An organic geochemical reconstruction of North American temperature gradients over the Cretaceous-Paleogene boundary

Latitudinal temperature gradients are a critical component of the climate system and control the transport of heat and moisture. However, this process is poorly understood during past intervals of extreme greenhouse climate, in particular owing to models suggesting that gradients must be much steeper than proxy data imply. Palaeotemperature records Late Cretaceous–Early Paleogene can provide insight into how the global climate system operates under greenhouse conditions.

Much of our understanding of palaeotemperatures and gradients therein during this interval comes from marine sea-surface temperature proxy data, with very few terrestrial records. These palaeoclimate reconstructions are hampered by poor temporal resolution, difficulties in correlating between sites, and limited spatial coverage.

Lipids from fossil peats across North America provide an opportunity to investigate terrestrial palaeotemperatures across the Cretaceous–Paleogene boundary and how these differ across a range of latitudes. Here we present a mean annual air temperature record spanning this interval from the Canadian High Arctic (~75°N palaeolatitude). Our data show that temperatures ranged from 0–18°C, compared with 13–27°C at contemporaneous peat-accumulating sites in Saskatchewan (~60°N palaeolatitude). These data indicate a temperature gradient of approximately 10°C. These values are similar to those modelled for the latest Cretaceous, and the latitudinal difference is comparable to the modern gradient across North America (UCAR), albeit ~20°C warmer.

Our study demonstrates that although the Arctic experienced high terrestrial temperatures, the K-Pg interval saw a well-defined latitudinal temperature gradient. Further, our reconstructions fill an existing gap in the terrestrial record and highlight the value of fossil peats in palaeoclimate studies.