Pollen and dinoflagellate cyst counts on sediment core M72/5_628-1 (MD72/5-25-GC1) from the Black Sea

High-resolution pollen and dinoflagellate cyst records from sediment core M72/5-25-GC1 were used to reconstruct vegetation dynamics in northern Anatolia and surface conditions of the Black Sea between 64 and 20 ka BP. During this period, the dominance of Artemisia in the pollen record indicates a steppe landscape and arid climate conditions. However, the concomitant presence of temperate arboreal pollen suggests the existence of glacial refugia in northern Anatolia. Long-term glacial vegetation dynamics reveal two major arid phases ~64-55 and 40-32 ka BP, and two major humid phases ~54-45 and 28-20 ka BP, correlating with higher and lower summer insolation, respectively. Dansgaard-Oeschger (D-O) cycles are clearly indicated by the 25-GC1 pollen record. Greenland interstadials are characterized by a marked increase in temperate tree pollen, indicating a spread of forests due to warm/wet conditions in northern Anatolia, whereas Greenland stadials reveal cold and arid conditions as indicated by spread of xerophytic biomes. There is evidence for a phase lag of ~500 to 1500 yr between initial warming and forest expansion, possibly due to successive changes in atmospheric circulation in the North Atlantic sector. The dominance of Pyxidinopsis psilata and Spiniferites cruciformis in the dinocyst record indicates brackish Black Sea conditions during the entire glacial period. The decrease of marine indicators (marine dinocysts, acritarchs) at ~54 ka BP and increase of freshwater algae (Pediastrum, Botryococcus) from 32 to 25 ka BP reveals freshening of the Black Sea surface water. This freshening is possibly related to humid phases in the region, to connection between Caspian Sea and Black Sea, to seasonal freshening by floating ice, and/or to closer position of river mouths due to low sea level. In the southern Black Sea, Greenland interstadials are clearly indicated by high dinocyst concentrations and calcium carbonate content, as a result of an increase in primary productivity. Heinrich events show a similar impact on the environment in the northern Anatolia/Black Sea region as Greenland stadials.

Geochemistry of Fe-Mn oxyhydroxide samples of ODP Hole 172-1060A

The strength of the North Atlantic Meridional Overturning Circulation during climatically highly variable Marine Isotope Stage (MIS) 3 has attracted much attention in recent years. Here we present high-resolution Nd isotope compositions of past seawater derived from authigenic Fe-Mn oxyhydroxides recovered from drift sediments on the Blake Ridge in the deep western North Atlantic (ODP Leg 172, Site 1060, 3481 m water depth). The data cover the period from 45 to 35 ka BP, tracing circulation changes during major Heinrich iceberg discharge event 4 (H4, ~40-39 ka BP). The Nd isotope record suggests that there was no northern-source water (NSW) mass like modern NADW at the deeper part of Blake Ridge at any time between 45 and 35 ka. This is fundamentally different from the hydrographic situation during the Holocene where NADW extends below 4500 m at this location. The epsilon-Nd of past deep water recorded in the Blake Ridge sediments was least radiogenic during Dansgaard/Oeschger (D/O) Interstadial (IS) 8 (epsilon-Nd = -11.3) and most radiogenic immediately preceding IS 9 (epsilon-Nd = -9.8). More radiogenic compositions were also recorded during H4 (-10.2 <= epsilon-Nd <= -9.9). The Nd isotope variability in MIS 3 matches that of a physical bottom current strength reconstruction from the same location. Neither record follows the pattern of Northern Hemisphere D/O climatic cycles. In our record, reduced mixing with northern source waters started in stadial 12 and lasted until after H4 in stadial 9, followed by a rapid increase in NSW contribution thereafter. This major change in the Nd isotope record predates the iceberg discharge event Heinrich 4 by more than 3 ka indicating a shallowing of the water mass boundary between Glacial North Atlantic Intermediate Water and Southern Source Water beneath. This early change in bottom water properties at the deep Blake Ridge suggests that North Atlantic deep water advection may already have decreased several thousand years before the actual iceberg discharge event and associated freshening of the surface waters in the North Atlantic. The change can thus not be attributed to climatic events in the North Atlantic but may be related to changes in flux of deep water from the South.

