delta Deuterium of alkenone and BIT index of sediment core 64PE304-80 samples

Reconstructing past ocean salinity is important for assessing paleoceanographic change and therefore past climatic dynamics. Commonly, sea water salinity reconstruction is based on foraminifera oxygen isotope ratio values combined with sea surface temperature reconstruction. However, the approach relies on multiple proxies, resulting in relatively large uncertainty and, consequently, relatively low accuracy of salinity estimates. An alternative tool for past ocean salinity reconstruction is the hydrogen isotope composition of long chain (C37) alkenones (dDalkenone). Here, we applied dDalkenone to a 39 ka long coastal sediment record from the Eastern South African continental shelf in the Mozambique Channel, close to the Zambezi River mouth. Despite changes in global sea water dD related to glacial - interglacial ice volume effects, no clear changes were observed in the dDalkenone record throughout the entire 39 ka. The BIT index record from the same core showed high BIT values during the glacial and low values during the Holocene. This indicates a more pronounced freshwater influence at the core location during the glacial, resulting in alkenones depleted in deuterium during that time and, thereby, explains the lack of a clear glacial-interglacial alkenone dD shift. Correlation between the BIT index and dDalkenone during the glacial period suggests that increased continental runoff potentially changed the growth conditions of the alkenone producing haptophytes, promoting coastal haptophyte species with generally more enriched dDalkenone values. We therefore suggest that the application of dDalkenone for reconstructing past salinity in coastal settings may be complicated by changes in the alkenone producing haptophyte community.

Multi-proxy record of planktonic and benthic foraminiferal d18O, and Mg/Ca-derived surface and lower thermocline temperatures in sediment core SO18471 (GIK18471), Timor Sea

Paleostudies of the Indonesian Throughflow (ITF) are largely based on temperature and salinity reconstructions of its near surface component, whereas the variability of its lower thermocline flow has rarely been investigated. We present a multi-proxy record of planktonic and benthic foraminiferal d18O, Mg/Ca-derived surface and lower thermocline temperatures, X-ray fluorescence (XRF)-derived runoff and sediment winnowing for the past 130 ka in marine sediment core SO18471. Core SO18471, retrieved from a water depth of 485 m at the southern edge of the Timor Strait close to the Sahul Shelf, sits in a strategic position to reconstruct variations in both the ITF surface and lower thermocline flow as well as to investigate hydrological changes related to monsoon variability and shelf dynamics over time. Sediment winnowing demonstrates that the ITF thermocline flow intensified during MIS 5d-a and MIS 1. In contrast during MIS 5e, winnowing was reduced and terrigenous input increased suggesting intensification of the local wet monsoon and a weaker ITF. Lower thermocline warming during globally cold periods (MIS 4 - MIS 2) appears to be related to a weaker and contracted thermocline ITF and advection of warm and salty Indian Ocean waters.

Table 1: Station list with macrobenthos biomass results from the ocean floor

Among the Siberian shelf seas the Kara Sea is most strongly influenced by riverine runoff with nearly 1500 km fresh water discharge per year. This fresh water, discharged mainly by Ob and Yenisei, contains about 3.1 * 106 and 4.6 * 106 tons of total organic carbon per year, respectively (Gordeev et al. 1996). Little is known about the relevance of this organic material for biological communities, neither for the Kara Sea nor for the adjacent deep basins of the central Arctic Ocean. Aiming at elucidating the fate of fluvial matter transported from the rivers via estuaries into the central Arctic Ocean and the relative importance of marine organic matter being produced such information is crucial. Here we present calculations on the organic carbon demand of the Kara Sea macrozoobenthos based on measured biomass (total wet weight [ww] per 0.25 m ) from quantitative box corer samples and empirical relationships between biomass, annual production, annual respiration, and carbon remineralisation. This bottom-up approach may serve as a first estimate of the carbon remineralization potential of a given zoobenthos community (or area) as long as no data on in situ respiration rates are available. Our data basis comprises 54 stations sampled in summer seasons 1997, 1999 and 2000 in the Kara Sea at water depths between 10 and 68 m. The geographical area represented by stations analysed covers roughly 178 000 km**2, which is about one fifth of the total Kara Sea area. In this area, 290 species of invertebrate macrozoobenthos were identified with polychaeta, Crustacea, mollusca and echinodermata being the most abundant. For all stations analysed, mean biomass values ranged between 4.3 and 778.1 g ww/m**2 with organic carbon demands between 3.5 and 43.2 mg C/m**2/d. For the area of 178 000 km2 a preliminary total consumption of 1.4 * 10**6t Corg/y (equivalent to 21.5 mg C/m**2/d) was calculated for the macrozoobenthos. An extrapolation of our data would lead to an annual carbon demand of about 5-7 * 106 t for the whole Kara Sea macrozoobenthos (or 15.5-21.7 mg C/m2/d).

