Reykjanes Ridge Sub-decadal Mean Grain Size Data ----------------------------------------------------------------------- World Data Center for Paleoclimatology, Boulder and NOAA Paleoclimatology Program ----------------------------------------------------------------------- NOTE: PLEASE CITE CONTRIBUTORS WHEN USING THIS DATA!!!!! NAME OF DATA SET: Reykjanes Ridge Sub-decadal Mean Grain Size Data LAST UPDATE: 10/2007 (Original receipt by WDC Paleo) CONTRIBUTOR: Ian R. Hall, Cardiff University IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2007-095 SUGGESTED DATA CITATION: Boessenkool, K.P., et al. 2007. Reykjanes Ridge Sub-decadal Mean Grain Size Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2007-095. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Boessenkool, K.P., I.R. Hall, H. Elderfield, and I. Yashayaev. 2007. North Atlantic climate and deep-ocean flow speed changes during the last 230 years. Geophys. Res. Lett., 34, L13614, doi:10.1029/2007GL030285. ABSTRACT: Variations in the near-bottom flow speed of Iceland-Scotland Overflow Water (ISOW) are documented in a 230-year-long deep-sea sediment record from the eastern flank of Reykjanes Ridge in the subpolar North Atlantic at (sub)decadal time scales. For recent decades, the ISOW palaeocurrent reconstructions show similarities with observational hydrographic data. Furthermore, recent ISOW flow changes fall mostly within the range of its variability of the past 230 years. The record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar North Atlantic with the North Atlantic Oscillation (NAO) index, with more (less) vigorous ISOW flow during negative (positive) phases of the NAO. Our results suggest that the changes in ISOW vigor are largely controlled by the transport and characteristics of Labrador Sea Water rather than variations in the overflow itself, with implications for the meridional overturning of the Atlantic Ocean and climate. ADDITIONAL REFERENCES: Bianchi, G.G., I.R. Hall, I.N. McCave, and L. Joseph. 1999. Measurement of the sortable silt current speed proxy using the Sedigraph 5100 and Coulter Multisizer IIe: Precision and accuracy. Sedimentology, 46, 1001–1014. Cundy, A.B. and I. W. Croudace. 1996. Sediment accretion and recent sea- level rise in the Solent, Southern England: inferences from radiometric and geochemical studies. Estuar. Coast. Shelf S., 43, 449-467. McCave, I.N., B. Manighetti, and S.G. Robinson. 1995. Sortable silt and fine sediment size composition slicing: Parameters for palaeocurrent speed and palaeoceanography. Paleoceanography, 10(3), 593– 610. Robbins, J.A. 1978. in The Biogeochemistry of Lead in the Environment Part A edited by J. O. Nriagu, pp. 285-293, Elsevier/North Holland Biomedical Press, Amsterdam. GEOGRAPHIC REGION: Reykjanes Ridge, subpolar North Atlantic PERIOD OF RECORD: 230 yrbp - present FUNDING SOURCE: U.K. Natural Environment Research Council Rapid Climate Change Programme. DESCRIPTION: Data are measurements of the palaeocurrent proxy 'sortable' silt mean grain size, which is the mean grain size of the 10–63-um terrigenous silt fraction [McCave et al., 1995]. They were measured on a Coulter Multisizer III [see Bianchi et al., 1999]. Decadal-scale changes in sortable silt mean grain size are interpreted to reflect changes in the near-bottom flow speed of Iceland-Scotland Overflow Water at it passes over