Benthic Carbon Remineralization and Iron Cycling in Relation to Sea Ice Cover Along the Eastern Continental Shelf of the Antarctic Peninsula

Abstract

Rapid and profound climatic and environmental changes have been predicted for the Antarctic Peninsula with so far unknown impact on the biogeochemistry of the continental shelves. In this study, we investigate benthic carbon sedimentation, remineralization and iron cycling using sediment cores retrieved on a 400 mile transect with contrasting sea ice conditions along the eastern shelf of the Antarctic Peninsula. Sediments at comparable water depths of 330–450 m showed sedimentation and remineralization rates of organic carbon, ranging from 2.5 to 13 and 1.8–7.2 mmol C m−2 d−1, respectively. Both rates were positively correlated with the occurrence of marginal sea ice conditions (5%–35% ice cover) along the transect, suggesting a favorable influence of the corresponding light regime and water column stratification on algae growth and sedimentation rates. From south to north, the burial efficiency of organic carbon decreased from 58% to 27%, while bottom water temperatures increased from −1.9 to −0.1°C. Net iron reduction rates, as estimated from pore‐water profiles of dissolved iron, were significantly correlated with carbon degradation rates and contributed 0.7%–1.2% to the total organic carbon remineralization. Tightly coupled phosphate‐iron recycling was indicated by significant covariation of dissolved iron and phosphate concentrations, which almost consistently exhibited P/Fe flux ratios of 0.26. Iron efflux into bottom waters of 0.6–4.5 μmol Fe m−2 d−1 was estimated from an empirical model. Despite the deep shelf waters, a clear bentho‐pelagic coupling is indicated, shaped by the extent and duration of marginal sea ice conditions during summer, and likely to be affected by future climate change.

Sediment oxygen consumption in Antarctic subglacial environments

“…We can also conclude that, given the broad oxic zone in both of these sedimentary environments and the inferred low flux of reductants, such as Fe 2+ , these sediments are unlikely a source of diffusive iron supply to the iron-limited Southern Ocean. The broad oxic zone measured in this study is at least $ 10 cm thicker than marine sediments on the eastern shelf of the Antarctic Peninsula (Baloza et al 2022). Baloza et al (2022) show that these sediments with deep oxygen penetration depths (at least 4 cm) have minimal fluxes of dissolved Fe to the water column and are not significant sources of Fe to the Southern Ocean water column.…”

“…Our Whillans Grounding Zone oxygen profiles indicate that most of the sedimentary oxygen consumption takes place in the upper 2–4 cm, similar to other Southern Ocean sites where up to 99% of the total O 2 consumption occurs in the upper 2–4 cm (Jørgensen et al 2022). Our measurements show that benthic habitats beneath ice shelves and isolated from the ice shelf edge are oligotrophic and would experience significant changes in biogeochemical function with ice sheet collapse leading to higher exports of particulate organic carbon or marginal sea ice conditions (Ingels et al 2021; Baloza et al 2022). Sedimentary oxygen consumption values from Mercer Subglacial Lake are lower than other oligotrophic or high Arctic lakes.…”

“…Whillans Grounding Zone sediment (0–62 cm) contained, on average, 0.18% total organic carbon (range: 0.03–0.21%; weight percent, carbon per gram dry weight sediment; Venturelli et al 2020), comparable to many parts of the Southern Ocean (Lee et al 2019, Baloza et al 2022). This sediment total organic carbon content is noteworthy, given that the Whillans Grounding Zone location is beneath an ice shelf and ~ 700 km from the open ocean.…”

“…This sediment total organic carbon content is noteworthy, given that the Whillans Grounding Zone location is beneath an ice shelf and ~ 700 km from the open ocean. Despite this distance from potential sources of carbon inputs from photoautotrophic processes, the Whillans Grounding Zone has a sedimentary oxygen consumption rate and total organic carbon content comparable to many locations within the Southern Ocean, including those sites that are near the Antarctic Peninsula (Baloza et al 2022). These Antarctic Peninsula Southern Ocean sites have direct sedimentation of primary productivity and, potentially, runoff from the Antarctic Peninsula.…”

The Iron “Redox Battery” in Sandy Sediments: Its Impact on Organic Matter Remineralization and Phosphorus Cycling

“…The significant role of microbial Fe(III) reduction in OM degradation has been suggested by many researchers (e.g., Canfield et al, 1993;Van Cappellen and Wang, 1996;Wunder et al, 2021;Baloza et al, 2022). Here we focused on the less crystallized, easily reducible Fe(III) (extracted with 0.5 M HCl) and explored its role as electron acceptor under advective flow in coastal sands characterized by variable redox conditions.…”