Termination IA Research Articles

The effectiveness of isometric contractions combined with eccentric – concentric training and simple lumbopelvic control exercises on pain and disability in chronic patellar tendinopathy: A case report

Paleoecological reconstructions of past climate are often based on a single taxonomic group with a consistent presence. Less is known about the relationship between multi-taxon community-wide change and climate variability. Here we reconstruct paleoecological change in a Late Quaternary (16.1–3.4 ka) sediment core from the California margin (418 m below sea level) of Santa Barbara Basin (SBB), USA, using Mollusca (Animalia) and Foraminifera (Rhizaria) microfossils. Building upon previous investigations, we use multivariate ordination and cluster analyses to interpret community-scale changes in these distinctly different taxonomic groups across discrete climate episodes. The strongest differences between seafloor biological communities occurred between glacial (prior to Termination IA, 14.7 ka) and interglacial climate episodes. Holocene communities were well partitioned, indicating that sub-millennial oceanographic variability was recorded by these microfossils. We document strong evidence of chemosynthetic trophic webs and sulfidic environments (from gastropod Alia permodesta and bivalve Lucinoma aequizonata), which characterized restricted intervals previously interpreted as well oxygenated (such as the Pre-Bølling Warming). Mollusc records indicate first-order trophic energetic shifts between detrital and chemosynthetically-fixed carbon. Molluscs associated with widely different physiological preferences occur here within single, decadal intervals of sediment, and as such mollusc assemblages may reflect significant inter-decadal oceanographic variability. Foraminifera assemblages provide exceptional records of the sequential, chronological progression of the deglacial climatic and oceanographic events, whereas mollusc assemblages reflect non-chronological similarities in reoccurring communities. Foraminifera taxa that drive community similarity here are also independently recognized as marker species for seafloor hypoxia regimes, which provides support for the idea that oxygenation change is a principal driver of seafloor environmental variability.

Community benthic paleoecology from high-resolution climate records: Mollusca and foraminifera in post-glacial environments of the California margin

Abstract Paleoecological reconstructions of past climate are often based on a single taxonomic group with a consistent presence. Less is known about the relationship between multi-taxon community-wide change and climate variability. Here we reconstruct paleoecological change in a Late Quaternary (16.1–3.4 ka) sediment core from the California margin (418 m below sea level) of Santa Barbara Basin (SBB), USA, using Mollusca (Animalia) and Foraminifera (Rhizaria) microfossils. Building upon previous investigations, we use multivariate ordination and cluster analyses to interpret community-scale changes in these distinctly different taxonomic groups across discrete climate episodes. The strongest differences between seafloor biological communities occurred between glacial (prior to Termination IA, 14.7 ka) and interglacial climate episodes. Holocene communities were well partitioned, indicating that sub-millennial oceanographic variability was recorded by these microfossils. We document strong evidence of chemosynthetic trophic webs and sulfidic environments (from gastropod Alia permodesta and bivalve Lucinoma aequizonata), which characterized restricted intervals previously interpreted as well oxygenated (such as the Pre-Bolling Warming). Mollusc records indicate first-order trophic energetic shifts between detrital and chemosynthetically-fixed carbon. Molluscs associated with widely different physiological preferences occur here within single, decadal intervals of sediment, and as such mollusc assemblages may reflect significant inter-decadal oceanographic variability. Foraminifera assemblages provide exceptional records of the sequential, chronological progression of the deglacial climatic and oceanographic events, whereas mollusc assemblages reflect non-chronological similarities in reoccurring communities. Foraminifera taxa that drive community similarity here are also independently recognized as marker species for seafloor hypoxia regimes, which provides support for the idea that oxygenation change is a principal driver of seafloor environmental variability.

Paleoceanographic insights on recent oxygen minimum zone expansion: lessons for modern oceanography.

