**3. Changing blue carbon capture and storage rates in polar seas**

Despite the relative constancy in many oceanographic parameters over geological time, the polar regions are quite dynamic in fluctuation between ice ages, the duration and rate of change to interglacial periods and within these, the position of the marginal sea ice zone, water masses and ice shelf extent. All of these can directly alter the biomass of organisms, their carbon capture and storage rates as well as direct carbon dioxide uptake and release by oceanic storage. Section 2 has highlighted that sediment carbonate levels [8] and organism blue carbon capture and storage rates [10, 15] all vary considerably between and within regions. Measuring any change over time necessarily must have georeferenced baselines to measure against but most 'long term monitoring' programmes are relatively young. One of the most notable multidecadal data sets is that for zooplankton, focused on krill and salps. Analysis of this was one of the first to show change in polar ecosystems (krill reductions) in response to climate [24]. However these organisms are mobile and ice edge associated, which highlight both problems in measurement and interpretation – are the less krill in there survey areas because there are less overall or because they are somewhere-else? Crustacean zooplankton, such as Krill, are important to blue carbon capture and storage rates [5, 6] and may be important to sequestration rates as well [4].

We know little about blue carbon capture, storage and sequestration rates for the vast majority of the seabed, and there are a tiny number of sites which have been monitored regularly for more than a decade. Recently a series of ice shelf disintegrations along the Antarctic Peninsula and some elsewhere have been accompanied by major increases in primary [18] and secondary [19] production. These new and increased stocks of seabed blue carbon there have been estimated to constitute ~7x105 tons of carbon per year equivalent to 10,000 hectares of tropical rainforest [19]. These ice shelf collapses have formed an increasing number of giant icebergs, which have also increased carbon capture in the water column through ocean fertilization [20]. Duprat et al. [20] estimated the increases in water column blue carbon of a number of such icebergs. Those estimates were later built upon in terms of their total blue carbon impact (trade-offs of creating new sink areas and ocean fertilization versus scouring potential) to show a 5000 km<sup>2</sup> iceberg contributes a net positive of 10<sup>6</sup> tons of carbon per year [17]. Ice shelf losses, iceberg production and arctic forest increases [2] are not the only sources of blue carbon change around the polar regions.

within and between regions, organisms, environments and time. Partitioning out the causes and effects of variability is key to meaningful estimates of blue carbon stocks and how they are likely to change. For example, young animals are likely to have higher specific growth rates (thus have high carbon capture but low storage values) whereas older animals would typically be larger but grow slower (and thus be associated with low carbon capture but high carbon storage values). Thus an event influencing population demographics (e.g. iceberg scour) could change carbon capture relative to storage rates, and this could alter depend on

Recent work in the Ross, Weddell and Bellingshausen seas have shown rapid growth rates, and changes in growth rates, are possible in polar organisms. Such blue carbon change has happened in response to wind-driven or ice shelf collapse promoted increased food availability [18, 19, 23] respectively, or increase in temperature [21]. With carbon sinks, sources and flux values being so important to global climate as well as projecting trends and predicting future scenarios it is clear that quantification of blue carbon has an important role in this, and the polar regions are the most poorly known. Understanding biological response to polar change has become even more important since it has become apparent that amongst the most

Despite the relative constancy in many oceanographic parameters over geological time, the polar regions are quite dynamic in fluctuation between ice ages, the duration and rate of change to interglacial periods and within these, the position of the marginal sea ice zone, water masses and ice shelf extent. All of these can directly alter the biomass of organisms, their carbon capture and storage rates as well as direct carbon dioxide uptake and release by oceanic storage. Section 2 has highlighted that sediment carbonate levels [8] and organism blue carbon capture and storage rates [10, 15] all vary considerably between and within regions. Measuring any change over time necessarily must have georeferenced baselines to measure against but most 'long term monitoring' programmes are relatively young. One of the most notable multidecadal data sets is that for zooplankton, focused on krill and salps. Analysis of this was one of the first to show change in polar ecosystems (krill reductions) in response to climate [24]. However these organisms are mobile and ice edge associated, which highlight both problems in measurement and interpretation – are the less krill in there survey areas because there are less overall or because they are somewhere-else? Crustacean zooplankton, such as Krill, are important to blue carbon capture and storage rates [5, 6] and

We know little about blue carbon capture, storage and sequestration rates for the vast majority of the seabed, and there are a tiny number of sites which have been monitored regularly for more than a decade. Recently a series of ice shelf disintegrations along the Antarctic Peninsula and some elsewhere have been accompanied by major increases in primary [18] and secondary [19] production. These new and increased stocks of seabed blue carbon there have been

rainforest [19]. These ice shelf collapses have formed an increasing number of giant icebergs,

tons of carbon per year equivalent to 10,000 hectares of tropical

severe physical changes have been associated with these areas.

may be important to sequestration rates as well [4].

estimated to constitute ~7x105

**3. Changing blue carbon capture and storage rates in polar seas**

which season it occurred in.

