ALBERT

Description: The transition from benthos to plankton requires multiple adaptations, yet so far it remains unclear how these are acquired in the course of the transition. To investigate this process, we analyzed the genetic diversity and distribution patterns of a group of foraminifera of the genus Bolivina with a tychopelagic mode of life (same species occurring both in benthos and plankton). We assembled a global sequence data set for this group from single-cell DNA extractions and occurrences in metabarcodes from pelagic environmental samples. The pelagic sequences all cluster within a single monophyletic clade within Bolivina. This clade harbors three distinct genetic lineages, which are associated with incipient morphological differentiation. All lineages occur in the plankton and benthos, but only one lineage exhibits no limit to offshore dispersal and has been shown to grow in the plankton. These observations indicate that the emergence of buoyancy regulation within the clade preceded the evolution of pelagic feeding and that the evolution of both traits was not channeled into a full transition into the plankton. We infer that in foraminifera, colonization of the planktonic niche may occur by sequential cooptation of independently acquired traits, with holoplanktonic species being recruited from tychopelagic ancestors

Description: Fossil shells of planktonic foraminifera serve as the prime source of information on past changes in surface ocean conditions. Because the population size of planktonic foraminifera species changes throughout the year, the signal preserved in fossil shells is biased toward the conditions when species production was at its maximum. The amplitude of the potential seasonal bias is a function of the magnitude of the seasonal cycle in production. Here we use a planktonic foraminifera model coupled to an ecosystem model to investigate to what degree seasonal variations in production of the species Neogloboquadrina pachyderma may affect paleoceanographic reconstructions during Heinrich Stadial 1 (∼ 18–15 cal ka B.P.) in the North Atlantic Ocean. The model implies that during Heinrich Stadial 1 the maximum seasonal production occurred later in the year compared to the Last Glacial Maximum (∼ 21–19 cal ka B.P.) and the preindustrial era north of 30°N. A diagnosis of the model output indicates that this change reflects the sensitivity of the species to the seasonal cycle of sea ice cover and food supply, which collectively lead to shifts in the modeled maximum production from the Last Glacial Maximum to Heinrich Stadial 1 by up to 6 months. Assuming equilibrium oxygen isotopic incorporation in the shells of N. pachyderma, the modeled changes in seasonality would result in an underestimation of the actual magnitude of the meltwater isotopic signal recorded by fossil assemblages of N. pachyderma wherever calcification is likely to take place.

Description: Diurnal vertical migration (DVM) is a widespread phenomenon in the upper ocean, but it remains unclear to what degree it also involves passively transported micro- and meso-zooplankton. These organisms are difficult to monitor by in situ sensing and observations from discrete samples are often inconclusive. Prime examples of such ambiguity are planktonic foraminifera, where contradictory evidence for DVM continues to cast doubt on the stability of species vertical habitats, which introduces uncertainties in geochemical proxy interpretation. To provide a robust answer, we carried out highly replicated randomised sampling with 41 vertically resolved plankton net hauls taken within 26 hours in a confined area of 400 km2 in the tropical North Atlantic, where DVM in larger plankton occurs. Manual enumeration of planktonic foraminifera cell density consistently reveals the highest total cell concentrations in the surface mixed layer (top 50 m) and analysis of cell density in seven individual species representing different shell sizes, life strategies and presumed depth habitats reveals consistent vertical habitats not changing over the 26 hours sampling period. These observations robustly reject the existence of DVM in planktonic foraminifera in a setting where DVM occurs in other organisms.

Description: Planktonic Foraminifera are unique paleo-environmental indicators through their excellent fossil record in ocean sediments. Their distribution and diversity are affected by different environmental factors including anthropogenically forced ocean and climate change. Until now, historical changes in their distribution have not been fully assessed at the global scale. Here we present the FORCIS (Foraminifera Response to Climatic Stress) database on foraminiferal species diversity and distribution in the global ocean from 1910 until 2018 including published and unpublished data. The FORCIS database includes data collected using plankton tows, continuous plankton recorder, sediment traps and plankton pump, and contains similar to 22,000, similar to 157,000, similar to 9,000, similar to 400 subsamples, respectively (one single plankton aliquot collected within a depth range, time interval, size fraction range, at a single location) from each category. Our database provides a perspective of the distribution patterns of planktonic Foraminifera in the global ocean on large spatial (regional to basin scale, and at the vertical scale), and temporal (seasonal to interdecadal) scales over the past century.