M.A. Arthur W.E. Dean J.C. Zachos 1989 <p><span>The normal, biologically productive ocean is characterized by a gradient of the&nbsp;</span>¹³<span>C/</span>¹²<span>C ratio from surface to deep waters. Here we present stable isotope data from planktonic and benthic micro-fossils across the Cretaceous/Tertiary boundary in the North pacific, which reveal a rapid and complete breakdown in this biologically mediated gradient. The fluxes of barium (a proxy for organic carbon) and CaCO</span>₃<span>&nbsp;also decrease significantly at the time of the major marine plankton extinctions. The implied substantial reduction in oceanic primary productivity persisted for&nbsp;</span><span class="stix">∼</span><span>0.5 Myr before the carbon isotope gradient was gradually re-established. In addition, the stable isotope and preservational data indicate that environmental change, including cooling, began at least 200 kyr before the Cretaceous/Tertiary boundary, and a peak warming of&nbsp;</span><span class="stix">∼</span><span>3 °C occurred 600 kyr after the boundary event.</span></p> application/pdf 10.1038/337061a0 en Springer Nature Geochemical evidence for suppression of pelagic marine productivity at the Cretaceous/Tertiary boundary article