Physical weathering intensity controls bioavailable primary iron(II) silicate content in major global dust sources

The speciation of iron (Fe) reaching the ocean, for instance in wind‐blown dust and coastal sediments, impacts its bioavailability to phytoplankton and its impact on atmospheric carbon dioxide (CO2) and climate. For dust reaching the Southern Ocean, primary Fe(II) silicates that are physically weathered from bedrock are highly bioavailable compared to more chemically weathered, Fe(III)‐rich species, suggesting that weathering in dust source regions impacts the bioavailable Fe supply. However, this phenomenon has not been studied in other important terrestrial Fe sources, where weathering regimes and source geology vary. Here, we use Fe X‐ray absorption spectroscopy on marine sediment cores to show that major global dust and sediment sources impacted by high physical weathering contain abundant primary minerals and thus are overlooked as a source of highly bioavailable Fe globally. Thus, it is important to consider the role of physical versus chemical weathering in Fe fertilization and biotic CO2 cycling

Silica cycling and isotopic composition in northern Marguerite Bay on the rapidly-warming western Antarctic Peninsula

The Southern Ocean is a key region for silica (Si) cycling, and the isotopic signatures established here influence the rest of the world's oceans. The climate and ecosystem of the Southern Ocean are changing rapidly, with the potential to impact Si cycling and isotope dynamics. This study examines high-resolution time-series dataset of dissolved Si concentrations and isotopic signatures, particulate Si concentrations and diatom speciation at a coastal site on the western Antarctic Peninsula (WAP), in order to characterise changes in Si cycling with respect to changes occurring in productivity and diatom assemblages. Dissolved and particulate Si phases reflect the dominant control of biological uptake, and combined with isotopic fractionation were consistent with a season of low/intermediate productivity. Biogenic Si is tightly coupled to both chlorophyll and particulate organic carbon at the sampling site, consistent with diatom-dominated phytoplankton assemblages along the WAP. Variability in diatom speciation has a negligible impact on the isotopic signature of dissolved Si in surface waters, although this is unlikely to hold for sediments due to differential dissolution of diatom species. A continued decline in diatom productivity along the WAP would likely result in an increasing unused Si inventory, which can potentially feed back into Si-limited areas, promoting diatom growth and carbon drawdown further afield

Controls on dissolved and particulate iron distribution in surface waters of the Western Antarctic Peninsula shelf

The Western Antarctic Peninsula (WAP) displays high but variable productivity and is also undergoing rapid change. Long-term studies of phytoplankton communities and primary production have suggested transient limitation by the micronutrient iron (Fe), but to date no data have been available to test this hypothesis. Here, we present the first spatially extensive, multi-year measurements of dissolved and particulate trace metals in surface waters to investigate the key sources and sinks of Fe in the central WAP shelf. Surface samples of dissolved and particulate metals were collected throughout the 700 × 200 km grid of the Palmer Long-Term Ecological Research program in three consecutive austral summers (2010 − 2012). Iron concentrations varied widely. Both dissolved and particulate Fe were high in coastal waters (up to 8 nmol kg− 1 and 42 nmol kg− 1, respectively). In contrast, very low Fe concentrations (< 0.1 nmol kg− 1) were widespread in mid- to outer-shelf surface waters, especially in the northern half of the sampling grid, suggesting possible Fe limitation of primary production on the shelf. Sea ice and dust inputs of Fe were minor, although their relative importance increased with distance from shore due to the larger near-shore sources. Sedimentary inputs were inferred from manganese distributions; these were more significant in the northern portion of the grid, and showed interannual variation in intensity. Overall, the interannual distribution of Fe was most closely correlated to that of meteoric water (glacial melt and precipitation). Although the Fe concentrations and relative contributions of dissolved and particulate Fe attributed to meltwater were variable throughout the sampling region, increasing glacial meltwater flux can be expected to increase the delivery of Fe to surface waters of the coastal WAP in the future

Continued glacial retreat linked to changing macronutrient supply along the West Antarctic Peninsula

