DUSTSPEC Workshop 2010

Program

Lamont Doherty Earth Observatory of Columbia University
May 24-26, 2010

May 24, Monday
Gisela Winckler and Natalie Mahowald: Welcome and introduction to goals
Barbara Maher: Dust and Climate: DUSTSPEC, including overview of the Dust Indicators and Records of Terrestrial and Marine Paleoenvironments (DIRTMAP) program
Joe Prospero: Key note: Current climate-dust observations: How to test dust-paleoclimate assumptions in the present day world
Helen M. Roberts: The role of terrestrial sediment records in understanding the dust cycle
Anna Wegner: The role of ice cores in understanding the dust cycle
David McGee and Gisela Winckler: The role of marine sediments in understanding the dust cycle
Alfredo Martínez-Garcia: Plio-Pleistocene dust flux variability in the Subantarctic Atlantic
Jan-Berend Stuut: Aridity changes in the Sahel and their relation to Atlantic-Ocean circulation during the last 57 kyr: inferences from marine sediments off Senegal

May 25, Tuesday
Ashley Ballantyne: Changes in continental dust deposition: implications for terrestrial biogeochemistry
Chris Measures: Dust deposition: The surface ocean’s perspective
John Crusius: Glacial flour as a reactive source of iron to the Gulf of Alaska: reflections on modern processes and their implications for the paleo record
Patrick De Deckker: Preliminary findings on the geochemical and microbiological fingerprinting of Australian aeolian dust
Sujoy Mukhopadhyay: Records of dust emission rates from the Sahara-Sahel region of Africa
Ron Miller: Climate impact of dust
Santiago Gasso: Features of modern dust activity and long range transport of dust from Patagonia based on satellite and surface observations
Paul Ginoux: Identification of natural and anthropogenic dust sources and their evolution for the past 3 decades

May 26, Wednesday
Break out groups, Plenary, and Conclusions

Presentation Summaries (some presentations available for download)

The following three presentations provided an introduction to the workshop and its goals, an overview of the DIRTMAP program, and a key note address by Joe Prospero.

Gisela Winckler (LDEO) and Natalie Mahowald (Cornell University) opened the workshop by welcoming the participants and outlining the agenda and goals of the workshop. The central goal of the workshop was to discuss the demands and challenges for the next generation dust data set compiling dust data from various climate archives, such as ice cores, loess deposits, marine sediments and sediment traps, lake sediments and corals. [download]

Barbara Maher (Lancaster University) presented an overview of the significance of paleo dust data and paleo dust cycle/climate modeling for developing an understanding of the direct and indirect role of dust in Earth system’s response to climate change. Her presentation portrayed the highly successful DIRTMAP (Dust Indicators and Records of Terrestrial and Marine Paleoenvironments) program, initiated by Karen Kohfeld and Sandy Harrison in 2001, the history of the program (DIRTMAP 1, 2 and 3) as well as the MAGIC (Mineral Aerosols and Glacial-Interglacial Cycles) project. [download]

Joe Prospero (University of Miami) focused on the interface between the atmospheric science community, with modern day dust observations, and the paleo dust community. He pointed out that the use of modern day dust studies as a tool to interpret paleo dust records is very limited because we do not yet fully understand the factors affecting modern day dust generation and transport. He emphasized that this is sometimes ignored by the paleo dust community who often applies simplified “ad hoc” assumptions about their linkages. He concluded that the modern atmospheric and paleo dust communities need to define a set of testable dust-climate hypotheses and cooperatively design field campaigns to address these hypotheses. [download]

The following three presentations were intended to provide an overview of the state-of-the-art techniques used to reconstruct dust records from three different types of archives: terrestrial sediments, ice cores and seafloor sediments.

