Piston Cores Research Articles

An early to mid-Pleistocene deep Arctic Ocean ostracode fauna with North Atlantic affinities

An early to middle Pleistocene ostracode fauna was discovered in sediment core P1-93-AR-23 (P23, 76.95°N, 155.07°W) from 951meter water depth from the Northwind Ridge, western Arctic Ocean. Piston core P23 yielded more than 30,000 specimens and a total of about 30 species. Several early to mid-Pleistocene species in the genera Krithe, Echinocythereis, Pterygocythereis, and Arcacythere are now extinct in the Arctic and show taxonomic affinities to North Atlantic Ocean species. Our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the Mid-Pleistocene Transition (MPT, ~1.2 to 0.7Ma) and the Mid-Brunhes Event (MBE, ~400ka) reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400,000years.

Chronostratigraphy and paleoceanography of a piston core (EBP-3) from the South Korea Plateau in the East Sea (Japan Sea)

A piston core (EBP-3) collected from the South Korea Plateau in the East Sea (Japan Sea) preserved typical alternations of thick, dark laminated mud layers and bioturbated hemipelagic mud layers, but included several intercalated volcanic lapilli layers. The age estimate of core EBP-3 was aided by correlation of biostratigraphic radiolarian data, the abundance of microfossils (warm-water radiolarians), and geochemical properties (CaCO3) with the proxies of the well-dated core MD01-2407 obtained from the Oki Ridge. A part from the Marine Isotope Stage (MIS) 11 to MIS 9 in the middle of core EBP-3 was missing, presumably because of erosion following the abrupt deposition of a volcanic lapilli layer. Despite some uncertainty, the age estimate of core EBP-3 revealed that the lower part of core EBP-3 represents MIS 13, as was also evident from a comparison with the oxygen isotope stratigraphy.Downcore biogenic opal and CaCO3 variations in core EBP-3 exhibited less distinct orbital-scale cyclic changes than cores from other areas in the East Sea (Japan Sea). However, differences in features were discernible between MIS 2 and MIS 12 in terms of their lithology and CaCO3 constituent, although both periods were characterized by relatively high levels of CaCO3 (about 30% for MIS 2 and about 50% for MIS 12). MIS 2 preserved a typical thick, dark laminated mud layer, whereas MIS 12 preserved a distinctly light mud layer with thin parallel laminations. This difference of the lithologic facies between MIS 2 and MIS 12 highlighted a discrepancy among the major constituents, indicating that planktonic foraminifera were dominant in MIS 2, whereas coccolithophores were dominant in MIS 12. Our results suggest that the thinly-laminated light mud layer, which is characterized by a high CaCO3 content primarily composed of coccolithophores in MIS 12, can be used as a reliable time marker for the establishment of chronostratigraphy in the East Sea.

Revisiting the origin of organic matter and depositional environment of sediment in the central Ulleung Basin, East Sea since the late Quaternary

By analyzing sedimentary geochemical data from three piston cores in the central Ulleung Basin, East Sea, we discuss the origin of organic matter and the depositional environment of sediments from Marine Isotope Stage (MIS) 3 to 1. Downcore profiles show that the values of TOC (Total Organic Carbon), TN (Total Nitrogen), and δ13Corg are the lowest values during MIS 2 and the highest during MIS 1. The relationship between TOC/TN and δ13Corg shows that most data fall in the region of the marine algae irrespective of MIS stage, which illustrates that the organic matter has been predominantly produced by a marine source rather than by a terrestrial source since the late Quaternary. However, depleted δ13Corg values are discretely observed during MIS 2 and MIS 3, particularly in dark laminated mud (DLM), which appears to reflect the influence of episodic event by the East Asian Monsoon rather than the organic matter source changing by lower sea level.Previous sedimentological studies in the Ulleung Basin reported that the depositional environment of sediment in MIS 2 was more reducing than during MIS 1 and MIS 3, but our geochemical data do not support this interpretation. The abundance of most redox-sensitive trace elements (e.g., Mn, V, U, and Mo) has not significantly varied from MIS 3 to MIS 1. In addition, the ratios of redox-sensitive trace elements (e.g., Ni/Co, V/Cr, V/Ni, U/Th, and V/(V + Ni)) indicate a predominantly oxic or suboxic environment. The bottom water condition was similarly oxic to suboxic, during times of sediment deposition since the late Quaternary. The sedimentary layers containing tephra and foraminiferal shell fragments illustrate abnormal element/Al ratios, suggesting that these allochthonous sediment sources are one of important factors controlling the geochemical composition of sediments in the Ulleung Basin.

