2025
|
Sartore, Nicolas B.; Wagner, Till J. W.; Siegfried, Matthew R.; Pujara, Nimish; Zoet, Lucas K.: Wave erosion, frontal bending, and calving at Ross Ice Shelf. In: The Cryosphere, vol. 19, iss. 1, pp. 249–265, 2025. @article{Sartore2025,
title = {Wave erosion, frontal bending, and calving at Ross Ice Shelf},
author = {Nicolas B. Sartore and Till J. W. Wagner and Matthew R. Siegfried and Nimish Pujara and Lucas K. Zoet},
doi = {https://doi.org/10.5194/tc-19-249-2025},
year = {2025},
date = {2025-01-20},
journal = {The Cryosphere},
volume = {19},
issue = {1},
pages = {249–265},
abstract = {Ice shelf calving constitutes roughly half of the total mass loss from the Antarctic ice sheet. Although much attention is paid to calving of giant tabular icebergs, these events are relatively rare. Here, we investigate the role of frontal melting and stresses at the ice shelf front in driving bending and calving on the scale of ∼100 m, perpendicular to the ice edge. We focus in particular on how buoyant underwater “feet” that protrude beyond the above-water ice cliff may cause tensile stresses at the base of the ice. Indirect and anecdotal observations of such feet at the Ross Ice Shelf front suggest that the resulting bending may be widespread and can trigger calving. We consider satellite observations together with an elastic beam model and a parameterization of wave erosion to better understand the dynamics at the ice shelf front. Our results suggest that on average frontal ablation rather consistently accounts for 20±5 m yr−1 of ice loss at Ross Ice Shelf, likely mostly due to wave erosion and smaller-scale, 𝒪(100 m), foot-induced calving. This constitutes only ∼2 % of the total frontal mass loss (since near-front ice velocities are ∼1000 m yr−1). Observational evidence suggests that sporadic larger events can skew this rate (we document one foot-induced calving event of size ∼1 km). Stresses from foot-induced bending are likely not sufficient to initiate crevassing but rather act to propagate existing crevasses. In addition, our results support recent findings by Buck (2024) that additional bending moments, likely due to temperature gradients in the ice, may play a role in driving frontal deflections. The highly variable environment, irregularity of pre-existing crevasse spacing, and complex rheology of the ice continue to pose challenges in better constraining the drivers behind the observed deformations and resulting calving rates.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ice shelf calving constitutes roughly half of the total mass loss from the Antarctic ice sheet. Although much attention is paid to calving of giant tabular icebergs, these events are relatively rare. Here, we investigate the role of frontal melting and stresses at the ice shelf front in driving bending and calving on the scale of ∼100 m, perpendicular to the ice edge. We focus in particular on how buoyant underwater “feet” that protrude beyond the above-water ice cliff may cause tensile stresses at the base of the ice. Indirect and anecdotal observations of such feet at the Ross Ice Shelf front suggest that the resulting bending may be widespread and can trigger calving. We consider satellite observations together with an elastic beam model and a parameterization of wave erosion to better understand the dynamics at the ice shelf front. Our results suggest that on average frontal ablation rather consistently accounts for 20±5 m yr−1 of ice loss at Ross Ice Shelf, likely mostly due to wave erosion and smaller-scale, 𝒪(100 m), foot-induced calving. This constitutes only ∼2 % of the total frontal mass loss (since near-front ice velocities are ∼1000 m yr−1). Observational evidence suggests that sporadic larger events can skew this rate (we document one foot-induced calving event of size ∼1 km). Stresses from foot-induced bending are likely not sufficient to initiate crevassing but rather act to propagate existing crevasses. In addition, our results support recent findings by Buck (2024) that additional bending moments, likely due to temperature gradients in the ice, may play a role in driving frontal deflections. The highly variable environment, irregularity of pre-existing crevasse spacing, and complex rheology of the ice continue to pose challenges in better constraining the drivers behind the observed deformations and resulting calving rates. |
2024
|
Polyakov, Igor V.; Ballinger, Thomas J.; Overland, James E.; Vavrus, Stephen J.; Danielson, Seth L.; Lader, Rick; Bhatt, Uma S.; Hendricks, Amy S.; Mueter, Franz J.: Atmospheric Pressure Rivalry Between the Arctic and Northern Pacific: Implications for Alaskan Climate Variability. In: International Journal of Climatology, 2024. @article{Polyakov2024,
title = {Atmospheric Pressure Rivalry Between the Arctic and Northern Pacific: Implications for Alaskan Climate Variability},
author = {Igor V. Polyakov and Thomas J. Ballinger and James E. Overland and Stephen J. Vavrus and Seth L. Danielson and Rick Lader and Uma S. Bhatt and Amy S. Hendricks and Franz J. Mueter},
doi = {https://doi.org/10.1002/joc.8638},
year = {2024},
date = {2024-10-23},
journal = { International Journal of Climatology},
abstract = {Located at the confluence of the Arctic and North Pacific and with Alaska at its heart, the Pacific Arctic Region (PAR) is a unique and interconnected regional climate system. Significant climatic changes in the PAR are described by a novel, mobile monthly Alaska Arctic Front (AAF) index, which is defined by sea level pressure differences between the migratory cores of the Beaufort High and Aleutian Low. Regional climate variability associated with the AAF shows prominent decadal signatures that are driven by the opposing effects of the North Pacific and the Arctic atmospheric pressure fields. Low AAF (negative phase) is dominated by North Pacific forcing, whereas high AAF (positive phase) is dominated by Arctic atmospheric processes. The recent (2011–2021) negative AAF phase, which is associated with the westward displacement of Aleutian Low explaining stronger northward winds and enhanced water transport northward through Bering Strait, is conducive to increased oceanic heat and freshwater content, reduced regional sea ice cover in the PAR, and to the expansion of Pacific species into the Arctic. These factors are all indicators of the Pacification of the Arctic Ocean, a key feature of climate change related to progression of anomalous Pacific water masses and biota into the polar basins. It is not yet clear if or when the recent phase of decadal variability will change and alter the rate of Pacification of the Arctic climate system.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Located at the confluence of the Arctic and North Pacific and with Alaska at its heart, the Pacific Arctic Region (PAR) is a unique and interconnected regional climate system. Significant climatic changes in the PAR are described by a novel, mobile monthly Alaska Arctic Front (AAF) index, which is defined by sea level pressure differences between the migratory cores of the Beaufort High and Aleutian Low. Regional climate variability associated with the AAF shows prominent decadal signatures that are driven by the opposing effects of the North Pacific and the Arctic atmospheric pressure fields. Low AAF (negative phase) is dominated by North Pacific forcing, whereas high AAF (positive phase) is dominated by Arctic atmospheric processes. The recent (2011–2021) negative AAF phase, which is associated with the westward displacement of Aleutian Low explaining stronger northward winds and enhanced water transport northward through Bering Strait, is conducive to increased oceanic heat and freshwater content, reduced regional sea ice cover in the PAR, and to the expansion of Pacific species into the Arctic. These factors are all indicators of the Pacification of the Arctic Ocean, a key feature of climate change related to progression of anomalous Pacific water masses and biota into the polar basins. It is not yet clear if or when the recent phase of decadal variability will change and alter the rate of Pacification of the Arctic climate system. |
Wang, Hong; An, Zhisheng; Zhang, Xu; Shu, Peixian; He, Feng; Liu, Weiguo; Lu, Hongxuan; Ming, Guodong; Liu, Lin; Zhou, Weijian: Westerly and Laurentide ice sheet fluctuations during the last glacial maximum. In: npj Climate and Atmospheric Science, vol. 7, pp. 213, 2024. @article{Wang2024,
title = {Westerly and Laurentide ice sheet fluctuations during the last glacial maximum},
author = {Hong Wang and Zhisheng An and Xu Zhang and Peixian Shu and Feng He and Weiguo Liu and Hongxuan Lu and Guodong Ming and Lin Liu and Weijian Zhou },
doi = {https://doi.org/10.1038/s41612-024-00760-9},
year = {2024},
date = {2024-09-10},
journal = {npj Climate and Atmospheric Science},
volume = {7},
pages = {213},
