(Table 1) Occurrences of Epimeria georgiana species complex (Amphipoda) in the Weddel and Scotia Sea

DNA barcoding revealed four well-supported clades among amphipod specimens that keyed out to Epimeria georgiana Schellenberg, 1931, three clades with specimens from the southern Scotia Arc and one clade with specimens from the Weddell Sea. Detailed morphological investigations of sequenced specimens were conducted, through light and scanning electron microscopy. High magnification (500-2,000 fold) revealed features such as comb-scales on the first antenna and trich bearing pits on the fourth coxal plate to be similar for all specimens in the four clades. Consistent microstructure character differences in the Weddell Sea specimens combined with high genetic distances (COI divergence>20%) allowed the description of Epimeria angelikae, a species new to science. Specimens of E. georgiana in the other three COI clades from the Scotia Arc were morphologically indistinguishable. Representative specimens of clade A are also illustrated in detail. Our results on the high genetic divergences in epimeriid amphipods support the theory of the southern Scotia Arc being a centre of Antarctic diversification.

Geochemistry of lower sheeted dike complex samples of ODP Holes 137-504B and 140-504B

Rocks of the lower sheeted dike complex of Hole 504B sampled during Leg 140 were analyzed for major and trace element compositions to investigate the effects of igneous processes and hydrothermal alteration on the compositions of the rocks. The rocks are relatively uniform in composition and similar to the shallower dikes. They are moderately evolved mid-ocean-ridge basalts (MORB) with relatively high MgO (7.9-10 wt%) and Mg# (0.60-0.70), and have unusually low incompatible element contents (TiO2 = 0.42-1.1 wt%, Zr = 23-62 ppm). Discrete compositional intervals in the hole reflect varying degrees of differentiation, and olivine and plagioclase accumulation in the rocks, and may be related to injection of packets of dikes having similar compositions. Systematic depletions of total REE, Zr, Y, TiO2, and P2O5 in centimeter-size patches are most likely attributed to exclusion of highly differentiated, late-stage interstitial liquids from small portions of the rocks. The rocks exhibit increased H2O+ reflecting hydrothermal alteration. Replacement of primary plagioclase by albite and oligoclase led to local gains of Na2O, losses of CaO, and slightly positive Eu anomalies. Some mobility of P2O5 led to minor increases and decreases in P2O5 contents, and some local mobility of Ti may have occurred during alteration of titanomagnetite to titanite. Higher temperatures of alteration in the lower sheeted dikes led to breakdown of pyroxene and sulfide minerals and losses of Zn, Cu, and S to hydrothermal fluids. Later addition of anhydrite to the rocks in microfractures and replacing plagioclase caused local increases in sulfur contents. The lower sheeted dikes are a major source of metals to hydrothermal fluids for the formation of metal sulfide deposits on and within the seafloor.