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The acidification of coastal waters is distinguished from the open ocean because of much stronger synergistic effects between anthropogenic forcing and local biogeochemical processes. However, ocean acidification research is still rather limited in polar coastal oceans. Here, we present a 16 year (2002–2018) observational dataset in the Chukchi Sea during the rapid sea‐ice melting season to determine the long‐term changes in pH and aragonite saturation state (Ωarag). We found that pH and Ωarag significantly declined in the water column with average rates of −0.0095 ± 0.0027 years−1 and −0.0333 ± 0.0098 years−1, respectively, and are 4–6 times faster than those solely due to increasing atmospheric CO2. We attributed the rapid acidification to the increased dissolved inorganic carbon owing to a combination of ice melt‐induced increased atmospheric CO2 invasion and subsurface remineralization induced by a stronger surface biological production as a result of the increased inflow of the nutrient‐rich Pacific water. Plain Language Summary: Anthropogenic CO2 absorbed by the ocean leads to a lower pH and the calcium carbonate saturation state (Ω) and threatens the marine ecosystems state of healthiness via a process called ocean acidification (OA). The Arctic Ocean is particularly sensitive to OA because more CO2 can be dissolved in cold water. This study used the observations collected over 16 years from 2002 to 2018 to estimate long‐term trends of Ωarag and pH in the Chukchi Sea. The results show that rapid acidification occurred in the water column during the rapid sea‐ice melting season from 2002 to 2018, leading to or approaching aragonite undersaturation. The rapid acidification is attributed to the enhanced increasing concentration of dissolved inorganic carbon. While sea ice melt induced uptake of anthropogenic CO2 partly explains the long‐term acidification, the remainder is due to the increased nutrient‐rich Pacific inflow water which promotes the high biological CO2 utilization in the surface waters but leads to stronger subsurface acidification due to the regenerated CO2. We suggest that the acidity in Chukchi Arctic Shelf waters will increase in the future if the increased inflow of Pacific water continues. Key Points: pH and Ωarag declined significantly from 2002 to 2018 during sea‐ice melting season, 4–6 times greater than air CO2 increases‐induced changesThe enhanced acidification in the Chukchi Sea is mainly driven by increased DIC, owing to atmospheric CO2 uptake and biological activityPWW has been in aragonite undersaturation since 2010; other water masses are expected to encounter Ωarag < 1 in 15 years [ABSTRACT FROM AUTHOR]

Sea‐ice dynamics can affect carbon cycling in polar oceans, with sea‐ice ikaite acting as a potentially important carbon pump. However, there is no large‐scale direct field evidence to support this. Here we used a unique data set that combined continuous measurements of atmospheric and water CO2 concentrations with water chemistry data collected over 1,200 km along the East Siberian Sea, the widest Arctic shelf sea. Our results reveal large spatial heterogeneity of sea‐ice ikaite contents, which directly interact with carbonate chemistry in the water column. Our findings demonstrate that the CO2 drawdown by sea‐ice ikaite dissolution could be as important as that by primary production. We suggest that the role of ikaite in regulating the seasonal carbon cycle on a regional scale could be more important than we previously thought. Effects of the warmer climate on sea ice loss might also play a role in the ikaite inventory. Plain Language Summary: The extent of sea ice in the Arctic Ocean has been known to be an active player in the carbon cycle. Recent studies have discovered that sea ice formation in winter leads to precipitation of calcium carbonate crystals (known as ikaite) and expels carbon dioxide (CO2) either to air or to deeper water with sinking of a heavy cold‐water mass (known as brine). In summer, ikaite in sea ice dissolves when the sea ice melts. This process takes CO2 away from air and convert it to dissolved inorganic carbon in surface ocean. Our study used non‐stop real‐time field measurements of air and water CO2 levels and water column data to investigate variability of carbonate chemistry across the East Siberian Sea. We observed that the distribution pattern of ikaite in sea ice varied largely with space. Ikaite dissolution in association with sea ice melting could take up similar amount of air CO2 as primary production does. Our findings suggest that more research efforts should be made to assess the effect of ikaite dynamics on the seasonal carbon cycle in a warmer climate. Key Points: Strong spatial heterogeneity of ikaite distribution in sea ice across East Siberian Sea is revealed via carbonate variability in water columnSea‐ice ikaite dissolution together with primary production was responsible for pCO2 drawdown in summer in the East Siberian SeaThe role of sea‐ice ikaite dynamics in the seasonal carbon cycle could be subject to change in a warmer climate [ABSTRACT FROM AUTHOR]

