Figure 1. Cryosphere retreat. A) Ice shelf collapse; giant iceberg A-76 calved from the Filchner–Ronne Ice Shelf in May 2021 (74°S Weddell Sea, Antarctica). B) Glacier retreat; the extent of newly ice-free areas and glacial meltwater plumes in Kongsfjorden (top; 79°N Svalbard archipelago) and Admiralty Bay (bottom; 62°S South Shetland islands). Landsat 8 satellite images were obtained from https://www.usgs.gov/ and natural colour composites were generated in ArcGIS Pro 2.8.0.
Impacts of cryosphere retreat in the surrounding marine environment vary in magnitude and scale. They include, but are not restricted to, both habitat loss and expansion, increased stratification of the water column (de Andrés et al. 2020), changes in underwater light regime, general circulation, transport of sediment and nutrients (Sundfjord et al. 2017, Skogseth et al. 2020) and increased ice-scouring (Gutt 2001, Barnes and Souster 2011a). All these are sources of ecological disturbance to the pelagic and benthic biocenosis associated with glacial and periglacial environments. The accumulation of stressors can further increase the vulnerability of polar marine food webs and ecosystem services such as commercial fisheries and climate regulation (Arrigo et al. 2020).
Rapid climate-forced environmental changes of polar marine ecosystems offer ideal scenarios to get further insights into ecological concepts such as equilibrium, resilience, and tipping points (Sahade et al. 2015, Dayton et al. 2019, Gutt et al. 2021). Many ecological elements of polar regions are approaching a level of potentially irreversible regime shifts, particularly in the Arctic and West Antarctic Peninsula, due to the magnitude and consistency of marine ice loss. While ecosystem response to environmental stress tends to be gradual, broad evidence suggests that shifts in community structure are more prone to threshold dynamics, and their tipping points occur at differing critical values of environmental pressure (Hillebrand et al. 2020). Thus, understanding the extent to which marine ice loss affects ecosystem components might help to predict future composition of the polar seas.
Biogeographical patterns of polar marine biocenosis are seldom investigated across various spatiotemporal scales and integrated into ecological studies. However, this integration gives complementary information to assess trends and drivers of ecosystem state, and helps to prioritise conservation efforts (Kennicutt et al. 2015). Elucidating threshold levels of pressure, above which ecosystem response magnitudes and their variances increase disproportionately, creates context for accelerating changes in the polar marine ecosystem and ecosystem-based management. Developing a risk assessment framework has been recently identified as an urgent transition in orientating whole-of-systems dynamics toward robust approaches for managing risks and uncertainties in polar marine ecosystems (Ottersen et al. 2022). To move forward, ecosystem-based management requires assessing the states of ecosystem components, their past and future dynamics, and response to cumulative environmental and anthropogenic pressures.
A decent amount of reviews and meta-analyses exist on the effect of climate-driven disturbances on different polar marine functional groups (Griffiths et al. 2017, Figuerola et al. 2021), while only few of them focus on wider ecosystem components (Morley et al. 2019, Gutt et al. 2021). Here, we review existing knowledge on how the loss of marine ice affects sympagic biota, phyto- and zooplankton, fish, seabirds, phyto- and zoobenthos, and marine mammals in the Arctic and Southern Ocean following the PRISMA EcoEvo extension (O’Dea et al. 2021) (Supplementary Materials). We identified the environmental stressors from marine ice loss and scored them based on a decision tree (modified from (Altman et al. 2011), Fig. S1) to qualitatively assess their potential net effect on ecosystem components (level 1, class 3 ecosystem-based risk assessment, (Holsman et al. 2017)) based on the most recent projections of the cryosphere by the end of this century (2100: reference year of the Representative Concentration Pathways RCP projections, AR6-IPCC, 2022).
Trends of marine ice dynamics
Warming and wetting have persisted as key climatic drivers in polar regions which will very likely continue through this century (Fox-Kemper et al. 2021), particularly in the areas of Atlantic and Pacific water inflow and West Antarctica (Fig. 2). Since 1979, the Arctic has warmed nearly four times faster than the global average (Rantanen et al. 2022), and summer sea surface temperature (SST) has increased about 0.5°C per decade (1982–2017) (Meredith et al. 2019) While the southernmost regions of the Southern Ocean have cooled down, the Antarctic Peninsula is considered an area of recent rapid regional (RRR) warming (Vaughan et al. 2003) where SST has already increased >1°C since the second half of the 20th century (Meredith and King 2005).