Sedimentological and benthic foraminiferal data pertaining to ODP Holes 208-1262A and 208-1263C

Eocene Thermal Maximum 2 (ETM2) occurred ~1.8 Myr after the Paleocene Eocene Thermal Maximum (PETM) and, like the PETM, was characterized by a negative carbon isotope excursion coupled with warming. We combined benthic foraminiferal and sedimentological records for Southeast Atlantic Sites 1263 (1500 m paleodepth) and 1262 (3600 m paleodepth) to show that benthic foraminiferal diversity and accumulation rates declined more precipitously and severely at the shallower site during peak ETM2. The sites are in close proximity, so differences in surface productivity cannot have caused this differential effect. Instead, on the basis of an analysis of climate modelling experiments, we infer that changes in ocean circulation pattern across ETM2 may have resulted in more pronounced warming at intermediate depths (Site 1263). The effects of more pronounced warming include increased metabolic rates, leading to a decrease in effective food supply and increased deoxygenation, thus potentially explaining the more severe benthic impacts at Site 1263. In response to more severe benthic disturbance, bioturbation may have decreased at Site 1263 as compared to Site 1262, hence differentially affecting the bulk carbonate record. We use a sediment-enabled Earth system model to test whether a reduction in bioturbation and/or the likely reduced carbonate saturation of more poorly ventilated waters can explain the more extreme excursion in bulk d13C and sharper transition in wt% CaCO3 at Site 1263. We find that both enhanced acidification and reduced bioturbation during peak ELMO conditions are needed to account for the observed features. Our combined ecological and modelling analysis illustrates the potential role of ocean circulation changes in amplifying local environmental changes and driving temporary, but drastic, loss of benthic biodiversity and abundance.

Sedimentological and paleoclimatological investigation of two sediment cores off Cape Barbas, North-West Africa

Two box cores taken off Cape Barbas (North-West Africa) have been studied using three methods. The analyses of the coarse fraction, of biogenic opal and of planktonic foraminifera revealed : 1. Core GIK12310-4 penetrates Z, Y, X and upper part of W zone, whereas core GIK12379-1 penetrates Z and upper part of Y zone. 2. Holocene sedimentation rates are 2.5 cm/1000 y for core GIK12310-4 and 6.0 cm/1000 y for core GIK12379-1. During the Y zone 5 cm/l000 y were sedimented incore GIK12310-4 and > 10-20 cm/1000 y in core GIK12379-1. 3. Paleoclimatohgical results are: arid climate and relatively warm water temperatures during the Holocene (Z zone) and during X zone; humid climate and relatively cool water temperatures within the Wuerm (Y zone) (with a non-dated more arid interval found in the middle part of the Y zone) and in the upper part of the W zone. 4. Increased contents of benthos and radiolaria in the Y zone indicate upwelling. Upwelling, characterized by high content of biogenic opal and low water temperatures, was found in core GIK12310-4 at 250 to 350 cm in the lower part of the Y zone. The plankton/benthos ratio of foraminifera, the benthos/radiolaria ratio and water temperatures derived from planktonic foraminifera, differ in both cores in the Holocene, and are nearly identical during the Wuerm.

Distribution of planktonic foraminifera in Pleistocene sediments of the New Jersey margin, NW Atlantic Ocean

Abundance records of planktonic foraminifera (>150 µm) from the upper 520 m of ODP Site 1073 (Hole 1073A, Leg 174A, 639 m water depth) have been integrated with SPECMAP-derived isotope stratigraphy, percentage of calcium carbonate, and coarse sediment fraction data in order to investigate the Pleistocene climatic history of the New Jersey margin. Six planktonic taxonomic groups dominate the foraminiferal assemblage at Site 1073: Neogloboquadrina pachyderma (d) (mean 33.8%), Turborotalita quinqueloba (18.5%), N. pachyderma (s) (18.4%), Globigerina bulloides group (11.4%), Globorotalia inflata group (9.4%), and Globigerinita glutinata (4.1%). Based on the distributions of these six foraminiferal groups, the Pleistocene section can be divided into three paleoclimatic intervals: Interval I (intermediate) corresponds to the Quaternary sediments from sequence boundary pp1 to the seafloor (79.5-0 mbsf; Emiliania huxleyi acme [85 ka] at 72 mbsf); Interval II (warm) occurs between sequence boundaries pp3 and pp1 (325-79.5 mbsf; last occurrence of Pseudoemiliania lacunosa [460 ka] at 330 mbsf); and Interval III (coldest) occurs between sequence boundaries pp4 and pp3 (520-325 mbsf; Calcareous nannofossils and dinocysts in proximity to pp4 indicate that the sedimentary record for 0.9-1.7 Ma is either missing altogether or highly condensed within the basal few meters of the section). Neogloboquadrina pachyderma (d) displays eight peaks of abundance which correlate, for the most part, with depleted delta18O values, increases in calcium carbonate percentages, low coarse fraction percentages, increased planktonic fragmentation (greater dissolution), and low N. pachyderma (s) abundances. These intervals are interpreted as representing warmer/interglacial conditions. Neogloboquadrina pachyderma (s) displays seven peaks of abundance which correlate, for the most part, with delta18O increases, decreases in calcium carbonate percentages, increases in coarse fraction percentages, and low N. pachyderma (d) abundances. These intervals are interpreted as representing cooler/glacial conditions. In Interval III, a faunal response to relative changes in sea-surface temperature is reflected by abundance peaks in Neogloboquadrina pachyderma (d), followed by Turborotalita quinqueloba and then N. pachyderma (s) (proceeding from warmest to coolest, respectively). This tripartite response is consistent with the oxygen isotope record and, although not as clear, also occurs in Intervals I and II. Six peaks/peak intervals of Globigerina bulloides abundance are closely matched by peaks in Globigerinita glutinata and occur within oxygen isotope stage (OIS) 2 (latter part) 3, 4, 5, 8, 9, 13(?), 14(?), and 15(?). We speculate that these intervals reflect increased upwelling and nutrient levels during both glacials and interglacials. Eight peak intervals of Globorotalia inflata show a general inverse correlation with G. bulloides and may reflect lowered nutrient and warmer surface waters.

