Description: The Clyde Sea Nephrops fishery produces large amounts of invertebrate discards. Of these, up to 80% (by numbers) are echinoderms, including the starfishAsterias rubens and the brittlestar Ophiura ophiura. The short- and longer-term mortality of these species was determined after trawling in order to gain reliableestimates of trawl-induced mortality. Short-term mortality was assessed after trawling and periods of aerial exposure on deck, and ranged from 0-31%, with A.rubens showing lower mortality. Mortality of haphazardly collected echinoderms of various sizes and degrees of damage was monitored over one month todetermine longer-term mortality. The effects of injury on starfish survival were also examined, as were the effects of trawling and aerial exposure on O. ophiurasurvival and A. rubens righting time. Injured A. rubens had a significantly higher long-term mortality (22-96%) than controls (4%). Trawling and aerial exposuresignificantly increased righting times of A. rubens, implying susceptibility to stress and an increased risk of predation. Moribund A. rubens developed white lesionscontaining bacteria (Vibrio metschnikovii and Acinetobacter sp.) and mortality rates only stabilised in the third week after trawling. In contrast, all trawled O. ophiuradied within 14d. Immediate re-immersion in sea water resulted in lower, but nevertheless high, mortality (91%). Our results suggest that post-trawling mortality ofdiscarded echinoderms has been underestimated in the past.

Description: The Clyde Sea Nephrops fishery produces large amounts of invertebrate discards. Of these, as much as 89% are decapod crustaceans, including the swimmingcrab Liocarcinus depurator (Linnaeus, 1758), the squat lobster Munida rugosa (Fabricius, 1775) and the hermit crab Pagurus bernhardus (Linnaeus, 1758). Theshort-term mortality of these species was assessed following trawling and periods of aerial exposure on deck (16-90min), and ranged from 2-25%, with Pagurusbernhardus showing the lowest mortality. Two experiments were performed to determine the longer-term survival of trawled decapods compared to those withexperimentally ablated appendages. Deliberately damaged decapods had a significantly lower longer-term survival (ca. 30%) than controls (72-83%). Survival oftrawled Liocarcinus depurator that had been induced to autotomize two appendages was slightly lower (74%) compared with intact creel-caught animals (92%).Mortality rates stabilised about 10d after trawling. Our results suggest that post-trawling mortality of discarded decapod crustaceans has been underestimated in thepast, owing to inadequate monitoring periods. Copyright 2001 International Council for the Exploration of the Sea

Description: This chapter assesses the current state of knowledge of the rate of change of global-averaged and regional sea-level in relation to climate change. We focus on the 20th and 21st centuries.However, because of the slow response to past conditions of the oceans and ice sheets and the consequent land movements, we consider changes in sea level prior to the historical record, andwe also look over a thousand years into the future.Past changes in sea levelFrom recent analyses, our conclusions are as follows:since the Last Glacial Maximum about 20 000 years ago, sea level has risen by over 120 m at locations far from present and former ice sheets, as a result of loss of mass from these ice sheets. There was a rapid rise between 15 000 and 6000 years ago at an average rate of 10 mm/yr.based on geological data, global average sea level may have risen at an average rate of 0.5 mm/yr over the last 6000 years and at an average rate of 0.1 to 0.2 mm/yr over the last 3000 years.vertical land movements are still occurring today as a result of these large transfers of mass from the ice sheets to the ocean.during the last 6000 years, global average sea-level variations on the time scales of a few hundred years and longer are likely to have been less than 0.3 to 0.5 m.based on tide gauge data, the rate of global average sea-level rise during the 20th century is in the range 1.0 to 2.0 mm/yr, with a central value of 1.5 mm/yr (as with other ranges of uncertainty, it is not implied that the central value is the best estimate).based on the few very long tide-gauge records, the average rate of sea-level rise has been larger during the 20th century than the 19th century.no significant acceleration in the rate of sea-level rise during the 20th century has been detected.there is decadal variability in extreme sea levels but no evidence of widespread increases in extremes other than that associated with a change in the mean.Factors affecting present day sea level changeGlobal average sea level is affected by many factors. Our assessment of the most important is as follows.Ocean thermal expansion leads to an increase in ocean volume at constant mass. Observational estimates of about 1 mm/yr over recent decades are similar to values of 0.7 to 1.1 mm/yr obtained from Atmosphere-Ocean General Circulation Models (AOGCMs) over a comparable period. Averaged over the 20th century, AOGCM simulations result in rates of thermal expansion of 0.3 to 0.7 mm/yr.The mass of the ocean, and thus sea level, changes as water is exchanged with glaciers and ice caps. Observational and modelling studies of glaciers and ice-caps indicate a contribution to sea-level rise of 0.2 to 0.4 mm/yr averaged over the 20th century.Climate changes during the 20th century are estimated from modelling studies to have led to contributions of between Ð0.2 and 0.0 mm/yr from Antarctica (the results of increasing precipitation) and 0.0 to 0.1 mm/yr from Greenland (from changes in both precipitation and runoff).Greenland and Antarctica have contributed 0.0 to 0.5 mm/yr over the 20th century as a result of long term adjustment to past climate changes.Changes in terrestrial storage of water over the period 1910 to 1990 are estimated to have contributed from Ð1.1 to +0.4 mm/yr of sea-level rise.The sum of these components indicates a rate of eustatic sea-level rise (corresponding to