Lithium concentrations and isotope composition of basalt samples from ODP/DSDP Sites from Costa Rica Rift

Ocean Drilling Program (ODP) Hole 504B near the Costa Rica Rift is the deepest hole drilled in the ocean crust, penetrating a volcanic section, a transition zone and a sheeted dike complex. The distribution of Li and its isotopes through this 1.8-km section of oceanic crust reflects the varying conditions of seawater alteration with depth. The upper volcanic rocks, altered at low temperatures, are enriched in Li (5.6-27.3 ppm) and have heavier isotopic compositions (delta7Li=6.6-20.8?) relative to fresh mid-ocean ridge basalt (MORB) due to uptake of seawater Li into alteration clays. The Li content and isotopic compositions of the deeper volcanic rocks are similar to MORB, reflecting restricted seawater circulation in this section. The transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization. Li enrichment in this zone is accompanied by relatively light isotopic compositions (-0.8-2.1?) which signify influence of basalt-derived Li during mineralization and alteration. Li decreases with depth to 0.6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high-temperature reaction zone. Rocks in the dike complex have variable isotopic values that range from -1.7 to 7.9?, depending on the extent of hydrothermal recrystallization and off-axis low-temperature alteration. Hydrothermally altered rocks are isotopically light because 6Li is preferentially retained in greenschist and amphibolite facies minerals. The delta7Li values of the highly altered rocks of the dike complex are complementary to those of high-temperature mid-ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage. The inventory of Li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of Li in the ocean. On balance, the upper 1.8 km of oceanic crusts remains a sink for oceanic Li. The observations at 504B and an estimated flux from the underlying 0.5 km of gabbro suggest that the global hydrothermal flux is at most 8*10**9 mol/yr, compatible with geophysical thermal models. This work defines the distribution of Li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle.

Oxygen and carbon isotope data for benthic foraminifera from DSDP Site 94-608 and ODP Site 208-1264

Small biserial foraminifera were abundant in the early Miocene (ca. 18.9-17.2 Ma) in the eastern Atlantic and western Indian Oceans, but absent in the western equatorial Atlantic Ocean, Weddell Sea, eastern Indian Ocean, and equatorial Pacific Ocean. They have been assigned to the benthic genus Bolivina, but their high abundances in sediments without evidence for dysoxia could not be explained. Apertural morphology, accumulation rates, and isotopic composition show that they were planktic (genus Streptochilus). Living Streptochilus are common in productive waters with intermittent upwelling. The widespread early Miocene high Streptochilus abundances may reflect vigorous but intermittent upwelling, inducing high phytoplankton growth rates. However, export production (estimated from benthic foraminiferal accumulation rates) was low, possibly due to high regeneration rates in a deep thermocline. The upwelled waters may have been an analog to Subantarctic Mode Waters, carrying nutrients into the eastern Atlantic and western Indian Oceans as the result of the initiation of a deep-reaching Antarctic Circumpolar Current, active Agulhas Leakage, and vigorous vertical mixing in the Southern Oceans.

Chronostratigraphy of sediments from the Bahamas

Continuous cores drilled during the Bahamas Drilling Project (BDP) and the Ocean Drilling Program (ODP) Leg 166 along a transect from the top of Great Bahama Bank to the basin in the Straits of Florida provide a unique data set to test the assumption in seismic stratigraphy that seismic reflections are time lines and, thus, have a chronostratigraphic significance. Seismic reflections that are identified as seismic sequence boundaries (SSBs) were dated by means of biostratigraphy in the five ODP sites and by a combination of biostratigraphy, magnetostratigraphy and Sr isotope stratigraphy in the two BDP sites. The seismic reflection horizons are carried across a variety of facies belts from shallow-water carbonates over slope carbonates to drift deposits in the Straits of Florida. Within this system 17 SSBs were identified and dated. Despite the fact that the seismic reflections cross several facies belts, their ages remain remarkably constant. The average offset in all sites is 0.38 Myr. In no cases do the seismic reflections cut across time lines. The age differences are the combined result of the biostratigraphic sampling frequency, the spacing of marker species that required extrapolation of ages, and the resolution of the seismic data. In addition, uncertainties of age determination in the proximal sites where age-diagnostic fauna are rare add to the age differences between sites. Therefore, it can be concluded that the seismic reflections, which mark the SSBs along the Bahamas Transect, are time lines and can be used as stratigraphic markers. This finding implies that depositional surfaces are preferentially imaged by reflected seismic waves and that an impedance contrast exists across these surfaces. Facies successions across the sequence boundaries indicate that the sequence boundaries coincide with the change of deposition from times of high to low sea level. In the carbonate setting of Great Bahama Bank, sea-level changes produce changes in sediment composition, sedimentation rate and diagenesis from the platform top to the basin. The combination of these factors generates differences in sonic velocity and, thus, in impedance that cause the seismic reflection. The impedance contrasts decrease from the proximal to the distal sites, which is reflected in the seismic data by a decrease of the seismic amplitude in the basinal area.

