Deep Sea Drilling Program Site Research Articles

British–Irish Ice Sheet and polar front history of the Goban Spur, offshore southwest Ireland over the last 250 000 years

Deep Sea Drilling Program (DSDP) Site 548 was cored in 1984 at a water depth of 1256 m on the Goban Spur, offshore southwest Ireland. Coring retrieved a ~100‐m‐thick Pleistocene contourite sequence. This study uses planktonic foraminiferal assemblage and benthic foraminiferal oxygen isotope analyses to establish an age model for the upper 40 m of this core. This site's multidisciplinary analyses of planktonic foraminiferal assemblages, lithic grains, facies and calcium carbonate concentration reveal a 250 000‐year record of the North Atlantic polar front variability and British–Irish Ice Sheet (BIIS) history. The sequence is characterized by alternations of ice rafted debris (IRD) laden pelagic mud facies with calcium carbonate‐rich silty sand contourite facies that track glacial/interglacial cycles. The polar front migrated southward across the area several times during glacial maxima and stadial periods, while warmer Mediterranean Outflow Water (MOW) flowed northward across the region during interglacial and interstadial periods depositing contourites. Lithic analyses reveal a complex history of IRD deposition associated with iceberg calving from the Laurentide Ice Sheet and northwest European ice sheets, mainly the BIIS. Comparison between the Goban Spur (DSDP Site 548) and the Celtic Margin (MD03‐2692) and central North Atlantic Integrated Ocean Drilling Program (IODP) Site U1308 suggests differences between the ‘non‐Laurentide Ice Sheet’ Heinrich Events (HE) 6 and 3 at the Goban Spur, with IRD from the BIIS being prominent during HE 6 and IRD from other European ice sheets north of the BIIS likely being more dominant during HE 3. The nature of lithics in IRD‐rich horizons during Terminations 3, 3A, 2 and 1 suggests significant iceberg calving episodes preceding BIIS retreat during the onset of interstadial intervals.

New evidences of subaerial volcanism as a trigger for the Kilian event (Aptian-Albian transition) and major climatic changes from offshore Morocco (DSDP Site 545)

The Aptian-Albian transition is characterized by the presence of four organic-rich intervals all linked with major disturbances of the carbon cycle. Among these, the second subevent of the oceanic anoxic event (OAE) 1b, also called Kilian event, has an Aptian-Albian transition age and is characterized by a negative carbon isotope excursion. On the contrary of the Paquier OAE1b subevent, the Kilian event was not extensively studied and its triggering mechanisms and its consequences on regional climates remain uncertain. Here we present a geochemical (Rock-Eval, Mercury) and mineralogical (clay minerals) study on late Aptian-early Albian sediment cores from the Deep-Sea Drilling Program (DSDP) Site 545 (offshore Morocco, Eastern North Atlantic) where a Kilian level equivalent is present. Mercury (Hg) content results show two main peaks in the late Aptian, immediately below and above the Kilian level equivalent. The absence of correlations between Hg and total organic carbon and Hg and CaCO 3 indicates that the mercury content is mainly related to subaerial volcanic activity, probably issued from the emplacement of the Kerguelen large igneous province in the Indian Ocean. Mineralogical analyses show that the clay content, in our studied interval, mainly reflect the weathering and climatic conditions in Northwest Africa. The evolution in clay mineral assemblages depicts three distinctive climatic intervals: (i) a seasonally contrasted semi-arid climate below the first Hg anomaly; (ii) a moister and warmer climate during the Kilian level equivalent deposition; and (iii) a rapid transition toward more arid climate post Kilian level equivalent deposition that is linked with the second Hg anomaly (large increases in illite and palygorskite). Therefore, our study confirms that the Kerguelen volcanic activity was probably the trigger of the Kilian event and shows that the resulting changes in the carbon cycle caused two major climate changes before and after the Kilian event and a long term aridification of Northwest Africa. • Hg anomalies occurs immediately below and above the Kilian level. • Kerguelen volcanic activity was likely the trigger of the Kilian event • Three distinct climatic periods can be recognized along the late Aptian. • late Aptian represents a turning point for the Cretaceous climate changes.