abstract = {The last glacial maximum (LGM) is widely acknowledged as the most recent cold period representing maximum global ice conditions. However, substantial warming is observed over Northern Hemisphere. Here, we show that the LGM climate shifted from very cold to fairly warm, followed by less cold conditions in the early Heinrich Stadial 1 (HS1) phases. Our synthesis of accurate AMS 14C dates refines the exact timing of Laurentide Ice Sheet (LIS) advances during the early LGM/HS1, constraining the chronology of the LIS decay during the late LGM. The summertime soil temperatures near ice fronts were found to increase by 1.3 °C from the early to late LGM and to decrease by 0.5 °C to the early HS1 phases, consistent with the cold-warm-cool climate patterns. The early/late LGM and early HS1 climates are found to be characterized by frequent cold/warm summers and cold winters since the world’s largest LIS began to decay.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The last glacial maximum (LGM) is widely acknowledged as the most recent cold period representing maximum global ice conditions. However, substantial warming is observed over Northern Hemisphere. Here, we show that the LGM climate shifted from very cold to fairly warm, followed by less cold conditions in the early Heinrich Stadial 1 (HS1) phases. Our synthesis of accurate AMS 14C dates refines the exact timing of Laurentide Ice Sheet (LIS) advances during the early LGM/HS1, constraining the chronology of the LIS decay during the late LGM. The summertime soil temperatures near ice fronts were found to increase by 1.3 °C from the early to late LGM and to decrease by 0.5 °C to the early HS1 phases, consistent with the cold-warm-cool climate patterns. The early/late LGM and early HS1 climates are found to be characterized by frequent cold/warm summers and cold winters since the world’s largest LIS began to decay. |
Eaves, Shaun R.; Mackintosh, Andrew N.; Pedro, Joel B.; Bostock, Helen C.; Ryan, Matthew T.; Norton, Kevin P.; Hayward, Bruce W.; Anderson, Brian M.; He, Feng; Jones, Richard S.; Lorrey, Andrew M.; Newnham, Rewi M.; Tims, Stephen G.; Vandergoes, Marcus J.: Coupled atmosphere-ocean response of the southwest Pacific to deglacial changes in Atlantic meridional overturning circulation Author links open overlay panel. In: Earth and Planetary Science Letters, vol. 641, pp. 118802, 2024. @article{Eaves2024,
title = {Coupled atmosphere-ocean response of the southwest Pacific to deglacial changes in Atlantic meridional overturning circulation Author links open overlay panel},
author = {Shaun R. Eaves and Andrew N. Mackintosh and Joel B. Pedro and Helen C. Bostock and Matthew T. Ryan and Kevin P. Norton and Bruce W. Hayward and Brian M. Anderson and Feng He and Richard S. Jones and Andrew M. Lorrey and Rewi M. Newnham and Stephen G. Tims and Marcus J. Vandergoes},
doi = {https://doi.org/10.1016/j.epsl.2024.118802},
year = {2024},
date = {2024-09-01},
journal = {Earth and Planetary Science Letters},
volume = {641},
pages = {118802},
abstract = {The last glacial termination was characterised by millennial-scale episodes of warming and cooling that appear offset between the hemispheres. It has been proposed that this bi-polar seesaw is the result of climate system feedbacks. A key debate, which remains unresolved, concerns the relative roles of the atmosphere and oceans in transmitting these climate responses between the hemispheres. In this study we present quantitative climate proxy data to show that air temperatures in New Zealand, as recorded by mountain glaciers, tracked millennial-scale warming and cooling of local surface temperatures of the adjacent Tasman Sea throughout the last glacial termination. Both realms were dominated by warming between 18 ka and 12 ka, interrupted by a multi-centennial to millennial-scale cooling event centred on 14 ka, coincident with the Antarctic Cold Reversal. Reconciling our climate proxy evidence with a transient climate model simulation of the glacial termination, we find that the timing and amplitude of temperature changes are consistent with changing Atlantic meridional overturning circulation (AMOC). The southwest Pacific region displays a particularly sensitive response to AMOC intensity changes, despite its far-field situation from the North Atlantic. This sensitivity represents the combined impact of fast-acting oceanic teleconnections and regional atmosphere-ocean response associated with changes to the southern westerly winds. Our findings highlight that recent hypotheses promoting the role of southern westerlies as a critical component of deglaciation may be complementary to, rather than competitive with, the bipolar seesaw paradigm.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The last glacial termination was characterised by millennial-scale episodes of warming and cooling that appear offset between the hemispheres. It has been proposed that this bi-polar seesaw is the result of climate system feedbacks. A key debate, which remains unresolved, concerns the relative roles of the atmosphere and oceans in transmitting these climate responses between the hemispheres. In this study we present quantitative climate proxy data to show that air temperatures in New Zealand, as recorded by mountain glaciers, tracked millennial-scale warming and cooling of local surface temperatures of the adjacent Tasman Sea throughout the last glacial termination. Both realms were dominated by warming between 18 ka and 12 ka, interrupted by a multi-centennial to millennial-scale cooling event centred on 14 ka, coincident with the Antarctic Cold Reversal. Reconciling our climate proxy evidence with a transient climate model simulation of the glacial termination, we find that the timing and amplitude of temperature changes are consistent with changing Atlantic meridional overturning circulation (AMOC). The southwest Pacific region displays a particularly sensitive response to AMOC intensity changes, despite its far-field situation from the North Atlantic. This sensitivity represents the combined impact of fast-acting oceanic teleconnections and regional atmosphere-ocean response associated with changes to the southern westerly winds. Our findings highlight that recent hypotheses promoting the role of southern westerlies as a critical component of deglaciation may be complementary to, rather than competitive with, the bipolar seesaw paradigm. |
Snoll, Brooke; Ivanovic, Ruza; Gregoire, Lauren; Sherriff-Tadano, Sam; Menviel, Laurie; Obase, Takashi; Abe-Ouchi, Ayako; Bouttes, Nathaelle; He, Chengfei; He, Feng; Kapsch, Marie; Mikolajewicz, Uwe; Muglia, Juan; Valdes, Paul: A multi-model assessment of the early last deglaciation (PMIP4 LDv1): a meltwater perspective. In: Climate of the Past , vol. 20, iss. 4, pp. 789-815, 2024. @article{Snoll2024,
title = {A multi-model assessment of the early last deglaciation (PMIP4 LDv1): a meltwater perspective},
author = {Brooke Snoll and Ruza Ivanovic and Lauren Gregoire and Sam Sherriff-Tadano and Laurie Menviel and Takashi Obase and Ayako Abe-Ouchi and Nathaelle Bouttes and Chengfei He and Feng He and Marie Kapsch and Uwe Mikolajewicz and Juan Muglia and Paul Valdes},
doi = {10.5194/cp-20-789-2024},
year = {2024},
date = {2024-04-05},
urldate = {2024-04-05},
journal = {Climate of the Past },
volume = {20},
issue = {4},
pages = {789-815},
abstract = {The last deglaciation (∼20–11 ka BP) is a period of a major, long-term climate transition from a glacial to interglacial state that features multiple centennial- to decadal-scale abrupt climate variations whose root cause is still not fully understood. To better understand this time period, the Paleoclimate Modelling Intercomparison Project (PMIP) has provided a framework for an internationally coordinated endeavour in simulating the last deglaciation whilst encompassing a broad range of models. Here, we present a multi-model intercomparison of 17 transient simulations of the early part of the last deglaciation (∼20–15 ka BP) from nine different climate models spanning a range of model complexities and uncertain boundary conditions and forcings. The numerous simulations available provide the opportunity to better understand the chain of events and mechanisms of climate changes between 20 and 15 ka BP and our collective ability to simulate them. We conclude that the amount of freshwater forcing and whether it follows the ice sheet reconstruction or induces an inferred Atlantic meridional overturning circulation (AMOC) history, heavily impacts the deglacial climate evolution for each simulation rather than differences in the model physics. The course of the deglaciation is consistent between simulations except when the freshwater forcing is above 0.1 Sv – at least 70 % of the simulations agree that there is warming by 15 ka BP in most places excluding the location of meltwater input. For simulations with freshwater forcings that exceed 0.1 Sv from 18 ka BP, warming is delayed in the North Atlantic and surface air temperature correlations with AMOC strength are much higher. However, we find that the state of the AMOC coming out of the Last Glacial Maximum (LGM) also plays a key role in the AMOC sensitivity to model forcings. In addition, we show that the response of each model to the chosen meltwater scenario depends largely on the sensitivity of the model to the freshwater forcing and other aspects of the experimental design (e.g. CO2 forcing or ice sheet reconstruction). The results provide insight into the ability of our models to simulate the first part of the deglaciation and how choices between uncertain boundary conditions and forcings, with a focus on freshwater fluxes, can impact model outputs. We can use these findings as helpful insight in the design of future simulations of this time period.