(Table 2) Radiocarbon content and 14C AMS ages of planktonic foraminifera from sediment cores Louis_1900 and Louis_2023

North American freshwater runoff records have been used to support the case that climate flickers were caused by shutdowns of the ocean thermohaline circulation (THC) resulting from reversals of meltwater discharges. Inconsistencies in the documentation of these meltwater switches, however, continue to fuel the debate on the cause/s of the oscillatory nature of the deglacial climate. New oxygen and carbon isotope records from the northern Gulf of Mexico depict in exceptional detail the succession of meltwater floods and pauses through the southern routing during the interval 16 to 8.9 ka (14C years BP; ka, kiloannum). The records underscore the bimodal role played by the Gulf of Mexico as a destination of meltwater discharges from the receding Laurentide Ice Sheet. The evidence indicates that the Gulf of Mexico acted as the principal source of superfloods at 13.4, 12.6, and 11.9 ka that reached the North Atlantic and contributed significantly to density stratification, disruption of ocean ventilation, and cold reversals. Gulf of Mexico lapsed into a "relief valve" position in post-Younger Dryas time, when meltwater discharges were rerouted south at 9.9, 9.7, 9.4, and 9.1 ka, thus temporarily interrupting North Atlantic-bound freshwater discharges from Lake Agassiz. The history of meltwater events in the Gulf of Mexico contradicts the model that meltwater flow via the eastern outlets into the North Atlantic disrupted the ocean THC, causing cooling, while diversions to the Gulf of Mexico via the Mississippi River enhanced THC and warming.

Benthic cyanobacterial mat (BCM) abundance on samples from the coast of Curacao

Benthic cyanobacterial mats (BCMs) are impacting coral reefs worldwide. However, the factors and mechanisms driving their proliferation are unclear. We conducted a multi-year survey around the Caribbean island of Curaçao, which revealed highest BCM abundance on sheltered reefs close to urbanised areas. Reefs with high BCM abundance were also characterised by high benthic cover of macroalgae and low cover of corals. Nutrient concentrations in the water-column were consistently low, but markedly increased just above substrata (both sandy and hard) covered with BCMs. This was true for sites with both high and low BCM coverage, suggesting that BCM growth is stimulated by a localised, substrate-linked release of nutrients from the microbial degradation of organic matter. This hypothesis was supported by a higher organic content in sediments on reefs with high BCM coverage, and by an in situ experiment which showed that BCMs grew within days on sediments enriched with organic matter (Spirulina). We propose that nutrient runoff from urbanised areas stimulates phototrophic blooms and enhances organic matter concentrations on the reef. This organic matter is transported by currents and settles on the seabed at sites with low hydrodynamics. Subsequently, nutrients released from the organic matter degradation fuel the growth of BCMs. Improved management of nutrients generated on land should lower organic loading of sediments and other benthos (e.g. turf and macroalgae) to reduce BCM proliferation on coral reefs.

Sedimentology on surface samples from the White Sea

In this study, the grain-size and clay-mineral compositions of 73 surface sediment samples collected in a variety of environmental settings in the White Sea are presented to characterize recent sedimentation processes, reconstruct transport pathways, and identify potential source areas of the terrigenous components. Areas >100 m deep are invariably characterized by silty clay, whereas areas <100 m deep exhibit more heterogeneous grain-size compositions plausibly explained by coastal erosion and (re-)distribution mechanisms, particularly tidal currents. The dominance of sand in the estuarine areas of the Onega and Dvina rivers as well as toward Gorlo Strait connecting the White Sea with the Barents Sea, is attributed to increased current speeds. Illite and smectite are the dominant clay minerals in recent sediments of the southwestern and eastern White Sea sectors, respectively. Their distribution patterns largely depend on the geology of the source areas and mirror surface circulation patterns, especially in Dvina Bay. Smectite is a key clay mineral in White Sea surface sediments as it reveals the dominating influence of the Northern Dvina's runoff on sedimentation and water circulation throughout the basin of the sea. In comparison to other Eurasian shelf seas, the White Sea is characterized by a greater diversity of clay-mineral assemblages, which range from illite- to smectite-dominated sectors containing variable amounts of chlorite and kaolinite.

