Title: Improving satellite estimates of ice mass loss from Antarctica using observations of relative sea-level change

Presenter: Dominic Hodgson

British Antarctic Survey

Authors: Dominic Hodgson¹, Pippa Whitehouse², Stephen Roberts¹, Elie Verleyen³, Wim Vyverman³, Koen Sabbe³, Michael Bentley²

1 - British Antarctic Survey, daho@bas.ac.uk

2 - Durham University

3 - University of Ghent

Abstract

Accurate satellite estimates of ice current mass loss from Antarctica depend on correcting for the continued response of the solid Earth to past ice-mass change which can be up to three times the total mass change measured by satellites. Past ice mass change is determined from Glacio Isostatic Adjustment models constrained by field data on relative sea-level change and present-day uplift rates. Over the last decade we have derived relative sea level data from around the coast of Antarctica based on a combination of geomorphological evidence of former marine limits and records from dated marine-freshwater transitions in sediments deposited in isolation basins. The isolation of lake basins at a range of different altitudes at each location was determined by analysing a combination of sedimentological, microfossil and biogeochemical markers contained in their sediments. The resulting relative sea level curves have been used to constrain a numerical ice sheet model providing a new Glacio Isostatic Adjustment correction for the GRACE satellite data from Antarctica. This has permitted more accurate constraints to be placed on current ice-mass loss.

Title: Characterizing the structure of the Ross Sea food-web: what are the priorities for monitoring ecosystem change due to climate and fishing?

Presenter: David Bowden

National Institute of Water and Atmospheric Research

Authors: Matthew H. Pinkerton, David Bowden and Janet M. Bradford-Grieve

National Institute of Water and Atmospheric Research (NIWA), Wellington 6241, New Zealand, m.pinkerton@niwa.co.nz

Abstract

A quantitative end-to-end trophic model was used to investigate the network characteristics of the food-web of the Ross Sea continental shelf and slope. We investigated: (1) biomass and productivity of the system by trophic level; (2) linkages between groups in the ecosystem using mixed trophic impact analysis; and (3) overall relative trophic importance of groups. The Ross Sea food-web was found to be a partially inverted pyramid with a pronounced peak in biomass in the lower-middle part of the food-web. The six groups with the highest indices of trophic importance were (in descending order of importance): phytoplankton, mesozooplankton, Antarctic silverfish, small demersal fishes, Antarctic krill and cephalopods. These groups should be the priorities for monitoring large-scale change in the Ross Sea ecosystem. Small pelagic fishes and crystal krill also had high trophic importance. The strongest top-down (predation) interaction in the multi-step analysis was Antarctic toothfish on medium-sized demersal fishes (mainly grenadiers and icefish) but the overall trophic importance of toothfish in the Ross Sea system was close to the middle of all groups. The analysis only considered trophic interactions at the spatial, temporal and ecological scale of the whole Ross Sea shelf and slope area, averaged over a typical year, in 35 trophic groups. Effects at smaller spatial and temporal scales, and effects concerning only parts of populations, are not resolved by the analysis. The analysis will hence likely underestimate bottom-up effects of changes to toothfish abundance on their predators, Weddell seals and type-C killer whales.