Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean

Abstract

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO2 has been absorbed by the oceans. Seawater pH levels have already decreased by 0.1 and are predicted to decline by ~ 0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). These negative effects may become even exacerbated by increasing sea temperatures. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make predictions about how OA might affect different taxa. We consider their geographic range, skeletal mineralogy, biological traits and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate shows response variation depending on mineralogical composition. Species-specific responses due to mineralogical composition suggest taxa with calcitic, aragonitic and HMC skeletons may be more vulnerable to the expected carbonate chemistry alterations, and low magnesium calcite (LMC) species may be mostly resilient. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits and physiological processes are also expected to influence species specific responses.

Drivers of Marine CO2‐Carbonate Chemistry in the Northern Antarctic Peninsula

“…For example, depths below 800 m in the 2010s are characterized by Ω ar with values below 1 (Figure 4e; i.e., undersaturated condition, prevailing dissolution over precipitation). It represents an issue for much more intense negative pH sws trends with impacts on calcified structures of marine organisms (i.e., decreasing Ω values, mainly with respect to aragonite, the most unstable carbonate calcium mineral) in the water column, such as pteropods, and on the seafloor, such as echinoderms and bryozoans (Acqua et al., 2019; Figuerola et al., 2020; Henley et al., 2020).…”

“…Concomitantly, hydrographic and biogeochemical changes in ocean water masses are taking place around Antarctica, such as freshening trends of shelf and deep waters (Azaneu et al., 2013; De Lavergne et al., 2014; Dotto et al., 2016; Haumann et al., 2016; Hellmer et al., 2011), increased frequency of Circumpolar Deep Water (CDW) intrusions into coastal environments (Henley et al., 2019; Moffat & Meredith, 2018) and pH reduction over different time scales (McNeil & Matear, 2008; Midorikawa et al., 2012; Roden et al., 2013; Sabine et al., 2008). These changes are already impacting and changing the behavior of Southern Ocean ecosystems, which impact ocean health for the development of the sensitive Antarctic biota with different environmental roles, such as biogeochemical recycling and vertical energy fluxes (Figuerola et al., 2020, 2021; Henley et al., 2020; Mendes et al., 2023).…”

“…) and pH reduction over different time scales (McNeil & Matear, 2008;Midorikawa et al, 2012;Roden et al, 2013;Sabine et al, 2008). These changes are already impacting and changing the behavior of Southern Ocean ecosystems, which impact ocean health for the development of the sensitive Antarctic biota with different environmental roles, such as biogeochemical recycling and vertical energy fluxes (Figuerola et al, 2020(Figuerola et al, , 2021Henley et al, 2020;Mendes et al, 2023).…”

A review of the scientific knowledge of the seascape off Dronning Maud Land, Antarctica

“…A warming ocean, especially warming near-bottom waters in the SO will, with its lowered capacity for O 2 , possibly reduce not only the size of the giants (Spicer and Morley 2019), but also the general respiratory capabilities of several species and even other physiological mechanisms such as the gut-movements of pycnogonids (Woods et al 2017). Some evidence suggests that the increase in ocean acidification will be particularly problematic for benthic calcifying animals associated with the narrow shelves of the eastern Weddell Sea (Figuerola et al 2021), as the sediments here are shown to have high levels of CaCO 3 (Hauck et al 2012).…”