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doi:10.2204/iodp.proc.329.101.2011 Site summariesDuring Expedition 329 we drilled and/or cored in 42 holes at 7 sites ranging from 3749 to 5707 meters below sea level (mbsl). We cored 1321.8 m of sediment and basalt and recovered 1168.8 m of core (Table T1). Downhole logs were collected in one hole. Site U1365The scientific objectives at Site U1365 (proposed Site SPG-1A) are
Site U1365 (5695 mbsl) is centrally located in ocean crust formed during the CNS. The tectonic history of this Australia-sized area is poorly constrained because correlatable magnetic seafloor anomalies are not present. Consequently, radiometric dating of the recovered basalt will provide important constraints on the tectonic and volcanic history of this region. The complete sedimentary succession was recovered by the advanced piston corer (APC) in Hole U1365A. Excluding a drilled-over chert interval in the lower sediment column, complete successions were also recovered from Holes U1365B and U1365C. Core recovery in the underlying basalt was unusually high (75%). However, slow penetration (<1 m/h) allowed us to drill only ~50 m of basalt, preventing us from reaching sufficient depth below seafloor to deploy downhole logging tools. Principal resultsSedimentThe sedimentary succession at Site U1365 is composed of three lithologic units. Unit I consists of medium-brown zeolitic metalliferous pelagic clay (0–44 mbsf). Unit II consists of porcellanite and chert (44–65 mbsf). Unit III consists of dark brown metalliferous clay (65–75 mbsf) (Fig. F15). Microbial cell counts are three or more orders of magnitude lower than at the same sediment depths in all sites previously cored by scientific ocean drilling and decline to near the minimum detection limit (MDL) at 15 mbsf. They are above the MDL (1.4 × 103 cells/cm3) in many samples (and below the MDL in many other samples) for the remainder of Unit I (Fig. F16). Because the chert cannot be disaggregated, the presence or absence of cells cannot be determined in Unit II. Cell counts are consistently below the MDL in the metalliferous clay at the base of the sediment column (Unit III). Dissolved oxygen is present throughout the entire sediment column at Site U1365. It declines most rapidly in the first several meters of the sediment column and then declines at increasingly lower rates with increasing depth in Unit I (Fig. F17A). We could not measure its concentration in the chert and porcellanite of Unit II. Its concentration is essentially constant throughout Unit III. Dissolved nitrate, dissolved phosphate, and DIC are also present throughout the sediment column. The increase in dissolved nitrate concentration (from ~35 to 45 µM) over the uppermost 20 mbsf is consistent with nitrate production by oxygen-fueled reduction of organic matter (Fig. F17B). Below the chert-dominated interval, dissolved nitrate concentration approximates the present deepwater value. Dissolved hydrogen concentration is below detection throughout most of the sediment column (with the exception of a 30 nM peak centered at 30 mbsf). The concentration of total nitrogen declines rapidly in the first 10 mbsf from 0.05 to 0.01 wt%. It then declines more slowly until it drops consistently beneath its MDL (~0.007 wt%) at 38 mbsf. Consistently, TOC declines rapidly over the first few meters below seafloor (from ~0.2 to 0.05 wt%) and remains below 0.05 wt% for the remainder of the sediment column (Fig. F18). BasaltThe drilled sequence of basement rock is composed of a series of massive basalt flows (Fig. F12). Massive flows at the top of deep-sea basement are unusual in ocean drilling history (e.g., ODP Site 1256 and Site 1243 [interpreted as a lava pond]). The low-temperature alteration is similar to alteration in the uppermost basalt at other ocean drilling sites (Menard, Natland, Jordan, Orcutt, et al., 1987; Laverne et al., 1996; Teagle et al., 1996; Teagle, Alt, Umino, Miyashita, Banerjee, Wilson, and the Expedition 306/312 Scientists, 2006). Relationships between igneous unit boundaries and alteration indicate that alteration at Site U1365 is strongly controlled by the structure of the basalt (Fig. F12). Ingress of seawater, secondary mineral precipitation, and wall-rock interaction is primarily restricted to regions between lava flows. A direct relationship between visual observations of alteration and NGR-based potassium content (Fig. F12) indicates that NGR can provide a more accurate and quantitative approach to estimating alteration extent than visual interpretation alone. Secondary minerals provide evidence of both oxidative and oxygen-poor alteration. Some samples have undergone several stages of vein opening and halo emplacement. Minerals indicative of oxygen-poor alteration are most prevalent