Recreational fishing (RF) is a large yet undervalued component of fisheries globally. While progress has been made in monitoring, assessing, and managing the sector in isolation, integration of RF into the management of multi‐sector fisheries has been limited, particularly relative to the commercial sector. This marginalises recreational fishers and reduces the likelihood of achieving the sector's objectives and, more broadly, achieving fisheries sustainability. We examined the nature and extent of RF inclusion in harvest strategies (HSs) for marine fisheries across 15 regions in 11 nations to define the gap in inclusion that has developed between sectors. We focused on high‐income nations with a high level of RF governance and used a questionnaire to elicit expert knowledge on HSs due to the paucity of published documents. In total, 339 HSs were considered. We found that RF inclusion in HSs was more similar to the small‐scale sector (i.e., artisanal, cultural, or subsistence) than the commercial sector, with explicit operational objectives, data collection, performance indicators, reference points, and management controls lacking in many regions. Where specified, RF objectives focused on sustainability, economic value and catch allocation rather than directly relating to the recreational fishing experience. Conflicts with other sectors included competition with the commercial sector for limited resources, highlighting the importance of equitable resource allocation policies alongside HSs. We propose that RF be explicitly incorporated into HSs to ensure fisheries are ecologically, economically, and socially sustainable, and we recommend that fisheries organisations urgently review HSs for marine fisheries with a recreational component to close the harvest strategy gap among sectors. [ABSTRACT FROM AUTHOR]

Melt from debris‐covered glaciers represents a regionally important freshwater source, especially in high‐relief settings as found in central Asia, Alaska, and South America. Sub‐debris melt is traditionally predicted from surface energy balance models that determine heat conduction through the supraglacial debris layer. Convection is rarely addressed, despite the porous nature of debris. Here we provide the first constraints on convection in supraglacial debris, through the development of a novel method to calculate individual conductive and nonconductive heat flux components from debris temperature profile data. This method was applied to data from Kennicott Glacier, Alaska, spanning two weeks in the summer of 2011 and two months in the summer of 2020. Both heat flux components exhibit diurnal cycles, the amplitude of which is coupled to atmospheric conditions. Mean diurnal nonconductive heat flux peaks at up to 43% the value of conductive heat flux, indicating that failure to account for it may lead to an incorrect representation of melt rates and their drivers. We interpret this heat flux to be dominated by latent heat as debris moisture content changes on a diurnal cycle. A sharp afternoon drop‐off in nonconductive heat flux is observed at shallow depths as debris dries. We expect these processes to be relevant for other debris‐covered glaciers. Debris properties such as porosity and tortuosity may play a large role in modulating it. Based on the present analysis, we recommend further study of convection in supraglacial debris for glaciers across the globe with different debris properties. Plain Language Summary: Glacier melt under a surface layer of rocky debris is typically predicted by determining the energy available at the debris surface, then calculating heat transferred via conduction through the debris layer. However, heat can also be transferred in the debris layer through other processes such as air movement and the evaporation of melt water. We analyzed temperature data in the debris to show that these processes are significant, accounting for up to 43% of heat transferred via conduction. These must thus be investigated further and incorporated into models of glacier melt. Key Points: We developed a new method to constrain supraglacial debris thermal properties and nonconductive heat fluxes from temperature profile dataNonconductive heat flux can be as much as 43% the conductive heat flux, thus it is important to understand its driving processesWe interpret nonconductive heat flux to be dominated by convection of moisture and latent heat flux as the debris diurnally wets and dries [ABSTRACT FROM AUTHOR]

CD47 regulates the trafficking of specific coding and noncoding RNAs into extracellular vesicles (EVs), and the RNA contents of CD47+ EVs differ from that of CD63+ EVs released by the same cells. Single particle interferometric reflectance imaging sensing combined with immunofluorescent imaging was used to analyse the colocalization of tetraspanins, integrins, and CD47 on EVs produced by wild type and CD47‐deficient Jurkat T lymphoblast and PC3 prostate carcinoma cell lines. On Jurkat cell‐derived EVs, β1 and α4 integrin subunits colocalized predominantly with CD47 and CD81 but not with CD63 and CD9, conserving the known lateral interactions between these proteins in the plasma membrane. Although PC3 cell‐derived EVs lacked detectable α4 integrin, specific association of CD81 with β1 and CD47 was preserved. Loss of CD47 expression in Jurkat cells significantly reduced β1 and α4 levels on EVs produced by these cells while elevating CD9+, CD63+, and CD81+ EVs. In contrast, loss of CD47 in PC3 cells decreased the abundance of CD63+ and CD81+ EVs. These data establish that CD47+ EVs are mostly distinct from EVs bearing the tetraspanins CD63 and CD9, but CD47 also indirectly regulates the abundance of EVs bearing these non‐interacting tetraspanins via mechanisms that remain to be determined. [ABSTRACT FROM AUTHOR]