Stable carbon and oxygen isotope ratios of benthic foraminifera from Paleocene to Oligocene sediments

Benthic oxygen and carbon isotopic results from a depth transect on Maud Rise, Antarctica, provide the first evidence for Warm Saline Deep Water (WSDW) in the Paleogene oceans. Distinct reversals occur in the oxygen isotopic gradient between the shallower Hole 689B (Eocene depth ~1400 m; present-day depth 2080 m) and the deeper Hole 690B (Eocene depth ~2250 m; present-day depth 2914 m). The isotopic reversals, well developed by at least 46 Ma (middle middle Eocene), existed for much of the remaining Paleogene. We do not consider these reversals to be artifacts of differential diagenesis between the two sites or to have resulted from other potentially complicating factors. This being so, the results show that deep waters at Hole 690B were significantly warmer than deep waters at the shallower Hole 689B. A progressive decrease and eventual reversal in benthic to planktonic delta18O gradients in Hole 690B, demonstrate that the deeper waters became warmer relative to Antarctic surface waters during the Eocene. The warmer deep waters of the Paleogene are inferred to have been produced at middle to low latitudes, probably in the Tethyan region which contained extensive shallow-water platforms, ideal sites for the formation of high salinity water through evaporative processes. The ocean during the Eocene, and perhaps the Paleocene, is inferred to have been two-layered, consisting of warm, saline deep waters formed at low latitudes and overlain by cooler waters formed at high latitudes. This thermospheric ocean, dominated by halothermal circulation we name Proteus. The Neogene and modern psychrospheric ocean Oceanus is dominated by thermohaline circulation of deep waters largely formed at high latitudes. An intermediate condition existed during the Oligocene, with a three-layered ocean that consisted of cold, dense deep waters formed in the Antarctic (Proto-AABW), overlain by warm, saline deep waters from low latitudes, and in turn overlain by cool waters formed in the polar regions. This we name Proto-oceanus which combined both halothermal and thermohaline processes. The sequence of high latitude, major, climatic change inferred from the oxygen isotopic records is as follows: generally cooler earlier Paleocene; warming during the late Paleocene; climax of Cenozoic warmth during the early Eocene and continuing into the early middle Eocene; cooling mainly in a series of steps during the remainder of the Paleogene. Superimposed upon this Paleogene pattern, the Paleocene/Eocene boundary is marked by a brief but distinct warming that involved deep to surface waters and a reduction in surface to deep carbon and oxygen isotopic gradients. This event coincided with major extinctions among the deep-sea benthic foraminifers as shown by Thomas (1990 doi:10.2973/odp.proc.sr.113.123.1990). Salinity has played a major role in deep ocean circulation, and thus paleotemperatures cannot be inferred directly from the oxygen isotopic composition of Paleogene benthic foraminifers without first accounting for the salinity effect.

Sea surface temperature reconstruction for the middle Miocene Southern Ocean

Magnesium/calcium data from Southern Ocean planktonic foraminifera demonstrate that high-latitude (~55°S) southwest Pacific sea surface temperatures (SSTs) cooled 6° to 7°C during the middle Miocene climate transition (14.2 to 13.8 million years ago). Stepwise surface cooling is paced by eccentricity forcing and precedes Antarctic cryosphere expansion by ~60 thousand years, suggesting the involvement of additional feedbacks during this interval of inferred low-atmospheric partial pressure of CO2 (pCO2). Comparing SSTs and global carbon cycling proxies challenges the notion that episodic pCO2 drawdown drove this major Cenozoic climate transition. SST, salinity, and ice-volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat/vapor transport, triggering ice growth and global cooling.

Nannofossil and stable isotope record across the Paleocene/Eocene Thermal Maximum in ODP Hole 183-1135A

