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1. On-shelf circulation of warm water toward the Totten Ice Shelf in East Antarctica

   https://doi.org/10.1038/s41467-023-39764-z  

   Hirano, Daisuke; Tamura, Takeshi; Kusahara, Kazuya; Fujii, Masakazu; Yamazaki, Kaihe; Nakayama, Yoshihiro; Ono, Kazuya; Itaki, Takuya; Aoyama, Yuichi; Simizu, Daisuke; et al (August 2023, Nature Communications)

   Abstract The Totten Glacier in East Antarctica, with an ice volume equivalent to >3.5 m of global sea-level rise, is grounded below sea level and, therefore, vulnerable to ocean forcing. Here, we use bathymetric and oceanographic observations from previously unsampled parts of the Totten continental shelf to reveal on-shelf warm water pathways defined by deep topographic features. Access of warm water to the Totten Ice Shelf (TIS) cavity is facilitated by a deep shelf break, a broad and deep depression on the shelf, a cyclonic circulation that carries warm water to the inner shelf, and deep troughs that provide direct access to the TIS cavity. The temperature of the warmest water reaching the TIS cavity varies by ~0.8 °C on an interannual timescale. Numerical simulations constrained by the updated bathymetry demonstrate that the deep troughs play a critical role in regulating ocean heat transport to the TIS cavity and the subsequent basal melt of the ice shelf. 

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2. Organic‐Matter Accumulation and Degradation in Holocene Permafrost Deposits Along a Central Alaska Hillslope

   https://doi.org/10.1029/2022JG007290  

   Marshall, Leah P.; Kaufman, Darrell S.; Anderson, R. Scott; McKay, Nicholas P.; Schuur, Edward A. (September 2023, Journal of Geophysical Research: Biogeosciences)

   Abstract The quantity and preservation of carbon‐rich organic matter (OM) underlying permafrost uplands, and the evolution of carbon accumulation with millennial climate change, are large sources of uncertainty in carbon cycle feedbacks on climate change. We investigated permafrost OM accumulation and degradation over the Holocene using a transect of sediment cores dating back to at least c. 6 ka, from a hillslope in the Eight Mile Lake watershed, central Alaska. We find decimeter‐scale organic‐rich (111 ± 45 kg C m⁻³) and organic‐poor (49 ± 30 kg C m⁻³) layers below an upper peat, which store 35% ± 11% and 41% ± 20% of the carbon in the upper 1 m, respectively. In organic‐poor layers, scattered¹⁴C ages of plant macrofossils and higher percentages of degradedAlnusandBetulapollen indicate reworking by cryoturbation and hillslope processes. Whereas organic carbon to nitrogen ratios generally indicate OM freshening up‐core, amino acid bacterial biomarkers, includingd‐enantiomers and gamma‐aminobutyric acid, suggest enhanced degradation prior to 5 ka. Carbon accumulation rates increased from ∼4 to 14 g C m⁻² year⁻¹from c. 8 to 0.2 ka, coinciding with decreasing temperatures and increasing moisture regionally, which may have promoted OM accumulation. Carbon stocks within the upper 1 m average 66 ± 13 kg C m⁻², varying from 77 kg C m⁻²in a buried depression on the upper slope to 48 kg C m⁻²downslope. We conclude that heterogeneity in preserved OM reflects a combination of hillslope geomorphic processes, cryoturbation, and climatic variations over the Holocene. 

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3. Ne viii in the Warm-hot Circumgalactic Medium of FIRE Simulations and in Observations

   https://doi.org/10.3847/1538-4357/ad63a0  

   Wijers, Nastasha A; Faucher-Giguère, Claude-André; Stern, Jonathan; Byrne, Lindsey; Sultan, Imran (September 2024, The Astrophysical Journal)

   Abstract The properties of warm-hot gas around ∼L_*galaxies can be studied with absorption lines from highly ionized metals. We predict Neviiicolumn densities from cosmological zoom-in simulations of halos with masses in ∼10¹²and ∼10¹³M_☉from the Feedback in Realistic Environments (FIRE) project. Neviiitraces the volume-filling, virial-temperature gas in ∼10¹²M_☉halos. In ∼10¹³M_☉halos the Neviiigas is clumpier, and biased toward the cooler part of the warm-hot phase. We compare the simulations to observations from the COS Absorption Survey of Baryon Harbors (or CASBaH) and COS Ultraviolet Baryon Survey (or CUBS). We show that when inferring halo masses from stellar masses to compare simulated and observed halos, it is important to account for the scatter in the stellar-mass–halo-mass relation, especially atM_⋆≳ 10^10.5M_☉. Median Neviiicolumns in the fiducial FIRE-2 model are about as high as observed upper limits allow, while the simulations analyzed do not reproduce the highest observed columns. This suggests that the median Neviiiprofiles predicted by the simulations are consistent with observations, but that the simulations may underpredict the scatter. We find similar agreement with analytical models that assume a product of the halo gas fraction and metallicity (relative to solar) ∼0.1, indicating that observations are consistent with plausible circumgalactic medium temperatures, metallicities, and gas masses. Variants of the FIRE simulations with a modified supernova feedback model and/or active galactic nuclei feedback included (as well as some other cosmological simulations from the literature) more systematically underpredict Neviiicolumns. The circumgalactic Neviiiobservations therefore provide valuable constraints on simulations that otherwise predict realistic galaxy properties. 

