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Journals dedicated to the polar sciences have been outliers. Within both the history of science and the history of media, they stand out in several ways, including their comparatively late establishment of peer-review. It was not until the second half of the 20th century, that polar sciences journals began to carry predominantly peer-reviewed original research rather than synopses of research published elsewhere. This Perspective piece uses the 40th anniversary of Polar Research as an opportunity to look at the past of polar sciences periodicals—and invites reflection on their future.

In 1980, at the invitation of Australia, the first Chinese scientists went to Antarctica. China was therefore a relative 'latecomer' to engage in Antarctic science. In the period since its first Antarctic expedition in 1984, China's presence in Antarctica has expanded both in terms of its logistics and infrastructure and its scientific research. This paper outlines the development of China's national Antarctic programmes under the influence of corresponding national policies from the late 1970s to the present, noting the application of various scientific disciplines to Antarctic fields. The paper outlines and analyses the broadening and deepening of China's Antarctic science research, infrastructure and engagement. [ABSTRACT FROM AUTHOR]

This paper discusses heightened interest in the potential audibility of the aurora borealis during the First and Second International PolarYears (IPYs) of 1882-3and1932-3.Galvanized bya growing volume of local accounts expressing belief in the elusive noises, written by the inhabitants of the Shetland Islands, northern Canada, andNorway, auroral researchers of each erawere determined to establish the objectivity of auroral sound. There was considerable speculation within the auroral research community as to whether the apparent noises were imagined or illusory, connected to discussions about the possibility of low-altitude aurorae. The anglophone auroral sound debate primarily played out within the official reports of IPY expeditions, the journal Nature, and a Shetland Island newspaper. I argue that the embodied senses were used exclusively to register the liminal sounds of the aurora across the two periods, despite developments in sound recording technologies, the primacy of mechanical objectivity, and instruments transported to the polar regions for the investigation of visual features of the phenomenon. This overlooked episode complicates narratives of polar science in the late nineteenth and early twentieth centuries by revealing a faith in the corporeal senses and the significant role of amateur observers. [ABSTRACT FROM AUTHOR]

Journals dedicated to the polar sciences have been outliers. Within both the history of science and the history of media, they stand out in several ways, including their comparatively late establishment of peer-review. It was not until the second half of the 20th century, that polar sciences journals began to carry predominantly peer-reviewed original research rather than synopses of research published elsewhere. This Perspective piece uses the 40th anniversary of Polar Research as an opportunity to look at the past of polar sciences periodicals--and invites reflection on their future. [ABSTRACT FROM AUTHOR]

A lasting legacy of the International Polar Year (IPY) 2007–2008 was the promotion of the Permafrost Young Researchers Network (PYRN), initially an IPY outreach and education activity by the International Permafrost Association (IPA). With the momentum of IPY, PYRN developed into a thriving network that still connects young permafrost scientists, engineers, and researchers from other disciplines. This research note summarises (1) PYRN's development since 2005 and the IPY's role, (2) the first 2015 PYRN census and survey results, and (3) PYRN's future plans to improve international and interdisciplinary exchange between young researchers. The review concludes that PYRN is an established network within the polar research community that has continually developed since 2005. PYRN's successful activities were largely fostered by IPY. With >200 of the 1200 registered members active and engaged, PYRN is capitalising on the availability of social media tools and rising to meet environmental challenges while maintaining its role as a successful network honouring the legacy of IPY. [ABSTRACT FROM AUTHOR]

Polar Educators International (PEI) is a volunteer-based organization designed to build collaborative relationships between educators and polar researchers. Founded in 2012, PEI was created out of the networks formed during the International Polar Year 2007–2008. This paper explores PEI's first five years (2012–17) of successes, challenges and opportunities that have led to the creation of an organization with over 1,500 members. Using a 'level of participation' framework for communities of practice, we examine the evolution of this educator-researcher network and focus on two key questions: 1) who has PEI reached and served over this time?, and 2) what are barriers to participation? Barriers include sustained engagement with researchers and establishing value within institutional frameworks that generally undervalue activities referred to as 'education and outreach' (EOC). EOC activities continue to be perceived as extra-curricular in both educator and researcher communities. Working to deepen collaboration with polar researchers and targeting a greater diversity of PEI's membership to fill core leadership functions should be future areas of focus for PEI as it looks to continue to shape polar EOC. Advancing and enhancing polar EOC extends well beyond PEI and should be a priority for the broader polar science and education communities. [ABSTRACT FROM AUTHOR]

