Abyssal NE Atlantic benthic foraminifera during the last 15 kyr: Relation to variations in seasonality of productivity

Benthic foraminiferal faunas (> 63 μm) and stable isotopes from the last 15 kyr were studied in BENGAL programme (high-resolution temporal and spatial study of the BENthic biology and Geochemistry of a north-eastern Atlantic abyssal Locality) kasten core 13078#16 from the Porcupine Abyssal Plain, NE Atlantic (48°49.91 N, 16°29.94 W, water depth 4844 m). Changes occurred in the accumulation rates, species composition, diversity, and stable isotopes during the last 15 kyr. Today, the area is strongly influenced by seasonal inputs of phytodetritus following the spring blooms in surface water primary productivity. Variations in the relative abundance of the two most abundant species, Epistominella exigua and Alabaminella weddellensis, which today show significant increases in abundance with the presence of phytodetritus on the sea-floor, are interpreted as resulting from changes in the seasonality of productivity. Seasonal productivity was higher during the Holocene than during the last deglaciation and Younger Dryas, probably coinciding with the retreat of the polar front to higher latitudes. This hypothesis is consistent with simultaneous decreases in the percentage of the polar planktic foraminifera Neogloboquadrina pachyderma (s), and increases in the percentage of Globigerina bulloides, a warmer water planktic foraminifera indicative of phytoplankton blooms and enhanced productivity. The relative abundance of the ‘phytodetritus species’ (E. exigua and A. weddellensis) covary between 14.7 and 8.1 kyr, but not between 7.8 and 1.2 kyr. Major decreases in the numbers per gram and accumulation rates of planktic and benthic foraminifera occurred at ∼ 12–8.5 kyr and at ∼ 4 kyr which correspond to decreases in the % sediment coarse fraction and published data on inorganic carbon contents suggesting that dissolution may have increased at these times. Relationships between benthic foraminiferal faunas and benthic stable isotope records suggest no simple relationship between faunal abundances and test isotope chemistry. For example, the abundances of phytodetritus species do not show strong correlations with either the δ¹³C values of E. exigua or the Δδ¹³C _{E. exigua − P. wuellerstorfi} record, which have previously been suggested as indicative of seasonality of productivity.     

Stepwise postglacial migration of benthic foraminifera into the abyssal northeastern Norwegian Sea

Accumulation rates of individual species (SpecAR) and relative abundances (percentages) of benthic foraminifera of an AMS ¹⁴C-dated high resolution sediment core from the Norwegian Seas (water depth: 2707 m) provide a record of the faunal fluctuations from the last glacial maximum across the Weichselian deglaciation to the Holocene. During glacial times, the total foraminifera accumulation remains at a very low level (< 100 specimens cm⁻² kyr⁻¹) and is dominated by two endofaunal species: Oridorsalis umbonatus (Reuss) and Siphotextularia rolshauseni (Phleger and Parker) and reworked specimens of the genus Elphidium. The following deglaciation period exhibits an increase of the AR of the total fauna at 14 kyr B.P. The species distribution is marked by the last appearance of S. rolshauseni and the first postglacial appearance of suspension feeding Cibicidoides wuellerstorfi (Schwager) 13 kyr B.P. The absolute maximum of benthic foraminiferal AR (2750 spec cm⁻² kyr⁻¹ occurred near 9 kyr B.P. at the end of the deglaciation. This maximum also marks the re-appearance of the agglutinating species Cribrostomoides subglobosus (Sars). The post-glacial interval is characterized by a twofold reduction of the total accumulation of benthic foraminifera. The species distribution shows two new species: Ammobaculites agglutinans (d'Orbigny, at 6 kyr B.P.) and Epistominella exigua (Brady, at 3.5 kyr B.P.). The total AR indicates benthic activity during glacial times was at a low level. It was significantly higher during the Holocene with an abrupt increase of benthic foraminiferal abundance from 10 to 9 kyr B.P. The Stepwise re-invasion into the postglacial deep-sea environment maybe related to specific habitat preference.     

