(Table 1) B content, d11B, d18O, degree of alteration, and lithology of basalts from ODP Hole 504B

Boron contents and boron isotopic compositions were determined for the uppermost 1.3 km section of typical 6.2 Ma oceanic crust from DSDP/ODP Hole 504B, Costa Rica Rift, Galapagos Spreading Center. Both the boron content and the d11B value in the oceanic crust are controlled by two types of alteration: 1. (1) low-temperature alteration (0 to 60°C; Zones I and II) and 2. (2) high-temperature hydrothermal alteration (200 to 400°C; Zones III and IV). Basalts subjected to the low-temperature alteration are characterized by their relatively high boron contents (0.69 to 19.3 ppm) and high d11B values (+2.2 to +10.6?), indicating uptake of boron into secondary phases in equilibrium with seawater or evolved seawater. Hydrothermally altered basalts contain less abundant boron (0.17 to 0.52 ppm) and relatively constant d11B values (?0.1 to +1.0?). Although basalts from the upper part of these hydrothermal zones (<1300 mbsf) show equilibrated boron content and d11B value with aqueous fluid, effective leaching of boron from basalt is predominant in the lower part (>1300 mbsf). Original boron content and d11B value of the Hole 504B MORB were 0.35 ppm and +0.2?, respectively. The present data provide fundamental information in understanding of the distribution of boron and boron isotopes in the oceanic crust.

Calcareous nannofossil biostratigraphy of ODP Leg 134 sites

Seven sites drilled in the central New Hebrides Island Arc during Ocean Drilling Program Leg 134 yielded varying quantities of upper Eocene through Pleistocene calcareous nannofossils. Most of the Miocene and Pliocene strata were absent from Sites 827-831 drilled along the collisional boundary between the Australia and Pacific plates where the North d'Entrecasteaux Ridge and Bougainville Guyot are being subducted. Sites 832 and 833, drilled in the intra-arc North Aoba Basin, contained upper Miocene through Pleistocene and early Pliocene through Pleistocene nannofossils, respectively. Detailed range charts displaying species abundances and age interpretations are presented for all of the sites. Despite problems of reworked assemblages, poor preservation, overgrowths and/or dilution from volcaniclastics, the nannofossil biostratigraphy delineates several repeated sections at Site 829 in the accretionary prism adjacent to Espiritu Santo Island. Paleogene pelagic sediments equivalent to those in a reference section at Site 828 appear to have been scraped from the downgoing North d'Entrecasteaux Ridge and accreted onto the forearc during the Pleistocene. Other sediments in the forearc include Pleistocene olistostromal trench-fill deposits containing clasts of various ages and compositions. Some of the clasts and olistoliths have affinities to rocks exposed on the neighboring islands and environs, whereas others are of uncertain origin. The matrix of the olistostromes is predominately Pleistocene, however, matrices of mixed nannofossil ages are frequently encountered. Comparisons of the mixed nannofossil ages in the matrices with sedimentological and structural data suggest that sediment mixing resulting from fault movement is subordinate to that occurring during deposition.

Distribution and abundance of nannofossils in DSDP Site 89-585

Late Aptian through middle Eocene nannofossil assemblages were recovered from a continuously cored section at Site 585. Poorly preserved assemblages of low diversity were observed in samples taken throughout both upper Aptian and/or lower Albian sandstone and mudstone and middle Cenomanian to lower Turonian claystone at the base of this section. A 70-m interval barren of nannofossils separates these poorly preserved assemblages from those recovered from an upper Campanian chalk farther uphole. This chalk marks the most significant change in carbonate deposition at this site, and deposition of interbedded zeolitic claystone and sediment of varied nannofossil content proceeded without major interruption until the early Paleocene (Fasciculithus tympaniformis Zone, CP4). A middle Eocene chalk (dated by nannofossils) unconformably overlies lower Paleocene sediment in both Holes 585 and 585A. Only a few interbeds of zeolitic claystone are present within 100 m of nannofossil-rich sediment above this unconformity. This entire interval is cautiously assigned to the Discoaster sublodoensis Zone (CP 12), which indicates a sedimentation rate almost an order of magnitude higher than expected from normal pelagic sedimentation. The most obvious feature of the assemblages examined from these cores is the amount of reworked material. Rare Nannoconus elongatus and Braarudosphaera sp. in several upper Campanian to middle Eocene samples demonstrate the contribution of pelagic material from upslope and, along with other reworked species throughout the Upper Cretaceous samples examined, provide evidence contradictory to an excursion of the calcium compensation depth to deep basinal settings in the western Pacific during the Campanian-Maestrichtian time (Thierstein, 1979). The overwhelming dominance of reworked species in all middle Eocene samples examined and the persistence of these assemblages throughout such a large thickness of sediment suggest that currents that redeposited material intensified at this time and may be associated with the formation of the lower Paleocene/middle Eocene unconformity at this site. A single surface core of calcareous ooze taken from Hole 585A dated as early Pleistocene contains abundant and well-preserved late Miocene and Pliocene species.