toward the base of the drilled basalt column. Tubelike microscale weathering features occur in altered glass and discrete clusters or masses adjacent to fractures and iron oxyhydroxide (Fig. F14). Similar features have been observed in marine basaltic glass elsewhere and attributed to microbial origin (Fisk et al., 1998). Multiple episodes of late-stage calcite precipitation and vein infill have occurred at Site U1365. These late fills suggest that alteration may be continuous or at least occur intermittently during the life of the ocean crust. Dissolved concentrations of magnesium and calcium in the lowermost sediment indicate that basalt-water interaction in the form of Mg exchange for Ca has occurred since seawater migrated into the formation. This exchange may continue to drive late-stage calcite precipitation. General resultsDownhole temperature was measured using the advanced piston corer temperature tool. Six measurements give a least-squares thermal gradient of 76°C/km. This result closely agrees with the thermal gradient observed by site survey cruise KNOX-02RR of 74°C/km (D’Hondt et al., 2011). The heat flow of 61 mW/m2 is typical for crust of this age. Bottom water temperature is 1.22°C and temperature at the sediment/basement interface is estimated to be 6.8°C. These temperatures are well within the range inhabited by psychrophilic microbes. A wide range of microbiology and biogeochemistry experiments was initiated shipboard. Experiments on major microbial processes and cultivation of viable microbes were initiated on samples taken at selected depths ranging from near the sediment/water interface to nearly 50 m into the basaltic basement. Subsamples for shore-based biogeochemical and molecular ecological studies were routinely taken from all of the distinct lithologic units. Site U1366
The scientific objectives at Site U1366 (proposed Site SPG-2A) are
Site U1366 (5129 mbsl) is located in ocean crust formed during the CNS. The complete sedimentary succession, from seafloor to underlying basalt, was recovered by APC coring in Hole U1366F. Partial successions, from seafloor to various depths, were also recovered from Holes U1366B–U1366E. Principal resultsThe sediment at Site U1366 is primarily clay and is assigned to two lithologic units: zeolitic metalliferous pelagic clay (Unit I) and metalliferous clay (Unit II) (Fig. F19). The principal components of the sediment are smectite, mica-group members, phillipsite, and red-brown to yellow-brown semiopaque oxide (RSO). Manganese nodules are relatively common at the seafloor and at depth in Unit I. The nodules generally produce peaks in NGR, magnetic susceptibility, and gamma ray attenuation density. Both clay and zeolite exhibit overall trends of decreasing abundance with increasing depth. NGR core logging can be used to quantify in situ concentrations of potassium, 238U-series isotopes and 232Th-series isotopes (Fig. F20). Prominent NGR features at Site U1366 include (1) a pronounced peak in 238U-series isotopes just below the seafloor and (2) NGR peaks associated with manganese nodules, which were temporarily removed from the core for additional NGR logging. The manganese nodules (at the seafloor and at depth) do not contribute to the 238U-isotope peak just below the seafloor. Cell counts for Site U1366 sediment are three or more orders of magnitude lower than at the same depths in all sediment cored gathered by previous scientific ocean drilling expeditions. Cell counts range from below the MDL (1.4 × 103 cells/cm3) to nearly 104 cells/cm3. They do not exhibit any consistent trend with depth (Fig. F21). The concentration of total nitrogen declines steadily from 0.04 wt% at the seafloor to below detection at 15 mbsf. TOC declines downhole to ~0.03 wt% at 10.75 mbsf (Fig. F22). Dissolved oxygen is present throughout the entire sediment column. Its concentration drops rapidly by 20 µM in the uppermost 3 mbsf and declines linearly with depth to ~110 µM at the sediment/basalt interface. Over the uppermost ~10 mbsf, dissolved nitrate and DIC increase slightly in concentration (from ~35 to ~40 µM and ~2.5 to ~2.7 mM, respectively) (Fig. F23A, F23B). Both are relatively stable for the remainder of the sediment column. These gradual increases are consistent with oxygen-fueled reduction of organic matter in the first 10 mbsf. Dissolved hydrogen concentration is below detection throughout the uppermost 15 m of the sediment column but rises by several tens of nannomolar as the basaltic basement is approached. Chloride concentrations increase monotonically from ~550 mM to reach a maximum of ~570 mM in the lowermost 5 m of the sediment column (a 3% increase) (Fig. F23C). This increase is most likely due to relict glacial seawater and, possibly, hydration of the underlying basement. A wide