Maastrichtian North Atlantic warming, increasing stratification, and foraminiferal paleobiology at three timescales

Abstract

[1] Analysis of 944 single specimens of three species of late Maastrichtian planktonic foraminifera (Racemiguembelina fructicosa, Contusotruncana contusa, and Rugoglobigerina rugosa) from 38 samples spanning the last 3 Myr of the Cretaceous shows consistent isotopic trends through time, consistent isotopic differences among taxa, and high within-sample isotopic variability throughout. Within-sample variability does not change systematically through time for any taxon, but average d 18 O values decrease by $1.5%, and average d 13 C values diverge up section. Comparing taxa, average d 18 O values are similar within most samples, but average d 13 C values generally decrease from R. fructicosa to R. rugosa to C. contusa. In addition, the withinsample variability of individual d 13 C measurements is larger for R. fructicosa than for either C. contusa or R. rugosa, an observation which is consistent with a photosymbiotic habitat for R. fructicosa. In terms of Maastrichtian paleoceanography the negative d 18 O trend of $1.5% corresponds to a temperature increase of $6°C, and the divergence of d 13 C values up section suggests an increasingly stratified water column in the western Atlantic through the late Maastrichtian. We suggest that these trends are best explained by increasing import of South Atlantic waters into the North Atlantic and an intensification of the Northern Hemisphere polar front.

The evolution of Late Cretaceous deep‐ocean circulation in the Atlantic basins: Neodymium isotope evidence from South Atlantic drill sites for tectonic controls

“…Later in the Maastrichtian (∼68 Ma), the extremely unradiogenic values found at Demerara Rise, which track the formation of the low‐latitude Demerara Bottom Water [ MacLeod et al ., ; Jiménez Berrocoso et al ., ], show a large radiogenic shift (Figure ) that coincides with the anomalous warming of the North Atlantic during a time of global cooling [ MacLeod et al ., ]. The interpreted switch of water masses at this time may be consistent with the “heat piracy” model to explain the warming, in which the onset of North Atlantic convection draws warm tropical waters to higher latitudes, explaining the apparent warming of the temperate regions [ MacLeod et al ., ; Isaza‐Londoño et al ., ; MacLeod et al ., ]. MacLeod et al .…”

Late Albian paleoceanography of the western subtropical North Atlantic

“…Seasonal variability is a confounding factor if depth is considered the controlling variable in temperature variations, but seasonality can also be exploited as a paleoceanographic signal [e.g., Rohling et al , 2004; Isaza‐Londoño et al , 2006]. All 12 modern planktonic foraminifera collected in a classic sediment trap study in the Sargasso Sea occurred in significant numbers during only 2 to 6 months each year and were rare or completely absent during the remaining months [ Deuser and Ross , 1989].…”

“…Seasonal changes in populations must also have occurred among fossil taxa, and isotopic values will track conditions during the season of growth. Characterizing isotopic variability in multiple single specimens from the same sample provides a way to assess intraannual and interannual variability that can be compared among samples [ Isaza‐Londoño et al , 2006]. This approach generates data with a temporal resolution (the ∼1 month life span of a planktonic foraminifer) appropriate for investigating changes in seasonality through a section, but it is analytically intensive and impractical unless understanding seasonality is the goal of the study.…”

“…This approach generates data with a temporal resolution (the ∼1 month life span of a planktonic foraminifer) appropriate for investigating changes in seasonality through a section, but it is analytically intensive and impractical unless understanding seasonality is the goal of the study. However, because isotopic variability among specimens can be high, differences between analyses of multiple specimens can include variance associated with interannual differences in temperature [ Isaza‐Londoño et al , 2006]. Thus the stability‐of‐signal concepts developed for the Quaternary may be useful in refining paleoecological interpretations [ Rohling et al , 2004].…”

Global climate change and planktic foraminiferal response in the Maastrichtian

“…This trend was interrupted two times in the Maastrichtian. The first oceanic warming phase began at ∼70 Ma and lasted until ∼68 Ma in the equatorial Pacific [ Li and Keller , 1998a; Li and Keller , 1999; Frank et al , 2005], persisting longer in the Atlantic [ MacLeod et al , 2005; Isaza‐Londoño et al , 2006]. This event is characterized by a 2°C–6°C temperature increase affecting both surface and deep water.…”