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1. Life in the PFAS lane: The impact of perfluoroalkyl substances on photosynthesis, cellular exudates, nutrient cycling, and composition of a marine microbial community

   https://doi.org/10.1016/j.scitotenv.2024.171977  

   Davis, Sarah N; Klumker, Shaley M; Mitchell, Alex A; Coppage, Marshall A.; Labonte, Jessica M; Quigg, Antonietta (June 2024, Science of the total environment)

   Jay Gan (Ed.)

   Perfluoroalkyl substances (PFAS) are of great ecological concern, however, exploration of their impact on bacteria-phytoplankton consortia is limited. This study employed a bioassay approach to investigate the effect of unary exposures of increasing concentrations of PFAS (perfluorooctane sulfonate (PFOS) and 6:2 fluorotelomer sulfonate (6:2 FTS)) on microbial communities from the northwestern Gulf of Mexico. Each community was examined for changes in growth and photophysiology, exudate production and shifts in community structure (16S and 18S rRNA genes). 6:2 FTS did not alter the growth or health of phytoplankton communities, as there were no changes relative to the controls (no PFOS added). On the other hand, PFOS elicited significant phototoxicity (p < 0.05), altering PSII antennae size, lowering PSII connectivity, and decreasing photosynthetic efficiency over the incubation (four days). PFOS induced a cellular protective response, indicated by significant increases (p < 0.001) in the release of transparent exopolymer particles (TEP) compared to the control. Eukaryotic communities (18S rRNA gene) changed substantially (p < 0.05) and to a greater extent than prokaryotic communities (16S rRNA gene) in PFOS treatments. Community shifts were concentration-dependent for eukaryotes, with the low treatment (5 mg/L PFOS) dominated by Coscinodiscophyceae (40 %), and the high treatment (30 mg/L PFOS) marked by a Trebouxiophyceae (50 %) dominance. Prokaryotic community shifts were not concentration dependent, as both treatment levels became depleted in Cyanobacteriia and were dominated by members of the Bacteroidia, Gammaproteobacteria, and Alphaproteobacteria classes. Further, PFOS significantly decreased (p < 0.05) the Shannon diversity and Pielou’s evenness across treatments for eukaryotes, and in the low treatment (5 mg/L PFOS) for prokaryotes. These findings show that photophysiology was not impacted by 6:2 FTS but PFOS elicited toxicity that impacted photosynthesis, exudate release, and community composition. This research is crucial in understanding how PFOS impacts microbial communities. 

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2. An idealized modeling study of the mid-latitude variability of the wind-driven meridional overturning circulation

   https://doi.org/10.1175/JPO-D-20-0317.1  

   Spall, Michael A. (May 2021, Journal of Physical Oceanography)

   Abstract The frequency and latitudinal dependence of the mid-latitude wind-driven meridional overturning circulation (MOC) is studied using theory and linear and nonlinear applications of a quasi-geostrophic numerical model. Wind-forcing is varied by either changing the strength of the wind or by shifting the meridional location of the wind stress curl pattern. At forcing periods less than the first mode baroclinic Rossby wave basin crossing time scale the linear response in the mid-depth and deep ocean is in phase and opposite to the Ekman transport. For forcing periods close to the Rossby wave basin crossing time scale, the upper and deep MOC are enhanced, and the mid-depth MOC becomes phase shifted, relative to the Ekman transport. At longer forcing periods the deep MOC weakens and the mid-depth MOC increases, but eventually for long enough forcing periods (decadal) the entire wind-driven MOC spins down. Nonlinearities and mesoscale eddies are found to be important in two ways. First, baroclinic instability causes the mid-depth MOC to weaken, lose correlation with the Ekman transport, and lose correlation with the MOC in the opposite gyre. Second, eddy thickness fluxes extend the MOC beyond the latitudes of direct wind forcing. These results are consistent with several recent studies describing the four-dimensional structure of the MOC in the North Atlantic. 

