Magnetic susceptibility variations in Upper Pleistocene deep-sea sediments of the NE Atlantic: implications for ice-rafting and paleocirculation at the last glacial maximum

Magnetic susceptibility (MS) variations are used to intercorrelate 17 Upper Pleistocene sediment cores taken from the NE Atlantic, between 40 degrees and 60 degrees N. The MS-based correlation depends on regionally consistent patterns of variation in the deposition of ice-rafted detritus (IRD) in response to Pleistocene glaciations, and especially to high-frequency ice-rafting episodes referred to in recent studies as ''Heinrich events.'' The sedimentological and rock-magnetic basis for the apparent relationship between the MS signal and IRD content of NE Atlantic sediments is examined by (1) comparing the MS profiles of selected cores with their records of coarse fraction (>150 mu m) lithic fragment abundance and Neogloboquadrina pachyderma (sin) percentages, and (2) normalizing MS by expressing it both on a carbonate-free basis, and as a quotient with anhysteretic remanent magnetization (a parameter sensitive to magnetic mineral grain size variations). These comparisons show that variations in bulk-sediment MS are only partly driven by simple carbonate dilution (+/- productivity and dissolution) effects. Changes in both the concentration and grain size of magnetic minerals within the lithogenic noncarbonate fraction also impose a significant influence on bulk MS values. In particular, horizons rich in IRD are associated with significant increases in the relative proportion of coarse grained (multidomain) ferrimagnetic particles in the sediment. This is because ice-rafting, in contrast to most other mechanisms capable of transporting detrital magnetic minerals to pelagic environments, has a high potential for delivering large ferrimagnetic grains as components of sand-sized, polycrystalline lithic fragments. This fundamental linkage between the IRD content and MS signal of NE Atlantic sediments is used to reconstruct the patterns of variation in IRD deposition and, by inference, surface currents of the last glacial maximum (LGM, similar to 18-19 ka) relative to the present-day NE Atlantic, using the time-slice mapping approach developed by the CLIMAP project group. Our LGM/Holocene MS ratio map, based on sample pairs from over 80 deep-sea cores, confirms that there was a weak, cyclonic gyre north of the polar front in the LGM North Atlantic. The gyre comprised a sluggish warm current in the NE Atlantic flowing north between latitudes 47 degrees and 62 degrees N, partly fed by subtropical waters from south of the polar front, and carrying large numbers of icebergs derived from several sources, most of which melted between Latitudes 45 degrees and 52 degrees N. The warm current probably continued its flow into the Iceland Basin, where it fed into a south-flowing current which transported melting icebergs from Iceland and Scandinavia along the western flank of the Reykjanes Ridge.

[1]  Richard Foster Flint,et al.  Glacial and Quaternary geology , 1971 .

[2]  J. King,et al.  A rapid method for magnetic granulometry with applications to environmental studies , 1981 .

[3]  J. D. Hays,et al.  Investigation of Late Quaternary Paleoceanography and Paleoclimatology , 1976 .

[4]  T. Crowley,et al.  Glacial North Atlantic 18,000 Years Ago: A climap Reconstruction , 1976 .

[5]  W. Bradley.  Geology and Biology of North Atlantic Deep-Sea Cores Between Newfoundland and Ireland , 1942 .

[6]  J. Bloemendal,et al.  25. ROCK-MAGNETIC STRATIGRAPHY OF LEG 108 SITES 658, 659, 661, AND 665, EASTERN TROPICAL ATLANTIC1 , 1989 .

[7]  A. Mcintyre,et al.  Time-Transgressive Deglacial Retreat of Polar Waters from the North Atlantic , 1973, Quaternary Research.

[8]  W. Berger.  Deep-sea carbonates; Pleistocene dissolution cycles , 1973 .

[9]  E. Olausson.  Climatological, geoeconomical and paleooceanographical aspects on carbonate deposition , 1965 .

[10]  N. Shackleton,et al.  History of Plio-Pleistocene Climate in the Northeastern Atlantic, Deep Sea Drilling Project Hole 552A , 1984 .

[11]  A. Dreimanis.  Quantitative Gasometric Determination of Calcite and Dolomite by Using Chittick Apparatus , 1962 .

[12]  N. Pisias,et al.  Late Pleistocene Paleoclimatology of the Central Equatorial Pacific: A Quantitative Record of Eolian and Carbonate Deposition , 1987, Quaternary Research.