The International Polar Year 2007–2008 stimulated a wide range of education, outreach and communication (EOC) related to polar research, and catalysed enthusiasm and networks that persist ten years on. Using a multi-method approach that incorporates case studies, auto-ethnographic interviews, and survey data, we interrogate the opportunities and limitations of polar EOC activities and propose a new framework for practical, reflexive, engagement design. Our research suggests that EOC activities are under-valued and often designed based on personal instinct rather than strategic planning, but that there is also a lack of accessible tools that support a more strategic design process. We propose three foci for increasing the professionalisation of practitioner approaches to EOC: (1) improved articulation of goals and objectives; (2) acknowledgement of different drivers, voices and power structures; and (3) increased practical training, resources and reporting structures. We respond to this by proposing a framework for planning and design of public engagement that provides an opportunity to become more transparent and explicit about the real goals of an activity and what "success" looks like. This is critical to effectively evaluate, learn from our experiences, share them with peers, and ultimately deliver more thoughtfully designed, effective engagement. [ABSTRACT FROM AUTHOR]

The development of formal discourse about education and outreach within the Antarctic Treaty Consultative Meetings (ATCM), and the influence of major international activities in this field, are described. This study reflects on the ATCM Parties' approach to implementing the ambition of the Protocol on Environmental Protection to the Antarctic Treaty Article 6.1.a, to promote the educational value of Antarctica and its environment, and examines the role of workshops and expert groups within the Scientific Committee on Antarctic Research (SCAR), the International Union for the Conservation of Nature (IUCN), and the Council of Managers of National Antarctic Programmes. These early initiatives, which emerged in the 1990s, were a prelude to the development and implementation of a large number of International Polar Year (IPY) education and outreach programmes. The establishment of an Antarctic Treaty System Intersessional Contact Group, and an online forum on education and outreach during the 2015 ATCM in Bulgaria, is a legacy of IPY and is the next step in fostering collaboration to engage people around the world in the importance and relevance of Antarctica to our daily lives. [ABSTRACT FROM AUTHOR]

Chironomidae larvae constituted the largest proportion of benthic invertebrates collected from 99 rivers stretching from northern Labrador (latitude 58°N) to northern parts of Ellesmere Island (82°N). We describe 92 species of Chironomidae (mainly larval forms) providing new descriptions, a revision for the adult female of Parametriocnemus boreoalpinus Gowin et Thienemann, a possible new genus (larval form only), and 9 larval forms that may represent a new species. In addition, new geographical distribution records are specified for 1 Nearctic species, 6 species in Canada, 10 for Labrador, and 17 for Nunavut. This work contributes to Environment Canada’s International Polar Year output (2007-2009).

International Polar Week is an educational activity that has been carried out since the International Polar Year 2007–2008 (known then as International Polar Days). This event, which brings together educators and polar scientists to promote polar science, is generally organised by the Association of Polar Early Career Scientists and Polar Educators International. Here we provide an overview of how International Polar Week started, and describe its implementation in Portugal, a "non-polar" country. We quantify the activities carried out during International Polar Weeks in Portugal between 2012 and 2017, which involved >96,000 students, >200 schools, >1900 educators and 100 polar scientists, with talks and Skype calls by polar scientists being the most frequent activities. Portugal's International Polar Weeks have involved students, educators and polar scientists from 18 other countries, in particular from the United Kingdom and Brazil. We conclude by providing recommendations to other countries wanting to implement International Polar Weeks. [ABSTRACT FROM AUTHOR]

A review of the results of Russian polar research performed in 2011-2014 is provided. It is based on material prepared by the Commission on Polar Meteorology of the National Geophysical Committee, Russian Academy of Sciences, for the National Report on Meteorology and Atmospheric Sciences submitted to General Assembly XXVI of the International Union of Geodesy and Geophysics [1]. [ABSTRACT FROM AUTHOR]

