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1. A global ocean dissolved organic phosphorus concentration database (DOPv2021)

   https://doi.org/10.1038/s41597-022-01873-7  

   Liang, Zhou; McCabe, Kelly; Fawcett, Sarah E.; Forrer, Heather J.; Hashihama, Fuminori; Jeandel, Catherine; Marconi, Dario; Planquette, Hélène; Saito, Mak A.; Sohm, Jill A.; et al (December 2022, Scientific Data)

   Abstract Dissolved organic phosphorus (DOP) concentration distributions in the global surface ocean inform our understanding of marine biogeochemical processes such as nitrogen fixation and primary production. The spatial distribution of DOP concentrations in the surface ocean reflect production by primary producers and consumption as an organic nutrient by phytoplankton including diazotrophs and other microbes, as well as other loss processes such as photolysis. Compared to dissolved organic carbon and nitrogen, however, relatively few marine DOP concentration measurements have been made, largely due to the lack of automated analysis techniques. Here we present a database of marine DOP concentration measurements (DOPv2021) that includes new (n = 730) and previously published (n = 3140) observations made over the last ~30 years (1990–2021), including 1751 observations in the upper 50 m. This dataset encompasses observations from all major ocean basins including the poorly represented Indian, South Pacific, and Southern Oceans and provides insight into spatial distributions of DOP in the ocean. It is also valuable for researchers who work on marine primary production and nitrogen fixation. 

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2. Bacterial transcriptional response to labile exometabolites from photosynthetic picoeukaryote Micromonas commoda

   https://doi.org/10.1038/s43705-023-00212-0  

   Ferrer-González, Frank X.; Hamilton, Maria; Smith, Christa B.; Schreier, Jeremy E.; Olofsson, Malin; Moran, Mary Ann (December 2023, ISME Communications)

   Abstract Dissolved primary production released into seawater by marine phytoplankton is a major source of carbon fueling heterotrophic bacterial production in the ocean. The composition of the organic compounds released by healthy phytoplankton is poorly known and difficult to assess with existing chemical methods. Here, expression of transporter and catabolic genes by three model marine bacteria ( Ruegeria pomeroyi DSS-3, Stenotrophomonas sp. SKA14, and Polaribacter dokdonensis MED152) was used as a biological sensor of metabolites released from the picoeukaryote Micromonas commoda RCC299. Bacterial expression responses indicated that the three species together recognized 38 picoeukaryote metabolites. This was consistent with the Micromonas expression of genes for starch metabolism and synthesis of peptidoglycan-like intermediates. A comparison of the hypothesized Micromonas exometabolite pool with that of the diatom Thalassiosira pseudonana CCMP1335, analyzed previously with the same biological sensor method, indicated that both phytoplankton released organic acids, nucleosides, and amino acids, but differed in polysaccharide and organic nitrogen release. Future ocean conditions are expected to favor picoeukaryotic phytoplankton over larger-celled microphytoplankton. Results from this study suggest that such a shift could alter the substrate pool available to heterotrophic bacterioplankton. 

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3. Photosynthetic processes in Antarctic sea ice during the spring melt

   https://doi.org/10.1002/lno.12596  

   Young, Jodi_N; Rundell, Susan; Cooper, Zachary_S; Dawson, Hannah_M; Carpenter, Shelly_D; Ryan‐Keogh, Thomas; Rowland, Elden; Bertrand, Erin_M; Deming, Jody_W (June 2024, Limnology and Oceanography)

   Abstract High‐latitude oceans experience strong seasonality where low light limits photosynthetic activity most of the year. This limitation is pronounced for algae within and underlying sea ice, and these algae are uniquely acclimated to low light levels. During spring melt, however, light intensity and daylength increase drastically, triggering blooms of ice algae that play important roles in carbon cycling and ecosystem productivity. How the algae acclimate to this dynamic and heterogeneous environment is poorly understood. Here, we measured¹⁴C‐carbon fixation rates, photophysiology, and ribulose 1,5‐bisphosphate carboxylase oxygenase (Rubisco) content of sea‐ice algae in coastal waters near the western Antarctic Peninsula during spring, ranging from a low‐light‐acclimated, bottom community to a light‐saturated bloom. Carbon fixation rates by sea‐ice algae were similar to other Antarctic sea‐ice measurements (2–49 mg C m⁻²d⁻¹), and there was little phytoplankton biomass in the underlying water at the time of sampling. Net‐to‐gross ratios of carbon fixation were generally high and showed no relationship with ice type. We found algal photophysiology and Rubisco concentrations varied in relation to the different types of ice, altering the balance between the photochemical and biochemical processes that constrain carbon fixation rates. For algae inhabiting the bottom layers of sea ice, rates of carbon fixation were largely constrained by light availability whereas in surface seawater, interior and rotten/brash ice, carbon fixation rates could be calculated with reasonable accuracy from measurements of Rubisco concentrations. This work provides additional insight and means to evaluate carbon fixation rates as sea ice continues to change in future. 

