Papers by Alvaro Montenegro
Geophysical Research Letters, 2006
1] We present analyses of new and previously published estimates of total (vegetation plus soil) ... more 1] We present analyses of new and previously published estimates of total (vegetation plus soil) carbon storage on exposed continental shelves during the LGM. Carbon stock estimates from environmental reconstructions vary from 113 to 202 Pg C. Estimates from vegetation models range from 112 to 323 Pg C. After standardization of exposed shelf area by a topographic model the range of best estimates for reconstructions and models converge to 182 -266 Pg C. Up to $10000 years before present, the time dependent estimate of the amount of inundated carbon is in good qualitative agreement with the increase in the atmospheric carbon reservoir. Given its relative size compared to the change in terrestrial carbon storage and the potential link between inundated carbon and atmospheric CO 2 increase, the carbon stock of the LGM exposed shelves cannot be ignored and merits more detailed attention from modelling and reconstruction efforts.
The prehistoric colonization of islands in Remote Oceania that began ∼3400 B.P. represents what w... more The prehistoric colonization of islands in Remote Oceania that began ∼3400 B.P. represents what was arguably the most expansive and ambitious maritime dispersal of humans across any of the world’s seas or oceans. Though archaeological evidence has provided a relatively clear picture of when many of the major island groups were colonized, there is still considerable debate as to where these settlers originated from and their strategies/trajectories used to reach habitable land that other datasets (genetic, linguistic) are also still trying to resolve. To address these issues, we have harnessed the power of high-resolution climatic and oceanographic datasets in multiple seafaring simulation platforms to examine major pulses of colonization in the region. Our analysis, which takes into consideration currents, land distribution, wind
periodicity, the influence of El Niño Southern Oscillation (ENSO) events, and “shortest-hop” trajectories, demonstrate that (i) seasonal and semiannual climatic changes were highly influential in structuring ancient Pacific voyaging; (ii) western Micronesia was likely settled from somewhere around the Maluku (Molucca) Islands; (iii) Samoa was the most probable staging area for the colonization of East Polynesia; and (iv) although there are major differences in success rates depending on time of year and the occurrence of ENSO events, settlement of Hawai’i and New Zealand is possible from the Marquesas or Society Islands, the same being the case for settlement of Easter Island from Mangareva or the Marquesas.
Journal of Geophysical Research Oceans, 2007
1] The deep variability in two areas of the Atlantic Western Boundary is studied. One site is loc... more 1] The deep variability in two areas of the Atlantic Western Boundary is studied. One site is located at 38°N, inshore of the Gulf Stream. The other is at 8°S, off the Brazilian coast. Analyses are centered on current time series estimated by a method that uses expendable bathythermograph derived dynamic heights to remove the near-surface signal from altimetric sea surface height. Both series are approximately 6 years long. Currents are compared to scatterometer derived alongshore wind stress and basin-wide wind stress curl.
Current Anthropology a World Journal of the Sciences of Man, 2006
Paleoparasitological findings and paleoclimate modelling simulations indicate that early peoples ... more Paleoparasitological findings and paleoclimate modelling simulations indicate that early peoples migrating via the “Clovis first” route across Beringia into North America could not have traversed the required distance in time to provide a reasonable explanation for the presence of the hookworm in the pre-Columbian Americas. The introduction of the hookworm into the Americas by a land migration at around 13,000 years BP could have happened only under extraordinary circumstances and even then would have required ...
The causes for the Permian-Triassic (PT) extinction, the largest mass extinction on record, remai... more The causes for the Permian-Triassic (PT) extinction, the largest mass extinction on record, remain unknown. The period is marked by large scale volcanic eruptions and evidence for widespread ocean anoxia, which have led to suggestions that these events generated, or played a part in, the extinction. Hypercapnia and ocean acidification caused by volcanic emissions of CO2 and CH4 have been put forward as potential kill mechanisms. We present the first PT boundary climate simulations conducted with a fully coupled climate-carbon cycle model, which allows for a direct evaluation of ocean acidity. The experiments also address the sensitivity of ocean circulation and oxygen levels to uncertainties in paleogeography and to different bottom topographies. Modeled temperature and precipitation are in good agreement with reconstructions and climate sensitive sediments. There is also good agreement between modeled vegetation and reconstructed biomes.The reduction in ocean pH brought about by th...
