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1. Quantifying the Impact of Vertical Resolution on the Representation of Marine Boundary Layer Physics for Global-Scale Models

   https://doi.org/10.1175/MWR-D-23-0078.1  

   Smalley, Mark A. ; Lebsock, Matthew D. ; Teixeira, Joao ( November 2023 , Monthly Weather Review)

   While GCM horizontal resolution has received the majority of scale improvements in recent years, ample evidence suggests that a model’s vertical resolution exerts a strong control on its ability to accurately simulate the physics of the marine boundary layer. Here we show that, regardless of parameter tuning, the ability of a single-column model (SCM) to simulate the subtropical marine boundary layer improves when its vertical resolution is improved. We introduce a novel objective tuning technique to optimize the parameters of an SCM against profiles of temperature and moisture and their turbulent fluxes, horizontal winds, cloud water, and rainwater from large-eddy simulations (LES). We use this method to identify optimal parameters for simulating marine stratocumulus and shallow cumulus. The novel tuning method utilizes an objective performance metric that accounts for the uncertainty in the LES output, including the covariability between model variables. Optimization is performed independently for different vertical grid spacings and value of time step, ranging from coarse scales often used in current global models (120 m, 180 s) to fine scales often used in parameterization development and large-eddy simulations (10 m, 15 s). Uncertainty-weighted disagreement between the SCM and LES decreases by a factor of ∼5 when vertical grid spacing is improved from 120 to 10 m, with time step reductions being of secondary importance. Model performance is shown to converge at a vertical grid spacing of 20 m, with further refinements to 10 m leading to little further improvement.

   In successive generations of computer models that simulate Earth’s atmosphere, improvements have been mainly accomplished by reducing the horizontal sizes of discretized grid boxes, while the vertical grid spacing has seen comparatively lesser refinements. Here we advocate for additional attention to be paid to the number of vertical layers in these models, especially in the model layers closest to Earth’s surface where climatologically important marine stratocumulus and shallow cumulus clouds reside. Our experiments show that the ability of a one-dimensional model to represent physical processes important to these clouds is strongly dependent on the model’s vertical grid spacing.

    

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2. Proximity to Undersaturation and the Influences on G. bulloides Area‐Density in Southern Indian Ocean Marine Sediments

   https://doi.org/10.1029/2021PA004249  

   Umling, N. E. ; Saad, B. ; Sikes, E. ; Goodkin, N. F. ( June 2021 , Paleoceanography and Paleoclimatology)

   The area density proxy of foraminiferal shell thickness and calcification intensity has the potential to provide information about past ocean CO₂content and has the benefit of small sample requirements, simple analytical techniques, and the ability to re‐use the analyzed foraminifera for other paleo‐proxies. Using a series of multicore core‐tops collected from the southeastern Indian Ocean (1.8–3.8 km water depth), we evaluate the reliability of utilizing area density values ofGlobigerina bulloidesfrom sediment cores to estimate surface ocean carbonate parameters. Because foraminifera in marine sediments can rarely be considered “pristine” (or “glassy”), we grouped area density measurements of shells to designate various stages of diagenesis. Visual signs of alteration were apparent at area density values as low as ∼0.122 × 10⁴ µg/µm², with deviations from the “pristine” endmember beginning at area density values of ∼0.087 × 10⁴ µg/µm². We find that increases in area density overprint the surface ocean carbonate signature in thicker (>0.122 × 10⁴ µg/µm²shells), but small increases associated with marine sedimentary burial and diagenesis can be accounted for, allowing this proxy to be applied back in time. Reconstructing the distribution of area density values in a given sample has the potential to provide valuable information on overall sample preservation by estimating the percent of well‐preserved shells (<0.122 × 10⁴ µg/µm²; %wp) in a given sample. Our %wp metric has the potential for use as a proxy for lysocline variability in addition to assessing the suitability of marine sediment samples for surface ocean reconstructions.