Glacial Holocene environment of the southeastern Okhotsk Sea: evidence from geochemical and palaeontological data

Environmental conditions and productivity changes in the southeastern Okhotsk Sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate, organic carbon and opal content data from two sediment cores. Species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence. AMS radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 ¹⁴C kyr and for correlation between environmental variations in the Okhotsk Sea, and regional and global climate changes. Benthic foraminiferal assemblages in the two cores (depth 1590 and 1175 m) varied with time, so that we could recognise seven zones with different species composition. Changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations. During the last glaciation, fluxes of organic matter to the sea floor showed strong seasonal variations, indicated by the presence of abundant A. weddellensis and infaunal Uvigerina spp. Benthic foraminiferal assemblages changed with warming at 12.5–11 and 10–8 ¹⁴C kyr BP, when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1A and 1B. Younger Dryas cooling caused a decline in productivity (11–10 kyr BP) affecting the benthic faunal community. Subsequent warming triggered intensive diatom production, opal accumulation and a strong oxygen deficiency, causing significant changes in benthic fauna assemblages from 5.26–4.4 kyr BP to present time.     

Palaeoenvironments of deposition of Neogene laminated diatom mat deposits from the eastern equatorial Pacific from studies of benthic foraminifera (sites 844, 849, 851)

Massive sedimentation of mats of the diatom Thalassiothrix longissima forming laminated diatom mat deposits (LDM) occurred intermittently in the equatorial Pacific throughout the Neogene from at least 15 to 4.8 m.y. ago. The background deposition was otherwise calcareous nannofossil diatom ooze (NO). Benthic foraminifera have been used to reconstruct the benthic environment of deposition and the role of both surface waters (as a source of food) and bottom waters (including their corrosivity) during LDM deposition. Three LDM events were studied: Site 844 (11.4 Ma, early Tortonian), Site 849 (4.8 Ma, early Zanclian and 6.6–6.8 Ma, early Messinian). A control section of NO spanning the 4.8 Ma event was studied from Site 851. In addition, the carbonate high NO immediately preceding the 4.8 Ma event was examined in Site 849. From the foraminiferal evidence it can be shown that the LDM was deposited under conditions of normal oxygenation because infaunal taxa are present throughout and there was an increase in epifaunal taxa such as Cibicides spp. However, there was a reduction in test size probably because only those smaller than 250 μm were able to move through the restricted sediment pore spaces caused by the diatom mat meshwork. The rate of accumulation of tests is highest in LDM interval and may reflect reduced predation from macrofaunal endobenthos. Among the epifaunal taxa, Nuttallides spp. show a decrease in abundance in the LDM and even immediately preceding it. This may be linked to a greater influence of corrosive AABW. Species known to feed opportunistically on phytodetritus (Epistominella exigua and Alabaminella weddellensis) are common in both NO and LDM. The increased relative abundance of A. weddellensis in the LDM may be due to this species being smaller than E. exigua and better able to exploit the food resource within the restrictive mat meshwork. The foraminiferal results corroborate the previous interpretation that preservation of lamination in the LDM is due to the physical exclusion of macro endobenthos rather than oxygen depletion of the bottom waters.     

Distribution of ostracod and benthic foraminiferal assemblages during the last 550 kyr in the East-Corsica basin,western Mediterranean Sea: A paleo-environmental reconstruction

The study of Quaternary sediments covering the last 550 kyr from the borehole GDEC-4-2, East-Corsica basin, was performed through the study of benthic meiofaunal assemblages (ostracoda and benthic foraminifera) whose distribution responds to climate changes, and glacial–interglacial variability in particular. The interglacial ostracod group is mainly composed of the Argilloecia acuminata, Cytheropteron alatum, Henryhowella sp., Polycope sp. and Cytherella sp., which indicate an enhanced surface productivity and possibly high bottom water temperature during these warm intervals. Benthic foraminifera, such as Hoeglundina elegans, Sigmoilopsis schlumbergeri, Bigenerina nodosaria and Hyalinea balthica are predominant during interglacial periods and also show an increasing surface productivity associated to warm intervals. Increase in surface productivity would contribute to an enhanced export of organic matter to sea floor at the GDEC-4-2 site during interglacial periods. The bottom temperature drop coupled with the important sedimentary inputs (associated to a significant quantity of refractory organic matter) during glacial periods was highlighted by the predominance of ostracoda, such as Paradoxostoma sp., Cytheropteron testudo, Bathycythere vanstraateni, Macrocypris sp., Echinocythereis echinata and benthic foraminifera as Bolivina spathulata, Bulimina costata, and Bulimina marginata. The distribution of some benthic foraminifera species describing a turnover system allowed the characterization of the last three climate cycles (MIS 8–9, MIS 6–7, MIS 1–5) probably marked by changes of bottom water paleoceanographic conditions in terms of temperature, salinity, bottom current intensity and surface productivity. The cyclic variations of the allochthonous group recorded over the last 550 kyr suggest a major role played by the eustatic factor, with the latter possibly favouring down slope transport. The distribution of this group allowed thus establishing a link between shelf-basin sediment transfer and climate, with enhanced shelf-basin sediment transfer during glacial low stands.     

