SUMMARY ERA-40 is a re-analysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The observing system changed considerably over this re-analysis period, with assimilable data provided by a succession of satellite-borne instruments from the 1970s onwards, supplemented by increasing numbers of observations from aircraft, ocean-buoys and other surface platforms, but with a declining number of radiosonde ascents since the late 1980s. The observations used in ERA-40 were accumulated from many sources. The first part of this paper describes the data acquisition and the principal changes in data type and coverage over the period. It also describes the data assimilation system used for ERA-40. This benefited from many of the changes introduced into operational forecasting since the mid-1990s, when the systems used for the 15-year ECMWF re-analysis (ERA-15) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis were implemented. Several of the improvements are discussed. General aspects of the production of the analyses are also summarized.A number of results indicative of the overall performance of the data assimilation system, and implicitly of the observing system, are presented and discussed. The comparison of background (short-range) forecasts and analyses with observations, the consistency of the global mass budget, the magnitude of differences between analysis and background fields and the accuracy of medium-range forecasts run from the ERA-40 analyses are illustrated. Several results demonstrate the marked improvement that was made to the observing system for the * Corresponding author: European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading RG2 9AX, UK. e-mail: adrian.simmons@ecmwf. southern hemisphere in the 1970s, particularly towards the end of the decade. In contrast, the synoptic quality of the analysis for the northern hemisphere is sufficient to provide forecasts that remain skilful well into the medium range for all years. Two particular problems are also examined: excessive precipitation over tropical oceans and a too strong Brewer-Dobson circulation, both of which are pronounced in later years. Several other aspects of the quality of the re-analyses revealed by monitoring and validation studies are summarized. Expectations that the 'second-generation' ERA-40 re-analysis would provide products that are better than those from the firstgeneration ERA-15 and NCEP/NCAR re-analyses are found to have been met in most cases.

The depositional history of the Storfjorden and Kveithola trough-mouth fans (TMFs) in the northwestern Barents\ud Sea has been investigatedwithin two coordinated Spanish and Italian projects in the framework of the International\ud Polar Year (IPY) Activity 367, NICE STREAMS. The investigation has been conducted using a multidisciplinary approach\ud to the study of sediment cores positioned on high-resolution multibeam bathymetry and TOPAS/CHIRP\ud sub-bottom profiles.\ud Core correlation and the age model were based on 27AMS 14C samples, rock magnetic parameters, lithofacies sequences,\ud and the presence of marker beds including two oxidized layers marking the post Last GlacialMaximum\ud (LGM) inception of deglaciation (OX-2) and the Younger Dryas cold climatic event (OX-1).\ud Sediment facies analysis allowed the distinction of a number of depositional processes whose onset appears\ud closely related to ice stream dynamics and oceanographic patterns in response to climate change. The glacigenic\ud diamictonwith lowwater content, high density, and high shear strength, deposited during glacial maxima, indicates\ud ice streams grounded at the shelf edge. Massive release of IRD occurred at the inception of deglaciation in\ud response to increased calving rates with possible outer ice streams lift off and collapse. The presence of a severalmeter-\ud thick sequence of interlaminated sediments deposited by subglacial outbursts of turbid meltwater\ud (plumites) indicates rapid ice streams' melting and retreat. Crudely-layered and heavily-bioturbated sediments\ud were deposited by contour currents under climatic/environmental conditions favorable to bioproductivity.\ud The extreme sedimentation rate of 3.4 cm a−1 calculated for the plumites from the upper-slope area indicates a\ud massive, nearly instantaneous (less than 150 years), terrigenous input corresponding to an outstanding meltwater\ud event.Wepropose these interlaminated sediments to represent the high-latitudemarine record ofMeltWater\ud Pulse 1a (MWP-1a). Different bathymetric and oceanographic conditions controlled locally the mode of glacial\ud retreat, resulting in different thickness of plumites on the upper continental slope of the Storfjorden and\ud Kveithola TMFs. It is possible that the southern part of Storfjorden TMF received additional sediments from the\ud deglaciation of the neighboring Kveithola ice stream

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17Particle fluxes were recorded over a one-year period in the southern Antarctic

The Southern Ocean plays a pivotal role in the control of atmospheric CO 2 levels, via both physical and biological sequestration processes. The biological carbon transfer to the ocean interior is tightly coupled to the availability of other elements, especially iron as a trace-limiting nutrient and dissolved silicon as the mineral substrate that allows diatoms to dominate primary production. Importantly, variations in the silicon cycling are large but not well understood. Here we use δ 30 Si measurements to track seasonal flows of silica to the deep sea, as captured by sediment trap time series, for the three major zones (Antarctic, AZ; Polar Frontal, PFZ; and Sub-Antarctic, SAZ) of the open Southern Ocean. Variations in the exported flux of biogenic silica (BSi) and its δ 30 Si composition reveal a range of insights, including that (i) the sinking rate of BSi exceeds 200 m d À1 in summer in the AZ yet decreases to very low values in winter that allow particles to remain in the water column through to the following spring, (ii) occasional vertical mixing events affect the δ 30 Si composition of exported BSi in both the SAZ and AZ, and (iii) the δ 30 Si signature of diatoms is well conserved through the water column despite strong BSi and particulate organic carbon (POC) attenuation at depth and is closely linked to the Si consumption in surface waters. With the strong coupling observed between BSi and POC fluxes in PFZ and AZ, these data provide new constraints for application to biogeochemical models of seasonal controls on production and export.