Gut content, fatty acid composition and metabolic rates of the amphipod Anonyx sarsi during POLARSTERN cruise ARK-XIX/1, ice station PS64/070-6

During a winter expedition to the western Barents Sea in March 2003, benthic amphipods of the species Anonyx sarsi were observed directly below pack ice. Only males and juveniles [16.0-37.0 mm long, 16.2-120.8 mg dry mass (DM)] were collected. Guts contained macroalgal fibres, fish eggs and flesh from large carrion. Amphipods had very low levels of total lipids (2.7-17.2% DM). Analysis of lipid biomarkers showed that some of the specimens had preyed on pelagic copepods. Individual respiration rates ranged over 0.4-1.7 ml O2/day (mean: 1.2 ml, SD: 0.5 ml). Individual ammonia excretion rates varied between 7.8 µg and 49.3 µg N/day (mean: 30.7 µg, SD: 15.2 µg). The atomic O:N ratio ranged over 35 to 71 (mean: 55, SD: 14), indicating lipid-dominated metabolism. Mass-specific respiration ranged over 9.8-16.6 ml O2/day/g DM (mean: 13.1 ml, SD: 2.2 ml). The metabolic rates of A. sarsi were twice as high as those of the truly sympagic amphipod Gammarus wilkitzkii, which is better adapted to the under-ice habitat by its energy-saving attached lifestyle. It is concluded that males and juveniles of A. sarsi were actively searching for food in the water column and at the ice underside, but that the nutritional status of the amphipods in late Arctic winter was generally very poor.

Isotopic data of atmospheric methane from EDML and Vostok ice cores over a full glacial cycle

The response of natural CH4 sources to climate changes will be an important factor to consider as concentrations of this potent greenhouse gas continue to increase. Polar ice cores provide the means to assess this sensitivity in the past and have shown a close connection between CH4 levels and northern hemisphere temperature variability over the last glacial cycle. However, the contribution of the various CH4 sources and sinks to these changes is still a matter of debate. Contemporaneous stable CH4 isotope records in ice cores provide additional boundary conditions for assessing changes in the CH4 sources and sinks. Here we present new ice core CH4 isotope data covering the last 160,000 years, showing a clear decoupling between CH4 loading and carbon isotopic variations over most of the record. We suggest that d13CH4 variations were not dominated by a change in the source mix but rather by climate- and CO2-related ecosystem control on the isotopic composition of the methane precursor material, especially in seasonally inundated wetlands in the tropics. In contrast, relatively stable d13CH4 intervals occurred during large CH4 loading changes concurrently with past climate changes implying that most CH4 sources (most notably tropical wetlands) responded simultaneously.

(Table 1) Age determination on monospecies planktonic foraminifera of sediment core AN25-934

Reconstruction of regional climate and the Okhotsk Sea (OS) environment for the Last Glacial Maximum (LGM), deglaciation and Holocene were performed on the basis of high-resolution records of ice rafted debris (IRD), CaCO3, opal, total organic carbon (TOC), biogenic Ba (Ba_bio) and redox sensitive element (Mn, Mo) content, and diatom and pollen results of four cores that form a north-southern transect. Age models of the studied cores were earlier established by AMS 14C data, oxygen - isotope chronostratigraphy and tephrochronology. According to received results, since 25 ka the regional climate and OS environmental conditions have changed synchronously with LGM condition, cold Heinrich event 1, Bølling -Allerød (BA) warming, Younger Dryas (YD) cooling and Pre-Boreal (PB) warming recorded in the Greenland ice core, North Atlantic sediment, and China cave stalagmites. Calculation of IRD MAR in sediment of north-south transect cores indicate an increase of sea ice formation several times in the glacial OS as compared to the Late Holocene. Accompanying ice formation, increased brine rejection and the larger potential density of surface water at the north shelf due to a drop of glacial East Asia summer monsoon precipitation and Amur River run off, led to strong enhancement of the role of the OS in glacial North Pacific Intermediate Water (NPIW) formation. The remarkable increase in OS productivity during BA and PB warming was probably related with significant reorganisation of the North Pacific deep water ventilation and nutrient input into the NPIW and OS Intermediate Water (OSIW). Seven Holocene OS millennial cold events based on the elevated values of the detrended IRD stack record over the IRD broad trend in the sediments of the studied cores have occurred synchronously with cold events recorded in the North Atlantic, Greenland ice cores and China cave stalagmites after 9 ka. Diatom production in the OS were mostly controlled by sea ice cover changes and surface water stratification induced by sea-ice melting; therefore significant opal accumulation in sediments of this basin begin from 4-6 ka ago simultaneously with a remarkable decrease of sea ice cover.