a change in ocean volume) from 1910 to 1990 ranging from Ð0.8 mm/yr to 2.2 mm/yr, with a central value of 0.7 mm/yr. The upper bound is close to the observational upper bound (2.0 mm/yr), but the central value bound is less than the observational lower bound (1.0 mm/yr), i.e. the sum of components is biased low compared to the observational estimates. The sum of components indicates an acceleration of only 0.2 mm/yr/century, with a range from Ð1.1 to +0.7 mm/yr/century, consistent with observational finding of no acceleration in sea-level rise during the 20th century. The estimated rate of sea-level rise from anthropogenic climate change from 1910 to 1990 (from modelling studies of thermal expansion, glaciers and ice-sheets) ranges from 0.3 to 0.8 mm/yr. It is very likely that 20th century warming has contributed significantly to the observed sea level rise, through thermal expansion of sea water and widespread loss of land ice.Projected sea-level changes from 1990 to 2100Projections of components contributing to sea-level change from 1990 to 2100 (this period is chosen for consistency with the IPCC Second Assessment Report), using a range of AOGCMs following the IS92a scenario (including the direct effect of sulphate aerosol emissions) give:thermal expansion of 0.11 to 0.43 m, accelerating through the 21st century.a glacier contribution of 0.01 to 0.23 m.a Greenland contribution of -0.02 to 0.09 m.an Antarctic contribution of -0.17 to 0.02 m.Including thawing of permafrost, deposition of sediment, and the ongoing contributions from ice sheets as a result of climate change since the Last Glacial Maximum, we obtain a range of global-average sea-level rise from 0.11 to 0.77 m. This range reflects systematic uncertainties in modelling.For the 35 SRES scenarios, we project a sea-level rise of 0.09 to 0.88 m for 1990 to 2100, with a central value of 0.48 m. The central value gives an average rate of 2.2 to 4.4 times the rate over the 20th century. If terrestrial storage continued at its present rates, the projections could be changed by -0.21 to 0.11 m. For an average AOGCM, the SRES scenarios give results which differ by 0.02 m or less for the first half of the 21st century. By 2100, they vary over a range amounting to about 50% of the central value. Beyond the 21st century, sea level rise will depend strongly on the emission scenario.The West Antarctic Ice Sheet (WAIS) has attracted special attention because it contains enough ice to raise sea level by 6 m and because of suggestions that instabilities associated with its being grounded below sea level may result in rapid ice discharge when the surrounding ice shelves are weakened. The range of projections given above makes no allowance for ice-dynamic instability of the WAIS. It is now widely agreed that major loss of grounded ice and accelerated sea-level rise are very unlikely during the 21st century.Our confidence in the regional distribution of sea level change from AOGCMs is low because there is little similarity between models. However, models agree on the qualitative conclusion that the range of regional variation is substantial compared with the global average sea-level rise. Nearly all models project greater than average rise in the Arctic Ocean and less than average rise in the Southern Ocean.Land movements, both isostatic and tectonic, will continue through the 21st century at rates which are unaffected by climate change. It can be expected that by 2100 many regions currently experiencing relative sea-level fall will instead have a rising relative sea level.Extreme high water levels will occur with increasing frequency (i.e. with reducing return period) as a result of mean sea-level rise. Their frequency may be further increased if storms become more frequent or severe as a result of climate change.Longer term changesIf greenhouse gas concentrations were stabilised, sea level would nonetheless continue to rise for hundreds of years. After 500 years, sea-level rise from thermal expansion may have reached only half of its eventual level, which models suggest may lie within ranges of 0.5 to 2.0 m and 1 to 4 m for CO2 levels twice and four times pre-industrial, respectively.Glacier retreat will continue and the loss of a substantial fraction of the total glacier mass is likely. Areas that are currently marginally glaciated are most likely to become ice-free.Ice sheets will continue to react to climate change during the next several thousand years even if the climate is stabilised. Models project that a local annual-average warming of larger than 3°C sustained for millennia would lead to virtually a complete melting of the Greenland ice sheet. For a warming over Greenland of 5.5°C, consistent with mid-range stabilisation scenarios, theGreenland ice sheet contributes about 3 m in 1000 years. For a warming of 8°C, the contribution is about 6 m, the ice sheet being largely eliminated. For smaller warmings, the decay of the ice sheet would be substantially slower.Current ice dynamic models project that the WAIS will contribute no more than 3 mm/yr to sea-level rise over the next thousand years, even if significant changes were to occur in the ice shelves. However, we note that its dynamics are still inadequately understood to make firm projections, especially on the longer time scales.Apart from the possibility of an internal ice dynamic instability, surface melting will affect the long-term viability of the Antarctic ice sheet. For warmings of more than 10°C, simple runoff models predict that an ablation zone would develop on the ice sheet surface. Irreversible disintegration of the WAIS would result because the WAIS cannot retreat to higher ground once its margins are subjected to surface melting and begin to recede. Such a disintegration would take at least a few millennia. Thresholds for total disintegration of the East Antarctic ice sheet by surface melting involve warmings above 20*C, a situation that has not occurred for at least 15 million years and which is far more than predicted by any scenario of climate change currently under consideration.