Collapse and recovery of the marine biological carbon pump across the Cretaceous-Paleogene mass extinction

<p indent="0mm">The Cretaceous-Paleogene (K-Pg) mass extinction that ended the age of the dinosaurs occurred 66 million years ago, with competing hypotheses including the Deccan Traps volcanic eruption, climate change, and sea level change. However, it is the Chicxulub asteroid impact that has been widely accepted as the most plausible cause. Whatever the reason, the Earth’s ecological environment changed dramatically, leading to a mass extinction of both terrestrial and marine life. Primary producers lie at the base of the food chain and support higher trophic levels, so play an important role in the marine ecosystem. The predominant primary producers in the ocean, coccolithophores (phytoplankton with small CaCO₃ scales covering their cell surface), were among those most severely devastated by the K-Pg mass extinction. So, studying fossil coccolithophores across the K-Pg boundary can provide a better understanding of the destruction and post-event recovery processes of marine primary production (PP) and export production (EP), and the changes and controlling mechanisms of the marine biological carbon pump in the current global climate change. The four hypotheses previously proposed to interpret the post-event primary production, namely strangelove ocean (collapsed PP), living ocean (collapsed EP), resilient ocean (continued PP and EP), and heterogeneous ocean (geography-dependent responses of PP and EP), are illustrated and compared, and their pros and cons reviewed. A dataset is compiled from multiple locations in the global ocean basin including Deep Sea Drilling Program Site 465, Ocean Drilling Program Sites 690, 1210, and 1262, and the outcrop at El Kef (Tunisia), with each location having a high-precision cyclostratigraphic time control and an ocean surface-to-deep (bulk carbonate-benthic foraminifera) <italic>δ</italic>¹³C vertical gradient. This global dataset is analyzed to explore the changes in the efficiency of global marine biological carbon pump after the K-Pg boundary event. Three important patterns are observed: (1) Prior to the K-Pg event, the vertical <italic>δ</italic>¹³C gradient in all ocean basins falls between 0.8‰–1.5‰ and is consistent with that in the modern ocean, and this gradient seems to gradually increase from the shelf to the deep ocean possibly due to higher efficiency of the biological carbon pump in the open ocean commonly characterized by oligotrophy; (2) the global ocean vertical <italic>δ</italic>¹³C gradient collapses after the K-Pg event, suggesting drastic changes in primary and/or export production in the euphotic zone; (3) the vertical <italic>δ</italic>¹³C gradient collapse results from the abrupt negative shift of the surface ocean <italic>δ</italic>¹³C, and the magnitude of this negative shift gradually decreases from the continental shelf to the deep sea, which may be related to the selective extinction of shallow-water grazers, swimming organisms and plankton, as well as the limited buffering capacity of shelf environments. After the K-Pg event, the main primary producers change from larger coccolithophores to smaller picoplankton, and the more recalcitrant dissolved organic carbon is able to sink to the seafloor due to the operation of the microbial carbon pump in the photic zone, leading to sustained efficiency of the biological carbon pump. Although the picoplankton-dominated biological carbon pump is not as efficient as that by coccolithophores, it is still capable of removing enough nutrients and harmful substances from the photic zone via long-term operation, not only providing food for higher trophic level organisms, but improving the marine physicochemical environment that deteriorated after the K-Pg asteroid impact. This process paves the way for the restoration and development of the entire marine ecosystem. The switch of key marine primary producers and the controlling factors involved are critical scientific issues that deserve more focus in future studies of the deep-time marine carbon cycle. The regional or global variation patterns in the biological carbon pump after the K-Pg event reveal how different marine ecosystems operate under extreme environmental stress, and provide a reference for better understanding and predicting how they respond to the ongoing rapid global climate change.

A re-evaluation of the basal age in the DSDP hole at Site 534, Central Atlantic

For 30 years, the initial sedimentation following the opening of the western Central Atlantic has been considered to be of Middle Callovian age (approximately 164.5 Ma) based on the biochronostratigraphical estimation for the basal sedimentary unit of the borehole from Site 534A of the Deep Sea Drilling Program (DSDP). That age has been used in kinematic models of the opening of the Central Atlantic. A reconsideration of the available biochronostratigraphical data and correlation of the δ¹³Ccarb record from Site 534A with those from the Tethyan and North Atlantic records suggest that the initial sedimentation at Site 534A is, in fact, of Middle Oxfordian age (approximately 160.6 Ma). The high biostratigraphic similarity among the basal sedimentary units of the boreholes at DSDP Site 534A and Ocean Drilling Program Site 801C in the Western Pacific suggest the same age for both sites. The Middle Oxfordian δ¹³Ccarb records from the different sites covary, marking the same palaeoenvironmental changes, although such an agreement was not previously acknowledged. A combination with additional data proposes that Middle Oxfordian age corresponds to the precise date of the opening of the Hispanic Corridor between the Atlantic and Pacific oceans.

