191 results on '"Harry J. Dowsett"'
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2. Past terrestrial hydroclimate sensitivity controlled by Earth system feedbacks
- Author
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Ran Feng, Tripti Bhattacharya, Bette L. Otto-Bliesner, Esther C. Brady, Alan M. Haywood, Julia C. Tindall, Stephen J. Hunter, Ayako Abe-Ouchi, Wing-Le Chan, Masa Kageyama, Camille Contoux, Chuncheng Guo, Xiangyu Li, Gerrit Lohmann, Christian Stepanek, Ning Tan, Qiong Zhang, Zhongshi Zhang, Zixuan Han, Charles J. R. Williams, Daniel J. Lunt, Harry J. Dowsett, Deepak Chandan, and W. Richard Peltier
- Subjects
Science - Abstract
In contrast to future projections, paleoclimate records often find wetter subtropics in tandem with elevated CO2. Here, a compilation of proxies and simulations are used to reveal the climate dynamics and feedbacks responsible for generating wet subtropics during the mid-Pliocene.
- Published
- 2022
- Full Text
- View/download PDF
3. Multi-variate Factorisation of Numerical Simulations
- Author
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Daniel J Lunt, Deepak Chandan, Harry J Dowsett, Alan M Haywood, George M Lunt, Jonathan C Rougier, Ulrich Salzmann, Gavin A Schmidt, and Paul J Valdes
- Subjects
Meteorology And Climatology - Abstract
Factorisation is widely used in the analysis of numerical simulations. It allows changes in properties of a system to be attributed to changes in multiple variables associated with that system. There are many possible factorisation methods; here we discuss three previously-proposed factorisations that have been applied in the field of climate modelling: the linear factorisation, the Stein and Alpert (1993) factorisation, and the Lunt et al (2012) factorisation. We show that, when more than two variables are being considered, none of these three methods possess all three properties of "uniqueness", "symmetry", and "completeness". Here, we extend each of these factorisations so that they do possess these properties for any number of variables, resulting in three factorisations – the "linear-sum" factorisation, the "shared-interaction" factorisation, and the "scaled-total" factorisation. We show that the linear-sum factorisation and the shared-interaction factorisation reduce to be identical. We present the results of the factorisations in the context of studies that used the previously-proposed factorisations. This reveals that only the linear-sum/shared-interaction factorisation possesses a fourth property – "boundedness", and as such we recommend the use of this factorisation in applications for which these properties are desirable.
- Published
- 2022
4. Biogeography and ecology of Ostracoda in the U.S. northern Bering, Chukchi, and Beaufort Seas.
- Author
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Laura Gemery, Thomas M Cronin, Lee W Cooper, Harry J Dowsett, and Jacqueline M Grebmeier
- Subjects
Medicine ,Science - Abstract
Ostracoda (bivalved Crustacea) comprise a significant part of the benthic meiofauna in the Pacific-Arctic region, including more than 50 species, many with identifiable ecological tolerances. These species hold potential as useful indicators of past and future ecosystem changes. In this study, we examined benthic ostracodes from nearly 300 surface sediment samples, >34,000 specimens, from three regions-the northern Bering, Chukchi and Beaufort Seas-to establish species' ecology and distribution. Samples were collected during various sampling programs from 1970 through 2018 on the continental shelves at 20 to ~100m water depth. Ordination analyses using species' relative frequencies identified six species, Normanicythere leioderma, Sarsicytheridea bradii, Paracyprideis pseudopunctillata, Semicytherura complanata, Schizocythere ikeyai, and Munseyella mananensis, as having diagnostic habitat ranges in bottom water temperatures, salinities, sediment substrates and/or food sources. Species relative abundances and distributions can be used to infer past bottom environmental conditions in sediment archives for paleo-reconstructions and to characterize potential changes in Pacific-Arctic ecosystems in future sampling studies. Statistical analyses further showed ostracode assemblages grouped by the summer water masses influencing the area. Offshore-to-nearshore transects of samples across different water masses showed that complex water mass characteristics, such as bottom temperature, productivity, as well as sediment texture, influenced the relative frequencies of ostracode species over small spatial scales. On the larger biogeographic scale, synoptic ordination analyses showed dominant species-N. leioderma (Bering Sea), P. pseudopunctillata (offshore Chukchi and Beaufort Seas), and S. bradii (all regions)-remained fairly constant over recent decades. However, during 2013-2018, northern Pacific species M. mananensis and S. ikeyai increased in abundance by small but significant proportions in the Chukchi Sea region compared to earlier years. It is yet unclear if these assemblage changes signify a meiofaunal response to changing water mass properties and if this trend will continue in the future. Our new ecological data on ostracode species and biogeography suggest these hypotheses can be tested with future benthic monitoring efforts.
- Published
- 2021
- Full Text
- View/download PDF
5. The Yorktown Formation: Improved Stratigraphy, Chronology, and Paleoclimate Interpretations from the U.S. Mid-Atlantic Coastal Plain
- Author
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Harry J. Dowsett, Marci M. Robinson, Kevin M. Foley, and Timothy D. Herbert
- Subjects
Pliocene ,Piacenzian ,Yorktown ,paleoclimate ,paleoecology ,Atlantic Coastal Plain ,Geology ,QE1-996.5 - Abstract
The Yorktown Formation records paleoclimate conditions along the mid-Atlantic Coastal Plain during the mid-Piacenzian Warm Period (3.264 to 3.025 Ma), a climate interval of the Pliocene in some ways analogous to near future climate projections. To gain insight into potential near future changes, we investigated Yorktown Formation outcrops and cores in southeastern Virginia, refining the stratigraphic framework. We analyzed 485 samples for alkenone-based sea surface temperature (SST) and productivity estimates from the Holland and Dory cores, an outcrop at Morgarts Beach, Virginia, and the lectostratotype of the Yorktown Formation at Rushmere, Virginia, and analyzed planktonic foraminferal assemblage data from the type section. Using the structure of the SST record, we improved the chronology of the Yorktown Formation by establishing the maximum age ranges of the Rushmere (3.3–3.2 Ma) and Morgarts Beach (3.2–3.15 Ma) Members. SST values for these members average ~26 °C, corroborating existing sclerochronological data. Increasing planktonic foraminifer abundance, productivity, and species diversity parallel increasing SST over the MIS M2/M1 transition. These records constitute the greatest temporal concentration of paleoecological estimates within the Yorktown Formation, aiding our understanding of western North Atlantic temperature patterns, seasonality and ocean circulation during this interval. We provide a chronologic framework for future studies analyzing ecological responses to profound climate change.