Background . The International Polar Year (IPY) 2007–2008 represented a unique opportunity to further stimulate cooperation and coordination on Arctic health research and increase the awareness and visibility of Arctic regions. The Arctic Human Health Initiative (AHHI) was a US-led Arctic Council IPY coordinating project that aimed to build and expand on existing International Union for Circumpolar Health (IUCH) and Arctic Council human health interests. The project aimed to link researchers with potential international collaborators and to serve as a focal point for human health research, education, outreach and communication activities during the IPY. The progress of projects conducted as part of this initiative up until the end of the Arctic Council Swedish chairmanship in May 2013 is summarized in this report. Design . The overall goals of the AHHI was to increase awareness and visibility of human health concerns of Arctic peoples, foster human health research, and promote health strategies that will improve health and well-being of all Arctic residents. Proposed activities to be recognized through the initiative included: expanding research networks that will enhance surveillance and monitoring of health issues of concern to Arctic peoples, and increase collaboration and coordination of human health research; fostering research that will examine the health impact of anthropogenic pollution, rapid modernization and economic development, climate variability, infectious and chronic diseases, intentional and unintentional injuries, promoting education, outreach and communication that will focus public and political attention on Arctic health issues, using a variety of publications, printed and electronic reports from scientific conferences, symposia and workshops targeting researchers, students, communities and policy makers; promoting the translation of research into health policy and community action including implementation of prevention strategies and health promotion; and promoting synergy and strategic direction of Arctic human health research and health promotion. Results . As of 31 March, 2009, the official end of the IPY, AHHI represented a total of 38 proposals, including 21 individual Expressions of Intent (EoI), and 9 full proposals (FP), submitted to the IPY Joint Committee for review and approval from lead investigators from the US, Canada, Greenland, Norway, Finland, Sweden and the Russian Federation. In addition, there were 10 National Initiatives (NI-projects undertaken during IPY beyond the IPY Joint Committee review process). Individual project details can be viewed at www.arctichealth.org. The AHHI currently monitors the progress of 28 individual active human health projects in the following thematic areas: health network expansion (5 projects), infectious disease research (7 projects), environmental health research (7 projects), behavioural and mental health research (4 projects), and outreach education and communication (5 projects). Conclusions . While some projects have been completed, others will continue well beyond the IPY. The IPY 2007–2008 represented a unique opportunity to further stimulate cooperation and coordination on Arctic health research and increase the awareness and visibility of Arctic regions.

Objectives . Evaluate the course of the International Union for Circumpolar Health (IUCH) and the Proceedings of the International Congress(s) on Circumpolar Health (ICCH) in the context of the concomitant historical events. Make recommendations for future circumpolar health research. Study design . Medline search and historical archive search of ICCH Proceedings. Methods . Search of all PubMed resources from 1966 concerning the circumpolar health movement. Two University of Alaska, Anchorage Archive Collections were searched: the C. E. Albrecht and Frank Pauls Archive Collections. Results . Fourteen sets of Proceedings manuscripts and one set of Proceedings Abstracts were evaluated. There was a trend towards consistent use of the existing journals with indexing in Index Medicus; shorter intervals between the Congress and Proceedings manuscript publication; and increased online availability of either the Table of Contents or Proceedings citations.Recent additions include online publication of full-length manuscripts and 2 instances of full peer-review evaluations of the Proceedings manuscripts. These trends in Proceedings publication are described within the course of significant events in the circumpolar health movement. During this period, the IUCH funds are at an all-time low and show little promise of increasing, unless significant alternative funds strategies are pursued. Conclusions . The IUCH has matured politically over these years, but some of the same questions persist over the years. There has been a trend towards more rapid dissemination of scientific content, more analytic documentation of epidemiologic study design and trend towards wider dissemination of scientific content through the Internet. Significant progress in each of those areas is still possible and desirable. In the meantime, the IUCH should encourage alternative funding strategies by developing a foundation to support on-going expenses, for example Hildes awards; explore venues to finance Council President and At-Large members travel costs; and seek grants to fund special projects, for example special supplements in the IJCH.

Within the polar science community the Polar (and Geophysical) Years represent signal events. We often read, largely within geoscience literature, that those events represented positive and dramatic steps forward in international science. From five recent books—two historical compilations and three personal narratives—augmented by interviews with a few key participants, a more cautious picture emerges, of remarkable successes but also of occasional or even persistent missteps and deficiencies. An improved understanding of the IPY concept and experience can provide useful guidance for future polar and global science.

