Abstract
Diminishing prospects for environmental preservation under climate change are intensifying efforts to boost capture, storage and sequestration (long-term burial) of carbon. However, as Earth’s biological carbon sinks also shrink, remediation has become a key part of the narrative for terrestrial ecosystems. In contrast, blue carbon on polar continental shelves have stronger pathways to sequestration and have increased with climate-forced marine ice losses—becoming the largest known natural negative feedback on climate change. Here we explore the size and complex dynamics of blue carbon gains with spatiotemporal changes in sea ice (60–100 MtCyear−1), ice shelves (4–40 MtCyear−1 = giant iceberg generation) and glacier retreat (< 1 MtCyear−1). Estimates suggest that, amongst these, reduced duration of seasonal sea ice is most important. Decreasing sea ice extent drives longer (not necessarily larger biomass) smaller cell-sized phytoplankton blooms, increasing growth of many primary consumers and benthic carbon storage—where sequestration chances are maximal. However, sea ice losses also create positive feedbacks in shallow waters through increased iceberg movement and scouring of benthos. Unlike loss of sea ice, which enhances existing sinks, ice shelf losses generate brand new carbon sinks both where giant icebergs were, and in their wake. These also generate small positive feedbacks from scouring, minimised by repeat scouring at biodiversity hotspots. Blue carbon change from glacier retreat has been least well quantified, and although emerging fjords are small areas, they have high storage-sequestration conversion efficiencies, whilst blue carbon in polar waters faces many diverse and complex stressors. The identity of these are known (e.g. fishing, warming, ocean acidification, non-indigenous species and plastic pollution) but not their magnitude of impact. In order to mediate multiple stressors, research should focus on wider verification of blue carbon gains, projecting future change, and the broader environmental and economic benefits to safeguard blue carbon ecosystems through law.
Highlights
Halting biodiversity loss, mitigating climate change and improving societal quality of life are not mutually exclusive, and nature-based solutions (NbS) are an important part of achieving these aims simultaneously
Antarctica’s opening fjords (Grange and Smith 2013). Both positive and negative impacts of glacial retreat have been noted along Antarctic fjords, e.g. southern Antarctic Peninsula fjords have little ice melt and lower sedimentation rates compared to those in the northern Antarctic Peninsula, where sedimentation can be high because those glaciers have retreated onto land
Antarctic continental shelves and coastlines are on the frontline of physical responses to climate change, and such physical changes have proved highly complex in space and time
Summary
Halting biodiversity loss, mitigating climate change and improving societal quality of life are not mutually exclusive, and nature-based solutions (NbS) are an important part of achieving these aims simultaneously. Restoration and rewilding inherently starts with plants as the base of food webs, involving carbon capture (through photosynthesis) and storage (in the body of organisms). Upon the death of these organisms, their bodies will pass through the food web and most of the carbon stored in them will be released as CO2 back into the water and atmosphere. The area/biomass of organisms capturing and storing carbon needs to be increased to remove more carbon than is being returned to the atmosphere to
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