Helen Roberts (Aberystwyth) presented an overview of terrestrial dust records, i.e. loess deposits and lake sediments. She focused on how loess sequences record complex temporal and climatic changes over long time scales. She summarized some of the challenges in interpreting records from loess deposits, such as the generation and interpretation of grain size records and accurate dating. Additionally, she presented some of the recent advances in optical luminescence dating.  [download]

Anna Wegner (Alfred Wegner Institut Bremerhaven) summarized progress in ice core dust records from Antarctica and Greenland over the past decade and their role in understanding changes in global dust patterns and the relation of these patterns to climate change over the past hundreds of thousand years. She highlighted recent advances such as the high-resolution records from the North Greenland Ice Core Project. [download]

David McGee and Gisela Winckler (LDEO) started off a sequence of talks about the use of marine records as an archive of aeolian dust fluxes. In his overview talk, David presented some of the challenges paleoceanographers face when extracting dust records from marine sediments, such as distinguishing dust from other detrital phases in sediments, or accurately estimating fluxes, rather than purely concentrations. [download]

Alfredo Martinez-Garcia (ETH Zuerich) focused on longer timescales, providing an overview of the climatic impacts of the variability in dust flux in the Southern Ocean from ODP site 1090 over the Plio-Pleistocene. [download]

Jan-Berend Stuut (NIOZ) presented some recent work on marine sediment records off the coast of North West Africa, a major deposition zone for the Saharan dust plume. The central goal of this project is to understand the link between dust input and droughts in North Africa during past climate change. Using sediment cores off Senegal, they reconstructed the history of eolian and fluvial sedimentation over the past 60,000 years. Separation of these two components is based on the assumption that the fluvial component is characterized by fine grain sizes (up to 10?m), while the eolian component is represented by coarser grains (up to 100 ?m). Many workshop participants were surprised by this assertion, and lively discussions ensued. [download]

Ashley Ballantyne (University of Colorado) portrayed the use of lake sediments in alpine settings in Colorado and Utah as an archive of continental dust fluxes. Geochemical fingerprinting using Nd isotopes and Sm/Nd ratios allowed Ashley and co-workers to separate the eolian dust component in these lake sediments from bedrock. The lake sediment records identify large changes in dust loading in the western United States in response to human activity in the past 200 years, such as the development of the Pacific railway or the Taylor Grazing Act in the 1930’s. In addition, the project identifies potentially climate-induced shifts in dust emissions over the past thousands of years. [download]

The following three presentations focused on modern dust-generating processes, either regionally or globally, and discussed their importance for interpreting paleo dust records from climate archives.

Chris Measures (University of Hawaii) pointed out that while we know something about how much dust gets up into the atmosphere, we know much less about how much of that dust is deposited in any given spot on the ocean surface, and even less about what happens to that dust once it is in the water. He measures and models dissolved alumin(i)um in the mixed layer of the ocean as a proxy for current dust deposition to the world ocean. Chris presented data from an impressive number of oceanic cruises traversing all the major ocean basins. This reflects the importance of coordinating efforts with initiatives such as GEOTRACES or SOLAS. [download]

John Crusius (USGS Woodshole) focused on characterizing the glacial-derived dust inputs to the Gulf of Alaska, an iron-limited HNLC (high-nutrient, low-chlorophyll) zone. He explained what he and his colleagues have learned about the seasonality of dust mobilization in the region: in the fall, when the braided glacial rivers are low and the fine glacial sediment is exposed, dust is picked up and deposited in the Gulf. However, the iron delivered to the surface ocean in the fall is likely to remain unused because phytoplankton are not very active in the fall. Have these conditions—either the timing or the intensity of the source–differed in the past? Crusius and his colleagues use a combination of remote sensing and field research to fill in the blanks in their understanding of the region. [download]

Patrick De Decker (Australian National University) reported on geochemical and microbiological characteristics of modern Australian dust. He reflected on the importance and the complexity of the Australian continent as a dust source to the Southern Ocean and Antarctica using new lead isotope data for different Australian regoliths. As an example of the complexity of using geochemical fingerprinting, he described how in a multi-day dust storm in 2009, the Sr-Nd fingerprint of the dust changed dramatically from the first day to the last. Patrick also presented a microbiological technique that could potentially be used as a fingerprinting method: by plating dust samples on agar and extracting DNA from the bacteria and microbes that grow, biological information can be used as a provenance source. [download]