Paleoceanography, 2011
1] The causes for the Permian-Triassic Boundary (PTB) extinction, the largest mass extinction on ... more 1] The causes for the Permian-Triassic Boundary (PTB) extinction, the largest mass extinction on record, remain enigmatic. The period is marked by large-scale volcanic eruptions and evidence for widespread ocean anoxia, which have led to suggestions that these events generated, or played a part in, the extinction. Furthermore, hypercapnia and ocean acidification caused by volcanic emissions of CO 2 and CH 4 have been put forward as potential kill mechanisms. We present the first PTB climate simulations in which ocean acidity is evaluated directly with a coupled climate-carbon cycle model. The experiments also address the sensitivity of ocean circulation and oxygen levels to uncertainties in paleogeography and to different bottom topographies. Modeled temperature and precipitation-evaporation are in good agreement with reconstructions and climate-sensitive sediments. There is also good agreement between modeled vegetation and reconstructed biomes. The reduction in ocean pH brought about by the increase in atmospheric CO 2 is biologically significant. Aragonite saturation levels are low enough to make the whole ocean unsuitable to aragonitic species, and large areas of the ocean become unsaturated in relationship to calcite. No general bottom anoxia is reproduced. Modeled deep ocean O 2 concentrations are not significantly impacted by changes in paleogeography and bathymetry, an indication that in our model a change in ocean dynamics resulting from climate warming is not sufficient by itself to generate widespread anoxic conditions during the period.
Journal of Geophysical Research, 2007
1] The deep variability in two areas of the Atlantic Western Boundary is studied. One site is loc... more 1] The deep variability in two areas of the Atlantic Western Boundary is studied. One site is located at 38°N, inshore of the Gulf Stream. The other is at 8°S, off the Brazilian coast. Analyses are centered on current time series estimated by a method that uses expendable bathythermograph derived dynamic heights to remove the near-surface signal from altimetric sea surface height. Both series are approximately 6 years long. Currents are compared to scatterometer derived alongshore wind stress and basin-wide wind stress curl.
Journal of Climate, 2010
A global climate model with horizontal resolutions in the ocean ranging from relatively coarse to... more A global climate model with horizontal resolutions in the ocean ranging from relatively coarse to eddy permitting is used to investigate the resolution dependence of the Southern Ocean response to poleward intensifying winds through the past and present centuries. The higher-resolution simulations show poleward migration of distinct ocean fronts associated with a more highly localized near-surface temperature response than in the lower-resolution simulations. The higher-resolution simulations also show increasing southward eddy heat transport, less high-latitude cooling, and greater sea ice loss than the lower-resolution simulations. For all resolutions, from relatively coarse to eddy permitting, there is poleward migration of the Antarctic Circumpolar Current in the Atlantic and the western half of the Indian basin. Finally, zonal transports associated with the Antarctic Circumpolar Current are shown to be sensitive to resolution, and this is discussed in the context of recent observed change.
Geophysical Research Letters, 2006
1] We present analyses of new and previously published estimates of total (vegetation plus soil) ... more 1] We present analyses of new and previously published estimates of total (vegetation plus soil) carbon storage on exposed continental shelves during the LGM. Carbon stock estimates from environmental reconstructions vary from 113 to 202 Pg C. Estimates from vegetation models range from 112 to 323 Pg C. After standardization of exposed shelf area by a topographic model the range of best estimates for reconstructions and models converge to 182 -266 Pg C. Up to $10000 years before present, the time dependent estimate of the amount of inundated carbon is in good qualitative agreement with the increase in the atmospheric carbon reservoir. Given its relative size compared to the change in terrestrial carbon storage and the potential link between inundated carbon and atmospheric CO 2 increase, the carbon stock of the LGM exposed shelves cannot be ignored and merits more detailed attention from modelling and reconstruction efforts.
Environmental Science & Policy, 2013
Downscaling Forest management a b s t r a c t This paper examines the risks associated with fores... more Downscaling Forest management a b s t r a c t This paper examines the risks associated with forest insect outbreaks in a changing climate from biological and forest management perspectives. Two important Canadian insects were considered: western spruce budworm (WSBW; Choristoneura occidentalis Freeman, Lepidoptera: Tortricidae), and spruce bark beetle (SBB; Dendroctonus rufipennis Kirby, Coleoptera: Curculionidae). This paper integrates projections of tree species suitability, pest outbreak risk, and bio-economic modelling.
