The large‐scale freshwater cycle of the Arctic

This paper synthesizes our understanding of the Arctic\u27s large‐scale freshwater cycle. It combines terrestrial and oceanic observations with insights gained from the ERA‐40 reanalysis and land surface and ice‐ocean models. Annual mean freshwater input to the Arctic Ocean is dominated by river discharge (38%), inflow through Bering Strait (30%), and net precipitation (24%). Total freshwater export from the Arctic Ocean to the North Atlantic is dominated by transports through the Canadian Arctic Archipelago (35%) and via Fram Strait as liquid (26%) and sea ice (25%). All terms are computed relative to a reference salinity of 34.8. Compared to earlier estimates, our budget features larger import of freshwater through Bering Strait and larger liquid phase export through Fram Strait. While there is no reason to expect a steady state, error analysis indicates that the difference between annual mean oceanic inflows and outflows (∼8% of the total inflow) is indistinguishable from zero. Freshwater in the Arctic Ocean has a mean residence time of about a decade. This is understood in that annual freshwater input, while large (∼8500 km3), is an order of magnitude smaller than oceanic freshwater storage of ∼84,000 km3. Freshwater in the atmosphere, as water vapor, has a residence time of about a week. Seasonality in Arctic Ocean freshwater storage is nevertheless highly uncertain, reflecting both sparse hydrographic data and insufficient information on sea ice volume. Uncertainties mask seasonal storage changes forced by freshwater fluxes. Of flux terms with sufficient data for analysis, Fram Strait ice outflow shows the largest interannual variability

Moving through MOOCS: pedagogy, learning design and patterns of engagement

Massive open online courses (MOOCs) are part of the lifelong learning experience of people worldwide. Many of these learners participate fully. However, the high levels of dropout on most of these courses are a cause for concern. Previous studies have suggested that there are patterns of engagement within MOOCs that vary according to the pedagogy employed. The current paper builds on this work and examines MOOCs from different providers that have been offered on the FutureLearn platform. A cluster analysis of these MOOCs shows that engagement patterns are related to pedagogy and course duration. Learners did not work through a three-week MOOC in the same ways that learners work through the first three weeks of an eight-week MOOC

Coupled wind-forced controls of the Bering–Chukchi shelf circulation and the Bering Strait throughflow: Ekman transport, continental shelf waves, and variations of the Pacific–Arctic sea surface height gradient

AbstractWe develop a conceptual model of the closely co-dependent Bering shelf, Bering Strait, and Chukchi shelf circulation fields by evaluating the effects of wind stress over the North Pacific and western Arctic using atmospheric reanalyses, current meter observations, satellite-based sea surface height (SSH) measurements, hydrographic profiles, and numerical model integrations. This conceptual model suggests Bering Strait transport anomalies are primarily set by the longitudinal location of the Aleutian Low, which drives oppositely signed anomalies at synoptic and annual time scales. Synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves, whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along-strait (meridional) pressure gradient. In particular, we show that storms centered over the Bering Sea excite continental shelf waves on the eastern Bering shelf that carry northward velocity anomalies northward through Bering Strait and along the Chukchi coast. The integrated effect of these storms tends to decrease the northward Bering Strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the Aleutian Basin and the Western Subarctic Gyre. Ekman suction then increases the water column density through isopycnal uplift, thereby decreasing the dynamic height, sea surface height, and along-strait pressure gradient. Storms displaced eastward over the Gulf of Alaska generate an opposite set of Bering shelf and Aleutian Basin responses. While Ekman pumping controls Canada Basin dynamic heights (Proshutinsky et al., 2002), we do not find evidence for a strong relation between Beaufort Gyre sea surface height variations and the annually averaged Bering Strait throughflow. Over the western Chukchi and East Siberian seas easterly winds promote coastal divergence, which also increases the along-strait pressure head, as well as generates shelf waves that impinge upon Bering Strait from the northwest

A Synthesis of Year-Round Interdisciplinary Mooring Measurements in the Bering Strait (1990-2014) and the RUSALCA Years (2004-2011)

