CP Climate of the Past CP Clim. Past 1814-9332 Copernicus Publications Göttingen, Germany 10.5194/cp-11-383-2015 Climate variability and ocean fertility during the Aptian Stage Bottini C. https://orcid.org/0000-0003-1287-5579 1 Erba E. https://orcid.org/0000-0001-6213-6550 1 Tiraboschi D. 1 Jenkyns H. C. 2 Schouten S. 3 Sinninghe Damsté J. S. 3 Department of Earth Sciences, Università degli Studi di Milano, 20133 Milan, Italy Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, P.O. Box 59, 1790 AB Den Burg Texel, the Netherlands 05 03 2015 11 3 383 402 Copyright: © 2015 C. Bottini et al. 2015 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://cp.copernicus.org/articles/11/383/2015/cp-11-383-2015.html The full text article is available as a PDF file from https://cp.copernicus.org/articles/11/383/2015/cp-11-383-2015.pdf

Several studies have been conducted to reconstruct temperature variations across the Aptian Stage, particularly during early Aptian Oceanic Anoxic Event (OAE) 1a. There is a general consensus that a major warming characterized OAE 1a, although some studies have provided evidence for transient "cold snaps" or cooler intervals during the event. The climatic conditions for the middle–late Aptian are less constrained, and a complete record through the Aptian is not available. Here we present a reconstruction of surface-water palaeotemperature and fertility based on calcareous nannofossil records from the Cismon and Piobbico cores (Tethys) and DSDP Site 463 (Pacific Ocean). The data, integrated with oxygen-isotope and TEX<sub>86</sub> records, provide a detailed picture of climatic and ocean fertility changes during the Aptian Stage, which are discussed in relation to the direct/indirect role of volcanism. Warm temperatures characterized the pre-OAE 1a interval, followed by a maximum warming (of ~ 1.5–2 °C) during the early phase of anoxia under intense volcanic activity of the Ontong Java Plateau (OJP). A short-lived cooling episode interrupted the major warming, following a rapid increase in weathering rates. Nannofossils indicate that mesotrophic conditions were reached when temperatures were at their highest and OJP volcanism most intense, thus suggesting that continental runoff, together with increased input of hydrothermal metals, increased nutrient supply to the oceans. The latter part of OAE 1a was characterized by cooling events, probably promoted by CO<sub>2</sub> sequestration during burial of organic matter. In this phase, high productivity was probably maintained by N<sub>2</sub>-fixing cyanobacteria, while nannofossil taxa indicating higher fertility were rare. The end of anoxia coincided with the cessation of volcanism and a pronounced cooling. The mid-Aptian was characterized by highest surface-water fertility and progressively decreasing temperatures, probably resulting from intense continental weathering drawing down <i>p</i>CO<sub>2</sub>. The lowest temperatures, combined with low fertility, were reached in the middle–late Aptian across the interval characterized by blooming of <i>Nannoconus truittii</i>. The prolonged cooling was followed by significant warming across the Aptian–Albian boundary. The data presented suggest that OJP activity played a direct role in inducing global warming during the early Aptian, whereas other mechanisms (weathering, deposition of organic matter) acted as feedback processes, favouring temporary cooler interludes.

