Ice-sheet mass loss is one of the clearest manifestations of climate change, with Antarctica discharging mass into the ocean via melting or through calving. The latter produces icebergs that can modify ocean water properties, often at great distances from source. This affects upper-ocean physics and primary productivity, with implications for atmospheric carbon drawdown. A detailed understanding of iceberg modification of ocean waters has hitherto been hindered by a lack of proximal measurements. Here unique measurements of a giant iceberg from an underwater glider enable quantification of meltwater effects on the physical and biological processes in the upper layers of the Southern Ocean, a region disproportionately important for global heat and carbon sequestration. Iceberg basal melting erodes seasonally produced winter water layer stratification, normally forming a strong potential energy barrier to vertical exchange of surface and deep waters, while freshwater run-off increases and shoals near-surface stratification. Nutrient-rich deeper waters, incorporating meltwater loaded with terrigenous material, are ventilated to below this stratification maxima, providing a potential mechanism for alleviating critical phytoplankton-limiting components. Regional historical hydrographic data demonstrate similar stratification changes during the passage of another large iceberg, suggesting that they may be an important pathway of aseasonal winter water modification.

The stable silicon isotopic composition of siliceous sponge skeletal elements, spicules, forms a potential proxy for past dissolved silicon (DSi) concentrations of bottom waters. Field-based studies have shown that there is a non-linear relationship between the concentration of ambient DSi and both the isotopic composition (denoted by 8 30 Si) of spicules and apparent isotopic fractionation by sponges during growth. There is considerable scatter in the calibration, with some studies highlighting variation within an individual sponge, and between individuals, in both monospecific and more diverse communities. Furthermore, some derived sponge forms, including hypersilicified and carnivorous sponges, appear to have anomalous isotopic fractionation, deviating significantly from other sponges. When reconstructing past DSi, it is only possible to differentiate spicules by their morphology, which in many cases will not be taxonomically diagnostic. However, there has yet to be a systematic study of core top and downcore 8 30 Si measurements from different spicule types. Here we address that gap using spicules extracted from two sediment cores taken at the summit of the Schulz Bank, a seamount located on the Arctic Mid-Ocean Ridge between the Norwegian and Greenland Seas. Mean isotopic compositions of downcore spicules of a given morphology were similar between nearby cores and mainly did not show any significant differences. Our results did reveal a systematic difference between spicule types extracted from a given sediment horizon, and a significant difference in the downcore mean compositions, between needle-like Oxea and other morphologies. These new findings imply that picking a single spicule type is best practice for palaeoceanographic applications of sponge archives, but the choice of Oxea spicules could bias these reconstructions towards high DSi concentrations.

Accelerated mass loss from the Greenland Ice Sheet leads to retreating glaciers and enhanced freshwater runoff to adjacent coastal regions, potentially providing additional essential nutrients, such as silicon, to downstream primary producers. However, the role of fjordic sediments in modulating the supply of silicon from glacial environments to marine ecosystems remains poorly constrained, particularly for the quantification of silicon fluxes from the sediments into overlying waters in high-latitude fjordic systems. In this study, we use the concentration and stable isotopic composition of dissolved silicon in pore waters and core-top waters, and amorphous silica phases (such as glacially-derived amorphous silica) in sediments and suspended particulate matter, collected from two fjords in the southwest Greenland margin to address this knowledge gap. We combine downcore observations with core incubations and isotope mass balance approaches to assess the benthic flux of dissolved silicon and deconvolve potential contributors to this flux during early diagenesis. Our results suggest that molecular diffusion only accounts for a portion of benthic dissolved silicon transport. Relative to surrounding continental shelves and highly-productive open ocean waters, the estimated benthic dissolved silicon flux at our sites is smaller in magnitude, supporting the role of fjords as a ‘trap’ for reactive silicon in high-latitude systems.