range of microbiology and biogeochemistry experiments was initiated shipboard. Experiments on major microbial processes and cultivations of viable microbes were initiated on samples taken at selected depths ranging from near the sediment/water interface to the sediment/basement contact. Subsamples for shore-based biogeochemical and molecular ecological studies were routinely taken from all of the distinct lithologic units. Site U1367Site U1367 (proposed Site SPG-4A) was selected as a drilling target because (1) its microbial activities and cell counts were expected to be characteristic of a setting midway between the western gyre edge and the gyre center, and (2) its basement age renders it a reasonable location for documenting microbial habitability and testing the extent of basalt alteration and openness to flow in a thinly sedimented region of ~33.5 Ma basaltic basement. The principal objectives at Site U1367 are
Site U1367 (4289 mbsl) is located in ocean crust formed during magnetic polarity Chron 13n (33.3–33.7 Ma; Gradstein et al., 2004). The complete sedimentary succession, from seafloor to underlying basalt, was recovered by APC coring in Holes U1367B–U1367E. The sediment/basalt contact varies by a few meters from hole to hole. The lowermost sediment and fragments of the underlying basalt were recovered by RCB coring in Hole U1367F. Core recovery of the basalt was unusually low (11%). Continuous fall-in of basaltic debris forced us to terminate the hole early, preventing us from reaching sufficient depth below seafloor to deploy downhole logging tools. Principal resultsSedimentThe sediment at Site U1367 is composed of 5.5–7 m of pelagic clay (lithologic Unit I) overlying ~16 m of Oligocene carbonate ooze (Unit II) (Fig. F24). The principal components of the clay are smectite and mica-group members, phillipsite (a zeolite), and RSO. The ooze is composed mainly of coccolithophores and RSO, accompanied by foraminifers. The clay and ooze differ significantly in several physical properties, including porosity, bulk density, electrical conductivity, magnetic susceptibility, and NGR. The transition from clay to ooze is gradual. The depth of the sediment/basalt interface varies by ~3 m from hole to hole. Although unit thickness and composition vary from hole to hole, general sediment composition is very similar in each hole. Microbial cell counts decline rapidly from ~105 cells/cm3 at 0.15 mbsf to the MDL (103 cells/cm3) at 2 mbsf. Cell counts are mostly below the MDL throughout the remaining sediment column. The concentration of total nitrogen declines to below detection (from 0.03% to 0.0%) in the uppermost 7 mbsf. TOC declines from 0.17 to 0.02 wt% over the same interval. Dissolved nitrate, dissolved phosphate, and DIC are present throughout the sediment column (Fig. F25). Dissolved oxygen also occurs throughout the column. Dissolved hydrogen concentration is below detection in most of the clay but above detection in most samples of the carbonate. BasaltThe recovered sequence of basement rock is composed of pillow basalt fragments with prominent chill margins. Secondary mineralization and wall-rock interaction is limited in the recovered basalt. However, it is likely that the most altered portions of the basalt were not recovered. A wide range of microbiology experiments was initiated shipboard. Experiments on major microbial processes and cultivations of viable microbes were initiated on samples taken at selected depths ranging from near the sediment/water interface to ~30 m into the basaltic basement. Subsamples were routinely taken from all of the distinct lithologic units for postcruise molecular assays and microbiological experiments. Site U1368Site U1368 (proposed Site SPG-6A) was selected as a drilling target because (1) its microbial activities and cell counts were expected to be characteristic of the gyre center and (2) its basement age renders it a reasonable location for testing the extent of microbial habitability and basalt alteration in a thinly sedimented region of ~13.5 Ma basaltic basement. The principal objectives at Site U1368 are