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4. Temperature sensitivity of carbon concentrating mechanisms in the diatom Phaeodactylum tricornutum

   https://doi.org/10.1007/s11120-023-01004-2  

   Li, Meng; Young, Jodi N. (March 2023, Photosynthesis Research)

   Abstract Marine diatoms are key primary producers across diverse habitats in the global ocean. Diatoms rely on a biophysical carbon concentrating mechanism (CCM) to supply high concentrations of CO₂around their carboxylating enzyme, RuBisCO. The necessity and energetic cost of the CCM are likely to be highly sensitive to temperature, as temperature impacts CO₂concentration, diffusivity, and the kinetics of CCM components. Here, we used membrane inlet mass spectrometry (MIMS) and modeling to capture temperature regulation of the CCM in the diatomPhaeodactylum tricornutum (Pt). We found that enhanced carbon fixation rates byPtat elevated temperatures were accompanied by increased CCM activity capable of maintaining RuBisCO close to CO₂saturation but that the mechanism varied. At 10 and 18 °C, diffusion of CO₂into the cell, driven byPt’s ‘chloroplast pump’ was the major inorganic carbon source. However, at 18 °C, upregulation of the chloroplast pump enhanced (while retaining the proportion of) both diffusive CO₂and active HCO₃⁻uptake into the cytosol, and significantly increased chloroplast HCO₃⁻concentrations. In contrast, at 25 °C, compared to 18 °C, the chloroplast pump had only a slight increase in activity. While diffusive uptake of CO₂into the cell remained constant, active HCO₃⁻uptake across the cell membrane increased resulting inPtdepending equally on both CO₂and HCO₃⁻as inorganic carbon sources. Despite changes in the CCM, the overall rate of active carbon transport remained double that of carbon fixation across all temperatures tested. The implication of the energetic cost of thePtCCM in response to increasing temperatures was discussed. 

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5. Hydroclimate Drives Seasonal Riverine Export Across a Gradient of Glacierized High‐Latitude Coastal Catchments

   https://doi.org/10.1029/2022WR033305  

   Jenckes, J.; Munk, L. A.; Ibarra, D. E.; Boutt, D. F.; Fellman, J.; Hood, E. (April 2023, Water Resources Research)

   Abstract Glacierized coastal catchments of the Gulf of Alaska (GoA) are undergoing rapid hydrologic fluctuations in response to climate change. These catchments deliver dissolved and suspended inorganic and organic matter to nearshore marine environments, however, these glacierized coastal catchments are relatively understudied and little is known about total solute and particulate fluxes to the ocean. We present hydrologic, physical, and geochemical data collected during April–October 2019–2021 from 10 streams along gradients of glacial fed to non‐glacial (i.e., precipitation) fed, in one Southcentral and one Southeast Alaska region. Hydrologic data reveal that glaciers drive the seasonal runoff patterns. The ẟ¹⁸O signature and specific conductance show distinctive seasonal variations in stream water sources between the study regions apparently due to the large amounts of rain in Southeast Alaska. Total dissolved solids concentrations and yields were elevated in the Southcentral region, due to lithologic influence on dissolved loads, however, the hydroclimate is the primary driver of the timing of dissolved and suspended yields. We show the yields of dissolved organic carbon is higher and that the δ¹³C_POCis enriched in the Southeast streams illustrating contrasts in organic carbon export across the GoA. Finally, we illustrate how future yields of solutes and sediments to the GoA may change as watersheds evolve from glacial influenced to precipitation dominated. This integrated analysis provides insights into how watershed characteristics beyond glacier coverage control properties of freshwater inputs to the GoA and the importance of expanding study regions to multiple hydroclimate regimes. 

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