Abstract In the Arctic and subarctic oceans, the relatively low supply of silicon (compared to other nutrients) can make it limiting for the growth of diatoms, a fundamental building block of the oceanic food web. Glaciers release large quantities of dissolved silicon and dissolvable solid amorphous silica phases into high‐latitude estuaries (fjords), but the role of these glacially‐derived silica phases in sustaining diatom growth in the coastal and open‐water sectors remains unknown. Here we show how stable and radiogenic silicon isotopes can be used together to address this question, using southwest Greenland as a case study. This study finds enhanced levels of detrital (i.e., mineral) amorphous silica, likely glacially‐sourced, sustaining a large portion of diatom growth observed off the coast, revealing how the phytoplankton community can function during high‐meltwater periods.

Greenland's fjord ecosystems are strongly influenced by meltwater discharge from glaciers. Marine-terminating glaciers can significantly enhance primary production during the melt season (compared to land-terminating glaciers), but their impact on secondary producers is not well understood. Here, we study seasonal changes in the zooplankton community (>50 mu m) and grazing rates along two fjord transects in southwest Greenland influenced by different glacier types. Zooplankton biomass was comparable between the fjords, but community composition differed during summer. Nuup Kangerlua, a predominantly marine-terminating system, was characterized by large, herbivorous copepods and a longer summer grazing period in connection with the summer bloom. Ameralik, influenced by a land-terminating glacier, was characterized by small, omnivorous copepods, particularly Microsetella norvegica and Oncaea spp., and indicated a faster post-bloom transition towards regenerated production. Local hydrographic conditions also impact copepod biomass. A station with high biomass was found in Ameralik, potentially linked to a frontal zone where fjord water masses meet, providing favorable grazing conditions. We hypothesize that a future transformation from marine- to land-terminating glaciers could result in an increased abundance of smaller copepods, as observed in Ameralik. Such a community would constitute a less lipid-rich food source for higher trophic levels.

Large icebergs (>20 km long) are responsible for most of the freshwater discharged into the Southern Ocean. We report on in situ and satellite observations made during the break-up phase around South Georgia of the giant tabular iceberg A-68A. The in situ measurements were obtained during a 4-day visit by a research vessel in February 2021, where physical, chemical and biological measurements were made at a range of distances away from the main and subsidiary icebergs. These results were compared to a far-field station 133 km away. Upstream of the iceberg field, water column structure was similar to ambient water although there was evidence of iceberg-associated phytoplankton as a likely remnant of the passage of the icebergs. Nevertheless, enhancement of primary productivity along the path of the icebergs was not resolved in either in situ or monthly mean satellite observations. There was a considerable brash-ice field moving ahead of the icebergs which limited the number of downstream sampling stations. One downstream station within 2 km of iceberg A-68P showed several ice-melt influenced features that distinguished it from most other stations. Firstly, there was a strong stratified meltwater influenced layer that reached to around 120 m. This had the effect of deepening underlying water masses, with the core of the temperature minimum layer around 50 m deeper than elsewhere. Secondly, there was evidence of rapid downward displacement of both particulate material and certain phytoplankton taxa that may be a further result of this water mass deepening. Thirdly, macronutrient profiles were altered, with concentrations of nitrate, silicic acid and phosphate characteristic of deeper layers being found closer to the surface and a dilution of the ambient nutrient pool just above the iceberg draft that we ascribe to meltwater released from basal melting. Meanwhile, nutrient recycling processes associated with organic matter remineralisation were also modified by the physical restructuring of the water column and biotic components. Finally, the ice-associated phytoplankton taxa Nitszchia/Pseudonitszchia, found in both upstream and downstream locations, were abundant at this < 2 km-distant station through melting out from the iceberg and subsequent rapid growth. Overall, we resolved alterations to water column structure, nutrient profiles and phytoplankton community composition at fine to medium scales around the iceberg field. Nevertheless, although there may have been longer term and larger scale impacts, the dynamic oceanographic environment, including the presence of a strong oceanographic front and shelf-edge processes, dominated during the collapse of A-68A.

