Climate model boundary conditions for four Cretaceous time slices

Abstract

Abstract. General circulation models (GCMs) are useful tools for investigating the characteristics and dynamics of past climates. Understanding of past climates contributes significantly to our overall understanding of Earth's climate system. One of the most time consuming, and often daunting, tasks facing the paleoclimate modeler, particularly those without a geological background, is the production of surface boundary conditions for past time periods. These boundary conditions consist of, at a minimum, continental configurations derived from plate tectonic modeling, topography, bathymetry, and a vegetation distribution. Typically, each researcher develops a unique set of boundary conditions for use in their simulations. Thus, unlike simulations of modern climate, basic assumptions in paleo surface boundary conditions can vary from researcher to researcher. This makes comparisons between results from multiple researchers difficult and, thus, hinders the integration of studies across the broader community. Unless special changes to surface conditions are warranted, researcher dependent boundary conditions are not the most efficient way to proceed in paleoclimate investigations. Here we present surface boundary conditions (land-sea distribution, paleotopography, paleobathymetry, and paleovegetation distribution) for four Cretaceous time slices (120 Ma, 110 Ma, 90 Ma, and 70 Ma). These boundary conditions are modified from base datasets to be appropriate for incorporation into numerical studies of Earth's climate and are available in NetCDF format upon request from the lead author. The land-sea distribution, bathymetry, and topography are based on the 1 • ×1 • (latitude × longitude) paleo Digital Elevation Models (paleoDEMs) of Christopher Scotese. Those paleoDEMs were adjusted using the paleogeographical reconstructions of Ronald BlakeyCorrespondence to: J. O. Sewall (jsewall@vt.edu) (Northern Arizona University) and published literature and were then modified for use in GCMs. The paleovegetation distribution is based on published data and reconstructions and consultation with members of the paleobotanical community and is represented as generalized biomes that should be easily translatable to many vegetation-modeling schemes.

The Aptian evaporites of the South Atlantic: a climatic paradox?

“…According to recent publications (Lentini et al, 2010), these humid conditions would have even played a role in the nature and the distribution of the sedimentary fill of rift basins of the central segment, influencing the type and quality of the source rocks and clastic facies distribution and carbonate. Along the Equator, our model results show high precipitation rates, which are overestimated regarding the data (Spicer et al, 1993;Beerling, 2000;Chumakov et al, 1995;Sewall et al, 2007). This bias is very likely linked to the prescribed zonal vegetation, which relies on present-day Plant Functionnal Types (PFTs), not adapted to the characteristics (e.g.…”

“…Here we attempt to provide our model with boundary conditions that are constrained at best for the Aptian. First, all simulations share the early Aptian global paleogeography of Sewall et al (2007) in which we slightly modified the mountain reliefs and the shorelines (Fig. 2).…”

“…Shorelines along Africa were also modified according to paleogeographic maps of Guillocheau et al (2008). The last change concerns the Central segment that was still continental on the reconstruction of Sewall et al (2007). However, the salt from the Central segment was deposited in a marine setting but during the late Aptian rather than the early Aptian.…”

“…Earth orbital parameters were set to present-day values. The vegetation was imposed according to Sewall et al (2007).…”

“…The latter is controlled by the influx of waters with lower salinity, supplied by Bathymetry (m) Relief (m) Ocean / Continent boundary of the from Sewall et al (2007) Ocean / Continent boundary of the Lower Aptian geography, from Sewall et al (2007) Figure 2 seawater or by a fluvial tributary and by the connection with an ocean or a sea, which supplies water of reduced salinity. When the total volume of seawater and freshwater input is lower than the water loss (evaporation), the water evolves to hypersalinity, and allows the deposition of different evaporitic minerals.…”