Icebergs, sea ice, blue carbon and Antarctic climate feedbacks

Abstract

Sea ice, including icebergs, has a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea-ice losses around West Antarctica's continental shelf generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions ice scour limits blue carbon storage ecosystem services, which work as a powerful negative feedback on climate change (less sea ice increases phytoplankton blooms, benthic growth, seabed carbon and sequestration). This resets benthic biota succession (maintaining regional biodiversity) and also fertilizes the ocean with nutrients, generating phytoplankton blooms, which cascade carbon capture into seabed storage and burial by benthos. Small icebergs scour coastal shallows, whereas giant icebergs ground deeper, offshore. Significant benthic communities establish where ice shelves have disintegrated (giant icebergs calving), and rapidly grow to accumulate blue carbon storage. When 5000 km2 giant icebergs calve, we estimate that they generate approximately 106 tonnes of immobilized zoobenthic carbon per year (t C yr−1). However, their collisions with the seabed crush and recycle vast benthic communities, costing an estimated 4 × 104 t C yr−1. We calculate that giant iceberg formation (ice shelf disintegration) has a net potential of approximately 106 t C yr−1 sequestration benefits as well as more widely known negative impacts.This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

Blue carbon gains from glacial retreat along Antarctic fjords: What should we expect?

“…Marine ice losses comprise multiple sources; sea ice (such as fast ice), ice shelves and glaciers. For seasonal sea ice losses and ice shelf disintegration, the quantification of blue (marine biological) carbon has been attempted (Barnes, 2017; Barnes et al, 2018) and is ongoing with the Changing Arctic Ocean Seafloor project throughout the Barents Sea. For glacial retreat, a third source of marine ice loss, the calculations for carbon sink capacity are problematic, as previous work has estimated average retreat rates rather than areas of glacier lost (=habitat gained; Cook et al, 2016).…”

Protecting Antarctic blue carbon: as marine ice retreats can the law fill the gap?

“…Further, the loss of more permanent ice-shelves and glacier retreat permits colonization of whole benthic (seabed) assemblages, including sedentary and sessile animals (for instance corals, sponges and bryozoans). The result is a profound increase in the ecological diversity and capacity of the system to accumulate blue carbon, in a similar manner to the forestry term of a carbon-stock (Barnes et al, 2018).…”

“…Antarctic continental shelves are very large and in deeper water experience uniquely minimal levels of (anthropogenic or natural) disturbance, making them particularly effective as carbon sinks (Barnes, 2015(Barnes, , 2017Barnes, Fleming, Sands, Quartino, & Deregibus, 2018). Climate change may amplify this potential (Turner & Comiso, 2017), in part through the natural increase in the abundance and longevity of phytoplankton where sea-ice is being lost over shallow continental shelf waters [see figure 2].…”

“…Maximizing the carbon sequestration potential of Antarctic polar blue carbon would have profound benefits for global climate mitigation efforts. The emergence of blue carbon ecosystems around Antarctica is expected to store as much as 80 million tonnes of carbon per year from the atmosphere; little work has been undertaken on sub-Antarctic continental shelves but blue carbon gains may prove to be in excess of 160 million tonnes (Barnes et al, 2018). However, realizing the mitigation potential of blue carbon will require a precautionary, whole-of-ecosystem approach; especially in the newly ice-free areas.…”

The marine system of the West Antarctic Peninsula: status and strategy for progress

“…The benthos is also an important carbon sink, representing considerable standing stocks of organic matter. As for the plankton and nekton, the WAP benthic community is also impacted by direct physical processes-such as iceberg scouring and glacial meltwater releases-that are likely to change in the future with consequences for diversity and carbon storage [14,15]. Physical processes also impact the benthos indirectly via the sinking of organic matter that originates in the photic zone (export production), which results in complex and highly variable pelagic-benthic coupling.…”