Tsunami-generated sediment wave channels at Lake Tahoe, California-Nevada, USA

A gigantic ∼12 km 3 landslide detached from the west wall of Lake Tahoe (California-Nevada, USA), and slid 15 km east across the lake. The splash, or tsunami, from this landslide eroded Tioga-age moraines dated as 21 ka. Lake-bottom short piston cores recovered sediment as old as 12 ka that did not reach landslide deposits, thereby constraining the landslide age as 21–12 ka. Movement of the landslide splashed copious water onto the countryside and lowered the lake level ∼10 m. The sheets of water that washed back into the lake dumped their sediment load at the lowered shoreline, producing deltas that merged into delta terraces. During rapid growth, these unstable delta terraces collapsed, disaggregated, and fed turbidity currents that generated 15 subaqueous sediment wave channel systems that ring the lake and descend to the lake floor at 500 m depth. Sheets of water commonly more than 2 km wide at the shoreline fed these systems. Channels of the systems contain sediment waves (giant ripple marks) with maximum wavelengths of 400 m. The lower depositional aprons of the system are surfaced by sediment waves with maximum wavelengths of 300 m. A remarkably similar, though smaller, contemporary sediment wave channel system operates at the mouth of the Squamish River in British Columbia. The system is generated by turbidity currents that are fed by repeated growth and collapse of the active river delta. The Tahoe splash-induced backwash was briefly equivalent to more than 15 Squamish Rivers in full flood and would have decimated life in low-lying areas of the Tahoe region.

Late quaternary glacial/interglacial cyclicity models of the Red Sea

The benthic foraminiferal faunas from samples of two piston cores retrieved along a north–south transect in the Red Sea were studied. The northern core was collected during Meteor cruise M 31/2, while the southern one was collected during the Sonne cruise 121. Benthic foraminiferal faunas from both sites exhibit large variability with respect to density, diversity, species composition and assemblages combined with stable oxygen and carbon isotope records of planktic and benthic foraminifera. One hundered thirty benthic foraminiferal species were identified in the investigated cores. The faunal data set of the northern core was reduced to five assemblages (factors) while the southern one was reduced to four assemblages. All assemblages were ranked according to their ecological significance. Besides, relative abundance of major benthic foraminiferal suborders [Textulariina (agglutinating foraminifera), Miliolina and Rotaliina], in addition to infaunal/epifaunal relative abundance were used as paleoenvironmental proxies allowing the reconstruction of past changes in deep-water salinity, ventilation and organic carbon fluxes at the sea-floor. Four distinct glacial/interglacial cycle during the past 380 Kyr have been recognized in the Red Sea. The identified four cycles reveal deviation in deep-sea ecosystem between the northern and southern Red Sea. In the northern Red Sea salinity fluctuations, productivity and deep-water ventilation and formation had the major impact on benthic foraminiferal pattern corresponding to glacial/interglacial cycles and glacio-eustatic sea level changes coupled with the impact of Mediterranean climate regime. On the otherhand, in the southern Red Sea region the oscillation trend of benthic foraminiferal pattern within the glacials and interglacials stages indicates a high frequency environmental alternation. This alternation is consistent with the extent of NE monsoonal wind that controls the intensity and extension of the productivity, which in turn determine organic matter fluxes and oxygen level at the sea floor.

Environmental evolution of the southern Chukchi Sea in the Holocene

The molluscan shells from three drill and two piston cores obtained in the southern Russian sector of the Chukchi Sea are dated by the AMS 14C measurement method back to 0.8–3.5 and 9.2–10.5 ka. The period of 9–10 ka was marked by increased sedimentation rates related to the transgression onset. The fossils in the lower Holocene section exhibit the successive upward replacement of brackish-water organisms by their marine counterparts. After the opening of the Bering Strait in the middle Holocene, the sedimentation was under influence of the increased bioproductivity of the waters. The climatic optimum in the Chukotka region corresponds to the early Holocene, while the late Holocene was characterized by the wider development of the ice cover on the shelf.