Site U1368 (3740 mbsl) is located in ocean crust formed during magnetic polarity Chron 5ABn (13.4–13.6 Ma; Gradstein et al., 2004). Most or all of the sedimentary succession was recovered by APC coring in Holes U1368B–U1368E. Basalt fragments were recovered from the basal cores of Holes U1368B and U1368D. The uppermost ~100 m of basalt was cored using RCB in Hole U1368F. Approximately 60 m of the basaltic basement was logged with both the triple combination and Formation MicroScanner tool string. Principal resultsSedimentThe sediment at Site U1368 is 15–16 m thick and consists of calcareous ooze, pelagic clay, and lithic sand. (Fig. F26). An additional 1 m of volcaniclastic breccia was recovered from an interval between basalt flows, 80 m below the upper sediment/basalt interface. The principal components of the ooze are calcareous nannofossils accompanied by RSO and foraminifers. Planktonic foraminiferal biostratigraphy indicates that the calcareous ooze spans from the middle Miocene to the middle Pliocene. Clay minerals are in relatively low abundance throughout the sediment. The lowermost sediment contains one to three sandy intervals that collectively contain a wide variety of minerals, including albite-anorthite, ankerite, augite, calcite, chlorite, hematite, and titanomagnetite. The volcaniclastic breccia contains altered basaltic lithic and vitric grains. Microbial cell counts decline rapidly from 105 to 106 cells/cm3 just below the seafloor to slightly more than 103 cells/cm3 at ~5 mbsf. Cell counts hover near the MDL (103 cells/cm3) for the remainder of the sediment column. The concentration of total nitrogen declines to below detection in the uppermost 10 cm below seafloor. TOC declines to 0.03 wt% over the uppermost 0.5 mbsf and remains low for the remainder of the sediment column. Dissolved nitrate, dissolved phosphate, DIC, and dissolved oxygen are present throughout the sediment column. Dissolved hydrogen concentration is below detection for the first 9.4 mbsf but above detection in half of the samples at greater depth (Fig. F27). BasaltThe recovered sequence of basement rock is composed of pillow basalt fragments with prominent chill margins. Estimates of potassium content derived from downhole NGR logging agree closely with potassium concentration estimates derived from NGR logging of whole-round cores (Fig. F28). A wide range of microbiology experiments was initiated shipboard. Experiments on major microbial processes and cultivations of viable microbes were initiated on samples from selected depths ranging from near the sediment/water interface to ~100 m into the basaltic basement. Subsamples were routinely taken from all of the distinct lithologic units for postcruise molecular assays and microbiological experiments. Site U1369Site U1369 (proposed Site SPG-10A) was selected as a drilling target because (1) its microbial activities and cell counts were expected to be characteristic of midway between gyre center and the southern gyre edge and (2) its basement age renders it a reasonable location for testing the extent of sediment-basement interaction in a thinly sedimented region of ~58 Ma basaltic basement.
The principal objectives at Site U1369 are
Site U1369 is located in the South Pacific Gyre at 5277 mbsl. Basement age is estimated from extrapolated magnetic models and changes in spreading rate recorded by neighboring magnetic profiles. Our best estimate of the crustal age is ~58 Ma and corresponds to magnetic polarity Chron 25r (57.2–58.4 Ma; Gradstein et al., 2004). The sedimentary succession was recovered by APC coring in Holes U1369B, U1369C, and U1369E. Basalt fragments were recovered from the basal cores of these holes. Principal resultsSedimentThe sediment at Site U1369 consists of ~16 m of zeolitic metalliferous clay. The sediment is massive in texture and contains visible burrows throughout. The principal components of the clay are phillipsite, RSO, and clay (Fig. F29). Manganese nodules were recovered from the sediment/water interface and from deeper in the sediment column. Micro- and nannofossils are almost completely absent. The sediment/basalt interface consists of vitric sand overlying altered basalt. Sediment thickness and composition are fairly uniform from hole to hole. Microbial cell counts decline rapidly from ~105 cells/cm3 just below the seafloor to ~103 cells/cm3 at ~2 mbsf (Fig. F30). Cell counts are below the MDL (~103 cells/cm3) for the remainder of the sediment column. Total nitrogen and TOC decrease rapidly from near the seafloor to ~3 mbsf and are extremely low for the remainder of the sediment column. Dissolved oxygen, dissolved nitrate, dissolved phosphate, and DIC are present throughout the sediment column (Fig. F31). Dissolved hydrogen concentration is consistently low throughout the column. A wide range of microbiology experiments was initiated shipboard. Experiments on major microbial processes and cultivations of viable microbes were initiated with samples from selected depths ranging from near the sediment/water interface to the sediment/basalt interface. Subsamples were routinely taken from all of the distinct lithologic units for postcruise molecular assays and microbiological experiments. Site U1370Site U1370 (proposed Site SPG-11B) was selected as a drilling target because (1) its microbial activities and cell counts were expected to be characteristic of midway between gyre center and the southern gyre edge and (2) its basement age renders it a reasonable location for testing the extent of sediment-basement interaction in a moderately sedimented region of 74–80 Ma basaltic basement. The principal objectives at Site U1370 are
