Scaling laws explain foraminiferal pore patterns

Abstract

Due to climate warming and increased anthropogenic impact, a decrease of ocean water oxygenation is expected in the near future, with major consequences for marine life. In this context, it is essential to develop reliable tools to assess past oxygen concentrations in the ocean, to better forecast these future changes. Recently, foraminiferal pore patterns have been proposed as a bottom water oxygenation proxy, but the parameters controlling foraminiferal pore patterns are still largely unknown. Here we use scaling laws to describe how both gas exchanges (metabolic needs) and mechanical constraints (shell robustness) control foraminiferal pore patterns. The derived mathematical model shows that only specific combinations of pore density and size are physically feasible. Maximum porosity, of about 30%, can only be obtained by simultaneously increasing pore size and decreasing pore density. A large empirical data set of pore data obtained for three pseudocryptic phylotypes of Ammonia , a common intertidal genus from the eastern Atlantic, strongly supports this conclusion. These new findings provide basic mechanistic understanding of the complex controls of foraminiferal pore patterns and give a solid starting point for the development of proxies of past oxygen concentrations based on these morphological features. Pore size and pore density are largely interdependent, and both have to be considered when describing pore patterns.

Biogeographic distribution of three phylotypes (T1, T2 and T6) of <i>Ammonia</i> (foraminifera, Rhizaria) around Great Britain: new insights from combined molecular and morphological recognition

“…The absolute and relative densities of the three phylotypes may show a large seasonal and inter-annual variability, as has been shown by most of the temporal studies of estuarine foraminiferal faunas (e.g. Lutze, 1968;Wefer, 1976;Murray, 1983;Cearreta, 1988;Murray, 1992;Gustafsson and Nordberg, 1999;Murray and Alve, 2000;Korsun and Hald, 2000;Morvan et al, 2006;Horton and Murray, 2007;Papaspyrou et al, 2013;Saad and Wade, 2017;Richirt et al, 2020;Choquel et al, 2021). Although different species appear to show different reproduction and growth periods, this has not yet been demonstrated for the different Ammonia phylotypes.…”

“…However, this observation seems to contrast with the recent arrival (around 2000) of T6 in the hyposaline Baltic Sea (Polovodova et al, 2009;Schweizer et al, 2011b;Bird et al, 2020). However, the Baltic Sea is also the largest anthropogenically induced hypoxic area in the world (Carstensen et al, 2014), and the success of phylotype T6 in this area could also reflect its larger tolerance of low oxygen concentrations (compared to phylotypes T1 and T2), due to its larger porosity (Richirt et al, 2019a(Richirt et al, , b, 2020.…”

“…Of the 116 sequenced individuals sampled at eight sites from the AMTEP project (Table 3), 26 were part of the 96 specimens used by Richirt et al (2019a) to develop the morphometric assignment method, and sequences of 10 individuals have already been published in GenBank (Table S2). Seven more individuals, from Lake Grevelingen, presented by Richirt et al (2020), have also been deposited in the GenBank database (accession numbers MN190684-MN190690).…”

Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

“…Absence of large-scale migrations and a preference for oxygen-depleted habitats indicate that the species is adapted to live for long periods of time, likely its entire lifespan, within low-oxygen conditions. Globorotaloides hexagonus has previously been associated with deep, low-oxygen water masses across the Indo-Pacific, including the eastern North Pacific (Sautter and Thunell, 1991;Ortiz et al, 1996;Davis et al, 2016), equatorial Pacific (Fairbanks et al, 1982;Rippert et al, 2016;Max et al, 2017;Rippert et al, 2017), Peru-Chile margin (Marchant et al, 1998), and Indian Ocean (Rao et al, 1989;Schiebel et al, 2004;Birch et al, 2013). The species is sometimes assumed to be extinct in the Atlantic, with recent iden-tifications of G. hexagonus in Atlantic sediments explicitly used to date sediments as pre-Holocene or ascribed to taxonomic error (e.g., Kucera et al, 2005;Siccha and Kucera, 2017).…”

“…A high test porosity and high pore density have been widely associated with low-oxygen environments in benthic foraminifera (Bernhard, 1986;Perez-Cruz and Machain-Castillo, 1990;Glock et al, 2011Glock et al, , 2012Kuhnt et al, 2013Kuhnt et al, , 2014Rathburn et al, 2018) and in cultured planktic foraminifera (Kuroyanagi et al, 2013). These characteristics may play a role in facilitating gas exchange (Leutenegger and Hansen, 1979;Corliss, 1985) and may represent a balance between the need for gas exchange and structural constraints (Richirt et al, 2019). However, increased porosity has also been associated with other parameters: increasing temperature Burke et al, 2018), decreasing nitrate availability (Glock et al, 2011(Glock et al, , 2018, and increasing test size (Burke et al, 2018).…”