Background. The Canadian International Polar Year (IPY) program made it possible to undertake much needed health research in 3 jurisdictions within the Canadian Inuit Nunangat (homeland) over a 2-year period: Inuvialuit Settlement Region (ISR), Nunavut Territory, and Nunatsiavut. Design. The Adult Inuit Health Survey (IHS) was a cross-sectional survey and provides baseline data upon which future comparisons can be made for prospectively assessing factors leading to the progression of chronic diseases among Canadian Inuit. With the help of the Canadian Coast Guard Ship Amundsen, which was equipped with research and laboratory facilities, 33 coastal communities were visited; land survey teams visited 3 inland communities. Results. The Adult IHS succeeded in obtaining important baseline information concerning the health status and living conditions of 2,595 adults living in ISR, Nunavut and Nunatsiavut. Conclusion. Information from this survey will be useful for future comparisons and the opportunity to link with the International Inuit Cohort, a follow-up evaluation, and for the development of future health policies and public health interventions.

The McMurdo Dry Valleys are one of the most arid environments on Earth. Over the soil landscape for the majority of the year, biological and ecosystem processes in the dry valleys are constrained by the low temperatures and limited availability of water. The prevalence of these physical limitations in controlling biological and ecosystem processes makes the dry valleys a climate-sensitive system, poised to experience substantial changes following projected future warming. Short-duration increases in summer temperatures are associated with pulses of water from melting ice reserves, including glaciers, snow and permafrost. Such pulses alter soil geochemistry by mobilizing and redistributing soil salts (via enhanced weathering, solubility and mobility), which can alter habitat suitability for soil organisms. Resulting changes in soil community composition or distribution may alter the biogeochemical processes in which they take part. Here, we review the potential impacts of meltwater pulses and present new field data documenting instances of meltwater pulse events that result from different water sources and hydrological patterns, and discuss their potential influence on soil biology and biogeochemistry. We use these examples to discuss the potential impacts of future climate change on the McMurdo Dry Valley soil ecosystem.

The fourth International Polar Year (IPY), which ended in March 2009, represented a ca. 50% increase in the funding of polar science, a major expansion of the observing effort across polar and subpolar seas, the deployment of a wide range of new and complex observing techniques and a gratifying new degree of international collaboration in their use. As a result, the IPY has revolutionized our polar data sets to provide our first real glimpse of the ocean–atmosphere–cryosphere operating as a complete system. Here we focus on one particular aspect of the emerging results—the “connectivities” that may develop between individual research projects over time, developing the complexity of our understanding in real if unexpected ways as new findings emerge, ramify and mesh within projects or between them. For simplicity, we illustrate this valuable but unpredictable process by using one particular Arctic–sub-Arctic project—Canada Three Oceans—as our initial reference point and attempting to trace out a small subset of its inter-connections across space, time, projects and disciplines.

Over the last 60 years, the perception of the Arctic Ocean has changed from a hostile, sluggish, steady, ice-covered environment with little global impact to an ocean that has become increasingly accessible, apparently rapidly changing, only partly ice-covered, and connected to the global meridional overturning circulation. Our new observations demonstrate that waters off Northwest Greenland constitute the final limb in the grand cyclonic circulation of the Atlantic layer in the Arctic Ocean. These waters with an Atlantic water mass signature are warming in Nares Strait to the west of Greenland as they are elsewhere. Estimates of the magnitude and uncertainty of this warming are emerging from both moored observations and historical hydrographic station data.Ocean temperatures sensed by instruments moored 3 m above the bottom between 228 and 366 m depth in Nares Strait suggest a mean warming of about 0.023 ± 0.015°C per year for the 2003–2009 period at 95% confidence. Salinity changes for the same period are not significantly different from zero. Nevertheless, oscillating bottom temperatures covary with salinities. Mean bottom salinities in Nares Strait exceed 34.56 psu while no water with salinities above 34.51 psu occurs in Baffin Bay to the south. These data indicate a dominantly northern source for the waters sensed by our moorings. Mean bottom temperatures hover near 0°C, which suggests minimal influence of waters from the northeastern Amundsen Basin in the Arctic Ocean. Thus, we conclude that the observed warming originates from the northeastern Canadian Basin to the southwest of our study area.In addition to these mean conditions, we find large interannual variability. For example, significant freshening emerges for the 2003–2006 period that reaches –0.02 ± 0.008 psu per year without significant concurrent temperature trends at three sensor locations. These data contrast with the 2007–2009 observational period when five different sensors all indicate warmer waters (0.063 ± 0.017°C per year) and saltier waters (0.027 ± 0.01 psu per year), which reverses the 2003–2006 freshening. We speculate that some of these observed changes are caused by a changing ice regime. During the 2003–2006 winters, ice was landfast, while during 2007–2009 it was generally mobile year-round. The warming impacts tidewater glaciers along northern Greenland with sill depths below 300 m, for example, Petermann Gletscher.