The flow through the Bering Strait, the only Pacific-Arctic oceanic gateway, has dramatic local, regional, and global impacts. Advanced year-round moored technology quantifies challengingly large temporal (subdaily, seasonal, and interannual) and spatial variability in the ~85 km wide, two-channel strait. The typically northward flow, intensified seasonally in the ~10–20 km wide, warm, fresh, nutrient-poor Alaskan Coastal Current (ACC) in the east, is otherwise generally homogeneous in velocity throughout the strait, although with higher salinities and nutrients and lower temperatures in the west. Velocity and water properties respond rapidly (including flow reversals) to local wind, likely causing most of the strait’s approximately two-layer summer structure (by “spilling” the ACC) and winter water-column homogenization. We identify island-trapped eddy zones in the central strait; changes in sea-ice properties (season mean thicknesses from 2 m); and increases in annual mean volume, heat, and freshwater fluxes from 2001 to present (2013). Tantalizing first results from year-round bio-optics, nitrate, and ocean acidification sensors indicate significant seasonal and spatial change, possibly driven by the spring bloom. Moored acoustic recorders show large interannual variability in sub-Arctic whale occurrence, related perhaps to water property changes. Substantial daily variability demonstrates the dangers of interpreting section data and the necessity for year-round interdisciplinary time-series measurements.This is the publisher’s final pdf. The published article is copyrighted by the Oceanography Society and can be found at: http://tos.org/oceanography/article/a-synthesis-of-year-round-interdisciplinary-mooring-measurements-in-the-ber Bering Strait physical oceanographic data are available via http://psc.apl.washington.edu/BeringStrait.html and the National Oceanographic Data Center (https://www.nodc.noaa.gov); ocean acidification data, via http://aoncadis.org; and marine mammal acoustic data, via http://aoncadis.org and http://AOOS.org

Mean and seasonal circulation of the eastern Chukchi Sea from moored timeseries in 2013-2014

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(5), (2021): e2020JC016863, https://doi.org/10.1029/2020JC016863.From late-summer 2013 to late-summer 2014, a total of 20 moorings were maintained on the eastern Chukchi Sea shelf as part of five independent field programs. This provided the opportunity to analyze an extensive set of timeseries to obtain a broad view of the mean and seasonally varying hydrography and circulation over the course of the year. Year-long mean bottom temperatures reflected the presence of the strong coastal circulation pathway, while mean bottom salinities were influenced by polynya/lead activity along the coast. The timing of the warm water appearance in spring/summer is linked to advection along the various flow pathways. The timing of the cold water appearance in fall/winter was not reflective of advection nor related to the time of freeze-up. Near the latitude of Barrow Canyon, the cold water was accompanied by freshening. A one-dimensional mixed-layer model demonstrates that wind mixing, due to synoptic storms, overturns the water column resulting in the appearance of the cold water. The loitering pack ice in the region, together with warm southerly winds, melted ice and provided an intermittent source of fresh water that was mixed to depth according to the model. Farther north, the ambient stratification prohibits wind-driven overturning, hence the cold water arrives from the south. The circulation during the warm and cold months of the year is different in both strength and pattern. Our study highlights the multitude of factors involved in setting the seasonal cycle of hydrography and circulation on the Chukchi shelf.The authors are extremely grateful to all of these individuals, and to the funding agencies that supported the respective field programs: The Bureau of Ocean Energy Management; The National Oceanic and Atmospheric Administration; The National Science Foundation; and The Japanese Agency for Marine-Earth Science and Technology. Support for this analysis was provided by the following grants: National Oceanic and Atmospheric Administration grant NA14OAR4320158; National Science Foundation grants PLR-1504333, OPP-1733564, PLR-1758565; North Pacific Research Board grants A91-99a and A91-00a; Chinese Arctic and Antarctic grant CXPT2020009; Natural Sciences and Engineering Research Council of Canada

Flow of bottom water in the northwestern Weddell Sea

The Weddell Sea is known to feed recently formed deep and bottom water into the Antarctic circumpolar water belt, from whence it spreads into the basins of the world ocean. The rates are still a matter of debate. To quantify the flow of bottom water in the northwestern Weddell Sea data obtained during five cruises with R/V Polarstern between October 1989 and May 1998 were used. During the cruises in the Weddell Sea, five hydrographic surveys were carried out to measure water mass properties, and moored instruments were deployed over a time period of 8.5 years to obtain quasi-continuous time series. The average flow in the bottom water plume in the northwestern Weddell Sea deduced from the combined conductivity-temperature-depth and moored observations is 1.3±0.4 Sv. Intensive fluctuations of a wide range of timescales including annual and interannual variations are superimposed. The variations are partly induced by fluctuations in the formation rates and partly by current velocity fluctuations related to the large-scale circulation. Taking into account entrainment of modified Warm Deep Water and Weddell Sea Deep Water during the descent of the plume along the slope, between 0.5 Sv and 1.3 Sv of surface-ventilated water is supplied to the deep sea. This is significantly less than the widely accepted ventilation rates of the deep sea. If there are no other significant sources of newly ventilated water in the Weddell Sea, either the dominant role of Weddell Sea Bottom Water in the Southern Ocean or the global ventilation rates have to be reconsidered