 References Ando, A., Kaiho, K., Kawahata, H., and Kakegawa, T.: Timing and magnitude of early Aptian extreme warming: Unraveling primary δ<sup>18</sup>O variation in indurated pelagic carbonates at Deep Sea Drilling Project Site 463, central Pacific Ocean, Palaeogeogr. Palaeocl., 260, 463–476, 2008. Bellanca, A., Claps, M., Erba, E., Masetti, D., Neri, R., Premoli Silva, I., and Venezia, F.: Orbitally induced limestone/marlstone rhythms in the Albian-Cenomanian Cismon section (Venetian region, northern Italy): sedimentology, calcareous and siliceous plankton distribution, elemental and isotope geochemistry, Palaeogeogr. Palaeocl., 126, 227–260, 1996. Bellanca, A., Erba, E., Neri, R., Premoli Silva, I., Sprovieri, M., Tremolada, F., and Verga, D.: Paleoceanographic significance of the Tethyan Livello Selli (Early Aptian) from the Hyblan Formation, northwestern Sicily: biostratigraphy and high-resolution chemostratigraphic records, Palaeogeogr. Palaeocl., 185, 175–196, 2002. Bernoulli, D. and Jenkyns, H. C.: Ancient oceans and continental margins of the Alpine-Mediterranean Tethys: deciphering clues from Mesozoic pelagic sediments and ophiolites, Sedimentology, 56, 149–190, 2009. Blättler, C. L., Jenkyns, H. C., Reynard, L. M., and Handerson, G. M.: Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes, Earth Planet. Sc. Lett., 309, 77–88, 2011. Bornemann, A., Pross, J., Reichelt, K., Herrle, J. O., Hemleben, C., and Mutterlose, J.: Reconstruction of short term palaeoceanographic changes during the formation of the Late Albian-Niveau Breistroffer- black shales (Oceanic Anoxic Event 1d, SE France), J. Geol. Soc. London, 162, 623–639, 2005. Bottini, C. and Mutterlose, J.: Integrated stratigraphy of Early Aptian black shales in the Boreal Realm: calcareous nannofossil and stable isotope evidence for global and regional processes, Newsl. Stratigr., 45, 115–137, 2012. Bottini, C., Cohen, A. S., Erba, E., Jenkyns, H. C., and Coe, A. L.: Osmium-isotope evidence for volcanism, weathering and ocean mixing during the early Aptian OAE 1a, Geology, 40, 583–586, 2012. Bralower, T. J.: Calcareous nannofossil biostratigraphy assemblages of the Cenomanian–Turonian boundary interval: Implications for the origin and timing of oceanic anoxia, Paleoceanography, 3, 275–316, 1988. Bralower, T. J., Sliter, W. V., Arthur, M. A., Leckie, R. M., Allard, D. J., and Schlanger, S. O.: Dysoxic/anoxic episodes in the Aptian-Albian (Early Cretaceous), in: The Mesozoic Pacific: Geology, Tectonics and Volcanism, edited by: Pringle, M., Sager, W. W., Sliter, W. V., and Stein, S., American Geophysical Union, Washington, D. C., Geoph. Monog. Series, 77, 5–37, 1993. Bralower, T. J., Arthur, M. A., Leckie, R. M., Sliter, W. V., Allard, D. J., and Schlanger, S. O.: Timing and paleoceanography of oceanic dysoxia/anoxia in the late Barremian to early Aptian, Palaios, 9, 335–369, 1994. Bralower, T. J., Leckie, R. M., Sliter, W. V., and Thierstein, H. R.: An integrated Cretaceous microfossil biostratigraphy, in: Geochronology Time Scales and Global Stratigraphic Correlation, edited by: Berggren, W. A., Kent, D. V., Aubry, M. P., and Hardenbol, J., Geochronology, Time Scales, and Global Stratigraphic Correlation, Spec. Publ.-SEPM (Soc. Sediment. Geol.), 54, 65–79, 1995. Bralower, T. J., Cobabe, E., Clement, B., Sliter, W. V., Osburne, C., and Longoria, J.: The record of global change in mid-Cretaceous, Barremian-Albian sections from the Sierra Madre, northeastern Mexico, J. Foramin. Res., 29, 418–437, 1999. Channell, J. E. T., Erba, E., Muttoni, G., and Tremolada, F.: Early Cretaceous magnetic stratigraphy in the APTICORE drill core and adjacent outcrop at Cismon (Southern Alps, Italy), and the correlation to the proposed Barremian/Aptian boundary stratotype, Bull. Geol. Soc. Am., 112, 1430–1443, 2000. Coccioni, R., Nesci, O., Tramontana, M., Wezel, C. F., and Moretti, E.: Descrizione di un livelloguida "Radiolaritico-Bituminoso-Ittiolitico" alla base delle Marne a Fucoidi nell'Appennino Umbro-Marchigiano, Boll. Soc. Geol. Ital., 106, 183–192, 1987 (in Italian). Coccioni, R., Franchi, R., Nesci, O., Wezel, C. F., Battistini, F., and Pallecchi, P.: Stratigraphy and mineralogy of the Selli Level (early Aptian) at the base of the Marne a Fucoidi in the Umbrian–Marchean Apennines (Italy), in: Cretaceous of the Western Tethys, edited by: Wiedmann, J., 3rd International Symposium Tübingen 1987 by Schweizerbart, Stuttgart, Germany, 563–584, 1989. Coccioni, R., Erba, E., and Premoli Silva, I.: Barremian-Aptian calcareous plankton biostratigraphy from the Gorgo a Cerbara section (Marche, Central Italy) and implication