We extend the ecological component (ECOGEM) of the carbon-centric Grid-Enabled Integrated Earth system model (cGEnIE) to include a diatom functional group. ECOGEM represents plankton community dynamics via a spectrum of ecophysiological traits originally based on size and plankton food web (phyto- and zooplankton; EcoGEnIE 1.0), which we developed here to account for a diatom functional group (EcoGEnIE 1.1). We tuned EcoGEnIE 1.1, exploring a range of ecophysiological parameter values specific to phytoplankton, including diatom growth and survival (18 parameters over 550 runs) to achieve best fits to observations of diatom biogeography and size class distribution as well as to global ocean nutrient and dissolved oxygen distributions. This, in conjunction with a previously developed representation of opal dissolution and an updated representation of the ocean iron cycle in the water column, resulted in an improved distribution of dissolved oxygen in the water column relative to the previous EcoGEnIE 1.0, with global export production (7.4 Gt C yr−1) now closer to previous estimates. Simulated diatom biogeography is characterised by larger size classes dominating at high latitudes, notably in the Southern Ocean, and smaller size classes dominating at lower latitudes. Overall, diatom biological productivity accounts for ∼20 % of global carbon biomass in the model, with diatoms outcompeting other phytoplankton functional groups when dissolved silica is available due to their faster maximum photosynthetic rates and reduced palatability to grazers. Adding a diatom functional group provides the cGEnIE Earth system model with an extended capability to explore ecological dynamics and their influence on ocean biogeochemistry.

After publication of this article [...].

On geological timescales, continental silicate weathering plays a crucial role regulating Earth’s climate. Accelerating this slow thermostat might be the key to help mitigate present-day global warming and ocean acidification through increased alkalinity generation produced by enhanced marine silicate weathering. Laboratory studies show that benthic dissolution of olivine minerals can stimulate oceanic CO2 uptake by increasing seafloor alkalinity release. Although enhanced benthic silicate weathering is an attractive solution to both CO2 problems, until now its efficiency remains unclear. This is because the intrinsic dissolution rate of silicates in the seafloor remains poorly constrained, while also the impact of secondary reactions such as carbonate precipitation and reverse silicate weathering (authigenic clay formation) remains poorly quantified. Thus, we first need to develop a detailed understanding of natural benthic silicate dissolution and the feedbacks on carbon and silicon cycles.Here, we couple two well-tested diagenetic model set-ups that resolve benthic carbon, redox and pH dynamics (organic matter degradation, re-oxidation of reduced species, equilibria reactions, carbonate dissolution and precipitation) and benthic silicon dynamics (biogenic silica dissolution, and authigenic silica precipitation) in the uppermost sediments. We use this new framework to resolve natural basalt and/or olivine weathering by explicitly accounting for the dissolution of key basalt constituents (basaltic glass, plagioclase, pyroxene, and olivine). We also account for reverse weathering through illite authigenic formation. The newly coupled model captures the observed shifts in porewater pH and carbonate system, and the dynamics of benthic alkalinity production and consumption associated with marine silicate weathering. We assess the impact of benthic redox state and basalt compositions on benthic alkalinity fluxes by performing an extensive sensitive study over the entire plausible parameter and bottom water forcing space. We find complex links between rates of benthic silicate weathering and net alkalinity production. Ultimately, we will apply the new model framework to explore the geological context of Iceland. As such, we will fully constrain natural rates of benthic silicate weathering associated to the substantial inputs of natural basalts to coastal and shelf sediments.

The protection of organic carbon through association with iron minerals (Fe R ) is an important factor in its stabilisation, long-term storage, and burial efficiency in marine sediments. However, large uncertainties still exist concerning the sources, lability, age, and composition of the organic matter associated with Fe R in natural sediments. Therefore, the timing and environmental setting of the carbon-iron bonding process remain elusive. Here we use radiocarbon (Δ 14 C) and stable isotopes (δ 13 C) of downcore bulk sedimentary organic matter, benthic foraminifera and the organic carbon fraction bound to Fe R to interrogate the source and age of the organic carbon pool associated with Fe R in Arctic marine sediments. In the Barents Sea, we find that the organic carbon associated with Fe R is younger overall than the bulk organic matter and is probably marine derived. The comparison to other investigations of OC-Fe R origins reveals that in large parts of Arctic shelf regions Fe R associated organic carbon is radiocarbon enriched and has a higher δ 13 C org value compared to the bulk sediment, irrespective of sediment depth/age. Our findings suggest a rapid and preferential binding of fresh and marine organic matter with Fe R . Hence, labile organic matter prone to decomposition is protected and stabilised, underlining the potential of the organic carbon–iron association as an efficient carbon burial mechanism.