Model-observation and reanalyses comparison at key locations for heat transport to the Arctic: Assessment of key lower latitude influences on the Arctic and their simulation

Blue-Action Work Package 2 (WP2) focuses on lower latitude drivers of Arctic change, with a focus on the influence of the Atlantic Ocean and atmosphere on the Arctic. In particular, warm water travels from the Atlantic, across the Greenland-Scotland ridge, through the Norwegian Sea towards the Arctic. A large proportion of the heat transported northwards by the ocean is released to the atmosphere and carried eastward towards Europe by the prevailing westerly winds. This is an important contribution to northwestern Europe's mild climate. The remaining heat travels north into the Arctic. Variations in the amount of heat transported into the Arctic will influence the long term climate of the Northern Hemisphere. Here we assess how well the state of the art coupled climate models estimate this northwards transport of heat in the ocean, and how the atmospheric heat transport varies with changes in the ocean heat transport. We seek to improve the ocean monitoring systems that are in place by introducing measurements from ocean gliders, Argo floats and satellites. These state of the art computer simulations are evaluated by comparison with key trans-Atlantic observations. In addition to the coupled models ‘ocean-only’ evaluations are made. In general the coupled model simulations have too much heat going into the Arctic region and the transports have too much variability. The models generally reproduce the variability of the Atlantic Meridional Ocean Circulation (AMOC) well. All models in this study have a too strong southwards transport of freshwater at 26°N in the North Atlantic, but the divergence between 26°N and Bering Straits is generally reproduced really well in all the models. Altimetry from satellites have been used to reconstruct the ocean circulation 26°N in the Atlantic, over the Greenland Scotland Ridge and alongside ship based observations along the GO-SHIP OVIDE Section. Although it is still a challenge to estimate the ocean circulation at 26°N without using the RAPID 26°N array, satellites can be used to reconstruct the longer term ocean signal. The OSNAP project measures the oceanic transport of heat across a section which stretches from Canada to the UK, via Greenland. The project has used ocean gliders to great success to measure the transport on the eastern side of the array. Every 10 days up to 4000 Argo floats measure temperature and salinity in the top 2000m of the ocean, away from ocean boundaries, and report back the measurements via satellite. These data are employed at 26°N in the Atlantic to enable the calculation of the heat and freshwater transports. As explained above, both ocean and atmosphere carry vast amounts of heat poleward in the Atlantic. In the long term average the Atlantic ocean releases large amounts of heat to the atmosphere between the subtropical and subpolar regions, heat which is then carried by the atmosphere to western Europe and the Arctic. On shorter timescales, interannual to decadal, the amounts of heat carried by ocean and atmosphere vary considerably. An important question is whether the total amount of heat transported, atmosphere plus ocean, remains roughly constant, whether significant amounts of heat are gained or lost from space and how the relative amount transported by the atmosphere and ocean change with time. This is an important distinction because the same amount of anomalous heat transport will have very different effects depending on whether it is transported by ocean or the atmosphere. For example the effects on Arctic sea ice will depend very much on whether the surface of the ice experiences anomalous warming by the atmosphere versus the base of the ice experiencing anomalous warming from the ocean. In Blue-Action we investigated the relationship between atmospheric and oceanic heat transports at key locations corresponding to the positions of observational arrays (RAPID at 26°N, OSNAP at ~55N, and the Denmark Strait, Iceland-Scotland Ridge and Davis Strait at ~67N) in a number of cutting edge high resolution coupled ocean-atmosphere simulations. We split the analysis into two different timescales, interannual to decadal (1-10 years) and multidecadal (greater than 10 years). In the 1-10 year case, the relationship between ocean and atmosphere transports is complex, but a robust result is that although there is little local correlation between oceanic and atmospheric heat transports, Correlations do occur at different latitudes. Thus increased oceanic heat transport at 26°N is accompanied by reduced heat transport at ~50N and a longitudinal shift in the location of atmospheric flow of heat into the Arctic. Conversely, on longer timescales, there appears to be a much stronger local compensation between oceanic and atmospheric heat transport i.e. Bjerknes compensation