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The last deglaciation (∼20–11 ka BP) is a period of a major, long-term climate transition from a glacial to interglacial state that features multiple centennial- to decadal-scale abrupt climate variations whose root cause is still not fully understood. To better understand this time period, the Paleoclimate Modelling Intercomparison Project (PMIP) has provided a framework for an internationally coordinated endeavour in simulating the last deglaciation whilst encompassing a broad range of models. Here, we present a multi-model intercomparison of 17 transient simulations of the early part of the last deglaciation (∼20–15 ka BP) from nine different climate models spanning a range of model complexities and uncertain boundary conditions and forcings. The numerous simulations available provide the opportunity to better understand the chain of events and mechanisms of climate changes between 20 and 15 ka BP and our collective ability to simulate them. We conclude that the amount of freshwater forcing and whether it follows the ice sheet reconstruction or induces an inferred Atlantic meridional overturning circulation (AMOC) history, heavily impacts the deglacial climate evolution for each simulation rather than differences in the model physics. The course of the deglaciation is consistent between simulations except when the freshwater forcing is above 0.1 Sv – at least 70 % of the simulations agree that there is warming by 15 ka BP in most places excluding the location of meltwater input. For simulations with freshwater forcings that exceed 0.1 Sv from 18 ka BP, warming is delayed in the North Atlantic and surface air temperature correlations with AMOC strength are much higher. However, we find that the state of the AMOC coming out of the Last Glacial Maximum (LGM) also plays a key role in the AMOC sensitivity to model forcings. In addition, we show that the response of each model to the chosen meltwater scenario depends largely on the sensitivity of the model to the freshwater forcing and other aspects of the experimental design (e.g. CO2 forcing or ice sheet reconstruction). The results provide insight into the ability of our models to simulate the first part of the deglaciation and how choices between uncertain boundary conditions and forcings, with a focus on freshwater fluxes, can impact model outputs. We can use these findings as helpful insight in the design of future simulations of this time period. |
Yu, Yanyan; snd Haibin Wu, Jie Yu; He, Feng; Vavrus, Stephen J.; Johnson, Amber; Zhang, Wenchao; Li, Qin; Guo, Zhengtang: Asynchronous Holocene human population changes in north and south China as related to animal resource utilization. In: Global and Planetary Change, vol. 235, iss. 0921-8181, pp. 104403, 2024. @article{Yu2024,
title = {Asynchronous Holocene human population changes in north and south China as related to animal resource utilization},
author = {Yanyan Yu and Jie Yu snd Haibin Wu and Feng He and Stephen J. Vavrus and Amber Johnson and Wenchao Zhang and Qin Li and Zhengtang Guo},
doi = {10.1016/j.gloplacha.2024.104403},
year = {2024},
date = {2024-04-01},
urldate = {2024-04-01},
journal = {Global and Planetary Change},
volume = {235},
issue = {0921-8181},
pages = {104403},
abstract = {During the Holocene, rich Neolithic and Bronze cultures developed in the middle and lower reaches of Yellow River valley (north China) and Yangtze River valley (south China), making them the core areas of past human activities. Thus, it is important to reveal the process and driving mechanism of regional population change. Agriculture development has always been taken as the key driver of population changes, and current studies mainly focus on the role that cultivation played, however, it is still unclear if animal resource utilization also contributed to regional population changes. Here, the spatiotemporal changes of population and domestic animal utilization levels in north and south China from 10 to 2 ka BP have been reconstructed based on 27,935 archaeological sites and faunal remains data from 94 sites, respectively, and the change in potential wild animal resources has been simulated by the Minimum Terrestrial Resource Model (MTRM). The results show asynchronous changes of population occurred in north and south China during 10–2 ka BP, which were correlated with regional domestic and potential wild animal resource utilization. In north China, more significant population growth corresponded to a greater increase of domestic animal ratios and a sharp decline of potential wild animal resources after 8 ka BP. In south China, less significant population growth was accompanied by a slower increase of domestic animal ratios and stable variations of potential wild animal resources. This research suggests that different changes of potential wild animal resources in north and south China contributed to spatial variations in survival pressure, utilization level of domestic animals, and population growth, which was further determined by asynchronous changes of precipitation in the two regions. This study explains the impact of climate changes on population from a new perspective.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
During the Holocene, rich Neolithic and Bronze cultures developed in the middle and lower reaches of Yellow River valley (north China) and Yangtze River valley (south China), making them the core areas of past human activities. Thus, it is important to reveal the process and driving mechanism of regional population change. Agriculture development has always been taken as the key driver of population changes, and current studies mainly focus on the role that cultivation played, however, it is still unclear if animal resource utilization also contributed to regional population changes. Here, the spatiotemporal changes of population and domestic animal utilization levels in north and south China from 10 to 2 ka BP have been reconstructed based on 27,935 archaeological sites and faunal remains data from 94 sites, respectively, and the change in potential wild animal resources has been simulated by the Minimum Terrestrial Resource Model (MTRM). The results show asynchronous changes of population occurred in north and south China during 10–2 ka BP, which were correlated with regional domestic and potential wild animal resource utilization. In north China, more significant population growth corresponded to a greater increase of domestic animal ratios and a sharp decline of potential wild animal resources after 8 ka BP. In south China, less significant population growth was accompanied by a slower increase of domestic animal ratios and stable variations of potential wild animal resources. This research suggests that different changes of potential wild animal resources in north and south China contributed to spatial variations in survival pressure, utilization level of domestic animals, and population growth, which was further determined by asynchronous changes of precipitation in the two regions. This study explains the impact of climate changes on population from a new perspective. |
Beal, Maxwell R. W.; Özdoğan, Mutlu; Block, Paul J.: A Machine Learning and Remote Sensing-Based Model for Algae Pigment and Dissolved Oxygen Retrieval on a Small Inland Lake. In: Water Resources Research, vol. 60, iss. 3, pp. e2023WR035744, 2024. @article{Beal2024,
title = {A Machine Learning and Remote Sensing-Based Model for Algae Pigment and Dissolved Oxygen Retrieval on a Small Inland Lake},
author = {Maxwell R. W. Beal and Mutlu Özdoğan and Paul J. Block},
doi = {10.1029/2023WR035744},
year = {2024},
date = {2024-02-28},
journal = {Water Resources Research},
volume = {60},
issue = {3},
pages = {e2023WR035744},
abstract = {Excessive algae growth can lead to negative consequences for ecosystem function, economic opportunity, and human and animal health. Due to the cost-effectiveness and temporal availability of satellite imagery, remote sensing has become a powerful tool for water quality monitoring. The use of remotely sensed products to monitor water quality related to algae and cyanobacteria productivity during a bloom event may help inform management strategies for inland waters. To evaluate the ability of satellite imagery to monitor algae pigments and dissolved oxygen conditions in a small inland lake, chlorophyll-a, phycocyanin, and dissolved oxygen concentrations are measured using a YSI EXO2 sonde during Sentinel-2 and Sentinel-3 overpasses from 2019 to 2022 on Lake Mendota, WI. Machine learning methods are implemented with existing algorithms to model chlorophyll-a, phycocyanin, and Pc:Chla. A novel machine learning-based dissolved oxygen modeling approach is developed using algae pigment concentrations as predictors. Best model results based on Sentinel-2 (Sentinel-3) imagery achieved R2 scores of 0.47 (0.42) for chlorophyll-a, 0.69 (0.22) for phycocyanin, and 0.70 (0.41) for Pc:Chla. Dissolved oxygen models achieved an R2 of 0.68 (0.36) when applied to Sentinel-2 (Sentinel-3) imagery, and Pc:Chla is found to be the most important predictive feature. Random forest models are better suited to water quality estimations in this system given built in methods for feature selection and a relatively small data set. Use of these approaches for estimation