Phytoplankton ecology and biogeochemistry of the warming Antarctic sea-ice zone

Marine productivity along the western Antarctic Peninsula (WAP) is declining. The WAP is site of the fastest regional warming in the southern hemisphere, and has experienced atmospheric and oceanic temperature increases leading to increased glacial inputs and reduced winter sea-ice cover. Sea-ice is a key link between climate and phytoplankton production, as melting sea-ice stratifies the water column and provides a source of micronutrients to surface waters. Reductions in ice cover have been accompanied by declining chlorophyll (chl; a proxy for phytoplankton biomass), and a shift to smaller cell sizes in phytoplankton communities. These reductions have implications for carbon drawdown and production available to higher trophic levels. However, little is known about phytoplankton shifts at the community level, as existing studies are based on satellite records and photosynthetic pigment analyses. To elucidate the nature of the changes within phytoplankton assemblages, high-resolution time-series data of diatom speciation are coupled to environmental data from five years in Ryder Bay (Adelaide Island, WAP). Long-term monitoring at this site by the British Antarctic Survey has identified a strong relationship between chl and water column stratification, and this study spans a wide range of physical conditions and biological production. By comparing high- and low-chl phytoplankton assemblages, this study investigates the mechanisms underlying productivity changes and the manner in which these changes impact nutrient cycling, drawdown and trophic transfer. The results presented here are the first full season in-situ records documenting differences in phytoplankton and diatom assemblages between highand low-chl years. The primary difference between chl conditions is a dramatic decline in diatom abundance. This analysis indicates that the mechanism producing low-chl seasons is less stratified surface waters, where light levels are much more variable than in high-chl years. Overall production is reduced, and small increases are seen in biomass of prymnesiophytes, which are better adapted to variable light. These shifts in phytoplankton composition and size structure are consistent with a southward propagation of observed climate change effects. Within the diatom community, changes in seasonal succession and a decrease in species richness occurred following low winter sea-ice. As the main component of high productivity and that most efficiently transferred to higher trophic levels, variation in diatom production due to environmental conditions is a mechanism to explain the observed WAP ecosystem changes and chl decline. Changes in phytoplankton stocks and composition also affect nutrient use, and here the use of silicon and iron (Si and Fe, respectively, which limit productivity in large areas of the Southern Ocean) is investigated. Seasonal Si budgets estimated from Si isotopes indicate a 40 – 70% decline in Si use between high-chl and intermediate-chl years, in agreement with other indices of productivity. The consequences of reduced demand and changing supply suggest future accumulation of Si in WAP surface waters. This should increase Si export away from the WAP shelf, which may act as a mechanism to enhance productivity and carbon drawdown in the wider Southern Ocean. Sources of Fe were assessed by direct measurement and naturally occurring radioisotopes of radium. These reveal significant inputs at the surface (due to glacial sources) and to deep waters (from shelf/slope sediments), which dominate supply to the surface mixed layer at different times. Iron availability and nutrient drawdown indicate that Fe is supplied to WAP surface waters in excess of biological demand. Projected changes to Fe sources and sinks indicate that continued warming will increase the WAP Fe inventory. As for Si, this excess Fe may also be advected away from the shelf, making this region a net Fe source to the Southern Ocean

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

226Ra determination via the rate of 222Rn ingrowth with the Radium Delayed Coincidence Counter (RaDeCC)