Late Cretaceous-Early Paleogene (Turonian? to early Danian) planktic foraminifera from DSDP site 356: a biostratigraphic reappraisal

Biostratigraphic results obtained with a systematic study of the planktic foraminiferal assemblages recovered from Upper Cretaceous-Lower Paleogene strata (Turonian? to early Danian in age) of Deep Sea Drilling Program (DSDP) Site 356, Sao Paulo Plateau, are presented and discussed herein. Fifty-nine planktic foraminiferal species were identifi ed within the studied interval, enabling the identifi cation of 11 planktic foraminiferal zones (Turonian? to early Danian in age): Marginotruncana schneegansi, Dicarinella concavata, Dicarinella asymetrica, Globotruncanita elevata, Contusotruncana plummerae, Radotruncana calcarata, Globotruncanella havanensis, Pseudoguembelina palpebra, Abathomphalus mayaroensis, Pseudoguembelina hariaensis and Pα. An unconformity spanning at least 0.96 Ma could also be suggested within core 31 (Maastrichtian in age), due to the absence of the Racemiguembelina fructicosa Interval Zone from the studied section. High sedimentation rates were estimated within the Santonian (Dicarinella asymentrica Total-range Zone) and the uppermost Maastrichtian (Pseudoguembelina hariaensis Interval Zone) of DSDP site 356, while lower and more constant values were suggested for the Campanian-lower Maastrichtian interval (Globotruncanita elevata Partial-range Zone to Pseudoguembelina palpebra Interval Zone). The reliability in identifying the Contusotruncana plummerae Interval Zone (Campanian in age) in Cretaceous sections of the South Atlantic Ocean is confi rmed herein.

Pollen-corrected leaf wax D/H reconstructions of northeast African hydrological changes during the late Miocene

Plant leaf wax hydrogen isotope (δDwax) reconstructions are increasingly being used to reconstruct hydrological change. This approach is based upon the assumption that variations in hydroclimatic variables, and in particular, the isotopic composition of precipitation (δDP), dominate δDwax. However modern calibration studies suggest that offsets between plant types may bias the δDwax hydrological proxy at times of vegetation change. In this study, I pair leaf wax analyses with published pollen data to quantify this effect and construct the first vegetation-corrected hydrogen isotopic evidence for precipitation (δDcorrP). In marine sediments from Deep Sea Drilling Program Site 231 in the Gulf of Aden spanning 11.4–3.8Ma (late Miocene and earliest Pliocene), I find 77‰ swings in δDwax that correspond to pollen evidence for substantial vegetation change. Similarities between δDP and δDcorrP imply that the hydrological tracer is qualitatively robust to vegetation change. However, computed vegetation corrections can be as large as 31‰ indicating substantial quantitative uncertainty in the raw hydrological proxy. The resulting δDcorrP values quantify hydrological change and allow us to identify times considerably wetter than modern at 11.09, 7.26, 5.71 and 3.89Ma. More generally, this novel interpretative framework builds the foundations of improved quantitative paleohydrological reconstructions with the δDwax proxy, in contexts where vegetation change may bias the plant-based proxy. The vegetation corrected paleoprecipitation reconstruction δDcorrP, represents the best available estimate as proof-of-concept, for an approach that I hope will be refined and more broadly applied.

Rock‐magnetic artifacts on long‐term relative paleointensity variations in sediments

Long‐term changes of geomagnetic field intensity, including possible dependence on lengths of polarity intervals, provide fundamentally important information for understanding the geodynamo. A positive correlation between paleointensity and polarity interval length was previously suggested from an Oligocene (ca. 23–34 Ma) relative paleointensity record at Deep Sea Drilling Program Site 522 in the Atlantic Ocean, which is the only continuous paleointensity data set published so far for this age interval. We have conducted a paleomagnetic study of Eocene to Oligocene sediments at three sites in the eastern equatorial Pacific Ocean. Our objectives include revisiting the issue of the paleointensity‐polarity length correlation. Magnetic properties of the sediments meet the frequently used criteria for reliable relative paleointensity estimation. Although short‐wavelength normalized remanence intensity fluctuations associated with polarity boundaries and possible geomagnetic excursions agree among the three sites, long‐term changes are inconsistent. Apparent positive correlation between normalized intensity and polarity length was observed, but the normalized intensity has an obvious anti‐correlation with the ratio of anhysteretic remanent magnetization (ARM) to isothermal remanent magnetization (IRM), which is mainly controlled by the relative abundance of biogenic and terrigenous magnetic minerals. Furthermore, the normalized intensity correlates with sedimentation rate. These facts indicate a lithological contamination on the normalized intensity records. The dependence on ARM/IRM and sedimentation rate is also evident at Site 522. It is inferred that variations in sedimentation rate and the relative abundance of biogenic magnetite on depositional remanent magnetization acquisition efficiency may not be well compensated by the normalization. It is therefore premature to conclude that stronger geomagnetic fields were recorded during longer polarity intervals from currently available normalized intensity records.

