Sea-level Response to Ice Sheet EvolutionSea-level Response to Ice Sheet EvolutionRobert Bindschadler and Sophie Nowicki, Code 614.1, NASA GSFCRobert Bindschadler and Sophie Nowicki, Code 614.1, NASA GSFC

Sea-level Response to Ice Sheet Evolution (SeaRISE) is a multi model study targeted at the 5th IPCC report by addressing “How large could the ice sheet contribution to future sea level be in the next 100 to 200 years?”

Current whole ice sheet models lack internal processes responsible for recently observed changes. SeaRISE strategy is to therefore prescribe external forcing and to compare the resulting model responses. The prescriptions are intentionally extreme to assess the possible upper bound of ice sheet contributions to future sea level and its associated uncertainties.

Figure 1: Antarctic ice sheet thickness for the year 2200 from the Penn State model of ice sheet response to a warmer ocean, simulated by imposing an increased melt rate beneath the ice shelves

A) No melting B) Melt: 2 m/yr

D) Melt: 200 m/yrC) Melt: 20 m/yr

Ice shelf thickness (m) Ice sheet thickness (m)

Name: Robert Bindschadler and Sophie Nowicki, NASA/GSFC E-mail: robert.a.bindschadler@nasa.gov, sophie.nowicki@nasa.gov

Phone: 301-614-5707, 301-614-5458

References: SeaRISE project description website: http://websrv.cs.umt.edu/isis/index.php/SeaRISE_Assessment

Data Sources: This project is a community organized effort, lead by NASA/GSFC, and partially funded by the NASA Cryospheric Science program. The participating institutions include Hokkaido University, Los Alamos National Laboratory, NASA/GSFC, NASA/JPL, New York University, Pennsylvania State University, Princeton University, University Corporation for Atmospheric Research, University of Alaska-Fairbanks, University of Bristol, University of Buffalo, University of California at Berkeley, University of California at Santa Cruz, University of Colorado, Universite Joseph Fourier, University of Maine, University of Maryland Baltimore County, University of Montana, University of Potsdam, University of Texas at Austin, University of Tokyo.

Technical Description of Images:Figure 1: Ice thickness in year 2200 as a response to warmer ocean. The external forcing in this sample experiment is implemented by setting the melt beneath the ice-shelves to A) 0 m/yr, B) 2m/yr, C) 20 m/yr and D) 200 m/yr. The simulations illustrating our approach are from the Pennsylvania State University ice sheet model. Results of any experiment are later differenced from the control runs (in this case 0 m/yr melt) to quantify the sensitivity of the model under consideration to the prescribed forcing. The range of model responses is then examined to assess individual model behaviors. Standard data sets of many essential parameters are provided to minimize the differences between models.

Scientific significance: In spite of the potential 3.5 to 5m sea-level rise from a deglaciation of the West Antarctic Ice Sheet, the latest IPCC predictions for sea-level in the 21st century, do not include the contributions from the Greenland and Antarctic ice sheets resulting from ongoing or future dramatic changes in ice flow. These exclusions are in part due to the present lack of understanding in the dynamics of outlet glaciers and marine ice sheets, believed to be responsible for the recent observed dramatic ice sheet changes. Our work is aimed to inform the 5 th IPCC with the possible range of ice sheet response and associated sea-level contribution. This example suggests that a melt rate of 20m/yr at the base of the ice shelves result in a disintegration of the West Antarctic ice sheet, which does not strongly affect the larger East Antarctic ice sheet. The extreme melt of 200m/yr does not seem to strongly alter the qualitative response of the Antarctic ice sheet.

Relevance for future science and relationship to Decadal Survey: The Decadal Survey identifies ice sheet, and their contribution to sea-level, as key issues in Climate Variability and Change. Our project provides guidance for addressing the scientific and societal important issue of ice sheet induced sea level rise using ice models by providing forcing experiments and a crucial dataset that comprise, for example, of the bedrock topography. We also demonstrate the effect of improved bedrock knowledge beneath the ice sheets on ice flow, by including bedrock canyons measured by Operation IceBridge in our dataset.