At the West Antarctic Peninsula (WAP), continued atmospheric and oceanic warming is causing significant physical and biogeochemical changes to glaciers and the marine environment. We compare sediment sources and drivers of macronutrient distributions at two bays along the WAP during austral summer 2020, using radioactive radium and stable oxygen isotopes to trace sedimentary influences and quantify different freshwater inputs. In the Ryder Bay, where the Sheldon Glacier is marine-terminating, radium activities at the sediment-water interface indicate considerable benthic mixing. Using radium isotope activity gradients to resolve radium and macronutrient fluxes, we find buoyant meltwater proximal to the glacier drives vigorous mixing of sediment and entrainment of macronutrient deep waters, on the order of 2.0 × 105 mol d−1 for nitrate. Conversely, in the Marian Cove, where the Fourcade Glacier terminates on land, low salinities and oxygen isotopes indicate a meltwater-rich surface layer <1 m thick and rich in sediment, and strong vertical mixing to the seafloor. A continued shift to land-terminating glaciers along the WAP may have a significant impact upon nutrient and sediment supply to the euphotic zone, with impacts upon primary productivity and carbon uptake efficiency. The future of primary production, carbon uptake, and food web dynamics is therefore linked to glacier retreat dynamics in the many fjords along the WAP

CRLF3 plays a key role in the final stage of platelet genesis and is a potential therapeutic target for thrombocythemia.

The process of platelet production has so far been understood to be a 2-stage process: megakaryocyte maturation from hematopoietic stem cells followed by proplatelet formation, with each phase regulating the peripheral blood platelet count. Proplatelet formation releases into the bloodstream beads-on-a-string preplatelets, which undergo fission into mature platelets. For the first time, we show that preplatelet maturation is a third, tightly regulated, critical process akin to cytokinesis that regulates platelet count. We show that deficiency in cytokine receptor-like factor 3 (CRLF3) in mice leads to an isolated and sustained 25% to 48% reduction in the platelet count without any effect on other blood cell lineages. We show that Crlf3-/- preplatelets have increased microtubule stability, possibly because of increased microtubule glutamylation via the interaction of CRLF3 with key members of the Hippo pathway. Using a mouse model of JAK2 V617F essential thrombocythemia, we show that a lack of CRLF3 leads to long-term lineage-specific normalization of the platelet count. We thereby postulate that targeting CRLF3 has therapeutic potential for treatment of thrombocythemia

Equity at sea: Gender and inclusivity in UK sea-going science

Today, we can celebrate a strong representation of women in sea-going science in the United Kingdom, providing positive role models for early-career female marine scientists. However, women continue to face challenges to their progression in their marine science careers, especially those who are also members of other under-represented groups. In this article we consider gender equity and equality in participation and leadership in sea-going marine science in the UK, discussing successes and lessons learned for the future. After a brief history of UK women in ocean science, and a summary of some recent advances in gender equality, we look at further areas in need of improvement, and ask whether successes in improved gender equality can be transferred to tackling other forms of under-representation in sea-going science

The biogeochemical impact of glacial meltwater from Southwest Greenland

Biogeochemical cycling in high-latitude regions has a disproportionate impact on global nutrient budgets. Here, we introduce a holistic, multi-disciplinary framework for elucidating the influence of glacial meltwaters, shelf currents, and biological production on biogeochemical cycling in high-latitude continental margins, with a focus on the silica cycle. Our findings highlight the impact of significant glacial discharge on nutrient supply to shelf and slope waters, as well as surface and benthic production in these regions, over a range of timescales from days to thousands of years. Whilst biological uptake in fjords and strong diatom activity in coastal waters maintains low dissolved silicon concentrations in surface waters, we find important but spatially heterogeneous additions of particulates into the system, which are transported rapidly away from the shore. We expect the glacially-derived particles – together with biogenic silica tests – to be cycled rapidly through shallow sediments, resulting in a strong benthic flux of dissolved silicon. Entrainment of this benthic silicon into boundary currents may supply an important source of this key nutrient into the Labrador Sea, and is also likely to recirculate back into the deep fjords inshore. This study illustrates how geochemical and oceanographic analyses can be used together to probe further into modern nutrient cycling in this region, as well as the palaeoclimatological approaches to investigating changes in glacial meltwater discharge through time, especially during periods of rapid climatic change in the Late Quaternary

