## 1 Introduction  
The middle Eocene climatic optimum (MECO) is still an enigmatic global warming event, which occurred at about 40 Ma and lasted \(\sim\)500-600 kyrs, that temporarily interrupted the long-term cooling trend initiated at the end of the early Eocene climate optimum (EECO, \(\sim\)49 Ma) (e.g., [1; 2; 3; 4]). The MECO was first recognized by \(\sim\)1% negative oxygen isotope excursion in bulk carbonate and benthic foraminiferal tests in Southern Ocean cores [5], and subsequently identified in the Atlantic Ocean, and central western Tethys [1; 6; 7; 8; 9; 10]. Bulk carbonate oxygen isotope records indicate \(\sim\)4-6 \({}^{\circ}\)C warming (assuming ice-free conditions), with a gradual onset and brief peak temperatures, followed by a rapid return to pre-event conditions [1]. The MECO has been described as a global carbon cycle perturbation [11], but the lack of a carbon isotope excursion (CIE) contemporaneous with warming and the duration of the climate anomaly suggest that the event was more complex than the earlier Paleogene hyperthermals [12]. There is no evidence for a sudden release of isotopically light carbon within the MECO warming phase, as for the hyperthermal events. Marine carbonate \(\delta^{13}\)C records show considerable geographic and bathymetric variability but are commonly characterized by rising rather than declining \(\delta^{13}\)C values during the initial gradual warming [1; 5; 9; 13]. A transient \(\sim\)0.5% negative CIE (\(\sim\)50 kyr) during the warming peak occurs at some but not all sites [1; 3; 7; 8; 9]. Dissolution in carbonate during the MECO has been recorded in deep-sea records and linked to a temporary rise of the CCD/lysocline due to the amplified contribution of CO\({}_{2}\) (e.g., [1]). The degree and nature of the global carbon cycle disturbance during peak MECO as reflected in the available \(\delta^{13}\)C records appear complex [12], and regional carbon cycle influences were likely important. To explain the timing and pattern of warming and \(\delta^{13}\)C values, [PERSON] et al. [1] hypothesized the enhanced degassing of relatively \({}^{13}\)C-enriched CO\({}_{2}\) from magmatic sources (i.e., volcanism) or metamorphic decarbonation in orogenic belts as the cause of the event. Indeed, an early stage of Ethiopian flood basalt activity might have occurred between 45 and 35 Ma [14], and the \"Mid-Tertiary Ignimbrite Flare-Up\" in Mexico started around 40-38 Ma [15]. An intriguing feature of the MECO is its abrupt termination. Different mechanisms may have acted to culminate this perturbation. Enhanced silicate weathering may have led to an initial temperature drop when CO\({}_{2}\) degassing stopped, and derived cooling could have promoted recovery of the organic carbon burial flux, accelerating the sequestration of the excess of carbon e.g., [16]. In marginal continental basins, eutrophication and deposition of organic-rich sediments are commonly associated with MECO warming and the period directly afterward [8; 17]. An increase in organic carbon burial after the MECO might have been efficient negative feedback to lower CO\({}_{2}\) levels, deepening the CCD [1; 8] and leading to the abrupt increase in carbonate \(\delta^{13}\)C values above the MECO peak warming interval [1; 6; 7; 8; 10]. Even though the MECO is attracting high attention by the scientific community, studies on the paleoenvironmental changes and paleobiotic effects across the MECO are still limited. As for planktic foraminifera, this event led to a significant crisis in the abundance of muricate planktic foraminifera (large acarininids and _Morozovelloides_[18; 19; 20]) from the MECO peak and temporary loss of photosymbionts (bleaching) in _Acarinina_[20], possibly caused by the warming itself. Integrated studies of various microfossil and geochemical proxies in a western Tethys section deposited at middle-bathyal paleodepth [8; 9; 18; 19; 21] record higher export productivity during the MECO peak and directly afterward.