Krister Stræte Karlsen

• Karlsen, Krister Stræte; Conrad, Clinton Phillips; Domeier, Mathew & Trønnes, Reidar G (2021). Spatiotemporal Variations in Surface Heat Loss Imply a Heterogeneous Mantle Cooling History. Geophysical Research Letters.  ISSN 0094-8276.  48(6) . doi: 10.1029/2020GL092119 Full text in Research Archive. Show summary

  Earth's heat budget is strongly influenced by spatial and temporal variations in surface heat flow caused by plate tectonic cycles. Here, we use a novel set of paleo‐seafloor age grids extending back to the mid‐Paleozoic to infer spatiotemporal variations in surface heat loss. The time‐averaged oceanic heat flow is 36.6 TW, or ∼25% greater than at present‐day. Our thermal budget for the mantle indicates that 149 K/Gyr of cooling occurred over this period, consistent with geochemical estimates of mantle cooling for the past 1 Gyr. Our analysis also suggests sustained rapid cooling of the Pacific mantle hemisphere, which may have cooled ∼50 K more than its African counterpart since 400 Ma. The extra heat released from the Pacific mantle may have been trapped there by the earlier long‐lived supercontinent Rodinia (∼1.1–0.7 Ga), and the Pacific mantle may still be hotter than the African mantle today.

• Karlsen, Krister Stræte; Domeier, Mathew; Gaina, Carmen & Conrad, Clinton Phillips (2020). A tracer-based algorithm for automatic generation of seafloor age grids from plate tectonic reconstructions. Computers & Geosciences.  ISSN 0098-3004.  140 . doi: 10.1016/j.cageo.2020.104508 Full text in Research Archive. Show summary

  The age of the ocean floor and its time-dependent age distribution control fundamental features of the Earth, such as bathymetry, sea level and mantle heat loss. Recently, the development of increasingly sophisticated reconstructions of past plate motions has provided models for plate kinematics and plate boundary evolution back in geological time. These models implicitly include the information necessary to determine the age of ocean floor that has since been lost to subduction. However, due to the lack of an automated and efficient method for generating global seafloor age grids, many tectonic models, most notably those extending back into the Paleozoic, are published without an accompanying set of age models for oceanic lithosphere. Here we present an automatic, tracer-based algorithm that generates seafloor age grids from global plate tectonic reconstructions with defined plate boundaries. Our method enables us to produce novel seafloor age models for the Paleozoic’s lost ocean basins. Estimated changes in sea level based on bathymetry inferred from our new age grids show good agreement with sea level record estimations from proxies, providing a possible explanation for the peak in sea level during the assembly phase of Pangea. This demonstrates how our seafloor age models can be directly compared with observables from the geologic record that extend further back in time than the constraints from preserved seafloor. Thus, our new algorithm may also aid the further development of plate tectonic reconstructions by strengthening the links between geological observations and tectonic reconstructions of deeper time.

• Karlsen, Krister Stræte; Conrad, Clinton Phillips & Magni, Valentina (2019). Deep water cycling and sea level change since the breakup of Pangea. Geochemistry Geophysics Geosystems.  ISSN 1525-2027.  20(6), s 2919- 2935 . doi: 10.1029/2019GC008232 Full text in Research Archive. Show summary

  First‐order variations in sea level exhibit amplitudes of ∼200 m over periods that coincide with those of supercontinental cycles (∼300–500 Myr). Proposed mechanisms for this sea level change include processes that change the container volume of the ocean basins and the relative elevation of continents. Here we investigate how unbalanced rates of water exchange between Earth's surface and mantle interior, resulting from fluctuations in tectonic rates, can cause sea level changes. Previous modeling studies of subduction water fluxes suggest that the amount of water that reaches sub‐arc depths is well correlated with the velocity and age of the subducting plate. We use these models to calibrate a parameterization of the deep subduction water flux, which we together with a parameterization of mid‐ocean ridge outgassing, then apply to reconstructions of Earth's tectonic history. This allows us to estimate the global water fluxes between the oceans and mantle for the past 230 Myr and compute the associated sea level change. Our model suggests that a sea level drop of up to 130 m is possible over this period and that it was partly caused by the ∼150Ma rift pulse that opened the Atlantic and forced rapid subduction of old oceanic lithosphere. This indicates that deep water cycling may be one of the more important sea level changing mechanisms on supercontinental time scales and provides a more complete picture of the dynamic interplay between tectonics and sea level change.

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• Karlsen, Krister Stræte; Conrad, Clinton Phillips & Magni, Valentina (2020). Deep water cycling and sea level change since the breakup of Pangea.
• Karlsen, Krister Stræte; Domeier, Mathew; Gaina, Carmen & Conrad, Clinton Phillips (2020). Tracer Tectonics. Show summary

  Tracer Tectonics (TracTec) is a Python toolbox for generating seafloor age grids from global plate tectonic reconstructions based on an algorithm developed by Krister S. Karlsen, in collaboration with Mathew Domeier, Carmen Gaina and Clinton P. Conrad, at the Centre for Earth Evolution and Dynamics, University of Oslo, Norway.

• Karlsen, Krister Stræte; Conrad, Clinton Phillips & Magni, Valentina (2019). Deep water cycling and sea level change since the breakup of Pangea.
• Karlsen, Krister Stræte; Conrad, Clinton Phillips & Magni, Valentina (2019). Deep water cycling and sea level change since the breakup of Pangea.
• Karlsen, Krister Stræte; Conrad, Clinton Phillips & Magni, Valentina (2018). Deep water cycling and sea level changes on a supercontinental time scale.
• Karlsen, Krister Stræte; Conrad, Clinton Phillips & Magni, Valentina (2018). Deep water recycling and cyclic sea level change on a supercontinental time scale.
• Karlsen, Krister Stræte; Conrad, Clinton Phillips & Magni, Valentina (2018). Deep water recycling and cyclic sea level change on a supercontinental time scale.

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