[13]  J. King,et al.  A rock‐magnetic study of giant piston core LL44‐GPC3 from the central North Pacific and its paleoceanographic implications , 1988 .

[14]  D. Macayeal.  A low‐order model of the Heinrich Event Cycle , 1993 .

[15]  J. King,et al.  45. ROCK-MAGNETIC STRATIGRAPHY OF SITE 645 (BAFFIN BAY) FROM ODP LEG 105 1 , 1989 .

[16]  W. Ruddiman.  Late Quaternary deposition of ice-rafted sand in the subpolar North Atlantic (lat 40° to 65°N) , 1977 .

[17]  W. Broecker,et al.  Correlations between climate records from North Atlantic sediments and Greenland ice , 1993, Nature.

[18]  P. Biscaye,et al.  Distribution of Quartz in Late Quaternary Atlantic Sediments in Relation to Climate , 1979, Quaternary Research.

[19]  S. Clemens,et al.  One Million Year Record of Summer Monsoon Winds and Continental Aridity from the Owen Ridge (Site 722), Northwest Arabian Sea , 1991 .

[20]  P. Weaver,et al.  Evidence for Heinrich layers off Portugal (Tore Seamount: 39 °N, 12 °W) , 1996 .

[21]  P. deMenocal,et al.  Origin of the sedimentary magnetic record at Ocean Drilling Program Sites on the Owen Ridge , 1993 .

[22]  R. Alley,et al.  Ice‐rafted debris associated with binge/purge oscillations of the Laurentide Ice Sheet , 1994 .

[23]  A. Mcintyre,et al.  The North Atlantic Ocean during the last deglaciation , 1981 .

[24]  W. Broecker,et al.  Origin of the northern Atlantic's Heinrich events , 1992 .

[25]  E. Boyle,et al.  On the Structure and Origin of Major Glaciation Cycles 1. Linear Responses to Milankovitch Forcing , 1992 .

[26]  C. Vergnaud-Grazzini,et al.  Dissolution and carbonate fluctuations in Pleistocene deep-sea cores: A review , 1980 .

[27]  P. deMenocal,et al.  Evidence for a change in the periodicity of tropical climate cycles at 2.4 Myr from whole-core magnetic susceptibility measurements , 1989, Nature.

[28]  C. Radhakrishnamurty,et al.  Susceptibility stratigraphy and paleomagnetism of some deep Pacific Ocean cores , 1972 .

[29]  W. O'reilly.  Rock and Mineral Magnetism , 1984 .

[30]  R. Boyce,et al.  Carbon and Carbonate Analyses, Leg 9 , 1972 .

[31]  N. Shackleton,et al.  Oxygen and Carbon Isotope Stratigraphy of Deep Sea Drilling Project Hole 552A: Plio-Pleistocene Glacial History , 1984 .

[32]  S. Hall,et al.  Magnetic Properties of Black Mud Turbidites from ODP Leg 116, Distal Bengal Fan, Indian Ocean , 1990 .

[33]  T. Walsh,et al.  Magnetic susceptibility stratigraphy of Pacific Pleistocene sediments , 1975, Nature.

[34]  D. Kent.  Apparent correlation of palaeomagnetic intensity and climatic records in deep-sea sediments , 1982, Nature.

[35]  D. Martinson,et al.  Graphic correlation of oxygen isotope stratigraphy application to the Late Quaternary , 1986 .

[36]  W. Broecker,et al.  Evidence for massive discharges of icebergs into the North Atlantic ocean during the last glacial period , 1992, Nature.

[37]  M. German,et al.  The Karbonat-Bombe, a simple device for the determination of the carbonate content in sediments, soils, and other materials , 1971 .

[38]  J. Bloemendal.  Paleoenvironmental Implications of the Magnetic Characteristics of Sediments from Deep Sea Drilling Project Site 514, Southeast Argentine Basin , 1983 .

[39]  E. Cortijo,et al.  Patterns of Ice-Rafted Detritus in the Glacial North Atlantic (40–55°N) , 1993 .

[40]  J. LaBrecque,et al.  Oligocene paleoceanography of the South Atlantic: paleoclimatic implications of sediment accumulation rates and magnetic susceptibility measurements , 1986 .

[41]  Nilva G. Kipp,et al.  New Transfer Function for Estimating Past Sea-Surface Conditions from Sea-Bed Distribution of Planktonic Foraminiferal Assemblages in the North Atlantic , 1976 .

[42]  L. W. Chambers,et al.  A 420,000-Year Record of Cyclicity in Oceanic and Atmospheric Processes from the Eastern Equatorial Pacific , 1986 .

