Deciphering the Antarctic MSA-sea Ice Link with a Combined Regional Forecast and Atmospheric Chemistry Model

University Of Washington, Seattle WA

Investigators

Abstract

Abstract PI: Cecilia M. Bitz Proposal Number: 0739127 Title: Deciphering the Antarctic MSA-sea ice link with a combined regional forecast and atmospheric chemistry model Intellectual merit: Sea ice plays multiple important roles in the climate system including reflecting solar radiation, influencing ocean heat uptake, contributing to dense water formation and protection of ice shelves by damping ocean wave action. Reliable records of Antarctic sea ice extent are only available since 1979. In order to further quantitative understanding of the role of Antarctic sea ice in climate, it would be highly desirable to have a longer term record of Antarctic sea ice conditions. Marine phytoplankton produce dimethylsulfide (DMS) which is emitted to the atmosphere where it can be oxidized to methanesulfonic acid (MSA) and sulfur dioxide and eventually deposited in continental ice. Sulfur dioxide can be converted to non seasalt (nss) sulfate or dry deposited to the ice. It has been suggested that MSA and nss sulfate deposited in ice cores can serve as a proxy for sea ice conditions although available evidence shows the relationship can be complicated by several factors including variability in emissions, variability in transport, reactions in transport and variability in deposition. Moreover there remain uncertainties with respect to the relationship between sea-ice and emissions. Whereas it might be presumed that sea ice would limit the growth of phytoplankton and prevent the escape of DMS, some of the highest concentrations of DMS in the marine environment have been measured in melting Antarctic sea ice. The Antarctic Integrated System Science Program ahs funded this project to use an interdisciplinary modeling approach to assess these factors and uncertainties to help determine whether and where sea ice conditions might be reliably extracted from MSA and nss sulfate levels in Antarctic ice cores ice cores. Specifically the MSA-climate relationship will be examined over the period of 1979-2002 using a relatively high resolution regional chemistry model based on the Community Multi-scale Air Quality (CMAQ) modeling system. Meteorological conditions will be input from hind-casts of Polar MM5 (Ohio State polar specific modifications of the fifth-generation Penn State University/National Center for Atmospheric Research Mesoscale Model)/ Large scale chemical boundary conditions will be input from a global chemical transport model, GEOS-Chem (Goddard Earth Observing System-Chemistry). Under collaborative arrangements with high latitude phytoplankton and sea ice algae experts, empirical DMS emissions within the model domain from sea ice will be developed and compared with modeled DMS emissions from an ocean general circulation model that includes sea ice, phytoplankton and sea ice algae. The overall model output will be compared with measurements from atmospheric monitoring sites and depositional records in snow and ice including widely distributed annually resolved records that are being undertaken as part of the International Polar Year (IPY) International Traverses of Antarctica for Science and Education (ITASE). Broader impacts: By investigating the links between MSA and nss sulfate levels in ice cores and sea ice conditions, this project could provide a basis to help advance the understanding of the role of Antarctic sea ice in the global climate system. The project directly combines expertise in global climate modeling, sea ice, and atmospheric chemistry and through collaboration, in marine phytoplankton ecology. A graduate student who is credited with conceiving of this proposal will be supported to conduct his PhD thesis on this interdisciplinary topic. As one element of the marine phytoplankton ecology collaboration, this student is intending to undertake an NSF East Asia Pacific Summer Institute internship in Australia with experts in sea ice algae dimethylsulfonic acid propionate (DMSP, a precursor to DMS) production. Outreach related to the research will be conducted at the annual Polar Science Weekend at the Pacific Science Center in Seattle. Two of the investigators are members of an underrepresented group (female) in climate related science and are early in their academic careers.