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June 2001, (Vol 11 No 4) Vol. 11, No. 4 ● June 2001 EARTH SYSTEM MONITOR NOAA altimetry sorts out Atlantic Ocean seafloor A guide to Malvinas plate controversy resolved using altimetry NOAA's data and information Karen M. Marks altimetry data to form “plate reconstructions,” services Laboratory for Satellite Altimetry essentially winding plate tectonics backwards in NOAA/NESDIS time to reconstruct the geography ocean basins. INSIDE Here we show how seafloor features such as frac- According to the theory of plate tectonics, ture zones and mid-ocean spreading ridges, that the continents have drifted around the globe as are mapped in gravity derived from satellite al- 3 the shapes of the ocean basins have changed timetry, can be used to solve problems of how News briefs over time. As a result, the patterns of ocean cir- seafloor in the south Atlantic Ocean evolved. culation and climate were different in the past More than two decades ago, LaBrecque and 5 because the locations of land masses and oceans Hayes (1979) proposed that a tectonic plate (the Coastal Services basins were different. Understanding of this Malvinas) existed on the western side of the Center—Observing & “paleo-geography” is an important part of inter- Agulhas Basin (Figure 1) during the Late Creta- monitoring the coastal preting the fossil record of paleo-climate and ceous, between the times of magnetic anomalies environment paleo-ecology, and this history sets the frame- 34y and 31 (about 83 to 68 million years ago). work for discussions of current and future ocean The presence of this plate could explain why the 7 circulation and climate change. While the pri- orientation of magnetic anomaly lineations (i.e., Errata–West Florida mary purpose for NOAA’s Laboratory for Satellite past locations of spreading at times called chlorophyll Altimetry is to provide continuous monitoring chrons) in the Agulhas Basin differ significantly of sea level to detect weather and climate phe- from similar anomalies in the South Atlantic. 9 nomena active today, LSA scientists can also use However, this additional plate complicates what Integrated Taxonomic — continued on page 2 Information System 10 Forecast for 2001 hurricane activity 11 Data products and services 12 Severe weather forecasting NT OF C E OM TM M R E A R P C E E D ★ ★ U N A C IT I E R D E ST AM ATES OF ▲ Figure 1. Gray shaded-relief image of gravity anomalies computed from Geosat and ERS-1 satellite altimeter data (Sandwell and Smith, 1997) over the South Atlantic. Gravity anomaly amplitudes range between < -35 mGal (black) and > 35 mGal (white) and are ”illuminated” from the east. Features are U.S. DEPARTMENT the Agulhas rift (AR), Agulhas fracture zone (AFZ), and the Mid-Atlantic ridge (MAR). Chain-lines are OF COMMERCE Chron 34y, and white lines are Chron 33r. The white box outlines the Agulhas Basin study area. The National Oceanic and Atmospheric extinct Agulhas rift segments are offset dextrally by fracture zones trending southwest-northeast (both Administration the ridge segments and fracture zones are linear gravity anomaly lows that are centered roughly along 15˚ E. longitude). 2 EARTH SYSTEM MONITOR June 2001 NOAA Altimetry, from page 1 For a second test, we moved mag- would otherwise be a simple opening of netic anomalies 33r and 27 on the EARTH SYSTEM MONITOR the south Atlantic Ocean as South western flank of the Mid-Atlantic ridge (i.e., on the South American plate) to The Earth System Monitor (ISSN 1068- America separated from Africa along 2678) is published quarterly by the NOAA Africa using the South America-Africa the Mid-Atlantic spreading ridge. As a Environmental Information Services office. result, the existence of the Malvinas 33r and 27 finite rotation poles, respec- Past issues are available online at http:// plate, and its size, has remained contro- tively. North of the Agulhas fracture www.nodc.noaa.gov/General/NODCPubs/ versial. zone, these rotations bring the South We conducted simple tests that American magnetic anomalies into Questions, comments, or suggestions confirm a Late Cretaceous plate is re- alignment with their conjugates on the for articles, as well as requests for quired in the Agulhas Basin. First, we African plate (see Figure 2). South of subscriptions and changes of address, should be directed to the Editor, plotted the marine gravity field from the Agulhas fracture zone, where Roger Torstenson. NOAA’s satellite altimetry in an oblique spreading on the Agulhas rift ceased by Mercator projection (Figure 2), having — continued on page 4 The mailing address for the Earth System the South America-Africa 33r-27 stage Monitor is: pole (which describes the separation of National Oceanographic Data Center South America from NOAA/NESDIS E/OC1 Africa between 79 and SSMC3, 4th Floor 61 million years ago) 1315 East-West Highway as the projection pole. Silver Spring, MD 20910-3282 On