Introduction to special collection on Arctic Ocean modeling and observational synthesis (FAMOS) 2: Beaufort Gyre phenomenon

Author Posting. © American Geophysical Union, 2020. 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 125(2), (2020): e2019JC015400, doi:10.1029/2019JC015400.One of the foci of the Forum for Artic Modeling and Observational Synthesis (FAMOS) project is improving Arctic regional ice‐ocean models and understanding of physical processes regulating variability of Arctic environmental conditions based on synthesis of observations and model results. The Beaufort Gyre, centered in the Canada Basin of the Arctic Ocean, is an ideal phenomenon and natural laboratory for application of FAMOS modeling capabilities to resolve numerous scientific questions related to the origin and variability of this climatologic freshwater reservoir and flywheel of the Arctic Ocean. The unprecedented volume of data collected in this region is nearly optimal to describe the state and changes in the Beaufort Gyre environmental system at synoptic, seasonal, and interannual time scales. The in situ and remote sensing data characterizing ocean hydrography, sea surface heights, ice drift, concentration and thickness, ocean circulation, and biogeochemistry have been used for model calibration and validation or assimilated for historic reconstructions and establishing initial conditions for numerical predictions. This special collection of studies contributes time series of the Beaufort Gyre data; new methodologies in observing, modeling, and analysis; interpretation of measurements and model output; and discussions and findings that shed light on the mechanisms regulating Beaufort Gyre dynamics as it transitions to a new state under different climate forcing.We would like to thank all FAMOS participants (https://web.whoi.edu/famos/ and https://famosarctic.com/) and collaborators of the Beaufort Gyre Exploration project (https://www.whoi.edu/beaufortgyre) for their continued enthusiasm, creativity, and support during all stages of both projects. This research is supported by the National Science Foundation Office of Polar Programs (projects 1845877, 1719280, and 1604085). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Arctic dynamic topography/geostrophic currents data were provided by the Centre for Polar Observation and Modelling, University College London (www.cpom.ucl.ac.uk/dynamic_topography; Armitage et al. (2016, 2017). The other data used in this paper are available at the NCAR/NCEP (https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html), NSIDC (https://nsidc.org/), NSF's Arctic data center (https://arcticdata.io/; Keywords for data search are “Beaufort Gyre”, “Krishfield” or “Proshutinsky”), and WHOI Beaufort Gyre exploration website (www.whoi.edu/beaufortgyre)

Cruise report: JGOFS Leg I International study of the North Atlantic Bloom : R/V Atlantis II Voyage 119.2, Funchal to Reykjavik, March/April 1989

With the support of the National Science Foundation, we have completed the first cruise devoted to the GOFS and JGOFS program for the North Atlantic Bloom studies between March 28 and April 6 on board R/V Atlantis II. The major task of this cruise, to deploy bottom-tethered mooring arrays with time-series sediment traps along with current meters at two critical stations, 34°N and 47°N along 20°W, was accomplished. All 6 sediment traps, 3 on each array, were set at 14-day intervals for 13 periods from April 3 to September 26, 1989. Their opening and closing times were synchronized throughout the period of deployment. The arrays and instruments will be recovered and redeployed in September/October, 1989. Ancillary water column data, such as CTD, fluorometry, pigments, and major nutrient distribution, were also successfully completed (except for transmissometry profiling at the 47°N station) in order to understand the prebloom setting at JGOFS 34°N, 47°N, and 60°N stations. At the 47°N station on April 2, the mixed layer depth was 248m.Funding was provided by the National Science Foundation through grant Number OCE 88-14228

Anomalous sea-ice reduction in the Eurasian Basin of the Arctic Ocean during summer 2010

Special Issue: The Second International Symposium on the Arctic Research (ISAR - 2

Eddys in the Arctic Ocean from IOEB ADCP data

Filtered and Earth-referenced ADCP data from the B92, B97 and S97 IOEBs were demodulated to remove inertial and near-inertial tidal frequencies, in order to highlight the low frequency components for examination of Arctic submesoscale eddys. This report describes the raw data, processing scheme, and numerical and graphical results of this analysis, which are also available at http://ioeb.whoi.edu/ioebeddys.htm. Using the demodulated timeseries of current profiles from each buoy, characteristics of 95 possible eddy encounters are quantified by (1) identifying anomalously large velocities associated with subsurface vortices, (2) determining the vortex centers and their drift, and (3) determining vortex properties as a function of radius and depth. Out of 44 total months of observations, 81 of the encounters were determined to be subsurface eddies, and 29 were eddy core encounters. Only 14 of the confirmed subsurface encounters were cyclonic, versus 66 anticyclonic, and one indeterminate. Within the southern and central Canadian basin portion of the Beaufort Gyre, halocline eddys with maximum velocities between 10 and 45 cm/s, centered around 140 m depth, and over 100 m thick were prevalent. Over the Northwind Ridge, eddy encounters were absent from any timeseries. Farther north and west over the Chukchi Cap, encounters resumed, but were generally smaller, more shallow and less intense (although these observations were mostly derived from a lower resolution transmitted data subset).Funding was provided by the National Science Foundation Grant No. OPP-9815303, and by the Office of Naval Research Grant No. N00014-97-1-0135