Site U1370 is located in the South Pacific Gyre at 5074 mbsl. The coring site is located within magnetic polarity Chron 33n, so the crustal age may range from 73.6 to 79.5 Ma (Gradstein et al., 2004). The sedimentary succession was recovered by APC coring in Holes U1370D, U1370E, and U1370F. Altered basaltic fragments were recovered from the basal cores of Holes U1370D and U1370F. Principal resultsSedimentThe sediment at Site U1370 is ~70 m thick. The dominant lithology is dark brown zeolitic metalliferous pelagic clay (Fig. F32). The principal components of the clay are RSO, phillipsite, and smectite. Lithologic Unit I lies between the sediment/water interface and the top of a nannofossil ooze (Unit II) at ~61 mbsf. Unit II is a relatively short (30–290 cm) pale yellow interval predominantly composed of coccolithophores, with trace phillipsite, and clay. Unit III is a thin clay interval containing 88% RSO and 12% clay that directly overlays the basaltic basement. Although volcanic glass is locally abundant (~43%) in Unit I, its overall abundance is only 7%, and it is completely absent in Units II and III. A large, fragmented manganese nodule was recovered in Hole U1370D at 10 mbsf, and fragments of a manganese-encrusted hardground were in recovered in Hole U1370F at 52 mbsf. Overall sediment structure at Site U1370 is massive, although occasional laminations and thin beds are visible in the lower half of Unit I. Planolites (horizontal) burrows are faintly visible in most of the clay and Trichichnus (vertical) burrows blend the upper and lower contacts of the nannofossil ooze and the overlying and underlying clay. Sediment thickness and composition are uniform from hole to hole. The nannofossil ooze was deposited during early Paleocene foraminiferal Zone P1. Its occurrence in this deep-sea clay sequence is attributed to deepening of the CCD and lysocline during the interval of decreased planktonic carbonate precipitation that followed the end-Cretaceous mass extinction (D’Hondt, 2005). Microbial cell counts were above the MDL (~103 cells/cm3) throughout much of the sediment column. The dissolved oxygen and nitrate profiles at Site U1370 (Fig. F33) exhibit much greater curvature than the profiles at previous Expedition 329 sites. Dissolved oxygen concentration decreases sharply in the uppermost several meters below seafloor and then more gradually to 40 mbsf. Below that depth, it decreases monotonically from ~10 µM to a few micromolar at the sediment/basalt interface. The rate of increase in dissolved nitrate concentration from surface sediment to 20 mbsf is higher than at previous sites (U1365–U1369), suggesting that organic nitrogen oxidation in the sediment is greater here than at those sites. The changes in dissolved oxygen and nitrate throughout the upper sediment column are attributed to oxygen consuming organic oxidation by sedimentary microbes. BasaltDissolved potassium concentration declines nearly linearly with depth in the sediment (Fig. F34), indicating a sink for dissolved potassium in the underlying basaltic basement. This sink is inferred to be basalt alteration (clay formation). A wide range of microbiology experiments was initiated shipboard. Experiments on major microbial processes and cultivations of viable microbes were initiated with samples taken at selected depths ranging from near the sediment/water interface to the sediment/basalt interface. Subsamples were routinely taken from all of the distinct lithologic units for postcruise molecular assays and microbiological experiments. Site U1371Site U1371 (proposed Site SPG-12A) was selected as a drilling target because (1) its microbial activities and cell counts were expected to be characteristic of the upwelling region just south of the gyre and (2) its basement age renders it a reasonable location for testing the extent of sediment-basement interaction in a moderately sedimented region of 71.5–73 Ma basaltic basement. The principal objectives at Site U1371 are
