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  • 1
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    Automated ice-tethered profilers for seawater observations under pack ice in all seasons (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 25 (2008): 2091-2105, doi:10.1175/2008JTECHO587.1.
    Description: An automated, easily deployed Ice-Tethered Profiler (ITP) instrument system, developed for deployment on perennial sea ice in the polar oceans to measure changes in upper ocean water properties in all seasons, is described, and representative data from prototype instruments are presented. The ITP instrument consists of three components: a surface subsystem that sits atop an ice floe; a weighted, plastic-jacketed wire-rope tether of arbitrary length (up to 800 m) suspended from the surface element; and an instrumented underwater unit that employs a traction drive to profile up and down the wire tether. ITPs profile the water column at a programmed sampling interval; after each profile, the underwater unit transfers two files holding oceanographic and engineering data to the surface unit using an inductive modem and from the surface instrument to a shore-based data server using an Iridium transmitter. The surface instrument also accumulates battery voltage readings, buoy temperature data, and locations from a GPS receiver at a specified interval (usually every hour) and transmits those data daily. Oceanographic and engineering data are processed, displayed, and made available in near–real time (available online at http://www.whoi.edu/itp). Six ITPs were deployed in the Arctic Ocean between 2004 and 2006 in the Beaufort gyre with various programmed sampling schedules of two to six one-way traverses per day between 10- and 750–760-m depth, providing more than 5300 profiles in all seasons (as of July 2007). The acquired CTD profile data document interesting spatial variations in the major water masses of the Canada Basin, show the double-diffusive thermohaline staircase that lies above the warm, salty Atlantic layer, measure seasonal surface mixed layer deepening, and document several mesoscale eddies. Augmenting the systems already deployed and to replace expiring systems, an international array of more than one dozen ITPs will be deployed as part of the Arctic Observing Network during the International Polar Year (IPY) period (2007–08) holding promise for more valuable real-time upper ocean observations for operational needs, to support studies of ocean processes, and to facilitate numerical model initialization and validation.
    Description: Initial development of the ITP concept was supported by the Cecil H. and Ida M. Green Technology Innovation Program. Funding for construction and deployment of the prototype ITPs was provided by the National Science Foundation Oceanographic Technology and Interdisciplinary Coordination (OTIC) Program and Office of Polar Programs (OPP) under Grant OCE-0324233. Continued support has been provided by the OPP Arctic Sciences Section under Awards ARC-0519899 and ARC-0631951, and internal WHOI funding.
    Keywords: Profilers ; Sea ice ; Instrumentation/sensors ; Arctic
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Arctic Ocean warming contributes to reduced polar ice cap (2011)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 2743–2756, doi:10.1175/2010JPO4339.1.
    Description: Analysis of modern and historical observations demonstrates that the temperature of the intermediate-depth (150–900 m) Atlantic water (AW) of the Arctic Ocean has increased in recent decades. The AW warming has been uneven in time; a local 1°C maximum was observed in the mid-1990s, followed by an intervening minimum and an additional warming that culminated in 2007 with temperatures higher than in the 1990s by 0.24°C. Relative to climatology from all data prior to 1999, the most extreme 2007 temperature anomalies of up to 1°C and higher were observed in the Eurasian and Makarov Basins. The AW warming was associated with a substantial (up to 75–90 m) shoaling of the upper AW boundary in the central Arctic Ocean and weakening of the Eurasian Basin upper-ocean stratification. Taken together, these observations suggest that the changes in the Eurasian Basin facilitated greater upward transfer of AW heat to the ocean surface layer. Available limited observations and results from a 1D ocean column model support this surmised upward spread of AW heat through the Eurasian Basin halocline. Experiments with a 3D coupled ice–ocean model in turn suggest a loss of 28–35 cm of ice thickness after 50 yr in response to the 0.5 W m−2 increase in AW ocean heat flux suggested by the 1D model. This amount of thinning is comparable to the 29 cm of ice thickness loss due to local atmospheric thermodynamic forcing estimated from observations of fast-ice thickness decline. The implication is that AW warming helped precondition the polar ice cap for the extreme ice loss observed in recent years.