- Published
- 2021
- Full Text
- View/download PDF
6. Evaluation of Arctic Warming in Mid-Pliocene Climate Simulations
- Author
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Wesley de Nooijer, Qiong Zhang, Qiang Zhang, Xiangyu Li, Chuncheng Guo, Kerim H Nisancioglu, Alan M Haywood, Julia C Tindall, Stephen J Hunter, Harry J Dowsett, Christian Stepanek, Gerrit Lohmann, Bette L Otto-Bliesner, Ran Feng, Linda E Sohl, Mark A Chandler, Ning Tan, Camille Contoux, Gilles Ramstein, Michiel L J Baatsen, Anna S von der Heydt, Deepak Chandan, W Richard Peltier, Ayako Abe-Ouchi, Wing-Le Chan, Youichi Kamae, and Chris M Brierley
- Subjects
Meteorology And Climatology - Abstract
Palaeoclimate simulations improve our understanding of the climate, inform us about the performance of climate models in a different climate scenario, and help to identify robust features of the climate system. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), derived from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The PlioMIP2 ensemble simulates Arctic (60–90∘ N) annual mean surface air temperature (SAT) increases of 3.7 to 11.6 ∘C compared to the pre-industrial period, with a multi-model mean (MMM) increase of 7.2 ∘C. The Arctic warming amplification ratio relative to global SAT anomalies in the ensemble ranges from 1.8 to 3.1 (MMM is 2.3). Sea ice extent anomalies range from −3.0 to −10.4×106 km2, with a MMM anomaly of −5.6×106 km2, which constitutes a decrease of 53 % compared to the pre-industrial period. The majority (11 out of 16) of models simulate summer sea-ice-free conditions (≤1×106 km2) in their mPWP simulation. The ensemble tends to underestimate SAT in the Arctic when compared to available reconstructions, although the degree of underestimation varies strongly between the simulations. The simulations with the highest Arctic SAT anomalies tend to match the proxy dataset in its current form better. The ensemble shows some agreement with reconstructions of sea ice, particularly with regard to seasonal sea ice. Large uncertainties limit the confidence that can be placed in the findings and the compatibility of the different proxy datasets. We show that while reducing uncertainties in the reconstructions could decrease the SAT data–model discord substantially, further improvements are likely to be found in enhanced boundary conditions or model physics. Lastly, we compare the Arctic warming in the mPWP to projections of future Arctic warming and find that the PlioMIP2 ensemble simulates greater Arctic amplification than CMIP5 future climate simulations and an increase instead of a decrease in Atlantic Meridional Overturning Circulation (AMOC) strength compared to pre-industrial period. The results highlight the importance of slow feedbacks in equilibrium climate simulations, and that caution must be taken when using simulations of the mPWP as an analogue for future climate change.
- Published
- 2020
- Full Text
- View/download PDF
7. The Pliocene Model Intercomparison Project Phase 2: Large-scale Climate Features and Climate Sensitivity
- Author
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Alan M Haywood, Julia C Tindall, Harry J Dowsett, Aisling M Dolan, Kevin M Foley, Stephen J Hunter, Daniel J Hill, Wing-Le Chan, Ayako Abe-Ouchi, Christian Stepanek, Gerrit Lohmann, Deepak Chandan, W Richard Peltier, Ning Tan, Camille Contoux, Gilles Ramstein, Xiangyu Li, Zhongshi Zhang, Chuncheng Guo, Kerim H Nisancioglu, Qiong Zhang, Qiang Li, Youichi Kamae, Mark A Chandler, Linda E Sohl, Bette L Otto-Bliesner, Ran Feng, Esther C Brady, Anna S von der Heydt, Michiel L J Baatsen, and Daniel H Lunt
- Subjects
Meteorology And Climatology - Abstract
The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ∼400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.7 and 5.2 ∘C relative to the pre-industrial era with a multi-model mean value of 3.2 ∘C. Annual mean total precipitation rates increase by 7 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases by 4.3 ∘C over land and 2.8 ∘C over the oceans. There is a clear pattern of polar amplification with warming polewards of 60∘ N and 60∘ S exceeding the global mean warming by a factor of 2.3. In the Atlantic and Pacific oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. There is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (equilibrium climate sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble Earth system response to a doubling of CO2 (including ice sheet feedbacks) is 67 % greater than ECS; this is larger than the increase of 47 % obtained from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea surface temperatures are used to assess model estimates of ECS and give an ECS range of 2.6–4.8 ∘C. This result is in general accord with the ECS range presented by previous Intergovernmental Panel on Climate Change (IPCC) Assessment Reports.
- Published
- 2020
- Full Text
- View/download PDF
8. Benthic Foraminiferal and Sedimentologic Changes in the Pliocene Yorktown Formation, Virginia, USA
- Author
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Whittney E. Spivey, Stephen J. Culver, David J. Mallinson, Harry J. Dowsett, and Martin A. Buzas
- Subjects
Paleontology ,Microbiology - Abstract
The Pliocene Yorktown Formation consists of four lithologic units that record three marine transgressive sequences along the U.S. mid-Atlantic margin. These units were deposited during a time when average sea-level and mean global temperatures were ∼25 m and ∼3°C higher than the pre-industrial, respectively, and global atmospheric CO2 concentrations were similar to present. Forty-five samples were collected along the James River near Rushmere, Virginia, and Spring Grove, Virginia, and were analyzed for benthic foraminifera community and sedimentological changes between each member of the formation. These data are useful for developing boundary conditions for shallow, near-shore environments for paleoclimate modeling. Foraminiferal analysis distinguishes six biofacies across the entire formation. The most notable change in grain-size occurs at the conformable boundary between the Rushmere and Morgarts Beach members, where the average percentage of sand decreases from ∼60% in the Rushmere Member to
- Published
- 2022
9. Integrating geological archives and climate models for the mid-Pliocene warm period
- Author
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Alan M. Haywood, Harry J. Dowsett, and Aisling M. Dolan
- Subjects
Science - Abstract
Abstract The mid-Pliocene Warm Period (mPWP) offers an opportunity to understand a warmer-than-present world and assess the predictive ability of numerical climate models. Environmental reconstruction and climate modelling are crucial for understanding the mPWP, and the synergy of these two, often disparate, fields has proven essential in confirming features of the past and in turn building confidence in projections of the future. The continual development of methodologies to better facilitate environmental synthesis and data/model comparison is essential, with recent work demonstrating that time-specific (time-slice) syntheses represent the next logical step in exploring climate change during the mPWP and realizing its potential as a test bed for understanding future climate change.
- Published
- 2016
- Full Text
- View/download PDF
10. MIOCENE NERITIC BENTHIC FORAMINIFERAL COMMUNITY DYNAMICS, CALVERT CLIFFS, MARYLAND, USA: SPECIES POOL, PATTERNS AND PROCESSES
- Author
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Harry J. Dowsett, Stephen J. Culver, Seth R. Sutton, David J. Mallinson, Martin A. Buzas, and Marci M. Robinson
- Subjects
010506 paleontology ,biology ,Rare species ,Paleontology ,Species diversity ,Context (language use) ,010502 geochemistry & geophysics ,biology.organism_classification ,01 natural sciences ,Foraminifera ,Oceanography ,Common species ,Benthic zone ,Abundance (ecology) ,Sequence stratigraphy ,Ecology, Evolution, Behavior and Systematics ,Geology ,0105 earth and related environmental sciences - Abstract
The presence/absence and abundance of benthic foraminifera in successive discrete beds (Shattuck “zones”) of the Miocene Calvert and Choptank formations, exposed at the Calvert Cliffs, Maryland, USA, allows for investigation of community dynamics over space and time. The stratigraphic distribution of benthic foraminifera is documented and interpreted in the context of sea-level change, sequence stratigraphy, and the previously published distribution of mollusks. Neritic benthic foraminiferal communities of four sea-level cycles over ∼4 million years of the middle Miocene, encompassing the Miocene Climatic Optimum and the succeeding middle Miocene Climate Transition, are dominated by the same abundant species. They differ in the varying abundance of common species that occur throughout most of the studied section and in the different rare species that appear and disappear. Transgressive systems tracts (TSTs) have higher species diversity than highstand systems tracts (HSTs) but much lower density of specimens. In contrast to some previous research, all beds in the studied section are interpreted as being from the inner part of a broad, low gradient shelf and were deposited at water depths of less than ∼50 m. It is suggested that species are recruited from a regional species pool of propagules throughout the duration of TSTs. Recruitment is curtailed during highstands leading to lower diversity in the HSTs.