for planktonic evolution, Cretaceous Res., 13, 517–537, 1992. De Lurio, J. L. and Frakes, L. A.: Glendonites as a paleoenvironmental tool: implications for early Cretaceous high latitude climates in Australia, Geochim. Cosmochim. Ac., 63, 1039–1048, 1999. Dumitrescu, M. and Brassell, S. C.: Compositional and isotopic characteristics of organic matter for the early Aptian oceanic anoxic event at Shatsky Rise, ODP leg 198, Palaeogeogr. Palaeocl., 235, 168–191, 2006. Dumitrescu, M., Brassell, S. C., Schouten, S., Hopmans, E. C., and Sinninghe Damsté, J. S.: Instability in tropical Pacific sea-surface temperatures during the early Aptian, Geology, 34, 833–866, 2006. Eldholm, O. and Coffin, M. F.: Large Igneous Provinces and plate tectonics, in: The History and Dynamics of Global Plate Motion, edited by: Richards, M., Gordon, R., and van der Hilst, R., American Geophysical Union, Washington, D.C., AGU Geophysical Monograph, 121, 309–326, 2000. Erba, E.: Aptian-Albian calcareous nannofossil biostratigraphy of the Scisti a Fucoidi cored at Piobbico (central Italy), Riv. Ital. Paleontol. S., 94, 249–284, 1988. Erba, E.: Calcareous nannofossil distribution in pelagic rhythmic sediments (Aptian-Albian Piobbico core, central Italy), Riv. Ital. Paleontol. S., 97, 455–484, 1992a. Erba, E.: Middle Cretaceous calcareous nannofossils from the Western Pacific (ODP Leg 129), Evidence for paleoequatorial crossing, in: Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 129, 189–201, 1992b. Erba, E.: Nannofossils and superplumes: the early Aptian nannoconid crisis, Paleoceanography, 9, 483–501, 1994. Erba, E.: Calcareous nannofossils and Mesozoic oceanic anoxic events, Mar. Micropaleontol., 52, 85–106, 2004. Erba, E.: The first 150 million years history of calcareous nannoplankton: Biosphere–geosphere interactions, Palaeogeogr. Palaeocl., 232, 237–250, 2006. Erba, E. and Larson, R.: The Cismon Apticore (Southern Alps, Italy): Reference section for the Lower Cretaceous at low latitudes, Riv. Ital. Paleontol. S., 104, 181–192, 1998. Erba, E. and Tremolada, F.: Nannofossil carbonate fluxes during the Early Cretaceous: phytoplankton response to nutrification episodes, atmospheric CO<sub>2</sub> and anoxia, Paleoceanography, 19, 1–18, 2004. Erba, E., Castradori, D., Guasti, G., and Ripepe, M.: Calcareous nannofossil and Milankovitch cycles: The example of the Albian Gault Clay Formation (southern England), Palaeogeogr. Palaeocl., 93, 47–69, 1992. Erba, E., Channell, J. E. T., Claps, M., Jones, C., Larson, R. L., Opdyke, B., Premoli Silva, I., Riva, A., Salvini, G., and Torricelli, S.: Integrated stratigraphy of the Cismon Apticore (Southern Alps, Italy): a reference section for the Barremian-Aptian interval at low latitudes, J. Foramin. Res., 29, 371–391, 1999. Erba, E., Bottini, C., Weissert, J. H., and Keller, C. E.: Calcareous Nannoplankton Response to Surface-Water Acidification Around Oceanic Anoxic Event 1a, Science, 329, 428–432, 2010. Erba, E., Bottini, C., Weissert, J. H., and Keller, C. E.: Response to Comment on "Calcareous Nannoplankton Response to Surface-Water Acidification Around Oceanic Anoxic Event 1a", Science, 332, p. 175, 2011. Erba, E., Duncan, R. A., Bottini, C., Tiraboschi, D., Weissert, H., Jenkyns, H. C., and Malinverno, A.: Environmental Consequences of Ontong Java Plateau and Kerguelen Plateau Volcanism, GSA Special Paper, 511, <a href="http://dx.doi.org/10.1130/2015.2511(15)">https://doi.org/10.1130/2015.2511(15)</a>, 2015. Föllmi, K. B.: Early Cretaceous life, climate and anoxia, Cretaceous Res., 35, 230–257, 2012. Föllmi, K. B. and Gainon, F.: Demise of the northern Tethyan Urgonian carbonate platform and subsequent transition towards pelagic conditions, The sedimentary record of the Col de la Plaine Morte area, central Switzerland, Sediment. Geol., 205, 142–159, 2008. Föllmi, K. B., Godet, A., Bodin, S., and Linder, P.: Interactions between environmental change and shallow water carbonate buildup along the northern Tethyan margin and their impact on the Early