Morphological abnormalities of planktonic foraminiferal tests in the SW Pacific Ocean over the last 550ky

Abstract

The paper focuses on the occurrence of morphologically abnormal specimens of planktonic foraminifera observed over the last 550ky in IMAGES core MD 97-2114 (East of New Zealand, SW Pacific). Abnormal tests occurred throughout the entire record in all the morphospecies characterising the assemblages but were relatively rare, with percentages not exceeding 1.5% of the total assemblage. No mass abnormality events were found. A range of malformations were observed from slight deformity with smaller or overdeveloped chambers to more severe deformity, with misplaced chambers, distorted spirals or double tests forming twinned individuals. They exhibited several different categories of morphological abnormalities, even within the same sample. Test abnormalities were most abundant in the morphospecies Globorotalia inflata, Globigerina bulloides and Orbulina universa and were characterised by a long-term decreasing trend up core with an alternating % abundance pattern at the glacial to interglacial scale between MIS 14 to MIS 8, recording the highest percentages during the interglacials. Normalised total abundance and abnormal abundance curves co-varied very closely for G. bulloides and O. universa, but for G. inflata two opposing excursions were observed during MIS 13 and 6 which may be linked to water column states. Although abnormal numbers were proportionately low, there appears to be a "natural" background number of malformations in the G. inflata population through time. There was no relationship between volcanic ash production and test abnormalities.

Blooms of aberrant planktic foraminifera across the K/Pg boundary in the Western Tethys: causes and evolutionary implications

“…To test the hypothesis that the main eruptive phase (phase 2) of the Deccan Traps may have been concentrated during the last ~50 or 100 Kyr of the Maastrichtian, we have for the first time appraised the rate of aberrant planktic foraminifera in the upper part of the P. hantkeninoides Subzone from El Kef and Aïn Settara, as a proxy for ecological stress episodes. Our results indicate that there was a low frequency of aberrants (generally <2.5%) across this interval (Tables 1, 2), similar to the levels recorded in recent deep-ocean sediments under “normal” environmental conditions and reflecting the natural background number of malformations among planktic foraminifers (Mancin and Darling 2015). Low extinction and speciation rates, as well as low volatility and taxonomic flux fluctuations (Figs.…”

“…Proliferation of Aberrant Planktic Foraminifera, Chemical Pollution, and Global Warming during the Earliest Danian.-The causes proposed to explain the abnormalities in planktic foraminiferal tests are still very vague, including biological factors (such as unusually high levels of intraspecific variability) or various chemical and physical stressors (see Mancin and Darling 2015). For example, Coccioni and Luciani (2006) speculated that blooms of aberrant G. irregularis across the K/ Pg boundary are explained as the result of rapid and extreme fluctuations in climate and sea level, as well as intense volcanism and meteoritic impact events, which could have stressed surface waters.…”

Systematic taxonomy of the Trilobatus sacculifer plexus and descendant Globigerinoidesella fistulosa (planktonic foraminifera)

“…However, we observe that forms with incipient protuberances do increase in abundance during the stratigraphical range of G. fistulosa (mid-Pliocene to early Pleistocene). Irregular final chambers and aberrant morphologies are common to all morphospecies of planktonic foraminifera (Mancin & Darling 2015), but are generally not treated any differently to 'normal' specimens in terms of taxonomy. For example, incipient protuberances also occur in unrelated morphospecies such as Globigerina bulloides (Mancin & Darling 2015, pl.…”

Evolutionary Transition in the Late Neogene Planktonic Foraminiferal Genus Truncorotalia

“…The second uncertainty is the notable loss of specimens between 5.2 and 5.3 Ma, before the shift. No typical Truncorotalia specimens are recovered from this interval, although rare, malformed individuals (i.e., specimens with aberrant morphologies) were found ( Mancin and Darling, 2015 ). Although malformed individuals were not included in this study, as we wanted to assess the transition within a standard population, it is worth noting that malforms reflect stressed populations and an abiotic response to oceanic conditions ( Mancin and Darling, 2015 , Kontakiotis et al., 2016 ).…”

“…No typical Truncorotalia specimens are recovered from this interval, although rare, malformed individuals (i.e., specimens with aberrant morphologies) were found ( Mancin and Darling, 2015 ). Although malformed individuals were not included in this study, as we wanted to assess the transition within a standard population, it is worth noting that malforms reflect stressed populations and an abiotic response to oceanic conditions ( Mancin and Darling, 2015 , Kontakiotis et al., 2016 ). Oceanic cooling at the terminal Miocene may have affected the Truncorotalia population, producing malforms, hinting at potential drivers behind the evolutionary events described here ( Hornibrook, 1981 , Malmgren and Berggren, 1987 , Stanley et al., 1988 , Lear et al., 2015 ).…”