Diatom biostratigraphy and datum levels of sediments from ODP Leg 167 sites

Ocean Drilling Program Leg 167 represents the first time since 1978 that the North American Pacific margin was drilled to study ocean history. More than 7500 m of Quaternary to middle Miocene (14 Ma) sediments were recovered from 13 sites, representing the most complete stratigraphic sequence on the California margin. Diatoms are found in most samples in variable abundance and in a moderately well-preserved state throughout the sequence, and they are often dominated by robust, dissolution-resistant species. The Neogene North Pacific diatom zonation of Yanagisawa and Akiba (1998, doi:10.5575/geosoc.104.395) best divides the Miocene to Quaternary sequences, and updated ages of diatom biohorizons estimated based on the geomagnetic polarity time scale of Cande and Kent (1995, doi:10.1029/94JB03098) are slightly revised to adjust the differences between the other zonations. Most of the early middle Miocene through Pleistocene diatom datum levels that have been proven to be of stratigraphic utility in the North Pacific appear to be nearly isochronous within the level of resolution constrained by sample spacing. The assemblages are characterized by species typical of middle-to-high latitudes and regions of high surface-water productivity, predominantly by Coscinodiscus marginatus, Stephanopyxis species, Proboscia barboi, and Thalassiothrix longissima. Latest Miocene through Pliocene assemblages in the region of the California Current, however, are intermediate between those of subarctic and subtropical areas. As a result, neither the existing tropical nor the subarctic (high latitude) zonal schemes were applicable for this region. An interval of pronounced diatom dissolution detected throughout the Pliocene sequence apparently correspond to a relatively warmer paleoceanographic condition resulting in a slackening of the southward flow of the California Current.

Marine diatoms in deep sea sediments

Long-term evolution is thought to take opportunities that arise as a consequence of mass extinction (as argued, for example, by Gould, 2002) and the following biotic recovery, but there is absolutely no evidence for this being the case. However, our study shows that eutrophication by oceanic mixing also played a part in the enhancement of several evolutionary events amongst marine organisms, and these results could indicate that the rates of oceanic biodiversification may be slowed if upwelling becomes weakened by future global warming. This paper defines three distinct evolutionary events of resting spores of the marine diatom genus Chaetoceros, to reconstruct past upwelling through the analysis of several DSDP, ODP and land-based successions from the North, South and equatorial Pacific as well as the Atlantic Ocean during the past 40 million years. The Atlantic Chaetoceros Explosion (ACE) event occurred across the E/O boundary in the North Atlantic, and is characterized by resting spore diversification that occurred as a consequence of the onset of upwelling following changes in thermohaline circulation through global cooling in the early Oligocene. Pacific Chaetoceros Explosion events-1 and -2 (PACE-1 and PACE-2) are characterized by relatively higher occurrences of iron input following the Himalayan uplift and aridification at 8.5 Ma and ca. 2.5 Ma in the North Pacific region. These events not only enhanced the diversification and increased abundance of primary producers, including that of Chaetoceros, other diatoms and seaweeds, but also stimulated the evolution of zooplankton and larger predators, such as copepods and marine mammals, which ate these phytoplankton and plants. Current thinking suggests new evolutionary niches open up after a mass extinction, but our study finds that eutrophication can also stimulate evolutionary diversification. Moreover, in the opposite fashion, our results show that as thermohaline circulation abates, global warming progresses and the ocean surface becomes warmer, many marine organisms will be affected by the environmental degradation.

Physical properties and abundance of diatoms of the ANDRILL AND1-1B drill core

In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing- McMurdo Ice Shelf) project recovered a 1285 m sediment core from beneath the Ross Ice Shelf near Hut Point Peninsula, Ross Island, Antarctica in a flexural moat associated with the volcanic loading of Ross Island. Contained within the upper ~600 m of this core are sediments recording 38 glacial to interglacial cycles of Early Pliocene to Pleistocene time, including 13 discrete diatomite units (DU). The longest of these, DU XI, is ~76 m thick, contains two distinct unconformities marked by layers of volcanic brecciated sands, and has been assigned an Early to Mid-Pliocene age (5-3 Ma). A detailed record (avg. sample spacing of 33 cm) of the siliceous microfossil assemblages have been generated for DU XI and used in conjunction with geochemical and sedimentological data to subdivide DU XI into four discrete subunits of continuous sedimentation. Within each unit, changes in diatom assemblages have been correlated with the d18O record, providing a temporal resolution as high as 600 yr, and allowing for the construction of a detailed age model and calculation of associated sediment accumulation rates within DU XI. Results indicate a productivity-dominated sedimentary record with higher sediment accumulation rates containing a greater proportion of hemipelagic mud occurring during relatively cool periods and reduced accumulation during warmer intervals. This implies that even during periods of substantial warmth, Milankovitch-paced changes in Antarctic ice volume can be linked to ecological changes recorded as shifts in diatom assemblages.