The Paleocene/Eocene Thermal Maximum (PETM, ca. 55 Ma) is an abrupt, profound perturbation of climate and the carbon cycle associated with a massive injection of isotopically light carbon into the ocean-atmosphere system. As such, it provides an analogue for understanding the interplay between phytoplankton and climate under modern anthropogenic global-warming conditions. However, the accompanying enhanced dissolution poses uncertainty on the reconstruction of the affected ecology and productivity. We present a high-resolution record of bulk isotopes and nannofossil absolute abundance from Ocean Drilling Program (ODP) Site 1135 on the Kerguelen Plateau, Southern Indian Ocean to quantitatively constrain for the first time the influence of dissolution on paleoecological reconstruction. Our bulk-carbonate isotope record closely resembles that of the classic PETM site at ODP Site 690 on the opposite side of the Antarctic continent, and its correlation with those from ODP Sites 690, 1262 and 1263 records allows recognition of 14 precessional cycles upsection from the onset of the carbon isotopic excursion (CIE). This, together with a full range of common Discoasteraraneus and an abundance crossover between Fasciculithus and Zygrhablithusbijugatus, indicates the presence of the PETM at Site 1135, a poorly known record with calcareous fossils throughout the interval. The strong correlation between the absolute abundances of Chiasmolithus and coccolith assemblages reveals a dominant paleoecological signal in the poorly preserved fossil assemblages, while the influence of dissolution is only strong during the CIE. This suggests that r-selected taxa can preserve faithful ecological information even in the severely-altered assemblages studied here, and therefore provide a strong case for the application of nannofossils to paleoecological studies in better-preserved PETM sections. The inferred nannoplankton productivity drops abruptly at the CIE onset, but rapidly increases after the CIE peak, both of which may be driven by nutrient availability related to ocean stratification and vertical mixing due to changed sea-surface temperatures.

Diurnal and seasonal measurements of seawater chemistry, temperature and PAR in Hurricane Hole, U.S. Virgin Islands - 2010-2012

Risk analyses indicate that more than 90% of the world's reefs will be threatened by climate change and local anthropogenic impacts by the year 2030 under "business-as-usual" climate scenarios. Increasing temperatures and solar radiation cause coral bleaching that has resulted in extensive coral mortality. Increasing carbon dioxide reduces seawater pH, slows coral growth, and may cause loss of reef structure. Management strategies include establishment of marine protected areas with environmental conditions that promote reef resiliency. However, few resilient reefs have been identified, and resiliency factors are poorly defined. Here we characterize the first natural, non-reef coral refuge from thermal stress and ocean acidification and identify resiliency factors for mangrove-coral habitats. We measured diurnal and seasonal variations in temperature, salinity, photosynthetically active radiation (PAR), and seawater chemistry; characterized substrate parameters; and examined water circulation patterns in mangrove communities where scleractinian corals are growing attached to and under mangrove prop roots in Hurricane Hole, St. John, US Virgin Islands. Additionally, we inventoried the coral species and quantified incidences of coral bleaching, mortality, and recovery for two major reef-building corals, Colpophyllia natans and Diploria labyrinthiformis, growing in mangrove-shaded and exposed (unshaded) areas. Over 30 species of scleractinian corals were growing in association with mangroves. Corals were thriving in low-light (more than 70% attenuation of incident PAR) from mangrove shading and at higher temperatures than nearby reef tract corals. A higher percentage of C. natans colonies were living shaded by mangroves, and no shaded colonies were bleached. Fewer D. labyrinthiformis colonies were shaded by mangroves, however more unshaded colonies were bleached. A combination of substrate and habitat heterogeneity, proximity of different habitat types, hydrographic conditions, and biological influences on seawater chemistry generate chemical conditions that buffer against ocean acidification. This previously undocumented refuge for corals provides evidence for adaptation of coastal organisms and ecosystem transition due to recent climate change. Identifying and protecting other natural, non-reef coral refuges is critical for sustaining corals and other reef species into the future.

Chemical and mineral compositions of sedimentary deposits and magmatic rocks from DSDP Legs 41, 45, 48, and 49

This collective monography by a group of lithologists from the Geological Institute of the USSR Academy of Sciences summarizes materials of the Deep-Sea Drilling Project from the Atlantic Ocean. It gives results of processing materials on the sequences drilled during DSDP Legs 41, 45, 48 and 49. These studies were based on lithological-facial analysis combined with detailed mineralogical-petrographic description. Its chapters give a number of ideas on formation of the Earth sedimentary cover, which can be used for compilation of regional and global schemes of ocean paleogeography, reconstruction of history of some structures in the World Ocean, correlation between sedimentary processes on continents and in oceans, estimation of perspectives for oil and gas fields and ore formation.

Chemical composition of Fe-Mn nodules and crusts from oceans and seas

Fluorine concentrations were determined ionometrically with an error of 0.02% in iron-manganese materials of the ocean. They were: 0.02-0.04% in ocean iron-manganese nodules, with the exception of two specimens (0.08% and 0.20% F); up to 0.02% in iron-manganese nodules of seas; 0.02-1.17% in ore crusts from ocean seamounts; and 0.02% in ore sediments of the Red Sea. Elevated fluorine content of ore crusts is associated with presence of calcium phosphate inclusions in them. Fluorine is not accumulated during iron-manganese nodule mineralization. Its average concentration in the nodules is half that in host deep-sea sediments.