Site U1371 is located in the South Pacific Gyre at 5301 mbsl. The coring site is located within magnetic polarity Chron 32n.2n, so the crustal age may range from 71.5 to 72.9 Ma (Gradstein et al., 2004). Based on a tectonic reconstruction of the region by Larson et al. (2002), the crust was accreted along the Pacific-Phoenix spreading center at ~73 Ma. The sedimentary succession was recovered by APC coring in Holes U1371D–U1371F. Additional mudline cores were recovered in Holes U1371B, U1371C, U1371G, and U1371H. Altered basaltic fragments were recovered from the basal core of Hole U1371F. Principal resultsSedimentThe sediment at Site U1371 consists of ~130 m of diatom ooze and pelagic clay, divided into two lithologic units based on their sharply contrasting mineralogy (Fig. F35). Unit I is ooze with average diatom and clay content of 56% and 17%, respectively. It is 104–107 m thick and contains numerous ash layers and multiple thin hardgrounds. Unit II is a blend of clay (32%), zeolite (30%), and RSO (15%). The transition from ooze to clay constitutes the upper 5 m of Unit II; this portion of Unit II contains as much as 26% diatoms. Other minor sedimentary components at Site U1371 include quartz, pyrite, manganese oxide/hydroxide, radiolarians, spicules, and silicoflagellates. The clay-bearing diatom ooze and pelagic clay at Site U1371 form interbedded intervals of highly fossiliferous and clay-rich layers. Bioturbation is a prominent feature of the sediment, causing diffuse boundaries on most beds. Overall sediment thickness and composition appear to be broadly uniform from hole to hole. Microbial cell counts were above the MDL (~103 cells/cm3) throughout much of the sediment column. Profiles of dissolved chemicals clearly indicate that most of the sediment column is anoxic, with thin oxic zones at the top and bottom of the column (Fig. F36). Manganese is a prominent net electron acceptor throughout most of the column. Dissolved oxygen concentration decreases rapidly within the first meter below seafloor and is below detection by ~5 mbsf. Below that depth, it is indistinguishable from zero until to a few meters above the sediment/basalt interface, when it rises to a few micromolar. Dissolved oxygen content generally matches sediment color, with dissolved oxygen present in the brown sediment at the top and bottom of the column but indistinguishable from zero throughout the gray sediment that characterized most of the column. Dissolved nitrate disappears within 2.5 mbsf but reappears above the sediment/basalt interface, from 105 to 120 mbsf (the deepest sample analyzed for nitrate). Dissolved ammonium rises from 0.35 µM at 0.15 mbsf to a maximum of ~55 µM between 30 and 65 mbsf and then decreases slightly to 40 µM at 97 mbsf (no deeper samples were analyzed for ammonium). Dissolved manganese strongly increases to ~360 µM in the uppermost 3 mbsf, exhibits four broad maxima and three local minima within the column, and decreases to ~70 µM at ~128 mbsf. Redox potential, measured by electrode, broadly mirrors the dissolved iron (Fe) profile, with positive potential and low dissolved Fe at the top and bottom of the sediment column, but generally low potential and high dissolved Fe content throughout most of the column. Three minima in redox potential within the column correspond to local maxima in dissolved Fe concentration. Throughout the sediment column, concentrations of dissolved phosphate and DIC are much higher at Site U1371 than at equivalent sediment depths at the sites within the gyre (Sites U1365–U1370). Concentrations of these chemical species peak a few meters below seafloor. Shipboard studies of Site U1371 found at least four additional results of note. First, the presence of pyrite in the uppermost 0–10 m of the sediment column suggests that sulfate and iron reduction have occurred in the near-seafloor zones of oxygen, nitrate, and manganese reduction. Second, the sulfate anomaly profile suggests that sulfate reduction and manganese reduction may broadly co-occur within the column. Third, dissolved oxygen and dissolved manganese appear to coexist for at least 13 m in the lowermost sediment column. Fourth, dissolved oxygen and dissolved hydrogen also appear to coexist in the lowermost sediment column. Postcruise studies will test (1) the co-occurrence of sulfate reduction, iron reduction, and other redox processes in this sediment column and (2) explanations of the co-occurrence of dissolved oxygen, manganese, and hydrogen deep in the column. BasaltThe presence of dissolved oxygen, nitrate, phosphate, and DIC in the lowermost sediment indicates that life is not inhibited in the upper basaltic basement by absence of electron acceptors, major nutrients, or carbon. Dissolved potassium concentration declines with depth in the sediment, indicating a sink for dissolved potassium in the underlying basaltic basement. This sink is inferred to be basalt alteration (clay formation). A wide range of microbiology and biogeochemistry experiments was initiated shipboard. Experiments on major microbial processes and cultivations of viable microbes were initiated with samples taken at selected depths ranging from near the sediment/water interface to the sediment/basalt interface. Subsamples were routinely taken from all of the distinct lithologic units for postcruise molecular assays and microbiological experiments. |
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