- Published
- 2021
11. The Yorktown Formation: Improved Stratigraphy, Chronology, and Paleoclimate Interpretations from the U.S. Mid-Atlantic Coastal Plain
- Author
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Timothy D Herbert, Kevin M. Foley, Marci M. Robinson, and Harry J. Dowsett
- Subjects
Alkenone ,geography ,QE1-996.5 ,geography.geographical_feature_category ,Piacenzian ,Yorktown Formation ,Pliocene ,Atlantic Coastal Plain ,Coastal plain ,Ocean current ,Yorktown ,paleoclimate ,paleoecology ,alkenones ,Climate change ,Geology ,Sea surface temperature ,Oceanography ,Paleoclimatology ,General Earth and Planetary Sciences - Abstract
The Yorktown Formation records paleoclimate conditions along the mid-Atlantic Coastal Plain during the mid-Piacenzian Warm Period (3.264 to 3.025 Ma), a climate interval of the Pliocene in some ways analogous to near future climate projections. To gain insight into potential near future changes, we investigated Yorktown Formation outcrops and cores in southeastern Virginia, refining the stratigraphic framework. We analyzed 485 samples for alkenone-based sea surface temperature (SST) and productivity estimates from the Holland and Dory cores, an outcrop at Morgarts Beach, Virginia, and the lectostratotype of the Yorktown Formation at Rushmere, Virginia, and analyzed planktonic foraminferal assemblage data from the type section. Using the structure of the SST record, we improved the chronology of the Yorktown Formation by establishing the maximum age ranges of the Rushmere (3.3–3.2 Ma) and Morgarts Beach (3.2–3.15 Ma) Members. SST values for these members average ~26 °C, corroborating existing sclerochronological data. Increasing planktonic foraminifer abundance, productivity, and species diversity parallel increasing SST over the MIS M2/M1 transition. These records constitute the greatest temporal concentration of paleoecological estimates within the Yorktown Formation, aiding our understanding of western North Atlantic temperature patterns, seasonality and ocean circulation during this interval. We provide a chronologic framework for future studies analyzing ecological responses to profound climate change.
- Published
- 2021
12. Very high Middle Miocene surface productivity on the U.S. mid-Atlantic shelf amid glacioeustatic sea level variability
- Author
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Marci M. Robinson, Harry J. Dowsett, and Timothy D. Herbert
- Subjects
Paleontology ,Oceanography ,Ecology, Evolution, Behavior and Systematics ,Earth-Surface Processes - Published
- 2022
13. 100‐kyr Paced Climate Change in the Pliocene Warm Period, Southwest Pacific
- Author
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Timothy D Herbert, Rocio P Caballero-Gill, and Harry J. Dowsett
- Subjects
Atmospheric Science ,Climatology ,Period (geology) ,Paleontology ,Climate change ,Oceanography ,Southern Hemisphere ,Geology - Published
- 2019
14. FORAMINIFERAL SIGNALS IN ATLANTIC COASTAL PLAIN SEDIMENTS
- Author
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Marci M. Robinson, Harry J. Dowsett, Seth R. Sutton, Kevin M. Foley, Whittney E. Spivey, and Jean M. Self-Trail
- Subjects
geography ,geography.geographical_feature_category ,Oceanography ,Coastal plain ,Geology - Published
- 2021
15. Estimating Piacenzian sea surface temperature using an alkenone-calibrated transfer function
- Author
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Harry J. Dowsett, Marci M. Robinson, and Kevin M. Foley
- Subjects
Sea surface temperature ,Alkenone ,Piacenzian ,Atmospheric sciences ,Transfer function ,Geology - Published
- 2021
16. Speaking to the past
- Author
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Harry J. Dowsett
- Subjects
Statistics and Probability ,0303 health sciences ,Phrase ,History ,010504 meteorology & atmospheric sciences ,Comment ,MEDLINE ,Library and Information Sciences ,Palaeoclimate ,01 natural sciences ,Linguistics ,Research data ,Computer Science Applications ,Education ,03 medical and health sciences ,Climate change ,lcsh:Q ,Statistics, Probability and Uncertainty ,lcsh:Science ,030304 developmental biology ,0105 earth and related environmental sciences ,Information Systems - Abstract
“Speak to the past and it shall teach thee”. I first read those words on a dedication tablet within the John Carter Brown library at Brown University where I was a graduate student. Little did I know the phrase would accurately describe the next three and a half decades of my career. Paleoclimate data are the language we use to look into the past to understand ourselves and ultimately our future.
- Published
- 2020
- Full Text
- View/download PDF
17. Multi-variate factorisation of numerical simulations
- Author
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Daniel John Lunt, Deepak Chandan, Harry J. Dowsett, Alan M. Haywood, George M. Lunt, Jonathan C. Rougier, Ulrich Salzmann, Gavin A. Schmidt, and Paul J. Valdes
- Abstract
Factorisation is widely used in the analysis of numerical simulations. It allows changes in properties of a system to be attributed to changes in multiple variables associated with that system. There are many possible factorisation methods; here we discuss three previously-proposed factorisations that have been applied in the field of climate modelling: the linear factorisation, the Stein and Alpert (1993) factorisation, and the Lunt et al (2012) factorisation. We show that, when more than two variables are being considered, none of these three methods possess all three properties of uniqueness, symmetry, and completeness. Here, we extend each of these factorisations so that they do possess these properties for any number of variables, resulting in three factorisations – the linear-sum factorisation, the shared-interaction factorisation, and the scaled-total factorisation. We show that the linear-sum factorisation and the shared-interaction factorisation reduce to be identical. We present the results of the factorisations in the context of studies that used the previously-proposed factorisations. This reveals that only the linear-sum/shared-interaction factorisation possesses a fourth property – boundedness, and as such we recommend the use of this factorisation in applications for which these properties are desirable.
- Published
- 2020
18. Supplementary material to 'Multi-variate factorisation of numerical simulations'
- Author
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Daniel John Lunt, Deepak Chandan, Harry J. Dowsett, Alan M. Haywood, George M. Lunt, Jonathan C. Rougier, Ulrich Salzmann, Gavin A. Schmidt, and Paul J. Valdes
- Published
- 2020
19. Supplementary material to 'Evaluation of Arctic warming in mid-Pliocene climate simulations'
- Author
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Wesley de Nooijer, Qiong Zhang, Qiang Li, Qiang Zhang, Xiangyu Li, Zhongshi Zhang, Chuncheng Guo, Kerim H. Nisancioglu, Alan M. Haywood, Julia C. Tindall, Stephen J. Hunter, Harry J. Dowsett, Christian Stepanek, Gerrit Lohmann, Bette L. Otto-Bliesner, Ran Feng, Linda E. Sohl, Ning Tan, Camille Contoux, Gilles Ramstein, Michiel L. J. Baatsen, Anna S. von der Heydt, Deepak Chandan, W. Richard Peltier, Ayako Abe-Ouchi, Wing-Le Chan, Youichi Kamae, and Chris M. Brierley
- Published
- 2020
20. A return to large-scale features of Pliocene climate: the Pliocene Model Intercomparison Project Phase 2
- Author
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Anna von der Heydt, Ran Feng, Linda E. Sohl, Bette L. Otto-Bliesner, W. Richard Peltier, Xiangyu Li, Aisling M. Dolan, Qiang Li, Kevin M. Foley, Christian Stepanek, Gerrit Lohmann, Kerim H. Nisancioglu, Esther C. Brady, Ning Tan, Alan M. Haywood, Gilles Ramstein, Daniel J. Hill, Mark A. Chandler, Deepak Chandan, Julia Tindall, Daniel J. Lunt, Qiong Zhang, Zhongshi Zhang, Harry J. Dowsett, Wing-Le Chan, Michiel Baatsen, Stephen J. Hunter, Chuncheng Guo, Ayako Abe-Ouchi, Yoichi Kamae, and Camille Contoux
- Subjects
010506 paleontology ,geography ,Series (stratigraphy) ,geography.geographical_feature_category ,Zonal and meridional ,Atmospheric sciences ,01 natural sciences ,13. Climate action ,Polar amplification ,Pliocene climate ,Environmental science ,Climate sensitivity ,Climate model ,Precipitation ,Ice sheet ,0105 earth and related environmental sciences - Abstract
The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ~ 400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution and based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.4 and 4.7 °C relative to pre-industrial with a multi-model mean value of 2.8 °C. Annual mean total precipitation rates increase by 6 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases are 1.3 °C greater over the land than over the oceans, and there is a clear pattern of polar amplification with warming polewards of 60° N and 60° S exceeding the global mean warming by a factor of 2.4. In the Atlantic and Pacific Oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. Although there are some modelling constraints, there is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (Equilibrium Climate Sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble earth system response to doubling of CO2 (including ice sheet feedbacks) is approximately 50 % greater than ECS, consistent with results from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea-surface temperatures are used to assess model estimates of ECS and indicate a range in ECS from 2.5 to 4.3 °C. This result is in general accord with the range in ECS presented by previous IPCC Assessment Reports.
