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  1. This dataset includes concentrations of dissolved (<0.4 micrometers (µm)) and labile particulate (0.4-5 µm and >5 µm) phosphorus (P), vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in shipboard incubation samples collected during the EXports Processes in the Oceans from RemoTe Sensing (EXPORTS) North Pacific (NP) cruise RR1813 on the R/V Roger Revelle near Ocean Station PAPA (Station P). 
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  2. This dataset includes concentrations of dissolved (<0.2 micrometers (µm)) manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in surface (~2 meters) samples collected between 15 August 2018 and 6 September 2018 during the EXports Processes in the Oceans from RemoTe Sensing (EXPORTS) cruise aboard R/V Roger Revelle cruise RR1813 at Ocean Station PAPA (Station P). 
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  3. This dataset includes concentrations of dissolved (<0.2 micrometers (µm)) manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in depth profile samples collected on 8 September 2018 during the EXports Processes in the Oceans from RemoTe Sensing (EXPORTS) cruise aboard R/V Roger Revelle cruise RR1813 at Ocean Station PAPA (Station P). 
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  4. Abstract

    Synechococcus are the most abundant cyanobacteria in high latitude regions and are responsible for an estimated 17% of annual marine net primary productivity. Despite their biogeochemical importance, Synechococcus populations have been unevenly sampled across the ocean, with most studies focused on low-latitude strains. In particular, the near absence of Synechococcus genomes from high-latitude, High Nutrient Low Chlorophyll (HNLC) regions leaves a gap in our knowledge of picocyanobacterial adaptations to iron limitation and their influence on carbon, nitrogen, and iron cycles. We examined Synechococcus populations from the subarctic North Pacific, a well-characterized HNLC region, with quantitative metagenomics. Assembly with short and long reads produced two near complete Synechococcus metagenome-assembled genomes (MAGs). Quantitative metagenome-derived abundances of these populations matched well with flow cytometry counts, and the Synechococcus MAGs were estimated to comprise >99% of the Synechococcus at Station P. Whereas the Station P Synechococcus MAGs contained multiple genes for adaptation to iron limitation, both genomes lacked genes for uptake and assimilation of nitrate and nitrite, suggesting a dependence on ammonium, urea, and other forms of recycled nitrogen leading to reduced iron requirements. A global analysis of Synechococcus nitrate reductase abundance in the TARA Oceans dataset found nitrate assimilation genes are also lower in other HNLC regions. We propose that nitrate and nitrite assimilation gene loss in Synechococcus may represent an adaptation to severe iron limitation in high-latitude regions where ammonium availability is higher. Our findings have implications for models that quantify the contribution of cyanobacteria to primary production and subsequent carbon export.

     
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  5. The growth of diatoms in the Southern Ocean, especially the region surrounding the West Antarctic Peninsula, is frequently constrained by low dissolved iron and other trace metal concentrations. This challenge may be overcome by mutualisms between diatoms and co-occurring associated bacteria, in which diatoms produce organic carbon as a substrate for bacterial growth, and bacteria produce siderophores, metal-binding ligands that can supply diatoms with metals upon uptake as well as other useful secondary compounds for diatom growth like vitamins. To examine the relationships between diatoms and bacteria in the plankton (diatom) size class (> 3 µm), we sampled both bacterial and diatom community composition with accompanying environmental metadata across a naturally occurring concentration gradient of macronutrients, trace metals and siderophores at 21 stations near the West Antarctic Peninsula (WAP). Offshore Drake Passage stations had low dissolved iron (0.33 ± 0.15 nM), while the stations closer to the continental margin had higher dissolved iron (5.05 ± 1.83 nM). A similar geographic pattern was observed for macronutrients and most other trace metals measured, but there was not a clear inshore-offshore gradient in siderophore concentrations. The diatom and bacteria assemblages, determined using 18S and 16S rDNA sequencing respectively, were similar by location sampled, and variance in both assemblages was driven in part by concentrations of soluble reactive phosphorous, dissolved manganese, and dissolved copper, which were all higher near the continent. Some of the most common diatom sequence types observed were Thalassiosira and Fragilariopsis , and bacteria in the plankton size fraction were most commonly Bacteroidetes and Gammaproteobacteria. Network analysis showed positive associations between diatoms and bacteria, indicating possible in situ mutualisms through strategies such as siderophore and vitamin biosynthesis and exchange. This work furthers the understanding of how naturally occurring gradients of metals and nutrients influence diatom-bacteria interactions. Our data suggest that distinct groups of diatoms and associated bacteria are interacting under different trace metal regimes in the WAP, and that diatoms with different bacterial partners may have different modes of biologically supplied trace metals. 
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  6. Abstract