Along with the dramatic decrease in global geomagnetic field intensity, recent observations demonstrate that the geomagnetic field in the Arctic has dramatically changed over the last century. This change is best illustrated by the recent migration of the North Magnetic Pole (which has been in the Canadian Arctic for the last 400 years) into the Arctic Ocean. Because historical records are short, paleomagnetic studies are needed to put these recent Arctic geomagnetic changes into a proper temporal context. This paper presents an overview of Arctic geomagnetism, paleomagnetism, and recent efforts to move our understanding forward by looking at recent or emerging high-resolution Holocene records from the Low and the High Arctic. These paleomagnetic records attest to the unique nature of the geomagnetic field in the High Arctic. They also highlight how the Arctic, and especially the High Arctic, is a unique vantage point for studying geodynamo processes associated with the tangent cylinder model of convective flow within Earth's core that could lead to differences in the behavior of the geomagnetic field observed at Earth's surface, and possible relationships to paleomagnetic secular variations at mid-latitudes.

This essay shares the broad outlines of Yup'ik and Inuit views of their coastal environment, with special emphasis on the role of sea ice and ocean swells. Nearshore conditions in the eastern Bering Sea and Canadian Arctic are used to show how shared knowledge can benefit both local residents and scientists working to better understand coastal processes. We propose a strategy that will allow integration of observations that occur at different scales, required to improve communication between stakeholders in a rapidly changing Arctic. The emerging question is how local observations can be linked to larger environmental issues in ways that speak to both indigenous and Western concerns.

In recent decades, the Arctic Ocean has changed dramatically. Exchanges through the main oceanic gateways indicate two main processes of global climatic importance—poleward oceanic heat flux into the Arctic Ocean and export of freshwater toward the North Atlantic. Since the 1990s, in particular during the International Polar Year (2007–2009), extensive observational efforts were undertaken to monitor volume, heat, and freshwater fluxes between the Arctic Ocean and the subpolar seas on scales from daily to multiyear. This paper reviews present-day estimates of oceanic fluxes and reports on technological advances and existing challenges in measuring exchanges through the main oceanic gateways to the Arctic.

Could a gradual warming trend, combined with a large atmospheric or oceanic event, and mediated by Arctic-specific feedbacks, lead to persistent changes in Arctic climate? Several recent observed shifts follow this pattern: they are large, they occur across the Earth system, they are happening decades earlier than suggested by climate models, and while they may or may not be irreversible, they at least carry multiple-year memory (i.e., they are longer than the extreme event that was their proximate cause). When the 2007 summer sea ice minimum occurred, Arctic temperatures had been rising and sea ice had been decreasing over the previous two decades. Nevertheless, it took an unusually persistent southerly wind pattern over the summer months, and perhaps ocean transport and other factors, to initiate the loss event. The abrupt warming and associated record ice loss in West Greenland in 2010 also fit this hypothesis, initiated by southerly winds associated with an unusual manifestation of a natural climate pattern, the North Atlantic Oscillation. Extensive forest fires are causing deep burning of the soil layer, changing the carbon response of Arctic landmasses with lasting effects. Anomalous atmospheric circulation patterns in winter 2009–2010 and December 2010 linked cold-air outbreaks from the Arctic with mid-latitudes. While continued anthropogenic forcing predicts continued temperature increases and sea ice loss, these larger variations or "surprises" introduce uncertainties in the timing and magnitude of future Arctic shifts, the degree to which they are reversible or not, and how they will influence future local and global climate. Climate models, while imperfect, can be run multiple times, in series that are called "ensemble members," to capture a range of potential responses to randomly occurring extreme events combined with continuing anthropogenic warming trends.