- Published
- 2020
21. Supplementary material to 'A return to large-scale features of Pliocene climate: the Pliocene Model Intercomparison Project Phase 2'
- Author
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Alan M. Haywood, Julia C. Tindall, Harry J. Dowsett, Aisling M. Dolan, Kevin M. Foley, Stephen J. Hunter, Dan J. Hill, Wing-Le Chan, Ayako Abe-Ouchi, Christian Stepanek, Gerrit Lohmann, Deepak Chandan, W. Richard Peltier, Ning Tan, Camille Contoux, Gilles Ramstein, Xiangyu Li, Zhongshi Zhang, Chuncheng Guo, Kerim H. Nisancioglu, Qiong Zhang, Qiang Li, Yoichi Kamae, Mark A. Chandler, Linda E. Sohl, Bette L. Otto-Bliesner, Ran Feng, Esther C. Brady, Anna S. von der Heydt, Michiel L. J. Baatsen, and Daniel J. Lunt
- Published
- 2020
22. PEAK WARMING DURING MARINE ISOTOPE STAGE 11 IN THE ARCTIC OCEAN BASED ON PLANKTIC FORAMINIFERA
- Author
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Helen K. Coxall, Rowan Lockwood, Alexa M. Regnier, Harry J. Dowsett, Marci M. Robinson, Matt O'Regan, and Thomas W. Cronin
- Subjects
Foraminifera ,Marine Isotope Stage 11 ,Oceanography ,biology ,Environmental science ,biology.organism_classification ,The arctic - Published
- 2020
23. SEA SURFACE TEMPERATURE PREFERENCES OF DENTOGLOBIGERINA ALTISPIRA DURING THE LATE PLIOCENE
- Author
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Kevin M. Foley, Harry J. Dowsett, and Marci M. Robinson
- Subjects
Sea surface temperature ,Oceanography ,Geology - Published
- 2020
24. North Atlantic Piacenzian Data Model Comparison: PRISM4 and PlioMIP2
- Author
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Harry J. Dowsett and Kevin M. Foley
- Subjects
Piacenzian ,Interval (graph theory) ,Global change ,Physical geography ,Data model (GIS) ,Geology - Abstract
The mid-Piacenzian (Pliocene) climate represents the most geologically recent interval of long-term average warmth, relative to the last million years, sharing similarities with the climate project...
- Published
- 2019
25. The mid-Piacenzian of the North Atlantic Ocean
- Author
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Whittney E. Spivey, Kevin M. Foley, Timothy D Herbert, Harry J. Dowsett, Marci M. Robinson, and Bette L. Otto-Bliesner
- Subjects
Piacenzian ,Oceanography ,Paleontology ,Geology - Published
- 2018
26. Icebergs in the Nordic Seas Throughout the Late Pliocene
- Author
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Yvonne Smith, Aisling M. Dolan, Harry J. Dowsett, Daniel J. Hill, Bjørg Risebrobakken, and Alan M. Haywood
- Subjects
Marine isotope stage ,Atmospheric Science ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Paleontology ,Glacier ,010502 geochemistry & geophysics ,Oceanography ,01 natural sciences ,Iceberg ,13. Climate action ,Paleoceanography ,Period (geology) ,Cryosphere ,Climate model ,Ice sheet ,Geology ,0105 earth and related environmental sciences - Abstract
The Arctic cryosphere is changing and making a significant contribution to sea level rise. The Late Pliocene had similar CO2 levels to the present and a warming comparable to model predictions for the end of this century. However, the state of the Arctic cryosphere during the Pliocene remains poorly constrained. For the first time we combine outputs from a climate model with a thermodynamic iceberg model to simulate likely source regions for ice-rafted debris (IRD) found in the Nordic Seas from Marine Isotope Stage M2 to the mid-Piacenzian Warm Period and what this implies about the nature of the Arctic cryosphere at this time. We compare the fraction of melt given by the model scenarios with IRD data from four Ocean Drilling Program sites in the Nordic Seas. Sites 911A, 909C, and 907A show a persistent occurrence of IRD that model results suggest is consistent with permanent ice on Svalbard. Our results indicate that icebergs sourced from the east coast of Greenland do not reach the Nordic Seas sites during the warm Late Pliocene but instead travel south into the North Atlantic. In conclusion, we suggest a continuous occurrence of marine-terminating glaciers on Svalbard and on East Greenland (due to the elevation of the East Greenland Mountains during the Late Pliocene). The study has highlighted the usefulness of coupled climate model-iceberg trajectory modeling for understanding ice sheet behavior when proximal geological records for Pliocene ice presence or absence are absent or are inconclusive.