The euphotic zone under Arctic Ocean sea ice : vertical extents and seasonal trends

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Limnology and Oceanography 62 (2017): 1910–1934, doi:10.1002/lno.10543.Eight Ice-Tethered Profilers were deployed in the Arctic Ocean between 2011 and 2013 to measure vertical distributions of photosynthetically active radiation (PAR) and other bio-optical properties in ice-covered water columns, multiple times a day over periods of up to a year. With the radiometers used on these profilers, PAR could be measured to depths of only ∼20–40 m in the central Arctic in late summer under sea ice ∼1 m thick. At lower latitudes in the Beaufort Gyre, late summer PAR was measurable under ice to depths exceeding 125 m. The maximum depths of measurable PAR followed seasonal trends in insolation, with isolumes shoaling in the fall as solar elevation decreased and deepening in spring and early summer after insolation resumed and sea ice diminished. PAR intensities were often anomalously low above 20 m, likely due to a shading effect associated with local horizontal heterogeneity in light transmittance by the overlying sea ice. A model was developed to parameterize these complex vertical PAR distributions to improve estimates of the water column diffuse attenuation coefficient and other related parameters. Such a model is necessary to separate the effect of surface ice heterogeneity on under-ice PAR profiles from that of the water column itself, so that euphotic zone depth in ice-covered water columns can be computed using canonical metrics such as the 1% light level. Water column diffuse attenuation coefficients derived from such autonomously-collected PAR profile data, using this model, agreed favorably with values determined manually in complementary studies.Woods Hole Oceanographic Institution; National Science Foundation Grant Number: ARC-085647

Ice-Ocean Environmental Buoys (IOEB) : technology and deployment in 1991-1992

Based upon the 1987-88 Arctic Environmental Drifting Buoy (AEDB), the Ice-Ocean Environmental Buoy (IOEB) was developed to acquire and telemeter in near real-time inter-relatable time-series data on atmospheric, oceanographic and ice physics in ice-covered oceans during all seasons. Two IOEBs were successfully deployed in two Arctic Sea Basin Stations in April, 1992. Since then, although some sensors malfunctioned, for 18 continuous months, they have been sending massive amounts of information. In this report we describe the technology which was developed for the 1991 IOEB. Mechanically, the IOEB consists of an extremely durable surface flotation package and an underwater mooring line of instruments and sensors. The apex contains data loggers for air, ice and engineering measurements, microcontroller modules for accumulating the data from all the instruments, and ARGOS platform transmit terminals (PTTs) for broadcasting the data. Extending above the surface float, a mast supports a wind monitor and air temperature probe, which along with a barometer provides meteorological data. Thermistor strings, vibrating wire stress sensors, and a thickness gauge are installed in the ice surrounding the buoy, and are interrogated by the modules inside the apex. In the ocean, 110m of conducting strength cable passes the data from conductivity/temperature recorders, an Acoustic Doppler Current Profier and data compression module, a dissolved oxygen sensor, a transmissometer and fluorometers to the PTT microcontrollers. Furthermore, a suspended particle collector and sediment trap transmit status information along the two-wire multidrop network cable. Because the IOEB differs from the AEDB by telemetering the majority of the scientific data, a complicated compression scheme is incorporated to broadcast the data from the 103 variables within the allowable 256-bit ARGOS data stream. Via Service ARGOS, this data currently becomes available to scientists in several countries within eight hours of transmission. In April 1992, two IOEBs were deployed at separate ice camps in the Arctic Ocean with battery power adequate to sustain the systems for over two years. One was deployed 115 miles from the North Pole in the center of the Transpolar Drift sea-ice current, and the other off of the coast of Alaska along the edge of the Beaufort Gyre. Airplanes capable of landing on ice were used for the transportation of the systems to their final destination. Simultaneously, a third, reduced version of the IOEB was deployed in the Weddell Sea by the Scott Polar Research Institute.Funding was provided by the Office of Naval Research, Arlington, Virginia, USA and Japan Marine Science and Technology Center, Yokosuka, Japan

The Arctic Environmental Drifting Buoy (AEDB) : report of field operations and results, August, 1987 - April 1988