This paper reviews current knowledge of sedimentation patterns in the Arctic Ocean during the pronounced climatic cycles of the last several hundred thousand years, an especially relevant time period that provides long-term context for present climate change. The review is largely based on data collected during recent research icebreaker cruises to the Arctic Ocean, with a focus on the 2005 Healy-Oden TransArctic Expedition (HOTRAX) and 2007 Lomonosov Ridge Off Greenland (LOMROG) expedition. The sediment cores and geophysical seafloor mapping data collected enable reconstruction of past oceanic environments. Evaluation of these data suggests that the two major Arctic Ocean circulation systems, the Trans-Polar Drift and the Beaufort Gyre, persisted throughout most of the Late to Middle Quaternary, approximately the last 0.5 to 0.7 million years. Extreme conditions, nonanalogous to modern environments, also occurred in the past, especially during Pleistocene glacial intervals. Some of these intervals likely featured much thickened and/or concentrated sea ice and incursions of ice shelves and armadas of megasized icebergs from the margins to the center of the Arctic Ocean. In contrast, much warmer conditions with reduced sea ice extent existed during interglacial periods. Characterization of ice conditions during these intervals is critical for evaluating the present and projected future reduction of Arctic sea ice.

Ice-Tethered Profilers (ITPs), first deployed in fall 2004, have significantly increased the number of high-quality upper-ocean water-property observations available from the central Arctic. This article reviews the instrument technology and provides a status report on performance, along with several examples of the science that ITPs and companion instrumentation support.

Ocean currents, water masses, and seasonal sea ice formation determine linkages among and barriers between the biotas of the Bering, Chukchi, and Beaufort Seas. The Bering Sea communicates with the Chukchi and Beaufort Seas via northward advection of water, nutrients, and plankton through Bering Strait. However, continuity of the ocean's physical properties is modulated by regional differences in heat, salt, and sea ice budgets, in particular, along the meridional gradient. Using summer density data from zooplankton, fish (bottom and surface trawl), and seabird surveys, we define three biogeographic provinces: the Eastern Bering Shelf Province (the eastern Bering Sea shelf south of Saint Lawrence Island), the Chirikov-Chukchi Province (the eastern Bering Sea shelf north of Saint Lawrence Island [Chirikov Basin] and Chukchi Sea), and the Beaufort Sea Province. Regional differences in summer distributions of biota largely reflect the underlying oceanography. Climate warming will reduce the duration and possibly the extent of seasonal ice cover in the Eastern Bering Shelf Province, but this warming may not lead to increased abundance of some subarctic species because seasonal ice cover and cold (< 2°C) bottom waters on the Bering shelf form a barrier to the northward migration of subarctic bottom fish species typical of the southeastern Bering Sea. While Arctic species that are dependent upon the summer extent of sea ice face an uncertain future, other Arctic species' resilience to a changing climate will be derived from waters that continue to freeze each winter.

Observational data show that the Arctic Ocean has significantly and rapidly changed over the last few decades, which is unprecedented in the observational record. Air and water temperatures have increased, sea ice volume and extent have decreased, permafrost has thawed, storminess has increased, sea level has risen, coastal erosion has progressed, and biological processes have become more complex and diverse. In addition, there are socio-economic impacts of Arctic environmental change on Arctic residents and the world, associated with tourism, oil and gas exploration, navigation, military operations, trade, and industry. This paper discusses important results of the Arctic Ocean Model Intercomparison Project, which is advancing the role of numerical modeling in Arctic Ocean and sea ice research by stimulating national and international synergies for high-latitude research.