- Published
- 2018
27. Biogeography and ecology of Ostracoda in the U.S. northern Bering, Chukchi, and Beaufort Seas
- Author
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Thomas M. Cronin, Harry J. Dowsett, Lee W. Cooper, Laura Gemery, and Jacqueline M. Grebmeier
- Subjects
Salinity ,Marine and Aquatic Sciences ,Oceanography ,Physical Chemistry ,Abundance (ecology) ,Crustacea ,Geological Facies ,Sedimentary Geology ,Multidisciplinary ,geography.geographical_feature_category ,Environmental Biomarkers ,Ecology ,Geography ,Arctic Regions ,Temperature ,Marine Ecology ,Geology ,Chemistry ,Biogeography ,Habitat ,Benthic zone ,Physical Sciences ,Medicine ,Seasons ,Environmental Monitoring ,Research Article ,Water mass ,Science ,Oceans and Seas ,Meiobenthos ,Marine Biology ,Bottom water ,Sea Water ,Biofacies ,Animals ,Seawater ,Ocean Temperature ,Ecosystem ,Shellfish ,Petrology ,geography ,Continental shelf ,Ecology and Environmental Sciences ,Aquatic Environments ,Biology and Life Sciences ,Paleontology ,Marine Environments ,Chemical Properties ,Earth Sciences ,Environmental science ,Sediment ,Paleoecology ,Paleobiology - Abstract
Ostracoda (bivalved Crustacea) comprise a significant part of the benthic meiofauna in the Pacific-Arctic region, including more than 50 species, many with identifiable ecological tolerances. These species hold potential as useful indicators of past and future ecosystem changes. In this study, we examined benthic ostracodes from nearly 300 surface sediment samples, >34,000 specimens, from three regions—the northern Bering, Chukchi and Beaufort Seas—to establish species’ ecology and distribution. Samples were collected during various sampling programs from 1970 through 2018 on the continental shelves at 20 to ~100m water depth. Ordination analyses using species’ relative frequencies identified six species,Normanicythere leioderma,Sarsicytheridea bradii,Paracyprideis pseudopunctillata,Semicytherura complanata,Schizocythere ikeyai, andMunseyella mananensis, as having diagnostic habitat ranges in bottom water temperatures, salinities, sediment substrates and/or food sources. Species relative abundances and distributions can be used to infer past bottom environmental conditions in sediment archives for paleo-reconstructions and to characterize potential changes in Pacific-Arctic ecosystems in future sampling studies. Statistical analyses further showed ostracode assemblages grouped by the summer water masses influencing the area. Offshore-to-nearshore transects of samples across different water masses showed that complex water mass characteristics, such as bottom temperature, productivity, as well as sediment texture, influenced the relative frequencies of ostracode species over small spatial scales. On the larger biogeographic scale, synoptic ordination analyses showed dominant species—N.leioderma(Bering Sea),P.pseudopunctillata(offshore Chukchi and Beaufort Seas), andS.bradii(all regions)—remained fairly constant over recent decades. However, during 2013–2018, northern Pacific speciesM.mananensisandS.ikeyaiincreased in abundance by small but significant proportions in the Chukchi Sea region compared to earlier years. It is yet unclear if these assemblage changes signify a meiofaunal response to changing water mass properties and if this trend will continue in the future. Our new ecological data on ostracode species and biogeography suggest these hypotheses can be tested with future benthic monitoring efforts.
- Published
- 2021
28. Endless Forams: >34,000 Modern Planktonic Foraminiferal Images for Taxonomic Training and Automated Species Recognition Using Convolutional Neural Networks
- Author
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Catherine V. Davis, Sian Lordsmith, Kirsty M. Edgar, Anna Jentzen, Nelson Rios, Isabel S. Fenton, Allison Y. Hsiang, Ulrike Baranowski, Tracy Aze, Jeroen Groeneveld, Bridget S. Wade, Aurore Movellan, Stephen Conn, Michael J. Henehan, Harry J. Dowsett, Lyndsey Fox, C. Giles Miller, Julie Meilland, Marina C. Rillo, Maryline J. Mleneck-Vautravers, Anieke Brombacher, Brett Metcalfe, Pincelli M. Hull, Earth and Climate, Swedish Museum of Natural History (NRM), National Oceanography Centre [Southampton] (NOC), University of Southampton, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), VU University Amsterdam, Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Vrije Universiteit Amsterdam [Amsterdam] (VU), and Vrije universiteit = Free university of Amsterdam [Amsterdam] (VU)
- Subjects
010506 paleontology ,Atmospheric Science ,010504 meteorology & atmospheric sciences ,Computer science ,species identification ,Oceanography ,computer.software_genre ,01 natural sciences ,Convolutional neural network ,Foraminifera ,planktonic foraminifera ,convolutional neural networks ,Citizen science ,Correct name ,supervised machine learning ,14. Life underwater ,[SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment ,0105 earth and related environmental sciences ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,Learning classifier system ,Species name ,Artificial neural network ,biology ,business.industry ,Paleontology ,biology.organism_classification ,marine microfossils ,global community macroecology ,Taxonomy (biology) ,Artificial intelligence ,business ,computer ,Natural language processing - Abstract
International audience; Planktonic foraminiferal species identification is central to many paleoceanographic studies, from selecting species for geochemical research to elucidating the biotic dynamics of microfossil communities relevant to physical oceanographic processes and interconnected phenomena such as climate change. However, few resources exist to train students in the difficult task of discerning amongst closely related species, resulting in diverging taxonomic schools that differ in species concepts and boundaries. This problem is exacerbated by the limited number of taxonomic experts. Here we document our initial progress toward removing these confounding and/or rate-limiting factors by generating the first extensive image library of modern planktonic foraminifera, providing digital taxonomic training tools and resources, and automating species-level taxonomic identification of planktonic foraminifera via machine learning using convolution neural networks. Experts identified 34,640 images of modern (extant) planktonic foraminifera to the species level. These images are served as species exemplars through the online portal Endless Forams (endlessforams.org) and a taxonomic training portal hosted on the citizen science platform Zooniverse (zooniverse.org/projects/ahsiang/ endless-forams/). A supervised machine learning classifier was then trained with~27,000 images of these identified planktonic foraminifera. The best-performing model provided the correct species name for an image in the validation set 87.4% of the time and included the correct name in its top three guesses 97.7% of the time. Together, these resources provide a rigorous set of training tools in modern planktonic foraminiferal taxonomy and a means of rapidly generating assemblage data via machine learning in future studies for applications such as paleotemperature reconstruction.
- Published
- 2019
29. QUANTIFYING THE IMPACTS OF THE MID-MIOCENE CLIMATE OPTIMUM AND MID-MIOCENE CLIMATE TRANSITION ON THE BENTHIC FORAMINIFERAL COMMUNITIES OF THE CHESAPEAKE GROUP, CALVERT CLIFFS, MD
- Author
-
Harry J. Dowsett, Seth R. Sutton, Martin A. Buzas, David J. Mallinson, Marci M. Robinson, and Stephen J. Culver
- Subjects
Oceanography ,Benthic zone ,Group (stratigraphy) ,Geology - Published
- 2019
30. FORAMINIFERAL AND SEDIMENTOLOGICAL ANALYSIS OF MID-MIOCENE SHATTUCK ZONES 10 THROUGH 17 FROM THE CALVERT CLIFFS, MARYLAND
- Author
-
Marci M. Robinson, Harry J. Dowsett, Martin A. Buzas, David J. Mallinson, Seth R. Sutton, and Stephen J. Culver
- Published
- 2019
31. GLOBAL PACING OF PLIOCENE CLIMATE BY NORTHERN HEMISPHERE PRECESSION: AN ENIGMA
- Author
-
Alexandrina Tzanova, Rocio P Caballero-Gill, Antonio C. Caruso, Timothy D Herbert, and Harry J. Dowsett
- Subjects
Paleontology ,Pliocene climate ,Northern Hemisphere ,Precession ,Geology - Published
- 2019
32. BENTHIC FORAMINIFERAL COMMUNITY CHANGES ACROSS THE PLIOCENE YORKTOWN FORMATION, SOUTHEASTERN VIRGINIA
- Author
-
Harry J. Dowsett, Marci M. Robinson, Martin A. Buzas, David J. Mallinson, Stephen J. Culver, and Whittney E. Spivey
- Subjects
Oceanography ,Yorktown Formation ,Benthic zone ,Geology - Published
- 2019
33. Mid-Piacenzian (Pliocene) Marine Paleoenvironments of the North Atlantic Region
- Author
-
Kevin M. Foley, Whittney E. Spivey, Harry J. Dowsett, and Marci M. Robinson
- Subjects
Piacenzian ,Oceanography ,Period (geology) ,Magnitude (mathematics) ,Climate model ,Geology ,Natural (archaeology) - Abstract
The Piacenzian (Late Pliocene) represents a natural laboratory within which frequency and magnitude of environmental changes during a period of past global warmth can be analyzed, climate models ca...