Glaciers are commonly conceptualized as bodies composed of snow and ice. Yet, many glaciers contain a substantial amount of rock, especially those abutting steep mountains. Mountain slopes erode, depositing rocks on glaciers below. This loose rock (or debris) is buried in glaciers and melts out lower down creating a debris cover. Debris cover reduces ice melt, which changes the shape and movement of glaciers. Glacier movement, specifically basal sliding, efficiently sculpts landscapes. To date, we know little about the impacts of surface debris on conditions below glaciers. To help remedy this, we run numerical model simulations which show that debris‐covered glaciers erode slower than glaciers unaffected by debris. Reduced melt under surface debris lowers sliding speeds and causes sediment to accumulate at the bed, potentially establishing conditions for surging. The influence of surface debris cover on the subglacial environment may hold substantial implications for alpine sediment storage and landscape evolution. Plain Language Summary: Glaciers are imagined as bodies composed entirely of snow and ice. But many glaciers, especially those in steep mountains contain a substantial amount of rock as well. Rocks are deposited on glaciers from steep mountain slopes above them. This loose rock (or debris), buried by snow, can completely cover glaciers' lower reaches as it melts out of the ice. Debris reduces melt, which changes the glacier shape and in turn how glaciers move down valley. To test how debris‐covered glaciers erode and sculpt landscapes we use numerical models. Our simulations show that debris‐covered glaciers erode landscapes at lower rates than glaciers unaffected by debris. The reduced amount of melt from debris cover causes glaciers to slide slower and causes sediment to accumulate under debris‐covered ice, shielding bedrock from erosion. The tendency for debris‐covered glaciers to build sediment layers at their bed may lead to the rapid speed up and advancement of glaciers, also known as surges. The influence of surface debris cover on the subglacial environment may hold substantial implications for alpine sediment storage and landscape evolution. Key Points: Erosion is reduced under debris‐covered ice because of compounding effects between reduced surface melt and the subglacial environmentTill accumulates under debris‐covered ice because surface melt is suppressed by surface debris coverDebris cover on glaciers promotes subglacial fluvial conditions that can store sediment in alpine environments, altering erosional patterns [ABSTRACT FROM AUTHOR]

Climate change affects the stability and erosion of high‐alpine rock walls above glaciers (headwalls) that deliver debris to glacier surfaces. Since supraglacial debris in the ablation zone alters the melt behaviour of the underlying ice, the responses of debris‐covered glaciers and of headwalls to climate change may be coupled. In this study, we analyse the beryllium‐10 (10Be)‐cosmogenic nuclide concentration history of glacial headwalls delivering debris to the Glacier d'Otemma in Switzerland. By systematic downglacier‐profile‐sampling of two parallel medial moraines, we assess changes in headwall erosion through time for small, well‐defined debris source areas. We compute apparent headwall erosion rates from 10Be concentrations ([10Be]), measured in 15 amalgamated medial moraine debris samples. To estimate both the additional 10Be production during glacial debris transport and the age of our samples we combine our field‐based data with a simple model that simulates downglacier debris trajectories. Furthermore, we evaluate additional grain size fractions for eight samples to test for stochastic mass wasting effects on [10Be]. Our results indicate that [10Be] along the medial moraines vary systematically with time and consistently for different grain sizes. [10Be] are higher for older debris, closer to the glacier terminus, and lower for younger debris, closer to the glacier head. Computed apparent headwall erosion rates vary between ~0.6 and 10.8 mm yr−1, increasing over a maximum time span of ~200 years towards the present. As ice cover retreats, newly exposed headwall surfaces may become susceptible to enhanced weathering and erosion, expand to lower elevations, and contribute formerly shielded bedrock of likely different [10Be]. Hence, we suggest that recently lower [10Be] reflect the deglaciation of the debris source areas since the end of the Little Ice Age. [ABSTRACT FROM AUTHOR]