of Pc:Chla and dissolved oxygen can increase the water quality information extracted from satellite imagery and improve characterization of algae conditions among inland waters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Excessive algae growth can lead to negative consequences for ecosystem function, economic opportunity, and human and animal health. Due to the cost-effectiveness and temporal availability of satellite imagery, remote sensing has become a powerful tool for water quality monitoring. The use of remotely sensed products to monitor water quality related to algae and cyanobacteria productivity during a bloom event may help inform management strategies for inland waters. To evaluate the ability of satellite imagery to monitor algae pigments and dissolved oxygen conditions in a small inland lake, chlorophyll-a, phycocyanin, and dissolved oxygen concentrations are measured using a YSI EXO2 sonde during Sentinel-2 and Sentinel-3 overpasses from 2019 to 2022 on Lake Mendota, WI. Machine learning methods are implemented with existing algorithms to model chlorophyll-a, phycocyanin, and Pc:Chla. A novel machine learning-based dissolved oxygen modeling approach is developed using algae pigment concentrations as predictors. Best model results based on Sentinel-2 (Sentinel-3) imagery achieved R2 scores of 0.47 (0.42) for chlorophyll-a, 0.69 (0.22) for phycocyanin, and 0.70 (0.41) for Pc:Chla. Dissolved oxygen models achieved an R2 of 0.68 (0.36) when applied to Sentinel-2 (Sentinel-3) imagery, and Pc:Chla is found to be the most important predictive feature. Random forest models are better suited to water quality estimations in this system given built in methods for feature selection and a relatively small data set. Use of these approaches for estimation of Pc:Chla and dissolved oxygen can increase the water quality information extracted from satellite imagery and improve characterization of algae conditions among inland waters. |
Reyes, Alberto V.; Carlson, Anders E.; Clark, Jorie; Guillaume, Louise; Milne, Glenn A.; Tarasov, Lev; Carlson, Elizabeth C. B.; He, Feng; Caffee, Marc W.; Wilcken, Klaus M.; Rood, Dylan H.: Timing of Cordilleran-Laurentide ice-sheet separation: Implications for sea-level rise. In: Quaternary Science Reviews, vol. 328, pp. 108554, 2024. @article{Reyes2024,
title = {Timing of Cordilleran-Laurentide ice-sheet separation: Implications for sea-level rise},
author = {Alberto V. Reyes and Anders E. Carlson and Jorie Clark and Louise Guillaume and Glenn A. Milne and Lev Tarasov and Elizabeth C.B. Carlson and Feng He and Marc W. Caffee and Klaus M. Wilcken and Dylan H. Rood},
doi = {doi.org/10.1016/j.quascirev.2024.108554},
year = {2024},
date = {2024-02-23},
journal = {Quaternary Science Reviews},
volume = {328},
pages = {108554},
abstract = {During the last deglaciation, collapse of the saddle between the North American Cordilleran and Laurentide ice sheets led to rapid ice-sheet mass loss and separation, with meltwater discharge contributing to deglacial sea-level rise. We directly date ice-sheet separation at the end of the saddle collapse using 64 10Be exposure ages along an ∼1200-km transect of the ice-sheet suture zone. Collapse began in the south by 15.4 ± 0.4 ka and ended by 13.8 ± 0.1 ka at ∼56°N. Ice-sheet model simulations consistent with the 10Be ages find that the saddle collapse contributed 6.2–7.2 m to global mean sea-level rise from ∼15.5 ka to ∼14.0 ka, or approximately one third of global mean sea-level rise over this period. We determine 3.1–3.6 m of the saddle collapse meltwater was released during Meltwater Pulse 1A ∼14.6-14.3 ka, constituting 20–40% of this meltwater pulse's volume. Because the separation of the Cordilleran and Laurentide ice sheets occurred over 1–2 millennia, the associated release of meltwater during the saddle collapse supplied a smaller contribution to the magnitude of Meltwater Pulse 1A than has been recently proposed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
During the last deglaciation, collapse of the saddle between the North American Cordilleran and Laurentide ice sheets led to rapid ice-sheet mass loss and separation, with meltwater discharge contributing to deglacial sea-level rise. We directly date ice-sheet separation at the end of the saddle collapse using 64 10Be exposure ages along an ∼1200-km transect of the ice-sheet suture zone. Collapse began in the south by 15.4 ± 0.4 ka and ended by 13.8 ± 0.1 ka at ∼56°N. Ice-sheet model simulations consistent with the 10Be ages find that the saddle collapse contributed 6.2–7.2 m to global mean sea-level rise from ∼15.5 ka to ∼14.0 ka, or approximately one third of global mean sea-level rise over this period. We determine 3.1–3.6 m of the saddle collapse meltwater was released during Meltwater Pulse 1A ∼14.6-14.3 ka, constituting 20–40% of this meltwater pulse's volume. Because the separation of the Cordilleran and Laurentide ice sheets occurred over 1–2 millennia, the associated release of meltwater during the saddle collapse supplied a smaller contribution to the magnitude of Meltwater Pulse 1A than has been recently proposed. |
2023
|
DuVivier, A. K.; Vavrus, S. J.; Holland, M. M.; Landrum, L.; Shields, C. A.; Thaker, R.: Investigating future Arctic sea ice loss and near-surface wind speed changes related to surface roughness using the Community Earth System Model. In: Journal of Geophysical Research: Atmospheres, vol. 128, iss. 20, 2023. @article{DuVivier2023,
title = {Investigating future Arctic sea ice loss and near-surface wind speed changes related to surface roughness using the Community Earth System Model},
author = {A. K. DuVivier and S. J. Vavrus and M. M. Holland and L. Landrum and C. A. Shields and R. Thaker},
doi = {doi.org/10.1029/2023JD038824},
year = {2023},
date = {2023-09-27},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {128},
issue = {20},
abstract = {The Arctic is undergoing a pronounced and rapid transformation in response to changing greenhouse gasses, including reduction in sea ice extent and thickness. There are also projected increases in near-surface Arctic wind. This study addresses how the winds trends may be driven by changing surface roughness and/or stability in different Arctic regions and seasons, something that has not yet been thoroughly investigated. We analyze 50 experiments from the Community Earth System Model Version 2 (CESM2) Large Ensemble and five experiments using CESM2 with an artificially decreased sea ice roughness to match that of the open ocean. We find that with a smoother surface there are higher mean wind speeds and slower mean ice speeds in the autumn, winter, and spring. The artificially reduced surface roughness also strongly impacts the wind speed trends in autumn and winter, and we find that atmospheric stability changes are also important contributors to driving wind trends in both experiments. In contrast to the clear impacts on winds, the sea ice mean state and trends are statistically indistinguishable, suggesting that near-surface winds are not major drivers of Arctic sea ice loss. Two major results of this work are: (a) the near-surface wind trends are driven by changes in both surface roughness and near-surface atmospheric stability that are themselves changing from sea ice loss, and (b) the sea ice mean state and trends are driven by the overall warming trend due to increasing greenhouse gas emissions and not significantly impacted by coupled feedbacks with the surface winds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Arctic is undergoing a pronounced and rapid transformation in response to changing greenhouse gasses, including reduction in sea ice extent and thickness. There are also projected increases in near-surface Arctic wind. This study addresses how the winds trends may be driven by changing surface roughness and/or stability in different Arctic regions and seasons, something that has not yet been thoroughly investigated. We analyze 50 experiments from the Community Earth System Model Version 2 (CESM2) Large Ensemble and five experiments using CESM2 with an artificially decreased sea ice roughness to match that of the open ocean. We find that with a smoother surface there are higher mean wind speeds and slower mean ice speeds in the autumn, winter, and spring. The artificially reduced surface roughness also strongly impacts the wind speed trends in autumn and winter, and we find that atmospheric stability changes are also important contributors to driving wind trends in both experiments. In contrast to the clear impacts on winds, the sea ice mean state and trends are statistically indistinguishable, suggesting that near-surface winds are not major drivers of Arctic sea ice loss. Two major results of this work are: (a) the near-surface wind trends are driven by changes in both surface roughness and near-surface atmospheric stability that are themselves changing from sea ice loss, and (b) the sea ice mean state and trends are driven by the overall warming trend due to increasing greenhouse gas emissions and not significantly impacted by coupled feedbacks with the surface winds. |
Hu, Aixue; Meehl, Gerald A.; Abe-Ouchi, Ayako; Han, Weiqing; Otto-Bliesner, Bette; He, Feng; Wu, Tongwen; Rosenbloom, Nan; Strand, Warren G.; Edwards, James: Dichotomy between freshwater and heat flux effects on oceanic conveyor belt stability and global climate. In: Communications Earth & Environment, vol. 4, pp. 246, 2023. @article{Hu2023,