    In the Southern Ocean, it is well‐known that iron (Fe) limits phytoplankton growth. Yet, other trace metals can also affect phytoplankton physiology. This study investigated feedbacks between phytoplankton growth and dissolved Fe, manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and cadmium (Cd) concentrations in Southern Ocean shipboard incubations. Three experiments were conducted in September–October 2016 near the West Antarctic Peninsula: Incubations 1 and 3 offshore in the Antarctic Circumpolar Current, and Incubation 2 inshore in Bransfield Strait. Additions of Fe and/or vitamin B12to inshore and offshore waters were employed and allowed assessment of metal (M) uptake relative to soluble reactive phosphorus (P) across a wide range of initial conditions. Offshore, treatments of >1 nmol L−1added Fe were Fe‐replete, whereas inshore waters were already Fe‐replete. Results suggest Mn was a secondary limiting nutrient inshore and offshore. No Fe‐vitamin B12colimitation was observed. Overall, M:P uptake in the incubations was closely related to initial dissolved M:P for Fe, Mn, Co, Ni, and Cd, and for Cu inshore. Final concentrations of Fe and Zn were similar across light treatments of the experiments despite very different phytoplankton responses, and we observed evidence for Co/Cd/Zn substitution and for recycling of biogenic metals as inventories plateaued. In dark bottles, the absence of Mn oxidation may have allowed more efficient recycling of Fe and other trace metals. Our results provide insight into factors governing trace metal uptake, with implications for phytoplankton community composition locally and preformed micronutrient bioavailability in Southern Ocean water masses.

     
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  7. Abstract

    The partial pressure of carbon dioxide (pCO2) was surveyed across the Amazon River plume and the surrounding western tropical North Atlantic Ocean (15–0°N, 43–60°W) during three oceanic expeditions (May–June 2010, September–October 2011, and July 2012). The survey timing was chosen according to previously described temporal variability in plume behavior due to changing river discharge and winds.In situsea surfacepCO2and air‐sea CO2flux exhibited robust linear relationships with sea surface salinity (SSS; 15 < SSS < 35), although the relationships differed among the surveys. Regional distributions ofpCO2and CO2flux were estimated using SSS maps from high‐resolution ocean color satellite‐derived (MODIS‐Aqua) diffuse attenuation coefficient at 490 nm (Kd490) during the periods of study. Results confirmed that the plume is a net CO2sink with distinctive temporal variability: the strongest drawdown occurred during the spring flood (−2.39 ± 1.29 mmol m−2 d−1in June 2010), while moderate drawdown with relatively greater spatial variability was observed during the transitional stages of declining river discharge (−0.42 ± 0.76 mmol m−2 d−1in September–October 2011). The region turned into a weak source in July 2012 (0.26 ± 0.62 mmol m−2 d−1) when strong CO2uptake in the mid‐plume was overwhelmed by weak CO2outgassing over a larger area in the outer plume. Outgassing near the mouth of the river was observed in July 2012. Our observations draw attention to the importance of assessing the variable impacts of biological activity, export, and air‐sea gas exchange before estimating regional CO2fluxes from salinity distributions alone.

     
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