Cretaceous carbon isotope record, Paleoceanography, 21, PA4211, <a href="http://dx.doi.org/10.1029/2006PA001313">https://doi.org/10.1029/2006PA001313</a>, 2006. Frakes, L. A. and Francis, J. E.: A guide to Phanerozoic cold polar climates from high-latitude ice-rafting in the Cretaceous, Nature, 333, 547–549, 1988. Herrle, J. O.: Reconstructing nutricline dynamics of Mid-Cretaceous oceans: Evidence from calcareous nannofossils from the Niveau Paquier black shale (SE France), Mar. Micropaleontol., 47, 307–321, 2003. Herrle, J. O. and Mutterlose, J.: Calcareous nannofossils from the Aptian–Lower Albian southeast France: paleoecological and biostratigraphic implication, Cretaceous Res., 24, 1–22, 2003. Herrle, J. O., Pross, J., Friedrich, O., Kössler, P., and Hemleben, C.: Forcing mechanisms for Mid-Cretaceous black shale formation: Evidence from the upper Aptian and lower Albian of the Vocontian Basin (SE France), Palaeogeogr. Palaeocl., 190, 399–426, 2003a. Herrle, J. O., Pross, J., Friedrich, O., and Hemleben, C.: Short-term environmental changes in the Cretaceous Tethyan ocean: micropalaeontological evidence from the Early Albian Oceanic Anoxic Event 1b, Terra Nova, 15, 14–19, 2003b. Herrle, J. O., Kößler, P., Friedrich, O., Erlenkeuser, H., and Hemleben, C.: High resolution carbon isotope records of the Aptian to Lower Albian from SE France and the Mazagan Plateau (DSDP Site 545): a stratigraphic tool for paleoceanographic and paleobiologic reconstruction, Earth Planet. Sc. Lett., 218, 149–161, 2004. Herrle, J. O., Kosler, P., and Bollmann, J.: Palaeoceanographic differences of early Late Aptian black shale events in the Vocontian Basin (SE France), Palaeogeogr. Palaeocl., 297, 367–376, 2010. Hochuli, P. A., Menegatti, A. P., Weissert, H., Riva, A., Erba, E., and Premoli Silva, I.: Episodes of high productivity and cooling in the early Aptian Alpine Tethys, Geology, 27, 657–660, 1999. Hong, S. K. and Lee, Y. I.: Evaluation of atmospheric carbon dioxide concentrations during the Cretaceous, Earth Planet. Sc. Lett., 327–328, 23–28, 2012. Hopmans, E. C., Weijers, J. W. H., Schefuß, E., Herfort, L., Sinninghe Damsté, J. S., and Schouten, S.: A novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids, Earth Planet. Sc. Lett., 224, 107–116, 2004. Hu, X., Kuidong, Z., Yilmaz, I. O., and Yongxiang, L.: Stratigraphic transition and palaeoenvironmental changes from the Aptian oceanic anoxic event 1a (OAE1a) to the oceanic red bed 1 (ORB1) in the Yenicesihlar section, central Turkey, Cretaceous Res., 38, 40–51, 2012. Huber, B. T. and Leckie, R. M.: Planktic foraminiferal species turnover across deep-sea Aptian/Albian boundary sections, J. Foramin. Res., 41, 53–95, 2011. Huguet, C., Schimmelmann, A., Thunell, R., Lourens, L. J., Sinninghe Damsté, J. S., and Schouten, S.: A study of the TEX<sub>86</sub> paleothermometer in the water column and sediments of the Santa Barbara Basin, California, Paleoceanography, 22, PA3203, <a href="http://dx.doi.org/10.1029/2006PA001310">https://doi.org/10.1029/2006PA001310</a>, 2007. Husinec, A., Harman, C. A., Regan, S. P., Mosher, D. A., Sweeney, R. J., and Read, J. F.: Sequence development influenced by intermittent cooling events in the Cretaceous Aptian greenhouse, Adriatic platform, Croatia, AAPG Bull., 96, 2215–2244, 2012. Jenkyns, H. C.: Carbon-isotope stratigraphy and paleoceanographic significance of the Lower Cretaceous shallow-water carbonates of Resolution Guyot, Mid-Pacific Mountains, in: Proceedings of the Ocean Drilling Program Scientific Results, edited by: Winterer, E. L., Sager, W. W., Firth, J. V., Sinton, J. M., College Station, Texas, 143, 99–104, 1995. Jenkyns, H. C.: Evidence for rapid climate change in the Mesozoic–Palaeogene greenhouse world, Philos. T. Roy. Soc. A, 361, 1885–1916, 2003. Jenkyns, H. C.: Geochemistry of oceanic anoxic events, Geochem. Geophy. Geosy., 11, Q03004, <a href="http://dx.doi.org/10.1029/2009GC002788">https://doi.org/10.1029/2009GC002788</a>, 2010. Jenkyns, H. C. and Wilson, P. A.: Stratigraphy, paleoceanography, and