- Published
- 2018
34. Data report: late Pliocene planktonic foraminifer assemblages from IODP Holes U1443B, U1443C, and U1445A
- Author
-
Harry J. Dowsett and Marci M. Robinson
- Subjects
Paleontology ,Plankton ,Geology - Published
- 2018
35. The PRISM4 (mid-Piacenzian) paleoenvironmental reconstruction
- Author
-
David B. Rowley, Kevin M. Foley, Harry J. Dowsett, Alan M. Haywood, Ulrich Salzmann, Aisling M. Dolan, Alessandro M. Forte, Marci M. Robinson, Jerry X. Mitrovica, Matthew J. Pound, Robert Moucha, and Mark A. Chandler
- Subjects
Piacenzian ,010504 meteorology & atmospheric sciences ,Stratigraphy ,lcsh:Environmental protection ,F800 ,F600 ,Present day ,010502 geochemistry & geophysics ,01 natural sciences ,lcsh:Environmental pollution ,Sea ice ,lcsh:TD169-171.8 ,Glacial period ,Sea level ,lcsh:Environmental sciences ,0105 earth and related environmental sciences ,lcsh:GE1-350 ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,Paleontology ,Vegetation ,Ocean surface topography ,13. Climate action ,Climatology ,lcsh:TD172-193.5 ,Climate model ,Geology - Abstract
The mid-Piacenzian is known as a period of relative warmth when compared to the present day. A comprehensive understanding of conditions during the Piacenzian serves as both a conceptual model and a source for boundary conditions as well as means of verification of global climate model experiments. In this paper we present the PRISM4 reconstruction, a paleoenvironmental reconstruction of the mid-Piacenzian ( ∼ 3 Ma) containing data for paleogeography, land and sea ice, sea-surface temperature, vegetation, soils, and lakes. Our retrodicted paleogeography takes into account glacial isostatic adjustments and changes in dynamic topography. Soils and lakes, both significant as land surface features, are introduced to the PRISM reconstruction for the first time. Sea-surface temperature and vegetation reconstructions are unchanged but now have confidence assessments. The PRISM4 reconstruction is being used as boundary condition data for the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) experiments.
- Published
- 2016
36. Integrating geological archives and climate models for the mid-Pliocene warm period
- Author
-
Aisling M. Dolan, Harry J. Dowsett, and Alan M. Haywood
- Subjects
Multidisciplinary ,010504 meteorology & atmospheric sciences ,business.industry ,Science ,Environmental resource management ,General Physics and Astronomy ,Environmental reconstruction ,Climate change ,General Chemistry ,Review Article ,Future climate ,010502 geochemistry & geophysics ,Bioinformatics ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,13. Climate action ,Period (geology) ,Environmental science ,Climate model ,business ,0105 earth and related environmental sciences - Abstract
The mid-Pliocene Warm Period (mPWP), analogous to future climate conditions, is considered a test-bed for the predictive capability of climate models. Here, Dowsett et al. review our understanding of the mPWP and discuss recent and future advances in the context of proxy data/model integration., The mid-Pliocene Warm Period (mPWP) offers an opportunity to understand a warmer-than-present world and assess the predictive ability of numerical climate models. Environmental reconstruction and climate modelling are crucial for understanding the mPWP, and the synergy of these two, often disparate, fields has proven essential in confirming features of the past and in turn building confidence in projections of the future. The continual development of methodologies to better facilitate environmental synthesis and data/model comparison is essential, with recent work demonstrating that time-specific (time-slice) syntheses represent the next logical step in exploring climate change during the mPWP and realizing its potential as a test bed for understanding future climate change.
- Published
- 2016
37. The PRISM palaeoclimate reconstruction and Pliocene sea-surface temperature
- Author
-
Harry J. Dowsett
- Subjects
Paleontology ,Sea surface temperature ,Prism ,Geomorphology ,Geology - Published
- 2018
38. Sea surface temperature estimates for the mid-Piacenzian Indian Ocean—Ocean Drilling Program sites 709, 716, 722, 754, 757, 758, and 763
- Author
-
Danielle K. Stoll, Marci M. Robinson, and Harry J. Dowsett
- Subjects
Indian ocean ,Sea surface temperature ,Oceanography ,Piacenzian ,Drilling ,Geology - Published
- 2018
39. PRISM marine sites—The history of PRISM sea surface temperature estimation
- Author
-
Marci M. Robinson, Kevin M. Foley, Christina R. Riesselman, and Harry J. Dowsett
- Subjects
Sea surface temperature ,Optics ,business.industry ,Prism ,business ,Geology - Published
- 2018
40. RECONSTRUCTING INDIAN MONSOON STRENGTH IN THE BAY OF BENGAL DURING THE PLIOCENE M2 EVENT: ESTIMATION OF PALEOSALINITY LEVELS
- Author
-
Marci M. Robinson, Kristen E. St. John, Kristen L. Steele, and Harry J. Dowsett
- Subjects
Monsoon of South Asia ,Estimation ,Oceanography ,Climatology ,Event (relativity) ,BENGAL ,Paleosalinity ,Bay ,Geology - Published
- 2017
41. Late Pliocene lakes and soils: a global data set for the analysis of climate feedbacks in a warmer world
- Author
-
Ulrich Salzmann, Alan M. Haywood, Harry J. Dowsett, Steven J. Pickering, Julia Tindall, and Matthew J. Pound
- Subjects
lcsh:GE1-350 ,Global and Planetary Change ,Stratigraphy ,lcsh:Environmental protection ,Northern Hemisphere ,Paleontology ,Vegetation ,15. Life on land ,F600 ,HadCM3 ,Oceanography ,lcsh:Environmental pollution ,13. Climate action ,Global distribution ,General Circulation Model ,Soil water ,parasitic diseases ,lcsh:TD172-193.5 ,Climate model ,lcsh:TD169-171.8 ,Precipitation ,Geology ,lcsh:Environmental sciences - Abstract
The global distribution of late Pliocene soils and lakes has been reconstructed using a synthesis of geological data. These reconstructions are then used as boundary conditions for the Hadley Centre General Circulation Model (HadCM3) and the BIOME4 mechanistic vegetation model. By combining our novel soil and lake reconstructions with a fully coupled climate model we are able to explore the feedbacks of soils and lakes on the climate of the late Pliocene. Our experiments reveal regionally confined changes of local climate and vegetation in response to the new boundary conditions. The addition of late Pliocene soils has the largest influence on surface air temperatures, with notable increases in Australia, the southern part of northern Africa and in Asia. The inclusion of late Pliocene lakes increases precipitation in central Africa and at the locations of lakes in the Northern Hemisphere. When combined, the feedbacks on climate from late Pliocene lakes and soils improve the data to model fit in western North America and the southern part of northern Africa.