Pollen record and age determination of a sediment profile from Lake Teletskoye, Russia

A high-resolution pollen record from Lake Teletskoye documents the climate-related vegetation history of the northern Altai Mountain region during the last millennium. Siberian pine taiga with Scots pine, fir, spruce, and birch dominated the vegetation between ca. AD 1050 and 1100. The climate was similar to modern. In the beginning of the 12th century, birch and shrub alder increased. Lowered pollen concentrations and simultaneous peaks in herbs (especially Artemisia and Poaceae), ferns, and charcoal fragments point to colder and more arid climate conditions than before, with frequent fire events. Around AD 1200, regional climate became warmer and more humid than present, as revealed by an increase of Siberian pine and decreases of dry herb taxa and charcoal contents. Climatic conditions were rather stable until ca. AD 1410. An increase of Artemisia pollen may reflect slightly drier climate conditions between AD 1410 and 1560. Increases in Alnus, Betula, Artemisia, and Chenopodiaceae pollen and in charcoal particle contents may reflect further deterioration of climate conditions between AD 1560 and 1810, consistent with the Little Ice Age. After AD 1850 the vegetation gradually approached the modern one, in conjunction with ongoing climate warming.

Pollen records of the Bykovsky Peninsula

New pollen and radiocarbon data from the Bykovsky Peninsula document the Late Pleistocene and Holocene environmental history of the Laptev Sea coast. More than 60 AMS-14C and conventional 14C dates indicate that the deposits accumulated during the last 60,000 radiocarbon yr BP. High concentration of green alga colonies (Pediustrum and Botryococcus) in the investigated sediment show that sedimentation was mostly in shallow water environments. Scarce grass and sedge communities dominated the vegetation 53-60 kyr BP. Climate was cold and dry. Open Poaceae and Cypcraccae associations with Asteraceae, Ranunculaceae, and Cichoriaceac, dominated in the area about 48-42.5 kyr BP. Steppic communities with Artemisia and shrubby tundra communities with Salix and Betula sect. Nanae were also present. Climate was dry, but relatively warm. Vegetation cover became denser about 42.5-33.5 kyr BP, reflecting more favorable climate conditions. Scarce Poaceae communities with some Caryophyllaceae, Asteraceae, Cichoriaceae, and Selaginella rupestris covered the Bykovsky Peninsula area during the Sartan (Late Weichselian) stage about 26-16 kyr BP. Disturbed, uncovered soils were very common in the area. Climate was extremely cold and dry. Poaceae and Cyperaceae associations with Caryophyllaceae, Asteraceae, Cichoriaceae dominated the vegetation in the late Sartan, ca 16-12.2 kyr BP. Climate was significantly warmer than in the early Sartan time. The lee Complex sedimentation was interrupted about 12 kyr BP; most likely it was connected with the beginning of the Allerod warnring. Shrubby (Betula sect. Nanae, Alnusfnuicosa, Salix, Ericales) tundra was widely distributed on the Bykovsky Peninsula during the early-middle Holacene. Climate was most favorable between 8200 and 4500 yr BP. Vegetation became similar to modern after 4500 yr BP, suggesting a deterioration of climate.

A late Quaternary planktonic foraminifer faunal record of rapid climatic changes of sediment core GIK17938-2

A high-resolution planktonic foraminifer record from a core recovered from the South China Sea (SCS) (Sonne 17938-2: 19°47.2'N, 117° 32.3E; 2840 m; Delta t c. 250-1000 years) shows rapid millennial-scale changes in the western Pacific marginal sea climate during the last 30,000 years. The SCS is the largest western Pacific marginal sea off the southeast Asian continent, the area today dominated by seasonal monsoon changes. Quantitative analyses of planktonic foraminifer faunal abundance data frorn the core indicate large downcore variations in the relative abundances of the dominant taxa since about 30,000 years ago in the isotope stage 3. Further analyses indicate that the abundance of G. inflata, a good indicator species for cold SST (~13°-19°C) and deep MLD (~100-125 m) waters shows abrupt shifts. During stages 2 and 3, the abundance record of G. infiata tends to be punctuated by quasi-periodie short intervals (~2000-3000 yrs) where its abundance reaches 15% or greater, superimposed on generally low (5-10%) background values. This pattern suggests an instability of surface ocean conditions of the SCS during the past 30,000 years. The abrupt abundance changes of G. infiata correlate well with similar climatic changes observed from a GISP2 ice core 8180, and North Atlantic core DSDP 609 N. pachyderma (s.) and lithic grain abundances during 'Heinrich evcnts'. These results suggest that the millennial-scale variability of climate is not peculiar to the Atlantic region. Apparently, the rapid SCS climatic changes during Heinrich events are driven by effective mechanisms, of particularly the effects of shifts in the latitudinal position of the Siberia High Pressure System.