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4. Expanding the Inventory of Molecule-rich Planetary Nebulae: New Observations of M4-17, Hu 1-1, M1-59, and Na 2

   https://doi.org/10.3847/1538-4357/ad83be  

   Gold, K R; Schmidt, D R; Ziurys, L M (November 2024, The Astrophysical Journal)

   Abstract Molecular observations of four planetary nebulae (PNe), M4-17, Hu 1-1, M1-59, and Na 2, were conducted at 1–3 mm using the Arizona Radio Observatory’s 12 m antenna and Submillimeter Telescope, and the Institut de Radioastronomie Millimétrique 30 m Telescope. Toward M4-17, HNC (J= 3 → 2), CCH (N= 2 → 1,N= 3 → 2), CN (N= 1 → 0,N= 2 → 1), H₂CO (J_Ka,Kc= 2_1,2→ 1_1,1,J_Ka,Kc= 2_0,2→ 1_0,1,J_Ka,Kc= 2_1,1→ 1_1,0), CS (J= 3 → 2,J= 5 → 4), and H¹³CN (J= 2 → 1) were detected. An almost identical set of transitions was identified toward Hu 1-1. Moreover, c–C₃H₂was detected in Hu 1-1 via three 2 mm lines:J_Ka,Kc= 3_1,2→ 2_2,1,J_Ka,Kc= 4_1,4→ 3_0,3, andJ_Ka,Kc= 3_{2, 2}→ 2_1,1. HNC, CCH, CN, CS, and H¹³CN were found in M1-59, as well as H₂S via itsJ_Ka,Kc= 1_1,0→ 1_0,1line—the first detection of this key sulfur species in PNe. In addition, CCH and CN were identified in the 27,000 yr old Na 2. Among these four sources, CN and CCH were the most prevalent molecules (after CO and H₂) with fractional abundances, relative to H₂, off∼ 0.9–7.5 × 10⁻⁷and 0.8–7.5 × 10⁻⁷, respectively. CS and HNC have abundances in the rangef∼ 0.5–5 × 10⁻⁸, the latter resulting in HCN/HNC ∼ 3 across all three PNe. The unusual species H₂CO, c–C₃H₂, and H₂S hadf∼ 3–4 × 10⁻⁷, 10⁻⁸, and 6 × 10⁻⁸. This study suggests that elliptical PNe such as Hu 1-1 can have a diverse molecular composition. The presence of CN, CCH, and HCO⁺in Na 2, with comparable abundances to younger PNe, demonstrates that molecular content is maintained into the late PN stage. 

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5. Phytoplankton community composition in the oligotrophic Argo Basin of the eastern Indian Ocean

   https://doi.org/10.1101/2025.08.14.670423  

   Selph, Karen E; Lampe, Robert H; Yingling, Natalia; Bhabu, Ria; Kranz, Sven A; Allen, Andrew E; Landry, Michael R (August 2025, bioRxiv)

   ABSTRACT Phytoplankton community composition during austral summer 2022 in the Argo Abyssal Plain (Argo Basin), a 5000-m deep area northwest of the Australian continent in the eastern Indian Ocean, is described in detail, including phytoplankton abundance, biomass, size structure, taxonomic identifications through DNA and pigment analyses, as well as the percent of functional mixotrophs. The region was characterized by warm (up to 30.5°C), stratified, oligotrophic (nitrogen-limited) waters, with integrated euphotic zone (EZ) chlorophyll a (CHLa) of 13 mg m^-2. The EZ mean CHLawas low in the upper layer (0.085 µg L^-1) and 0.32 µg L^-1at the pronounced deep CHLamaxima. EZ-integrated phytoplankton carbon averaged 1229 mg C m^-2.Prochlorococcuswas the dominant taxon throughout the EZ, but the lower EZ had ∼4-times more eukaryotic carbon biomass than the upper EZ, along with a distinct community. In the upper EZ, prymnesiophytes, dinoflagellates and prasinophyte taxa without prasinoxanthin had the highest contributions to monovinyl chlorophyll a (MV-CHLa). In the lower EZ the community was more diverse, with prymnesiophytes, dinoflagellates, prasinophyte taxa with prasinoxanthin, pelagophytes, and cryptophytes all comprising significant contributions to MV-CHLa. Diatoms were a minor part of the community. In the upper EZ, a higher percent of the community showed mixotrophy (35-84%) relative to the lower EZ (30-51%). Although a low abundance, nitrogen-fixing organisms (symbionts of diatoms and cyanobacteria taxa) were ubiquitous. Overall, the community was similar to that found at the Hawaii Ocean Time-series site and the central Gulf of Mexico. 

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