ISI Document Delivery No.: 278HU Times Cited: 0 Cited Reference Count: 23 Cited References: Annett AL, 2013, ANTARCT SCI, V25, P445, DOI 10.1017/S0954102012000892 Bourquin M, 2011, MAR CHEM, V126, P132, DOI 10.1016/j.marchem.2011.05.001 Burnett WC, 2006, SCI TOTAL ENVIRON, V367, P498, DOI 10.1016/j.scitotenv.2006.05.009 BUTTS J, 1988, MAR CHEM, V25, P349, DOI 10.1016/0304-4203(88)90115-6 Charette MA, 2012, LIMNOL OCEANOGR-METH, V10, P451, DOI 10.4319/lom.2012.10.451 Charette MA, 2001, LIMNOL OCEANOGR, V46, P465 Foster DA, 2004, MAR CHEM, V87, P59, DOI 10.1016/j.marchem.2004.02.003 Garcia-Solsona E, 2008, MAR CHEM, V109, P198, DOI 10.1016/j.marchem.2007.11.006 GIFFIN C, 1963, J GEOPHYS RES, V68, P1749, DOI 10.1029/JZ068i006p01749 Hsieh YT, 2011, J ANAL ATOM SPECTROM, V26, P1338, DOI 10.1039/c1ja10013k Ku TL, 2008, RADIOACTIV ENVIRONM, V13, P307, DOI 10.1016/S1569-4860(07)00009-5 KU TL, 1976, EARTH PLANET SC LETT, V32, P236, DOI 10.1016/0012-821X(76)90064-9 Moatar F, 2010, J RADIOANAL NUCL CH, V283, P3, DOI 10.1007/s10967-009-0001-2 Moore WS, 1996, J GEOPHYS RES-OCEANS, V101, P1321, DOI 10.1029/95JC03139 Moore WS, 2008, MAR CHEM, V109, P188, DOI 10.1016/j.marchem.2007.06.015 MOORE WS, 1995, GEOCHIM COSMOCHIM AC, V59, P4285, DOI 10.1016/0016-7037(95)00242-R Moore WS, 2003, BIOGEOCHEMISTRY, V66, P75, DOI 10.1023/B:BIOG.0000006065.77764.a0 Peterson RN, 2009, LIMNOL OCEANOGR-METH, V7, P196 Rama, 1996, GEOCHIM COSMOCHIM AC, V60, P4645 Rodellas V, 2012, J HYDROL, V466, P11, DOI 10.1016/j.jhydrol.2012.07.005 Sun Y, 1998, MAR CHEM, V62, P299, DOI 10.1016/S0304-4203(98)00019-X van Beek P, 2010, J ENVIRON RADIOACTIV, V101, P521, DOI 10.1016/j.jenvrad.2009.12.002 Waska H, 2008, J ENVIRON RADIOACTIV, V99, P1859, DOI 10.1016/j.jenvrad.2008.08.008 Geibert, Walter Rodellas, Valenti Annett, Amber van Beek, Pieter Garcia-Orellana, Jordi Hsieh, Yu-Te Masque, Pere Masque, Pere/B-7379-2008 Masque, Pere/0000-0002-1789-320X National Environmental Research Council through "UK Geotraces" [NE/H008497/1]; Scottish Alliance for GeoSciences and the Environment; MICINN (Spain) [AP2008-03044]; "Antarctic Science" research bursary, the British Antarctic Survey, NERC's Collaborative Gearing Scheme by the Natural Sciences and Engineering Research Council of Canada; "Antarctic Science" research bursary, the British Antarctic Survey, NERC's Collaborative Gearing Scheme by the University of Edinburgh; British Council-Egide "Alliance" scheme; prize ICREA Academia; Generalitat de Catalunya We would like to gratefully acknowledge support from funding agencies: W. G. and Y.-T. Hsieh from the National Environmental Research Council through "UK Geotraces" (NE/H008497/1); W. G. from the Scottish Alliance for GeoSciences and the Environment; V. R. for a PhD fellowship (AP2008-03044) from MICINN (Spain); A. A. from the "Antarctic Science" research bursary, the British Antarctic Survey, NERC's Collaborative Gearing Scheme, by the Natural Sciences and Engineering Research Council of Canada and by the University of Edinburgh; W. G., A. A., and P. v. B. received travel support from the British Council-Egide "Alliance" scheme; P. M. through the prize ICREA Academia, funded by the Generalitat de Catalunya. Thanks go to Gideon Henderson, Raja Ganeshram, and Michiel Rutgers van der Loeff; their contributions were essential to enable us to finish this manuscript. Three anonymous reviewers have provided helpful insights that contributed to improve the manuscript substantially. 0 AMER SOC LIMNOLOGY OCEANOGRAPHY WACO LIMNOL OCEANOGR-METHWe present a new method to determine Ra-226 in aqueous environmental samples, based on the rate of ingrowth of Rn-222 from Ra-226, using the radium delayed coincidence counter (RaDeCC). We use the same instrument setup that is used for the determination of Ra-223 and Ra-224. In contrast to methods published earlier, the approach does not require a modification of the counting equipment, counting separately for Ra-226, or waiting for radioactive equilibrium. We show that the calibration works from as low as 10 dpm (0.166 Bq) per sample, up to more than 1000 dpm (16.7 Bq). Although uncertainties are larger (typically around 10%) than reported uncertainties for gamma counting, liquid scintillation, or mass spectrometry at comparable activities, the simple setup, low cost, and robustness of the method make it a useful approach for underway measurements, combinations with short-lived radium isotopes, or monitoring purposes when limited funding or infrastructure is available

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

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

Internal tsunamigenesis and ocean mixing driven by glacier calving in Antarctica

Ocean mixing around Antarctica exerts key influences on glacier dynamics and ice shelf retreats, sea ice, and marine productivity, thus affecting global sea level and climate. The conventional paradigm is that this is dominated by winds, tides, and buoyancy forcing. Direct observations from the Antarctic Peninsula demonstrate that glacier calving triggers internal tsunamis, the breaking of which drives vigorous mixing. Being widespread and frequent, these internal tsunamis are at least comparable to winds, and much more important than tides, in driving regional shelf mixing. They are likely relevant everywhere that marine-terminating glaciers calve, including Greenland and across the Arctic. Calving frequency may change with higher ocean temperatures, suggesting possible shifts to internal tsunamigenesis and mixing in a warming climate