Comparative roles of upwelling and glacial iron sources in Ryder Bay, coastal western Antarctic Peninsula

Iron (Fe) is an essential micronutrient for phytoplankton, and is scarce in many regions including the open Southern Ocean. The western Antarctic Peninsula (WAP), an important source region of Fe to the wider Southern Ocean, is also the fastest warming region of the southern hemisphere. The relative importance of glacial versus marine Fe sources is currently poorly constrained, hindering projections of how changing oceanic circulation, productivity, and glacial dynamics may affect the balance of Fe sources in this region.Dissolved and total dissolvable Fe concentrations were measured throughout the summer bloom period at a coastal site on the WAP. Iron inputs to the surface mixed layer in early summer were strongly correlated with meteoric meltwater from glaciers and precipitation. A significant source of Fe from underlying waters was also identified, with dissolved Fe concentrations of up to 9.5 nM at 200 m depth. These two primary Fe sources act on different timescales, with glacial sources supplying Fe during the warm summer growing period, and deep water replenishing Fe over annual periods via deep winter mixing.Iron supply from deep water is sufficient to meet biological demand relative to macronutrient supply, making Fe limitation unlikely in this area even without additional summer Fe inputs from glacial sources. Both glacial and deep-water Fe sources may increase with continued climate warming, potentially enhancing the role of the WAP as an Fe source to offshore waters

The effects of Cu and Fe availability on the growth and Cu : C ratios of marine diatoms

We investigated the effects of copper (Cu) and iron (Fe) availability on the growth rates, cellular Cu content, and steady-state Cu uptake rates of eight species of centric diatoms (coastal and oceanic strains). Whereas Fe and Cu availability had a significant effect on the growth rates of both costal and oceanic diatoms, an interaction between Fe and Cu availability and growth rates was only observed for the oceanic diatoms. Determination of cellular Cu : carbon (C) quotas using the radiotracers (67)Cu and (14)C revealed that under Cu-sufficient conditions oceanic diatoms had elevated Cu : C ratios relative to coastal strains, regardless of Fe availability. Two species (one oceanic and one coastal) significantly increased their Cu demands in response to Fe limitation, indicating upregulation of the Cu-dependent high-affinity Fe uptake system in these organisms. The changes in cellular Cu : C ratios were accompanied by variations in steady-state Cu uptake rates. Thus, in some cases Cu uptake rates appear to be regulated by the cell in response to Fe availability. Rates of Cu acquisition also responded significantly to Cu variability. The variation in Cu uptake was more closely correlated with changes in total Cu concentration in the medium than in inorganic, free Cu concentrations, implying that organic Cu complexes may be bioavailable to diatoms. These findings indicate a greater biological role for Cu than was previously thought in open ocean regions

Use of radium isotopes to estimate mixing rates and trace sediment inputs to surface waters in northern Marguerite Bay, Antarctic Peninsula

In the western Antarctic Peninsula region, micronutrient injection facilitates strong plankton blooms that support productive food webs, unlike large areas of the low-productivity Southern Ocean.We use naturally occurring radioisotopes of radium to constrain rates of chemical fluxes into Ryder Bay (a small coastal embayment in northern Marguerite Bay), and hence to evaluate possible sources of sediment-derived micronutrients and estimate sediment-ocean mixing rates. We present the first coupled, short-lived radium isotope (223Ra and 224Ra) measurements from Antarctic waters, both present at very low activities (mean 0.155 and 3.21 dpmm-3, respectively), indicating much lower radium inputs than in other coastal environments. Longer-lived 228Ra activity was also lower than existing nearshore values, but higher than open ocean waters, indicating some degree of coastal radium input on timescales exceeding the week-to-month range reflected by 223Ra and 224Ra. Using a simple diffusion model along a shore to mid-bay transect, effective horizontal eddy diffusivity estimates ranged from 0.22–0.83m2 s-1 from 223Ra and 224Ra, respectively, much lower than already-low mixing estimates for the Southern Ocean. Significant radium enrichment and much faster mixing (18m2 s-1) was found near a marine-terminating glacier and consequently any sediment-derived micronutrient inputs in this location are more probably dominated by glacial processes than groundwater, land runoff, or marine sediment sources