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  • 1
    Publication Date: 2018-03-06
    Description: Any use of observational data for data assimilation requires adequate information of their representativeness in space and time. This is particularly important for sparse, non-synoptic data, which comprise the bulk of oceanic in situ observations in the Arctic. To quantify spatial and temporal scales of temperature and salinity variations, we estimate the autocorrelation function and associated decorrelation scales for the Amerasian Basin of the Arctic Ocean. For this purpose, we compile historical measurements from 1980 to 2015. Assuming spatial and temporal homogeneity of the decorrelation scale in the basin interior (abyssal plain area), we calculate autocorrelations as a function of spatial distance and temporal lag. The examination of the functional form of autocorrelation in each depth range reveals that the autocorrelation is well described by a Gaussian function in space and time. We derive decorrelation scales of 150–200 km in space and 100–300 days in time. These scales are directly applicable to quantify the representation error, which is essential for use of ocean in situ measurements in data assimilation. We also describe how the estimated autocorrelation function and decorrelation scale should be applied for cost function calculation in a data assimilation system.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
    Publication Date: 2020-07-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 3
    Publication Date: 2016-11-29
    Description: Recent decades have shown substantial changes in the Arctic Ocean, yet observations are still relatively sparse compared to most other parts of the world's oceans. Results from numerical models still differ in the distribution of key variables, such as the pathways of liquid freshwater. From salinity and temperature profiles observed by a variety of platforms since 1992 we are able to show a substantial freshening in the upper Arctic Ocean impacting an increase in stratification between the mixed-layer and the lower halocline. Based on temperature and salinity profiles, we will present an objective analysis of mixed-layer depth, sea surface height and geostrophic velocity during the recent two decades. We are able to derive decadal trends as well as seasonal cycles during the most recend decade. Surface geostrophic velocity points to a flow in the Amerasian Basin toward the Lomonosov Ridge. Although most of the freshwater volume increase occurred on the Amerasian side of the Arctic Ocean, the changes on the Eurasian side have strong implications not only for the stratification but also the vertical exchange of nutrients in the upper ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 4
    Publication Date: 2018-03-06
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 5
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    In:  EPIC3WCRP Open Science Conference Climate Research in Service to Society -- Session C40: The Changing Cryosphere and Its Role in the Climate System, Denver, USA
    Publication Date: 2016-11-29
    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 6000 to 10000 km≥ in the Arctic Ocean (water depth greater than 500 m). 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. Observations from 2009-2010 suggest that LFW content is at similar or higher levels relative to 2006-2008. The observed change in LFW is likely to influence the vertical exchange of heat and freshwater exchange in the Arctic Ocean, and hence the modification of the circulating Atlantic Water. Furthermore, the additional LFW must ultimately be released from the Arctic Ocean to the regions of deep-water formation in the North Atlantic in future years.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
    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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  • 7
    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 Deep Sea Research Part I: Oceanographic Research Papers 102 (2015): 43-54, doi:10.1016/j.dsr.2015.04.004.
    Description: Over the past few decades, sea ice retreat during summer has been enhanced in the Pacific sector of the Arctic basin, likely due in part to increasing summertime heat flux of Pacific-origin water from the Bering Strait. Barrow Canyon, in the northeast Chukchi Sea, is a major conduit through which the Pacific-origin water enters the Arctic basin. This paper presents results from 6 repeat high-resolution shipboard hydrographic/velocity sections occupied across Barrow Canyon in summer 2010. The different Pacific water masses feeding the canyon – Alaskan coastal water (ACW), summer Bering Sea water (BSW), and Pacific winter water (PWW) – all displayed significant intra-seasonal variability. Net volume transports through the canyon were between 0.96 and 1.70 Sv poleward, consisting of 0.41–0.98 Sv of warm Pacific water (ACW and BSW) and 0.28–0.65 Sv of PWW. The poleward heat flux also varied strongly, ranging from 8.56 TW to 24.56 TW, mainly due to the change in temperature of the warm Pacific water. Using supplemental mooring data from the core of the warm water, along with wind data from the Pt. Barrow weather station, we derive and assess a proxy for estimating heat flux in the canyon for the summer time period, which is when most of the heat passes northward towards the basin. The average heat flux for 2010 was estimated to be 3.34 TW, which is as large as the previous record maximum in 2007. This amount of heat could melt 315,000 km2 of 1-meter thick ice, which likely contributed to significant summer sea ice retreat in the Pacific sector of the Arctic Ocean.