The acidification of coastal waters is distinguished from the open ocean because of much stronger synergistic effects between anthropogenic forcing and local biogeochemical processes. However, ocean acidification research is still rather limited in polar coastal oceans. Here, we present a 17‐year (2002–2019) observational data set in the Chukchi Sea to determine the long‐term changes in pH and aragonite saturation state (Ωarag). We found that pH and Ωarag declined in different water masses with average rates of −0.0047 ± 0.0026 years−1 and −0.017 ± 0.009 years−1, respectively, and are ∼2–3 times faster than those solely due to increasing atmospheric CO2. We attributed the rapid acidification to the increased dissolved inorganic carbon owing to a combination of ice melt‐induced increased atmospheric CO2 invasion and subsurface remineralization induced by a stronger surface biological production as a result of the increased inflow of the nutrient‐rich Pacific water. Plain Language Summary: Anthropogenic CO2 absorbed by the ocean leads to a lower pH and the calcium carbonate saturation state (Ω) and threatens the marine ecosystems state of healthiness via a process called ocean acidification (OA). The Arctic Ocean is particularly sensitive to OA because more CO2 can be dissolved in cold water. This study used the observations collected over 17 years from 2002 to 2019 to estimate long‐term trends of Ωarag and pH in the Chukchi Sea. The results show that rapid acidification occurred throughout all water masses from 2002 to 2019, leading to or approaching aragonite undersaturation. The rapid acidification is attributed to the enhanced increasing concentration of dissolved inorganic carbon. While sea ice melt induced uptake of anthropogenic CO2 partly explains the long‐term acidification, the remainder is due to the increased nutrient‐rich Pacific inflow water which promotes the high biological CO2 utilization in the surface waters but leads to stronger subsurface acidification due to the regenerated CO2. We suggest that the acidity in Chukchi Arctic Shelf waters will increase in the future if the increased inflow of Pacific water continues. Key Points: pH and Ωarag declined at −0.0047 ± 0.0026 years−1 and −0.017 ± 0.009 years−1 from 2002 to 2019, 2–3 times greater than atmospheric CO2 projectedThe enhanced acidification in Chukchi Sea is mainly driven by enhanced dissolved inorganic carbon, owing to atmospheric CO2 uptake and biological activityAragonite undersaturation in Pacific Winter Water has been observed from 2010; other water masses are expected to encounter Ωarag < 1 within 15 years [ABSTRACT FROM AUTHOR]

ABSTRACT 10Be dating of moraines has greatly improved our ability to constrain the timing of past glaciations and thus past cold events. However, the spread in ages from a single moraine is often greater than would be expected from measurement uncertainty, making paleoclimatic interpretations equivocal. Here we present 28 new 10Be ages from ice-cored Neoglacial moraines on Baffin Island, Arctic Canada, and explore the processes at play in moraine formation and evolution through field observations and a numerical debris-covered glacier model. The insulating effect of debris cover modifies glacier lengths and results in the development of ice-cored moraines over multiple advances and thousands of years. Although ice cores can persist for several millennia, spatially variable ice core melt-out contributes to moraine degradation and boulder destabilization, making it likely that the 10Be clock is reset on moraine boulders in these settings. Thus, exposure ages from ice-cored moraines must be interpreted with caution. The oldest ages, after excluding samples with inheritance, provide the best estimates of initial moraine formation. Three Baffin Island moraines yield 10Be ages suggesting formation at 5.2, 4.6 and 3.5 ka, respectively, adding to a growing body of evidence for significant summer cooling millennia before the Little Ice Age. [ABSTRACT FROM AUTHOR]

This large-scale quasi-synoptic study gives a comprehensive picture of sea-air CO2 fluxes during the melt season in the central and outer Laptev Sea (LS) and East Siberian Sea (ESS). During a 7 week cruise we compiled a continuous record of both surface water and air CO2 concentrations, in total 76,892 measurements. Overall, the central and outer parts of the ESAS constituted a sink for CO2, and we estimate a median uptake of 9.4 g C m−2 yr−1 or 6.6 Tg C yr−1. Our results suggest that while the ESS and shelf break waters adjacent to the LS and ESS are net autotrophic systems, the LS is a net heterotrophic system. CO2 sea-air fluxes for the LS were 4.7 g C m−2 yr−1, and for the ESS we estimate an uptake of 7.2 g C m−2 yr−1. Isotopic composition of dissolved inorganic carbon (δ13CDIC and δ13CCO2) in the water column indicates that the LS is depleted in δ13CDIC compared to the Arctic Ocean (ArcO) and ESS with an offset of 0.5‰ which can be explained by mixing of δ13CDIC-depleted riverine waters and 4.0 Tg yr−1 respiration of OCter; only a minor part (0.72 Tg yr−1) of this respired OCter is exchanged with the atmosphere. Property-mixing diagrams of total organic carbon and isotope ratio (δ13CSPE-DOC) versus dissolved organic carbon (DOC) concentration diagram indicate conservative and nonconservative mixing in the LS and ESS, respectively. We suggest land-derived particulate organic carbon from coastal erosion as an additional significant source for the depleted δ13CDIC. [ABSTRACT FROM AUTHOR]