Stable carbon and oxygen isotope ratios of benthic and planktonic foraminifera of ODP Hole 171-1049C

Ocean anoxic events were periods of high carbon burial that led to drawdown of atmospheric carbon dioxide, lowering of bottom-water oxygen concentrations and, in many cases, significant biological extinction (Arthur et al., 1990; Erbacher et al., 1996, doi:10.1130/0091-7613(1996)024<0499:EPORAO>2.3.CO;2; Kuypers et al., 1999, doi:10.1038/20659; Jenkyns, 1997; Hochuli et al., 1999, doi:10.1130/0091-7613(1999)027<0657:EOHPAC>2.3.CO;2). Most ocean anoxic events are thought to be caused by high productivity and export of carbon from surface waters which is then preserved in organic-rich sediments, known as black shales. But the factors that triggered some of these events remain uncertain. Here we present stable isotope data from a mid-Cretaceous ocean anoxic event that occurred 112 Myr ago, and that point to increased thermohaline stratification as the probable cause. Ocean anoxic event 1b is associated with an increase in surface-water temperatures and runoff that led to decreased bottom-water formation and elevated carbon burial in the restricted basins of the western Tethys and North Atlantic. This event is in many ways similar to that which led to the more recent Plio-Pleistocene Mediterranean sapropels, but the greater geographical extent and longer duration (~46 kyr) of ocean anoxic event 1b suggest that processes leading to such ocean anoxic events in the North Atlantic and western Tethys were able to act over a much larger region, and sequester far more carbon, than any of the Quaternary sapropels.

Pollen and spore counts of sediment core GeoB12624

In tropical eastern Africa, vegetation distribution is largely controlled by regional hydrology, which has varied over the past 20 000 years. Therefore, accurate reconstructions of past vegetation and hydrological changes are crucial for a better understanding of climate variability in the tropical southeastern African region. We present high-resolution pollen records from a marine sediment core recovered offshore of the Rufiji River delta. Our data document significant shifts in pollen assemblages during the last deglaciation, identifying, through changes in both upland and lowland vegetation, specific responses of plant communities to atmospheric (precipitation) and coastal (coastal dynamics and sea-level changes) alterations. Specifically, arid conditions reflected by a maximum pollen representation of dry and open vegetation occurred during the Northern Hemisphere cold Heinrich event 1 (H1), suggesting that the expansion of drier upland vegetation was synchronous with cold Northern Hemisphere conditions. This arid period is followed by an interval in which forest and humid woodlands expanded, indicating a hydrologic shift towards more humid conditions. Droughts during H1 and the shift to humid conditions around 14.8 kyr BP in the uplands are consistent with latitudinal shifts of the intertropical convergence zone (ITCZ) driven by high-latitude Northern Hemisphere climatic fluctuations. Additionally, our results show that the lowland vegetation, consisting of well-developed salt marshes and mangroves in a successional pattern typical for vegetation occurring in intertidal habitats, has responded mainly to local coastal dynamics related to marine inundation frequencies and soil salinity in the Rufiji Delta as well as to the local moisture availability. Lowland vegetation shows a substantial expansion of mangrove trees after ~ 14.8 kyr BP, suggesting an increased moisture availability and river runoff in the coastal area. The results of this study highlight the decoupled climatic and environmental processes to which the vegetation in the uplands and the Rufiji Delta has responded during the last deglaciation.

(Table 1) Major element composition of core 5022-2CP, Laguna Potrok Aike, southern Patagonia

Total organic carbon, total inorganic carbon, biogenic silica content and total organic carbon/total nitrogen ratios of the Laguna Potrok Aike lacustrine sediment record are used to reconstruct the environmental history of south-east Patagonia during the past 51 ka in high resolution. High lake level conditions are assumed to have prevailed during the Last Glacial, as sediments are carbonate-free. Increased runoff linked to permafrost and reduced evaporation due to colder temperatures and reduced influence of Southern Hemispheric Westerlies (SHW) may have caused these high lake levels with lake productivity being low and organic matter mainly of algal or cyanobacterial origin. Aquatic moss growth and diatom blooms occurred synchronously with southern hemispheric glacial warming events such as the Antarctic A-events, the postglacial warming following the LGM and the Younger Dryas chronozone. During these times, a combination of warmer climatic conditions with related thawing permafrost could have increased the allochthonous input of nutrients and in combination with warmer surface waters increased aquatic moss growth and diatom production. The SHW were not observed to affect southern Patagonia during the Last Glacial. The Holocene presents a completely different lacustrine system because (a) permafrost no longer inhibits infiltration nor emits meltwater pulses and (b) the positioning of the SHW over the investigated area gives rise to strong and dry winds. Under these conditions total organic carbon, total organic carbon/total nitrogen ratios and biogenic silica cease to be first order productivity indicators. On the one hand, the biogenic silica is influenced by dissolution of diatoms due to higher salinity and pH of the lake water under evaporative stress characterizing low lake levels. On the other hand, total organic carbon and total organic carbon/total nitrogen profiles are influenced by reworked macrophytes from freshly exposed lake level terraces during lowstands. Total inorganic carbon remains the most reliable proxy for climatic variations during the Holocene as high precipitation of carbonates can be linked to low lake levels and high autochthonous production. The onset of inorganic carbon precipitation has been associated with the southward shift of the SHW over the latitudes of Laguna Potrok Aike. The refined age-depth model of this record suggests that this shift occurred around 9.4 cal. ka BP.