Hydrocarbons, sterols and alkenones at time series station KERFIX

Hydrocarbons, sterols and alkenones were analyzed in samples collected from a 10 month sediment trap time series deployed in the Indian Ocean sector of the Southern Ocean. Fluxes and within-class distributions varied seasonally. During higher mass and organic carbon (OC) flux periods, which occurred in austral summer and fall, fresh marine inputs were predominant. Vertical fluxes were most intense in January, but limited to one week in duration. They were, however, low compared with other oceanic regions. In contrast, low mass and OC flux periods were characterized by a strong unresolved complex mixture (UCM) in the hydrocarbon fraction and a high proportion of stanols as a result of zooplanktonic grazing. Terrigenous inputs were not detectable. The alkenone compositions were consistent with previous data on suspended particles from Antarctic waters. However, UK'37 values diverged from the linear and exponential fits established by Sikes et al. (1997, doi:10.1016/S0016-7037(97)00017-3) in the low temperature range. The seasonal pattern of alkenone production implied that IPT (integrated production temperature) is likely to be strongly imprinted by austral summer and fall SST (sea surface temperature).

Sedimentology and Cd/Ca ratios of benthic foraminifera from ODP Site 172-1060 in the western Nort Atlantic

The Western Boundary Undercurrent (WBUC), off eastern America, is an important component of the Atlantic Meridional Overturning circulation and is the principal route for southward transport of North Atlantic waters and southward return of Southern Source Water (SSW). Here a direct flow speed proxy (mean grain size of the sortable silt) is used to infer the vigour of flow of the palaeo-WBUC at Blake Outer Ridge, (ODP Site 1060, depth 3481 m) during Marine Isotope Stage (MIS) 3. The overall shape of the flow speed proxy record shows a complex pattern of variability, with generally more vigorous flow and larger-scale flow variations between 35 and 60 ka than in the younger part of MIS 3 and MIS 2 (b35 ka). Six events of reduced bottom flow vigour (Slow Events, SEs) occur. These appear uncorrelated with Heinrich events, but are instead synchronous with the warming phases of Antarctic Warm Events A-1 to A-4 (with one new one, A-1a and one poorly defined, 'A-0'). This indicates that Antarctic climate exerts a stronger control on deep flow vigour in the North Atlantic during MIS 3 than Northern Hemisphere climate. The correspondence of SEs with Antarctic warming suggests a weaker WBUC flow due to reduced volume flux at SSW source or reduced SSW density. Because the variability of the lower limb of the WBUC was not connected to sharp North Atlantic changes in temperature, it is unlikely that the Dansgaard/Oeschger cycles were associated with a mode of MOC variation involving wholeocean overturn, but more likely with perturbations of only the shallow Glacial Gulf Stream-Glacial Northern Source Intermediate Water cell. Nutrient proxies (benthic carbon isotopes and Cd/Ca of Uvigerina peregrina) at this site show similar trends to the GRIP delta18O record. This correlation has previously been attributed mainly to hydrographic and flow changes but is here shown to be better explained by variations in surface ocean productivity and subsequent decomposition of 12C rich organic material on the sea floor.

Three species distribution models for the marine diatom Fragilariopsis kerguelensis of the Southern Ocean, links to NetCDF files

Fragilariopsis kerguelensis, a dominant diatom species throughout the Antarctic Circumpolar Current, is coined to be one of the main drivers of the biological silicate pump. Here, we study the distribution of this important species and expected consequences of climate change upon it, using correlative species distribution modeling and publicly available presence-only data. As experience with SDM is scarce for marine phytoplankton, this also serves as a pilot study for this organism group. We used the maximum entropy method to calculate distribution models for the diatom F. kerguelensis based on yearly and monthly environmental data (sea surface temperature, salinity, nitrate and silicate concentrations). Observation data were harvested from GBIF and the Global Diatom Database, and for further analyses also from the Hustedt Diatom Collection (BRM). The models were projected on current yearly and seasonal environmental data to study current distribution and its seasonality. Furthermore, we projected the seasonal model on future environmental data obtained from climate models for the year 2100. Projected on current yearly averaged environmental data, all models showed similar distribution patterns for F. kerguelensis. The monthly model showed seasonality, for example, a shift of the southern distribution boundary toward the north in the winter. Projections on future scenarios resulted in a moderately to negligibly shrinking distribution area and a change in seasonality. We found a substantial bias in the publicly available observation datasets, which could be reduced by additional observation records we obtained from the Hustedt Diatom Collection. Present-day distribution patterns inferred from the models coincided well with background knowledge and previous reports about F. kerguelensis distribution, showing that maximum entropy-based distribution models are suitable to map distribution patterns for oceanic planktonic organisms. Our scenario projections indicate moderate effects of climate change upon the biogeography of F. kerguelensis.