(Table 1) Calcium carbonate abundance in ODP Leg 164 sites@en

Diffuse reflectance spectra measured during shipboard core description with a hand-held Minolta spectrophotometer are reliable data for interpreting sediment composition. Factor analysis of these spectra indicates that only Glad Cling WrapTM, a polyethylene food wrap, should be used to cover wet cores during measurement because it introduces substantially less noise into the spectra than other brands of plastic food wrap. This validates our previous recommendation that only Glad Cling WrapTM should be used to cover wet core surfaces before spectral analysis on board ship. Factor analysis also indicates that the red end of the spectrum was a little noisy; however, it is unclear if this noise was produced by the Glad Cling WrapTM, by the Minolta instrument, or by the sediment being analyzed when wet (water tends to affect the red end of the spectrum more than the violet). Comparison of spectra taken directly from wet cores on board ship with the Minolta CM-2002 to those taken from dried, prepared samples with our shore-based Perkin-Elmer Lambda 6 spectrophotometer indicates that water mutes the spectral signal. Although factor analysis of the Perkin-Elmer data produced five factors, four of those factors are the same as the factors extracted from the wet core data with the Minolta. This suggests that the water content in the wet cores was not high enough to seriously hinder interpretation of sediment composition. These four common factors are interpreted as carbonate, chlorite or glauconite, organic matter, and iron oxides (probably a mixture of hematite and goethite). The presence of hematite can be attributed to hematite-rich sediment derived from the Canadian Maritime provinces, which has been transported southward by the Western Boundary Undercurrent (WBUC) along North American continental margin. Based on the distribution of hematite down the Leg 164 holes, the WBUC apparently has washed over the Leg 164 sites on the crest of the Blake Ridge only during the Holocene and very latest Pleistocene.借助手持Minolta分光光度计在船载岩芯描述过程中获取的漫反射光谱，是解读沉积物组成的可靠数据。 对这些光谱开展因子分析后表明，测量期间仅可使用Glad Cling WrapTM保鲜膜（一种聚乙烯食品保鲜膜）覆盖湿态岩芯，因其相较于其他品牌的塑料食品保鲜膜，引入的光谱噪声显著更低。这一结果验证了我们此前的建议：在船载光谱分析前，仅可使用Glad Cling WrapTM保鲜膜覆盖湿岩芯表面。 因子分析同时显示，光谱的红端存在轻微噪声，但目前尚无法确定该噪声源自Glad Cling WrapTM保鲜膜、Minolta仪器，还是湿态待测沉积物——相较于紫光波段，水对红光波段光谱的影响通常更强。将船载环境下直接使用Minolta CM-2002分光光度计对湿岩芯测得的光谱，与岸基环境下使用珀金埃尔默（Perkin-Elmer）Lambda 6分光光度计对干燥预处理样品测得的光谱进行对比后发现，水会抑制光谱信号。 尽管对珀金埃尔默仪器获取的数据进行因子分析得到了5个因子，但其中4个因子与使用Minolta仪器从湿岩芯数据中提取的因子完全一致。这表明湿岩芯的含水量并未高到会严重阻碍沉积物组成解读的程度。我们将这4个共有因子解读为碳酸盐、绿泥石或海绿石、有机质以及氧化铁（大概率为赤铁矿与针铁矿的混合物）。 赤铁矿的存在可归因于源自加拿大滨海省的富赤铁矿沉积物，该类沉积物沿北美大陆边缘被西部边界底流（Western Boundary Undercurrent, WBUC）向南搬运。根据Leg 164钻孔中赤铁矿的分布特征可知，WBUC仅在全新世及更新世末期才会流经布雷克脊峰顶的Leg 164站位。