Climate-driven body-size trends in the ostracod fauna of the deep Indian Ocean

Abstract: Body size is a common focus of macroevolutionary, macroecological and palaeontological investigations. Here, we document body-size evolution in 19 species-level ostracod lineages from the deep Indian Ocean (Deep Sea Drilling Program Site 253) over the past 40 myr. Body-size trajectories vary across taxa and time intervals, but most lineages (16/19) show net gains in body size. Because many modern ostracod taxa are larger in colder parts of their geographical range, we compared the timing and magnitude of these size changes to established Cenozoic deep-water cooling patterns confirmed through δ18O measurements of benthic foraminifera in the samples studied. These data show a significant negative correlation between size changes and temperature changes (ostracods get larger as temperatures get colder), and that systematic size increases only occur during intervals of sustained cooling. In addition, statistical support for an explicit temperature-tracking model exceeds that of purely directional evolution. We argue that this Cope’s Rule pattern is driven by secular changes in the environment, rather than any universal or intrinsic advantages to larger body sizes, and we note some difficulties in the attempts to link Cope’s Rule to observations made within a single generation.

West Antarctic Ice Sheet evolution: New insights from a seismic tomographic 3D depth model in the Eastern Ross Sea (Antarctica)

This work presents the results of the research project WISE (West Antarctic Ice Sheet Evolution) the main aim of which is to provide new insights about WAIS (West Antarctic Ice Sheet) evolution in the Eastern Ross Sea (Antarctica) since the late Miocene times, from morphological and geophysical analysis of glacial sediments. A square grid of 1230 km high-resolution multi-channel seismic reflection data, multi-beam bathymetry data and nine Sound Velocity Profiles (SVP) were collected in January 2006 from the northwestern sector of the Glomar Challenger Basin (Eastern Ross Sea), and tied to Deep Sea Drilling Program site 271. This work provides a detailed seismic stratigraphic analysis of the Miocene–Quaternary Ross Sea Sequences (RSS) 5–8, previously mapped using regional lower-resolution seismic profiles. Eight seismic units are identified on WISE high-resolution seismic profiles. These units and their boundaries in most of the cases match with previously published stratigraphy, although three new horizons have been identified as reflecting lateral and time-transgressive facies changes. We applied travel time reflection tomography to obtain a detailed 3D model of the investigated area, defined by a depth–seismic velocity volume and by the geometry of 5 selected surfaces. The resulting model is used to reconstruct the geomorphological and depositional history of this sector of the outer continental shelf and to infer ice sheet dynamics during Miocene to Quaternary times. A high velocity anomaly observed in units below the Ross Sea Unconformity 2 (RSU2) of Pliocene age (3–3.7 Ma) is interpreted as indicative of glacial sediments over-compacted by large scale grounding ice sheet expansion. The low velocity of the unit above RSU1 (ca. 0.7 Ma), is associated with normally compacted sediments. Contour depth and isopach maps show migration of the sediment depocenter from RSS-6 to RSS-8, indicating a change in the direction of grounding ice advance over the continental shelf. Acoustic facies and seismic velocity changes occurred during deposition of RSS-8, possibly reflecting a major change in the WAIS dynamics in late Pliocene–Quaternary times.

Mid‐Miocene paleoproductivity in the Atlantic Ocean and implications for the global carbon cycle

A prominent, middle Miocene (17.5–13.5 Ma) carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13C depleted organic carbon in marine sediments or enhanced carbon burial in peat/lignite deposits on land. Here we test the hypothesis that the marine δ13C record reflects a change in productivity with proxy records from three Atlantic Ocean sites (Deep Sea Drilling Program Site 608 and Ocean Drilling Program Sites 925 and 1265). Our multiproxy approach is based on benthic foraminiferal accumulation rates, elemental ratios (Ba/Al and P/Al), the δ13C of bulk sedimentary organic matter, and dissolution indices. We compare these proxies to benthic foraminiferal δ13C values measured on the same samples. Our results indicate that marine paleoproductivity in the Atlantic Ocean is not related to the benthic foraminiferal δ13C excursion. A numerical box model confirms that marine productivity cannot account for the δ13C maximum. The model shows that sequestration of 1.5 × 1018 mol C in the terrestrial realm over a period of 3 Ma leads to a 0.9‰ δ13C increase in the deep ocean, which is near the observed records. Therefore, an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean's carbon pool with 13C, which is consistent with coeval lignite deposits worldwide. The δ13C values of bulk sedimentary organic matter parallel the δ13C of dissolved inorganic carbon as reflected by benthic foraminiferal δ13C values suggesting no significant change in atmospheric pCO2 levels over the investigated period.