(Table 1) Age determination of sediment core AAS-62/2

Variations in the Indian summer monsoon (ISM) intensity during the last 16.7?ka have been studied using organic carbon (Corg), d15N of sedimentary organic matter, CaCO3, sediment texture, d18OC, and Mg/Ca-derived sea surface temperature, d18O of sea water and sea surface salinity, in a 14C-dated sediment core from the eastern Arabian Sea. The d18O in water and planktonic foraminifera shells off the central west coast of India may be controlled by the ISM intensity as this area receives high precipitation and land runoff. Also, the Corg and CaCO3 contents of sediments and d15N of sedimentary organic matter may be linked to ISM-induced productivity and denitrification. The results of the present study reveal that between 16 and 15.2 ka BP, the ISM was weak with minor fluctuations and started intensifying around 15.2 ka BP, at the onset of the Bølling-Ållerød (B-A) event. The B-A event is characterized by higher water column denitrification rates comparable to the present day. The ISM signatures observed in the d18OC record of B-A event compare well with those from Timta cave of the western Himalayas and also the Asian summer monsoon signatures from the Hulu caves in China and warming signatures in Greenland Ice Sheet Project 2 (GISP2) suggesting atmospheric teleconnections through Intertropical Convergence Zone. The boundary between the Younger Dryas and the Holocene is discernible with small episodes of abrupt events of increased ISM intensity. This decrease in d18OC values at ~11.8 ka BP is contemporary with June solar insolation maximum at 30° north and the increase in methane in the GISP2 ice core supporting episodes of warmer climate and increase in ISM intensity. The ISM seems to have been most stable between 7 and 5.6 ka BP. The core exhibits periodicity of 500 years that is comparable to the Atlantic water formation and the Chinese monsoon.

Temperature variabilty in the southeastern Black-Sea during 64-20ka BP

The Eurasian inland propagation of temperature anomalies during glacial millennial-scale climate variability is poorly understood but this knowledge is crucial to understanding hemisphere-wide atmospheric teleconnection patterns and climate mechanisms. Based on biomarkers and geochemical paleothermometers, a pronounced continental temperature variability between 64,000 and 20,000 years ago, coinciding with the Greenland Dansgaard-Oeschger cycles, was determined in a well-dated sediment record from the formerly enclosed Black Sea. Cooling during Heinrich events was not stronger than during other stadials in the Black Sea. This is corroborated by modeling results showing that regular Dansgaard-Oeschger cycles penetrated deeper into the Eurasian continent than Heinrich events. The pattern of coastal ice-rafted detritus suggests a strong dependence on the climate background state, with significantly milder winters during periods of reduced Eurasian ice sheets and an intensified meridional atmospheric circulation.

Pollen profile and age determination for sediment core M72/5_619-1 (22-GC3)