    Description: This study was supported by JAMSTEC (IP and VI), NOAA (IP, VI, and ID), NSF (IP,VA,VI, ID, JT, andMS),NASA(IP andVI), BMBF (ID), and UK NERC (SB) grants.
    Keywords: Arctic ; Forcing ; Temperature ; Sea ice ; Heating ; Coupled models
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Eddies in the Canada Basin, Arctic Ocean, observed from ice-tethered profilers (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 133–145, doi:10.1175/2007JPO3782.1.
    Description: Five ice-tethered profilers (ITPs), deployed between 2004 and 2006, have provided detailed potential temperature θ and salinity S profiles from 21 anticyclonic eddy encounters in the central Canada Basin of the Arctic Ocean. The 12–35-m-thick eddies have center depths between 42 and 69 m in the Arctic halocline, and are shallower and less dense than the majority of eddies observed previously in the central Canada Basin. They are characterized by anomalously cold θ and low stratification, and have horizontal scales on the order of, or less than, the Rossby radius of deformation (about 10 km). Maximum azimuthal speeds estimated from dynamic heights (assuming cyclogeostrophic balance) are between 9 and 26 cm s−1, an order of magnitude larger than typical ambient flow speeds in the central basin. Eddy θ–S and potential vorticity properties, as well as horizontal and vertical scales, are consistent with their formation by instability of a surface front at about 80°N that appears in historical CTD and expendable CTD (XCTD) measurements. This would suggest eddy lifetimes longer than 6 months. While the baroclinic instability of boundary currents cannot be ruled out as a generation mechanism, it is less likely since deeper eddies that would originate from the deeper-reaching boundary flows are not observed in the survey region.
    Description: The engineering design work for the ITP was initiated by the Cecil H. and Ida M. Green Technology Innovation Program (an internal program at the Woods Hole Oceanographic Institution). Prototype development and construction were funded jointly by the U.S. National Science Foundation (NSF) Oceanographic Technology and Interdisciplinary Coordination Program and Office of Polar Programs (OPP) under Award OCE-0324233. Continued support has been provided by the OPP Arctic Sciences Section under Award ARC-0519899 and internal WHOI funding.
    Keywords: Arctic ; Eddies ; Profilers ; Stability ; Salinity
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Influences of the ocean surface mixed layer and thermohaline stratification on Arctic Sea ice in the central Canada Basin (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2010. 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 115 (2010): C10018, doi:10.1029/2009JC005660.
    Description: Variations in the Arctic central Canada Basin mixed layer properties are documented based on a subset of nearly 6500 temperature and salinity profiles acquired by Ice-Tethered Profilers during the period summer 2004 to summer 2009 and analyzed in conjunction with sea ice observations from ice mass balance buoys and atmosphere-ocean heat flux estimates. The July–August mean mixed layer depth based on the Ice-Tethered Profiler data averaged 16 m (an overestimate due to the Ice-Tethered Profiler sampling characteristics and present analysis procedures), while the average winter mixed layer depth was only 24 m, with individual observations rarely exceeding 40 m. Guidance interpreting the observations is provided by a 1-D ocean mixed layer model. The analysis focuses attention on the very strong density stratification at the base of the mixed layer in the Canada Basin that greatly impedes surface layer deepening and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth/decay. The observations additionally suggest that efficient lateral mixed layer restratification processes are active in the Arctic, also impeding mixed layer deepening.
    Description: Support for the ITP program and this study was provided by the U. S. National Science Foundation and the Woods Hole Oceanographic Institution. Support for the IMB program came from the National Science Foundation and the National Oceanographic and Atmospheric Administration.
    Keywords: Mixed layer ; Arctic
    Repository Name: Woods Hole Open Access Server
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  • 5
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    An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006-2008 period (2011)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 58 (2011): 173-185, doi:10.1016/j.dsr.2010.12.002.
