Planktic foraminifera are marine protists with calcium carbonate shells. Their abundance and evolution correlate with paleoceanographic and climatic changes, making them valuable environmental indicators. The Early Eocene Climatic Optimum (EECO, ~53–49 Ma) was the warmest long-term interval of the Cenozoic. In addition, several short-term (< 200 kyr) global warming events, the hyperthermals, occurred before and during this interval. The EECO provides indeed an exceptional opportunity to explore the marine biota resilience to extreme warmth through a long- and short-term perspective. Recent studies on planktic foraminiferal response to the EECO record that the two symbiont-bearing mixed layer genera Morozovella and Acarinina, dominating early Paleogene tropical and subtropical surface oceans, permanently switched their abundance and diversity in the Atlantic and Tethys oceans close to the EECO onset (J event). This change began at equatorial latitudes and gradually spread to tropical and temperate regions. In addition, at tropical, equatorial, and southern temperate Atlantic sites, all the Morozovella species modify their coiling direction from preferentially dextral to sinistral coiling (probably cryptic species) within the EECO, <200 kyr after the K/X event. Another major change from the Atlantic Ocean is the virtual disappearance of the genus Chiloguembelina from the K/X event. Expanding from previous works, this research aimed to extend the analysis of planktic foraminifera to other paleoceanographic settings outside the Atlantic Ocean and Tethys, focusing on Pacific ODP Sites 1209–1210 (Shatsky Rise), Hole 762C (Indian Ocean), and Site U1510 (Tasman Sea). Results show that Morozovella abundance in the subtropical Pacific declined at 53.28 Ma, EECO onset, coupled by Acarinina increase, confirming Atlantic findings. Despite expectations of reduced foraminiferal production, assemblage test size slightly increased. Species replacement within communities highlights the resilience of pelagic carbonate production, emphasizing the critical role of planktic foraminifera in regulating the marine food web and global carbon cycling (Chapter 1) The Morozovella/Acarinina abundance switch prompts investigation into environmental triggers. Unexpectedly, Morozovella test size increased, while Acarinina’s decreased. Lower δ13C values in Acarinina suggest this genus likely evaded the higher temperatures at the surface by migrating to deeper layers. However, reduced light likely weakened its symbiosis, limiting test size. In contrast, Morozovella remained shallower in the mixed layer, sustaining symbiosis and larger size but with limited ecological flexibility (Chapter 2). At southern high latitudes (Exmouth Plateau, Indian Ocean; Tasman Sea, Pacific), Morozovella did not decline, indicating cooler conditions may have provided refugia. Conversey, Acarinina dominated globally, confirming its ecological adaptability (Chapter 3). The global disappearance of Chiloguembelina from the K/X hyperthermal through the EECO suggests a response to food supply reduction and thermocline changes, including enhanced oxygenation (Chapters 1-3). Additionally, the switch in Morozovella coiling from dextral to sinistral <200 kyr after the K/X event was recorded at all sites whereas Acarinina lacks preferential coiling. This suggests that Morozovella decline can be read as dextral morphotypes drop. The survivors’ dextral forms show slightly lower δ13C values than dextrals, indicating a deeper habitat and reduced symbiosis. This ecological strategy, more pronounced in Acarinina, favoured this genus, allowing it to thrive during the EECO, and only partially the sinistral morozovellids forms, which survived with respect to dextral morphotypes but only in small abundance (Chapter 4). These findings provide critical insights into planktic foraminiferal adaptation to extreme warmth, relevant for future climate projections.
I foraminiferi planctonici sono protisti marini con gusci di carbonato di calcio. La loro abbondanza ed evoluzione sono correlate ai cambiamenti paleoceanografici e climatici, rendendoli importanti indicatori per la ricostruzione degli ambienti passati. L’ Early Eocene Climatic Optimum (EECO, ~53–49 Ma) è l’intervallo più caldo del Cenozoico. Durante l’EECO si sono verificati anche eventi di riscaldamento globale di breve durata (<200 kyr), noti come 'ipertermali'. Questo intervallo offre quindi l' opportunità di studiare la resilienza del biota marino al riscaldamento estremo, considerando una prospettiva sia a lungo che a breve termine. Studi recenti sui foraminiferi planctonici documentano che i due generi portatori di simbionti, Morozovella e Acarinina, predominanti nel mixed layer di oceani tropicali e subtropicali dell’inizio del Paleogene, hanno subito un cambiamento permanente in abbondanza e diversità negli oceani Atlantico e Tetide all’inizio dell’EECO (evento J). Inoltre, tutte le specie di Morozovella hanno modificato la direzione di avvolgimento del guscio (coiling) da destrorso a sinistrorso (specie criptiche) entro l’EECO, < 200 kyr dopo l’evento K/X. Un altro cambiamento significativo nell’ Atlantico è stata la quasi scomparsa del genere Chiloguembelina dall’evento K/X. Lo scopo di questa ricerca è di estendere l'analisi dei foraminiferi planctonici a contesti paleoceanografici al di fuori dell’Atlantico e della Tetide, concentrandosi sui sites 1209–1210 (Shatsky Rise, Pacifico), Hole 762C (Oceano Indiano) e Site U1510 (Mar di Tasmania). Dai risultati emerge che l’abbondanza di Morozovella è diminuita a 53.28 Ma, all’inizio dell’EECO, nel Pacifico subtropicale, confermando i dati atlantici. Nonostante le aspettative di una ridotta produzione di foraminiferi, la dimensione dei gusci nell’assemblage è leggermente aumentata. Lo species replacement all'interno delle comunità evidenzia la resilienza della produzione carbonatica pelagica, sottolineando il ruolo critico dei foraminiferi planctonici nella regolazione della rete alimentare marina e del ciclo globale