title = {Dichotomy between freshwater and heat flux effects on oceanic conveyor belt stability and global climate},
author = {Aixue Hu and Gerald A. Meehl and Ayako Abe-Ouchi and Weiqing Han and Bette Otto-Bliesner and Feng He and Tongwen Wu and Nan Rosenbloom and Warren G. Strand and James Edwards },
url = {https://www.nature.com/articles/s43247-023-00916-0},
doi = {https://doi.org/10.1038/s43247-023-00916-0},
year = {2023},
date = {2023-07-10},
journal = {Communications Earth & Environment},
volume = {4},
pages = {246},
abstract = {The Atlantic meridional overturning circulation is an important global-scale oceanic circulation, and its changes may be responsible for past abrupt climate change events. By using two versions of a coupled climate model, here we show that the stability of this circulation depends not only on the background climate, but also on the type of primary external forcing: freshwater vs. greenhouse gases. When freshwater forcing is dominant, hysteresis of this circulation (an abrupt collapse/reactivation) becomes possible only under simulated glacial conditions with closed Bering Strait. Under present day and future conditions, both freshwater and greenhouse gas forcings could collapse this circulation, but only greenhouse gas forcing produced a bi-stable equilibrium state comparable to abrupt climate change. Our results demonstrate that the Bering Strait status (open vs. closed) may facilitate or prohibit the existence of this circulation’s hysteresis, irrespective of the background climate conditions, but is directly related to the primary forcing.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Atlantic meridional overturning circulation is an important global-scale oceanic circulation, and its changes may be responsible for past abrupt climate change events. By using two versions of a coupled climate model, here we show that the stability of this circulation depends not only on the background climate, but also on the type of primary external forcing: freshwater vs. greenhouse gases. When freshwater forcing is dominant, hysteresis of this circulation (an abrupt collapse/reactivation) becomes possible only under simulated glacial conditions with closed Bering Strait. Under present day and future conditions, both freshwater and greenhouse gas forcings could collapse this circulation, but only greenhouse gas forcing produced a bi-stable equilibrium state comparable to abrupt climate change. Our results demonstrate that the Bering Strait status (open vs. closed) may facilitate or prohibit the existence of this circulation’s hysteresis, irrespective of the background climate conditions, but is directly related to the primary forcing. |
Castagno, Andrew P.; Wagner, Till J. W.; Cape, Mattias R.; Lester, Conner W.; Bailey, Elizabeth; Alves-de-Souza, Catharina; York, Robert A.; Fleming, Alyson H.: Increased sea ice melt as a driver of enhanced Arctic phytoplankton blooming. In: Global Change Biology , vol. 00, pp. 1-12, 2023. @article{Castagno2023,
title = {Increased sea ice melt as a driver of enhanced Arctic phytoplankton blooming},
author = {Andrew P. Castagno and Till J. W. Wagner and Mattias R. Cape and Conner W. Lester and Elizabeth Bailey and Catharina Alves-de-Souza and Robert A. York and Alyson H. Fleming},
url = {https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.16815},
doi = {https://doi.org/10.1111/gcb.16815},
year = {2023},
date = {2023-06-18},
journal = {Global Change Biology },
volume = {00},
pages = {1-12},
abstract = {Phytoplankton primary production in the Arctic Ocean has been increasing over the last two decades. In 2019, a record spring bloom occurred in Fram Strait, characterized by a peak in chlorophyll that was reached weeks earlier than in other years and was larger than any previously recorded May bloom. Here, we consider the conditions that led to this event and examine drivers of spring phytoplankton blooms in Fram Strait using in situ, remote sensing, and data assimilation methods. From samples collected during the May 2019 bloom, we observe a direct relationship between sea ice meltwater in the upper water column and chlorophyll a pigment concentrations. We place the 2019 spring dynamics in context of the past 20 years, a period marked by rapid change in climatic conditions. Our findings suggest that increased advection of sea ice into the region and warmer surface temperatures led to a rise in meltwater input and stronger near-surface stratification. Over this time period, we identify large-scale spatial correlations in Fram Strait between increased chlorophyll a concentrations and increased freshwater flux from sea ice melt.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Phytoplankton primary production in the Arctic Ocean has been increasing over the last two decades. In 2019, a record spring bloom occurred in Fram Strait, characterized by a peak in chlorophyll that was reached weeks earlier than in other years and was larger than any previously recorded May bloom. Here, we consider the conditions that led to this event and examine drivers of spring phytoplankton blooms in Fram Strait using in situ, remote sensing, and data assimilation methods. From samples collected during the May 2019 bloom, we observe a direct relationship between sea ice meltwater in the upper water column and chlorophyll a pigment concentrations. We place the 2019 spring dynamics in context of the past 20 years, a period marked by rapid change in climatic conditions. Our findings suggest that increased advection of sea ice into the region and warmer surface temperatures led to a rise in meltwater input and stronger near-surface stratification. Over this time period, we identify large-scale spatial correlations in Fram Strait between increased chlorophyll a concentrations and increased freshwater flux from sea ice melt. |
Roach, Lettie A.; Eisenman, Ian; Wagner, Till J. W.; Donohoe, Aaron: Asymmetry in the Seasonal Cycle of Zonal-Mean Surface Air Temperature. In: Geophysical Research Letters, vol. 50, iss. 10, pp. e2023GL103403, 2023. @article{Roach2023,
title = {Asymmetry in the Seasonal Cycle of Zonal-Mean Surface Air Temperature},
author = {Lettie A. Roach and Ian Eisenman and Till J. W. Wagner and Aaron Donohoe},
url = {https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GL103403},
doi = {https://doi.org/10.1029/2023GL103403},
year = {2023},
date = {2023-05-13},
urldate = {2023-05-13},
journal = {Geophysical Research Letters},
volume = {50},
issue = {10},
pages = {e2023GL103403},
abstract = {At most latitudes, the seasonal cycle of zonal-mean surface air temperature is notably asymmetric: the length of the warming season is not equal to the length of the cooling season. The asymmetry varies spatially, with the cooling season being ∼40 days shorter than the warming season in the subtropics and the warming season being ∼100 days shorter than the cooling season at the poles. Furthermore, the asymmetry differs between the Northern Hemisphere and the Southern Hemisphere. Here, we show that these observed features are broadly captured in a simple model for the evolution of temperature forced by realistic insolation. The model suggests that Earth's orbital eccentricity largely determines the hemispheric contrast, and obliquity broadly dictates the meridional structure. Clouds, atmospheric heat flux convergence, and time-invariant effective surface heat capacity have minimal impacts on seasonal asymmetry. This simple, first-order picture has been absent from previous discussions of the surface temperature seasonal cycle.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
At most latitudes, the seasonal cycle of zonal-mean surface air temperature is notably asymmetric: the length of the warming season is not equal to the length of the cooling season. The asymmetry varies spatially, with the cooling season being ∼40 days shorter than the warming season in the subtropics and the warming season being ∼100 days shorter than the cooling season at the poles. Furthermore, the asymmetry differs between the Northern Hemisphere and the Southern Hemisphere. Here, we show that these observed features are broadly captured in a simple model for the evolution of temperature forced by realistic insolation. The model suggests that Earth's orbital eccentricity largely determines the hemispheric contrast, and obliquity broadly dictates the meridional structure. Clouds, atmospheric heat flux convergence, and time-invariant effective surface heat capacity have minimal impacts on seasonal asymmetry. This simple, first-order picture has been absent from previous discussions of the surface temperature seasonal cycle. |
Beer, Emma; Eisenman, Ian; Wagner, Till J. W.; Fine, Elizabeth C.: A Possible Hysteresis in the Arctic Ocean due to Release of Subsurface Heat during Sea Ice Retreat. In: Journal of Physical Oceanography, vol. 53, iss. 5, pp. 1323-1335, 2023. @article{Beer2023,
title = {A Possible Hysteresis in the Arctic Ocean due to Release of Subsurface Heat during Sea Ice Retreat},
author = {Emma Beer and Ian Eisenman and Till J. W. Wagner and Elizabeth C. Fine},
url = {https://journals.ametsoc.org/view/journals/phoc/53/5/JPO-D-22-0131.1.xml},