Sediments from the Black Sea, a region historically dominated by forests and steppe landscapes, are a valuable source of detailed information on the changes in regional terrestrial and aquatic environments at decadal to millennial scales. Here we present multi-proxy environmental records (pollen, dinoflagellate cysts, Ca, Ti and oxygen isotope data) from the uppermost 305 cm of the core 22-GC3 (42°13.53' N, 36°29.55' E) collected from a water depth of 838 m in the southern part of the Black Sea in 2007. The records span the last ~ 18 kyr (all ages are given in cal kyr BP). The pollen data reveal the dominance of the Artemisia-steppe in the region, suggesting rather dry/cold environments ~ 18-14.5 kyr BP. Warming/humidity increase during melt-water pulses (~ 16.1-14.5 kyr BP), indicated by d18O records from the 22-GC3 core sediment and from the Sofular Cave stalagmite, is expressed in more negative d13C values from the Sofular Cave, usually interpreted as the spreading of C3 plants. The records representing the interstadial complex (~ 14.5-12.9 kyr BP) show an increase in temperature and moisture, indicated by forest development, increased primary productivity and reduced surface run-off, whereas the switch from primary terrigenous to primary authigenic Ca origin occurs ~ 500 yr later. The Younger Dryas cooling is clearly demonstrated by more negative d13C values from the Sofular Cave and a reduction of pines. The early Holocene (11.7-8.5 kyr BP) interval reveals relatively dry conditions compared to the mostly moist and warm middle Holocene (8.5-5 kyr BP), which is characterized by the establishment of the species-rich warm mixed and temperate deciduous forests in the low elevation belt, temperate deciduous beech-hornbeam forests in the middle and cool conifer forest in upper mountain belt. The border between the early and middle Holocene in the vegetation records coincides with the opening of the Mediterranean corridor at ~ 8.3 kyr BP, as indicated by a marked change in the dinocyst assemblages and in the sediment lithology. Changes in the pollen assemblages indicate a reduction in forest cover after ~ 5 kyr BP, which was likely caused by increased anthropogenic pressure on the regional vegetation.

(Table 1) Radiocarbon ages of Bivalvia shells obtained from core ASV13_1157, Novaya Zemlya Trench

It is shown that sediments accumulated in the Southern Novaya Zemlya Trench at both deglaciation and marine stages. Permanent sea ice sheet existed during the deglaciation, and glacier meltwater was intensely delivered to the bottom layer. Along with the dominant sediment supply from the Southern Island of Novaya Zemlya, southern continental sources also played a noticeable role at that stage. Seasonal sea ice freezing led to the formation of cold brines at the marine stage. Like paleoproductivity, these processes were irregular. Dissolution of calcareous benthic foraminiferal tests considerably intensified after about 7 ka BP owing to a stronger Atlantic water advection into the Western Arctic and consequent increase in paleoproductivity, whereas the relative role of southern sedimentary provenances decreased. Sedimentation rates were constant (45 cm/ka) during the entire marine stage.

GDGT and n-alkane data of sediment core GeoB4901-8

The tight coupling between the atmospheric and oceanic circulation in the equatorial Atlantic region makes this area an important region for paleoclimatic research. Previous studies report the occurrence of large amounts of terrigenous material and soil organic carbon (SOC) within the marine sediments of the eastern Gulf of Guinea. We use the accumulation rates (AR) of branched glycerol dialkyl glycerol tetraethers (GDGTs) to identify variations in SOC delivery to the Niger Fan over the last 35 ka, and compare these records to long-chain n-alkanes as a proxy for higher plant material, to an inorganic proxy for terrigenous input (aluminum AR) and to indicators for the marine productivity (AR of carbonate and crenarchaeol). In addition, sea surface temperatures (SSTs) are calculated based on the TEX86H index and environmental factors affecting the SST-reconstructions are discussed. Our results indicate that Al AR are closely connected to the rate of mean sea level change after 15 ka BP, with an additional influence of the increased monsoonal precipitation and extended vegetation cover corresponding to the African Humid Period (14.8-5.5 ka BP). Branched GDGT AR appears to be determined by shelf erosion in addition to the interplay of monsoonal precipitation and vegetation cover controlling soil erosion. Long-chain n-alkane concentrations clearly show a different trend than the other proxies, which might be due to their predominant eolian transport. Paleo-SSTs show a clear shift from colder temperatures during the last glacial period (20-22 °C) to warmer temperatures during the Holocene (24-26 °C). However, TEX86H-based SSTs are cold-biased compared to recent SSTs and Mg/Ca-based SST reconstructions, which is probably caused by a high seasonality of the Thaumarchaeota, with a maximum productivity of these organisms during the cold summer months. However, a sub-surface production of GDGTs and/or a potential bias of SST reconstruction by terrestrial input could not be completely excluded.