[43]  J. Morley,et al.  The effect of accumulation rate on the spectrum of geologic time series : evidence from two south atlantic sediment cores , 1984 .

[44]  J. King,et al.  A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: Some results from lake sediments , 1982 .

[45]  D. Dunlop.  The rock magnetism of fine particles , 1981 .

[46]  B. Molnia.  Distal Glacial-Marine Sedimentation: Abundance, Composition, and Distribution of North Atlantic Ocean Pleistocene Ice-Rafted Sediment , 1983 .

[47]  J. Bloemendal,et al.  Paleoenvironmental implications of rock‐magnetic properties of Late Quaternary sediment cores from the eastern equatorial Atlantic , 1988 .

[48]  J. King,et al.  44. THE RELATIONSHIP BETWEEN VARIATIONS IN ROCK-MAGNETIC PROPERTIES AND GRAIN SIZE OF SEDIMENTS FROM ODP HOLE 645C 1 , 1989 .

[49]  W. Dean,et al.  Milankovitch cycles in Neocene deep‐sea sediment , 1986 .

[50]  J. Bloemendal,et al.  Rock magnetism of Late Neogene and Pleistocene deep‐sea sediments: Relationship to sediment source, diagenetic processes, and sediment lithology , 1992 .

[51]  C. Jacobs,et al.  King's Trough Flank: geological and geophysical investigations of its suitability for high-level radioactive waste disposal , 1983 .

[52]  H. Heinrich,et al.  Origin and Consequences of Cyclic Ice Rafting in the Northeast Atlantic Ocean During the Past 130,000 Years , 1988, Quaternary Research.

[53]  M. Ewing,et al.  Pleistocene Glacial-Marine Zones in North Atlantic Deep-Sea Sediments , 1965, Nature.

[54]  Andrew McIntyre,et al.  Northeast Atlantic Paleoclimatic Changes over the Past 600,000 Years , 1976 .

[55]  W. Ruddiman,et al.  Ice-rafted evidence of long-term North Atlantic circulation , 1985 .

[56]  B. Maher.  Magnetic properties of some synthetic sub-micron magnetites , 1988 .

[57]  W. Prell,et al.  Climatic change and CaCO3 preservation: An 800,000 year bathymetric Reconstruction from the central equatorial Pacific Ocean , 1989 .

[58]  S. Robinson.  The late Pleistocene palaeoclimatic record of North Atlantic deep-sea sediments revealed by mineral-magnetic measurements , 1986 .

[59]  W. Ruddiman,et al.  Vertical Mixing of Ice-Rafted Volcanic Ash in North Atlantic Sediments , 1972 .

[60]  D. Macayeal.  Binge/purge oscillations of the Laurentide Ice Sheet as a cause of the North Atlantic's Heinrich events , 1993 .

[61]  W. Ruddiman.  North Atlantic Ice-Rafting: A Major Change at 75,000 Years Before the Present , 1977, Science.

[62]  D. Canfield,et al.  Dissolution and pyritization of magnetite in anoxie marine sediments , 1987 .

[63]  C. Radhakrishnamurty,et al.  Magnetic susceptibility stratigraphy in ocean sediment cores , 1968 .

[64]  S. Robinson.  Applications for whole-core magnetic susceptibility measurements of deep-sea sediments: ODP Leg 115 results , 1990 .

[65]  I. N. McCave,et al.  Orbital forcing of bottom-current enhanced sedimentation on Feni Drift, NE Atlantic, during the mid-Pleistocene , 1994 .

[66]  P. Weaver,et al.  Detection of Repenetration and Sediment Disturbance in Open-Barrel Gravity Cores: RESEARCH-METHOD PAPER , 1983 .

[67]  S. Robinson.  Lithostratigraphic applications for magnetic susceptibility logging of deep-sea sediment cores: examples from ODP Leg 115 , 1993, Geological Society, London, Special Publications.

[68]  J. Imbrie,et al.  Oceanic Response to Orbital Forcing in the Late Quaternary: Observational and Experimental Strategies , 1989 .

[69]  D. G. Watts,et al.  Spectral analysis and its applications , 1968 .

[70]  A. Aksu,et al.  Middle to Late Quaternary Sediment Fluxes in the Labrador Sea, ODP Leg 105, Site 646: a Synthesis of Rock-Magnetic, Oxygen-Isotopic, Carbonate, and Planktonic Foraminiferal Data , 1989 .