Vegetation, soil and site characteristics of samples taken along the Yamal Transet in 2007-2008

The overarching goal of the Yamal portion of the Greening of the Arctic project is to examine how the terrain and anthropogenic factors of reindeer herding and resource development combined with the climate variations on the Yamal Peninsula affect the spatial and temporal patterns of vegetation change and how these changes are in turn affecting traditional herding of the indigenous people of the region. The purpose of the expeditions was to collect groundobservations in support of remote sensing studies at four locations along a transect that traverses all the major bioclimate subzones of the Yamal Peninsula. This data report is a summary of information collected during the 2007 and 2008 expeditions. It includes all the information from the 2008 data report (Walker et al. 2008) plus new information collected at Kharasavey in Aug 2008. The locations included in this report are Nadym (northern taiga subzone), Laborovaya (southern tundra = subzone E of the Circumpolar Arctic Vegetation Map (CAVM), Vaskiny Dachi (southern typical tundra = subzone D), and Kharasavey (northern typical tundra = subzone C). Another expedition is planned for summer 2009 to the northernmost site at Belyy Ostrov (Arctic tundra = subzone B). Data are reported from 10 study sites - 2 at Nadym, 2 at Laborovaya, and 3 at Vaskiny Dachi and 3 at Kharasavey. The sites are representative of the zonal soils and vegetation, but also include variation related to substrate (clayey vs. sandy soils). Most of the information was collected along 5 transects at each sample site, 5 permanent vegetation study plots, and 1-2 soil pits at each site. The expedition also established soil and permafrost monitoring sites at each location. This data report includes: (1) background for the project, (2) general descriptions and photographs of each locality and sample site, (3) maps of the sites, study plots, and transects at each location, (4) summary of sampling methods used, (5) tabular summaries of the vegetation data (species lists, estimates of cover abundance for each species within vegetation plots, measured percent ground cover of species along transects, site factors for each study plot), (6) summaries of the Normalized Difference Vegetation Index (NDVI) and leaf area index (LAI) along each transect, (7) soil descriptions and photos of the soil pits at each study site, (8) summaries of thaw measurements along each transect, and (9) contact information for each of the participants. One of the primary objectives was to provide the Russian partners with full documentation of the methods so that Russian observers in future years could repeat the observations independently.

Methane, helium isotope and hydrogen data from the Nibelungen hydrothermal area, Mid Atlantic Ridge

Hydrothermal emission of mantle helium appears to be directly related to magma production rate, but other processes can generate methane and hydrogen on mid-ocean ridges. In an on-going effort to characterize these processes in the South Atlantic, the flux and distribution of these gases were investigated in the vicinity of a powerful black smoker recently discovered at 8°17.9' S, 13°30.4' W. The vent lies on the shoulder of an oblique offset in the Mid-Atlantic Ridge and discharges high concentrations of methane and hydrogen. Measurements during expeditions in 2004 and 2006 show that the ratio of CH4 to 3He in the neutrally buoyant plume is quite high, 4 x 10**8. The CTD stations were accompanied by velocity measurements with lowered acoustic Doppler current profilers (LADCP), and from these data we estimate the methane transport to have been 0.5 mol/sec in a WSW-trending plume that seems to develop during the ebb tidal phase. This transport is an order of magnitude greater than the source of CH4 calculated from its concentration in the vent fluid and the rise height of the plume. From this range of methane fluxes, the source of 3He is estimated to be between 0.14 and 1.2 nmol/sec. In either case, the 3He source is significantly lower than expected from the spreading rate of the Mid-Atlantic Ridge. From the inventory of methane in the rift valley adjacent to the vent, it appears that the average specific rate of oxidation is 2.6 to 23/yr, corresponding to a turnover time between 140 and 16 days. Vertical profiles of methane in the surrounding region often exhibited Gaussian-like distributions, and the variances appear to increase with distance from the vent. Using a Gaussian plume model, we obtained a range of vertical eddy diffusivities between 0.009 and 0.08 m2m2/sec. These high values may be due to tidally driven internal waves across the promontory on which the vent is located.