doi = {https://doi.org/10.1175/JPO-D-22-0131.1},
year = {2023},
date = {2023-05-01},
urldate = {2023-05-01},
journal = {Journal of Physical Oceanography},
volume = {53},
issue = {5},
pages = {1323-1335},
abstract = {The Arctic Ocean is characterized by an ice-covered layer of cold and relatively fresh water above layers of warmer and saltier water. It is estimated that enough heat is stored in these deeper layers to melt all the Arctic sea ice many times over, but they are isolated from the surface by a stable halocline. Current vertical mixing rates across the Arctic Ocean halocline are small, due in part to sea ice reducing wind–ocean momentum transfer and damping internal waves. However, recent observational studies have argued that sea ice retreat results in enhanced mixing. This could create a positive feedback whereby increased vertical mixing due to sea ice retreat causes the previously isolated subsurface heat to melt more sea ice. Here, we use an idealized climate model to investigate the impacts of such a feedback. We find that an abrupt “tipping point” can occur under global warming, with an associated hysteresis window bounded by saddle-node bifurcations. We show that the presence and magnitude of the hysteresis are sensitive to the choice of model parameters, and the hysteresis occurs for only a limited range of parameters. During the critical transition at the bifurcation point, we find that only a small percentage of the heat stored in the deep layer is released, although this is still enough to lead to substantial sea ice melt. Furthermore, no clear relationship is apparent between this change in heat storage and the level of hysteresis when the parameters are varied.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Arctic Ocean is characterized by an ice-covered layer of cold and relatively fresh water above layers of warmer and saltier water. It is estimated that enough heat is stored in these deeper layers to melt all the Arctic sea ice many times over, but they are isolated from the surface by a stable halocline. Current vertical mixing rates across the Arctic Ocean halocline are small, due in part to sea ice reducing wind–ocean momentum transfer and damping internal waves. However, recent observational studies have argued that sea ice retreat results in enhanced mixing. This could create a positive feedback whereby increased vertical mixing due to sea ice retreat causes the previously isolated subsurface heat to melt more sea ice. Here, we use an idealized climate model to investigate the impacts of such a feedback. We find that an abrupt “tipping point” can occur under global warming, with an associated hysteresis window bounded by saddle-node bifurcations. We show that the presence and magnitude of the hysteresis are sensitive to the choice of model parameters, and the hysteresis occurs for only a limited range of parameters. During the critical transition at the bifurcation point, we find that only a small percentage of the heat stored in the deep layer is released, although this is still enough to lead to substantial sea ice melt. Furthermore, no clear relationship is apparent between this change in heat storage and the level of hysteresis when the parameters are varied. |
Clare, Ryan M.; Desai, Ankur R.; Martin, Jonathan E.; Notaro, Michael; Vavrus, Stephen J.: Extratropical Cyclone Response to Projected Reductions in Snow Extent over the Great Plains. In: Atmosphere, vol. 14, iss. 5, pp. 783, 2023. @article{Clare2023,
title = {Extratropical Cyclone Response to Projected Reductions in Snow Extent over the Great Plains},
author = {Ryan M. Clare and Ankur R. Desai and Jonathan E. Martin and Michael Notaro and Stephen J. Vavrus },
doi = {https://doi.org/10.3390/atmos14050783},
year = {2023},
date = {2023-04-26},
journal = {Atmosphere},
volume = {14},
issue = {5},
pages = {783},
abstract = {Extratropical cyclones develop in regions of enhanced baroclinicity and progress along climatological storm tracks. Numerous studies have noted an influence of terrestrial snow cover on atmospheric baroclinicity. However, these studies have less typically examined the role that continental snow cover extent and changes anticipated with anthropogenic climate change have on cyclones’ intensities, trajectories, and precipitation characteristics. Here, we examined how projected future poleward shifts in North American snow extent influence extratropical cyclones. We imposed 10th, 50th, and 90th percentile values of snow retreat between the late 20th and 21st centuries as projected by 14 Coupled Model Intercomparison Project Phase Five (CMIP5) models to alter snow extent underlying 15 historical cold-season cyclones that tracked over the North American Great Plains and were faithfully reproduced in control model cases, providing a comprehensive set of model runs to evaluate hypotheses. Simulations by the Advanced Research version of the Weather Research and Forecast Model (WRF-ARW) were initialized at four days prior to cyclogenesis. Cyclone trajectories moved on average poleward (μ = 27 +/− σ = 17 km) in response to reduced snow extent while the maximum sea-level pressure deepened (μ = −0.48 +/− σ = 0.8 hPa) with greater snow removed. A significant linear correlation was observed between the area of snow removed and mean trajectory deviation (r2 = 0.23), especially in mid-winter (r2 = 0.59), as well as a similar relationship for maximum change in sea-level pressure (r2 = 0.17). Across all simulations, 82% of the perturbed simulation cyclones decreased in average central sea-level pressure (SLP) compared to the corresponding control simulation. Near-surface wind speed increased, as did precipitation, in 86% of cases with a preferred phase change from the solid to liquid state due to warming, although the trends did not correlate with the snow retreat magnitude. Our results, consistent with prior studies noting some role for the enhanced baroclinity of the snow line in modulating storm track and intensity, provide a benchmark to evaluate future snow cover retreat impacts on mid-latitude weather systems.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Extratropical cyclones develop in regions of enhanced baroclinicity and progress along climatological storm tracks. Numerous studies have noted an influence of terrestrial snow cover on atmospheric baroclinicity. However, these studies have less typically examined the role that continental snow cover extent and changes anticipated with anthropogenic climate change have on cyclones’ intensities, trajectories, and precipitation characteristics. Here, we examined how projected future poleward shifts in North American snow extent influence extratropical cyclones. We imposed 10th, 50th, and 90th percentile values of snow retreat between the late 20th and 21st centuries as projected by 14 Coupled Model Intercomparison Project Phase Five (CMIP5) models to alter snow extent underlying 15 historical cold-season cyclones that tracked over the North American Great Plains and were faithfully reproduced in control model cases, providing a comprehensive set of model runs to evaluate hypotheses. Simulations by the Advanced Research version of the Weather Research and Forecast Model (WRF-ARW) were initialized at four days prior to cyclogenesis. Cyclone trajectories moved on average poleward (μ = 27 +/− σ = 17 km) in response to reduced snow extent while the maximum sea-level pressure deepened (μ = −0.48 +/− σ = 0.8 hPa) with greater snow removed. A significant linear correlation was observed between the area of snow removed and mean trajectory deviation (r2 = 0.23), especially in mid-winter (r2 = 0.59), as well as a similar relationship for maximum change in sea-level pressure (r2 = 0.17). Across all simulations, 82% of the perturbed simulation cyclones decreased in average central sea-level pressure (SLP) compared to the corresponding control simulation. Near-surface wind speed increased, as did precipitation, in 86% of cases with a preferred phase change from the solid to liquid state due to warming, although the trends did not correlate with the snow retreat magnitude. Our results, consistent with prior studies noting some role for the enhanced baroclinity of the snow line in modulating storm track and intensity, provide a benchmark to evaluate future snow cover retreat impacts on mid-latitude weather systems. |
Sutheimer, Colleen M.; Meunier, Jed; Drobyshev, Igor; Stambaugh, Michael C.; Hotchkiss, Sara C.; Rebitzke, Eric; Radeloff, Volker C.: Climate forcing of regional fire years in the upper Great Lakes Region, USA. In: International Journal of Wildland Fire, vol. 32, pp. 796-813, 2023. @article{Sutheimer2023,
title = {Climate forcing of regional fire years in the upper Great Lakes Region, USA},
author = {Colleen M. Sutheimer and Jed Meunier and Igor Drobyshev and Michael C. Stambaugh and Sara C. Hotchkiss and Eric Rebitzke and Volker C. Radeloff},
doi = {https://doi.org/10.1071/WF22205},
year = {2023},
date = {2023-03-16},
journal = {International Journal of Wildland Fire},
volume = {32},
pages = {796-813},
abstract = {Background: Drivers of fire regimes vary among spatial scales, and fire history reconstructions are often limited to stand scales, making it difficult to partition effects of regional climate forcing versus individual site histories.
