Equatorward phytoplankton migration during a cold spell within the Late Cretaceous super-greenhouse

Abstract

Abstract. Oceanic Anoxic Event 2 (OAE2), a ∼ 600 kyr episode close to the Cenomanian–Turonian boundary (ca. 94 Ma), is characterized by relatively widespread marine anoxia and ranks amongst the warmest intervals of the Phanerozoic. The early stages of OAE2 are, however, marked by an episode of widespread transient cooling and bottom water oxygenation: the Plenus Cold Event. This cold spell has been linked to a decline in atmospheric pCO2, resulting from enhanced global organic carbon burial. To investigate the response of phytoplankton to this marked and rapid climate shift we examined the biogeographical response of dinoflagellates to the Plenus Cold Event. Our study is based on a newly generated geochemical and palynological data set from a high-latitude Northern Hemisphere site, Pratts Landing (western Alberta, Canada). We combine these data with a semi-quantitative global compilation of the stratigraphic distribution of dinoflagellate cyst taxa. The data show that dinoflagellate cysts grouped in the Cyclonephelium compactum–membraniphorum morphological plexus migrated from high to mid-latitudes during the Plenus Cold Event, making it the sole widely found (micro)fossil to mark this cold spell. In addition to earlier reports from regional metazoan migrations during the Plenus Cold Event, our findings illustrate the effect of rapid climate change on the global biogeographical dispersion of phytoplankton.

Water-mass evolution in the Cretaceous Western Interior Seaway of North America and equatorial Atlantic

“…Singh, 1983;Bloch et al, 1999), albeit with higher numbers of boreal P -cyst taxa including Isabelidinium magnum and Eurydinium glomeratum, and (ii) in coeval sediments from European shelves (e.g. Foucher, 1980;Jarvis et al, 1988Jarvis et al, , 2011Fitzpatrick, 1995;Pearce et al, 2003Pearce et al, , 2009Lignum, 2009), which also correspond with the influx of boreal macro-fauna (Jefferies, 1962(Jefferies, , 1963Gale and Christensen, 1996;Voigt et al, 2006;Jarvis et al, 2011). Evidence for the southward incursion of a northerly sourced water mass during the latest Cenomanian is recorded in all the studied sections spanning the central and eastern part of the KWIS and therefore does not support a more complex oceanographic system such as that modelled by Slingerland et al (1996) and Kump and Slingerland (1999).…”

“…beds 68-78 at Rock Canyon, Pueblo, Colorado; Eicher and Worstell, 1970), where it spans only part of the OAE-2 interval and was subsequently termed the benthic oxic zone by Keller and Pardo (2004). It should be noted that the benthonic/benthic oxic zone in the KWIS has also been shown to correspond with the equatorial migration of boreal dinoflagellate cyst (dinocyst) taxa (Eldrett et al, 2014;van Helmond et al, 2016) and has been correlated with a short-lived climate cooling episode termed the Plenus Cold Event (PCE; Eldrett et al, 2014;van Helmond et al, 2014van Helmond et al, , 2016Elderbak and Leckie, 2016), whereby similarly cool boreal waters invaded northern and central Europe (Jefferies, 1963;Gale and Christensen, 1996;Voigt et al, 2006;Jarvis et al, 2011) and equatorial waters cooled by up to 4 • C (Forster et al, 2007). It is therefore difficult to reconcile the late Cenomanian northerly inflow of a warm Tethyan water mass into the southern KWIS, at a time of global cooling, southerly restriction in benthic fauna, and coeval equatorial migration of boreal taxa and associated water mass in the KWIS and Europe.…”

Comparing Seawater Temperature Proxy Records for the Past 90 Myrs From the Shallow Shelf Record Bass River, New Jersey

“…At 518 m, the lowermost constraints based on Sr‐isotopes indicate an age of ~82 Ma (+/−2.5 Myr). Additionally, two tie points at ~592 m, representing the onset of the carbon isotope excursion associated with Ocean Anoxic Event 2, indicate an age of 94.64 (+/−0.12 Ma); Bowman & Bralower, ; Eldrett et al, ; Sugarman et al, ; van Helmond et al, ) and the first consistent presence of the dinocyst morphological complex Cyclonephelium compactum‐membraniphorum during the Plenus Cold Event (van Helmond et al, ), which is ~10 kyr younger. We assumed constant sedimentation rates between these two oldest age tie points and the oldest Sr‐isotopic age, resulting in an age of ~90.9 Ma for sample interval 1, but with large maximum uncertainty of +/−8.7 Myrs based on the largest “distance” to the closest age tie points (Figure ).…”

“…We updated the original age model of the entire section (Miller, Sugarman, et al, ) using the most recent tie points based on strontium (Sr) and carbon isotope stratigraphy, biostratigraphy (nannofossils, foraminifera, dinoflagellates, and diatoms), and magnetostratigraphy. Among others, analyses at Bass River resulted in the identification of Oceanic Anoxic Event 2, the Cretaceous‐Paleogene boundary event, and the Paleocene‐Eocene Thermal Maximum (Cramer et al, ; Hernandez & Feigenson, ; Olsson et al, ; Sugarman et al, ; van Helmond et al, ). All biostratigraphic and magnetostratigraphic ages were assigned an age following the Gradstein et al () time scale.…”

Basalt‐seawater interaction, the Plenus Cold Event, enhanced weathering and geochemical change: deconstructing Oceanic Anoxic Event 2 (Cenomanian–Turonian, Late Cretaceous)

“…This interval of re‐oxygenation has been termed the ‘Benthonic Zone’ or ‘Benthic Oxic Zone’ (Eicher & Worstell, ; Keller & Pardo, ; Prokoph et al ., ; Eldrett et al ., ), locally contains boreal dinocysts (belonging to the Cyclonephelium compactum – membraniphorum morphological plexus) and, by reference to its causative phenomenon, is hereafter ascribed to the ‘Benthic Oxic Event’. The event has been recognized in Texas, Colorado (including at Pueblo, the type locality for the base of the Turonian stage: Kennedy et al ., ), Wyoming, Kansas and South Dakota in the USA, Alberta and Manitoba in Canada but is poorly expressed in some marginal areas (for example, Utah) of the Western Interior Seaway (West et al ., ; Prokoph et al ., ; van Helmond et al ., ). The same event, equally characterized by a relative increase in benthonic foraminifera, has also been recognized in organic‐rich sediments from Demerara Rise (Fig.…”