Impact of river channel shifts on tetraether lipids in the Rhône prodelta (NW Mediterranean): Implication for the BIT index as an indicator of palaeoflood events

We tested the applicability of the BIT (branched and isoprenoid tetraether) index as a proxy for palaeoflood events in the river-dominated continental margin of the Gulf of Lions (NW Mediterranean). We compared the concentrations of branched glycerol dialkyl glycerol tetraethers (br GDGTs) and crenarchaeol in suspended particulate matter (SPM) collected downstream in the Rhône River, as well as in surface sediments and a ca. 8m piston core from the Rhône prodelta. The core covered the last 400yr, with four distinct intervals recording the river influence under natural and man-induced shifts in four main channels of the river mouth (Bras de Fer, Grand Rhône, Pégoulier and Roustan). The results indicate that there are mixed sources of br GDGTs and crenarchaeol in the prodelta, complicating application of the BIT index as an indicator of continental organic carbon input and thus as a palaeoflood proxy. However, the sedimentary BIT record for the period when continental material was delivered by the river more directly to the core site (Roustan phase; 1892 to the present) mimics the historical paleoflood record. This shows the potential of the BIT index as a palaeoflood proxy, provided that the delivery route of the continental material by rivers to the core sites remains constant over time. The study also highlights the idea that shifts in river channels should be taken into account for the use of the BIT index as a palaeoflood proxy.

The role of North Brazil Current transport in the paleoclimate of the Brazilian Nordeste margin and paleoceanography of the western tropical Atlantic during the late Quaternary

Reconstructions of surface paleoceanographic conditions of the western equatorial Atlantic and past climates of the adjacent Northeast Brazilian (the “Nordeste”) continental margin were undertaken by analyzing sediments from a piston core and associated gravity and box cores recovered from 3107 meter water depth at 0° 20′ N on the equatorial Brazilian continental slope. The record is dated by radiocarbon analysis and oxygen isotopic stratigraphy of planktonic foraminifers and spans from near-modern to approximately 110 Ka.High-resolution XRF analysis provides insight into the paleoclimate history of the Nordeste during the last glacial interval. Several large-amplitude and abrupt peaks are observed in the time series of Ti/Ca and are usually accompanied by peaks of Fe/K. Together these record periods of increased precipitation and intense weathering on the adjacent continent and increased terrestrial sediment discharge from Nordeste rivers into the Atlantic. Within the limits of dating accuracy, most Ti/Ca peaks correlate with Heinrich events in the North Atlantic. This record thus corroborates, and extends back in time, the previous record of Arz et al. (1998) determined on sediment cores from farther southeast along the Nordeste margin.Stable oxygen isotopic analysis and Mg/Ca paleothermometry on the near-surface-dwelling planktonic foraminiferal species Globierinoides ruber find that mean sea-surface temperature (SST) during glacial time (20–55 Ka, n=97) was 23.89±0.79°C and the mean SST during the late Holocene (0–5 Ka, n=14) was 26.89±0.33°C. SSTs were 0.5–2°C higher and inferred sea-surface salinities were lower during most of the periods of elevated Ti/Ca, thus, as observed in previous studies, the western equatorial Atlantic was warm (at least locally) and the adjacent southern tropical continent was wet at the same time that the high-latitude North Atlantic was cold.Using the SYNTRACE-CCSM3 fully coupled climate model with transient forcing for the period 22 Ka to present, we find that decreased transport of the North Brazil Current co-occurs with reduced Atlantic meridional overturning circulation, and colder-than-normal SSTs in the North Atlantic region. These simulated conditions are invariably associated with significantly increased precipitation in the Nordeste region.

