◽  
A. Sluijs ◽  
...  
Keyword(s):  
New Jersey ◽  
Seawater Temperature ◽  
The Past ◽  
Proxy Records ◽  
Temperature Proxy

Performance evaluation of ensemble precipitation forecasts and satellite products for the spring 2019 severe floods in Iran

2021 ◽  
Author(s):  
Saleh Aminyavari ◽  
Bahram Saghafian ◽  
Ehsan Sharifi
Keyword(s):  
Spatial Distribution ◽  
Weather Prediction ◽  
Precipitation Amount ◽  
Warning System ◽  
Extreme Precipitation Events ◽  
Spatial Coverage ◽  
Precipitation Estimates ◽  
Precipitation Threshold ◽  
Precipitation Thresholds ◽  
Precipitation Events

<p>In this study, the performance of ensemble precipitation forecasts of three numerical weather prediction (NWP) models within the TIGGE database as well as the integrated multi-satellite retrievals for global precipitation measurement (GPM), namely IMERG-RT V05B, for precipitation estimates were evaluated in recent severe floods in Iran over the March–April 2019 period. The evaluations were conducted in two modes: spatial distribution of precipitation and the dichotomous evaluation in four precipitation thresholds (25, 50, 75, and 100 mm per day). The results showed that the United Kingdom Met Office (UKMO) model, in terms of spatial coverage and satellite estimates as well as the precipitation amount, were closer to the observations. Although, generally, the models captured the spatial distribution of heavy precipitation events, the hot spots were not located in the correct area. The National Centers for Environmental Forecast (NCEP) model performed well at low precipitation thresholds, while at high thresholds, its performance decreased significantly. On the contrary, the accuracy of IMERG improved when the precipitation threshold increased. The UKMO had better forecasts than the other models at the 100 mm/day precipitation threshold, whereas the Medium-Range Weather Forecasts (ECMWF) had acceptable forecasts in all thresholds and was able to forecast precipitation events with a lower false alarm ratio and better detection when compared to other models. Although, the models and IMERG product underestimated or overestimated the amount of precipitation, but they were able to detect most extreme precipitation events. Overall, the results of this study show the IMERG precipitation estimates and NWP ensemble forecasts performed well in the three major flood events in spring 2019 in Iran. Given wide spread damages caused by the floods, the necessity of establishing an efficient flood warning system using the best precipitation products is advised.</p><p> </p>

scholarly journals A Source–Receptor Perspective on the Polar Hydrologic Cycle: Sources, Seasonality, and Arctic–Antarctic Parity in the Hydrologic Cycle Response to CO2 Doubling

2017 ◽  
Vol 30 (24) ◽  
pp. 9999-10017 ◽  
Author(s):  
Hansi K. A. Singh ◽  
Cecilia M. Bitz ◽  
Aaron Donohoe ◽  
Philip J. Rasch
Keyword(s):  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Critical Role ◽  
Winter Season ◽  
Hydrologic Cycle ◽  
The Arctic ◽  
Moisture Sources ◽  
Proxy Records ◽  
Transport Length

Numerical water tracers implemented in a global climate model are used to study how polar hydroclimate responds to CO2-induced warming from a source–receptor perspective. Although remote moisture sources contribute substantially more to polar precipitation year-round in the mean state, an increase in locally sourced moisture is crucial to the winter season polar precipitation response to greenhouse gas forcing. In general, the polar hydroclimate response to CO2-induced warming is strongly seasonal: over both the Arctic and Antarctic, locally sourced moisture constitutes a larger fraction of the precipitation in winter, while remote sources become even more dominant in summer. Increased local evaporation in fall and winter is coincident with sea ice retreat, which greatly augments local moisture sources in these seasons. In summer, however, larger contributions from more remote moisture source regions are consistent with an increase in moisture residence times and a longer moisture transport length scale, which produces a robust hydrologic cycle response to CO2-induced warming globally. The critical role of locally sourced moisture in the hydrologic cycle response of both the Arctic and Antarctic is distinct from controlling factors elsewhere on the globe; for this reason, great care should be taken in interpreting polar isotopic proxy records from climate states unlike the present.

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