evolution of Cretaceous Pacific guyots: relics from a greenhouse Earth, Am. J. Sci., 299, 341–392, 1999. Jenkyns, H. C., Schouten-Huibers, L., Schouten, S., and Sinninghe Damsté, J. S.: Warm Middle Jurassic–Early Cretaceous high-latitude sea-surface temperatures from the Southern Ocean, Clim. Past, 8, 215–226, <a href="http://dx.doi.org/10.5194/cp-8-215-2012">https://doi.org/10.5194/cp-8-215-2012</a>, 2012. Jones, C. E. and Jenkyns, H. C.: Seawater strontium isotopes, oceanic anoxic events, and seafloor hydrothermal activity in the Jurassic and Cretaceous, Am. J. Sci., 301, 112–149, 2001. Keller, C. E., Hochuli, P. A., Weissert, H., Weissert, H., Bernasconi, S. M., Giorgioni, M., and Garcia, T. I.: A volcanically induced climate warming and floral change preceded the onset of OAE1a (Early Cretaceous), Palaeogeogr. Palaeocl., 305, 43–49, 2011. Kemper, E.: Das Klima der Kreide-Zeit, Geologisches Jahrbuch A, 96, 5–185, 1987 (in German). Kim, J.-H., van der Meer, J., Schouten, S., Helmke, P., Willmott, V., Sangiorgi, F., Koç, N., Hopmans, E. C., and Sinninghe Damsté, J. S.: New indices and calibrations derived from the distribution of crenarchaeal isoprenoid tetraether lipids: Implications for past sea surface temperature reconstructions, Geochim. Cosmochim. Ac., 74, 4639–4654, 2010. Kuhnt, W., Holbourn, A., and Moullade, M.: Transient global cooling at the onset of early Aptian oceanic anoxic event (OAE) 1a, Geology, 39, 323–326, 2011. Kuroda, J., Tanimizu, M., Hori, R. S., Suzuki, K., Ogawa, N. O., Tejada, M. L. G., Coffin, M. F., Coccioni, R., Erba, E., and Ohkouchi, N.: Lead isotopic record of Barremian-Aptian marine sediments: Implications for large igneous provinces and the Aptian climatic crisis, Earth Planet. Sc. Lett., 307, 126–134, 2011. Kuypers, M. M. M., van Breugel, Y., Schouten, S., Erba, E., and Sinninghe Damsté, J. S.: N<sub>2</sub>-fixing cyanobacteria supplied nutrient N for Cretaceous oceanic anoxic events, Geology, 32, 853–856, 2004. Larson, R. L.: Geological consequences of superplumes, Geology, 19, 963–966, 1991. Larson, R. L. and Erba, E.: Onset of the mid-Cretaceous greenhouse in the Barremian-Aptian: Igneous events and the biological, sedimentary and geochemical responses, Paleoceanography, 14, 663–678, 1999. Leckie, R. M., Bralower, T. J., and Cashman, R.: Oceanic anoxic events and plankton evolution: Biotic response to tectonic forcing during the Mid-Cretaceous, Paleoceanography, 17, PA1041, <a href="http://dx.doi.org/10.1029/2001PA000623">https://doi.org/10.1029/2001PA000623</a>, 2002. Li, X., Jenkyns, H. C., Zhang, C., Wang, Y., Liu, L., and Cao, K.: Carbon isotope signatures changes during middle- of pedogenic carbonates from SE China: rapid atmospheric <i>p</i>CO<sub>2</sub> late Early Cretaceous time, Geol. Mag., 151, 830–849, 2014. Lopes dos Santos, R., Prange, M., Castañeda, I. S., Schefuß, E., Mulitza, S., Schulz, M., Niedermeyer, E. M., Sinninghe Damsté, J. S., and Schouten, S.: Glacial–interglacial variability in Atlantic Meridional Overturning Circulation and thermocline adjustments in the tropical North Atlantic, Earth Plan. Sc. Lett., 300, 407–414, 2010. Lorenzen, J., Kuhnt, W., Holbourn, A., Flögel, S., Moullade, M., and Tronchetti, G.: A new sediment core from the Bedoulian (Lower Aptian) stratotype at Roquefort-La Bédoule, SE France, Cretaceous Res., 39, 6–16, 2013. Luciani, V., Cobianchi, M., and Jenkyns, H. C.: Biotic and geochemical response to anoxic events: the Aptian pelagic succession of the Gargano Promontory (southern Italy), Geol. Mag., 138, 277–298, 2001. Mahanipour, A., Mutterlose, J., Kani, A. L., and Adabi, M. H.: Palaeoecology and biostratigraphy of early Cretaceous (Aptian) calcareous nannofossils and the δ<sup>13</sup>C<sub>carb</sub> isotope record from NE Iran, Cretaceous Res., 32, 331–356, 2011. Malinverno, A., Erba, E., and Herbert, T. D.: Orbital tuning as an inverse problem: Chronology of the early Aptian oceanic anoxic event 1a (Selli Level) in the Cismon APTICORE, Paleoceanography, 25, PA2203, <a