Climate-driven Oxygen Minimum Zone (OMZ) expansions in the geologic record provide an opportunity to characterize the spatial and temporal scales of OMZ change. Here we investigate OMZ expansion through the global-scale warming event of the most recent deglaciation (18-11 ka), an event with clear relevance to understanding modern anthropogenic climate change. Deglacial marine sediment records were compiled to quantify the vertical extent, intensity, surface area and volume impingements of hypoxic waters upon continental margins. By integrating sediment records (183-2,309 meters below sea level; mbsl) containing one or more geochemical, sedimentary or microfossil oxygenation proxies integrated with analyses of eustatic sea level rise, we reconstruct the timing, depth and intensity of seafloor hypoxia. The maximum vertical OMZ extent during the deglaciation was variable by region: Subarctic Pacific (~600-2,900 mbsl), California Current (~330-1,500 mbsl), Mexico Margin (~330-830 mbsl), and the Humboldt Current and Equatorial Pacific (~110-3,100 mbsl). The timing of OMZ expansion is regionally coherent but not globally synchronous. Subarctic Pacific and California Current continental margins exhibit tight correlation to the oscillations of Northern Hemisphere deglacial events (Termination IA, Bølling-Allerød, Younger Dryas and Termination IB). Southern regions (Mexico Margin and the Equatorial Pacific and Humboldt Current) exhibit hypoxia expansion prior to Termination IA (~14.7 ka), and no regional oxygenation oscillations. Our analyses provide new evidence for the geographically and vertically extensive expansion of OMZs, and the extreme compression of upper-ocean oxygenated ecosystems during the geologically recent deglaciation.

Vertical oxygen minimum zone oscillations since 20 ka in Santa Barbara Basin: A benthic foraminiferal community perspective

[1] Here we present a history of deoxygenation of upper intermediate waters during the last deglaciation from Santa Barbara Basin (SBB), based on quantitative analyses of benthic foraminiferal assemblages, from a new shallow piston core above basin sill depth (MV0811-15JC, 418m), and previously described sequences in the deeper basin (MD02-2504, 481m and MD02-2503, 570m). We document a 152m depth transect of benthic foraminiferal assemblages to extract changing community structure (density, diversity, and evenness) and improve paleoenvironmental interpretation of late Quaternary vertical oscillations in the upper boundary of the oxygen minimum zone (OMZ). Close interaction between changes in open margin OMZ and that of the restricted SBB is documented using these quantitative techniques. MV0811-15JC, while being unlaminated, contains strongly hypoxic foraminiferal assemblages (including species Bolivina tumida and Nonionella stella), coeval with preserved sediment laminations in the deeper cores. Last Glacial Maximum (LGM) assemblages across this transect contained oxic fauna and high diversity. At 14.7ka, glacial termination IA, hypoxic benthic fauna appeared across the transect, recording hypoxic waters (<0.5mlL 1 ) <300m from the ocean surface. Bolling/Allerod (B/A) assemblages uniquely stand out in the record, exhibited by low density, diversity, and evenness, and taxonomic composition reflecting extreme and stressful hypoxia and methane-rich environments. Younger Dryas assemblages were diverse and composed of oxic fauna, similar to LGM assemblages. Termination IB initiated another deoxygenation shift, followed by OMZ-associated faunal and density patterns. This analysis strengthens the quantitative assessment of oxygen concentrations involved in deglacial OMZ change and reveals the unexpected, remarkable shallowness of OMZ influence during the B/A.

Climatically driven emissions of hydrocarbons from marine sediments during deglaciation

Marine hydrocarbon seepage emits oil and gas, including methane ( approximately 30 Tg of CH(4) per year), to the ocean and atmosphere. Sediments from the California margin contain preserved tar, primarily formed through hydrocarbon weathering at the sea surface. We present a record of variation in the abundance of tar in sediments for the past 32,000 years, providing evidence for increases in hydrocarbon emissions before and during Termination IA [16,000 years ago (16 ka) to 14 ka] and again over Termination IB (11-10 ka). Our study provides direct evidence for increased hydrocarbon seepage associated with deglacial warming through tar abundance in marine sediments, independent of previous geochemical proxies. Climate-sensitive gas hydrates may modulate thermogenic hydrocarbon seepage during deglaciation.