Current Anthropology, 2006
Versions of a global climate model, with horizontal resolutions ranging from coarse to ocean eddy... more Versions of a global climate model, with horizontal resolutions ranging from coarse to ocean eddy-permitting, are used to investigate the resolution dependence of the 21st century Southern Ocean response to poleward intensifying winds. Results show that the migration of distinct ocean fronts at higher resolutions is associated with a strong local intensification of the near-surface temperature response. There is also less high latitude cooling and a greater loss of sea ice thickness at eddy-permitting resolutions, in conjunction with an increase in southward ocean resolved eddy heat transport. All simulations show poleward migration of the ACC in the Atlantic and the western half of the Indian basin, with only slight changes elsewhere. The response of ACC transport at eddy-permitting resolutions is shown to be sensitive to variations in the horizontal ocean viscosity parameter. At higher viscosity, ACC tranport is shown to increase throughout the forcing period, while at lower viscosity the transport response tends to stabilize. This implies that the affect of windstress forcing on ACC transport in models is dependent on the resolution of mesoscale eddy activity on decadal timescales. Horizontal viscosity sensitivity of ACC transport response at 0.2x0.4 resolution to poleward intensifying wind forcing over years 2060-2080. Horizontal viscosity sensitivity of Southern Ocean temperature response at 0.2x0.4 resolution to poleward intensifying wind forcing over years 2060-2080.
The causes for the Permian-Triassic (PT) extinction, the largest mass extinction on record, remai... more The causes for the Permian-Triassic (PT) extinction, the largest mass extinction on record, remain unknown. The period is marked by large scale volcanic eruptions and evidence for widespread ocean anoxia, which have led to suggestions that these events generated, or played a part in, the extinction. Hypercapnia and ocean acidification caused by volcanic emissions of CO2 and CH4 have been put forward as potential kill mechanisms. We present the first PT boundary climate simulations conducted with a fully coupled climate-carbon cycle model, which allows for a direct evaluation of ocean acidity. The experiments also address the sensitivity of ocean circulation and oxygen levels to uncertainties in paleogeography and to different bottom topographies. Modeled temperature and precipitation are in good agreement with reconstructions and climate sensitive sediments. There is also good agreement between modeled vegetation and reconstructed biomes.The reduction in ocean pH brought about by the increase in atmospheric CO2 is biologically significant. Aragonite saturation levels are low enough to make the whole ocean unsuitable to present day corals and large areas of the ocean become unsaturated in relationship to calcite. No general bottom anoxia is reproduced. Modeled deep ocean O2 concentrations are not significantly impacted by changes in paleogeography and bathymetry, in a indication that a change in ocean dynamics resulting from climate warming is not sufficient by itself to generate widespread anoxic conditions during the period.
PLOS ONE, 2016
Deforestation is associated with increased atmospheric CO2 and alterations to the surface energy ... more Deforestation is associated with increased atmospheric CO2 and alterations to the surface energy and mass balances that can lead to local and global climate changes. Previous modelling studies show that the global surface air temperature (SAT) response to deforestation depends on latitude, with most simulations showing that high latitude deforestation results in cooling, low latitude deforestation causes warming and that the mid latitude response is mixed. These earlier conclusions are based on simulated large scal land cover change, with complete removal of trees from whole latitude bands. Using a global climate model we examine the effects of removing fractions of 5% to 100% of forested areas in the high, mid and low latitudes. All high latitude deforestation scenarios reduce mean global SAT, the opposite occurring for low latitude deforestation, although a decrease in SAT is simulated over low latitude deforested areas. Mid latitude SAT response is mixed. In all simulations deforested areas tend to become drier and have lower SAT, although soil temperatures increase over deforested mid and low latitude grid cells. For high latitude deforestation fractions of 45% and above, larger net primary productivity, in conjunction with colder and drier conditions after deforestation cause an increase in soil carbon large enough to produce a net decrease of atmospheric CO2. Our results reveal the complex interactions between soil carbon dynamics and other climate subsystems in the energy partition responses to land cover change.
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Papers by Alvaro Montenegro
periodicity, the influence of El Niño Southern Oscillation (ENSO) events, and “shortest-hop” trajectories, demonstrate that (i) seasonal and semiannual climatic changes were highly influential in structuring ancient Pacific voyaging; (ii) western Micronesia was likely settled from somewhere around the Maluku (Molucca) Islands; (iii) Samoa was the most probable staging area for the colonization of East Polynesia; and (iv) although there are major differences in success rates depending on time of year and the occurrence of ENSO events, settlement of Hawai’i and New Zealand is possible from the Marquesas or Society Islands, the same being the case for settlement of Easter Island from Mangareva or the Marquesas.
periodicity, the influence of El Niño Southern Oscillation (ENSO) events, and “shortest-hop” trajectories, demonstrate that (i) seasonal and semiannual climatic changes were highly influential in structuring ancient Pacific voyaging; (ii) western Micronesia was likely settled from somewhere around the Maluku (Molucca) Islands; (iii) Samoa was the most probable staging area for the colonization of East Polynesia; and (iv) although there are major differences in success rates depending on time of year and the occurrence of ENSO events, settlement of Hawai’i and New Zealand is possible from the Marquesas or Society Islands, the same being the case for settlement of Easter Island from Mangareva or the Marquesas.