Transport of dissolved black carbon from the Prydz Bay Shelf, Antarctica to the deep Southern Ocean

Abstract

Dissolved black carbon (DBC) is one of the largest pools of molecularly identifiable carbon in the ocean. In the deep ocean, DBC appears to persist for millennia, whereas it can be rapidly degraded by sunlight in surface waters. In Antarctica, the downward transport of dense shelf water (DSW) exports a massive volume of water to the deep Southern Ocean each year. If this sinking DSW is enriched in DBC, it may allow a route for DBC to escape degradation by sunlight in the surface ocean and become sequestered in the deep waters of the global ocean. To investigate this possibility, we quantified dissolved organic carbon (DOC), DBC, and ancillary properties in the waters of an Antarctic shelf sea (Prydz Bay) and adjacent waters. DBC concentrations in Prydz Bay DSW (1.2 ± 0.3 μmol L−1) were elevated compared to those in circumpolar deep water (0.49 ± 0.07 μmol L−1). The water column distribution of DBC in Prydz Bay suggested that sediments were the main source of DBC in DSW. A mixing model incorporating seawater oxygen isotopes (H2δ18O) indicated that Prydz Bay DSW transported DBC and DOC into the deep Southern Ocean. We estimate that the downward transport of DSW from Prydz Bay could contribute 4–9% (66–150 Gg yr−1) and 2–4% (3700–8500 Gg yr−1) to the DBC and DOC concentrations in Antarctic Bottom Water, respectively. Thus, the downward transport of DBC along the Antarctic shelf/slope is likely a significant source of DBC to the deep waters of the Southern and Global Ocean.

Fate of dissolved black carbon in the deep Pacific Ocean

“…The DBC concentrations in the deep water in the subtropical South Pacific (Fig. 1b ) are similar to those in CDW in the Southern Ocean (5.9 ± 0.8 µgC L −1 ), which were determined by the same BPCA method 42 . The decrease in the DBC concentration with deep-ocean meridional circulation (Fig.…”

“…A major origin of DBC in CDW is related to the meridional overturning circulation and is therefore associated with North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) 41 . At least some of the DBC in AABW is reported to be derived from Antarctic shelf sediments 42 . The DBC concentrations in the deep water in the subtropical South Pacific (Fig.…”

Utilization of Soot and 210 Po-210 Pb Disequilibria to Constrain Particulate Organic Carbon Fluxes in the Northeastern South China Sea

“…In addition, previous studies have shown that the higher DBC concentrations in the upper 100 m of the SCS (avg. 0.97 ± 0.22 µmol-C L −1 , n = 79) (Fang et al, 2017) compared to those observed in Prydz Bay, Antarctica (0.75 ± 0.26 µmol-C L −1 , n = 17, Fang et al, 2018) should largely result from the enhanced emissions around the SCS.…”

“…Around 34 ± 26% of biomass-generated BC (40-215 Tg yr −1 , including dissolved BC, i.e., DBC and PBC) gets into the oceans via river discharge (Jones et al, 2020). These reports indicate that the ocean is an important reservoir of BC (Masiello and Druffel, 1998;Fang et al, 2018). With an increase in BC emissions from the increase in both fossil fuel combustion and fires emissions, the riverine BC is expected to increase the refractory carbon pool in abyssal oceans (Cheng et al, 2008;Dittmar et al, 2012).…”

A Continental Shelf Pump for CO2 on the Adélie Land Coast, East Antarctica

“…This signal is transferred to DSW by deep convection in winter (Shadwick et al, 2014). As a result, DSW outflows are also likely enriched in organic matter, as observed in the dense overflows from the Ross Sea (Bercovici et al, 2017) and Cape Darnely and Prydz Bay in East Antarctica (Fang et al, 2018; Murakami et al, 2020).…”