Influence of sampling on magnetic susceptibility anisotropy of soft sediments: comparison between gravity and piston cores

Anisotropy of magnetic susceptibility (AMS) has been used extensively for determining mineral orientatrections. In terms of the sample coordinate, Kmax declinations in the three gravity cores are oriented along the core-splitting surface, whereas Kmax declinations in the three piston cores are perpendicular to the splitting surface. We attribute the artificial AMS to the stress created by the deformation of core liners when being split. When interpreting AMS data from sediment cores, it is necessary to investigate the influence of sampling using the sample coordinates. In this paper, we also report over-sampling and under-sampling of piston cores from a comparison of down-core magnetic susceptibility variations between piston and gravity cores. It is noteworthy that under-sampling as well as over-sampling can occur in the uppermost few meters of piston cores.

Geochemical response to pulsed sedimentation: Implications for the use of Mo as a paleo-proxy

Deglacial sediments in piston core JT96-02 from the continental slope off western Canada contain numerous centimeter-thick, iron sulfide-rich layers. Major and minor element chemistry, as well as C and N isotopic data suggest that these layers represent background hemipelagic sedimentation. Intervening gray silty clay layers, each of which exhibits a fining-upward trend, are distal turbidites. The iron sulfides precipitated in response to the emplacement of each turbidite, which slowed oxygen diffusion into the sediment allowing anoxic conditions to develop in the underlying relatively organic-rich deposits. Resulting sulfate reduction and precipitation of Fe-sulfide fostered Mo enrichment (>2μg/g). It may also explain Ni, Cr, V, and Co enrichments, although differences in detrital mineralogy cannot be ruled out, particularly for Ni and Cr. Rhenium is also enriched, albeit slightly, within the sulfide layers, but low Re/Mo ratios (~0.78ng/g/μg/g) suggest that anoxic conditions developed very rapidly. Metals with high lithogenic concentrations (Cd and U) are not obviously enriched in the sulfide layers because there was insufficient time for noticeable authigenic accumulation before deposition of the next turbidite which severed diffusive communication with overlying seawater, the primary source of metals. Silver is also slightly higher in the sulfide layers, possibly linked to higher marine organic matter content. In summary, the pulsed character of sedimentation during the deglaciation led to episodic enrichment of Mo and occurred independently of changes in bottom water oxygen or organic carbon content. This observation potentially complicates the use of Mo as a paleo-proxy in some continental margin environments.

Presentation of the 2013 Charles Schuchert Award of the Paleontological Society to Bridget S. Wade

The Charles Schuchert Award is presented to a person under 40 whose work early in his or her career reflects excellence and promise in the science of paleontology, and thus reflects the objectives and standards of the Paleontological Society. Dr. Bridget S. Wade is the 2013 recipient of the Charles Schuchert Award. Since receiving her Ph.D. Bridget has produced outstanding achievements in micropaleontology and paleoceanography. She is internationally recognized for her research on Paleogene climate and oceanography, Cenozoic planktonic foraminiferal taxonomy, evolution, and extinction. She has broadened her research skills through numerous collaborations and work at multiple institutions, including Leeds University (B.Sc., Advanced Research Fellowship), the University of Edinburgh (Ph.D.), Cardiff University (NERC Postdoctoral Fellowship), Rutgers University (Lindemann Research Fellowship), and Texas A&M University (Assistant Professorship). She recently was appointed to a Professorship in the Department of Earth Sciences at University College, London. Since receiving her Ph.D. in 2001, Bridget's research quality and productivity have been consistently high, having published a total of 41 papers in high profile, peer reviewed journals and among these she is the lead author on 15 papers. Her research integrates geology, foraminiferal taxonomy and biostratigraphy with stable isotope geochemistry, astrochronology, and magnetostratigraphy, the latter of which enables high-resolution age stratigraphic control. Bridget's extensive field work includes ocean drilling and piston coring cruises, field work in Cyprus, Italy, Tanzania, Mozambique, Trinidad, Puerto Rico, Australia, and various regions of the U.S. has provided detailed links between biotic, paleoclimatic and paleoceanographic events that occurred during the Cenozoic. Her research has led to significant improvements in the Cenozoic time scale and increased accuracy and resolution of the timing of evolution, extinction and acme events for Cenozoic planktonic foraminifera. Bridget is a leading contributor to studies of critical intervals of climate change during the Cenozoic. Some of Bridget's more …

Physical and acoustic properties of inner shelf sediments in the South Sea, Korea