Aims: To evaluate regional-scale historical fire regimes over 350 years, we analysed an extensive fire-scar network, spanning 240 km across the upper Great Lakes Region in North America.
Methods: We estimated fire frequency, identified regionally widespread fire years (based on the fraction of fire-scarred tree samples, fire extent index (FEI), and synchronicity of fire years), and evaluated fire seasonality and climate–fire relationships.
Key results: Historically, fire frequency and seasonality were variable within and among Great Lakes’ ecoregions. Climate forcing at regional scales resulted in synchronised fires, primarily during the late growing season, which were ubiquitous across the upper Great Lakes Region. Regionally significant fire years included 1689, 1752, 1754, 1791, and 1891.
Conclusions: We found significant climate forcing of region-wide fire regimes in the upper Great Lakes Region.
Implications: Historically, reoccurring fires in the upper Great Lakes Region were instrumental for shaping and maintaining forest resilience. The climate conditions that helped promote widespread fire years historically may be consistent with anticipated climate–fire interactions due to climate change.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Background: Drivers of fire regimes vary among spatial scales, and fire history reconstructions are often limited to stand scales, making it difficult to partition effects of regional climate forcing versus individual site histories.
Aims: To evaluate regional-scale historical fire regimes over 350 years, we analysed an extensive fire-scar network, spanning 240 km across the upper Great Lakes Region in North America.
Methods: We estimated fire frequency, identified regionally widespread fire years (based on the fraction of fire-scarred tree samples, fire extent index (FEI), and synchronicity of fire years), and evaluated fire seasonality and climate–fire relationships.
Key results: Historically, fire frequency and seasonality were variable within and among Great Lakes’ ecoregions. Climate forcing at regional scales resulted in synchronised fires, primarily during the late growing season, which were ubiquitous across the upper Great Lakes Region. Regionally significant fire years included 1689, 1752, 1754, 1791, and 1891.
Conclusions: We found significant climate forcing of region-wide fire regimes in the upper Great Lakes Region.
Implications: Historically, reoccurring fires in the upper Great Lakes Region were instrumental for shaping and maintaining forest resilience. The climate conditions that helped promote widespread fire years historically may be consistent with anticipated climate–fire interactions due to climate change. |
Batchelor, C. J.; Marcott, S. A.; Orland, I. J.; He, F.; Edwards, R. L.: Decadal warming events extended into central North America during the last glacial period. In: Nature Geoscience , vol. 16, pp. 257–261, 2023. @article{Batchelor2023,
title = {Decadal warming events extended into central North America during the last glacial period},
author = {C. J. Batchelor and S. A. Marcott and I. J. Orland and F. He and R. L. Edwards},
url = {https://www.nature.com/articles/s41561-023-01132-3},
doi = {https://doi.org/10.1038/s41561-023-01132-3},
year = {2023},
date = {2023-03-02},
journal = {Nature Geoscience },
volume = {16},
pages = {257–261},
abstract = {The connection between abrupt high-latitude warming during the last glacial period—Dansgaard–Oeschger (DO) events—and rapid climate changes at lower latitudes has revealed inter-hemispheric teleconnections in the ocean–atmosphere system. Links between DO events and climate variability in mid-latitude, mid-continent settings remain, however, poorly understood, especially in North America where climate archives with sufficient time resolution are scarce. Here we examine a speleothem that grew from ~70–50 thousand years ago (ka) in Wisconsin (United States) and combine fluorescent imaging of its growth banding with an annual-resolution oxygen isotope (δ18O) record. Eight large (2.0–3.0‰) negative δ18O excursions, each with an onset in <10 annual growth bands, occur between 61–55 ka, when DO events 17–14 are recorded in the ice core of the North Greenland Ice Core Project. Although the age model does not allow these δ18O excursions to be matched to specific DO events, their magnitude and rapid onset support a credible link. Isotope-enabled climate simulations suggest that abrupt DO warming would increase the δ18O of annual precipitation in the study area and corroborate that warming of >10 °C in <10 years is thus required to produce the observed negative δ18O excursions. Our findings of expansive abrupt DO warming in central North America has implications for environmental, climate and ice sheet dynamics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The connection between abrupt high-latitude warming during the last glacial period—Dansgaard–Oeschger (DO) events—and rapid climate changes at lower latitudes has revealed inter-hemispheric teleconnections in the ocean–atmosphere system. Links between DO events and climate variability in mid-latitude, mid-continent settings remain, however, poorly understood, especially in North America where climate archives with sufficient time resolution are scarce. Here we examine a speleothem that grew from ~70–50 thousand years ago (ka) in Wisconsin (United States) and combine fluorescent imaging of its growth banding with an annual-resolution oxygen isotope (δ18O) record. Eight large (2.0–3.0‰) negative δ18O excursions, each with an onset in <10 annual growth bands, occur between 61–55 ka, when DO events 17–14 are recorded in the ice core of the North Greenland Ice Core Project. Although the age model does not allow these δ18O excursions to be matched to specific DO events, their magnitude and rapid onset support a credible link. Isotope-enabled climate simulations suggest that abrupt DO warming would increase the δ18O of annual precipitation in the study area and corroborate that warming of >10 °C in <10 years is thus required to produce the observed negative δ18O excursions. Our findings of expansive abrupt DO warming in central North America has implications for environmental, climate and ice sheet dynamics. |
Yu, Yanyan; He, Feng; Vavrus, Stephen J.; Johnson, Amber; Wu, Haibin; Zhang, Wenchao; Yin, Qiuzhen; Ge, Junyi; Deng, Chenglong; Petraglia, Michael D.; Guo, Zhengtang: Climatic factors and human population changes in Eurasia between the Last Glacial Maximum and the early Holocene. In: Global and Planetary Change, vol. 221, pp. 104054, 2023. @article{Yu2023,
title = {Climatic factors and human population changes in Eurasia between the Last Glacial Maximum and the early Holocene},
author = {Yanyan Yu and Feng He and Stephen J. Vavrus and Amber Johnson and Haibin Wu and Wenchao Zhang and Qiuzhen Yin and Junyi Ge and Chenglong Deng and Michael D. Petraglia and Zhengtang Guo},
url = {https://www.sciencedirect.com/science/article/pii/S0921818123000279},
doi = {https://doi.org/10.1016/j.gloplacha.2023.104054},
year = {2023},
date = {2023-02-01},
journal = {Global and Planetary Change},
volume = {221},
pages = {104054},
abstract = {Archaeological records document a significant expansion of populations from the Last Glacial Maximum (LGM, ∼23–19 ka) to the early Holocene (EH, ∼9 ka) in Eurasia, which is often attributed to the influence of orbital-scale climate changes. Yet, information remains limited concerning the climatic factor(s) which were responsible for conditioning demographic patterns. Here, we present results from an improved Minimalist Terrestrial Resource Model (MTRM), forced by a transient climate simulation from the LGM to the EH. Simulated potential hunter-gatherer population densities and spatial distributions across Eurasia are supported by observed archaeological sites in Europe and China. In the low latitudes, potential population size change was predominantly controlled by precipitation and its strong influence on plant and animal resources. In the middle-high latitudes, temperature was the dominant driver in influencing potential population size change and animal resource availability. Different regional responses of potential populations to climate change across Eurasia - owing to variations in available food resources between the LGM and EH - provide a better understanding of human dispersal during the Late Pleistocene.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Archaeological records document a significant expansion of populations from the Last Glacial Maximum (LGM, ∼23–19 ka) to the early Holocene (EH, ∼9 ka) in Eurasia, which is often attributed to the influence of orbital-scale climate changes. Yet, information remains limited concerning the climatic factor(s) which were responsible for conditioning demographic patterns. Here, we present results from an improved Minimalist Terrestrial Resource Model (MTRM), forced by a transient climate simulation from the LGM to the EH. Simulated potential hunter-gatherer population densities and spatial distributions across Eurasia are supported by observed archaeological sites in Europe and China. In the low latitudes, potential population size change was predominantly controlled by precipitation and its strong influence on plant and animal resources. In the middle-high latitudes, temperature was the dominant driver in influencing potential population size change and animal resource availability. Different regional responses of potential populations to climate change across Eurasia - owing to variations in available food resources between the LGM and EH - provide a better understanding of human dispersal during the Late Pleistocene. |