Pre-Bølling warming in Santa Barbara Basin, California: surface and intermediate water records of early deglacial warmth

A new piston core from Santa Barbara Basin, California provides evidence of the timing, magnitude, and character of deglaciation, including evidence of warming prior to Termination IA. IMAGES Site MD02-2503 (570 m water depth) consists of intermittently laminated hemipelagic sediments extending to Interstadial (D/O) event 6 (∼34 ka), that accumulated at ∼135 cm/ka. During the deglacial episode (16.75–10 ka), δ 18O values decreased by 3.2‰ in the planktonic species Globigerina bulloides, indicating a total warming of 8–9 °C recorded by surface-dwelling foraminifera (inferred by removing the 1‰ influence of ice volume change). Similarly, benthic species ( Bolivina argentea and Uvigerina peregrina) record a 1.65‰ δ 18O decrease across the deglacial, interpreted as a 2–3 °C warming at upper intermediate depths. δ 18O values of both planktonic and benthics indicate that surface and intermediate waters began to warm ∼2 ka prior to Termination IA, beginning at ∼16.5 ka. Intermediate water warming exhibits similar structure and synchronous timing with surface waters. These findings are consistent with a growing number of records from around the globe that exhibit pre-Bølling warming prior to Termination IA, and extends the record of such processes to the northern Pacific.

Paleomonsoon precipitation deduced from a sediment core from the equatorial Indian Ocean

Rapid shifts in past climate recorded in polar ice sheets have elicited various explanations relating to either thermohaline circulation changes by ice-rafting or natural greenhouse gas concentrations modulated by climatic conditions in the tropics. To compare the tropical paleoclimate record with the polar record, one must choose sediment cores from highly productive ocean regions. Necessarily, such regions reflect the wind records in the tropics, because high productivity is associated with upwelling driven by winds. Comparing tropical precipitation records with high-latitude records is, however, a more difficult task because sediments recording paleoprecipitation usually have low sedimentation rates, and offer coarser resolution relative to polar ice cores. Here, we present δ 18O data of three planktonic species of Foraminifera (a proxy for precipitation) from such a sediment core, spanning the past 35 ka for the equatorial Indian Ocean, which falls under the southwest monsoon (SWM) realm. Results show that minimum SWM precipitation occurred at the Last Glacial Maximum, with a subsequent increase at Termination IA. During the Holocene, SWM precipitation intensified uniformly up to the core top (∼2.2 ka b.p.), as revealed by generally decreasing δ 18O values. Variations in precipitation are consistent with climate changes recorded in polar ice sheets. Although the different resolutions of the two records preclude a rigorous comparison, abrupt cooling/warming events appear to be accompanied by sudden reduction/enhancement in (SWM) rainfall. Thus, mechanisms with time scales much shorter than a millennium, such as natural greenhouse warming (e.g., CH4 concentration), controlled by emissions from the tropics, could have played a major role in high-latitude climate change.

Climatic dependence of the organic matter contributions in the north eastern Norwegian Sea over the last 15,000 years

Lipids are used for the evaluation of the different organic matter contributions in the north eastern Norwegian Sea (M23258 site, 75°N, 14°E) over the last 15,000 years. Development of a mass balance model based on the down-core quantification of the C37 alkenones, the odd carbon numbered n-alkanes (Aodd) and the unresolved complex mixture of hydrocarbons (UCM) has allowed three main organic matter inputs involving marine, continental and ancient reworked organic matter to be recognized. The model shows good agreement between measured and reconstructed TOC values. Similarly, a strong parallelism is observed between predicted components such as marine TOC and carbonate content, which was determined independently. Representation of the model results within a time scale based on 15 AMS-14C measurements shows that the main changes in organic matter constituents are coincident with the major climatic events of the last 15,000 years. Thus, the predominance of reworked organic matter is characteristic of Termination Ia (up to 70%), continental organic matter was dominant during the Bølling-Allerød (B-A) and Younger Dryas (YD) periods (about 85%) and a strong increase of marine organic matter occurred in the Holocene (between 50 and 75%). This agreement reflects the main hydrographic changes that determined the deposition of sedimentary materials between 0 and 15 cal ka: ice-rafted detritus from the Barents continental platform, ice-melting waters from the Arctic fluvial system discharging into the Barents Sea and dominance of North Atlantic currents, respectively. In this respect, the high-resolution down-core record resulting from the mass balance and lipid measurements allows for the identification of millennial scale events such as the increase of reworked organic matter at the final retreat of the Barents ice sheet at the end of the deglaciation period (Termination Ib).