(Table 1) Composition of lipids in particulate matter and bottom sediments of the Baltic Sea

Lipid contents in the upper layer of bottom sediments in the Baltic Sea range from 0.37 to 2.66 mg/g (1.2-25.8% Corg). It is shown that the main factors determining composition of lipids in bottom precipitates are relative roles of different sources of lipids in sediments and conditions of sediment accumulation. Runoff of the Daugava River into the Gulf of Riga contributes simple low-polarity lipids. Sterols and certain bound fatty acids originate in living organic matter. Polar lipids are formed by inheritance of complex phospholipids and glycolipids from plankton and/or by formation of polycondensates.

R-ArcticNet, A Regional Hydrographic Data Network for the Pan-Arctic Region (ISO-image of CD-ROM)

We describe the contemporary hydrography of the pan-Arctic land area draining into the Arctic Ocean, northern Bering Sea, and Hudson Bay on the basis of observational records of river discharge and computed runoff. The Regional Arctic Hydrographic Network data set, R-ArcticNET, is presented, which is based on 3754 recording stations drawn from Russian, Canadian, European, and U.S. archives. R-ArcticNET represents the single largest data compendium of observed discharge in the Arctic. Approximately 73% of the nonglaciated area of the pan-Arctic is monitored by at least one river discharge gage giving a mean gage density of 168 gages per 106 km2. Average annual runoff is 212 mm yr?1 with approximately 60% of the river discharge occurring from April to July. Gridded runoff surfaces are generated for the gaged portion of the pan-Arctic region to investigate global change signals. Siberia and Alaska showed increases in winter runoff during the 1980s relative to the 1960s and 1970s during annual and seasonal periods. These changes are consistent with observations of change in the climatology of the region. Western Canada experienced decreased spring and summer runoff.

Geochemistry of sediment cores GeoB4901-3 and GeoB4901-8 from the southern flank of the Niger Fan

Time series of terrigenous source elements (Al, K, Ti, Zr) from core GeoB4901-8 recovered from the deep-sea fan of the Niger River record variations in riverine sediment discharge over the past 245,000 yr. Although the flux rates of all the elements depend on physical erosion, which is mainly controlled by the extent of vegetation coverage in central Africa, element/Al ratios reflect conditions for chemical weathering in the river basin. Maximum sediment input to the ocean occurs during cold and arid periods, when precipitation intensity and associated freshwater runoff are reduced. High carbonate contents during the same periods indicate that the sediment supply has a positive effect on river-induced marine productivity. In general, variations in the terrestrial signals contain a strong precessional component in tune with changes in low-latitude solar radiation. However, the terrestrial signal lags the insolation signal by several thousand years. K/Al, Ti/Al, and Zr/Al records reveal that African monsoonal precipitation depends on high-latitude forcing. We attribute the shift between insolation cycle and river discharge to the frequently reported nonlinear response of African climate to primary orbital configurations, which may be caused by a complex interaction of the secondary control parameters, such as surface albedo and/or thermohaline circulation.

Table 2: Stream flow measurement at the gauge station Vernagtbach

From 1974 to 1982 repeated tracer tests using fluorescent dyes were carried out in the highly glaciated drainage basin of Vernagtbach. These tests enabled the quantitative determination of the runoff in the forefield of the Vernagtferner, the calculation of travel times of the stream water and estimations of the relative contributions to the entire runoff originating from individual streams. In addition, tracer tests were carried out in the firn area of the glacier resulting in data concerning the storage and travel time of meltwater inside the glacier.