the eastern flank of Reykjanes Ridge in the subpolar North Atlantic. Box Core RAPID-21-12B (57º27.09'N, 27º54.53'W, 2630m. depth, core length 54.3 cm.) was collected on 12 July 2004 during cruise 159 of RRS Charles Darwin. Pb analyses of sediment box core RAPID-21-12B: 210Pb dating of sediment core RAPID-21-12B was carried out at Sussex University, Brighton, U.K. Twelve 1-cm thick sub-samples from the working half were dried, weighed and lightly ground before being counted on a Canberra well-type ultra-low background Hyper-Pure Germanium gamma ray spectrometer to determine the activities of 210Pb and other gamma emitters. Spectra were analysed using the Genie 2000 system, and accumulated using a 16K channel integrated multichannel analyzer. Energy and efficiency calibrations were carried out using bentonite clay spiked with a mixed gamma-emitting radionuclide standard, QCYK8163, and checked against an IAEA marine sediment certified reference material (IAEA 135). Detection limits depend on radionuclide gamma energy, count time and sample mass, but were typically ca. 10 Bq/kg for 210Pb, and 3 Bq/kg for 137Cs, for a 150,000 second count time. 210Pb shows a maximum activity of 330 Bq/kg in the uppermost sample (0-1cm depth) of core RAPID-21-12B, followed by an approximately exponential decline in activity with depth (see auxiliary material of Boessenkool et al., 2007) down to near-constant 210Pb activities of 35 - 45 Bq/kg (average 39 Bq/kg) below 30 cm core depth, which are likely to approximate to the supported 210Pb activity [Cundy and Croudace, 1996]. The 210Pb-excess activity was estimated by subtraction of this supported 210Pb activity. These estimated supported activities are similar to activities measured for the 226Ra daughter product 214Pb (see auxiliary material of Boessenkool et al., 2007) - as samples were not counted in air-tight vials it is unlikely that all 226Ra daughter products will be in radioactive equilibrium, however the measured 214Pb activities do provide an additional estimate of the supported 210Pb activity. Sediment accumulation rates were determined using the simple model of 210Pb dating [Robbins, 1978], where the sedimentation rate is given by the slope of the least squares fit for the natural log of the 210Pbexcess activity versus depth. For core RAPID-21-12B the thus obtained sediment accumulation rate is 2.3 mm/yr (2-sigma range = 2.0-2.8 mm/yr). The equivalent dry bulk mass accumulation rate is 0.07 g (cm exp-2)/yr (2-sigma range = 0.05-0.09 g(cm exp-2)/yr. Both rates should be considered maximum values however due to the possible effects of bioturbation on the 210Pb profile. In addition, six samples from the upper 11 cm of the core were analyzed for 137Cs and 241Am: only 137Cs was detected, and only in sample 0-1 cm. For the age-depth model (see auxiliary material of Boessenkool et al., 2007) the undisturbed top of the sequence was taken as the year 2004. See also auxiliary information connected to cited reference on ftp://ftp.agu.org/apend/gl/2007gl030285/ DATA: 1. Pb analyses of sediment box core RAPID-21-12B. Column 1: Depth, cm, depth range beneath top of sediment core. Column 2: 210Pb, Bq/kg, activity of 210Pb. Column 3: Err_210, Bq/kg, counting error of 210Pb. Column 4: 214Pb, Bq/kg, activity of 214Pb. Column 5: Err_214, Bq/kg, counting error of 214Pb. Column 6: Time, s, Counting time. Depth 