6 research outputs found
Bedmap2: improved ice bed, surface and thickness datasets for Antarctica
We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60° S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved data-coverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km3) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72 m lower and the area of ice sheet grounded on bed below sea level is increased by 10%. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets
Closing the loop Approaches to monitoring the state of the Arctic Mediterranean during the International Polar Year 20072008
During the 4th International Polar Year 2007â2009 (IPY), it has become increasingly obvious that we need to prepare for a new era in the Arctic. IPY occurred during the time of the largest retreat of Arctic sea ice since satellite observations started in 1979. This minimum in September sea ice coverage was accompanied by other signs of a changing Arctic, including the unexpectedly rapid transpolar drift of the Tara schooner, a general thinning of Arctic sea ice and a double-dip minimum of the Arctic Oscillation at the end of 2009. Thanks to the lucky timing of the IPY, those recent phenomena are well documented as they have been scrutinized by the international research community, taking advantage of the dedicated observing systems that were deployed during IPY. However, understanding changes in the Arctic System likely requires monitoring over decades, not years. Many IPY projects have contributed to the pilot phase of a future, sustained, observing system for the Arctic. We now know that many of the technical challenges can be overcome.
The Norwegian projects iAOOS-Norway, POLEWARD and MEOP were significant ocean monitoring/research contributions during the IPY. A large variety of techniques were used in these programs, ranging from oceanographic cruises to animal-borne platforms, autonomous gliders, helicopter surveys, surface drifters and current meter arrays. Our research approach was interdisciplinary from the outset, merging ocean dynamics, hydrography, biology, sea ice studies, as well as forecasting. The datasets are tremendously rich, and they will surely yield numerous findings in the years to come. Here, we present a status report at the end of the official period for IPY. Highlights of the research include: a quantification of the Meridional Overturning Circulation in the Nordic Seas (âthe loopâ) in thermal space, based on a set of up to 15-year-long series of current measurements; a detailed map of the surface circulation as well as characterization of eddy dispersion based on drifter data; transport monitoring of Atlantic Water using gliders; a view of the water mass exchanges in the Norwegian Atlantic Current from both Eulerian and Lagrangian data; an integrated physicalâbiological view of the ice-influenced ecosystem in the East Greenland Current, showing for instance nutrient-limited primary production as a consequence of decreasing ice cover for larger regions of the Arctic Ocean. Our sea ice studies show that the albedo of snow on ice is lower when snow cover is thinner and suggest that reductions in sea ice thickness, without changes in sea ice extent, will have a significant impact on the arctic atmosphere. We present up-to-date freshwater transport numbers for the East Greenland Current in the Fram Strait, as well as the first map of the annual cycle of freshwater layer thickness in the East Greenland Current along the east coast of Greenland, from data obtained by CTDs mounted on seals that traveled back and forth across the Nordic Seas. We have taken advantage of the real-time transmission of some of these platforms and demonstrate the use of ice-tethered profilers in validating satellite products of sea ice motion, as well as the use of Seagliders in validating ocean forecasts, and we present a sea ice drift product â significantly improved both in space and time â for use in operational ice-forecasting applications.