Benthic foraminiferal record from Santa Barbara basin

The oxygen minimum zone (OMZ) of the late Quaternary California margin experienced abrupt and dramatic changes in strength and depth in response to changes in intermediate water ventilation, ocean productivity, and climate at orbital through millennial time scales. Expansion and contraction of the OMZ is exhibited at high temporal resolution (107-126 year) by quantitative benthic foraminiferal assemblage changes in two piston cores forming a vertical profile in Santa Barbara Basin (569 m, basin floor; 481 m, near sill depth) to 34 and 24 ka, respectively. Variation in the OMZ is quantified by new benthic foraminiferal groupings and new dissolved oxygen index based on documented relations between species and water-mass oxygen concentrations. Foraminiferal-based paleoenvironmental assessments are integrated with principal component analysis, bioturbation, grain size, CaCO3, total organic carbon, and d13C to reconstruct basin oxygenation history. Fauna responded similarly between the two sites, although with somewhat different magnitude and taxonomic expression. During cool episodes (Younger Dryas and stadials), the water column was well oxygenated, most strongly near the end of the glacial episode (17-16 ka; Heinrich 1). In contrast, the OMZ was strong during warm episodes (Bølling/Allerød, interstadials, and Pre-Boreal). During the Bølling/Allerød, the OMZ shoaled to <360 m of contemporaneous sea level, its greatest vertical expansion of the last glacial cycle. Assemblages were then dominated by Bolivina tumida, reflecting high concentrations of dissolved methane in bottom waters. Short decadal intervals were so severely oxygen-depleted that no benthic foraminifera were present. The middle to late Holocene (6-0 ka) was less dysoxic than the early Holocene.

Characterization of the defined MDC types and compilation of MDC initiation times (excel-file 19 kB)

Mud accumulates on continental shelves under a variety of environmental conditions and results in a diverse formation of mud depocenters (MDCs). Their three-dimensional architectures have been in the focus of several recent studies. Due to some terminological confusion concerning MDCs, the present study sets out to define eight individual MDC types in terms of surface sediment distribution and internal geometry. Under conditions of substantial sediment supply, prodeltas (distal zones off river deltas; triangular sheets), subaqueous deltas (disconnected from deltas by strong normal-to-shore currents; wedge-like clinoforms), and mud patches (scattered distribution) and mud blankets (widespread covers) are formed. Forced by hydrodynamic conditions, mud belts in the strict sense (detached from source; elongated bodies), and shallow-water contourite drifts (detached from source; growing normal to prevailing current direction; triangular clinoforms) develop. Controlled by local morphology, mud entrapments (in depressions, behind morphological steps) and mud wedges (triangular clinoforms growing in flow direction) are deposited. Shelf mud deposition took place (1) during early outer-shelf drowning (~14 ka), (2) after inner-shelf inundation to maximum flooding (9.5-6.5 ka), and (3) in sub-recent times (<2 ka). Subsequent expansion may be (1) concentric, in cases where the depocenter formed near the fluvial source, (2) uni-directional, extending along advective current transport paths, and (3) progradational, forming clinoforms that grow either parallel or normal to the bottom current direction. Classical mud belts may be initiated around defined nuclei, the remote sites of which are determined by seafloor morphology rather than the location of the source. From a stratigraphic perspective, mud depocenters coincide with sea-level highstand-related, shelf-wide condensed sections. They often show a conformable succession from transgressive to highstand systems tract stages.