this projection, fracture zones formed EDITOR by South America- R. Torstenson Africa motion during Telephone: 301-713-3281 ext.107 this time should be Fax: 301-713-3302 horizontal. Indeed, E-mail: [email protected] those lying north of the Agulhas fracture zone plot horizontally DISCLAIMER between magnetic Mention in the Earth System Monitor of anomalies 33r and 27, commercial companies or commercial products does not constitute an endorse- indicating they formed ment or recommendation by the National by South America- Oceanic and Atmospheric Administration Africa spreading. or the U.S. Department of Commerce. However, the Agulhas Use for publicity or advertising purposes of fracture zone and frac- information published in the Earth System ture zones generated Monitor concerning proprietary products on the Agulhas rift or the tests of such products is not between anomalies 33r authorized. and 27 do not lie hori- zontally on this pro- jection. Instead, they ATMOSPH ND ER A IC ° IC A make a ~10 angle to N D A M E I the horizontal. This C N O I S ▲ L T Figure 2. Monthly gravity anomalies plotted using demonstrates they were A R N A T O I an oblique Mercator projection, with the South America- I O not formed by South T N A Africa 33r-27 stage pole as the projection pole. Magnetic N America-Africa spreading U .S E anomalies are 33r (white circles), and 27 (squares), those . C during this time period. D R E E P M rotated from the western ridge flank are 33r (stars) and A M RT CO 27 (triangles). Black circles are fracture zone picks. MENT OF On this projection, fracture zones formed by South America-Africa motion during this period shold be U.S. DEPARTMENT OF COMMERCE horizontal. An independent Malvinas plate is required Donald Evans, Secretary NOAA/NESDIS because the Agulhas fracture zone and those generated 1315 East West Highway on the Agulhas rift are not horizontal, and the South National Oceanic and Silver Spring, Maryland 20910 America-Africa 33r-27 stage rotation does not bring Atmospheric Administration E-mail: Malvinas 33r anomalies into alignment with their conju- Scott Gudes, Acting Under Secretary and Administrator [email protected] gates on the African plate. June 2001 EARTH SYSTEM MONITOR 3 Space environmental papers GCOS activities published News briefs Under the United Nations Framework Helen E. Coffey of NOAA’s National Convention on Climate Change, countries Geophysical Data Center (NGDC) had Greatest measured solar flare are required to submit detailed reports on two papers published in refereed journals A monster solar active region NOAA their Global Climate Observing System recently. She is co-author of ”Comparison AR9393 crossed the solar disk in April. It (GCOS) activities. Howard Diamond, the of Sunspot Area Data Bases,” by T. grew to an area 14 times the Earth's sur- U.S. GCOS program manager, is coordi- Baranyi, L. Gyori, A. Ludmany and H.E. face and had a complex reversed-polarity nating the preparation of this report. The Coffey, that appears in the January 2001 magnetic configuration. The complexity effort is being supported by a subgroup, issue of Monthly Notices of the Royal Astro- warned of possible large eruptions in the chaired by NCDC’s Russ Vose, addressing nomical Society, Volume 323. This paper area. On April 2, 2001, the largest solar atmospheric monitoring systems in the resulted from a proposal in Solar Influ- X-ray flare ever recorded occurred when United States. The subgroup has com- ences on Global Change that she had the region was in the northwest quadrant pleted its chapter, describing surface, written for the Debrecen Heliophysical of the Sun. Luckily, the region had upper air, and atmospheric constituent Observatory, Hungary, to reduce sunspot rotated past central meridian and most observing networks operated by the U.S. blocking data in Total Solar Irradiance effects were directed to outer space. Earth models. The second paper entitled did receive high-energy protons from this Dark Sky Reserves ”When do the geomagnetic Aa and Ap eruption. Mr. Peter Goering of the Muskoka indices disagree?” by H.E. Coffey and E.H. An earlier flare on March 31, 2001 Heritage Foundations, in Canada, recently Erwin, both of NGDC, appears in a recent was more geo-effective, causing aurora as contacted NGDC about the development issue of the Journal of Atmospheric and far south as Mexico and power system of Dark Sky Reserves. He has been head- Solar-Terrestrial Physics. The paper was disturbances in New York. Fortunately, ing an effort to have a Dark Sky Park cre- originally presented at the 1999 Interna- this storm occurred over the weekend ated in Canada. Beneficiaries include tional Union of Geodesy and Geomag- when power system use is 50% lower amateur astronomers and anyone inter- netism (IUGG) meeting in Birmingham, than during the workweek; also, air con- ested in limiting the use of electrical England.
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