Linkages between surface and deep circulations in the southern Japan Sea during the last 27,000 years: Evidence from planktic foraminiferal assemblages and stable isotope records

We analyzed planktic foraminiferal assemblages, oxygen and carbon isotope records, and the presence or absence of laminations to reconstruct the paleoenvironments of the southern Japan Sea since the last glacial period. Data were collected from two well-dated cores. One core (water depth 999 m) included thinly laminated mud layers, the other (water depth 283 m) contained nonlaminated sediments. Tephrochronology and accelerator mass spectrometry ¹⁴C dating of 14 horizons revealed that the two cores contained continuous records of the last 27 cal kyr. A total of 13 planktic foraminiferal species belonging to six genera were identified in down-core samples. The typical indicators of the Tsushima Current water, Globigerinoides ruber, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, Globigerinoides tenellus, and Globigerinita glutinata occurred since 9.3 cal kyr BP. Neogloboquadrina incompta, which was the dominant species in the Tsushima Current region of the modern Japan Sea, first occurred at 8.2 cal kyr BP and dominated the assemblage since 7.3 cal kyr BP. These results clearly indicate that the warm Tsushima Current started to inflow into the Japan Sea at 9.3 cal kyr BP, and the modern surface conditions in the southern Japan Sea were essentially established at 7.3 cal kyr BP. Our data and comparison of the presence or absence of laminated sediments in three locations from the southern Japan Sea suggest that deep circulation during the deglacial period was weaker than that at present. In addition, deep circulation in the modern Japan Sea, which supplies oxygen-rich water to the entire basin, started probably in association with the first inflow of the Tsushima Current beginning at 9.3 cal kyr BP.     

High-resolution sea surface temperature and salinity dynamics in the northern Okinawa Trough over the last 24 kyr

Based on the high-resolution Mg/Ca and oxygen isotope ratio (δ¹⁸O) of planktonic foraminifera Globigerinoides ruber, sea surface temperature (SST) and salinity (SSS) were reconstructed in Core PC-1 from the northern Okinawa Trough during the last 24 kyr. From the last glacial maximum to Holocene, SST varied from 20.2°C to 24.6°C. Millennial-scale climatic events of the SST during the last glacial, such as the Heinrich events, Bølling-Allerød warming, and Younger Dryas, have been identified, which are synchronous with the climate changes in the North Atlantic, suggesting a teleconnection between the northwestern Pacific and the North Atlantic. During the last 24 kyr, the SSS variation can be divided into three parts: (1) during 21–15.5 ka, there was a significantly low SSS; (2) during 15.5–11.7 ka, the SSS increased obviously; (3) since 11.7 ka, the SSS is relatively stable. In order to discuss the main factors influencing the SSS in the northern Okinawa Trough, the relative abundance of Pulleniatina obliquiloculata and the oxygen isotope difference between the northern and middle Okinawa Trough (Δδ¹⁸O_sw) have been used to indicate the intensity of the Kuroshio Current and Changjiang freshwater discharge, respectively. The Δδ¹⁸O_sw result shows that there is a large amount of Changjiang freshwater emptied into the northern Okinawa Trough during 18–15.5 ka, which is caused by the subtropical monsoon rain band lingering in the lower reaches of the Changjiang River drainage, supporting the Jet Transition Hypothesis. As the Kuroshio Current strengthened since 15.5 ka as indicated by the increased relative abundance of P. obliquiloculata, the variation of Kuroshio Current became the more important contribution to the SSS in the study region. The results of our study indicate that the key factor influencing the SSS in the northern Okinawa Trough is variable during the last 24 kyr.     