The Carbon Sink Variability in the NW Subpolar North AtlanticThe Carbon Sink Variability in the NW Subpolar North AtlanticSergio Signorini, SAIC, Code 614.2, NASA GSFC

The North Atlantic is a major oceanic carbon sink. Understanding its biogeochemistry and how it varies on seasonal and interannual time scales is critical for projecting climate change scenarios and the impacts of increasing atmospheric CO2 concentrations on marine ecosystems.

A numerical model of the ocean dynamics, ecosystem, and carbon chemistry is used to evaluate changes over the past 30 years at a site southwest of Iceland. The model predictions are compared with field observations of sea surface temperature (SST, top), dissolved inorganic carbon (DIC, middle) and the partial pressure of CO2 (pCO2, bottom). Figure 1: Comparison between modeled and observed SST, DIC, and air and sea pCO2 showing good agreement.

Name: Sergio Signorini, SAIC, NASA/GSFC Ocean Ecology BranchE-mail: sergio.signorini@nasa.govPhone: 301-286-9891

References:•Signorini, S. R., and C. R. McClain (2003), Further Studies on Oceanic Biogeochemistry and Carbon Cycling, Technical Memorandum, NASA/TM-2003-212245, 212251pp pp, NASA Goddard Space Flight Center, Greenbelt.•Signorini, S. R., et al. (2001a), Modeling biogeochemical-physical interactions and carbon flux in the Sargasso Sea (Bermuda Atlantic Time-series Study site), 37 pp, NASA Goddard Space Flight Center, Greenbelt, MD.

•Signorini, S. R., et al. (2001b), Seasonal and interannual variability of phytoplankton, nutrients, TCO2, pCO2, and O2 in the eastern Subarctic Pacific, J. Geophys. Res., 106, 31,197-131,215.

Data Sources: The surface ocean pCO2 data for 2005 were acquired from the CDIAC web site (http://cdiac.ornl.gov/oceans/VOS_Program/nuka_arctica.html). Multi-year dissolved inorganic carbon (DIC) data from the sub-polar North Atlantic region were obtained from the CARINA web site (http://cdiac.ornl.gov/ftp/oceans/CARINA/CARINA_Database/). Multi-year DIC, alkalinity, surface ocean pCO2, and nutrient in situ data from SURATLANTE were obtained directly from one of the co-authors (Nicolas Metzl).

Technical Description of Image: The image provides a comparison between modeled and observed SST, DIC, and air and sea pCO2 showing good agreement. Both model and observations show pCO2 ocean growth rates higher than the mean atmospheric growth rate, which implies a decrease of the carbon sink in more recent years.Figure 1Top: Time series of model (solid line) and observed (blue and red dots) SST. Middle: Time series of model (solid line) and observed (blue and red dots) Dissolved Inorganic Carbon (DIC).Bottom: Time series of modeled (solid line) and observed (red, blue and black dots) surface ocean pCO2, and observed (green line) atmospheric pCO2 provided as a reference.

Scientific significance: Understanding how carbon is transferred between the atmosphere and ocean and how it is transformed in the water column by biological and chemical processes are essential to understanding the planetary carbon budget, especially the effects and feedbacks resulting from increasing fluxes of carbon into the atmospheric from fossil fuel combustion and deforestation. The results shown are from a coupled ocean dynamical-ecosystem-carbon chemistry model at a site in the subpolar North Atlantic just south of Iceland. The model has three phytoplankton species (diatoms, dinoflagellates, and coccolithophores which exhibit a distinct seasonal succession. The model accurately predicts this succession based on comparisons with satellite ocean color data (chlorophyll-a, primary production, calcite, and particulate organic carbon). As shown in the figures, the model also accurately predicts SST, DIC, and pCO2 based on comparisons with in situ data. The ocean pCO2 is increasing at a faster rate than the atmospheric pCO2 and this has been linked to deep water increases due to convection from non-local sources.

Relevance for future science and relationship to Decadal Survey: One of the primary science themes of the PACE and Aerosol, Cloud, and Ecology (ACE) missions is the ocean carbon cycle. Remote sensing can provide estimates of several key carbon constituents, e.g., calcite and particulate organic carbon, and rates like net primary production, but only near the surface. To understand the carbon cycle and budget more completely requires comprehensive models of all relevant processes. The global data sets from PACE and ACE will be used to constrain and validate these coupled models leading to much more accurate estimates of how much carbon is being sequestered by the ocean and the effects of ocean warming and acidification on marine ecosystems.