Core sediment sampling has been conducted to investigate the physical and acoustic properties of inner shelf sediments in the South Sea, Korea. Thirty-two piston core samples were analyzed for sediment texture (grain size as well as, fractions of sand, silt, and clay), physical properties (porosity, water content, bulk density, grain density, and shear strength), and acoustic properties (compressional wave velocity and attenuation). The sediments in the study area consist mostly of homogenous mud. The study area can be divided into two different areas (south of Namhae Island and southeast of Naro Island) by texture, and physical and acoustic properties. The mean grain size generally decreases seaward from the mouth of Yeosu Sound and eastward in the southeast area of Naro Island. The compressional wave velocity decreases southeastward from 1500 to 1480 m/s and then increases to 1520 m/s due to relict sediments deposited in mid-shelf of the South Sea. Porosity, water content, and bulk density show an inverse pattern to velocity. The geoacoustic properties of the study area are generally similar to those of continental terrace sediment studied by Hamilton in the North Pacific. The area south of Namhae Island area matches Hamilton's model better than the area southeast of Naro Island. This result is believed to be related to the higher silt and sand contents as well as lower clay content than southeast of Naro Island.

Physical property variations related to seismic units in the offshore sediments of the Heuksan Mud Belt, southeastern Yellow Sea, Korea

Sixteen piston core samples collected from the Heuksan Mud Belt on the southeastern inner shelf of Korea were analyzed to characterize sediment property and distribution in relation to interpreted seismic units. The results from seven of 16 cores are presented in this study using core locations along a seismic track line. Variations in physical properties with depth gradually increased and/or decreased, depending on the characteristics of the specific property. Property patterns are primarily the result of dewatering caused by compaction and/or consolidation. Significant variations in depth are due to differences in sediment texture. In particular, core P03 is largely composed of sandy sediments below 170 cm. All core data come from three specific seismic Units: I, IIa and IIb, in descending order. The seismic patterns that define these units are interpreted as related to the rate of sea-level change during transgressions and depositional processes during the Holocene. Regionally, the variation of physical properties along the seismic profile is likely to reflect the relative characteristics of the seismic units. Unit I is characterized by low shear strength/wet bulk density and high porosity. Unit IIa appears to have higher shear strength than Units I and IIb. Unit IIb shows high wet bulk density and velocity. These observations suggest that the physical properties are mainly controlled by depositional processes related to sea-level change. Clay fabric analysis that uses a scanning electron microscope for two core samples shows the change of particle arrangement due to compaction caused by overburden loading with burial depth. In the upper part of the core, edge-to-edge and edge-to-face contacts dominate. In contrast, face-to-face contact characterized by the well-oriented arrangement of clay particles frequently occurs in the lower parts of the cores, indicating sediment compaction or initial consolidation caused by overburden pressure.