Reconstruction of Indian monsoon variability over the past 230,000 years: Planktic foraminiferal evidence from the NW Arabian Sea open-ocean upwelling area

We determined the faunal composition and total number of tests (#/g) of planktic foraminifera (> 125 μm) in core KH00-05 GOA 6 near Oman in order to decipher monsoon-induced variability of oceanographic productivity in the open-ocean upwelling area in the northwest Arabian Sea. The core contains a continuous record of sedimentation over the last 230 kyr, with the age model based on oxygen isotope and accelerator mass spectrometry ¹⁴C dates. We focused on species (Globigerina bulloides and Globigerinita glutinata) typical for SW monsoonal upwelling and species typical for NE monsoon conditions (Neogloboquadrina incompta, Neogloboquadrina dutertrei, Globigerinoides ruber, and Globigerinoides sacculifer). The changes in relative abundance of these monsoonal indicators suggest that the open-ocean upwelling area was dominated by the SW monsoon during interglacial periods, but by the NE monsoon during glacial periods.Increases in total test abundance during glacial periods confirmed that the NE monsoon rather than SW monsoon contributes largely to planktic foraminiferal productivity in this area. We argue that three types of circumstances resulted in high productivity, with nine high productivity events occurring at a 23-kyr frequency. The first type caused high productivity events at 102 and 199 ka (interglacial periods), characterized by the dominance of upwelling species, indicating high productivity during strong SW monsoons, correlated with high July insolation at 45° N. An exceptional high productivity event occurred at 37 ka during interglacial marine isotope stage (MIS) 3, with contributions from both SW and NE monsoons. The second type of high productivity event occurred at 61, 147, and 175 ka, during glacial periods, characterized by dominance of NE monsoon species, and correlated with low January insolation at 45° N. In addition, a high productivity event at 85 ka (interglacial period) also was induced by enhanced NE monsoons. The last two high productivity events occurred during transitional periods from glacial to interglacial (MIS 6/5.5 and 2/1), were characterized by the replacement of NE monsoon species with upwelling species, and corresponded to abrupt climate warming, suggesting that they are related to both accelerated SW monsoon systems and reduced NE monsoon systems.     

Coccolithophores in the equatorial Atlantic Ocean: response to seasonal and Late Quaternary surface water variability

The present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial Atlantic. Data from a range of different samples, from the plankton, surface sediments as well as sediment cores are shown and compared with each other.In general, the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns. Cell densities reached a maximum of up to 300×10³ coccospheres/l in the upwelling area of the equatorial Atlantic. Here, Emiliania huxleyi is the dominant species with relatively high cell numbers, whereas Umbellosphaera irregularis and Umbellosphaera tenuis are characteristic for oligotrophic surface waters. Although they are observed in high relative abundances, these species only occur in low absolute numbers. The lower photic zone is dominated by high abundances and considerable cell numbers of Florisphaera profunda.The geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses. However, abundances of the oligotrophic species Umbellosphaera irregularis and Umbellosphaera tenuis are strongly diminished, causing an increase in relative abundance of the lower photic zone taxa Florisphaera profunda and Gladiolithus flabellatus.During the past 140,000 years the surface water circulation of the equatorial Atlantic has changed drastically, as can be seen from changes in the coccolithophore species composition, absolute coccolith numbers, as well as coccolith accumulation rates. Significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial Atlantic during the last glacial interval (oxygen isotope stages 2–4), which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site. In the western equatorial Atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods, which probably is caused by a deepening of the thermocline.     

Pleistocene fluctuations in the Agulhas Current Retroflection based on the calcareous plankton record

