Distribution of planktonic foraminifera in the subtropical South Atlantic: depth hierarchy of controlling factors

Abstract

Abstract. Temperature appears to be the best predictor of species composition of planktonic foraminifera communities, making it possible to use their fossil assemblages to reconstruct sea surface temperature (SST) variation in the past. However, the role of other environmental factors potentially modulating the spatial and vertical distribution of planktonic foraminifera species is poorly understood. This is especially relevant for environmental factors affecting the subsurface habitat. If such factors play a role, changes in the abundance of subsurface-dwelling species may not solely reflect SST variation. In order to constrain the effect of subsurface parameters on species composition, we here characterize the vertical distribution of living planktonic foraminifera community across an east–west transect through the subtropical South Atlantic Ocean, where SST variability was small, but the subsurface water mass structure changed dramatically. Four planktonic foraminifera communities could be identified across the top 700 m of the transect. Gyre and Agulhas Leakage surface faunas were predominantly composed of Globigerinoides ruber, Globigerinoides tenellus, Trilobatus sacculifer, Globoturborotalita rubescens, Globigerinella calida, Tenuitella iota, and Globigerinita glutinata, and these only differed in terms of relative abundances (community composition). Upwelling fauna was dominated by Neogloboquadrina pachyderma, Neogloboquadrina incompta, Globorotalia crassaformis, and Globorotalia inflata. Thermocline fauna was dominated by Tenuitella fleisheri, Globorotalia truncatulinoides, and Globorotalia scitula in the west and by G. scitula only in the east. The largest part of the standing stock was consistently found in the surface layer, but SST was not the main predictor of species composition either for the depth-integrated fauna across the stations or at individual depth layers. Instead, we identified a pattern of vertical stacking of different parameters controlling species composition, reflecting different aspects of the pelagic habitat. Whereas productivity appears to dominate in the mixed layer (0–60 m), physical properties (temperature, salinity) become important at intermediate depths and in the subsurface, a complex combination of factors including oxygen concentration is required to explain the assemblage composition. These results indicate that the seemingly straightforward relationship between assemblage composition and SST in sedimentary assemblages reflects vertically and seasonally integrated processes that are only indirectly linked to SST. It also implies that fossil assemblages of planktonic foraminifera should also contain a signature of subsurface processes, which could be used for paleoceanographic reconstructions.

Population dynamics and reproduction strategies of planktonic foraminifera in the open ocean

“…This partly explains why, as mentioned in the introduction, the model of synchronised reproduction has been challenged by the absence of recordable signal in many sediment trap and plankton tow studies (Lončarić et al, 2005;Rebotim et al, 2017;Iwasaki et al, 2017;Greco et al, 2019;Lessa et al, 2020;Chernihovsky et al, 2020). However, the concept of the emergence of the canonical trajectory from a large background juvenile mortality was raised already in one of the first studies dedicated to the synchronisation concept in planktonic foraminifera (Bijma et al, 1990).…”

“…These appealing and logical schemes became widely adopted, so much that we almost omitted that the presented depictions of life cycles of most species were idealised, that they still required additional observations, and that there remains a host of problems and uncertainties challenging the presented models. Next to the discovery of active photosymbiosis (Takagi et al, 2019) in species whose hypothetical OVM trajectories extend below the photic zone, there have been numerous observations of stable vertical habitats in the plankton (Rebotim et al, 2017;Iwasaki et al, 2017;Greco et al, 2019;Lessa et al, 2020) as well as shell flux patterns in sediment traps (Lončarić et al, 2005;Chernihovsky et al, 2020), showing no evidence of OVM and reproduction synchronised by the lunar cycle. Even where plankton tow and sediment trap could be interpreted as indicative for cohort growth (synchronised reproduction), the timing of reproduction with respect to the lunar cycle appeared to vary within species and among species (e.g.…”

Mg∕Ca, Sr∕Ca and stable isotopes from the planktonic foraminifera <i>T. sacculifer</i>: testing a multi-proxy approach for inferring paleotemperature and paleosalinity

“…Mg concentrations were calculated using masses 24 and 26; Sr concentrations were calculated with mass 88. One big advantage in using LA-ICP-MS measurements is that single laser pulses remove only a few nanometers of material, which allows high-resolution trace element profiles to be acquired (e.g., Reichart et al, 2003;Regenberg et al, 2006;Dueñas-Bohórquez et al, 2009Hathorne et al, 2009;Munsel et al, 2010;Dissard et al, , 2010aEvans et al, 2013Evans et al, , 2015Steinhardt, 2014Steinhardt, , 2015Fehrenbacher et al, 2015;Langer et al, 2016;Koho et al, 2015Koho et al, , 2017Fontanier et al, 2018;de Nooijer et al, 2007de Nooijer et al, , 2014de Nooijer et al, , 2017aJentzen et al, 2018;Schmitt et al, 2019;Levi et al, 2019). Element concentrations were calculated for the individual ablation profiles integrating the different isotopes (glitter software).…”

Population dynamics and reproduction strategies of planktonic foraminifera in the open ocean

“…challenged by the absence of recordable signal in many sediment trap and plankton tow studies (Lončarić et al, 2005;Rebotim et al, 2017;Iwasaki et al, 2017;Greco et al, 2019;Lessa et al, 2020;Chernihovsky et al, 2020).…”