A B S T R A C TToxic chemicals within and adsorbed to microplastics (0.05-5 mm) have the potential to biomagnify in food webs. However, microplastic concentrations in highly productive, coastal habitats are not well understood. Therefore, we quantified the presence of microplastics in a benthic community and surrounding environment of a remote marine reserve on the open coast of California, USA. Concentrations of microplastic particles in seawater were 36.59 plastics/L and in sediments were 0.227 ± 0.135 plastics/g. Densities of microplastics on the surfaces of two morphologically distinct species of macroalgae were 2.34 ± 2.19 plastics/g (Pelvetiopsis limitata) and 8.65 ± 6.44 plastics/g (Endocladia muricata). Densities were highest in the herbivorous snail, Tegula funebralis, at 9.91 ± 6.31 plastics/g, potentially due to bioaccumulation. This study highlights the need for further investigations of the prevalence and potential harm of microplastics in benthic communities at remote locations as well as human population centers.

Aims Some biogeographical regions act primarily as donors of colonists to other regions, while others act predominantly as recipient areas. How some biotas become dominant while others do not is a largely historical question that has received surprisingly little attention from biogeographers. Here, we seek to answer this question for the cold‐water North Pacific biota, which did not exist forty million years ago but which is now the principal donor biota outside the tropics. Location We focus on the cool‐temperate coastal North Pacific Ocean over the last 36.5 million years. Taxon We consider all multicellular taxa for which adequate fossil, phylogenetic and biogeographical data exist. Methods After placing North Pacific geographical events in the broader context of ocean gateways opening and closing elsewhere in the world, we discuss the history and factors affecting the planktonic and benthic productivity in the North Pacific based on a review and critical evaluation of the literature. A synthesis of primary sources was used to evaluate the origins and fates of North Pacific lineages, with special emphasis on movements to, within and from the North Pacific during the Cenozoic era. Results During the Late Eocene to earliest Miocene, the cooling North Pacific received colonists from adjacent warm‐water regions and the cold Southern Hemisphere, where temperate conditions had existed since at least the Cretaceous. From the Miocene onward, the North Pacific biota began to spread to the Southern Hemisphere and through Bering Strait to the Arctic and North Atlantic Oceans. Within the North Pacific, lineages during the early cooling phases spread predominantly from west to east, but in the Early Middle Miocene this pattern reversed, with later expansions going in both directions. An increase in productivity, powered by the evolution of highly productive seaweeds and by consumers with high metabolic rates, accompanied the transformation of the North Pacific from a recipient to donor biota. Main conclusions The North Pacific replaced the Southern Hemisphere temperate biota as the principal donor biota during the Miocene through a combination of increasing productivity, low magnitudes of extinction and intense competition and predation in an ocean basin with a long coastline.

Abstract. Salt marshes and seagrass meadows can sequester and store high quantities of organic carbon (OC) in their sediments relative to other marine and terrestrial habitats. Assessing carbon stocks, carbon sources, and the transfer of carbon between habitats within coastal seascapes are each integral in identifying the role of blue carbon habitats in coastal carbon cycling. Here, we quantified carbon stocks, sources, and exchanges in seagrass meadows, salt marshes, and unvegetated sediments in six bays along the California coast. In the top 20 cm of sediment, the salt marshes contained approximately twice as much OC as seagrass meadows did, 4.92 ± 0.36 kg OC m−2 compared to 2.20 ± 0.24 kg OC m−2, respectively. Both salt marsh and seagrass sediment carbon stocks were higher than previous estimates from this region but lower than global and US-wide averages, respectively. Seagrass-derived carbon was deposited annually into adjacent marshes during fall seagrass senescence. However, isotope mixing models estimate that negligible amounts of this seagrass material were ultimately buried in underlying sediment. Rather, the vast majority of OC in sediment across sites was likely derived from planktonic/benthic diatoms and/or C3 salt marsh plants.

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The carbon cycle in East Lake (Newberry Volcano, Oregon, USA) is fueled by volcanic CO2 inputs with traces of Hg and H2S. The CO2 dissolves in deep lake waters and is removed in shallow waters through largely diffusive surface degassing and photosynthesis. Escaping gas and photosynthate have low δ13C values, leading to δ13C(DIC) (DIC—dissolved inorganic carbon) as high as +5.7‰ in surface waters, well above the common global lake range. A steep δ13C depth gradient is further established by respiration and absorption of light volcanic CO2 in bottom waters. The seasonal CO2 degassing starts at >100 t CO2/day after ice melting in the spring and declines to ~40 t/day in late summer, degassing ~11,700 t CO2/yr. Thus, volcano monitoring through gas fluxes from crater lakes should consider lacustrine processes that modulate the volcanic gas output over time. The flux contribution of a bubbling CO2 “hotspot” increased from 20% to >90% of the lake-wide CO2 flux from 2015 to 2019 CE, followed by a “toxic gas alert” in July 2020. East Lake is an active volcanic lake with a “geogenic” ecosystem driven primarily by hydrothermal inputs.