Evolution of heat transport pathways in the Indonesian Ar-chipelago during last deglaciation

The Indonesian Archipelago provides important heat transport pathways of the Western Pacific Warm Pool between the northern Indian Ocean and western equatorial Pacific Ocean, that exert important impacts on global climate change. This study investigated AMS 14C, δ18O, planktonic foraminifer assemblages and sedimentation rates in three piston cores collected in the Indonesian Archipelago. The results indicate that changes in the Indonesian Archipelago heat transport pathways were phase characteristic and in steps during the last deglaciation. In the deglaciation Termination IA, at about 12.5 kaBP, sea level rose rapidly in a short time period, and Makassar and Lombok straits widened suddenly for warm and fresh water from the Pacific to pour into the Java Sea and eastern Indian Ocean. During the Termination IB, about 9.5 kaBP, sea level rose rapidly again, and the South China Sea (SCS) started to connect with the Java Sea. With monsoon actions, a large amount of fresh water from the SCS shelf area flew through the Indonesian Archipelago.

Changes in Arctic Ocean paleoproductivity and hydrography during the last 145 kyr: The benthic foraminiferal record

The benthic foraminiferal record of two sediment cores at 900 and 2500 rn water depth in the marginal Arctic Ocean reflects fluctuations in paleoproductivity, ice sheet extent, and Atlantic water inflow. Highest paleoproductivity is observed in interglacial periods, and at the termination of interstadials to stadials within oxygen isotope substages (OIS) 6.3, 5.3, 5.1, 3.1, and Termination Ia. Stable and high paleoproductivity at the ice‐edge during terminations is indicated by the Melonis zaandami benthic foraminiferal association. Periods of glacial ice sheet advance or retreat from the core site are dominated by benthic foraminiferal associations related to seasonal organic carbon flux. Temperate saline Atlantic water entered the Arctic Ocean within OIS 6.3, 5.5 and the Holocene. Coincident paleoproductivity maxima are related to extended seasonal ice retreat. During glacial periods of stagnating Atlantic water advection unusual low paleoproductivity values are observed in the Arctic Ocean, indicating increasing ice coverage. Deep water was poorly ventilated during these periods and the deeper site became exposed to corrosive bottom waters.

The Late Weichselian glaciation of the Franz Victoria Trough, northern Barents Sea: ice sheet extent and timing

High resolution seismic profiles (PARASOUND, 4 kHz) and three sediment cores from the Franz Victoria Trough and the adjacent continental slope were studied in order to constrain the timing and extent of the northern Svalbard/Barents Sea ice sheet during the Late Weichselian glaciation. Stacked debris flow lobes and layers of glacimarine diamicton on the lower continental slope indicate that large quantities of glacially derived sediments were deposited by the northern Svalbard/Barents Sea ice sheet directly onto the upper continental slope at approximately 23 14 C ka. A grounding-line advance to the shelf break is supported by the identification of diamicton, interpreted as till, in the seismic profile near the shelf break. After several ice sheet instabilities marked by significant input of ice rafted detritus to the continental margin, the disintegration of the northern Svalbard/Barents Sea ice sheet (Termination Ia) is indicated by a distinct pulse of ice rafted detritus at 15.4 14 C ka and the transition to an isotopically defined meltwater signal. The drastic change in sedimentary pattern on the upper continental slope, dated to about 13.4 14 C ka, is interpreted as grounding-line retreat from the shelf edge. A further stepwise retreat of the northern Svalbard/Barents Sea ice sheet is indicated by pulses of ice rafted detritus which appear to be contemporaneous with the onset of distinct ice rafting events in adjacent areas and pulses of glacimarine sedimentation in the southwestern Barents Sea. q 2000 Elsevier Science B.V. All rights reserved.