There are strong reasons to gather data on polar oceanogrphy and climatology in real time using fully automated, unattended instrumentation systems for long periods; particularly during the inaccessible winter months when moving ice is extremely hazardous. We deployed an Artic Environmental Drifting Buoy (AEDB) on 4 August 1987 at 86°7'N, 22°3'E off of the FS Polarstern on a large 3.7 m thick ice island. The AEDB consisted of 2 major components: a 147 cm diameter surface float housing ARGOS transmitters and a data logger for ice-profiling thermistors, and a 125 m long mooring line attached to the sphere and fed though a 1m diameter ice hole. Along the mooring were deployed 2 fluorometers, conductivity and temperature loggers, an Acoustic Doppler Current Profiler (ADCP), a current meter, and a time-series sediment trap/micro-filter pump/transmissometer unit. The AEDB proceeded southwesterly with the Transpolar Drift at an average speed of 15.3 km/day, with a maximum speed of 88.8 km/day. On 2 January 1988, the AEDB dropped into the water while passing through the Fram Strait and for the remaining drift period was either free-floating on the water surface or underneath the sea ice. Throughout this period, the transmitters onboard successfully transmitted position, temperature, and strain caused by ice on the sphere. Although the sediment trap package was lost during the drift, valuable data was collected by the other instruments throughout the experiment. The ice thermistor data was used to determine oceanic heat flux, while continuous ADCP observations over the Yermak Plateau provided a wealth of information for understanding internal waves in the ice-covered ocean. The buoy was recovered by the Icelandic ship R/S Arni Fridriksson on 15 April 1988 at 65°17'N, 31°38'W, off southeatern Greenland, completing 3,900km of drift in 255 days. We are in the process of constructing the next automated stations which are planned for deployment in both the north and south polar regions in 1991-92.Funding was provided by the Office of Naval Research, through grant Number NOOOI4-87,88,89,J-1288

Partitioning of Kinetic Energy in the Arctic Ocean's Beaufort Gyre

Kinetic energy (KE) in the Arctic Ocean's Beaufort Gyre is dominated by the mesoscale eddy field that plays a central role in the transport of freshwater, heat, and biogeochemical tracers. Understanding Beaufort Gyre KE variability sheds light on how this freshwater reservoir responds to wind forcing and sea ice and ocean changes. The evolution and fate of mesoscale eddies relate to energy pathways in the ocean (e.g., the exchange of energy between barotropic and baroclinic modes). Mooring measurements of horizontal velocities in the Beaufort Gyre are analyzed to partition KE into barotropic and baroclinic modes and explore their evolution. We find that a significant fraction of water column KE is in the barotropic and the first two baroclinic modes. We explain this energy partitioning by quantifying the energy transfer coefficients between the vertical modes using the quasi‐geostrophic potential vorticity conservation equations with a specific background stratification observed in the Beaufort Gyre. We find that the quasi‐geostrophic vertical mode interactions uphold the persistence of KE in the first two baroclinic modes, consistent with observations. Our results explain the specific role of halocline structure on KE evolution in the gyre and suggest depressed transfer to the barotropic mode. This limits the capacity for frictional dissipation at the sea floor and suggests that energy dissipation via sea ice‐ocean drag may be prominent

Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 4 (2018): eaat6773, doi:10.1126/sciadv.aat6773.Arctic Ocean measurements reveal a near doubling of ocean heat content relative to the freezing temperature in the Beaufort Gyre halocline over the past three decades (1987–2017). This warming is linked to anomalous solar heating of surface waters in the northern Chukchi Sea, a main entryway for halocline waters to join the interior Beaufort Gyre. Summer solar heat absorption by the surface waters has increased fivefold over the same time period, chiefly because of reduced sea ice coverage. It is shown that the solar heating, considered together with subduction rates of surface water in this region, is sufficient to account for the observed halocline warming. Heat absorption at the basin margins and its subsequent accumulation in the ocean interior, therefore, have consequences for Beaufort Gyre sea ice beyond the summer season.Support was provided by the National Science Foundation Division of Polar Programs under award numbers 1303644, 1350046, and 1603660

Beaufort Gyre Freshwater Experiment : deployment operations and technology 2003

The Beaufort Gyre Freshwater Experiment (BGFE) observational program was designed to measure the freshwater content of the upper ocean and sea ice in the Beaufort Gyre of the Arctic Ocean using bottom-tethered moorings, drifting buoys, and hydrographic stations. The mooring program required the development of a safe and efficient deployment method by which the subsurface system could be deployed in waters surrounded by sea ice. This report documents the mooring procedure used to deploy the three BGFE moorings from the CCGS Louis S. St- Laurent, during the Joint Western Arctic Climate Study – 2003 (August 6 – September 7). The technical details of the instrumentation attached to each mooring and the specific deployment parameters are described. Specifics pertaining to the deployment of four surface-tethered drifters in the ice are also documented.Funding was provided by the National Science Foundation under Grant Number OPP-0230184