Calcareous nannofossils in Neogene sediments of ODP Leg 117 holes

Calcareous nannofossils were studied in 574 Neogene samples recovered from eight sites drilled in block-faulted basins on the continental margin of Oman. This portion of the Arabian Sea experiences seasonal upwelling associated with the southwest monsoon. Not surprisingly, some of the more typical Neogene warm-water nannoplankton are either missing entirely or are extremely rare in these sediments. Coccolithus pelagicus, a typical cold-water indicator, is extremely abundant in many samples of late Pliocene to early Pleistocene age. These intervals correspond to periods of Northern Hemisphere glaciation. Reworked Late Cretaceous and Cenozoic nannofossils are found in a majority of the samples. They were probably carried from the Arabian Peninsula or the continent of Africa on strong southwest summer winds. Ages for the various nannofossil events were calculated by projecting the nannofossil datums onto the magnetostratigraphic scale for Sites 724, 727, and 728. These are the first ages for the various nannofossil datums derived from Oman Margin sediments. The following ages have been calculated for these nannofossil events: FAD Emiliania huxleyi, 0.23 Ma; LAD Pseudoemiliania lacunosa, 0.38 Ma; FAD Helicosphaera inversa, 0.42 Ma; top of acme of Reticulofenestra sp. A, 0.70 Ma; FAD Gephyrocapsaparallela, 0.85 Ma; LAD Gephyrocapsa spp. (large), 1.07 Ma; LAD Helicosphaera sellii, 1.34 Ma; LAD Calcidiscus macintyrei, 1.47 Ma; FAD Gephyrocapsa oceanica, 1.53 Ma; FAD Gephyrocapsa caribbeanica, 1.80 Ma; LAD Discoaster brouweri, 2.03 Ma; LAD Discoasterpentaradiatus, 2.31 Ma; LAD Discoaster surculus, 2.42; LAD Discoaster tamalis, 2.77 Ma; LAD Sphenolithus abies, 3.44 Ma; and LAD Reticulofenestra pseudoumbilica, 3.44 Ma.

(Table 1) Nutrient concentrations and carbon isotopes of sea ice segments and brine sampled during Nathaniel B. Palmer cruises NBP98-07 and NBP06-08, Ross Sea

We examined controls on the carbon isotopic composition of sea ice brines and organic matter during cruises to the Ross Sea, Antarctica in November/December 1998 and November/December 2006. Brine samples were analyzed for salinity, nutrients, total dissolved inorganic carbon (sum CO2), and the 13C/12C ratio of Sum CO2 (d13C(sum CO2)). Particulate organic matter from sea ice cores was analyzed for percent particulate organic carbon (POC), percent total particulate nitrogen (TPN), and stable carbon isotopic composition (d13C(POC)). Sum CO2 in sea ice brines ranged from 1368 to 7149 µmol/kg, equivalent to 1483 to 2519 µmol/kg when normalized to 34.5 psu salinity (s sum CO2), the average salinity of Ross Sea surface waters. Sea ice primary producers removed up to 34% of the available sum CO2, an amount much higher than the maximum removal observed in sea ice free water. Carbonate precipitation and CO2 degassing may reduce s sum CO2 by a similar amount (e.g., 30%) in the most hypersaline sea ice environments, although brine volumes are low in very cold ice that supports these brines. Brine d13C(sum CO2) ranged from -2.6 to +8.0 per mil while d13C(POC) ranged from -30.5 to -9.2 per mil. Isotopic enrichment of the sum CO2 pool via net community production accounts for some but not all carbon isotopic enrichment of sea ice POC. Comparisons of s sum CO2, d13C(sum CO2), and d13C(POC) within sea ice suggest that epsilon p (the net photosynthetic fractionation factor) for sea ice algae is ~8 per mil smaller than the epsilon p observed for phytoplankton in open water regions of the Ross Sea. These results have implications for modeling of carbon uptake and transformation in the ice-covered ocean and for reconstruction of past sea ice extent based on stable isotopic composition of organic matter in sediment cores.

(Table 1) Concentration of iron, DIP and silicic acid in water samples taken during Nathaniel B. Palmer cruises NBP06-01 and NBP06-08 (CORSACS I+II), Ross Sea

The Ross Sea polynya is among the most productive regions in the Southern Ocean and may constitute a significant oceanic CO2 sink. Based on results from several field studies, this region has been considered seasonally iron limited, whereby a "winter reserve" of dissolved iron (dFe) is progressively depleted during the growing season to low concentrations (~0.1 nM) that limit phytoplankton growth in the austral summer (December-February). Here we report new iron data for the Ross Sea polynya during austral summer 2005-2006 (27 December-22 January) and the following austral spring 2006 (16 November-3 December). The summer 2005-2006 data show generally low dFe concentrations in polynya surface waters (0.10 ± 0.05 nM in upper 40 m, n = 175), consistent with previous observations. Surprisingly, our spring 2006 data reveal similar low surface dFe concentrations in the polynya (0.06 ± 0.04 nM in upper 40 m, n = 69), in association with relatively high rates of primary production (~170-260 mmol C/m**2/d). These results indicate that the winter reserve dFe may be consumed relatively early in the growing season, such that polynya surface waters can become "iron limited" as early as November; i.e., the seasonal depletion of dFe is not necessarily gradual. Satellite observations reveal significant biomass accumulation in the polynya during summer 2006-2007, implying significant sources of "new" dFe to surface waters during this period. Possible sources of this new dFe include episodic vertical exchange, lateral advection, aerosol input, and reductive dissolution of particulate iron.