210Pb Err_210 214Pb Err_214 Time 0-1 330 26 37 2 24000 2-3 194 20 58 3 24000 4-5 204 19 34 2 23000 6-7 148 18 46 3 20000 8-9 129 14 33 2 26000 10-11 94 11 37 2 36000 2. Sortable silt mean grain size (mean grain size of the 10-63 micrometer fraction) of core RAPID-21-12B Column 1: Depth (cm) Column 2: Top (cm) Column 3: Bottom (cm) Column 4: Age Column 5: Sortable silt mean grain size (micrometer) Depth Top Bottom Age Sortable silt mean grain size 0.25 0 0.5 2004 15.69 0.75 0.5 1 2001.83 15.58 1.25 1 1.5 1999.65 15.38 1.75 1.5 2 1997.48 15.6 2.25 2 2.5 1995.3 15.53 2.75 2.5 3 1993.13 15.69 3.25 3 3.5 1990.96 15.71 3.75 3.5 4 1988.78 15.65 4.25 4 4.5 1986.61 15.71 4.75 4.5 5 1984.43 15.88 5.25 5 5.5 1982.26 15.97 5.75 5.5 6 1980.09 15.83 6.25 6 6.5 1977.91 15.91 6.75 6.5 7 1975.74 15.79 7.25 7 7.5 1973.57 15.76 7.75 7.5 8 1971.39 15.95 8.25 8 8.5 1969.22 15.98 8.75 8.5 9 1967.04 15.9 9.25 9 9.5 1964.87 16.02 9.75 9.5 10 1962.7 15.87 10.25 10 10.5 1960.52 16.2 10.75 10.5 11 1958.35 15.73 11.25 11 11.5 1956.17 15.53 11.75 11.5 12 1954 15.59 12.25 12 12.5 1951.83 15.82 12.75 12.5 13 1949.65 15.83 13.25 13 13.5 1947.48 15.56 13.75 13.5 14 1945.3 15.46 14.25 14 14.5 1943.13 15.62 14.75 14.5 15 1940.96 15.9 15.25 15 15.5 1938.78 15.69 15.75 15.5 16 1936.61 15.51 16.25 16 16.5 1934.43 15.75 16.75 16.5 17 1932.26 15.95 17.25 17 17.5 1930.09 15.84 17.75 17.5 18 1927.91 15.59 18.25 18 18.5 1925.74 15.55 18.75 18.5 19 1923.57 15.66 19.25 19 19.5 1921.39 15.67 19.75 19.5 20 1919.22 15.58 20.25 20 20.5 1917.04 15.82 20.75 20.5 21 1914.87 15.68 21.25 21 21.5 1912.7 15.52 21.75 21.5 22 1910.52 15.81 22.25 22 22.5 1908.35 15.77 22.75 22.5 23 1906.17 15.67 23.25 23 23.5 1904 15.63 23.75 23.5 24 1901.83 15.66 24.25 24 24.5 1899.65 15.63 24.75 24.5 25 1897.48 15.59 25.25 25 25.5 1895.3 15.8 25.75 25.5 26 1893.13 15.79 26.25 26 26.5 1890.96 15.91 26.75 26.5 27 1888.78 15.81 27.25 27 27.5 1886.61 15.84 27.75 27.5 28 1884.43 16.02 28.25 28 28.5 1882.26 15.73 28.75 28.5 29 1880.09 16.25 29.25 29 29.5 1877.91 16.19 29.75 29.5 30 1875.74 15.72 30.25 30 30.5 1873.57 15.96 30.75 30.5 31 1871.39 15.76 31.25 31 31.5 1869.22 15.96 31.75 31.5 32 1867.04 15.86 32.25 32 32.5 1864.87 15.64 32.75 32.5 33 1862.7 16.04 33.75 33.5 34 1858.35 15.99 34.25 34 34.5 1856.17 15.86 34.75 34.5 35 1854 16.02 35.25 35 35.5 1851.83 15.81 35.75 35.5 36 1849.65 16.01 36.25 36 36.5 1847.48 15.78 36.75 36.5 37 1845.3 15.71 37.25 37 37.5 1843.13 15.74 37.75 37.5 38 1840.96 15.75 38.25 38 38.5 1838.78 15.76 38.75 38.5 39 1836.61 15.8 39.25 39 39.5 1834.43 15.49 39.75 39.5 40 1832.26 15.8 40.25 40 40.5 1830.09 15.68 40.75 40.5 41 1827.91 15.55 41.25 41 41.5 1825.74 15.9 41.75 41.5 42 1823.57 15.96 42.25 42 42.5 1821.39 15.93 42.75 42.5 43 1819.22 16.04 43.25 43 43.5 1817.04 15.73 43.75 43.5 44 1814.87 15.88 44.25 44 44.5 1812.7 15.7 44.75 44.5 45 1810.52 15.93 45.25 45 45.5 1808.35 15.81 45.75 45.5 46 1806.17 15.87 46.25 46 46.5 1804 15.88 46.75 46.5 47 1801.83 15.77 47.25 47 47.5 1799.65 15.79 47.75 47.5 48 1797.48 15.97 48.25 48 48.5 1795.3 15.89 48.75 48.5 49 1793.13 15.89 49.25 49 49.5 1790.96 15.89 49.75 49.5 50 1788.78 15.93 50.25 50 50.5 1786.61 15.91 50.75 50.5 51 1784.43 15.69 51.25 51 51.5 1782.26 15.69 51.75 51.5 52 1780.09 15.83 52.25 52 52.5 1777.91 15.85 52.75 52.5 53 1775.74 15.9 53.25 53 53.5 1773.57 15.9 53.75 53.5 54 1771.39 15.73 54.15 53.9 54.4 1769.65 15.67