Arctic sea ice cover has declined over the past few decades. The end of summer September ice extent reached a record minimum in 2007. While there has been a modest recovery since then, the past four years (2007–2010) show the lowest sea ice extent in the 30-year satellite record. Submarine and satellite ice thickness measurements show a factor of two decrease (3 m to 1. 4 m) from 1957–1976 to 2003–2007. There has been a shift from sea ice cover consisting mainly of ice more than a year old to ice less than a year old. These changes have resulted in a less robust ice cover that is more sensitive to dynamic and thermodynamic forcing. Changes in atmospheric pressure fields in recent years have affected the distribution of ice in the Arctic Basin. Increases in advected ocean heat through Bering Strait may serve as a trigger for ice retreat in the Chukchi and Beaufort Seas. More open water has led to enhanced solar heat input and warming of the upper ocean and greater ice melt. While there may not be a tipping point for Arctic sea ice cover, positive feedbacks do contribute to rapid changes. The declining Arctic sea ice cover is affecting human activities.

Since the Arctic Ocean began forming in the Early Cretaceous 112–140 million years ago, the Arctic region has undergone profound oceanographic and paleoclimatic changes. It has evolved from a warm epicontinental sea to its modern state as a cold isolated ocean with extensive perennial sea ice cover. Our understanding of the long-term paleoclimate evolution of the Arctic remains fragmentary but has advanced dramatically in the past decade through analysis of new marine and terrestrial records, supplemented by important insights from paleoclimate models. Improved understanding of how these observations fit into the long-term evolution of the global climate system requires additional scientific drilling in the Arctic to provide detailed and continuous paleoclimate records, and to resolve the timing and impact of key tectonic and physiographic changes to the ocean basin and surrounding landmasses. Here, we outline the long-term paleoclimatic evolution of the Arctic, with a focus on integrating both terrestrial and marine records.

The porous nature of sea ice not only provides a habitat for ice algae but also opens a pathway for exchanges of organic matter, nutrients, and gases with the seawater below and the atmosphere above. These constituents permeate the ice cover through air-ice gas exchange, brine drainage, seawater entrainment into the ice, and air-sea gas exchange within leads and polynyas. The central goal in sea ice biogeochemistry since the 1980s has been to discover the physical, biological, and chemical rates and pathways by which sea ice affects the distribution and storage of biogenic gases (namely CO2, O2, and dimethyl sulfide) between the ocean and the atmosphere. Historically, sea ice held the fascination of scientists for its role in the ocean heat budget, and the resulting view of sea ice as a barrier to heat and mass transport became its canonical representation. However, the recognition that sea ice contains a vibrant community of ice-tolerant organisms and strategic reserves of carbon has brought forward a more nuanced view of the "barrier" as an active participant in polar biogeochemical cycles. In this context, the organisms and their habitat of brine and salt crystals drive material fluxes into and out of the ice, regulated by liquid and gas permeability. Today, scientists who study sea ice are acutely focused on determining the flux pathways of inorganic carbon, particulate organics, climate-active gases, excess carbonate alkalinity, and ultimately, the role of all of these constituents in the climate system. Thomas and Dieckmann (2010) recently reviewed sea ice biogeochemistry, and so we do not attempt a comprehensive review here. Instead, our goal is to provide a historical perspective, along with some recent discoveries and observations to highlight the most outstanding questions and possibly useful avenues for future research.

The Arctic Ocean is a potentially important sink for atmospheric carbon dioxide (CO2) with a recent estimate suggesting that the region contributes from 5 to 14% of the global ocean's net uptake of CO2. In the western Arctic Ocean, the focus of this paper, the Chukchi Sea is a strong ocean sink for CO2 that is partially compensated for by outgassing of CO2 from the East Siberian Sea shelf. The Arctic marine carbon cycle and exchange of CO2 between the ocean and atmosphere appear particularly sensitive to environmental changes, including sea ice loss, warming, changes in seasonal marine phytoplankton primary production, changes in ocean circulation and freshwater inputs, and even the impacts of ocean acidification. In the near term, further sea ice loss, increases in phytoplankton growth rates, and other environmental and physical changes in the Arctic are expected to cause a limited net increase in the uptake of CO2 by Arctic surface waters. Recent studies suggest that this enhanced uptake will be short lived, with surface waters rapidly warming and equilibrating with the atmosphere. Furthermore, release of large stores of carbon from the surrounding Arctic landmasses through rivers into the Arctic Ocean and further warming over the next century may alter the Arctic from a CO2 sink to a source over the next century.