Large-scale patterns of net community production (NCP) were estimated during the late summer cruise ARK-XXVI/3 (TransArc, August/September 2011) to the central Arctic Ocean. Several approaches were used based on the following: (i) continuous measurements of surface water oxygen to argon ratios (O2/Ar), (ii) underway measurements of surface partial pressure of carbon dioxide ( pCO2), (iii) discrete samples of dissolved inorganic carbon, and (iv) dissolved inorganic nitrogen and phosphate. The NCP estimates agreed well within the uncertainties associated with each approach. The highest late summer NCP (up to 6 mol C m−2) was observed in the marginal sea ice zone region. Low values (<1 mol C m−2) were found in the sea ice-covered deep basins with a strong spatial variability. Lowest values were found in the Amundsen Basin and moderate values in the Nansen and Makarov Basins with slightly higher estimates over the Mendeleev Ridge. Our findings support a coupling of NCP to sea ice coverage and nutrient supply and thus stress a potential change in spatial and temporal distribution of NCP in a future Arctic Ocean. To follow the evolution of NCP in space and time, it is suggested to apply one or several of these approaches in shipboard investigations with a time interval of 3 to 5 years. [ABSTRACT FROM AUTHOR]

Climate change is expected to have a strong effect on the Eastem Siberian Arctic Shelf (ESAS) region, which includes 40% of the Arctic shelves and comprises the Laptev and East Siberian seas. The largest organic carbon pool, the dissolved organic carbon (DOC), may change significantly due to changes in both riverine inputs and transformation rates; however, the present DOC inventories and transformation patterns are poorly understood. Using samples from the International Siberian Shelf Study 2008, this study examines for the first time DOC removal in Arctic shelf waters with residence times that range from months to years. Removals of up to l0%-20% were found in the Lena River estuary, consistent with earlier studies in this area, where surface waters were shown to have a residence time of approximately 2 months. In contrast, the DOC concentrations showed a strong nonconservative pattern in areas with freshwater residence times of several years. The average losses of DOC were estimated to be 30%-50% during mixing along the shelf, corresponding to a first-order removal rate constant of 0.3 yr-1. These data provide the first observational evidence for losses of DOC in the Arctic shelf seas, and the calculated DOC deficit reflects DOC losses that are higher than recent model estimates for the region. Overall, a large proportion of riverine DOC is removed from the surface waters across the Arctic shelves. Such significant losses must be included in models of the carbon cycle for the Arctic Ocean, especially since the breakdown of terrestrial DOC to CO2 in Arctic shelf seas may constitute a positive feedback mechanism for Arctic climate warming. These data also provide a baseline for considering the effects of future changes in carbon fluxes, as the vast northern carbon-rich permafrost areas draining into the Arctic are affected by global warming. [ABSTRACT FROM AUTHOR]

The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales and, have the potential to cause rapid changes in the earth system. The response of the carbon cycle of the Arctic to changes in climate is a major issue of global concern, yet there has not been a comprehensive review of the status of the contemporary carbon cycle of the Arctic and its response to climate change. This review is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle of the Arctic to ongoing climatic change. While it is clear that there are substantial stocks of carbon in the Arctic, there are also significant uncertainties associated with the magnitude of organic matter stocks contained in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic. In the context of the global carbon cycle, this review demonstrates that the Arctic plays an important role in the global dynamics of both CO2 and CH4. Studies suggest that the Arctic has been a sink for atmospheric CO2 of between 0 and 0.8 Pg C/yr in recent decades, which is between 0% and 25% of the global net land/ocean flux during the 1990s. The Arctic is a substantial source of CH4 to the atmosphere (between 32 and 112 Tg CH4/yr), primarily because of the large area of wetlands throughout the region. Analyses to date indicate that the sensitivity of the carbon cycle of the Arctic during the remainder of the 21st century is highly uncertain. To improve the capability to assess the sensitivity of the carbon cycle of the Arctic to projected climate change, we recommend that (I) integrated regional studies be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from these integrated studies be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts. [ABSTRACT FROM AUTHOR]