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).