Blue carbon storage in a sub-Antarctic marine protected area

Abstract

High-latitude ecosystems have been overlooked in carbon budgets, which traditionally focus on mangroves, salt marshes, and seagrasses. The benthic assemblages and their Nature Contributions to People in Namuncurá - Burdwood Bank I and II, two offshore sub-Antarctic Marine Protected Areas (MPAs), are the conservation values. Here we show that the carbon reservoirs of these MPAs can be greater than those of their Antarctic counterparts, which, together with their extension, emphasize the need to maintain their protected status. Considering their total area, these MPAs stored in biomass 52,085.78 Mg C, corresponding 34,964.16 Mg to organic carbon (OC) and 17,121.62 Mg to inorganic carbon (IC). Surficial sediments stored 933,258,336 Mg C with 188,089,629 Mg of OC and 745,168,707 Mg of IC. However, when accounting for CO₂ production through CaCO₃ precipitation, the IC fractions decrease to 3,150.37 Mg C and 137,111,042 Mg C for biomass and sediments, respectively. We assume low sediment deposition due to the oceanic location, as direct sedimentation rates for these areas are unavailable. Most blue carbon assessments have focused solely on OC, despite the formation of CaCO₃ releases CO₂, decreasing net carbon storage. We compared various approaches for incorporating carbonates into carbon estimations. These results underscore the importance of including IC into carbon assessments and highlights the importance of sub-Antarctic benthic ecosystems as nature-based solutions to climate change.

Keywords: Blue carbon; Carbonates; Marine protected areas; Nature contributions to people.

Fig. 1

Areas and sampled locations: Beagle Channel (BC), Atlantic Shelf of Tierra del Fuego (AS) and Marine Protected Area Namuncurá – Burdwood Bank I and Burdwood Bank II (BB). The different colours indicate the origins of the samples used for the different analyses. IA isotopic analysis, LOI loss on ignition method.

Fig. 2

Carbon contents in sediments. (A) Percentage of inorganic carbon of dry mass: only samples analysed by both LOI and IA are shown. (B) percentage of organic matter of dry mass by the LOI method; (C) percentage of organic carbon of dry mass by the IA method; diamonds are outliers.

Fig. 3

Carbon stock in sediments. (A) organic carbon and (B) inorganic carbon stock (n = 10 in BC, n = 4 in AS, n = 26 in BB). Diamonds are outliers.

Fig. 4

Carbon stock in biomass. Comparisons between BB and BC. AS was included as a point because of the small sample size, n = 2). Diamonds are outliers. Stars represent the raw data.

Fig. 5

Organic and inorganic carbon per phylum. Panels (A) and (B) show the relative percentages of organic and inorganic carbon per phylum across the four locations. Panels (C) and (D) depict the stock of carbon at each sampling station arranged by location. BC Beagle Channel, AS Atlantic coast, S: BB slope, P: BB plateau. “Broken pieces” refers to parts of largely live animals fragmented by trawl, mainly sponges and bryozoans.