    

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3. Transient exposure to novel high temperatures reshapes coastal phytoplankton communities

   https://doi.org/10.1038/s41396-019-0525-6  

   Kling, Joshua D. ; Lee, Michael D. ; Fu, Feixue ; Phan, Megan D. ; Wang, Xinwei ; Qu, Pingping ; Hutchins, David A. ( October 2019 , The ISME Journal)

   Average sea surface temperatures are expected to rise 4° this century, and marine phytoplankton and bacterial community composition, biogeochemical rates, and trophic interactions are all expected to change in a future warmer ocean. Thermal experiments typically use constant temperatures; however, weather and hydrography cause marine temperatures to fluctuate on diel cycles and over multiple days. We incubated natural communities of phytoplankton collected from California coastal waters during spring, summer, and fall under present-day and future mean temperatures, using thermal treatments that were either constant or fluctuated on a 48 h cycle. As assayed by marker-gene sequencing, the emergent microbial communities were consistent within each season, except when culture temperatures exceeded the highest temperature recorded in a 10-year local thermal dataset. When temperature treatments exceeded the 10-year maximum the phytoplankton community shifted, becoming dominated by diatom amplicon sequence variants (ASVs) not seen at lower temperatures. When mean temperatures were above the 10-year maximum, constant and fluctuating regimes each selected for different ASVs. These findings suggest coastal microbial communities are largely adapted to the current range of temperatures they experience. They also suggest a general hypothesis whereby multiyear upper temperature limits may represent thresholds, beyond which large community restructurings may occur. Now inevitable future temperature increases that exceed these environmental thresholds, even temporarily, may fundamentally reshape marine microbial communities and therefore the biogeochemical cycles that they mediate.

    

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4. New constraints on the last deglaciation of the Cordilleran Ice Sheet in coastal Southeast Alaska

   https://doi.org/10.1017/qua.2020.32  

   Lesnek, Alia J. ; Briner, Jason P. ; Baichtal, James F. ; Lyles, Alex S. ( July 2020 , Quaternary Research)

   null (Ed.)

   Abstract Understanding marine-terminating ice sheet response to past climate transitions provides valuable long-term context for observations of modern ice sheet change. Here, we reconstruct the last deglaciation of marine-terminating Cordilleran Ice Sheet (CIS) margins in Southeast Alaska and explore potential forcings of western CIS retreat. We combine 27 new cosmogenic 10 Be exposure ages, 13 recently published 10 Be ages, and 25 new 14 C ages from raised marine sediments to constrain CIS recession. Retreat from the outer coast was underway by 17 ka, and the inner fjords and sounds were ice-free by 15 ka. After 15 ka, the western margin of the CIS became primarily land-terminating and alpine glaciers disappeared from the outer coast. Isolated alpine glaciers may have persisted in high inland peaks until the early Holocene. Our results suggest that the most rapid phase of CIS retreat along the Pacific coast occurred between ~17 and 15 ka. This retreat was likely driven by processes operating at the ice-ocean interface, including sea level rise and ocean warming. CIS recession after ~15 ka occurred during a time of climatic amelioration in this region, when both ocean and air temperatures increased. These data highlight the sensitivity of marine-terminating CIS regions to deglacial climate change. 

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5. Plastics in Porifera: The occurrence of potential microplastics in marine sponges and seawater from Bocas del Toro, Panamá

   https://doi.org/10.7717/peerj.11638  

   Fallon, Bailey R. ; Freeman, Christopher J. ( January 2021 , PeerJ)

   null (Ed.)

   Microplastics (MP) are now considered ubiquitous across global aquatic environments. The ingestion of MP by fish and other marine vertebrates is well studied, but the ingestion of MP by marine invertebrates is not. Sponges (Phylum Porifera) are particularly understudied when it comes to MP ingestion, even though they are widely distributed across benthic habitats, can process large volumes of seawater, and can retain small particles within their water filtration systems. This study examines the presence of potential MP (PMP) in wild marine sponges and seawater collected in Bocas del Toro, Panamá. Subsurface seawater and tissue from six common Caribbean sponge species was collected in Saigon Bay, a heavily impacted, shallow-water coral reef. Seawater samples were filtered onto glass fiber filters to retain any PMP present and sponge tissue was digested with bleach, heated and filtered. Filters were examined using fluorescence microscopy to quantify PMP. An average of 107 ± 25 PMP L –1 was detected in seawater from Saigon Bay with particles ranging in size between 10 μm and ~3,000 μm. The number of PMP found in sponge tissue ranged between 6 ± 4 and 169 ± 71 PMP g –1 of dry tissue. Most particles found in sponge samples were very small (10–20 μm), but fibers greater than 5,000 μm were detected. Our results indicate that PMP exists within the tissues of the sponges we studied, but future studies should confirm the presence of MP in sponges using chemical analysis. Most importantly, the discrepancy between low levels of PMP in our sponge samples and high levels in the surrounding seawater highlights the potential for sponges to resist and/or egest MP. Finally, we provide a critical evaluation of our methods to improve their use in future MP work with benthic marine organisms. 

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