Establishment of the western Pacific warm pool during the Pliocene: Evidence from planktic foraminifera, oxygen isotopes, and Mg/Ca ratios

This study presents new evidence of when and how the Western Pacific Warm Pool (WPWP) was established in its present form. We analyzed planktic foraminifera, oxygen isotopes, and Mg/Ca ratios in upper Miocene through Pleistocene sediments collected at Deep Sea Drilling Program (DSDP) Site 292. These data were then compared with those reported from Ocean Drilling Program (ODP) Site 806. Both drilling sites are located in the western Pacific Ocean. DSDP Site 292 is located in the northern margin of the modern WPWP and ODP Site 806 near the center of the WPWP. Three stages of development in surface-water conditions are identified in the region using planktic foraminferal data. During the initial stage, from 8.5 to 4.4 Ma, Site 806 was overlain by warm surface water but Site 292 was not, as indicated by the differences in faunal compositions and sea-surface temperature (SST) between the two sites. In addition, the vertical thermal gradient at Site 292 was weak during this period, as indicated by the small differences in the δ 18O values between Globigerinoides sacculifer and Pulleniatina spp. During stage two, from 4.4 to 3.6 Ma, the SST at Site 292 rapidly increased to 27 °C, but the vertical thermal gradient had not yet be strengthened, as shown by Mg/Ca ratios and the presence of both mixed-layer dwellers and thermocline dwellers. Finally, a warm mixed layer with a high SST ca. 28 °C and a strong vertical thermal gradient were established at Site 292 by 3.6 Ma. This event is marked by the dominance of mixed-layer dwellers, a high and stable SST, and a larger differences in the δ 18O values between G. sacculifer and Pulleniatina spp. Thus, evidence of surface-water evolution in the western Pacific suggests that Site 292 came under the influence of the WPWP at 3.6 Ma. The northward expansion of the WPWP from 4.4 to 3.6 Ma and the establishment of the modern WPWP by 3.6 Ma appear to be closely related to the closure of the Indonesian and Central American seaways.

East Mariana Basin tholeiites: Cretaceous intraplate basalts or rift basalts related to the Ontong Java plume?

Studies of seafloor magnetic anomaly patterns suggest the presence of Jurassic oceanic crust in a large area in the western Pacific that includes the East Mariana, Nauru and Pigafetta Basins. Sampling of the igneous crust in this area by the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Program (ODP) allows direct evaluation of the age and petrogenesis of this crust. ODP Leg 129 drilled a 51 m sequence of basalt pillows and massive flows in the central East Mariana Basin. 40 Ar 39 Ar ages determined in this study for two Leg 129 basalts average 114.6 ± 3.2 Ma. This age is in agreement with the Albian-late Aptian paleontologic age of the overlying sediments, but is distinctively younger than the Jurassic age predicted by magnetic anomaly patterns in the basin. Compositionally, the East Mariana Basin basalts are uniformly low-K tholeiites that are depleted in highly incompatible elements compared to moderately incompatible ones, which is typical of mid-ocean ridge basalts (MORB) erupted near hotspots. The Sr, Nd and Pb isotopic compositions of the tholeiites ( 87 Sr 86 Sr init = 0.70360–0.70374 ; 143 Nd 144 Nd init = 0.512769–0.512790 ; 206 Pb 204 Pb meas = 18.355–18.386 ) also overlap with some Indian Ocean Ridge MORB, although they are distinct from the isotopic compositions of Jurassic basalts drilled in the Pigafetta Basin, the oldest Pacific MORB. The isotopic compositions of the East Mariana Basin tholeiites are also similar to those of intraplate basalts, and in particular, to the isotopic signature of basalts from the nearby Ontong Java and Manihiki Plateaus. The East Mariana Basin tholeiites also share many petrologic and isotopic characteristics with the oceanic basement drilled in the Nauru Basin at DSDP Site 462. In addition, the new 110.8 ± 1.0 Ma 40 Ar 39 Ar age for two flows from the bottom of Site 462 in the Nauru Basin is indistinguishable from the age of the East Mariana Basin flows. Thus, while magnetic anomaly patterns predict that the igneous basement in the Nauru and East Mariana Basins is Jurassic in age, the geochemical and chronological results discussed here suggest that the basement formed during a Cretaceous rifting event within the Jurassic crust. This magmatic and tectonic event was created by the widespread volcanism responsible for the genesis of the large oceanic plateaus of the western Pacific.