Beal, Maxwell R. W.; Wilkinson, Grace M.; Block, Paul J.: Large scale seasonal forecasting of peak season algae metrics in the Midwest and Northeast U.S.. In: Water Research, vol. 229, pp. 119402, 2023. @article{Beal2023,
title = {Large scale seasonal forecasting of peak season algae metrics in the Midwest and Northeast U.S.},
author = {Maxwell R.W. Beal and Grace M. Wilkinson and Paul J. Block},
url = {https://www.sciencedirect.com/science/article/pii/S0043135422013471},
doi = {10.1016/j.watres.2022.119402},
year = {2023},
date = {2023-02-01},
journal = {Water Research},
volume = {229},
pages = {119402},
abstract = {In recent decades, many inland lakes have seen an increase in the prevalence of potentially harmful algae. In many inland lakes, the peak season for algae abundance (summer and early fall in the northern hemisphere) coincides with the peak season for recreational use. Currently, little information regarding expected algae conditions is available prior to the peak season for productivity in inland lakes. Peak season algae conditions are influenced by an array of pre-season (spring and early summer) local and global scale variables; identifying these variables for forecast development may be useful in managing potential public health threats posed by harmful algae. Using the LAGOS-NE dataset, pre-season local and global drivers of peak-season algae metrics (represented by chlorophyll-a) are identified for 178 lakes across the Northeast and Midwest U.S. from readily available gridded datasets. Forecasting models are built for each lake conditioned on relevant pre-season predictors. Forecasts are assessed for the magnitude, severity, and duration of seasonal chlorophyll concentrations. Regions of pre-season sea surface temperature, and pre-season chlorophyll-a demonstrate the most predictive power for peak season algae metrics, and resulting models show significant skill. Based on categorical forecast metrics, more than 70% of magnitude models and 90% of duration models outperform climatology. Forecasts of high and severe algae magnitude perform best in large mesotrophic and oligotrophic lakes, however, high algae duration performance appears less dependent on lake characteristics. The advance notice of elevated algae biomass provided by these models may allow lake managers to better prepare for challenges posed by algae during the high use season for inland lakes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In recent decades, many inland lakes have seen an increase in the prevalence of potentially harmful algae. In many inland lakes, the peak season for algae abundance (summer and early fall in the northern hemisphere) coincides with the peak season for recreational use. Currently, little information regarding expected algae conditions is available prior to the peak season for productivity in inland lakes. Peak season algae conditions are influenced by an array of pre-season (spring and early summer) local and global scale variables; identifying these variables for forecast development may be useful in managing potential public health threats posed by harmful algae. Using the LAGOS-NE dataset, pre-season local and global drivers of peak-season algae metrics (represented by chlorophyll-a) are identified for 178 lakes across the Northeast and Midwest U.S. from readily available gridded datasets. Forecasting models are built for each lake conditioned on relevant pre-season predictors. Forecasts are assessed for the magnitude, severity, and duration of seasonal chlorophyll concentrations. Regions of pre-season sea surface temperature, and pre-season chlorophyll-a demonstrate the most predictive power for peak season algae metrics, and resulting models show significant skill. Based on categorical forecast metrics, more than 70% of magnitude models and 90% of duration models outperform climatology. Forecasts of high and severe algae magnitude perform best in large mesotrophic and oligotrophic lakes, however, high algae duration performance appears less dependent on lake characteristics. The advance notice of elevated algae biomass provided by these models may allow lake managers to better prepare for challenges posed by algae during the high use season for inland lakes. |
Vavrus, S. J.; Kruse, S.; A. Puz,; Patz, J. A.: Applying climate change science: From extreme weather events to sea level rise. In: Climate Change and Public Health, Second Edition, 2023. @article{Vavrus2023,
title = {Applying climate change science: From extreme weather events to sea level rise},
author = {S. J. Vavrus and S. Kruse and A. Puz, and J. A. Patz},
year = {2023},
date = {2023-01-01},
journal = {Climate Change and Public Health, Second Edition},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2022
|
Francis, Jennifer A.; Skific, Natasa; Vavrus, Steven J.; Cohen, Judah: Measuring “Weather Whiplash” Events in North America: A New Large-Scale Regime Approach. In: Journal of Geophysical Research: Atmospheres, vol. 127, iss. 17, pp. e2022JD036717, 2022. @article{nokey,
title = {Measuring “Weather Whiplash” Events in North America: A New Large-Scale Regime Approach},
author = {Jennifer A. Francis and Natasa Skific and Steven J. Vavrus and Judah Cohen
},
doi = { https://doi.org/10.1029/2022JD036717},
year = {2022},
date = {2022-09-07},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {127},
issue = {17},
pages = {e2022JD036717},
abstract = {The term “weather whiplash” was recently coined to describe abrupt swings in weather conditions from one extreme to another, such as from a prolonged, frigid cold spell to anomalous warmth or from drought to heavy precipitation. These events are often highly disruptive to agriculture, ecosystems, and daily activities. In this study, we propose and demonstrate a novel metric to identify weather whiplash events (WWEs) and track their frequency over time. We define a WWE as a transition from one persistent continental-scale circulation regime to another distinctly different pattern, as determined using an objective pattern clustering analysis called self-organizing maps. We focus on the domain spanning North America and the eastern N. Pacific Ocean. A matrix of representative atmospheric patterns in 500-hPa geopotential height anomalies is created from 72 years of daily fields. We analyze the occurrence of WWEs originating with long-duration events (LDEs) (defined as lasting four or more days) in each pattern, as well as the associated extremes in temperature and precipitation. A WWE is detected when the pattern 2 days following a LDE is substantially different, measured using internal matrix distances and thresholds. Changes in WWE frequency are assessed objectively based on reanalysis and historical climate model simulations, and for the future using climate model projections. Temporal changes in the future under representative concentration pathway 8.5 forcing are more robust than those in recent decades. We find consistent increases in WWEs originating in patterns with an anomalously warm Arctic and decreases in cold-Arctic patterns.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The term “weather whiplash” was recently coined to describe abrupt swings in weather conditions from one extreme to another, such as from a prolonged, frigid cold spell to anomalous warmth or from drought to heavy precipitation. These events are often highly disruptive to agriculture, ecosystems, and daily activities. In this study, we propose and demonstrate a novel metric to identify weather whiplash events (WWEs) and track their frequency over time. We define a WWE as a transition from one persistent continental-scale circulation regime to another distinctly different pattern, as determined using an objective pattern clustering analysis called self-organizing maps. We focus on the domain spanning North America and the eastern N. Pacific Ocean. A matrix of representative atmospheric patterns in 500-hPa geopotential height anomalies is created from 72 years of daily fields. We analyze the occurrence of WWEs originating with long-duration events (LDEs) (defined as lasting four or more days) in each pattern, as well as the associated extremes in temperature and precipitation. A WWE is detected when the pattern 2 days following a LDE is substantially different, measured using internal matrix distances and thresholds. Changes in WWE frequency are assessed objectively based on reanalysis and historical climate model simulations, and for the future using climate model projections. Temporal changes in the future under representative concentration pathway 8.5 forcing are more robust than those in recent decades. We find consistent increases in WWEs originating in patterns with an anomalously warm Arctic and decreases in cold-Arctic patterns. |