Life in a temperate Polar sea: a unique taphonomic window on the structure of a Late Cretaceous Arctic marine ecosystem

Abstract

As the earth faces a warming climate, the rock record reminds us that comparable climatic scenarios have occurred before. In the Late Cretaceous, Arctic marine organisms were not subject to frigid temperatures but still contended with seasonal extremes in photoperiod. Here, we describe an unusual fossil assemblage from Devon Island, Arctic Canada, that offers a snapshot of a ca 75 Myr ago marine palaeoecosystem adapted to such conditions. Thick siliceous biogenic sediments and glaucony sands reveal remarkably persistent high primary productivity along a high-latitude Late Cretaceous coastline. Abundant fossil faeces demonstrate that this planktonic bounty supported benthic invertebrates and large, possibly seasonal, vertebrates in short food chains. These ancient organisms filled trophic roles comparable to those of extant Arctic species, but there were fundamental differences in resource dynamics. Whereas most of the modern Arctic is oligotrophic and structured by resources from melting sea ice, we suggest that forested terrestrial landscapes helped support the ancient marine community through high levels of terrigenous organic input.

Late Cretaceous seasonal ocean variability from the Arctic

“…3). This is in stark contrast to Campanian coastal and shelf sediments from the Canadian Arctic Islands to the south in which there is much fragmented diatom material 23 . The absence of the near-shore, benthic diatom Paralia in both the CESAR-6 and Fl-437 cores (present in the Campanian shelf sediments to the south 23 ) further indicates a pelagic basinal environment.…”

The Feeding Habits of Mesosauridae

“…Fossilized feces, gastric contents, and regurgitations ("bromalites, " sensu Hunt et al, 1994; see also Hunt and Lucas, 2012) can tell us a lot about the dietary behavior of extinct organisms (Chin and Kirkland, 1998;Chin et al, 2008;Bajdek et al, 2014;Qvarnström et al, 2016). They mostly fossilize in situ (Hu et al, 2010;Bajdek, 2013), as isolated coprolites (Eriksson et al, 2011;Dentzien-Dias et al, 2012;Niedźwiedzki et al, 2016) or associated with the producer's skeleton (Hone et al, 2015;Wang et al, 2016).…”

Late Cretaceous seasonal palaeoclimatology and diatom palaeoecology from laminated sediments

“…The preservation of lamination is consistent with the anoxic bottom waters of a silled Arctic basin with only shallow water connections to the world ocean through the Turgay Strait, the Fram Strait and the narrowing Western Interior Seaway (Hay, 2008). The slightly older, shallower water, coastal and shelf sequences in Canadian Arctic Islands show evidence for widespread diatom productivity and the presence of a vigorous marine ecosystem (Chin et al, 2008;Witkowski et al, 2011). The Late Cretaceous Arctic summers were temperate, but there is widespread evidence for freezing winter temperatures from fossil leaf analysis (Spicer and Herman, 2010;Tomsich et al, 2010) possible frosts from tree rings (Falcon-Lang et al, 2004) and vertebrate enamels (Amiot et al, 2004).…”

“…In earlier publications we reported the main elements of the Late Cretaceous seasonal cycle and the results of time series analysis of inter-annual to decadal scale climate variability Davies et al, 2011;Davies et al, 2012). In this contribution we report the complete floral compositions of the two sections together with more detailed speciesbased diatom ecological interpretations and place these in a palaeoceanographic and palaeoclimatic context that complements recent palaeoecological studies of the Late Cretaceous from shallower coastal water environments of the Canadian Arctic (Chin et al, 2008;Witkowski et al, 2011). 4…”

“…Such interpretations are also complemented by judgements based on morphological features, (e.g. chain formation), sedimentary facies associations and geographic distribution as well as palaeontological and palaeoecological data from other groups (for example in the studies of Chin et al, 2008;Witkowski et al, 2011).…”