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1. Ecological connectivity in Pacific deep-sea hydrothermal vent metacommunities

   https://doi.org/10.3354/meps14182  

   Fleming, BFM ; Beaulieu, SE ; Mills, SW ; Gaggiotti, OE ; Mullineaux, LS ( November 2022 , Marine Ecology Progress Series)

   Larval dispersal and connectivity between patchy, transient, deep-sea hydrothermal vent communities are important for persistence and recovery from disturbance. We investigated connectivity in vent metacommunities using the taxonomic similarity between larvae and adults to estimate the extent of exchange between communities and determine the relative roles of larval dispersal and environmental limitations (species sorting) in colonization. Connectivity at vent fields in 3 Pacific regions, Pescadero Basin, northern East Pacific Rise (EPR), and southern Mariana Trough, varied substantially and appeared to be driven by different processes. At Pescadero Basin, larval and adult taxa were similar, despite the existence of nearby (within 75 km) vent communities with different species composition, indicating limited larval transport and low connectivity. At EPR, larval and adult taxa differed significantly, despite the proximity of nearby vents with similar benthic composition, indicating substantial larval transport and potentially strong species sorting, but other factors may also explain these results. At the Mariana Trough, the larvae and adults differed significantly, indicating high larval transport but environmental limitations on colonization. We demonstrate that analysis of routinely collected samples and observations provides an informative indicator of metacommunity connectivity and insights into drivers of community assembly.
2. Low-volume magmatism linked to flank deformation on Isla Santa Cruz, Galápagos Archipelago, using cosmogenic 3He exposure and 40Ar/39Ar dating of fault scarps and lavas

   https://doi.org/10.1007/s00445-022-01575-3  

   Schwartz, D. M. ; Harpp, K. ; Kurz, M. D. ; Wilson, E. ; Van Kirk, R. ( August 2022 , Bulletin of Volcanology)

   Isla Santa Cruz is a volcanic island located in the central Galápagos Archipelago. The island’s northern and southern flanks are deformed by E–W-trending normal faults not observed on the younger Galápagos shields, and Santa Cruz lacks the large summit calderas that characterize those structures. To construct a chronology of volcanism and deformation on Santa Cruz, we employ⁴⁰Ar/³⁹Ar geochronology of lavas and³He exposure dating of fault scarps from across the island. The combination of Ar–Ar dating with in situ-produced cosmogenic exposure age data provides a powerful tool to evaluate fault chronologies. The⁴⁰Ar/³⁹Ar ages indicate that the island has been volcanically active since at least 1.62 ± 0.030 Ma (2SD). Volcanism deposited lavas over the entire island until ~ 200 ka, when it became focused along an E–W-trending summit vent system; all dated lavas < 200 ka were emplaced on the southern flank. Structural observations suggest that the island has experienced two major faulting episodes. Crosscutting relationships of lavas indicate that north flank faults formed after 1.16 ± 0.070 Ma, but likely before 416 ± 36 ka, whereas the faults on the southern flank of the island initiated between 201 ± 37 and 32.6 ± 4.6 ka, based on³He exposure dating of fault surfaces. The data are consistent with a model wherein the northeastern faults are associated with regional extension owingmore »to the young volcano’s location closer to the Galápagos Spreading Center at the time. The second phase of volcanism is contemporaneous with the formation of the southern faults. The expression of this younger, low-volume volcanic phase was likely related to the elongate island morphology established during earlier deformation. The complex feedback between tectonic and volcanic processes responsible for southward spreading along the southern flank likely generated persistent E-W-oriented magmatic intrusions. The formation of the Galápagos Transform Fault and sea-level fluctuations may be the primary causes of eruptive and deformational episodes on Santa Cruz.

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3. The Role of Neutral Hydrogen in Setting the Abundances of Molecular Species in the Milky Way’s Diffuse Interstellar Medium. II. Comparison between Observations and Theoretical Models

   https://doi.org/10.3847/1538-4357/ac4160  

   Rybarczyk, Daniel R. ; Gong, Munan ; Stanimirović, Snežana ; Babler, Brian ; Murray, Claire E. ; Winters, Jan Martin ; Luo, Gan ; Dame, T. M. ; Steffes, Lucille ( February 2022 , The Astrophysical Journal)

   We compare observations of Hifrom the Very Large Array (VLA) and the Arecibo Observatory and observations of HCO⁺from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Northern Extended Millimeter Array (NOEMA) in the diffuse (A_V≲ 1) interstellar medium (ISM) to predictions from a photodissociation region (PDR) chemical model and multiphase ISM simulations. Using a coarse grid of PDR models, we estimate the density, FUV radiation field, and cosmic-ray ionization rate (CRIR) for each structure identified in HCO⁺and Hiabsorption. These structures fall into two categories. Structures withT_s< 40 K, mostly withN(HCO⁺) ≲ 10¹²cm⁻², are consistent with modest density, FUV radiation field, and CRIR models, typical of the diffuse molecular ISM. Structures with spin temperatureT_s> 40 K, mostly withN(HCO⁺) ≳ 10¹²cm⁻², are consistent with high density, FUV radiation field, and CRIR models, characteristic of environments close to massive star formation. The latter are also found in directions with a significant fraction of thermally unstable Hi. In at least one case, we rule out the PDR model parameters, suggesting that alternative mechanisms (e.g., nonequilibrium processes like turbulent dissipation and/or shocks) are required to explain the observed HCO⁺in this direction. Similarly, while our observations and simulations of the turbulent, multiphase ISM agree thatmore »HCO⁺formation occurs along sight lines withN(H I) ≳ 10²¹cm⁻², the simulated data fail to explain HCO⁺column densities ≳ few × 10¹²cm⁻². Because a majority of our sight lines with HCO⁺had such high column densities, this likely indicates that nonequilibrium chemistry is important for these lines of sight.