East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea

Based on the study of 10 sediment cores and 40 core-top samples from the South China Sea (SCS) we obtained proxy records of past changes in East Asian monsoon climate on millennial to bidecadal time scales over the last 220,000 years. Climate proxies such as global sea level, estimates of paleotemperature, salinity, and nutrients in surface water, ventilation of deep water, paleowind strength, freshwater lids, fluvial and/or eolian sediment supply, and sediment winnowing on the sea floor were derived from planktonic and benthic stable-isotope records, the distribution of siliciclastic grain sizes, planktonic foraminifera species, and the U K 37 biomarker index. Four cores were AMS- 14C-dated. Two different regimes of monsoon circulation dominated the SCS over the last two glacial cycles, being linked to the minima and maxima of Northern Hemisphere solar insolation. (1) Glacial stages led to a stable estuarine circulation and a strong O 2-minimum layer via a closure of the Borneo sea strait. Strong northeast monsoon and cool surface water occurred during winter, in part fed by an inflow from the north tip of Luzon. In contrast, summer temperatures were as high as during interglacials, hence the seasonality was strong. Low wetness in subtropical South China was opposed to large river input from the emerged Sunda shelf, serving as glacial refuge for tropical forest. (2) Interglacials were marked by a strong inflow of warm water via the Borneo sea strait, intense upwelling southeast of Vietnam and continental wetness in China during summer, weaker northeast monsoon and high sea-surface temperatures during winter, i.e. low seasonality. On top of the long-term variations we found millennial- to centennial-scale cold and dry, warm and humid spells during the Holocene, glacial Terminations I and II, and Stage 3. The spells were coeval with published variations in the Indian monsoon and probably, with the cold Heinrich and warm Dansgaard–Oeschger events recorded in Greenland ice cores, thus suggesting global climatic teleconnections. Holocene oscillations in the runoff from South China centered around periodicities of 775 years, ascribed to subharmonics of the 1500-year cycle in oceanic thermohaline circulation. 102/84-year cycles are tentatively assigned to the Gleissberg period of solar activity. Phase relationships among various monsoon proxies near the onset of Termination IA suggest that summer-monsoon rains and fluvial runoff from South China had already intensified right after the last glacial maximum (LGM) insolation minimum, coeval with the start of Antarctic ice melt, prior to the δ 18O signals of global sea-level rise. Vice versa, the strength of winter-monsoon winds decreased in short centennial steps only 3000–4000 years later, along with the melt of glacial ice sheets in the Northern Hemisphere.

Late Quaternary climatic variations on the Latium and Campanian Margin of the Tyrrhenian Sea

A multidisciplinary investigation was carried out on two cores, MC 82-12 (Palinuro intraslope basin) and ML 83-21 (Pontinia intraslope basin), recovered during a cruise carried out in 1983, in the eastern part of the Tyrrhenian Sea, funded by C.N.R. Quantitative analyses of planktonic foraminifers, along with oxygen and carbon stable isotopes analyses, and mineralogical and petrological studies on tephra layers allowed to recognize and date, by means of isotopic stratigraphy, the main climatic events of the Late Quaternary: the Last Glacial Maximum, the Younger Dryas event, as well as Termination IA and IB. The planktonic assemblages recognized in the two cores correlate well between them and with the oxygen isotopic signal, even if there are some discrepancies, related to oceanographic factors other than temperature influencing the foraminifers distribution.

