(Supplement T1) Clay mineral compositions at the Aleutian Basin of the Bering Sea from IODP sites 323-U1343

The clay mineral composition at IODP Exp. 323 Site U1343 in the Bering Sea was analyzed so as to unravel their provenance over glacial-interglacial cycles for the last 2.4 Ma. Smectite was negatively correlated with the sum of illite and chlorite; therefore, their ratio [S/(I + C)] was used as an indicator of clay mineral composition changes. In general, the S/(I + C) ratio was rather similar for glacial and interglacial periods during most of the last 2.4 Ma. In addition, these results overlap with those of surface sediments in the modern East Aleutian Basin, which suggests that smectite-rich clay particles are delivered from the Aleutians by the northward Bering Slope Current (BSC) rather than from rivers in western Alaska. However, some clay mineral compositions of the glacial periods after the Mid-Pleistocene Transition (MPT: 1.25-0.7 Ma) were characterized by low illite and relatively high smectite. During this period, extensive ice-rafting might have transported the smectite-rich clay particles to Site U1343 from the glacial shelf off Alaska and/or from glacial rivers from that area.

Chemical composition of clay minerals from ODP Leg 168 sites

The exchangeable cation compositions of organic-poor terrigenous sediments containing smectite as primary ion exchanger from a series of holes along ODP Leg 168 transect on the eastern flank of the Juan de Fuca Ridge have been examined as a function of distance from the ridge axis and burial depth. The total cation exchange capacity (CEC) values of the sediments ranged from 2 to 59 meq/100 g, increasing with increases in the wt.% smectite. At the seafloor, the exchangeable cation compositions involving Na, K, Mg, and Ca, expressed in terms of equivalent fraction, are nearly constant regardless of the different transect sites: XNa = 0.21 ± 0.04, XK = 0.08 ± 0.01, XMg = 0.33 ± 0.09, and XCa = 0.38 ± 0.09. The calculated selectivity coefficients of the corresponding quaternary exchange reactions, calculated using porewater data, are in log units -5.45 ± 0.39 for Na, 1.97 ± 0.49 for K, 0.42 ± 0.41 for Mg, and 3.06 ± 0.69 for Ca. The exchangeable cation compositions below the seafloor change systematically with distance from the ridge crest and burial depth, conforming to the trends of the same cations in the porewaters. The selectivities for Na and Mg are roughly constant at temperatures from 2 to 66°C, indicating that the equivalent fractions of these two cations are independent of sediment alteration taking place on the ridge flank. Unlike Na and Mg, the temperature influence is significant for K and Ca, with Ca-selectivity decreases being coupled with increases in K-selectivity. Although potentially related to diagenetic and/or hydrothermal mineral precipitation or recrystallization, no evidence of such alteration was detected by XRD and TEM. In sites where upwelling of hydrothermal fluids from basement is occurring, the K-selectivity of the sediment is appreciably higher than at the other sites and corresponds to the formation of (Fe, Mg) rich smectite and zeolites. Our study indicates that local increases in K-selectivity at hydrothermal sites are caused by the formation of these authigenic minerals.

Clay mineraology and grain size composition of surface sediments from South Pacific Ocean

The reconstruction of low-latitude ocean-atmosphere interactions is one of the major issues of (paleo-)environmental studies. The trade winds, extending over 20° to 30° of latitude in both hemispheres, between the subtropical highs and the intertropical convergence zone, are major components of the atmospheric circulation and little is known about their long-term variability on geological time-scales, in particular in the Pacific sector. We present the modern spatial pattern of eolian-derived marine sediments in the eastern equatorial and subtropical Pacific (10°N to 25°S) as a reference data set for the interpretation of SE Pacific paleo-dust records. The terrigenous silt and clay fractions of 75 surface sediment samples have been investigated for their grain-size distribution and clay-mineral compositions, respectively, to identify their provenances and transport agents. Dust delivered to the southeast Pacific from the semi- to hyper-arid areas of Peru and Chile is rather fine-grained (4-8 µm) due to low-level transport within the southeast trade winds. Nevertheless, wind is the dominant transport agent and eolian material is the dominant terrigenous component west of the Peru-Chile Trench south of ~ 5°S. Grain-size distributions alone are insufficient to identify the eolian signal in marine sediments due to authigenic particle formation on the sub-oceanic ridges and abundant volcanic glass around the Galapagos Islands. Together with the clay-mineral compositions of the clay fraction, we have identified the dust lobe extending from the coasts of Peru and Chile onto Galapagos Rise as well as across the equator into the doldrums. Illite is a very useful parameter to identify source areas of dust in this smectite-dominated study area.

Nd and Pb isotope signatures of the clay-size fraction of sediment core MD99-2227

Nd and Pb isotopes were measured on the fine fraction of one sediment core drilled off southern Greenland. This work aims to reconstruct the evolution of deep circulation patterns in the North Atlantic during the Holocene on the basis of sediment supply variations. For the last 12 kyr, three sources have contributed to the sediment mixture: the North American Shield, the Pan-African and Variscan crusts, and the Mid-Atlantic Ridge. Clay isotope signatures indicate two mixtures of sediment sources. The first mixture (12.2-6.5 ka) is composed of material derived from the North American shield and from a "young" crustal source. From 6.5 ka onward the mixture is characterized by a young crustal component and by a volcanic component characteristic of the Mid-Atlantic Ridge. Since the significant decrease in proximal deglacial supplies, the evolution of the relative contributions of the sediment sources suggests major changes in the relative contributions of the deep water masses carried by the Western Boundary Undercurrent over the past 8.4 kyr. The progressive intensification of the Western Boundary Undercurrent was initially associated mainly with the transport of the Northeast Atlantic Deep Water mass until 6.5 ka and with the Denmark Strait Overflow Water thereafter. The establishment of the modern circulation at 3 ka suggests a reduced influence of the Denmark Strait Overflow Water, synchronous with the full appearance of the Labrador Seawater mass. Our isotopic data set emphasizes several changes in the relative contribution of the two major components of North Atlantic Deep Water throughout the Holocene.

Mineralogy of the clay fraction from Cenozoic Strata at DSDP Leg 94

Leg 94 Sites are located in a large geographic area of the northeastern Atlantic. Clay mineral analyses of the sediments recovered on Leg 94 (Eocene to the present), together with results obtained from previous DSDP legs (47B, 48, 80, 81, 82), provide greater insight into the paleoenvironmental evolution of the northeastern Atlantic. The characteristics of Eocene clay sediments are regional, reflecting, in the absence of strong bottom currents, the influence of neighboring petrographic environments: basic volcanic rocks (Sites 403-406, 552, and 608) and acid volcanic rocks (Sites 508 to 510). During the Oligocene, atmospheric circulation patterns left their mineralogical signatures in the southern part of the area investigated (Sites 558 and 608), whereas during the Miocene the intrusion of northern water masses led to the gradual homogenization of the clay sedimentation throughout the North Atlantic. In the late Pliocene, input from glacial sources became widespread.