A summertime rainy season in the Arctic forests of the Eocene

Abstract

The discovery of exceptionally well-preserved fossil wood revealed that extensive forests existed north of the Arctic Circle during the Eocene (ca. 45-55 Ma). Subsequent paleobotanical studies led researchers to suggest eastern Asia as a modern analog, based on the distribution of nearest living relatives. During the last decade, proxybased reconstructions of mean annual paleoprecipitation, productivity, and relative humidity have led workers to characterize the climate of the Arctic forests as similar to today's temperate forests of the Pacifi c Northwest. Using a new model, we reconstructed the seasonal timing of paleoprecipitation from high-resolution intra-ring carbon isotope measurements of fossil wood. We showed that the Eocene Arctic forests experienced, on average, 3.1 times more precipitation during summer than winter, entirely dissimilar to the Pacifi c Northwest where summer precipitation is only one-half to one-sixth of the winter precipitation. This new result shows that although mean annual climate conditions may have been similar to the mean annual conditions the Pacifi c Northwest, consideration of seasonality implies that the temperate forests of eastern Asia represent the best overall modern analog for the Eocene Arctic forests.

Was the Arctic Eocene ‘rainforest’ monsoonal? Estimates of seasonal precipitation from early Eocene megafloras from Ellesmere Island, Nunavut

“…High latitude environments that were temperate and wet, such as the Canadian High Arctic, Spitzbergen and North Sea, instead experienced an increase in both temperature and precipitation (Uhl et al, 2007;Greenwood et al, 2010;Eldrett et al, 2014). The north polar region of the early Paleogene represents an environment that has no satisfactory modern analogue, relegating it to fossil environment status, as defined in Jacques et al (2014), although the winter-wet west coast forests of North America and the coastal forests of east Asia have been suggested as possible analogues (Greenwood et al, 2010;Schubert et al, 2012). Extensive studies in the literature document the presence of flora and fauna in the early Cenozoic that exist nowhere near these latitudes today (e.g., Hickey et al, 1983;Dawson et al, 1993;Basinger, 1991, 1995;McIver and Basinger, 1999;LePage, 2001LePage, , 2007Lepage, 2003;Eberle, 2005;Eberle et al, 2014;Harrington et al, 2012).…”

Leaf habit of Late PermianGlossopteristrees from high-palaeolatitude forests

“…Only in the last decade, however, have high-resolution (more than three measurements per ring) isotope analyses been completed on single growth rings in modern trees (e.g. Barbour et al 2002;Helle & Schleser 2004;Poussart et al 2004;Skomarkova et al 2006;Ohashi et al 2009;Schubert & Jahren 2011) and sub-fossil wood (Jahren & Sternberg 2003Schubert et al 2012). The high-resolution sampling of growth rings reveals changes in the δ 13 C value of wood throughout a growing season that correspond to intra-ring patterns that are reproducible from year to year and reproducible between different species that share similar leaf longevity (Helle & Schleser 2004).…”

First FossilAlligatorfrom the Late Eocene of Nebraska and the Late Paleogene Record of Alligators in the Great Plains

“…High-resolution carbon isotope analysis across tree rings in mummified wood from Muskox River on northern Banks Island (,50 km south of the Eames River locality) and Stenkul Fiord on southern Ellesmere Island allow the reconstruction of seasonal precipitation patterns in the Eocene Arctic [37]. Incorporation of intra-ring d 13 C values into a model based upon extant evergreen taxa [38] suggest that evergreen trees growing in the Eocene Arctic forests experienced three times more precipitation during summer than winter, a seasonal pattern analogous to today's temperate forests in eastern Asia [37].…”