- Published
- 2014
42. Simulations of the mid-Pliocene Warm Period using two versions of the NASA/GISS ModelE2-R Coupled Model
- Author
-
Linda E. Sohl, J. Jonas, Maxwell Kelley, Harry J. Dowsett, and Mark A. Chandler
- Subjects
010506 paleontology ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Global warming ,lcsh:QE1-996.5 ,Climate change ,Atmospheric model ,01 natural sciences ,lcsh:Geology ,Sea surface temperature ,13. Climate action ,Effects of global warming ,Climatology ,Sea ice ,Pliocene climate ,Environmental science ,Climate model ,0105 earth and related environmental sciences - Abstract
The mid-Pliocene Warm Period (mPWP) bears many similarities to aspects of future global warming as projected by the Intergovernmental Panel on Climate Change (IPCC, 2007). Both marine and terrestrial data point to high-latitude temperature amplification, including large decreases in sea ice and land ice, as well as expansion of warmer climate biomes into higher latitudes. Here we present our most recent simulations of the mid-Pliocene climate using the CMIP5 version of the NASA/GISS Earth System Model (ModelE2-R). We describe the substantial impact associated with a recent correction made in the implementation of the Gent-McWilliams ocean mixing scheme (GM), which has a large effect on the simulation of ocean surface temperatures, particularly in the North Atlantic Ocean. The effect of this correction on the Pliocene climate results would not have been easily determined from examining its impact on the preindustrial runs alone, a useful demonstration of how the consequences of code improvements as seen in modern climate control runs do not necessarily portend the impacts in extreme climates. Both the GM-corrected and GM-uncorrected simulations were contributed to the Pliocene Model Intercomparison Project (PlioMIP) Experiment 2. Many findings presented here corroborate results from other PlioMIP multi-model ensemble papers, but we also emphasise features in the ModelE2-R simulations that are unlike the ensemble means. The corrected version yields results that more closely resemble the ocean core data as well as the PRISM3D reconstructions of the mid-Pliocene, especially the dramatic warming in the North Atlantic and Greenland-Iceland-Norwegian Sea, which in the new simulation appears to be far more realistic than previously found with older versions of the GISS model. Our belief is that continued development of key physical routines in the atmospheric model, along with higher resolution and recent corrections to mixing parameterisations in the ocean model, have led to an Earth System Model that will produce more accurate projections of future climate.
- Published
- 2013
43. Response to reviewer 2
- Author
-
Harry J. Dowsett
- Published
- 2016
44. Sensitivity of Pliocene Arctic climate to orbital forcing, atmospheric CO2 and sea ice albedo parameterisation
- Author
-
Alan M. Haywood, Harry J. Dowsett, Steven J. Pickering, and Fergus W. Howell
- Subjects
Arctic sea ice decline ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Ice-albedo feedback ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Arctic ice pack ,Arctic geoengineering ,Geophysics ,13. Climate action ,Space and Planetary Science ,Geochemistry and Petrology ,Climatology ,Sea ice thickness ,Earth and Planetary Sciences (miscellaneous) ,Sea ice ,Cryosphere ,Sea ice concentration ,Geology ,0105 earth and related environmental sciences - Abstract
General circulation model (GCM) simulations of the mid-Pliocene Warm Period (mPWP, 3.264 to 3.025 Myr ago) do not reproduce the magnitude of Northern Hemisphere high latitude surface air and sea surface temperature (SAT and SST) warming that proxy data indicate. There is also large uncertainty regarding the state of sea ice cover in the mPWP. Evidence for both perennial and seasonal mPWP Arctic sea ice is found through analyses of marine sediments, whilst in a multi-model ensemble of mPWP climate simulations, half of the ensemble simulated ice-free summer Arctic conditions. Given the strong influence that sea ice exerts on high latitude temperatures, an understanding of the nature of mPWP Arctic sea ice would be highly beneficial. Using the HadCM3 GCM, this paper explores the impact of various combinations of potential mPWP orbital forcing, atmospheric CO 2 concentrations and minimum sea ice albedo on sea ice extent and high latitude warming. The focus is on the Northern Hemisphere, due to availability of proxy data, and the large data–model discrepancies in this region. Changes in orbital forcings are demonstrated to be sufficient to alter the Arctic sea ice simulated by HadCM3 from perennial to seasonal. However, this occurs only when atmospheric CO 2 concentrations exceed 300 ppm. Reduction of the minimum sea ice albedo from 0.5 to 0.2 is also sufficient to simulate seasonal sea ice, with any of the combinations of atmospheric CO 2 and orbital forcing. Compared to a mPWP control simulation, monthly mean increases north of 60°N of up to 4.2 °C (SST) and 9.8 °C (SAT) are simulated. With varying CO 2 , orbit and sea ice albedo values we are able to reproduce proxy temperature records that lean towards modest levels of high latitude warming, but other proxy data showing greater warming remain beyond the reach of our model. This highlights the importance of additional proxy records at high latitudes and ongoing efforts to compare proxy signals between sites.
- Published
- 2016
45. The Pliocene Model Intercomparison Project (PlioMIP) Phase 2:scientific objectives and experimental design
- Author
-
Alan M. Haywood, Aisling M. Dolan, David B. Rowley, Mark A. Chandler, Ayako Abe-Ouchi, Daniel J. Lunt, Harry J. Dowsett, Ulrich Salzmann, Matthew J. Pound, Bette L. Otto-Bliesner, and Stephen J. Hunter
- Subjects
010506 paleontology ,010504 meteorology & atmospheric sciences ,Meteorology ,Stratigraphy ,lcsh:Environmental protection ,Climate change ,Atmospheric Model Intercomparison Project ,Context (language use) ,F600 ,01 natural sciences ,lcsh:Environmental pollution ,Paleoclimatology ,Pliocene climate ,Bathymetry ,lcsh:TD169-171.8 ,lcsh:Environmental sciences ,0105 earth and related environmental sciences ,lcsh:GE1-350 ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,Paleontology ,13. Climate action ,Climatology ,lcsh:TD172-193.5 ,Environmental science ,Climate model ,Ice sheet - Abstract
The Pliocene Model Intercomparison Project (PlioMIP) is a co-ordinated international climate modelling initiative to study and understand climate and environments of the Late Pliocene, as well as their potential relevance in the context of future climate change. PlioMIP examines the consistency of model predictions in simulating Pliocene climate and their ability to reproduce climate signals preserved by geological climate archives. Here we provide a description of the aim and objectives of the next phase of the model intercomparison project (PlioMIP Phase 2), and we present the experimental design and boundary conditions that will be utilized for climate model experiments in Phase 2. Following on from PlioMIP Phase 1, Phase 2 will continue to be a mechanism for sampling structural uncertainty within climate models. However, Phase 1 demonstrated the requirement to better understand boundary condition uncertainties as well as uncertainty in the methodologies used for data–model comparison. Therefore, our strategy for Phase 2 is to utilize state-of-the-art boundary conditions that have emerged over the last 5 years. These include a new palaeogeographic reconstruction, detailing ocean bathymetry and land–ice surface topography. The ice surface topography is built upon the lessons learned from offline ice sheet modelling studies. Land surface cover has been enhanced by recent additions of Pliocene soils and lakes. Atmospheric reconstructions of palaeo-CO2 are emerging on orbital timescales, and these are also incorporated into PlioMIP Phase 2. New records of surface and sea surface temperature change are being produced that will be more temporally consistent with the boundary conditions and forcings used within models. Finally we have designed a suite of prioritized experiments that tackle issues surrounding the basic understanding of the Pliocene and its relevance in the context of future climate change in a discrete way.