Diatom biostratigraphy, Argon ages and chronology of ODP Hole 183-1138A

A thick Neogene section was recovered in the upper ~300 m of Ocean Drilling Program Hole 1138A, drilled on the Central Kerguelen Plateau in the Indian sector of the Southern Ocean. Sediment lithologies consist primarily of mixed carbonate and biosiliceous clays and oozes, with several thin (1-3 cm) tephra horizons. The tephras are glass rich, well sorted, and dominantly trachytic to rhyolitic in composition. Volcaniclastic material in these horizons is interpreted to have originated from Heard Island, 180 km northwest of Site 1138, and was likely emplaced through both primary ash fall and turbiditic, submarine flows. A Neogene age-depth model for Hole 1138A is constructed primarily from 36 diatom biostratigraphic datums. Nannofossil and planktonic foraminifer biostratigraphy provides supporting age information. Additionally, four high-precision 40Ar-39Ar ages are derived from ash and tephra horizons, and these radiometric ages are in close agreement with the biostratigraphic ages. The integrated age-depth model reveals a reasonably complete lower Miocene to upper Pleistocene section in Hole 1138A, with the exception of a ~1-m.y. hiatus at the Miocene/Pliocene boundary. Another possible hiatus is also identified at the Oligocene/Miocene boundary. High Neogene sedimentation rates and the presence of both calcareous and siliceous microfossils, combined with datable tephra horizons, establish Site 1138 as a suitable target for future drilling legs with paleoceanographic objectives. This report also proposes two new diatom species, Fragilariopsis heardensis and Azpeitia harwoodii, from Pliocene strata of Hole 1138A.

Late Glacial and Holocene data from sediment cores MD99-2236 and MD99-2256

The Laurentide Ice Sheet (LIS) was a large, dynamic ice sheet in the early Holocene. The glacial events through Hudson Strait leading to its eventual demise are recorded in the well-dated Labrador shelf core, MD99-2236 from the Cartwright Saddle. We develop a detailed history of the timing of ice-sheet discharge events from the Hudson Strait outlet of the LIS during the Holocene using high-resolution detrital carbonate, ice rafted detritus (IRD), d18O, and sediment color data. Eight detrital carbonate peaks (DCPs) associated with IRD peaks and light oxygen isotope events punctuate the MD99-2236 record between 11.5 and 8.0 ka. We use the stratigraphy of the DCPs developed from MD99-2236 to select the appropriate DeltaR to calibrate the ages of recorded glacial events in Hudson Bay and Hudson Strait such that they match the DCPs in MD99-2236. We associate the eight DCPs with H0, Gold Cove advance, Noble Inlet advance, initial retreat of the Hudson Strait ice stream (HSIS) from Hudson Strait, opening of the Tyrrell Sea, and drainage of glacial lakes Agassiz and Ojibway. The opening of Foxe Channel and retreat of glacial ice from Foxe Basin are represented by a shoulder in the carbonate data. DeltaR of 350 years applied to the radiocarbon ages constraining glacial events H0 through the opening of the Tyrell Sea provided the best match with the MD99-2236 DCPs; DeltaR values and ages from the literature are used for the younger events. A very close age match was achieved between the 8.2 ka cold event in the Greenland ice cores, DCP7 (8.15 ka BP), and the drainage of glacial lakes Agassiz and Ojibway. Our stratigraphic comparison between the DCPs in MD99-2236 and the calibrated ages of Hudson Strait/Bay deglacial events shows that the retreat of the HSIS, the opening of the Tyrell Sea, and the catastrophic drainage of glacial lakes Agassiz and Ojibway at 8.2 ka are separate events that have been combined in previous estimates of the timing of the 8.2 ka event from marine records. SW Iceland shelf core MD99-2256 documents freshwater entrainment into the subpolar gyre from the Hudson Strait outlet via the Labrador, North Atlantic, and Irminger currents. The timing of freshwater release from the LIS Hudson Strait outlet in MD99-2236 matches evidence for freshwater forcing and LIS icebergs carrying foreign minerals to the SW Iceland shelf between 11.5 and 8.2 ka. The congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the LIS through Hudson Strait into the subpolar gyre and provides specific time periods when pulses of LIS freshwater were present to influence climate.

Mineralogy of sediments at DSDP Leg 67 Hole

Seven sites were drilled during Leg 67 along a transect across the Middle America Trench off Guatemala: four (Sites 494, 496, 497, and 498) on continental slope, two (Sites 499 and 500) on Trench floor, and one (Site 495) on the Cocos Plate. We studied the mineralogy of sediments from Sites 494, 495, 496, 499, and 500. Our objective was to investigate the origin and source of separate minerals and mineral assemblages, giving special attention to the influence of the alteration of basalts on the sediment mineralogy, which we expected to be particularly important in layers just above oceanic basement.