Climate Variability and Relationship with Ocean Fertility during the Aptian

Abstract:

The late Barremian- Aptian time interval was marked by intense volcanic activity of the Greater Ontong Java Event (GOJE) and Kerguelen Plateau (KP) which induced a global perturbations in the ocean-atmosphere system including the early Aptian Oceanic Anoxic Event (OAE) 1a. Here, we present updated surface-water paleotemperature and fertility changes based on calcareous nannofossil records from the Tethys and Pacific Ocean. The detailed picture of climatic and ocean fertility variations during the Aptian, is discussed in relation to the role of volcanism. The pre-OAE 1a interval was characterized by relatively warm temperatures reaching a maximum in the early phase of anoxia under intense activity of the GOJE. Following accelerated weathering rates a short-lived (~35ky) cooling episode interrupted the major warming. Nannofossils indicate that mesotrophic conditions are associated with highest temperatures and GOJE volcanism. The last part of OAE 1a was characterized by cool snaps, probably promoted by CO₂ sequestration via burial of organic matter (OM) under persistent igneous activity. The end of anoxia coincided with the cessation of volcanism and a marked cooling.

Massive subaerial volcanism of the KP was associated with cool conditions during the late Aptian, implying the dominant effect of atmospheric CO2 drawdown via enhanced weathering, also promoting relatively high nutrient recycling. Lowest temperatures and low fertility, were reached across the interval marked by blooming of Nannoconus truittii.

The almost exclusively submarine GOJE triggered greenhouse conditions during OAE 1a, whereas weathering and burial of OM acted as feedback processes favouring temporary cooler interludes. Extrusion of the subaerial KP was associated with prolonged cooling, indicating that, in a global context, weathering processes might have been relatively more important than CO₂-induced warming.