Anomalous boundary scavenging in the Middle Atlantic Bight: evidence from 230Th, 231Pa, 10Be and 210Pb

231Pa/230Th evidence for a weakened but persistent Atlantic meridional overturning circulation during Heinrich Stadial 1

“…The average ratio for HS1 (0.074 ± 0.009; n ¼ 26) is somewhat greater than the LGM value, but not significantly different at the 95% confidence level; this study 15,16,21,22,25,27,30,39,40,54 . The average 231 Pa/ 230 Th ratio in Holocene sediment north of 50°S (0.070 ± 0.004; n ¼ 165) is greater than Yu et al, a result that is significant at the 95% confidence level (Yu et al Holocene 231 Pa/ 230 Th: 0.060 ± 0.004; n ¼ 68); this study 1,15,16,[20][21][22]25,27,28,30,39,40,[54][55][56][57][58][59][60][61][62][63][64][65][66] . Because many of the older data were generated using alpha counting, the relative errors are somewhat larger.…”

Variations in the particulate flux of Th-230 and Pa-231 and paleoceanograhpic applications of the Pa-231/Th-231 ratio

“…I conclude, therefore, that the large variations of F /P of 230Th reported from sediments from one up to as much as ten in those margin sediments (Mangini and Diester-Haass, 1983), in SEEP-I &II (Anderson et al, 1991), and the western and the eastern equatorial Atlantic sediments (Francois, et al, 1991) must be due to sediment redistribution. The V /P values show a strong tendency for significant horizontal transport of 231pa from the open ocean to regions of higher particle flux (Table 3. This shows that the extent of horizontal transport for 231pa is much greater than it is for 230Th.…”

“…Many 74 observations of water columns, sediment traps, and sediments from previous works have shown that fractionation between 230Th and 231pa occurs everywhere within an ocean basin (DeMaster, 1981;Anderson et al, 1983 a&b;Bacon et al, 1985;Yang et al, 1986;Taguchi et al, 1989;Francois et. al., 1990;Francois and Bacon, 1991;Anderson et al, 1991;Lao, 1991;Rutgers VanDer Loeff and Berger, 1993).…”

“…A particle reactive chemical substance is introduced into the ocean in dissolved form, and it is partitioned by particle dynamic processes that include adsorption, complexation and biological uptake (Anderson et al, 1991) during the chemical substance's scavenging pathway through the water column. While the flux of particulate matter through the water column seems to be the principle factor regulating the overall intensity of scavenging, it may not be the unique process responsible for the phenomenon of fractionation between 230Th and 231 Pa.…”

Thorium speciation in seawater

“…These Th isotopes are primarily produced by natural uranium isotopes ( 238 U, 235 U and 234 U) that are soluble in seawater. In marine systems, Th has proven to be a very useful tracer of a wide range of oceanographic processes ranging from particle cycling (Bacon and Rutgers van der Loeff, 1989;Whitfield, 1990, 1991;Dunne et al, 1997) and carbon export flux (e.g., Murray et al, 1989;Buesseler, 1998, and references therein; Benitez-Nelson et al, 2001) to boundary scavenging (Moore, 1981;Anderson et al, 1994;Santschi et al, 1999, Smoak et al, 2000 and paleocirculation (Yu et al, 1996;Marchal et al, 2000;Moran et al, 2002). This is because Th's chemical properties are relatively simple: Th has only one stable oxidation state, IV, under all redox conditions in natural waters, and Th (IV) ions are extremely particle reactive.…”