Description: Die Rekonstruktion des Stroemungsfeldes im Ozean aus in situDaten ist eine der aeltesten Aufgaben der modernen Ozeanographie. Indieser Arbeit wird ein stationaeres, nichtlineares Modell entwickeltund vorgestellt, das die geostrophische Stroemung entlang eineshydrographischen Schnittes aus hydrographischen Daten schaetzt. DasModell wird erweitert, um diese Schaetzungen durch Messungen derabsoluten Oberflaechenauslenkung durch Satellitenaltimetrie zuverbessern. Dabei kommen Methoden der Variationsrechnung zum Einsatz,insbesondere die adjungierte Methode.Die absolute Oberflaechenauslenkung muss relativ zu einerAequipotentialflaeche, dem Geoid, angegeben werden. Verglichen mit derQualitaet ozeanographischer Messungen sind die Schaetzungen des Geoidsungenau und von geringer Aufloesung. Dadurch ist der Einsatz derOberflaechenauslenkungsdaten auf Anwendungen beschraenkt, diegrossraeumige Phaenomene der Ozeanzirkulation beschreiben. NeueSatellitenmissionen, die zu genauen, hoch aufloesenden Geoidmodellenfuehren werden, sind jedoch in Planung und Vorbereitung. In dieserArbeit wird eine Methode vorgestellt, die die Behandlung derOberflaechenauslenkungsdaten unter genauer Beruecksichtigung ihrerFehlerkovarianz ermoeglicht.Ein erster Test des Modell in einem Szenarium mit einem kleinenDatensatz demonstriert einige der Modelleigenschaften. Man muss dermathematischen Unterbestimmung des Modell begegnen, indem mangenuegend a priori Informationen ueber den Zustand des Ozeanseinfuehrt. Diese unabhaengigen Informationen koennten einemhydrographischen Atlas entstammen.Zwillingsexperimente mit einen synthetischen Datensatz der FLAMEGruppe zeigen, wie wichtig verbesserte Geoidmodelle sind, wenn man dasGeschwindigkeitsfeld entlang eines hydrographischen Schnittes schaetzenmoechte. Wenn die Oberflaechenauslenkungsdaten nach Massgabe derFehlerabschaetzung fuer die zukuenftigen Geoidmodelle GRACE und GOCEberuecksichtigt werden, dann koennen Volumen- und Temperaturtransporteum bis zu 55% genauer geschaetzt werden als ohneOberflaechenauslenkungsdaten. Mit den Fehlerschaetzungen des momentanbesten Geoidmodells EGM96 sind nur Verbesserungen bis 18% moeglich.Das inverse Modell schaetzt Nettovolumentransporte durch einenwichtigen Schnitte ueber den Antarktische Zirkumpolarstrom von145-166 Sv. Diese Werte stimmen mit denen anderer Autoren ueberein.Die Fehlerschaetzungen belaufen sich auf 13 Sv ohne bis 11 Sv mitDaten der Oberflaechenauslenkung. Diese Daten sind auf das EGM96Geoidmodell bezogen und gemaess seiner Fehlerkovarianz gewichtet. DieDaten der Oberflaechenauslenkung und eine Schaetzung durch das inverseModell weichen voneinander um mehr als die Fehlerschaetzungen ab.