    Description: Unprecedented summer-season sampling of the Arctic Ocean during the period 2006−2008 makes possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins. In comparison to observations from 1992−1999, LFW content relative to a salinity of 35 in the layer from the surface to the 34 isohaline increased by 8400 ± 2000 km3 in the Arctic Ocean (water depth greater than 500m). This is close to the annual export of freshwater (liquid and solid) from the Arctic Ocean reported in the literature. Observations and a model simulation show regional variations in LFW were both due to changes in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a mean freshening of the water column above this depth, associated with an increased net sea ice melt and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a quarter of the salinity contribution, and non-linear effects due to both factors were negligible.
    Description: This work was supported by the Co-Operative Project “The North Atlantic as Part of the Earth System: From System Comprehension to Analysis of Regional Impacts” funded by the German Federal Ministry for Education and Research (BMBF) and by the European Union Sixth Framework Programme project DAMOCLES (Developing Arctic Modelling and Observing Capabilities for Long-term Environment Studies), contract number 018509GOCE.
    Keywords: Arctic ; Freshwater ; Observation ; Model ; IPY ; Upper Ocean
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 6
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    Horizontal density structure and restratification of the Arctic Ocean surface layer (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 659–668, doi:10.1175/JPO-D-11-0125.1.
    Description: Ice-tethered profiler (ITP) measurements from the Arctic Ocean’s Canada Basin indicate an ocean surface layer beneath sea ice with significant horizontal density structure on scales of hundreds of kilometers to the order 1 km submesoscale. The observed horizontal gradients in density are dynamically important in that they are associated with restratification of the surface ocean when dense water flows under light water. Such restratification is prevalent in wintertime and competes with convective mixing upon buoyancy forcing (e.g., ice growth and brine rejection) and shear-driven mixing when the ice moves relative to the ocean. Frontal structure and estimates of the balanced Richardson number point to the likelihood of dynamical restratification by isopycnal tilt and submesoscale baroclinic instability. Based on the evidence here, it is likely that submesoscale processes play an important role in setting surface-layer properties and lateral density variability in the Arctic Ocean.
    Description: Funding was provided by the National Science Foundation Office of Polar Programs Arctic Sciences Section under Awards ARC-0519899, ARC-0856479, and ARC-0806306. Support was also provided by the Woods Hole Oceanographic Institution Arctic Research Initiative.
    Description: 2012-10-01
    Keywords: Arctic ; Ocean dynamics
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Turbulence and diapycnal mixing in Drake Passage (2013)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 2143–2152, doi:10.1175/JPO-D-12-027.1.
    Description: Direct measurements of turbulence levels in the Drake Passage region of the Southern Ocean show a marked enhancement over the Phoenix Ridge. At this site, the Antarctic Circumpolar Current (ACC) is constricted in its flow between the southern tip of South America and the northern tip of the Antarctic Peninsula. Observed turbulent kinetic energy dissipation rates are enhanced in the regions corresponding to the ACC frontal zones where strong flow reaches the bottom. In these areas, turbulent dissipation levels reach 10−8 W kg−1 at abyssal and middepths. The mixing enhancement in the frontal regions is sufficient to elevate the diapycnal turbulent diffusivity acting in the deep water above the axis of the ridge to 1 × 10−4 m2 s−1. This level is an order of magnitude larger than the mixing levels observed upstream in the ACC above smoother bathymetry. Outside of the frontal regions, dissipation rates are O(10−10) W kg−1, comparable to the background levels of turbulence found throughout most mid- and low-latitude regions of the global ocean.
    Description: This work was supported by the U.S. National Science Foundation and by the Natural Environment Research Council of the United Kingdom.
    Description: 2013-06-01
    Keywords: Southern Ocean ; Turbulence ; Diapycnal mixing
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Vertical kinetic energy and turbulent dissipation in the ocean (2015)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 7639–7647, doi:10.1002/2015GL065043.