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3. Interaction between perfluoro‐octanoic sulfonate and common antibiotics induces developmental anomalies and lethality in Xenopus laevis

   https://doi.org/10.1002/dvdy.764  

   Harrison, Emma; Chattapadhyay, Shreya; Neka, Ganad; Baskin, Maya; Richmond, Nora; Nguyen, Quynh; Wade, Isabel; Anekal, Arya; Lucanish, Olive; Young, John_J (January 2025, Developmental Dynamics)

   Abstract BackgroundPerfluoroalkyl substances (PFAS) are persistent environmental contaminants previously used for industrial purposes as a non‐stick coating and flame retardant. The stability of these molecules prevents their breakdown, which results in ground water contamination across the globe. Perfluoroalkyl substances molecules are known to bioaccumulate in various organisms. However, the health consequences remain unclear due to the large number of molecules in the PFAS family and different effects on various tissues. Here, we use the frogXenopus laevisto investigate the developmental consequences of exposure to the PFAS molecule perfluoro‐octanoic sulfonate (PFOS). ResultsWe find that exposure to high levels of PFOS results in significant axial shortening of developing tadpoles. Further, we find that PFOS exposure results in a dose‐dependent formation of a cellular mass in the dorsal fin. Unexpectedly, we found that these developmental phenotypes are exacerbated upon co‐exposure with commonly used antibiotics. Specifically, PFOS and gentamicin co‐treatment results in increased apoptosis, loss of cellular integrity, and increased overall lethality. ConclusionsOur results suggest a mechanism whereby gentamicin reaches levels that are toxic to mitochondria only in the presence of PFOS. These findings add to our understanding of PFOS exposure to vertebrate development and present an added concern with potential interactions with antibiotics. 

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4. Time-dependent response of the overturning circulation and pycnocline depth to Southern Ocean surface wind stress changes

   https://doi.org/10.1175/JPO-D-21-0214.1  

   Hailu Kong and Malte F. Jansen (February 2022, Journal of Physical Oceanography)

   Changes in the Southern Ocean (SO) surface wind stress influence both the meridional overturning circulation (MOC) and stratification not only in the SO but in the global oceans, which can take multiple millennia to fully equilibrate. We use a hierarchy of models to investigate the time-dependent response of the MOC and low-latitude pycnocline depth (which quantifies the stratification) to SO wind stress changes: a two-layer analytical theory, a multi-column model (PyMOC), and an idealized general circulation model (GCM). We find that in both the GCM and PyMOC, the MOC has a multi-decadal adjustment timescale while the pycnocline depth has a multi-centennial timescale. The two-layer theory instead predicts the MOC and pycnocline depth to adjust on the same, multi-decadal timescale. We argue that this discrepancy arises because the pycnocline depth depends on the bulk stratification, while the MOC amplitude is sensitive mostly to isopycnals within the overturning cell. We can reconcile the discrepancy by interpreting the “pycnocline depth” in the theory as the depth of a specific isopycnal near the maximum of the MOC. We also find that SO stationary eddies respond very quickly to a sudden wind stress change, compensating for most of the change in the Ekman-driven MOC. This effect is missing in the theory, where the eddy-induced MOC only follows the adjustment of the pycnocline depth. Our results emphasize the importance of depth-dependence in the oceans’ transient response to changes in surface boundary conditions, and the distinct role played by stationary eddies in the SO. 

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5. Characterizing the Interannual Variability of North Atlantic Subpolar Overturning

   https://doi.org/10.1029/2025GL114672  

   Fu, Yao; Lozier, M_Susan; Bower, Amy; Burmeister, Kristin; Carrilho_Biló, Tiago; Cyr, Frédéric; Cunningham, Stuart_A; deYoung, Brad; Dilmahamod, Ahmad_Fehmi; de_Jong, M_Femke; et al (September 2025, Geophysical Research Letters)

   Abstract Variability of the Atlantic Meridional Overturning Circulation (MOC) has drawn extensive attention due to its impact on the global redistribution of heat and freshwater. Here we present the latest time series (2014–2022) of the Overturning in the Subpolar North Atlantic Program and characterize MOC interannual variability. We find that any single boundary current captures ∼30% of subpolar MOC interannual variability. However, to fully resolve MOC variability, a wide swath across the eastern subpolar basin is needed; in the Labrador Sea both boundaries are needed. Through a volume budget analysis for the subpolar basins' lower limbs, we estimate the magnitude of unresolved processes (e.g., diapycnal mixing) required to close the mean budget (∼2 Sv). We find that in the eastern subpolar basin surface‐forced transformation variability is linked to lower limb volume variability, which translates to MOC changes within the same year. In contrast, this linkage is weak in the Labrador Sea. 

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