Sujoy Mukhopadhyay (Harvard) presented an overview of using corals as high-resolution archive for reconstructing depositional dust fluxes. This new technique is based on measuring the terrigenous 4He content of corals. 4He is present in mineral dust, and when dust grains fall into the ocean and onto corals, the corals incorporate the grains into their structure. The amount of 4He in the corals, then, can be taken as a proxy of how much dust was being deposited at the growth site at a given time. Sujoy described the records he has developed from Red Sea corals—his reconstructions show fascinating correlations with other major dust records, but also some very interesting deviations. [download]

The final three presentations of the DUSTSPEC workshop looked at modeling- or remote sensing-related aspects of dust research.

Ron Miller (NASA GISS) reviewed the various potential ways dust can impact climate, including the ‘dirt snow’ effect (i.e., darkening of bright surface such as ice sheets), iron fertilization, direct, indirect and semi-direct changes in radiative forcing and effects on precipitation and clouds. He described the complexities of trying to model dust’s climate impact when so much remains not fully understood about its functional roles in the ocean and atmosphere. [download]

Santiago Gasso (NASA/GEST) talked about using remote sensing techniques to track large-scale Southern Hemisphere atmospheric circulation events. He uses MODIS satellite data in conjunction with on-the-ground weather reports from stations and airports, cobbling the reports together to get a sense of how storms move and transport dust. Can the peaks in summer dust influx to the EPICA region be correlated with specific storms that happen in South America?  [download]

Paul Ginoux (GFDL Princeton) talked about the use of satellite data to capture and quantify dust emissions. In addition to presenting an overview of the different available dust data satellite products (e.g., TOMS, MODIS, CALIOP), he described methodological developments, such as using optical properties to separate dust particles from other aerosols and freshly emitted dust particles from aged dust particles. Based on this analysis, he presented regional maps for North Africa, North America, South America, Asia, Australia and the Arabian peninsula that distinguish between contributions from natural, anthropogenic and land-use sources. [download]

Notes were prepared by Gisela Winckler and Alejandra Borunda (LDEO).

List of attendees

Eric Achterberg, National Oceanography Centre Southampton, University of Southampton, UK
Samuel Albani, Università degli Studi di Milano-Bicocca, Italy
Bob Anderson, LDEO, Columbia University
Ashley Ballantyne, University of Colorado, Boulder
Aloys Bory, Université des Sciences et Technologies de Lille, France
Ale Borunda, Columbia University
Joanna Bullard, Loughborough University, UK
John Crusius, USGS Woods Hole
Patrick de Deckker, ANU, Canberra, Australia
Peter deMenocal, LDEO, Columbia University
Diego Gaiero, Universidad Nacional de Córdoba, Argentina
Santiago Gasso, NASA Goddard Earth Science and Technology, University of Maryland Baltimore
Paul Ginoux, GFDL, Princeton
Gi Young Jeong, Andong, Korea
Michael Kaplan, LDEO, Columbia University
Bess Koffman, University of Maine
Doug Mackie, University of Otago, New Zealand
Barbara Maher, University of Lancaster, UK
Natalie Mahowald, Cornell University
Alfredo Martinez-Garcia, ETH Zuerich, Switzerland
Joe Mason, University of Wisconsin
David McGee, University of Minessota/LDEO
Chris Measures, University of Hawaii
Ute Merkel, University of Bremen, Germany
Ron Miller, NASA GISS, New York
Chris Moy, USGS Woodshole
Sujoy Mukhopadhyay, Harvard University
Rick Murray, Boston University
Joe Prospero, University of Miami
Helen Roberts, Aberystwyth University
Toni Rosell-Mele, Oregon State University, Autonomous University of Barcelona
Denis-Didier Rousseau, CERES-ERTI, Paris, France
Sascha Serno, LDEO, Columbia University
Jan-Berend Stuut, NIOZ, Texel, The Netherlands
Paul Vallelonga, University of Copenhagen, Denmark
Anna Wegner, Alfred Wegner Institute Bremerhaven, Germany
Gisela Winckler, LDEO, Columbia University

For a complete list of participants and their contact information, please click here.