14C specific radiocarbon ages and bulk ages accompanied by geochemical proxys from surface sediment samples in the Black Sea

Transfer of organic carbon (OC) from the terrestrial to the oceanic carbon pool is largely driven by riverine and aeolian transport. Before transport, however, terrigenous organic matter can be retained in intermediate terrestrial reservoirs such as soils. Using compound-specific radiocarbon analysis of terrigenous biomarkers their average terrestrial residence time can be evaluated. Here we show compound-specific radiocarbon (14C) ages of terrigenous biomarkers and bulk 14C ages accompanied by geochemical proxy data from core top samples collected along transects in front of several river mouths in the Black Sea. 14C ages of long chain n-alkanes, long chain n-fatty acids and total organic carbon (TOC) are highest in front of the river mouths, correlating well with BIT (branched and isoprenoid tetraether) indices, which indicates contribution of pre-aged, soil-derived terrigenous organic matter. The radiocarbon ages decrease further offshore towards locations where organic matter is dominated by marine production and aeolian input potentially contributes terrigenous organic matter. Average terrestrial residence times of vascular plant biomarkers deduced from n-C29+31 alkanes and n-C28+30 fatty acids ages from stations directly in front of the river mouths range from 900 ± 70 years to 4400 ± 170 years. These average residence times correlate with size and topography in climatically similar catchments, whereas the climatic regime appears to control continental carbon turnover times in morphologically similar drainage areas of the Black Sea catchment. Along-transect data imply petrogenic contribution of n-C29+31 alkanes and input via different terrigenous biomarker transport modes, i.e., riverine and aeolian, resulting in aged biomarkers at offshore core locations. Because n-C29+31 alkanes show contributions from petrogenic sources, n-C28+30 fatty acids likely provide better estimates of average terrestrial residence times of vascular plant biomarkers. Moreover, sedimentary n-C28 and n-C30 fatty acids appear clearly much less influenced by autochthonous sources than n-C24 and n-C26 fatty acids as indicated by increasing radiocarbon ages with increasing chain-length and are, thus, more representative as vascular plant biomarkers.

Snow line of the rhine-linth glacier in the upper wurm

The Wurmian Glaciation of the Alpine Foreland has been reconstructed in different phases as a result of investigations in the Rhine-Bodan region as well as in the Linth area. The whole High Glacial is divided in four main phases: ice advance into the piedmont basins, building-up of the foreland glaciation, high stages and retreat into the inner Alps. This epoch took up perhaps less than 12,000 years. During the period of building, an average increase of ice thickness of about 12 cm per year was sufficient to form an extensive foreland glacier within 5000-7000 years. The snow lines of the stades of the piedmont glaciation as well as of the local glaciers are calculated. Snow lines at about 1500 m a.s.l. led to an inner alpine ice build-up and an advance of glaciers towards the piedmont basins. To produce the foreland ice sheet, low snow lines of 900-1000 m a.s.l. were necessary. An interstadial phase before the maximum glaciation is evidenced by sediment sequences and a 14C-date of 22,100 BP. The chronology of ice retreat after 18 ka BP is still uncertain.

Seasonal variations in surface metabolite composition of Fucus vesiculosus and Fucus serratus sampled at outer Kiel Fjord (August 2012 - July 2013)

The chemical composition of surface associated metabolites of two Fucus species (Fucus vesiculosus and Fucus serratus) was analysed by means of gas chromatography-mass spectrometry (GC-MS) to describe temporal patterns in chemical surface composition. Method: The two perennial brown macroalgae F. vesiculosus and F. serratus were sampled monthly at Bülk, outer Kiel Fjord, Germany (54°27'21 N / 10°11'57 E) over an entire year (August 2012 - July 2013). Per month and species six non-fertile Fucus individuals were collected from mixed stands at a depth of 0.5 m under mid water level. For surface extraction approx. 50 g of the upper 5-10 cm apical thalli tips were cut off per species. The surface extraction of Fucus was performed according to the protocol of de Nys and co-workers (1998) with minor modifications (see Rickert et al. 2015). GC/EI-MS measurements were performed with a Waters GCT premier (Waters, Manchester, UK) coupled to an Agilent 6890N GC equipped with a DB-5 ms 30 m column (0.25 mm internal diameter, 0.25 mM film thickness, Agilent, USA). The inlet temperature was maintained at 250°C and samples were injected in split 10 mode. He carrier gas flow was adjusted to 1 ml min-1. Alkanes were used for referencing of retention times. For further details (GC-MS sample preparation and analysis) see the related publication (Rickert et al. submitted to PLOS ONE).