We present a database from substantial collections of macronutrient data made on 20 oceanographic cruises, primarily from around the island of South Georgia and the Scotia Sea. This sector of the Southern Ocean was studied comprehensively during the Discovery Investigations between ∼1920 and 1950 and resulted in the hugely influential Discovery Reports. Following this pioneering research period, there was a lull of several decades prior to the British Antarctic Survey (BAS) initiation of an offshore biological programme to study the ecology of the South Atlantic sector of the Southern Ocean. These studies began in the late 1970s and have continued until the present day. Between 1980 and 2009, the programme included macronutrient measurements as part of an integrated ecosystem analysis. In addition to South Georgia and the Scotia Sea, measurements were also made in the Bellingshausen Sea and the waters to the west of the Antarctic Peninsula. Data were collected during all months of the year with the exceptions of May and June and compiled into a database. Vertical profile samples were taken from water bottles, while data along transects were collected by monitoring the ship's non-toxic seawater supply. Nutrients measured were silicate (Si(OH)4–Si), phosphate (PO4–P), nitrate (NO3–N), ammonium (NH4–N), and nitrite (NO2–N). Our database includes nutrient data along with contemporaneous temperature and salinity data where available. Further background and supporting information is included for context. The profile and underway sample data have been deposited at the UK Polar Data Centre and are publicly available in NetCDF and CSV formats from https://doi.org/10.5285/4014370F-8EB2-492B-A5F3-6DC68BF12C1E (Whitehouse et al., 2022).

The Challenger Society for Marine Science (CSMS) is the learned society for marine scientists based in the United Kingdom, with a membership of over 470 people from >100 institutions, across all academic career stages. Members of the CSMS have been interested in improving the representation of a diverse range of identities in UK marine science, largely driven by their own experiences of inequity in the discipline, such as the challenges faced by women (Hendry et al., 2020). The structural exclusion of individuals by race, sex, ethnicity, social class, disability, sexuality, and the compound sum of these factors can result in a lack of diversity during recruitment and poor retention. Since 2021, CSMS has formed the first UK-wide equity, diversity, inclusion, and accessibility (EDIA) working group for marine scientists, with the aim of coordinating action to address the causes of exclusion and to improve representation across the discipline. The group of 25 volunteers meets each month to discuss a topical agenda, and the chair of the working group sits on the council of CSMS, providing EDIA input from the working group on society-wide strategic decisions.

Oceanographic changes adjacent to Antarctica have global climatic and ecological impacts. However, this is the most challenging place in the world to obtain marine data due to its remoteness and inhospitable nature, especially in winter. Here, we present more than 2000 Conductivity-Temperature-Depth (CTD) profiles and associated water sample data collected with (almost uniquely) full year-round coverage from the British Antarctic Survey Rothera Research Station at the west Antarctic Peninsula. Sampling is conducted from a small boat or a sled, depending on the sea ice conditions. When conditions allow, sampling is twice weekly in summer and weekly in winter, with profiling to nominally 500 m and with discrete water samples taken at 15 m water depth. Daily observations are made of the sea ice conditions in the area. This paper presents the first 20 years of data collection, 1997-2017. This time series represents a unique and valuable resource for investigations of the high-latitude ocean’s role in climate change, ocean/ice interactions, and marine biogeochemistry and carbon drawdown.