Paleoclimatic significance of the stratigraphic occurrence of photosynthetic biomarker pigments in the Nordic seas

Research Article| January 01, 1997 Paleoclimatic significance of the stratigraphic occurrence of photosynthetic biomarker pigments in the Nordic seas Antoni Rosell-Melé; Antoni Rosell-Melé 1School of Chemistry, University of Bristol, BS8 1TS Bristol, United Kingdom Search for other works by this author on: GSW Google Scholar Nalân Koç Nalân Koç 2Department of Geology, University of Bergen, N-5007 Bergen, Norway Search for other works by this author on: GSW Google Scholar Author and Article Information Antoni Rosell-Melé 1School of Chemistry, University of Bristol, BS8 1TS Bristol, United Kingdom Nalân Koç 2Department of Geology, University of Bergen, N-5007 Bergen, Norway Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1997) 25 (1): 49–52. https://doi.org/10.1130/0091-7613(1997)025<0049:PSOTSO>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Antoni Rosell-Melé, Nalân Koç; Paleoclimatic significance of the stratigraphic occurrence of photosynthetic biomarker pigments in the Nordic seas. Geology 1997;; 25 (1): 49–52. doi: https://doi.org/10.1130/0091-7613(1997)025<0049:PSOTSO>2.3.CO;2 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 SocietyGeology Search Advanced Search Abstract Sedimentary chlorins and porphyrins are diagenetic products of chlorophyll molecules and are considered to be chemical fossils or biomarkers of phototrophic organisms. The stratigraphic occurrence of such components was investigated in four cores from the Nordic seas that span the last deglacial period. The presence of chlorins in all the samples deposited during the Younger Dryas and at the end of the last glacial period indicated that photosynthetic activity occurred during these cold episodes and hence that ice-free conditions existed, at least seasonally, in the Nordic seas. Vanadyl porphyrins were found in sediments deposited during Termination Ia in only two of the cores, close to the Barents Shelf. We argue that they derive from erosion and advection of organic-rich deposits as ice-rafted debris during melting of the Barents ice sheet. Thus, we suggest that the sedimentary occurrence of vanadyl porphyrins in Nordic sea cores can be used as a marker of ice-rafted debris from the Barents ice sheet. The absence of such components during Termination Ib indicates that the complete destruction of the Barents ice sheet took place during the first stage of the deglaciation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Late Quaternary sedimentation on the Mid-Atlantic Reykjanes Ridge: clay mineral assemblages and depositional environment

Sediment samples from the Mid-Atlantic Reykjanes Ridge (59°N) were taken to get information about sediment genesis and to identify different sources during the late Quaternary. Samples were investigated by X-ray diffraction and grain-size analyses. The clay mineral assemblages in sediments of the Reykjanes Ridge reflect paleoceanographic changes during the late Quaternary. Holocene sediments are characterized by high contents of smectite, mainly of less developed crystallinity. In the spatial distribution of clay minerals high smectite concentrations on the eastern flank and slightly decreasing concentrations on the western flank of the Reykjanes Ridge indicate the action of bottom-water transport. The smectite originates mainly from the volcanogenous Icelandic shelf and reflects the influence of Iceland-Scotland Overflow Water (ISOW). Stratigraphic variability in the clay mineral composition reflects predominantly the influence of different sources, resulting from oceanographic and glacial transport processes. During glacial time sediment transport is due mainly to input by icebergs. Increasing amounts of illite, chlorite, and kaolinite characterize ice-rafted sediments of the “Heinrich layers”. In these sediments smectite crystallinity is well developed. In contrast, several other ice-rafted layers contain smectite with low crystallographic order, similar to smectites of Holocene age. The icelandic source was proved by distinct amounts of basaltic glass in the coarse-grained sediment. At approximately 55 ka increasing amounts of chlorite and kaolinite suggest an enhanced influx of warm North Atlantic surface waters. This hypothesis is supported by a high carbonate shell production at this time. Relative low concentrations and the well-developed crystallinity of smectite minerals characterize the Last Glacial Maximum (LGM; 18–16 ka), indicating a reduced supply of fine icelandic material. Shortly after the LGM, at the beginning of termination IA, a distinct increase in fine-grained quartz (<2µm) and smectite are visible, which are proposed to reflect a supply of fine-grained ice-rafted material. At 13 ka linear increasing smectite concentrations of lower crystallographic order indicate increasing supply of fine-grained material from Iceland, linked to reinitiation of bottom currents of the ISOW. Full reinitiation is indicated at around 10 ka, where a strong increase in smectite of low crystallographic order is detected.

