Box 1. Definition of key terms related to cryosphere, polar biocenosis, ecosystem services and other processes
1. Cryosphere Marine ice-related definitions were taken from WMO Sea Ice Nomenclature (2014). WMO classifies ice into two major categories; sea and glacier ice. Sea ice grows and melts within ocean waters. First-year ice (FYI) develops from young ice, is of not more than one winter’s growth, and has an average thickness of 0.3-2 m. Multi-year ice (MYI) is old ice that has survived at least two summers’ melt and can be >3m thick. Ice shelves are floating platforms of ice that can reach up to 1500 m thickness. They are formed when ice sheets (continental ice) or glaciers meet the sea (Ingels et al. 2018). Glacier ice is ice in or originating from a glacier, whether on land or floating at the sea surface as icebergs. Icebergs are massive forms of floating ice greatly varying in shape, protruding >5m above sea level. The largest category is tabular berg, which forms by calving from an ice shelf (mega icebergs, Fig.1) while small icebergs can extend 5-15 above sea level, and be 15-60 m in length. 2. Polar biocenosis Sympagic communities are those living in association with the sea ice microhabitats and include algae, bacteria, fungi, heterotrophic protozoans, and metazoans such as nematodes, rotifers and copepods. Ice-obligate species are those that require sea ice for either breeding, hunting or rearing offspring. e.g. polar bear, walrus, Adélie penguin. Cryophilic species are those restricted to the polar biome Cryotolerant species are those with broad environmental preferences including, but not limited to, the polar biome (adapted from Bringloe et al. 2022). Vulnerable marine ecosystems (VMEs) are hotspots of biodiversity and ecosystem functioning in the deep sea (Ashford et al. 2019). They have low recovery potential and are highly vulnerable to disturbances. VMEs designation is a critical management framework to prevent significant adverse impacts due to fishing activity. e.g., cold-water coral reefs, and deep-sea sponge aggregations, cup coral fields. 3. Ecosystem Services (ES) ES can be divided into Regulating (climate regulation, biological control), Habitat/Supporting (life cycle maintenance, gene pool protection, nutrient cycling), Provisioning (food, medicinal and genetic resources, raw materials), and Cultural (heritage, recreation, spiritual) (Steiner et al. 2021) Blue Carbon is the carbon biologically captured and stored in marine ecosystems (Nellemann et al. 2009) including coastal, open ocean, and deep-sea ecosystems. Blue carbon offers potential as a Nature-based Solution (NbS) to climate change, hence complies with the climate regulation ES (Christianson et al. 2022). Carbon capture (hours to months) primary producers (planktic and benthic) use dissolved inorganic CO2 and transform it into biomass (organic carbon, OC). Carbon immobilisation (years to centuries) benthic calcifiers absorb dissolved inorganic carbon (DIC) to form shells and skeletons. Hard skeletal matrices are less prone to microbial action, thus have longer times of permanence. Carbon sequestration (centuries to millennia) carbon buried in anoxic sediments is out of the carbon cycle over geological times (Bax et al. 2021). 4. Other Tipping points or critical threshold is a point at which a small perturbation can cause a considerable change in future states of a system. The timescale at which this occurs is set by internal dynamics of the system (Lenton and Williams 2013).