Piston core (PS2487-6), recovered south of Cape Town, and sediment surface samples, recovered in the area of the Agulhas Current retroflection, were used to construct paleoceanographic scenarios for the late Quaternary in a region with an important role in global water mass transfer. Coccolithophore (calcareous nannofossil) and planktonic foraminifera assemblages and oxygen isotope data were collected. Stratigraphic control is based on calibration of the δ¹⁸O stratigraphic signals with calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes. Study of the surface sediments permits the characterisation of the Agulhas Current, Subtropical Convergence and Subantarctic coccolithophore assemblages. The Agulhas Current assemblage has relatively high proportions of Florisphaera profunda, Gephyrocapsa oceanica and Umbilicosphaera spp. These species are absent or present in low proportions in subantarctic waters. The abundance of coccolithophores during isotope stages 1, 5 and 7 is characteristic of relatively warm, stratified surface waters, with a deep nutricline and chlorophyll maximum, which strongly suggests that the area was under the influence of the Agulhas Current retroflection. The incursion of Globigerinoides ruber, abundant today in the Agulhas Current, also supports this interpretation. Conversely, during glacial stages 2–4 and 6, a strong reduction in warm and stratified water indicators can be observed, together with an increase in cold-eutrophic species.The interval from isotope stages 8 to 12 displays an assemblage dominated by Gephyrocapsa caribbeanica, the highest values being seen in the so-called Mid-Brunhes event, accompanied by a clear reduction in subtropical Holocene species. During the glacial interval from isotope stages 10–12, G. caribbeanica dominated the assemblage. The ecological interpretation of this species is controversial due to a clear evolutionary overprint. Isotope stage 12 is here interpreted as having been the coldest one in the period studied. It is characterised by a strong increase in Neogloboquadrina pachyderma (dextral and sinistral) and a remarkable decrease in tropical and subtropical planktonic foraminifera. From isotope stage 13 to 18, a hiatus is interpreted. Below this hiatus the stratigraphic resolution is poorer, although the glacial–interglacial cyclicity is well defined in the Agulhas Current Retroflection area (Core PS2487-6) for the last 25 isotope stages. The glacial–interglacial cyclicity is thought to be due to a fluctuation in the Subtropical Convergence Zone, probably linked to the eastward and westward displacement of the Agulhas Current retroflection. In any case, the core studied was always in a subtropical environment, under the influence of the Agulhas Current, which was enhanced during interglacial periods. For the whole of the interval studied, increases in Calcidiscus leptoporus, Umbilicosphaera spp., and Syracosphaera spp. among the calcareous nannofossils, and in G. ruber and Globigerinoides sacculifer within the planktonic foraminifera, clearly respond to interglacial pulses, reaching maximum values during short periods close to the major deglaciations.     

Sedimentary response to sea level and climate changes in the inner sea of Maldives carbonate platform over the past 30 kyr

We applied AMS ¹⁴C dates, Mg/Ca estimated sea surface temperature (SST), planktonic foraminiferal abundance, coarse component and X-ray diffraction mineral composition analyses for an International Ocean Discovery Program (IODP) sediment Hole U1467C in the Maldives inner sea, to reveal factors that affected the depositional process in the Maldives inner sea over the past 30 kyr. We found that the linear sedimentation rate (LSR) in Holocene (6.8 cm/kyr) was obviously higher than that in glacial period (3.45 cm/kyr); the average SST during the Holocene was 2–3°C higher than that in glacial stage. High abundance of planktonic foraminifera occurred during the glacial period, which was consistent with the variation of pelagic biogenic component. Reef-sourced material showed apparent high percentage during the Holocene (43.5%), in contrast to the low values during the glacial stage (20.7%). Terrigenous matter, only accounting for a small percentage in carbonate platform, was relatively high during the glacial period than that in the Holocene. We therefore conclude that reef-sourced material, dominated in the glacial-interglacial sediment sources, was mainly affected by sea level and climate changes. During glacial stage, sea level low-stand and weakened weathering in Maldives limited the input of the eroded material into the inner sea, resulting in low LSR; while the Holocene high sea level accompanied with rapid growth of the reef atoll and enhanced weathering, brought more reef-sourced material to the inner sea, leading to increased LSR and lowered abundance of planktonic foraminifera. The sea level and climate-controlled reef-sourced material changes are the key to understand the sedimentary process of the Maldives inner sea. Our study will shed some light on the evolution of glacial-interglacial sedimentary process of carbonate platform.     

Recent abyssal benthic foraminiferal biofacies of the eastern equatorial Indian Ocean