PHENOTYPIC PLASTICITY, SPECIATION, AND PHYLOGENY IN EARLY DANIAN PLANKTIC FORAMINIFERA

Research Article| April 01, 2014 PHENOTYPIC PLASTICITY, SPECIATION, AND PHYLOGENY IN EARLY DANIAN PLANKTIC FORAMINIFERA Eduardo A. M. Koutsoukos Eduardo A. M. Koutsoukos Geologie-Paläontologie Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 234, DE-69120 Heidelberg, Germany. E-mail: ekoutsoukos@gmail.com Search for other works by this author on: GSW Google Scholar Author and Article Information Eduardo A. M. Koutsoukos Geologie-Paläontologie Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 234, DE-69120 Heidelberg, Germany. E-mail: ekoutsoukos@gmail.com Publisher: Cushman Foundation for Foraminiferal Research Received: 20 Mar 2013 Accepted: 10 Dec 2013 First Online: 13 Jul 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2014 Cushman Foundation for Foraminiferal Research Journal of Foraminiferal Research (2014) 44 (2): 109–142. https://doi.org/10.2113/gsjfr.44.2.109 Article history Received: 20 Mar 2013 Accepted: 10 Dec 2013 First Online: 13 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Eduardo A. M. Koutsoukos; PHENOTYPIC PLASTICITY, SPECIATION, AND PHYLOGENY IN EARLY DANIAN PLANKTIC FORAMINIFERA. Journal of Foraminiferal Research 2014;; 44 (2): 109–142. doi: https://doi.org/10.2113/gsjfr.44.2.109 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract A piston core drilled at a water depth of 2809 m off Rio de Janeiro, southeastern Brazil, recovered a 1.83-m thick section of unconsolidated muddy sediments, representing a complete stratigraphic succession across the Cretaceous–Paleogene (K/Pg) boundary. The sediments yielded abundant, strikingly pristine tests of planktic and benthic foraminifera, unaffected by diagenetic alteration or recrystallization.The sedimentary record ranges from the uppermost Maastrichtian (P. hantkeninoides Zone) to the lower Danian (zones P0–P1c), spanning a time interval of about 3–4 Myr through the K/Pg transition. A detailed taxonomic appraisal of the recovered planktic foraminiferal assemblages is presented, together with an evaluation of lineage relationships, phylogenetic trends, and the sequence of evolutionary events that took place among the Globigerinina at the beginning of the Cenozoic.The numerous recent taxonomic studies of Danian planktic foraminifera notwithstanding, the significance of phenotypic varieties has never been assessed in a paleoecological context. Whereas the cancellate-walled, low trochospiral, large-sized Praemurica (Truncorotaloididae) and Parasubbotina and Subbotina (Globigerinidae) lineages evidently underwent rapid speciation over a relatively narrow phenotypic range, the small-sized Praemurica, the distinctly elevated trochoid Eoglobigerina (Globigerinidae), the Parvulorugoglobigerina, and the coiled to elongate morphotypes of the Guembelitria and Woodringina (all members of the family Guembelitriidae) and Chiloguembelina (Chiloguembelinidae) lineages show phenotypic plasticity over a much broader range. This dichotomy correlates with inferred differences in life-history parameters among these planktic taxa, including pelagic-dwelling preferences, related to reproductive and feeding strategies and to water-mass trophic levels.Two new early Danian planktic foraminiferal species are established herein: Praemurica nikolasi n. sp., the earliest recorded Truncorotaloididae and cancellate species, likely evolved directly from Hedbergella monmouthensis near the base of Zone P0 and probably giving rise to all subsequent cancellate lineages of the early Danian; and Globoconusa victori n. sp., evolved from Globoconusa daubjergensis within Zone P1c. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Late Quaternary carbonate deposition at the bottom of the world

Carbonate sediments on polar shelves hold great potential for improving understanding of climate and oceanography in regions of the globe that are particularly sensitive to global change. Such deposits have, however, not received much attention from sedimentologists and thus remain poorly understood. This study investigates the distribution, composition, diagenesis, and stratigraphic context of Late Quaternary calcareous sediments recovered in 15 piston cores from the Ross Sea shelf, Antarctica. Results are used to develop a depositional model for carbonate deposition on glaciated, polar shelves. The utility of the deposits as analogs for the ancient record is explored. In the Ross Sea, carbonate-rich lithofacies, consisting of poorly sorted skeletal sand and gravel, are concentrated in the west and along the outer reaches of the continental shelf and upper slope. Analysis of fossil assemblages shows that deposits were produced by numerous low-diversity benthic communities dominated locally by stylasterine hydrocorals, barnacles, or bryozoans. Radiocarbon dating indicates that carbonate sedimentation was episodic, corresponding to times of reduced siliciclastic deposition. Most accumulation occurred during a time of glacial expansion in the lead-up to the Last Glacial Maximum. A more recent interval of carbonate accumulation postdates the early Holocene sea level rise and the establishment of the modern grounding line for the Ross Ice Shelf. When carbonate factories were inactive, fossil debris was subjected to infestation by bioeroders, dissolution, fragmentation, and physical reworking. This study reveals the episodic nature of carbonate deposition in polar settings and a reciprocal relationship with processes that deliver and redistribute siliciclastic debris. Carbonate production is most active during colder periods of the glacial–interglacial cycle, a potential new sedimentological paradigm for polar carbonate systems. Low accumulation rates and long residence times on the seafloor leave sediments vulnerable to significant post-depositional modification, processes that profoundly affect the appearance of deposits as they enter the rock record. Comparison with other examples of polar carbonates highlights the utility of these Late Quaternary deposits as a well-constrained analog that can aid in the recognition and interpretation of similar deposits from the ancient record.