href="http://dx.doi.org/10.1029/2009PA001769">https://doi.org/10.1029/2009PA001769</a>, 2010. Malinverno, A., Hildebrandt, J., Tominaga, M., and Channell, J. E. T.: M-sequence geomagnetic polarity time scale (MHTC12) that steadies global spreading rates and incorporates astrochronology constraints, J. Geophys. Res., 117, B06104, <a href="http://dx.doi.org/10.1029/2012JB009260">https://doi.org/10.1029/2012JB009260</a>, 2012. Malkoč, M., Mutterlose, J., and Pauly, S.: Timing of the Early Aptian δ<sup>13</sup>C excursion in the Boreal Realm, Newsl. Stratigr., 43, 251–273, 2010. Marshall, J. D.: Climatic and oceanographic isotopic signals from the carbonate rock record and their preservation, Geol. Mag., 129, 143–160, 1992. Maurer, F., van Buchem, F. S. P., Eberli, G. P., Pierson, B. J., Raven, M. J., Larsen, P., Al-Husseini, M. I., and Vincent, B.: Late Aptian long-lived glacio-eustatic lowstand recorded on the Arabian Plate, Terra Nova, 25, 87–94, 2012. McAnena, A., Flögel, S., Hofmann, P., Herrle, J. O., Griesand, A., Pross, J., Talbot, H. M., Rethemeyer, J., Wallmann, K., and Wagner, T.: Atlantic cooling associated with a marine biotic crisis during the mid-Cretaceous period, Nat. Geosci., 6, 558–651, 2013. Méhay, S., Keller, C. E., Bernasconi, S. M., Weissert, H., Erba, E., Bottini, C., and Hochuli, P. A.: A volcanic CO<sub>2</sub> pulse triggered the Cretaceous Oceanic Anoxic Event 1a and a biocalcification crisis, Geology, 37, 819–822, 2009. Mélières, F., Deroo, G., and Herbin, J. P.: Organic-matter-rich and hypersiliceous Aptian sediments from western Mid-Pacific Mountains, Deep Sea Drilling Project, Initial Reports, 62, 903–915, 1978. Menegatti, A. P., Weissert, H., Brown, R. S., Tyson, R. V., Farrimond, P., Strasser, A., and Caron, M.: High-resolution δ<sup>13</sup>C-stratigraphy through the early Aptian Livello Selli of the Alpine Tethys, Paleoceanography, 13, 530–545, 1998. Millán, M. I., Weissert, H. J., Fernandez-Mendiola, P. A., and Garcia-Mondejar, J.: Impact of Early Aptian carbon cycle perturbations on evolution of a marine shelf system in the Basque-Cantabrian Basin (Aralar, N Spain), Earth Planet. Sc. Lett., 287, 392–401, 2009. Moullade, M., Kuhnt, W., Berger, J. A., Masse, J., and Tronchetti, G.: Correlation of biostratrigraphic and stable isotope events in the Aptian historical stratotype of La Bedoule (southern France), Comptes Rendus de l'Academie des Sciences Serie II, 327, 693–698, 1998. Mutterlose, J.: Temperature-controlled migration of calcareous nannofloras in the north-west European Aptian, in: Nannofossils and their applications, edited by: Crux, J. A. and van Heck, S. E., Ellis Horwood, Chichester, England, 122–142, 1989. Mutterlose, J.: Migration and evolution patterns of floras and faunas in marine Early Cretaceous sediments of NW Europe, Palaeogeogr. Palaeocl., 94, 261–282, 1992. Mutterlose, J. and Bottini, C.: Early Cretaceous chalks from the North Sea giving evidence for global change, Nature Communications, 4, 1686, <a href="http://dx.doi.org/10.1038/ncomms2698">https://doi.org/10.1038/ncomms2698</a>, 2013. Mutterlose, J., Bornemann, A., and Herrle, J. O.: Mesozoic calcareous nannofossils – state of the art, Palaeont. Z., 79, 113–133, 2005. Mutterlose, J., Bornemann, A., and Herrle, J.: The Aptian–Albian cold snap: Evidence for "mid" Cretaceous icehouse interludes, Neues Jahrb. Geol. P.-A., 252, 217–225, 2009. Mutterlose J., Malkoč, M., Schouten, S., Sinninghe Damsté, J. S., and Forster, A.: TEX<sub>86</sub> and stable δ<sup>18</sup>O paleothermometry of early Cretaceous sediments: Implications for belemnite ecology and palaeotemperature proxy application, Earth Planet. Sc. Lett., 298, 286–298, 2010. Mutterlose, J., Bottini, C., Schouten, S., and Sinninghe Damsté, J. S.: High sea-surface temperatures during the early Aptian OAE 1a in the Boreal Realm, Geology, 42, 439–442, 2014. Pauly, S., Mutterlose, J., and Wray, D. S.: Palaeoceanography of Lower Cretaceous (Barremian–Lower Aptian) black shales from northwest Germany evidenced by