Study of Recent abyssal benthic foraminifera from core-top samples in the eastern equatorial Indian Ocean has identified distinctive faunas whose distribution patterns reflect the major hydrographic features of the region. Above 3800 m, Indian Deep Water (IDW) is characterized by a diverse and evenly-distributed biofacies to whichGlobocassidulina subglobosa, Pyrgo spp.,Uvigerina peregrina, andEggerella bradyi are the major contributors.Nuttalides umbonifera andEpistominella exigua are associated with Indian Bottom Water (IBW) below 3800 m. Within the IBW fauna,N. umbonifera andE. exigua are characteristic of two biofacies with independent distribution patterns.Nuttalides umbonifera systematically increases in abundance with increasing water depth. TheE. exigua biofacies reaches its greatest abundance in sediments on the eastern flank of the Ninetyeast Ridge and in the Wharton-Cocos Basin. The hydrographic transition between IDW and IBW coincides with the level of transition from waters supersaturated to waters undersaturated with respect to calcite and with the depth of the lysocline. Carbonate saturation levels, possibly combined with the effects of selective dissolution on the benthic foraminiferal populations, best explain the change in faunas across the IDW/IBW boundary and the bathymetric distribution pattern ofN. umbonifera. The distribution of theE. exigua fauna cannot be explained with this model.Epistominella exigua is associated with the colder, more oxygenated IBW of the Wharton-Cocos Basin. The distribution of this biofacies on the eastern flank of the Ninetyeast Ridge agrees well with the calculated bathymetric position of the northward flowing deep boundary current which aerates the eastern basins of the Indian Ocean.     

The surface ocean productivity response of deeper water benthic foraminifera in the Atlantic Ocean

We test the relationship of deep sea benthic foraminiferal assemblage composition to the surface ocean productivity gradient in the low latitude Atlantic Ocean using 81 surface sediment samples from a water depth range between 2800 and 3500 m. The samples are selected so that the surface ocean productivity gradient, controlling the flux of organic carbon to the seabed, will be the most important environmental variable. The first two principal components of the assemblage data account for 73% of data variance and are clearly linked to the productivity gradient across the Atlantic. These components show that under higher productivity the assemblages contain a higher abundance of Uvigerina peregrina, Melonis barleeanum, Globobulimina spp. and other taxa with probable infaunal microhabitats. Alabaminella weddellensis, a species linked to episodic phytoplankton debris falls, is also important in these assemblages. As productivity decreases there is a regular shift in assemblage composition so that low productivity assemblages are dominated by Globocassidulina subglobosa and several Cassidulina species along with Epistominella exigua. We hypothesize that these taxa are epifaunal to very shallow infaunal since nearly all organic carbon oxidation occurs near the sediment-water interface in low productivity settings. Discriminant function analysis of the foraminiferal assemblages, with groups selected on the basis of surface ocean productivity, shows clear separation among five productivity levels we used. This analysis demonstrates that productivity variations have a strong influence on assemblage composition. Finally, we used two groups of samples from the Rio-Grande Rise representing water depths from 2007 to 2340 m and 2739 to 3454 m to test for effects produced by changing water depth. All these samples are from a low productivity region and represent nearly identical environmental conditions. Although the low productivity nature of all the Rio-Grande Rise samples is obvious, there are assemblage differences between our depth groups. We cannot account for the assemblage differences with changes in organic carbon flux, dissolution effects or other physical/chemical properties of the ocean. Thus there are as yet unidentified factors related to water depth which cause some assemblage variation in the low productivity setting we investigated.     

Paleoenvironmental changes in northwest Mongolia during the last 27?kyr inferred from organic components in the Lake Hovsgol sediment core record

We studied organic components in the X106 sediment core (length 130.3 cm, water depth 236 m, 50°53′01″N, 100°21′22″E) from Lake Hovsgol to elucidate the biological production, source of organic components, and paleoenvironmental and paleolimnological changes during the last 27 kyr in northwest Mongolia. Total organic carbon (TOC) contents (0.20–0.70%) in the core of the last glacial period increased dramatically and attained 3.16–5.85% in the postglacial period (Holocene), together with the increase of the contribution of terrestrial organic matter. Biological production (both terrestrial and aquatic production) based on the TOC contents in the Holocene was 14 times higher than that in the last glacial period. The B?lling-Aller?d warm period and Younger Dryas cool period were both observed at depths of 55–50 cm (ca. 15–13 cal kyr BP) and 50–45 cm (ca. 13–11 cal kyr BP), respectively. We propose here a terrestrial/aquatic index (TAI) for organic matter in lake sediments. The TAI values suggest that terrestrial organic matter in the bottom of the core was less than 10%, increased to 48% in the B?lling-Aller?d warm period, decreased abruptly to 20% in the Younger Dryas cool period, and again increased to 30–40% in the Holocene. Normal-C₃₁ alkane (a biomarker of herbaceous land plants) and n-C₁₈ alkanoic acid (marker of plankton) decreased from the last glacial period to the Holocene, whereas n-C₂₃ alkane and n-C₂₂ alkanoic acid (a marker of higher vascular plants) increased from the last glacial period to the Holocene. Scarce herbaceous plant vegetation, such as Artemisia spp. of the lake basin in the last glacial period, changed into an abundance of higher woody plant vegetation (e.g., Pinus spp., Betula spp. and/or Larix spp.) in the Holocene. Stanol/sterol ratios suggest that relatively high oxygen tension of the lake bottom in ca. 27–22 cal kyr BP decreased from this age to the present, though benthic organisms are still abundant.     