Tracking Holocene glacial and high-altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments (Lake Blanc Huez, Western French Alps)

Holocene palaeoenvironmental evolution and glacial fluctuations at high-altitude in the western French Alps are reconstructed based on a multiproxy approach within Lake Blanc Huez (2550 m a.s.l.) drainage basin. The combination of seismic profiling (3.5 kHz), piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the Holocene. Over the last 9700 years, the Holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal BP. During the Early Holocene, the organic lacustrine facies reflects reduced glacial activity in the catchment. This major glacial retreat seems to result from solar forcing and high summer insolation. After 5400 cal BP, lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion, suggesting a progressive transition to wetter climatic conditions. This climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations, characterizing the beginning of the Neoglacial period. Both colder temperature and humid climate induced significant glacier advance, since 4700 cal BP. Over this global trend, three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern Westerlies regimes across the North Atlantic and Western Europe. They are dated from 8700 to 7000, 4700 to 2500 and 1200 to 200 cal BP. These wetter phases drastically contrast with periods of reduced glacial activities dated from the Early Bronze Age (ca 3870–3770 cal BP), the Iron Age (ca 2220–2150 cal BP), the Roman period (ca AD115–330) and the Medieval Warm Period (ca AD760–1160). In addition, these dryer periods are associated with mining activities at high-altitude.

Late Quaternary paleoseismic sedimentary archive from deep central Gulf of Corinth: time distribution of inferred earthquake-induced layers

<p>A sedimentary archive corresponding to the last 17 cal kyr BP has been studied by means of a giant piston core retrieved on board R/V MARION-DUFRESNE in the North Central Gulf of Corinth. Based on previous methodological improvements, grain-size distribution and Magnetic Susceptibility Anisotropy (MSA) have been analysed in order to detect earthquake-induced deposits. We indentified 36 specific layers -Homogenites+Turbidites (HmTu) - intercalated within continuous hemipelagictype sediments (biogenic or bio-induced fraction and fine-grained siliciclastic fraction). The whole succession is divided into a non-marine lower half and a marine upper half. The “events” are distributed through the entire core and they are composed of two terms: a coarse-grained lower term and an upper homogeneous fine-grained term, sharply separated. Their average time recurrence interval could be estimated for the entire MD01-2477 core. The non-marine and the marine sections yielded close estimated values for event recurrence times of around 400 yrs to 500 yrs.</p>

Different nature of glacial CaCO3 constituents between MIS 2 and MIS 12 in the East Sea/Japan Sea and its paleoceanographic implication

Two piston cores (PC-05 and PC-08) were collected on the Yamato Rise in the East Sea/Japan Sea during the KR07-12 cruise. Both cores showed typical alternations of light (high L*) and dark (low L*) layers, which are characteristic in the hemi-pelagic sediment deposited in the deep part of the East Sea/Japan Sea. A composite core was achieved with the successful replacement of almost half of the upper part of core PC-05 by the entirety of core PC-08 based on the co-equivalence of L* values and the dark layers, because an interval (170 cm–410 cm) of core PC-05 was considerably disturbed due to fluidization during the core execution. Chronostratigraphy of the composite core was constructed by the direct comparison of L* values to the well-dated core MD01-2407 that was obtained in the Oki Ridge. The lower-bottom of the composite core extended to Marine Isotope Stage (MIS) 14, based on the age estimate by LR04 stacks. Downcore opal variation of the composite core exhibited the distinct orbital-scale cyclic changes; high during the interglacial and low during the glacial periods. However, downcore CaCO3 variation showed no corresponding orbital-scale cyclic change between glacial and interglacial periods. Some intervals of both periods were high in CaCO3 content. Frequent and large fluctuations in CaCO3 content seemed to be more related to the presence of dark layers containing thin lamination (TL) within the glacial and interglacial intervals. It is worthy to note that MIS 2 and MIS 12 are characterized by distinctly high CaCO3 content, showing up to 18% and 73%, respectively, among the glacial periods. Furthermore, in terms of lithology, MIS 2 was characterized by a thick dark layer (low L* values) with TL, whereas MIS 12 preserved the distinctly light layer (high L* values) with parallel laminations. Another remarkable dissimilarity between MIS 2 and MIS 12 was the nature of their CaCO3 constituent; the CaCO3 constituent of MIS 2 consisted of mostly planktonic foraminifera, whereas that of MIS 12 was mostly dump of coccolithophorids, regardless the presence of planktonic foraminifera. The distinctness of the CaCO3 constituents between MIS 2 and MIS 12 indicates that the preservation of CaCO3 contents was different temporarily during the glacial periods in the East Sea/Japan Sea. Enhanced CaCO3 preservation in MIS 2 is attributed primarily to less dissolution during the sinking through the water column or at the seafloor, but increased CaCO3 preservation in MIS 12 is mainly due to the high primary production in the surface water. With respect to the different function of the biological pump which controls CO2 cycles, the East Sea/Japan Sea clearly experienced carbonate-ocean-like state during MIS 12, despite normally silica-ocean-like state.