calcareous nannofossils and geochemistry, Cretaceous Res., 42, 28–43, 2013. Petrizzo, M. R., Huber, B. T., Gale, A. S., Barchetta, A., and Jenkyns, H. C.: Abrupt planktic foraminiferal turnover across the Niveau Kilian at Col de Pré-Guittard (Vocontian Basin, southeast France): new criteria for defining the Aptian/Albian boundary, Newsl. Stratigr., 45, 55–74, 2012. Peybernès, C., Giraud, F., Jaillard, E., Robert, E., Masrour, M., Aoutem, M., and Içame, N.: Stratigraphic framework and calcareous nannofossil productivity of the Essaouira-Agadir Basin (Morocco) during the Aptian-Early Albian: Comparison with the north-Tethyan margin, Cretaceous Res., 39, 149–169, 2013. Premoli Silva, I., Ripepe, M., and Tornaghi, M. E.: Planktonic foraminiferal distribution record productivity cycles: evidence from the Aptian-Albian Piobbico core (central Italy), Terra Nova, 1, 443–448, 1989a. Premoli Silva, I., Erba, E., and Tornaghi, M. E.: Paleoenvironmental signals and changes in surface fertility in mid-Cretaceous Corg-rich pelagic facies of the Fucoid Marls (central Italy), Geobios, Mémoire Spécial, 11, 225–236, 1989b. Premoli Silva, I., Erba, E., Salvini, G., Verga, D., and Locatelli, C.: Biotic changes in Cretaceous anoxic events, J. Foramin. Res., 29, 352–370, 1999. Price, G. D.: The evidence and implications of polar ice during the Mesozoic, Earth-Sci. Rev., 48, 183–210, 1999. Price, G. D.: New constraints upon isotope variation during the early Cretaceous (Barremian-Cenomanian) from the Pacific Ocean, Geol. Mag., 140, 513–522, 2003. Price, G. D., Williamson, T., Henderson, R. A., and Gagan, M. K.: Barremian–Cenomanian palaeotemperatures for Australian seas based on new oxygen-isotope data from belemnite rostra, Palaeogeogr. Palaeocl., 358–360, 27–39, 2012. Roth, P. H.: Mid-Cretaceous calcareous nannoplankton from the central Pacific: implications for Paleoceanography, Deep Sea Drilling Project, Initial Reports, 62, 471–489, 1981. Roth, P. H. and Krumbach, K. R.: Middle Cretaceous calcareous Nannofossil biogeography and preservation in the Atlantic and Indian oceans: implication for paleogeography, Mar. Micropaleontol., 10, 235–266, 1986. Rückheim, S., Bornemann, A., and Mutterlose, J.: Planktic foraminifera from the mid-Cretaceous (Barremian-Early Albian) of the North Sea Basin: Palaeoecological and palaeoceanographic implications, Mar. Micropaleontol., 58, 83–102, 2006. Schouten, S., Hopmans, E. C., Schefuss, E., and Sinninghe Damsté, J. S.: Distributional variations in marine crenarchaeotal membrane lipids: A new organic proxy for reconstructing ancient sea water temperatures?, Earth Planet. Sc. Lett., 204, 265–274, 2002. Schouten, S., Hopmans, S., Forster, A., Van Breugel, Y., Kuypers, M. M. M., and Sinninghe Damsté, J. S.: Extremely high sea-surface temperatures at low latitudes during the middle Cretaceous as revealed by archaeal membrane lipids, Geology, 31, 1069–1072, 2003. Schouten, S., Hopmans, E. C., and Sinninghe Damsté, J. S.: The effect of maturity and depositional redox conditions on archaeal tetraether lipid palaeothermometry, Org. Geochem., 35, 567–571, 2004. Schouten, S., Huguet, C., Hopmans, E. C., Kienhuis, M. V. M., and Sinninghe Damsté, J. S.: Analytical methodology for TEX<sub>86</sub> paleothermometry by high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry, Anal. Chem., 79, 2940–2944, 2007. Sinninghe Damsté, J. S., Hopmans, E. C. Schouten, S., van Duin, A. C. T., and Geenevasen, J. A. J.: Crenarchaeol: the characteristic core glycerol dibiphytanyl glycerol tetraether membrane lipid of cosmopolitan pelagic crenarchaeota, J. Lipid Res., 43, 1641–1651, 2002. Stein, M., Follmi, K. B., Westermann, S., Godet, A., Adatte, T., Matera, V., Fleitmann, D., and Berner, Z.: Progressive palaeoenvironmental change during the Late Barremian-Early Aptian as prelude to Oceanic Anoxic Event 1a: Evidence from the Gorgo a Cerbara section (Umbria-Marche basin, central Italy), Palaeogeogr. Palaeocl., 302, 396–406, 2011. Stein, M., Westermann, S., Adatte, T., Matera, V., Fleitmann, D., Spangenberg, J. E., and