Varieties of a single cosmopolitan diatom species associated with surface water masses in the North Pacific

A time series of 65 sediment trap samples, representing 48-month changes in diatom flora, and 62 sediment core-tops from the western North Pacific Ocean were analyzed. Varieties of a single diatom species were found to be characteristic of two surface water masses bounded by the Kuroshio Current. Thalassionema nitzschioides var. incurvata, var. inflata and var. parva dominate in warm saline waters in the Subtropical Gyre, while T. nitzschioides sensu stricto is abundant in less-saline waters northwest of this current. Time series data on percent abundances for the three T. nitzschioides varieties in the T. nitzschioides complex are compared with path variations of the current south of Japan. Inter-annual fluctuations in percent abundance are linked to changes in surface water masses over the sediment traps in association with migration of the Kuroshio paths. This finding makes the percent abundance a useful tool for deciphering path migrations of the Kuroshio Current in the geologic past. Down-core analyses of two sediment cores collected beneath the modern Kuroshio Current were performed. A sharp increase in percent abundances from 12 to 9 kyr BP, with an abrupt change around 11 kyr BP, records the previously reported transition of the Kuroshio Current from a predominantly offshore path to its modern path. Path migrations of the Kuroshio Current may be inferred from percent abundances of these diatoms, which comprise a new proxy for delineating the paleoclimate of the northwestern Pacific in relation to changes in northward heat transport from the western equatorial Pacific Ocean by the western boundary current.     

An Early Cenomanian (Late Cretaceous) maximum flooding bioevent in NW Europe: Correlation,sedimentology and biofacies

The Early Cenomanian (mid-Mantelliceras dixoni Zone) Schloenbachia/Inoceramus virgatus Event of NW Europe is recorded in five calcareous ‘marl’-limestone couplets rich in inoceramid bivalves of the Inoceramus virgatus plexus. The 1.3–6.8m thick beds represent a bundle of precession couplets inferred to have been deposited during a short-term cycle of sea-level change triggered by the 100kyr short eccentricity cycle within the Milankovitch periodicities. A burrowed omission surface terminates the Schloenbachia/Inoceramus virgatus Event in most places. Rock accumulation rates vary in different sections between 13 and 68Bubnoff units (mm/kyr) for the complete 100kyr cycle with extreme values ranging from 10 to 100Bubnoffs at shorter (i.e., 20kyr precession couplet) scales. Taphonomic and microfacies trends suggest deposition below fair-weather wave base with frequent to sporadic reworking of the sea-floor by storm waves for proximal and medial sections. The distal sections were close to, or even slightly below, maximum storm wave base. The biofacies of the Schloenbachia/Inoceramus virgatus Event is strongly dominated by inoceramid bivalves (65–85%). The two representatives of Inoceramus virgatus, I. virgatus virgatus Schlüter and I. virgatus scalprum Böhm, are not geographic subspecies as they co-occur in the same beds. However, proximal morphs tend to be more strongly ribbed and flatter whereas distal ones are more inflated and smoother, representing ecophenotypes of one polymorphic species. Taphonomic observations and shell morphology suggest that the inoceramids lived as epibyssate recliners. The low species richness and fossil content of the event strata (without the inoceramid bivalves) are attributed to low fluxes of organic matter to the sea-bed during the maximum flooding interval of Cenomanian depositional sequence Ce III. The inoceramids of the virgatus plexus are inferred to have been very effective filter feeders flourishing under nutrient-depleted, low-energy conditions. The Schloenbachia/Inoceramus virgatus Event is an example of a maximum flooding bioevent, forming a widespread marker dominated largely by autochthonous biota.     

