Circumpolar Deep Water and Shelf Sediments Support Late Summer Microbial Iron Remineralization

Smith, Abigail J. R.; Ratnarajah, Lavenia; Holmes, Thomas M.; Wuttig, Kathrin; Townsend, Ashley T.; Westwood, Karen J.; Cox, Martin J.; Bell, Elanor M.; Nicol, Stephen; Lannuzel, Delphine

doi:10.1029/2020gb006921

Cited by 10 publications

(20 citation statements)

References 119 publications

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“…Analysis of dFe was previously described in Smith et al (2021), following methods developed in Wuttig et al (2019). Briefly, dissolved trace elements were preconcentrated from seawater using an offline seaFAST preconcentration system (SC-4 DX seaFAST S2/pico, ESI, Omaha, NE, USA) and concentrations were determined using a Thermo Fisher Scientific ELEMENT 2 SF-ICP-MS (Central Science Laboratory, University of Tasmania; medium resolution mode, Wuttig et al, 2019).…”

Section: Dissolved Ironmentioning

confidence: 99%

“…Briefly, dissolved trace elements were preconcentrated from seawater using an offline seaFAST preconcentration system (SC-4 DX seaFAST S2/pico, ESI, Omaha, NE, USA) and concentrations were determined using a Thermo Fisher Scientific ELEMENT 2 SF-ICP-MS (Central Science Laboratory, University of Tasmania; medium resolution mode, Wuttig et al, 2019). Detailed methodology, certified reference material analyses, blanks, and detection limits for the ENRICH dFe dataset are given in Smith et al (2021).…”

Section: Dissolved Ironmentioning

confidence: 99%

“…At the slope, DSW and mCDW extending from the shelf break were carried west by the Antarctic Slope Current (ASC, Williams et al, 2010). The full distribution of major oceanographic fronts and water masses during the study period are described by Smith et al (2021).…”

Section: Complexation Of Fe In Waters Across the Mertz Regionmentioning

confidence: 99%

“…Free ligand (L') and total ligand-dissolved Fe ratio (Lt:dFe) profiles from the entire survey, coloured by chlorophyll fluorescence. Euphotic depth is represented by grey shaded box at a maximum depth of 55 m. Smith et al 10.3389/fmars.2022.948772 Positive correlations between dFe and AOU suggest bacteria remineralise Fe in AASW (R = 0.54, P < 0.05) and mCDW (R = 0.64, P < 0.05) along the slope (Smith et al, 2021). High levels of bacterial production at Stations 14 and 16, is also associated with sea-ice melt (Section 3.2).…”

Section: Chlorophyll Fluorescence and Bacterial Productionmentioning

confidence: 99%

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Identifying potential sources of iron-binding ligands in coastal Antarctic environments and the wider Southern Ocean

et al. 2022

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The availability of iron (Fe) to marine microbial communities is enhanced through complexation by ligands. In Fe limited environments, measuring the distribution and identifying the likely sources of ligands is therefore central to understanding the drivers of marine productivity. Antarctic coastal marine environments support highly productive ecosystems and are influenced by numerous sources of ligands, the magnitude of which varies both spatially and seasonally. Using competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) with 2-(2-thiazolylazo)-p-cresol (TAC) as a competing artificial ligand, this study investigates Fe-binding ligands (FeL) across the continental shelf break in the Mertz Glacier Region, East Antarctica (64 - 67°S; 138 - 154°E) during austral summer of 2019. The average FeL concentration was 0.86 ± 0.5 nM Eq Fe, with strong conditional stability constants (Log KFeL) averaging 23.1 ± 1.0. The strongest binding ligands were observed in modified circumpolar deep water (CDW), thought to be linked to bacterial Fe remineralisation and potential siderophore release. High proportions of excess unbound ligands (L’) were observed in surface waters, as a result of phytoplankton Fe uptake in the mixed layer and euphotic zone. However, FeL and L’ concentrations were greater at depth, suggesting ligands were supplied with dissolved Fe from upwelled CDW and particle remineralisation in benthic nepheloid layers over the shelf. Recent sea-ice melt appeared to support bacterial production in areas where Fe and ligands were exhausted. This study is included within our newly compiled Southern Ocean Ligand (SOLt) Collection, a database of publicly available Fe-binding ligand surveys performed south of 50°S. A review of the SOLt Collection brings attention to the paucity of ligand data collected along the East Antarctic coast and the difficulties in pinpointing sources of Fe and ligands in coastal environments. Elucidating poorly understood ligand sources is essential to predicting future Fe availability for microbial populations under rapid environmental change.