Föllmi, K. B.: Late Barremian–Early Aptian palaeoenvironmental change: The Cassis-La Bédoule section, southeast France, Cretaceous Res., 37, 209–222, 2012. Tejada, M. L. G., Katsuhiko, S., Kuroda, J., Coccioni, R., Mahoney, J. J., Ohkouchi, N., Sakamoto, T., and Tatsumi, Y.: Ontong Java Plateau eruption as a trigger for the early Aptian oceanic anoxic event, Geology, 37, 855–858, 2009. Thiede, J., Dean, W. E., Rea, D. K., Vallier, T. L., and Adelseck, C. G.: The geologic history of the Mid-Pacific Mountains in the central North Pacific Ocean: A synthesis of Deep-Sea Drilling studies, Deep Sea Drilling Project, Initial Reports, 62, 1073–1120, 1981. Thierstein, H. R. and Roth, P. H.: Stable isotopic and carbonate cyclicity in Lower Cretaceous deep-sea sediments: Dominance of diagenetic effects, Mar. Geol., 97, 1–34, 1991. Tiraboschi, D., Erba, E., and Jenkyns, H. C.: Origin of rhythmic Albian black shales (Piobbico core, central Italy) Calcareous nannofossil quantitative and statistical analysis and paleoceanographic reconstructions, Paleoceanography, 24, PA2222, <a href="http://dx.doi.org/10.1029/2008PA001670">https://doi.org/10.1029/2008PA001670</a>, 2009. Tornaghi, M. E., Premoli Silva, I., and Ripepe, M.: Lithostratigraphy and planktonic foraminiferal biostratigraphy of the Aptian-Albian "Scisti a Fucoidi" in the Piobbico core, Marche, Italy: Background for cyclostratigraphy, Riv. Ital. Paleontol. S., 95, 223–264, 1989. Tremolada, F., Erba, E., and Bralower, T. J.: Late Barremian to Early Aptian calcareous nannofossil paleoceanography and paleoecology from the Ocean Drilling Program Hole 641C (Galicia Margin), Cretaceous Res., 87, 887–897, 2006. van Breugel, Y., Schouten, S., Tsikos, H., Erba, E., Price, G. D., and Sinninghe Damsté, J. S.: Synchronous negative carbon isotope shifts in marine and terrestrial biomarkers at the onset of the early Aptian oceanic anoxic event 1a: Evidence for the release of <sup>13</sup>C-depleted carbon into the atmosphere, Paleoceanography, 22, PA1210, <a href="http://dx.doi.org/10.1029/2006PA001341">https://doi.org/10.1029/2006PA001341</a>, 2007. Watkins, D. K.: Nannoplankton productivity fluctuations and rhythmically-bedded pelagic carbonates of the Greenhorn Limestone (Upper Cretaceous), Palaeogeogr. Palaeocl., 74, 75–86, 1989. Weijers, J. W. H., Schouten, S., Spaargaren, O. C., and Sinninghe Damsté, J. S.: Occurrence and distribution of tetraether membrane lipids in soils: Implication for the use of the TEX<sub>86</sub> proxy and the BIT index, Org. Geochem., 37, 1680–1693, 2006. Weissert, H.: C-isotope stratigraphy, a monitor of palaeoenvironmental change: a case study from the Early Cretaceous, Surv. Geophys., 10, 1–61, 1989. Weissert, H. and Erba, E.: Volcanism, CO<sub>2</sub> and palaeoclimate: a Late Jurassic–Early Cretaceous carbon and oxygen isotope record, J. Geol. Soc. London, 161, 695–702, 2004. Weissert, H. and Lini, A.: Ice Age interludes during the time of Cretaceous greenhouse climate?, in: Controversies in Modern Geology, edited by: Muller, D. W., McKenzie, J. A., and Weissert, H., Academic, San Diego, California, USA, 173–191, 1991. Weissert, H., Lini, A., Föllmi, K. B., and Kuhn, O.: Correlation of Early Cretaceous carbon isotope stratigraphy and platform drowning events: A possible link?, Palaeogeogr. Palaeocl., 137, 189–203, 1998. Williams, J. R. and Bralower, T. J.: Nannofossil assemblage, fine fraction stable isotopes, and the paleoceanography of the Valanginian-Barremian (Early Cretaceous) North Sea Basin, Paleoceanography, 10, 815–839, 1995. Wise Jr., S. W.: Mesozoic-Cenozoic history of calcareous nannofossils in the region of the Southern Ocean, Palaeogeogr. Palaeocl., 67, 157–179, 1988. Zakharov, Y. D., Baraboshkin, E. Y., Weissert, H., Michailova, I. A., Smyshlyaeva, O. P., and Safronov, P. P.: Late Barremian–early Aptian climate of the northern middle latitudes: Stable isotope evidence from bivalve and cephalopod molluscs of the Russian Platform, Cretaceous Res., 44, 183–201, 2013.