We consider real-time acquisition of data from the ocean interior to be a vital component of a sustained Arctic Ocean Observing System, and we conclude by presenting an outline for an observing system for the European sector of the Arctic Ocean
A consistent data set of Antarctic ice sheet topography, cavity geometry, and global bathymetry
Sub-ice shelf circulation and freezing/melting rates in ocean general circulation models depend critically on an accurate and consistent representation of cavity geometry. Existing global or pan-Antarctic data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional fields into a global data set. We use the S-2004 global 1-min bathymetry as the backbone and add an improved version of the BEDMAP topography (ALBMAP bedrock topography) for an area that roughly coincides with the Antarctic continental shelf. The position of the merging line is individually chosen in different sectors in order to get the best out of each data set. High-resolution gridded data for ice shelf topography and cavity geometry of the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves, and for Pine Island Glacier are carefully merged into the ambient ice and ocean topographies. Multibeam survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and blended into the existing bathymetry map. The resulting global 1-min topography data set (RTopo-1) contains maps for upper and lower ice surface heights, bedrock topography, and consistent masks for open ocean, grounded ice, floating ice, and bare land surface
Biologging in the global ocean observing system
Miniature electronic data recorders and transmitters have revolutionized the way we study animals over the past decades, particularly marine animals at sea. But, very recently, animal-borne instruments have also been designed and implemented that provide in situ hydrographic data from parts of the oceans where little or no other data are currently available (even from beneath the ice in polar regions). Ocean data is delivered from animal-borne instruments via satellites in near real-time, which would enrich the Global Ocean Observing System if animal-borne instruments were deployed systematically. In the last 10 years, studies involving more than 10 countries (Australia, Brazil, Canada, France, Germany, Greenland, Norway, South Africa, UK, USA) have demonstrated how highly accurate oceanographic sensors, integrated into standard animal, biologging instruments, can provide data of equal or better quality than XBT/XCTD data. Here, we present some of the pioneering studies and demonstrate that we now have enough information for many marine species to predict where they will go â within reasonable limits. Thus, we can direct sampling effort to particularly interesting and productive regions and maximize data return. In the future, biologging could certainly play an important part in the Global Ocean Observing System, by providing complementary data to more traditional sampling technologies - especially in the high latitudes. This paper will make a core contribution to the Plenary Sessions 4A, 4B and 5A and will be relevant to 2A, 2B and 3A
New insights into Southern Ocean physical and biological processes revealed by instrumented elephant seals
In recent years, the international âSouthern Elephant
seals as Oceanographic Samplersâ (SEaOS) project has
deployed miniaturized conductivity-temperature-depth
satellite-relayed data loggers (CTD-SRDL) on elephant
seals 1) to study their winter foraging ecology in
relation to oceanographic conditions, and 2) to collect
hydrographic data from polar regions, which are
otherwise sparsely sampled. We summarize here the
main results that have been published in both science
components since 2003/2004. Instrumented southern
elephant seals visit different regions within the Southern
Ocean (frontal zones, continental shelf, and/or ice
covered areas) and forage in a variety of different water
masses (e.g. Circumpolar Deep Water upwelling
regions, High Salinity Shelf Water), depending on their
geographic distribution. Adult females and juvenile
males from Kerguelen Is. forage pelagically in frontal
zones of the Southern Indian Ocean, while adult males
forage benthically over the Kerguelen Plateau and the
Antarctic Continental Shelf, with the two groups feeding
at different trophic levels as shown by stable isotopes
analysis. Oceanographic studies using the data
collected from the seals have, to date, concentrated on
circumpolar and regional studies of the Antarctic
Circumpolar Current (ACC) circulation. The
temperature and salinity profiles documented by
elephant seals at high latitudes, including below sea ice,
have permitted quasi-circumpolar mapping of the
southernmost fronts of the ACC. By merging
conventional data and the high temporal and spatial
resolution data collected by seal-borne SRDLs, it has
been possible to describe precisely 1) the large-scale
features of the ACC in the South Atlantic and its
variability; 2) the circulation pattern over the
Kerguelen plateau, revealing that the poorly known
Fawn Trough concentrates an important proportion of
the ACC flow in that region. Seals that foraged in ice
covered areas have made eulerian time series available
that have allowed for the estimation of sea ice formation
rates, a parameter that is otherwise difficult to obtain,
while also providing a unique description of the
wintertime ocean circulation over the central Weddell
Sea continental shelf. Finally, we present the first data
collected by a newly-developed fluorescence sensor that
has been embedded in the regular CTD-SRDL and
deployed on elephant seals at Kerguelen. The
fluorometer data obtained have offered the first synoptic
view of the 3 dimensional distribution of temperature,
salinity and fluorescence over a vast sector of the
Southern Indian Ocean, allowing us to describe both
vertical and horizontal variations in chlorophyll.
This paper will make a core contribution to the Plenary
Sessions 2C, 3A and 4A, and will be relevant to 2A and 2