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Section: Dissolved Ironmentioning

confidence: 99%

Section: Dissolved Ironmentioning

confidence: 99%

Section: Complexation Of Fe In Waters Across the Mertz Regionmentioning

confidence: 99%

Section: Chlorophyll Fluorescence and Bacterial Productionmentioning

confidence: 99%

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Identifying potential sources of iron-binding ligands in coastal Antarctic environments and the wider Southern Ocean

et al. 2022

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“…Additionally, this information may be useful when investigating hypotheses on the role of whales in the ecosystem, for which overall movements through an area might be compared with phytoplankton, bacteria, and biogeochemistry e.g. iron concentrations (Smith et al, 2021). Natural behaviours and movements may also inform assessment of anthropogenic impacts, for example, by providing baseline data against which impacts can be evaluated (Lomac-MacNair and Smultea, 2016).…”

Section: Introductionmentioning

confidence: 99%

Surfacing rates, swim speeds, and patterns of movement of Antarctic blue whales

et al. 2023

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During three surveys in the austral summers of 2013, 2015, 2019, data on Antarctic blue whale blow rates, dive times, swim speeds, and broadscale movements were collected using video photogrammetric tracking and intra-voyage photo-identification. A total of 24.4 hours of video observations were suitable for blow interval or movement analysis. Similar to other blue whale populations, Antarctic blue whale dive behaviour comprised a sequence of short dives followed by a long dive with a mean dive time for short dives of 17.6 s, and a mean long dive time of 189.3 s. Two separate methods were used to estimate the average blow rate for Antarctic blue whales, giving estimates of 59.7 and 63.2 blows per hour. The overall mean swim speed over the course of all suitable video track segments was 1.59 ms-1, but there were significant differences between years in the mean of the overall movement rate for each track; average movement rates were lower in 2015 compared to 2013 and 2019 (0.90 ms-1, 1.84 and 1.55 ms-1 respectively), with higher rates of turning in 2015. In 2019, there was faster overall movement through the study area in a consistent direction. The total number of photo-identified blue whales re-sighted intra-season in 2013 was nine (out of 50 identified individuals); in 2015 it was seven (out of 46); in 2019 two (out of 25). Whales remained for several days with little overall movement within the 2015 study area, whereas they were moving through the study area in 2019, which would explain the low number of intra-season resights. The predominant heading in 2019 was towards the area of Antarctic blue whale concentrations at the entrance to the Ross Sea observed in previous years. The photo-identification data also show a high proportion of resighted whales with coherent movements. This suggests that Antarctic blue whales might travel together, at least over periods of several days or sometimes up to a month. The differences between behaviours in 2015 and 2019 in particular may be related to differences in the characteristics of krill swarms between the study areas.

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Biological uptake, water mass mixing and scavenging prevent transport of manganese-rich waters from the Antarctic shelf

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Merwe

Wuttig

et al. 2022

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Manganese (Mn) is an essential element for photosynthetic life, yet concentrations in Southern Ocean open waters are very low, resulting from biological uptake along with limited external inputs. At southern latitudes, waters overlying the Antarctic shelf are expected to have much higher Mn concentrations due to their proximity to external sources such as sediment and sea ice. In this study, we investigated the potential export of Mn-rich Antarctic shelf waters toward depleted open Southern Ocean waters. Our results showed that while high Mn concentrations were observed over the shelf, strong biological uptake decreased dissolved Mn concentrations in surface waters north of the Southern Antarctic Circumpolar Current Front (< 0.1 nM), limiting export of shelf Mn to the open Southern Ocean. Conversely, in bottom waters, mixing between Mn-rich Antarctic Bottom Waters and Mn-depleted Low Circumpolar Deep Waters combined with scavenging processes led to a decrease in dissolved Mn concentrations with distance from the coast. Subsurface dissolved Mn maxima represented a potential reservoir for surface waters (0.3 -0.6 nM). However, these high subsurface values decreased with distance from the coast, suggesting these features may result from external sources near the shelf in addition to particle remineralization. Overall, these results imply that the lower-than-expected lateral export of trace metal-enriched waters contributes to the extremely low (< 0.1 nM) and potentially co-limiting Mn concentrations previously reported further north in this Southern Ocean region.

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Circumpolar Deep Water and Shelf Sediments Support Late Summer Microbial Iron Remineralization

Cited by 10 publications

References 119 publications

Identifying potential sources of iron-binding ligands in coastal Antarctic environments and the wider Southern Ocean

Identifying potential sources of iron-binding ligands in coastal Antarctic environments and the wider Southern Ocean

Surfacing rates, swim speeds, and patterns of movement of Antarctic blue whales

Biological uptake, water mass mixing and scavenging prevent transport of manganese-rich waters from the Antarctic shelf

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