Why is the South Orkney Island shelf
(the world’s first high seas marine protected area) a carbon
immobilization hotspot ?
Supplementary Information
Supplementary materials
The calculation to derive benthic carbon immobilization can be done in different ways.
1) Using the same values of mean standing stock of benthic carbon per area as in Peck et al. (2010)
the million km2 area losing sea ice overlies 1.625 x 107 tonnes of carbon. The annual increment for
1.625 x 107 tonnes of carbon at the specific growth rate of the current study species (>6 x 10-4 day-1)
x 365 is ~3.6 x 106 tonnes of carbon per year. The projected increase in benthos sequestration by
2060 is this value (3.6 x 106) multiplied by four, which is nearly 1. 5 x 107 tonnes of carbon per year,
thus the proportion due to sea ice losses is the new value (1.5 x 107) minus normal annual
sequestration (3.6 x 106) which equals ~107 tonnes of new carbon sequestration in the benthos
alone.
2) Alternatively Barnes (2015) details an attempt at a more accurate derivation was by measurement
of a) age spectra of each of six species from trawls and benthic images. b) the density of each species
using benthic cameras and c) annual growth (drymass-ashfree drymass –carbon proportion
calculations) increments of each species, which were then age meaned for each area. From these,
annual mass increases could be calculated for each species of each region [sum for each age of (age
proportion x density x age-meaned mass)]. For these SOI = 1.5,14.3,21.1, 0.8,0.4 and 0.8 for the six
species = 38.9mg C m2 total. Multiply up by shelf area (4.4x104 for SOI), then convert to tonnes per
square km, and finally multiply up by ~32 to convert study species to all benthos. Finally add each
regional total together. To increase conservatism of the estimate, the total was reduced down to
3x106 tonnes to account for large areas of the Ross & Weddell shelves (the largest seas) which were
not sampled but in which benthos are known to be considerably lower in density and productivity.
For more detail of method see Barnes (2015) suppl material.
Figure S1 Ratio of annual Carbon accumulation (immobilization) by C. nutti with age at SOI compared
with elsewhere. The other (Southern Ocean) locations are given in the legend and the dashed line
represents equality with SOI values.
Figure S2 Specific growth rates of 35 cheilostome bryozoan species across regions. Cellarinella watersi in
the Amundsen Sea, the slowest growing species, is shown as a black triangle. Mean specific growth
rates for temperate, tropic and polar data (A= Antarctic, R=Arctic) with literature data are from
Barnes et al. (2007) and references therein.
Fig S1
Ratio of Carbon mobilization per individual at
South Orkney shelf / South Georgia shelf
Ratio of Carbon mobilization per individual at
South Orkney shelf / Amundsen Sea shelf
Fig 1b
Fig S2
3.0
Amundsen Sea
Ross Sea
Weddell Sea
Bellingshausen Sea
0
2
4
1.2
2.5
1.1
2.0
1.5
1.0
1.0
1.6
0.9
South Georgia
1.4
1.2
1.0
0.8
0.6
6
Age / years
8
10
Ratio of Carbon mobilization per individual at
South Orkney shelf / other Antarctic shelf seas
Fig 1a
Ln (Specific growth rate.day-1)
0
-2
-4
A
R
-6
-8
Tropical
Temperate
region
Polar