Many studies use traditional alkaline leach digestions to quantify biogenic silica (bSiO2) in sediments. Studies from river-plume systems demonstrate this methodology precludes information on other operational Si reactive pools, missing potentially valuable information on early diagenetic products. We build on previous studies by broadly examining the reactive Si pools in Mississippi River plume-influenced coastal sediments. The magnitude of Si released among operational pools across the region revealed large spatial variations in the conservation of detrital materials. Contrary to other analyses using different approaches, we suggest the availability of detrital sourced components (i.e. Al, Fe and Mn) may be a factor limiting authigenesis and resulting Si storage capacity in coastal sediments by this chemical mechanism. Overall, these data suggest authigenic precipitates may be forming as a function of bSiO2 accumulation, thereby implying that bSiO2 acts as the primary substrate for formation of authigenic products. The amount of authigenic Si products, relative to bSiO2, appears to be larger in this region than other systems studied to date, and this may be due to regional eutrophication which has led to an increase in sediment bSiO2 compounding the substrate available for authigenic precipitates. Thus, regions which have all experienced increased sediment bSiO2 accumulation coincident with eutrophication, may be primed for substantial authigenic product formation and increased Si sequestration.

The biological carbon pump is responsible for much of the decadal variability in the ocean carbon dioxide (CO2) sink, driving the transfer of carbon from the atmosphere to the deep ocean. A mechanistic understanding of the ecological drivers of particulate organic carbon (POC) flux is key both to the assessment of the magnitude of the ocean CO2 sink and for accurate predictions as to how this will change with changing climate. This is particularly important in the Southern Ocean, a key region for the uptake of CO2 and the supply of nutrients to the global thermocline. In this study we examine sediment-trap-derived particle fluxes and stable isotope signatures of carbon (C), nitrogen (N), and biogenic silica (BSi) at a study site in the biologically productive waters of the northern Scotia Sea in the Southern Ocean. Both deep (2000 m) and shallow (400 m) sediment traps exhibited two main peaks in POC, particulate N, and BSi flux: one in austral spring and one in summer, reflecting periods of high surface productivity. Particulate fluxes and isotopic compositions were similar in both deep and shallow sediment traps, highlighting that most remineralisation occurred in the upper 400 m of the water column. Differences in the seasonal cycles of isotopic compositions of C, N, and Si provide insights into the degree of coupling of these key nutrients. We measured increasing isotopic enrichment of POC and BSi in spring, consistent with fractionation during biological uptake. Since we observed isotopically light particulate material in the traps in summer, we suggest physically mediated replenishment of lighter isotopes of key nutrients from depth, enabling the full expression of the isotopic fractionation associated with biological uptake. The change in the nutrient and remineralisation regimes, indicated by the different isotopic compositions of the spring and summer productive periods, suggests a change in the source region of material reaching the traps and associated shifts in phytoplankton community structure. This, combined with the occurrence of advective inputs at certain times of the year, highlights the need to make synchronous measurements of physical processes to improve our ability to track changes in the source regions of sinking particulate material. We also highlight the need to conduct particle-specific (e.g. faecal pellets, phytoplankton detritus, zooplankton moults) isotopic analysis to improve the use of this tool in assessing particle composition of the sinking material and to develop our understanding of the drivers of biogeochemical fluxes.

A key challenge in understanding carbon cycling in the Southern Ocean is disentangling long-term responses from significant spatial and temporal variability in physical and biogeochemical parameters. As such, there is a critical need for regional long-term observations for the model validation and testing needed for a better mechanistic understanding of primary production drivers. We present a new macronutrient data product for the South Atlantic sector of the Southern Ocean, including depth profiles and underway surface measurements of nitrate, nitrite, ammonium, phosphate, silicic acid, temperature and salinity, collected from 1980 to 2009 and covering most months of the year (https://doi.org/10/h3qr). Using this data product, we explore the differences in shallow and deep-water nutrients around the island of South Georgia that are observed between years. We discuss both the biological and physical driving mechanisms behind this variability, which are interconnected with climate feedbacks. The new data product provides an unprecedented view of biogeochemical cycling in biologically productive regions of the Southern Ocean across a critical period in recent climate history, and illustrates the importance of building these scientifically valuable and FAIR (findability, accessibility, interoperability, and reusability) observational datasets.