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4. Diazotrophic <i>Trichodesmium</i> impact on UV–Vis radiance and pigment composition in the western tropical South Pacific

   https://doi.org/10.5194/bg-15-5249-2018  

   Dupouy, Cécile ; Frouin, Robert ; Tedetti, Marc ; Maillard, Morgane ; Rodier, Martine ; Lombard, Fabien ; Guidi, Lionel ; Picheral, Marc ; Neveux, Jacques ; Duhamel, Solange ; et al ( January 2018 , Biogeosciences)

   Abstract. We assessed the influence of the marine diazotrophic cyanobacterium Trichodesmium on the bio-optical properties of western tropical South Pacific (WTSP) waters (18–22°S, 160°E–160°W) during the February–March 2015 OUTPACE cruise. We performed measurements of backscattering and absorption coefficients, irradiance, and radiance in the euphotic zone with a Satlantic MicroPro free-fall profiler and took Underwater Vision Profiler 5 (UPV5) pictures for counting the largest Trichodesmium spp. colonies. Pigment concentrations were determined by fluorimetry and high-performance liquid chromatography and picoplankton abundance by flow cytometry. Trichome concentration was estimated from pigment algorithms and validated by surface visual counts. The abundance of large colonies counted by the UVP5 (maximum 7093coloniesm⁻³) was well correlated to the trichome concentrations (maximum 2093trichomesL⁻¹) with an aggregation factor of 600. In the Melanesian archipelago, a maximum of 4715trichomesL⁻¹ was enumerated in pump samples (3.2m) at 20°S,16730°E. High Trichodesmium abundance was always associated with absorption peaks of mycosporine-like amino acids (330, 360nm) and high particulate backscattering, but not with high Chl a fluorescence or blue particulate absorption (440nm). Along the west-to-east transect, Trichodesmium together with Prochlorococcus represented the major part of total chlorophyll concentration; themore »contribution of other groups were relatively small or negligible. The Trichodesmium contribution to total chlorophyll concentration was the highest in the Melanesian archipelago around New Caledonia and Vanuatu (60%), progressively decreased to the vicinity of the islands of Fiji (30%), and reached a minimum in the South Pacific Gyre where Prochlorococcus dominated chlorophyll concentration. The contribution of Trichodesmium to zeaxanthin was respectively 50, 40 and 20% for these regions. During the OUTPACE cruise, the relationship between normalized water-leaving radiance (nL_w) in the ultraviolet and visible and chlorophyll concentration was similar to that found during the BIOSOPE cruise in the eastern tropical Pacific. Principal component analysis (PCA) of OUTPACE data showed that nL_w at 305, 325, 340, 380, 412 and 440nm was strongly correlated to chlorophyll and zeaxanthin, while nL_w at 490 and 565nm exhibited lower correlations. These results, as well as differences in the PCA of BIOSOPE data, indicated that nL_w variability in the greenish blue and yellowish green during OUTPACE was influenced by other variables associated with Trichodesmium presence, such as backscattering coefficient, phycoerythrin fluorescence and/or zeaxanthin absorption, suggesting that Trichodesmium detection should involve examination of nL_w in this spectral domain.

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5. Recent warming reverses forty-year decline in catastrophic lake drainage and hastens gradual lake drainage across northern Alaska

   https://doi.org/10.1088/1748-9326/ac3602  

   Lara, Mark J. ; Chen, Yaping ; Jones, Benjamin M. ( November 2021 , Environmental Research Letters)

   Lakes represent as much as ∼25% of the total land surface area in lowland permafrost regions. Though decreasing lake area has become a widespread phenomenon in permafrost regions, our ability to forecast future patterns of lake drainage spanning gradients of space and time remain limited. Here, we modeled the drivers of gradual (steady declining lake area) and catastrophic (temporally abrupt decrease in lake area) lake drainage using 45 years of Landsat observations (i.e. 1975–2019) across 32 690 lakes spanning climate and environmental gradients across northern Alaska. We mapped lake area using supervised support vector machine classifiers and object based image analyses using five-year Landsat image composites spanning 388 968 km². Drivers of lake drainage were determined with boosted regression tree models, using both static (e.g. lake morphology, proximity to drainage gradient) and dynamic predictor variables (e.g. temperature, precipitation, wildfire). Over the past 45 years, gradual drainage decreased lake area between 10% and 16%, but rates varied over time as the 1990s recorded the highest rates of gradual lake area losses associated with warm periods. Interestingly, the number of catastrophically drained lakes progressively decreased at a rate of ∼37% decade⁻¹from 1975–1979 (102–273 lakes draining year⁻¹) to 2010–2014 (3–8 lakes drainingmore »year⁻¹). However this 40 year negative trend was reversed during the most recent time-period (2015–2019), with observations of catastrophic drainage among the highest on record (i.e. 100–250 lakes draining year⁻¹), the majority of which occurred in northwestern Alaska. Gradual drainage processes were driven by lake morphology, summer air and lake temperature, snow cover, active layer depth, and the thermokarst lake settlement index (R²_adj= 0.42, CV = 0.35,p< 0.0001), whereas, catastrophic drainage was driven by the thawing season length, total precipitation, permafrost thickness, and lake temperature (R²_adj= 0.75, CV = 0.67,p< 0.0001). Models forecast a continued decline in lake area across northern Alaska by 15%–21% by 2050. However these estimates are conservative, as the anticipated amplitude of future climate change were well-beyond historical variability and thus insufficient to forecast abrupt ‘catastrophic’ drainage processes. Results highlight the urgency to understand the potential ecological responses and feedbacks linked with ongoing Arctic landscape reorganization.

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