    Description: MI, TK, YF, KO and DS were supported by Green Network of Excellence Program (GRENE Program), Arctic Climate Change Research Project ‘Rapid Change of the Arctic Climate System and its Global Influences’ by Ministry of Education, Culture, Sports, Science and Technology Japan. RP was supported by grant ARC-1203906 from the US National Science Foundation. CA was supported by grant ARC-1023331 from the US National Science Foundation and by the Cooperative Institute for the North Atlantic Region (NOAA Cooperative AgreementNA09OAR4320129) with funds provided by the US National Oceanographic and Atmospheric Administration through an Interagency Agreement between the US Bureau of Ocean and Energy Management and the National Marine Mammal Laboratory. SV was supported by the Department of Fisheries and Oceans Canada. MI and TK were supported by the Japan Agency for Marine-Earth Science and Technology. MI, TK, YF and KO were supported by Grant no. 2014-23 from Joint Research Program of the Institute of Low Temperature Science, Hokkaido University. YF and KO were supported by grants-in-aid 20221001 for scientific research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. JTM was supported by grant PLR-1041102 from the US National Science Foundation.
    Keywords: Polar oceanography ; Arctic Ocean ; Chukchi Sea ; Heat fluxes ; Volume transports ; Water properties
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
    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): 7453-7471, doi:10.1029/2018JC013825.
    Description: A high‐resolution regional ocean model together with moored hydrographic and velocity measurements is used to identify the pathways and mechanisms by which Pacific water, modified over the Chukchi shelf, crosses the shelf break into the Canada Basin. Most of the Pacific water flowing into the Arctic Ocean through Bering Strait enters the Canada Basin through Barrow Canyon. Strong advection allows the water to cross the shelf break and exit the shelf. Wind forcing plays little role in this process. Some of the outflowing water from Barrow Canyon flows to the east into the Beaufort Sea; however, approximately 0.4 to 0.5 Sv turns to the west forming the newly identified Chukchi Slope Current. This transport occurs at all times of year, channeling both summer and winter waters from the shelf to the Canada Basin. The model indicates that approximately 75% of this water was exposed to the mixed layer within the Chukchi Sea, while the remaining 25% was able to cross the shelf during the stratified summer before convection commences in late fall. We view the Ό(0.5) Sv of the Chukchi Slope Current as replacing Beaufort Gyre water that would have come from the east in the absence of the cross-topography flow in Barrow Canyon. The weak eastward flow on the Beaufort slope is also consistent with the local disruption of the Beaufort Gyre by the Barrow Canyon outflow.
    Description: Bureau of Ocean and Energy Management Grant Number: M12AC00008; DOC | National Oceanic and Atmospheric Administration (NOAA) Grant Number: NA16OAR4310248; National Science Foundation (NSF) Grant Numbers: PLR-1415489, OCE-1533170
    Description: 2019-04-22
    Keywords: Canada Basin ; Halocline ; Ventilation ; Chukchi Sea
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 961-968, doi:10.1002/2013GL058121.
    Description: Freshwater in the Arctic Ocean plays an important role in the regional ocean circulation, sea ice, and global climate. From salinity observed by a variety of platforms, we are able, for the first time, to estimate a statistically reliable liquid freshwater trend from monthly gridded fields over all upper Arctic Ocean basins. From 1992 to 2012 this trend was 600±300 km3 yr−1. A numerical model agrees very well with the observed freshwater changes. A decrease in salinity made up about two thirds of the freshwater trend and a thickening of the upper layer up to one third. The Arctic Ocean Oscillation index, a measure for the regional wind stress curl, correlated well with our freshwater time series. No clear relation to Arctic Oscillation or Arctic Dipole indices could be found. Following other observational studies, an increased Bering Strait freshwater import to the Arctic Ocean, a decreased Davis Strait export, and enhanced net sea ice melt could have played an important role in the freshwater trend we observed.
    Description: This work was supported by the cooperative project 03F0605E, funded by the German Federal Ministry for Education and Research (BMBF), and by the European Union Sixth Framework Programme project DAMOCLES, contract 018509GOCE.
    Description: 2014-08-12
    Keywords: Arctic ; Liquid freshwater ; Observation ; Model
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    Format: text/plain
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  • 10
    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 7523–7548, doi:10.1002/2014JC010273.
    Description: Pacific Water flows northward through Bering Strait and penetrates the Arctic Ocean halocline throughout the Canadian Basin sector of the Arctic. In summer, Pacific Summer Water (PSW) is modified by surface buoyancy fluxes and mixing as it crosses the shallow Chukchi Sea before entering the deep ocean. Measurements from Ice-Tethered Profilers, moorings, and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the PSW component of the halocline in the Central Canada Basin with increasing trends in integrated heat and freshwater content, a consequence of PSW layer thickening as well as layer freshening and warming. It is shown here how properties in the Chukchi Sea in summer control the temperature-salinity properties of PSW in the interior by subduction at isopycnals that outcrop in the Chukchi Sea. Results of an ocean model, forced by idealized winds, provide support to the mechanism of surface ocean Ekman transport convergence maintaining PSW ventilation of the halocline.
    Description: Funding was provided by the National Science Foundation Division of Polar Programs under award 1107623, 1313614, 1107412, 1107277, 1303644, and 0938137 and by Yale University. ICMMG model development was supported by the Russian Fund for Basic Research (14-05-00730A).
    Keywords: Arctic Ocean ; Halocline ventilation ; Pacific Water
    Repository Name: Woods Hole Open Access Server
    Type: Article
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