A reexamination of northeast Atlantic sea surface temperature and salinity over the last 16 kyr

We present a 15 kyr sea surface temperature (SST) record for a high sedimentation rate core (KNR51‐29GGC) from the Feni Drift off of Ireland, based on an organic geochemical technique for paleotemperature estimation, U37K′. We compare the U37K′ temperature record to planktonic foraminiferal δ18O and foraminiferal assemblage SST estimates from the same sample horizons. U37K′ gives SST estimates of 13°C for the early deglacial and 18°C for the Holocene and Recent, whereas assemblages give estimates of 9°C and 13°C, respectively. As in nearby core V23‐81, we find Ash Zone 1, the Younger Dryas increase in Neogloboquadrina pachyderma sinistral abundance, and maximum abundance of this species during glaciation. N. pachyderma dextral oxygen isotopic analyses have a late glacial to interglacial range of 1.5‰. A reduction of about 1 ‰ in δ18O occurred at about 12 ka, whereas U37K′ and the foraminiferal fauna indicate a 2°C warming. This implies a 0.9‰ salinity effect on δ18O which we attribute to meltwater freshening. All three parameters indicate cooling during the Younger Dryas. U37K′ SST estimates show that the major shift from deglacial to interglacial temperatures occurred after the Younger Dryas in termination 1b, in contrast to the assemblage data, which show this jump in SST at the end of the glaciation during termination Ia. Differences between the two SST estimators, which may result from their different (floral versus faunal) sources, are more pronounced between transitions Ia and Ib. This may reflect different habitats under the unusual sea surface conditions of the deglaciation.

High resolution stratigraphy of the Faeroe-Shetland Channel and its relation to North Atlantic paleoceanography: the last 87 kyr

Two piston cores from the Faeroe-Shetland Channel have been investigated for stratigraphic and paleoceanographic correlation with Atlantic Ocean and Norwegian Sea records. The high resolution cores have been analyzed for the downcore distribution of planktic and benthic foraminifera and oxygen isotopes. AMS 14C dates and the position of Ash layers I and II form the basis for the correlation. Core NA81-10 covers the period from isotope stage 3 to Recent (stage 1), while core NA81-04 covers isotope stages 5a to 1. The Holocene is well represented in core NA81-10 by 2 m of sediment, whereas it is only 50 cm in core NA81-04 which is situated directly under the main core of the Norwegian Sea Deep Water outflow. The transition of isotope stage 2 to stage 1 is affected by dissolution and thus is less clearly represented. AMS 14C dates show that Termination IA begins at 16 ka and ends at about the 13 ka level. The Last Glacial Maximum (LGM; defined at 19-16 ka) is characterized by an IRD peak, faunal (planktic foraminifera) maxima (dated at 17.3 and 18.25 ka) and a high percentage of Globigerina quinqueloba. Apparently open water conditions and circulation within the Norwegian Sea prevailed at least from 22.5 to 14.8 ka, during the greatest part of stage 2 (including the LGM) and well onto Termination IA. A preservation maximum is observed throughout stage 2. Isotope stage 3, with a nearly complete record of isotope substages is well represented in both cores. Oxygen isotope depletion peaks correlate with fauna minima and in time to North Atlantic Heinrich events (H5-H1). Faunal data indicate that deep water is generated within the Norwegian-Greenland Sea repeatedly since 26 ka, with stops prior to 26 ka, 22.5–20.8/20.5 ka and between 14.9 and 13 ka (H3, H2 and H1). All isotope depletion peaks since ca. 50 ka are anticorrelated with fauna and are mainly controlled by surface salinity changes. Isotope stages and substages are directly correlated to fauna peaks and temperature between 87 and ca. 50 ka. The Faeroe-Shetland Channel record shows that repeated presences of Atlantic Surface Water and deep convection alternating with convection shutdowns have occurred within the Norwegian Sea-Greenland Sea from the beginning of stages 5a to 1.