48 Carbon Capture, Utilization and Sequestration

Sea ice extent, particularly 'fast ice' (the freezing of the sea surface, anchored to land) has been one of the most drastic physical changes in the polar regions, particularly throughout the Arctic. Sea ice changes and primary production responses have been more complex around Antarctica [25], but crucially most sea ice losses have been over productive continental shelf whereas most of the sea ice gains have been over deeper slope and abyssal ocean depths [16]. Historical expedition zoobenthic collections and modern samples of longer lived animals with relevant information in skeletons has shown that blue carbon capture rates may have doubled over the last 25 years around West Antarctica [26]. The mechanism for this seems to be that reduced extent (in time and space) of sea ice leads to longer (but not necessarily larger biomass) phytoplankton blooms, resulting in longer meal times for primary consumers resulting in more carbon storage as growth (**Figure 7**). The total blue carbon increases driven by sea ice losses [17, 26] probably greatly exceed those caused by ice shelf collapse/giant iceberg formation [17–20]. However, from what we currently know, change in polar blue carbon is a complex of increases

**Figure 7.** Schematic showing influence of ozone losses on phytoplankton carbon capture and zoobenthic carbon storage on polar seabeds.

[18], sea ice loss [25] and iceberg production [20]. It also seems likely that polar macroalgal production could increase spatial and temporal extent with exposure of new habitats, sea ice reduction and increased light energy reaching the shallows. These negatively feedback

depending on how much reaches the seabed and how much is recycled in the microbial loop and reworked following bioturbation. All natural carbon sequestration is via burial, mainly at the seabed, where zoobenthic assemblages (consumers) live. They are an important part of the negative feedback on climate, as new and longer availability of phytoplankton is converted into increased growth (organic carbon to tissues and inorganic carbon to skeletons). The feedback value is complicated to measure because it is dynamic in space and time but also because of simultaneous positives and negatives. For example ice shelf loss leads to more open water, a) reducing albedo, thus potential to absorb more heat; b) reduces buttressing of ice sheets, thus potential for this to accelerate coastwards, c) increasing potential for gas exchange, d) generating new phytoplankton blooms, e) opening new habitat for zoobenthos and f) generating giant icebergs with ocean fertilization potential [17–20]. Even the latter components themselves each contain contrasting feedbacks on climate, for example calving of an

giant iceberg such as that to break off Larsen C in 2017 may scour and recycle 4x10<sup>4</sup>

factors such as increased heat absorption and less than expected growth gains.

benthic carbon but algal capture and seabed zoobenthic storage of new carbon contributes

probably similar to that of Arctic Taiga expansion [2], although this too has also complicating

see http://nsidc.org/) so biological responses to these are the largest measured natural negative feedback on climate change. These are dwarfed as an organic carbon store by tropical forests, but these are not increasing as a result of climate change and thus not a negative feedback (their genuine sequestration potential is also low, as burial rates of carbon are very small except for water logged swamp forests). The magnitude of polar blue carbon negative feedback from sea ice losses depends on whether the carbon is calculated from primary production, secondary production, immobilized carbon or sequestered carbon. The sequestration value is considered to be as low as two orders of magnitude different along the cascade from algal production to buried sequestered benthos (**Figure 9**). Scaling up from regional samples suggests that between 2002 and 2015 the zoobenthic blue carbon negative

in terms of sequestration [16] along the West Antarctic Peninsula continental shelf alone.

continental shelves, such as the Kerguelen Plateau doubles this [17], equivalent to 1–2% of global anthropogenic output. It is clear this feedback is dynamic, polar blue carbon storage has demonstrably increased in coincidence with climate-forced sea ice changes, at least around West Antarctica [26]. Global climate change, ozone losses and other indirect (e.g. non indigenous species invasions) or direct (e.g. harvesting) anthropogenic pressures have the potential to have major impacts on marine biodiversity [27], and thus considerably increase

tons of carbon per year [17]. The magnitude of this negative feedback is

whereas ice shelf losses approximate to ~30,000 km<sup>2</sup>

T C in immobilization or 1.6x10<sup>6</sup>

T C yr.−1 but including outer Subantarctic

km2

with increasing atmospheric

Blue Carbon on Polar and Subpolar Seabeds http://dx.doi.org/10.5772/intechopen.78237

are genuinely sequestered,

tCyr−1 of

51

tons C

) the annual zoobenthic

(mitigate) on climate change through increased capture of CO<sup>2</sup>

content. Only very small proportions of this captured CO<sup>2</sup>

of CO<sup>2</sup>

a net positive of 10<sup>6</sup>

Sea-ice loss areas exceed 1,000,000 km<sup>2</sup>

feedback averaged ~10<sup>7</sup> T C in production, 4.5x10<sup>6</sup>

blue carbon feedback is estimated at 30-80x10<sup>6</sup>

or decrease polar blue carbon.

Scaled up to the whole Antarctic continental shelf area (4.4x10<sup>6</sup>

**Figure 8.** Trends in zoobenthic blue carbon accumulation around the Southern Ocean. The key to cell (3x3 degrees) colors are red (biggest increase) to blue (biggest decrease) [17]. Cells with question marks are samples awaiting analysis (from the Antarctic circumnavigation expedition and future British Antarctic survey scientific cruises.

and decreases (**Figure 8**). Around the Southern Ocean blue carbon increases are most associated with West Antarctic seas and decreases with the East Antarctic coasts [17] but the vast majority of all shelf carbon stocks and change is unknown. It seems likely that the biggest blue carbon changes are near coast caused by ice shelf collapse [18–20], iceberg scour [19] and glacier retreat driven sedimentation [22] but there could also be significant offshore change associated with a shifting seasonal sea ice margin [4, 24, 25]. Given the higher potential ectotherm growth performances at slightly higher sea temperatures [21] it also seems likely that the Arctic and subpolar regions are key areas to quantify blue carbon budgets for. Quantifying these becomes one of the key steps in estimating biotic feedbacks on climate change.
