Climate variability and relationship with ocean fertility during the Aptian Stage

Abstract

Abstract. Several studies have been conducted to reconstruct temperature variations across the Aptian Stage, particularly during the Early Aptian Oceanic Anoxic Event (OAE)1a. There is a general consensus that a major warming characterized the 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 TEX86 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 ~2–3 °C) during the early phase of anoxia under intense volcanic activity of the Ontong Java Plateau (OJP). A short-lived (~35 ky) cooling episode interrupted the major warming, following a rapid increase of weathering rates. Nannofossils indicate that eutrophic 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 CO2 sequestration during burial of organic matter. In this phase, high productivity was probably maintained by N2-fixing cyanobacteria while nannofossil taxa indicating high fertility were rare. The end of anoxia coincided with the cessation of volcanism and a pronounced cooling. The mid-Aptian was characterized by high surface-water fertility and progressively decreasing temperatures, probably resulting from intense continental weathering drawing down pCO2. The lowest temperatures, combined with low fertility, were reached in the middle–late Aptian across the interval characterized by blooming of Nannoconus truittii. 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.

Multistratigraphic records of the Lower Cretaceous (Valanginian–Cenomanian) Puez key area in N. Italy

“…Several records and reference sections, especially from localities around the Tethys, demonstrate the significance of the Early-Middle Cretaceous period when the ocean-climate system became increasingly perturbed and unstable from the Valanginian to the Cenomanian (Weissert, 1989;Föllmi et al, 1994;Weissert and Erba, 2004;Muttoni et al, 2005;Godet et al, 2006Godet et al, , 2008Mutterlose et al, 2014;Pictet et al, 2015). These climatic perturbations were mainly related toincreasing volcanic activity, especially in large igneous provinces, which triggered episodes of rapid climate warming, ocean acidification and increased organic carbon burial (Erba, 1994;Larson and Erba, 1999;Baudin et al, 1999Baudin et al, , 2002Baudin et al, , 2005Jenkyns, 2003;Méhay et al, 2009;Erba et al, 2010;Keller et al, 2011;Bottini et al, 2015). The evidence, however, also shows that the oceanic system became gradually more sensitive to mid-and short-term climatic fluctuations (Sprovieri et al, 2006;Giorgioni et al, 2012).…”

The OAE1a in Cuchía (Early Aptian, Spain): C and O geochemistry and global correlation

“…Kunht, Holbourn and Moullade 2011;Lorenzen et al 2013;Maurer et al 2012;Bottini et al 2015). They rely on the assumption that weak carbonate diagenesis can change the mean δ 18 O value of a series, but usually preserves the high-frequency O-isotope variations (e.g.…”

Environmental consequences of Ontong Java Plateau and Kerguelen Plateau volcanism

“…In particular, OAE 1a is marked by a complex C isotopic anomaly that has been recognized in the Tethys, North Atlantic, and Pacifi c Oceans (Weissert, 1989;Weissert and Lini, 1991;Grötsch, 1993;Bralower et al, 1994Bralower et al, , 1999Jenkyns, 1995;Vahrenkamp, 1996Vahrenkamp, , 2010Ferreri et al, 1997;Menegatti et al, 1998;Erba et al, 1999;Jenkyns and Wilson, 1999;Luciani et al, 2001;Ando et al, 2002;Bellanca et al, 2002;Price, 2003;Immenhauser et al, 2005;Millán et al, 2009;Hu et al, 2012a;Huck et al, 2012;Bottini et al, 2014), and in terrestrial sequences (Gröcke et al, 1999;Hesselbo et al, 2000;Jahren et al, 2001;Heimhofer et al, 2003). An initial negative spike documented in marine and terrestrial records suggests a large input of isotopically light carbon into the ocean-atmosphere system, perhaps due to intensifi ed volcanogenic CO 2 emissions during the GOJE (Larson, 1991a;Weissert and Lini, 1991;Bralower et al, 1994;Erba, 1994;Weissert et al, 1998;Menegatti et al, 1998;Larson and Erba, 1999;Price, 2003), methane liberation from gas-hydrate dissociation (Gröcke et al, 1999;Hesselbo et al, 2000;Jahren et al, 2001;Beerling et al, 2002;…”

“…Late Aptian cool climate lasting as much as a few million years is counterintuitive, given extensive and repeated volcanism during emplacement of the Kerguelen LIP. Chemical weathering of rocks exposed on land is a relatively slow process for pulling down excess CO 2 , especially under persistent volcanic activity, and therefore alone seems an implausible cause for the late-late Aptian global cooling (Bottini et al, 2014(Bottini et al, , 2015. Burial of substantial amounts of organic matter in the Southern Ocean and in the South Atlantic over 2.5 m.y.…”

“…Short-and long-term temperature changes have been reconstructed for the latest Barremian through Aptian time interval using micropaleontological proxies (e.g., Kemper, 1987;Premoli Silva et al, 1989a, 1999Hochuli et al, 1999;Herrle and Mutterlose, 2003;Heimhofer et al, 2004;Rückheim et al, 2006a;Mutterlose et al, 2009;Keller et al, 2011;McAnena et al, 2013;Bottini et al, 2014Bottini et al, , 2015, stable oxygen isotopes (Weissert and Lini, 1991;Jenkyns, 1995;Menegatti et al, 1998;Luciani et al, 2001;Bellanca et al, 2002;Price, 2003;Ando et al, 2008;Millán et al, 2009;Kuhnt et al, 2011;Jenkyns et al, 2012;Hu et al, 2012a;Price et al, 2012;Maurer et al, 2012;Bottini et al, 2014), and biomarkers (Schouten et al, 2003;Mutterlose et al, 2010;Keller et al, 2011;McAnena et al, 2013;Bottini et al, 2014Bottini et al, , 2015. A global warming marked OAE 1a, while generally cooler temperatures persisted in the late Aptian, as indicated by the presence of glendonites and possible ice-rafted debris at high latitudes (Kemper, 1987;Frakes and Francis, 1988;De Lurio and Frakes, 1999;Price, 1999).…”