Late Quaternary glacial-interglacial changes in sediment composition at the East Greenland continental margin and their paleoceanographic implications

Stable isotope records, and sedimentological and organic-geochemical investigations of marine sediments from the east Greenland Sea at 70 °N provide important information about glacial-interglacial variations of paleoenvironments through the last 225 kyr. The oxygen isotope records established on the planktonic foraminifer N. pachyderma sin. show some excursions from the global climate pattern, probably due to local/regional overprint by meltwater supply. The cold, low-saline East Greenland Current and fluctuations in sea-ice covering were a crucial element controlling the carbonate production in the subsurface/surface water column in the east Greenland Sea over the last 225 kyr. The beginning of Termination Ia is AMS 14C dated at about 15.8 kyr B.P. and interpreted as a Greenland Ice Sheet meltwater signal. The stage 2/3 boundary is dated at about 25 kyr B.P. The timing of the onset of the last deglacial meltwater event is about 800 years earlier than that of the Barents Shelf Ice Sheet meltwater signal recorded in the Fram Strait. Several major pulses of increased supply of coarse-grained terrigenous material by glacio-marine processes occurred during the last 225 kyr. The supply of coarse-grained ice-rafted debris at the East Greenland continental slope reached maximum values during the last glacial maximum (stage 2/Weichselian, 15–19 kyr B.P.). The drastic climatic change and the gradual retreat of continental ice masses/glaciers during the last deglaciation (Termination I) are clearly documented in the marine sedimentary sequences from shelf and upper slope environments. This process resulted in distinctly decreased supply and deposition of ice-rafted debris in the open shelf-upper slope environments. During Termination I, the sea-ice cover also decreased, causing an increase in surface-water productivity, indicated by increased organic carbon and biogenic opal deposition.

Paleohydrology and paleoclimatology off Northwest Africa during the last glacial-interglacial transition and the Holocene: Palynological evidences

Pollen and dinoflagellate cyst analyses of deep-sea core located off Morocco provide a continuous record of paleoclimatic and paleohydrological change off Northwestern Africa since the last glacial episode. The stratigraphy is given by isotopic analysis ( δ 18O) of planktonic foraminifera, which shows a two-step deglaciation. Xeric conditions on the adjacent land, marked by the increase of steppe taxa ( Artemisia, Chenopodiaceae/Amaranthaceae, Ephedra), and the development of the montane taxon, Cedrus atlantica are observed before Termination IA and during the Younger Dryas. These intervals are also marked by a high abundance of Pinus pollen grains, which indicates a strengthening of the northeastern (NE) trade winds. Variations of the surface water temperatures are shown by the fluctuations of dinoflagellate cyst assemblages which reflect a cooling of the surface waters during Termination IA and the Younger Dryas episode. Intensification of the upwelling system off Morocco resulting from enhanced trade winds occurred during these two key-periods. Quercus forests, which are an important part of the present-day vegetation of the Maghreb region, developed around 8500 yr B.P. Dinoflagellate cyst assemblages suggest that present-day oceanic conditions were established during this period.

Late Quaternary central Mediterranean biochronology

A high-resolution biochronology is presented for the Late Quaternary of the central Mediterranean. In the Late Pleistocene-Holocene successions three assemblage zones are distinguished on the basis of frequency patterns of planktic foraminifera. The age of these zones is determined by Accelerator Mass Spectrometry (AMS) 14C dating. The zonal boundaries are dated at 12,700 yr B.P. (the end of Termination Ia) and 9600 yr B.P. (the start of Termination Ib), respectively. The AMS dates show that major changes in the planktic and benthic realms occurred synchronously over wide areas, although records of individual species may show important regional differences. In the studied areas, resedimentation processes revealed by anomalous successions of 14C dates, play a far more important role than indicated by the sedimentological and micropaleontological data. Possibly these processes contribute to the very high accumulation rates in the glacial Zone III. Although the AMS technique has increased the accuracy of 14C-measurements, admixture of older carbonate may still lead to substantial age differences between areas with different sedimentary regimes.