- Published
- 2016
46. Latitudinal species diversity gradient of marine zooplankton for the last three million years
- Author
-
Gene Hunt, Marci M. Robinson, Harry J. Dowsett, Moriaki Yasuhara, and Danielle K. Stoll
- Subjects
Ecology ,Fossils ,Climate Change ,Oceans and Seas ,Temperature ,Biodiversity ,Species diversity ,Climate change ,Last Glacial Maximum ,Biology ,Zooplankton ,Interglacial ,Animals ,Marine ecosystem ,Ecology, Evolution, Behavior and Systematics ,Macroecology ,Forecasting - Abstract
High tropical and low polar biodiversity is one of the most fundamental patterns characterising marine ecosystems, and the influence of temperature on such marine latitudinal diversity gradients is increasingly well documented. However, the temporal stability of quantitative relationships among diversity, latitude and temperature is largely unknown. Herein we document marine zooplankton species diversity patterns at four time slices [modern, Last Glacial Maximum (18,000 years ago), last interglacial (120,000 years ago), and Pliocene (~3.3-3.0 million years ago)] and show that, although the diversity-latitude relationship has been dynamic, diversity-temperature relationships are remarkably constant over the past three million years. These results suggest that species diversity is rapidly reorganised as species' ranges respond to temperature change on ecological time scales, and that the ecological impact of future human-induced temperature change may be partly predictable from fossil and paleoclimatological records.
- Published
- 2012
47. On the causes of mid-Pliocene warmth and polar amplification
- Author
-
Ulrich Salzmann, Alan M. Haywood, Daniel J. Lunt, Claire Loptson, Paul J. Valdes, Harry J. Dowsett, and Gavin A. Schmidt
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Global warming ,Northern Hemisphere ,Climate change ,Orography ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Geophysics ,13. Climate action ,Space and Planetary Science ,Geochemistry and Petrology ,Climatology ,Earth and Planetary Sciences (miscellaneous) ,Polar amplification ,sense organs ,Ice sheet ,skin and connective tissue diseases ,Southern Hemisphere ,Geology ,0105 earth and related environmental sciences ,Orographic lift - Abstract
The mid-Pliocene (approximately 3 to 3.3 Ma ago), is a period of sustained global warmth in comparison to the late Quaternary (0 to approximately 1 Ma ago), and has potential to inform predictions of long-term future climate change. However, given that several processes potentially contributed, relatively little is understood about the reasons for the observed warmth, or the associated polar amplification. Here, using a modelling approach and a novel factorisation method, we assess the relative contributions to mid-Pliocene warmth from: elevated CO2, lowered orography, and vegetation and ice sheet changes. The results show that on a global scale, the largest contributor to mid-Pliocene warmth is elevated CO2. However, in terms of polar amplification, changes to ice sheets contribute significantly in the Southern Hemisphere, and orographic changes contribute significantly in the Northern Hemisphere. We also carry out an energy balance analysis which indicates that that on a global scale, surface albedo and atmospheric emmissivity changes dominate over cloud changes. We investigate the sensitivity of our results to uncertainties in the prescribed CO2 and orographic changes, to derive uncertainty ranges for the various contributing processes.
- Published
- 2012
48. Aerosols shift lake ecosystem
- Author
-
Harry J. Dowsett
- Subjects
0301 basic medicine ,010504 meteorology & atmospheric sciences ,Limnology ,Lake ecosystem ,Loess plateau ,respiratory system ,Environmental Science (miscellaneous) ,complex mixtures ,01 natural sciences ,03 medical and health sciences ,030104 developmental biology ,Hydrology (agriculture) ,Climatology ,Environmental science ,Physical geography ,Monsoon precipitation ,Social Sciences (miscellaneous) ,0105 earth and related environmental sciences - Abstract
Anthropogenic aerosols over the Chinese Loess Plateau have diminished monsoon precipitation and concomitant soil erosion that plagues the region. Now, a reconstruction documents the differences between historical warming events and the present, highlighting the paradoxical implications of decreasing atmospheric aerosols.
- Published
- 2017
49. Sensitivity of Pliocene ice sheets to orbital forcing
- Author
-
Alan M. Haywood, Steven J. Pickering, Aisling M. Dolan, Daniel J. Lunt, Harry J. Dowsett, Daniel J. Hill, and Stephen J. Hunter
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Ice stream ,Paleontology ,Antarctic sea ice ,010502 geochemistry & geophysics ,Oceanography ,01 natural sciences ,Arctic ice pack ,Ice-sheet model ,13. Climate action ,Climatology ,Sea ice thickness ,Sea ice ,Cryosphere ,Ice sheet ,Ecology, Evolution, Behavior and Systematics ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The stability of the Earth's major ice sheets is a critical uncertainty in predictions of future climate and sea level change. One method of investigating the behaviour of the Greenland and the Antarctic ice sheets in a warmer-than-modern climate is to look back at past warm periods of Earth history, for example the Pliocene. This paper presents climate and ice sheet modelling results for the mid-Pliocene warm period (mPWP; 3.3 to 3.0 million years ago), which has been identified as a key interval for understanding warmer-than-modern climates (Jansen et al., 2007). Using boundary conditions supplied by the United States Geological Survey PRISM Group (Pliocene Research, Interpretation and Synoptic Mapping), the Hadley Centre coupled ocean–atmosphere climate model (HadCM3) and the British Antarctic Survey Ice Sheet Model (BASISM), we show large reductions in the Greenland and East Antarctic Ice Sheets (GrIS and EAIS) compared to modern in standard mPWP experiments. We also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid-Pliocene. While GrIS volumes are lower than modern under even the most extreme (cold) mid-Pliocene orbit (losing at least 35% of its ice mass), the EAIS can both grow and shrink, losing up to 20% or gaining up to 10% of its present-day volume. The changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid-Pliocene. However, we have also shown that the response of the ice sheets to mPWP orbital hemispheric forcing can be in anti-phase, whereby the greatest reductions in EAIS volume are concurrent with the smallest reductions of the GrIS. If this anti-phase relationship is in operation throughout the mPWP, then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible. This suggests that maximum eustatic sea level rise does not correspond to orbital maxima, but occurs at times where the anti-phasing of Northern and Southern Hemisphere ice sheet retreat is minimised.
- Published
- 2011
50. Bathymetric controls on Pliocene North Atlantic and Arctic sea surface temperature and deepwater production
- Author
-
S. M. Jones, Marci M. Robinson, Alan M. Haywood, Paul J. Valdes, Daniel J. Hill, and Harry J. Dowsett
- Subjects
geography ,geography.geographical_feature_category ,Arctic dipole anomaly ,Paleontology ,Subsidence (atmosphere) ,Mid-ocean ridge ,Oceanography ,Latitude ,Sea surface temperature ,Arctic ,Climatology ,Atlantic multidecadal oscillation ,Bathymetry ,Ecology, Evolution, Behavior and Systematics ,Geology ,Earth-Surface Processes - Abstract
The mid-Pliocene warm period (MPWP; ~ 3.3 to 3.0 Ma) is the most recent interval in Earth's history in which global temperatures reached and remained at levels similar to those projected for the near future. The distribution of global warmth, however, was different than today in that the high latitudes warmed more than the tropics. Multiple temperature proxies indicate significant sea surface warming in the North Atlantic and Arctic Oceans during the MPWP, but predictions from a fully coupled ocean–atmosphere model (HadCM3) have so far been unable to fully predict the large scale of sea surface warming in the high latitudes. If climate proxies accurately represent Pliocene conditions, and if no weakness exists in the physics of the model, then model boundary conditions may be in error. Here we alter a single boundary condition (bathymetry) to examine if Pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of North Atlantic Ocean ridges. We find an increase in both Arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened Greenland–Scotland Ridge. These results offer both a mechanism for the warming in the North Atlantic and Arctic Oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of Pliocene northern North Atlantic and Arctic Ocean conditions. Determining the causes of Pliocene warmth remains critical to fully understanding comparisons of the Pliocene warm period to possible future climate change scenarios.
- Published
- 2011
Catalog
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