An in‐depth Sr‐Nd‐Pb‐He‐Os isotope and trace element study of the EMII‐defining Samoan hot spot lavas leads to a new working hypothesis for the origin of this high 87Sr/86Sr mantle end‐member. Systematics of the Samoan fingerprint include (1) increasing 206Pb/204Pb with time ‐ from 18.6 at the older, western volcanoes to 19.4 at the present‐day hot spot center, Vailulu'u Seamount, (2) en‐echelon arrays in 206Pb/204Pb – 208Pb/204Pb space which correspond to the two topographic lineaments of the 375 km long volcanic chain – this is much like the Kea and Loa Trends in Hawai'i, (3) the highest 87Sr/86Sr (0.7089) of all oceanic basalts, (4) an asymptotic decrease in 3He/4He from 24 RA [Farley et al., 1992] to the MORB value of 8 RA with increasing 87Sr/86Sr, and (5) mixing among four components which are best described as the “enriched mantle”, the depleted FOZO mantle, the (even more depleted) MORB Mantle, and a mild HIMU (high 238U/204Pb) mantle component. A theoretical, “pure” EMII lava composition has been calculated and indicates an extremely smooth trace element pattern of this end‐member mantle reservoir. The standard recycling model (of ocean crust/sediment) fails as an explanation for producing Samoan EM2, due to these smooth spidergrams for EM2 lavas, low 187Os/188Os ratios and high 3He/4He (>8 RA). Instead, the origin of EM2 has been modeled with the ancient formation of metasomatised oceanic lithosphere, followed by storage in the deep mantle and return to the surface in the Samoan plume.

, most models for the creation of the EM1 and EM2 mantle reservoirs invoke a small portion of lithologically distinct sediments that have been recycled into the mantle 9,13 .

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New tungsten isotope data for modern ocean island basalts (OIB) from Hawaii, Samoa, and Iceland reveal variable W/W, ranging from that of the ambient upper mantle to ratios as much as 18 parts per million lower. The tungsten isotopic data negatively correlate with He/He. These data indicate that each OIB system accesses domains within Earth that formed within the first 60 million years of solar system history. Combined isotopic and chemical characteristics projected for these ancient domains indicate that they contain metal and are repositories of noble gases. We suggest that the most likely source candidates are mega-ultralow-velocity zones, which lie beneath Hawaii, Samoa, and Iceland but not beneath hot spots whose OIB yield normal W and homogeneously lowHe/He.

The terrestrial glacial record reflects past snowline variability and atmospheric temperature changes. When combined with secure chronologies, these data can be used to test models of ice-age climate. We present new in situ cosmogenic 10 Be, 26 Al, and 3 He exposure ages, supported by limiting 40 Ar/ 39 Ar and 14 C ages, for seven of the youngest moraines east of Lago Buenos Aires, Argentina, 46.5؇S, that were deposited by a large outlet glacier of the Patagonian Ice Cap. Following a major glaciation that deposited extensive moraines prior to 109 ka, paired 10 Be-26 Al ages indicate that the next youngest complex of moraines was deposited from 23.0 ؎ 1.2 to 15.6 ؎ 1.1 ka (1). During the last glaciation, ice was at its maximum extent prior to 22 ka and at least five moraines were deposited in less than 10 k.y. These data are in good agreement with three 14 C ages of ca. 16 ka from varved sediment banked on top of the youngest of these five moraines and limiting 3 He ages, which range from ca. 33 to 19 ka. The most extensive ice marginal deposits preserved within the last 109 k.y. were formed during marine oxygen isotope stage

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