PALEOENVIRONMENTAL AND PALEOCLIMATIC IMPLICATIONS OF ENHANCED HOLOCENE DISCHARGE FROM THE MISSISSIPPI RIVER BASED ON THE SEDIMENTOLOGY AND GEOCHEMISTRY OF A DEEP CORE (JPC-26) FROM THE GULF OF MEXICO

Several meltwater floods initiated by the Laurentide Ice Sheet (LIS) drained to the Gulf of Mexico (GOM) through the Mississippi River during the last deglaciation (10–21 cal ka [calibrated kiloannum]). Such floods have been efficiently captured in the geochemical record of the Jumbo Piston Core 26 (JPC-26) from the northwestern GOM as distinct peaks in the content distribution of Si, Al, and Fe due to their common occurrence throughout North America. On the other hand, peaks in the content distribution of Ti, K, Zr, and V adequately describe the sediment source of each flooding event due to their clustered areal distribution in North America. The presence of three distinct peaks in the distribution of Si, Al, and Fe at 8.5, 5.2–7.6, and 2.9–3.5 cal ka indicates that events of enhanced Mississippi River discharge (EMRD) occurred during the Holocene as well. The geochemical signature of these flooding events suggests that their origin and sediment source is variable, depending on the retreating state of the LIS and the prevailing precipitation patterns in North America during these time periods. A comparison of the 8.5 and 2.9–3.5 cal ka EMRD events with the oxygen isotope and gas (CH 4) records of the Greenland Ice Sheet Project 2 (GISP-2) ice core denotes that these events might be linked to short global warming episodes associated with periods of increased solar irradiance. The 5.2–7.6calka EMRD event isassociated with theHolocene Thermal Maximum, which resulted in the intensification of the North American monsoonal circulation.

Subsurface methane sources and migration pathways within a gas hydrate mound system, Gulf of Mexico

Geochemical profiles were coupled with seismic information to examine subsurface hydrocarbon source, migration, and fate at a Gulf of Mexico carbonate‐gas hydrate mound (Woolsey Mound). Three seafloor features were investigated in detail: (1) major faults resulting from a rising salt body, (2) an acoustic backscatter anomaly, and (3) a pockmark associated with a major fault. We analyzed sulfate, chloride, dissolved inorganic carbon, and hydrocarbon concentrations, and carbon isotopes in pore water extracted from 20 m piston cores to characterize gas source and calculate methane flux. Dissolved biogenic methane dominated the off‐fault sites, while the contribution of thermogenic methane increased near a major fault where thermogenic gas hydrates were recovered. Within the pockmark, methane concentrations were low and isotopes indicated a biogenic source. Since pockmarks are typically formed from expulsive fluid flow, this suggests that either the pockmark is the legacy of a conduit that has become plugged or that the expulsed fluid is confined within the fault walls. At the acoustic anomaly, nonsteady state sulfate profiles suggested temporal variability in methane flux. Estimates from >75 gravity cores collected across Woolsey Mound since 2002 were mapped to display the spatial variability in methane flux relative to the faults. Methane flux to the seafloor was generally low, but increased several fold near the faults suggesting that the faults may provide conduits for hydrocarbons to bypass the “microbial biofilter” and cross the sediment water interface.