Monitoring Alaskan Arctic shelf ecosystems through collaborative observation networks

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Danielson, S. L., Grebmeier, J. M., Iken, K., Berchok, C., Britt, L., Dunton, K. H., Eisner, L., V. Farley, E., Fujiwara, A., Hauser, D. D. W., Itoh, M., Kikuchi, T., Kotwicki, S., Kuletz, K. J., Mordy, C. W., Nishino, S., Peralta-Ferriz, C., Pickart, R. S., Stabeno, P. S., Stafford. K. M., Whiting, A. V., & Woodgate, R. Monitoring Alaskan Arctic shelf ecosystems through collaborative observation networks. Oceanography, 35(2), (2022): 52, https://doi.org/10.5670/oceanog.2022.119.Ongoing scientific programs that monitor marine environmental and ecological systems and changes comprise an informal but collaborative, information-rich, and spatially extensive network for the Alaskan Arctic continental shelves. Such programs reflect contributions and priorities of regional, national, and international funding agencies, as well as private donors and communities. These science programs are operated by a variety of local, regional, state, and national agencies, and academic, Tribal, for-profit, and nongovernmental nonprofit entities. Efforts include research ship and autonomous vehicle surveys, year-long mooring deployments, and observations from coastal communities. Inter-program coordination allows cost-effective leveraging of field logistics and collected data into value-added information that fosters new insights unattainable by any single program operating alone. Coordination occurs at many levels, from discussions at marine mammal co-management meetings and interagency meetings to scientific symposia and data workshops. Together, the efforts represented by this collection of loosely linked long-term monitoring programs enable a biologically focused scientific foundation for understanding ecosystem responses to warming water temperatures and declining Arctic sea ice. Here, we introduce a variety of currently active monitoring efforts in the Alaskan Arctic marine realm that exemplify the above attributes.Funding sources include the following: ALTIMA: BOEM M09PG00016, M12PG00021, and M13PG00026; AMBON: NOPP-NA14NOS0120158 and NOPP-NA19NOS0120198; Bering Strait moorings: NSF-OPP-AON-PLR-1758565, NSF-OPP-PLR-1107106; BLE-LTER: NSF-OPP-1656026; CEO: NPRB-L36, ONR N000141712274 and N000142012413; DBO: NSF-AON-1917469 and NOAA-ARP CINAR-22309.07; HFR, AOOS Arctic glider, and Passive Acoustics at CEO and Bering Strait: NA16NOS0120027; WABC: NSF-OPP-1733564. JAMSTEC: partial support by ArCS Project JPMXD1300000000 and ArCS II Project JPMXD1420318865; Seabird surveys: BOEM M17PG00017, M17PG00039, and M10PG00050, and NPRB grants 637, B64, and B67. This publication was partially funded by the Cooperative Institute for Climate, Ocean, & Ecosystem Studies (CICOES) under NOAA Cooperative Agreement NA20OAR4320271, and represents contribution 2021-1163 to CICOES, EcoFOCI-1026, and 5315 to PMEL. This is NPRB publication ArcticIERP-43

The Arctic freshwater system : changes and impacts

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): G04S54, doi:10.1029/2006JG000353.Dramatic changes have been observed in the Arctic over the last century. Many of these involve the storage and cycling of fresh water. On land, precipitation and river discharge, lake abundance and size, glacier area and volume, soil moisture, and a variety of permafrost characteristics have changed. In the ocean, sea ice thickness and areal coverage have decreased and water mass circulation patterns have shifted, changing freshwater pathways and sea ice cover dynamics. Precipitation onto the ocean surface has also changed. Such changes are expected to continue, and perhaps accelerate, in the coming century, enhanced by complex feedbacks between the oceanic, atmospheric, and terrestrial freshwater systems. Change to the arctic freshwater system heralds changes for our global physical and ecological environment as well as human activities in the Arctic. In this paper we review observed changes in the arctic freshwater system over the last century in terrestrial, atmospheric, and oceanic systems.The authors gratefully acknowledge the National Science Foundation (NSF) for funding this synthesis work. This paper is principally the work of authors funded under the NSF-funded Freshwater Integration (FWI) study