Pest management systems affect composition but not abundance of phytoseiid mites (Acari: Phytoseiidae) in apple orchards

We examined the faunal composition and abundance of phytoseiid mites (Acari: Phytoseiidae) in apple orchards under different pest management systems in Hungary. A total of 30 apple orchards were surveyed, including abandoned and organic orchards and orchards where integrated pest management (IPM) or broad spectrum insecticides (conventional pest management) were applied. A total of 18 phytoseiid species were found in the canopy of apple trees. Species richness was greatest in the organic orchards (mean: 3.3 species/400 leaves) and the least in the conventional orchards (1.4), with IPM (2.1) and abandoned (2.7) orchards showing intermediate values. The phytoseiid community’s Rényi diversity displayed a similar pattern. However, the total phytoseiid abundance in the orchards with different pest management systems did not differ, with abundance varying between 1.8 and 2.6 phytoseiids/10 leaves. Amblyseius andersoni, Euseius finlandicus, and Typhlodromus pyri were the three most common species. The relative abundance of A. andersoni increased with the pesticide load of the orchards whereas the relative abundance of E. finlandicus decreased. The abundance of T. pyri did not change in the apple orchards under different pest management strategies; regardless of the type of applied treatment, they only displayed greater abundance in five of the orchards. The remaining 15 phytoseiid species only occurred in small numbers, mostly from the abandoned and organic orchards. We identified a negative correlation between the abundance of T. pyri and the other phytoseiids in the abandoned and organic orchards. However, we did not find any similar link between the abundance of A. andersoni and E. finlandicus.     

High frequency palaeoceanographic changes during the past 140?000 yr recorded by the organic matter in sediments of the Iberian Margin

Biogenic records of the marine palaeoproductivity (carbonates, organic carbon, and C₃₇ alkenones) and the molecular stratigraphy of past sea surface temperatures (SSTs; U₃₇^K′) were studied at high resolution in two cores of the Iberian Margin. The comparison of these records indicates that the oceanographic conditions switched abruptly during the past 160 kyr between three kinds of regimes. A first regime with high (17-22°C) SST and low productivity typifies the interglacial periods, marine isotopic stages (MIS) 5 and 1. Several periods during MIS 6, 2, and the terminations II and I are characterised by about 4-5°C colder SST and a higher organic matter accumulation, both of which define the second regime. This anticorrelation between SST and marine productivity suggests that these variations are related to the intensity of the coastal upwelling. By contrast with this upwelling behaviour, extremely low biological productivity and very cold SST (6-12°C) occurred during short phases of glacial MIS 6, 4, and 2, and as abrupt events (≈1 kyr or less) during MIS 3. The three oceanographic regimes are consistent with micropalaeontological changes in the same cores based on foraminifera and diatoms.The general trend of these hydrologic changes follows the long-term glacial/interglacial cycle, but the millennium scale variability is clearly related to Heinrich events and Dansgaard-Oeschger cycles. Strengthening of the upwelling corresponds probably to an intensification of the subtropical atmospheric circulation over the North Atlantic which was influenced by the presence of continental ice sheets. However, extreme glacial conditions due to massive discharges of icebergs interrupted the upwelling. Interestingly, both terminations II and I coincided with strong but transient intensification of the upwelling.     

Developmental features and associated symbiont bacterial diversity in essential life cycle stages of Heterostelium colligatum

Dictyostelium discoideum is a specialized amoebozoan protist that can feed on, carry and disperse bacteria. However, the symbiont bacterial diversity in other species of dictyostelids and the diversity associated with essential life cycle stages are still unknown until now. Here, another species of dictyostelids, Heterostelium colligatum, a new record for tropical China, was isolated from the soil collected in Xishuangbanna Tropical Botanical Garden, Yunnan Province, China. We describe the complete life cycle of this species and illustrate details of spore-to-spore development. The symbiont bacterial diversity and relative abundance associated with life cycle stages of H. colligatum, including the aggregation, pseudoplasmodium, and sorocarp stages, were investigated by high throughput metagenomic techniques. H. colligatum appears to be capable of carrying different types of bacteria during its life history in addition to those used as a food resource. The dominant groups of those three stages in its life cycle were the Proteobacteria, Actinobacteria and Firmicutes. The relative abundance of the dominant phyla and shared OTUs were different for the aggregation, pseudoplasmodium, and sorocarp stages. A comparison of the symbiont bacterial assemblages associated with D. discoideum and H. colligatum indicated that different dictyostelid species carried different species of symbiont associated bacteria.     

Ciliate community structure and interactions within the planktonic food web in two alpine lakes of contrasting transparency

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