del carbonio (Capitolo 1). Anche nel Pacifico subtropicale si è verificato lo switch nell’abbondanza relativa tra Morozovella e Acarinina. La dimensione dei gusci di Morozovella è inaspettatamente aumentata, mentre quella di Acarinina è diminuita. Valori minori di δ¹³C in Acarinina suggeriscono una sua migrazione in profondità per evitare le alte temperature superficiali. Tuttavia, la riduzione di luce potrebbe aver indebolito la simbiosi, limitando la dimensione delle taglie. Morozovella, rimanendo in superficie, ha mantenuto la simbiosi e una dimensione maggiore, ma con una flessibilità ecologica limitata (Capitolo 2). Alle alte latitudini meridionali (Oceano Indiano e Mar di Tasmania), Morozovella non è diminuita, indicando che condizioni più fredde potrebbero aver fornito rifugio. Tuttavia, Acarinina ha dominato globalmente, confermando la sua maggiore adattabilità. La scomparsa globale di Chiloguembelina dall’evento K/X suggerisce una risposta alla riduzione di nutrienti nel termoclino (Capitolo 3). Lo switch nel coiling di Morozovella da destrorso a sinistrorso, <200 kyr dopo l’evento K/X, è stato registrato in tutti i sites, mentre Acarinina non mostra una preferenza nell’avvolgimento. Il declino di Morozovella può essere interpretato come la diminuzione delle forme destrorse, che, con valori di δ13C minori, indicano un habitat più profondo e una simbiosi ridotta. Questa strategia ecologica, più accentuata in Acarinina, ha favorito questo genere durante l’EECO, con la sopravvivenza parziale di Morovella sinistrorse, sopravvissute ai morfotipi destrorsi, ma in piccole quantità (Capitolo 4). Questi risultati forniscono preziose informazioni sull'adattamento dei foraminiferi planctonici al caldo estremo, con implicazioni rilevanti per le proiezioni climatiche future.
Impact of extreme warmth, excess of CO2 pressure abd carbon cycle perturbations on marine biota: planktic foraminiferal resilience to the early Eocene climatic optimum (EECO, 53-49 MA)
FILIPPI, GIULIA
2025
Abstract
Planktic foraminifera are marine protists with calcium carbonate shells. Their abundance and evolution correlate with paleoceanographic and climatic changes, making them valuable environmental indicators. The Early Eocene Climatic Optimum (EECO, ~53–49 Ma) was the warmest long-term interval of the Cenozoic. In addition, several short-term (< 200 kyr) global warming events, the hyperthermals, occurred before and during this interval. The EECO provides indeed an exceptional opportunity to explore the marine biota resilience to extreme warmth through a long- and short-term perspective. Recent studies on planktic foraminiferal response to the EECO record that the two symbiont-bearing mixed layer genera Morozovella and Acarinina, dominating early Paleogene tropical and subtropical surface oceans, permanently switched their abundance and diversity in the Atlantic and Tethys oceans close to the EECO onset (J event). This change began at equatorial latitudes and gradually spread to tropical and temperate regions. In addition, at tropical, equatorial, and southern temperate Atlantic sites, all the Morozovella species modify their coiling direction from preferentially dextral to sinistral coiling (probably cryptic species) within the EECO, <200 kyr after the K/X event. Another major change from the Atlantic Ocean is the virtual disappearance of the genus Chiloguembelina from the K/X event. Expanding from previous works, this research aimed to extend the analysis of planktic foraminifera to other paleoceanographic settings outside the Atlantic Ocean and Tethys, focusing on Pacific ODP Sites 1209–1210 (Shatsky Rise), Hole 762C (Indian Ocean), and Site U1510 (Tasman Sea). Results show that Morozovella abundance in the subtropical Pacific declined at 53.28 Ma, EECO onset, coupled by Acarinina increase, confirming Atlantic findings. Despite expectations of reduced foraminiferal production, assemblage test size slightly increased. Species replacement within communities highlights the resilience of pelagic carbonate production, emphasizing the critical role of planktic foraminifera in regulating the marine food web and global carbon cycling (Chapter 1) The Morozovella/Acarinina abundance switch prompts investigation into environmental triggers. Unexpectedly, Morozovella test size increased, while Acarinina’s decreased. Lower δ13C values in Acarinina suggest this genus likely evaded the higher temperatures at the surface by migrating to deeper layers. However, reduced light likely weakened its symbiosis, limiting test size. In contrast, Morozovella remained shallower in the mixed layer, sustaining symbiosis and larger size but with limited ecological flexibility (Chapter 2). At southern high latitudes (Exmouth Plateau, Indian Ocean; Tasman Sea, Pacific), Morozovella did not decline, indicating cooler conditions may have provided refugia. Conversey, Acarinina dominated globally, confirming its ecological adaptability (Chapter 3). The global disappearance of Chiloguembelina from the K/X hyperthermal through the EECO suggests a response to food supply reduction and thermocline changes, including enhanced oxygenation (Chapters 1-3). Additionally, the switch in Morozovella coiling from dextral to sinistral <200 kyr after the K/X event was recorded at all sites whereas Acarinina lacks preferential coiling. This suggests that Morozovella decline can be read as dextral morphotypes drop. The survivors’ dextral forms show slightly lower δ13C values than dextrals, indicating a deeper habitat and reduced symbiosis. This ecological strategy, more pronounced in Acarinina, favoured this genus, allowing it to thrive during the EECO, and only partially the sinistral morozovellids forms, which survived with respect to dextral morphotypes but only in small abundance (Chapter 4). These findings provide critical insights into planktic foraminiferal adaptation to extreme warmth, relevant for future climate projections.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14242/218697
URN:NBN:IT:UNIFE-218697