Sedimentology of sites 14-141, 41-366, 47-397 and 79-544B

Along the N-S-transect of DSDP-Sites 5446, 397, 141, and 366, oxygen and carbon isotopes, flux rates of calcium carbonate, terrigenous matter, and biogenic opal, clay minerals and the size distribution of terrigenous partictes were determined in order to assess the ties between atmospheric and oceanic surface and deep-water circulation off northwest Africa during the late Neogene. During the last 9 m.y., both the paleoceanography in the eastern Atlantic and west African paleodimates were intimately correlated with the evolution of the polar ice sheets as reflected in the benthos d18O curves of the 4 DSDP-Sites. These records make it possible to distinguish six major time intervals which were charaterized by long-term persistent regimes of climatic stability or climatic change. Short-term, "Milankovitch"-type cycles superimpose the long-term climatic evolution and may reflect the chronostratigraphic control fluctuations of the solar insolation persisting back to pre-Pleistocene times. Relatively stable, warm climates prevailed during the late Tortonian/early Messinean, 9 to 6 m.y., and the early Pliocene, 4.5 to 3.5 m.y. ago. Based on d18O curves, the amplitudes of short-term climatic variation were generally low, and the ice sheets were smaller than during peak Holocene time. Oceanic circulation and resulting paleoproductivity in upwelling zones were insignificant. The strength of dust supplying meridional trade winds was low (3 to 5 m/s), interglacial-style zonal winds near the ITCZ were dominant, as indicated by the high abundance of kaolinite. Phases of fluvial sediment supply were common. Humidity was characteristic of the climate in northwest Africa for the major part of this time. Major episodes of climatic deterioration in the subtropics occurred in the latest Miocene/early Pliocene, between some 5.6 and 5.2 and between 4.9 and 4.6 m.y. ago, in the late Pliocene, between 3.2 and 2.4 m.y. ago, and again in the Quaternary, near 1 m.y. ago. The episodes were correlated with marked increases of the global ice volume, as revealed by drastic increases of d18O values. They suggest sea-level falls of up to 70 m below the present sea level in the latest Miocene and earliest Pliocene and of 145 m in the latest Pliocene and Quaternary. The climatic changes resulted in strongly enhanced meridional trade winds as suggested by coarser terrigenous grain-sizes, increased mass accumulation rates of eolian dust, and changes in clay-mineral composition from dominantly kaolinite to illite and chlorite. The meridional trade winds reached speeds of 8 to 10 m/s with a maximum near 15 m/s. The enhanced winds probably led t o intensified coastal upwelling as shown by the contemporaneous local increase i n the deposition of biogenic silica and the local depletion of 13C at Site 397. The most drastic environmental changes near 2.4 and 1 m.y. ago coincide with hiatuses which may indicate phases of general erosion due to strongly enhanced deep-water circulation in the northeast At1antic along the northwest African continental margin. The occasional occurrence of quartz grains coarser than 250 µm may suggest ice-rafted debris in sediments off Morocco. During these time intervals the climate in NW-Africa was dominantly arid. Nevertheless, fluvial runoff (and humidity) continued to be important during intermittent warm phases of the short-term climatic cycles. During the end and the beginning of (inter-) glacial times, fluvial supply of nutrients seems to be the dominant factor, controling phases of enhanced paleoproductivity observed off northwest Africa, whereas during phases of glacial maximum strenger fertility of (increased) coastal upwelling becomes more important. A long-term evolution of paleoenvironments during the last 40 m.y. is depicted in the sediments of Site 366 and is clearly controlled by the plate tectonic route of this Site. During Oligocene times, Site 366 lay in the center of the equatorial upwelling, as shown by the high content of biogenic silica contributing up to 100 % of the carbonate-free sediment fraction >6 µm. The influence of equatorial upwelling abruptly terminated near 15 m.y. ago, a change in the record exaggerated by a hiatus of about 2 m.y. Prior to 25 m.y., the terrigenous input at the paleolatitude of Site 366 was restricted t o eolian sediment supply from South Africa by southeasterly trade winds, as shown by dominantly illite and chlorite in the clay fraction and extremely fine-grained terrigenous matter. Near the Oligocene/Miocene boundary, Site 366 drifted across the equator into the belt of the northeasterly trade winds, which is inferred from the increased content of kaolinite and coarser grain sizes of the terrigenous sediment fraction. The clay-mineral and grain-size compositions of Site 366 do not reflect a noteworthy northward shift of the ITCZ during late Miocene and early Pliocene times, i.e. no marked global circulation asymmetry due to the possible absence of a major Northern Hemisphere glaciation (Flohn 1981). This lack of a more northerly position of the ITCZ may result from a bipolar glaciation already existing during late Miocene times, such as also suggested by the evidence of tillites on Iceland and in southern Alaska during those intervals (e.g., Denton & Amstrong 1969, Mudie & Helgason 1983).