    Description: Oceanic internal waves are closely linked to turbulence. Here a relationship between vertical wave number (kz) spectra of fine-scale vertical kinetic energy (VKE) and turbulent dissipation ε is presented using more than 250 joint profiles from five diverse dynamic regimes, spanning latitudes between the equator and 60°. In the majority of the spectra VKE varies as inline image. Scaling VKE with inline image collapses the off-equatorial spectra to within inline image but underestimates the equatorial spectrum. The simple empirical relationship between VKE and ε fits the data better than a common shear-and-strain fine-scale parameterization, which significantly underestimates ε in the two data sets that are least consistent with the Garrett-Munk (GM) model. The new relationship between fine-scale VKE and dissipation rate can be interpreted as an alternative, single-parameter scaling for turbulent dissipation in terms of fine-scale internal wave vertical velocity that requires no reference to the GM model spectrum.
    Description: National Science Foundation Grant Numbers: OCE-0728766, OCE-0425361, OCE-0424953, OCE-1029722, OCE-0622630, OCE-1030309, OCE-1232962, and Office of Naval Research Grant Number: N00014-10-10315
    Keywords: Internal waves ; Turbulence ; Mixing ; Vertical kinetic energy ; Finestructure parameterization
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Internal waves in the Arctic : influence of ice concentration, ice roughness, and surface layer stratification (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. 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 123 (2018): 5571-5586, doi:10.1029/2018JC014096.
    Description: The Arctic ice cover influences the generation, propagation, and dissipation of internal waves, which in turn may affect vertical mixing in the ocean interior. The Arctic internal wavefield and its relationship to the ice cover is investigated using observations from Ice‐Tethered Profilers with Velocity and Seaglider sampling during the 2014 Marginal Ice Zone experiment in the Canada Basin. Ice roughness, ice concentration, and wind forcing all influenced the daily to seasonal changes in the internal wavefield. Three different ice concentration thresholds appeared to determine the evolution of internal wave spectral energy levels: (1) the initial decrease from 100% ice concentration after which dissipation during the surface reflection was inferred to increase, (2) the transition to 70–80% ice concentration when the local generation of internal waves increased, and (3) the transition to open water that was associated with larger‐amplitude internal waves. Ice roughness influenced internal wave properties for ice concentrations greater than approximately 70–80%: smoother ice was associated with reduced local internal wave generation. Richardson numbers were rarely supercritical, consistent with weak vertical mixing under all ice concentrations. On decadal timescales, smoother ice may counteract the effects of lower ice concentration on the internal wavefield complicating future predictions of internal wave activity and vertical mixing.
    Description: Seagliders Grant Number: N00014‐12‐10180; Deployment and subsequent analysis efforts of the ITP‐Vs Grant Numbers: N00014‐12‐10799, N00014‐12‐10140; Joint Ocean Ice Studies cruise; Beaufort Gyre Observing System
    Description: 2019-02-14
    Keywords: Internal waves ; Arctic ; Near‐inertial ; Ice roughness ; Ice concentration
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Ice-tethered profiler measurements of dissolved oxygen under permanent ice cover in the Arctic Ocean (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 27 (2010): 1936-1949, doi:10.1175/2010JTECHO772.1.
    Description: Four ice-tethered profilers (ITPs), deployed between 2006 and 2009, have provided year-round dissolved oxygen (DO) measurements from the surface mixed layer to 760-m depth under the permanent sea ice cover in the Arctic Ocean. These ITPs drifted with the permanent ice pack and returned 2 one-way profiles per day of temperature, salinity, and DO. Long-term calibration drift of the oxygen sensor can be characterized and removed by referencing to recently calibrated ship DO observations on deep isotherms. Observed changes in the water column time series are due to both drift of the ITP into different water masses and seasonal variability, driven by both physical and biological processes within the water column. Several scientific examples are highlighted that demonstrate the considerable potential for sustained ITP-based DO measurements to better understand the Arctic Ocean circulation patterns and biogeochemical processes beneath the sea ice.
    Description: The National Science Foundation Office of Polar Programs Arctic Sciences Section under Awards ARC-0519899, ARC-0856479, and ARC-0806306 provided funding.
    Keywords: Profilers ; Ice shelves ; Arctic
    Repository Name: Woods Hole Open Access Server
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