Radiocarbon age, Mg/Ca and d18O measurements on planktonic foraminifera of sediment core GeoB12605-3

The sea surface temperature (SST) of the tropical Indian Ocean is a major component of global climate teleconnections. While the Holocene SST history is documented for regions affected by the Indian and Arabian monsoons, data from the near-equatorial western Indian Ocean are sparse. Reconstructing past zonal and meridional SST gradients requires additional information on past temperatures from the western boundary current region. We present a unique record of Holocene SST and thermocline depth variations in the tropical western Indian Ocean as documented in foraminiferal Mg/Ca ratios and d18O from a sediment core off northern Tanzania. For Mg/Ca and thermocline d18O, most variance is concentrated in the centennial to bicentennial periodicity band. On the millennial time scale, an early to mid-Holocene (~7.8-5.6 ka) warm phase is followed by a temperature drop by up to 2°C, leading to a mid-Holocene cool interval (5.6-4.2 ka). The shift is accompanied by an initial reduction in the difference between surface and thermocline foraminiferal d18O, consistent with the thickening of the mixed layer and suggestions of a strengthened Walker circulation. However, we cannot confirm the expected enhanced zonal SST gradient, as the cooling of similar magnitude had previously been found in SSTs from the upwelling region off Sumatra and in Flores air temperatures. The SST pattern probably reflects the tropical Indian Ocean expression of a large-scale climate anomaly rather than a positive Indian Ocean Dipole-like mean state.

Sea surface temperature reconstruction for the middle Pleistocene from sediment core MD03-2699

Past sea surface water conditions of the western Iberian Margin were reconstructed based on biomarker analyses of a marine deep sea core MD03-2699 from the Estremadura Spur north off Lisbon, providing new insights into orbital and suborbital-scale climate variability between marine isotope stage (MIS) 15 to MIS 9 (580 to 300 ka). We use biomarker-based proxy records such as the alkenone unsaturated index to estimate sea surface temperature (SST), the total alkenone concentration to reconstruct phytoplankton productivity, and terrestrial biomarkers to evaluate the continental input. The results extend the existing biomarker record, namely the SST for the Iberian Margin, back to the sixth climatic cycle (580 ka). A general trend of stable interglacials contrasts with glacial periods and glacial inceptions which are marked by high-frequency variability. Thus, several short-lived climatic coolings were identified by large SST decreases, the occurrence of ice-rafted detritus and high percentages of the tetraunsaturated alkenone C 37:4. Some of these events were extremely cold and similar in their general trends to the well-known Heinrich events of the last glaciation. We identified eight Heinrich-type events between 580 and 300 ka. The general deglaciation pattern detected between MIS 15 and MIS 9 is similar in their general trends to that characterizing the more recent climatic cycles, i.e., marked by two coolings separated by a short warming episode which may reflect the southward, northward, and southward migration of the Polar Front.

(Table 1) Age control points and of sediment core MD01-2444

The marine isotopic stage 3 (MIS3) at Ocean Drilling Program (ODP) Site 1060 (Gulf Stream) shows both sharp onset and end of interstadials, the existence of very short lived warm events during stadials, and points to differences in detail between the sea surface temperature (SST) record from the western North Atlantic and the atmospheric temperature record inferred from d18O in Greenland ice. Investigating MIS3 and obtaining comparable data from other locations appears crucial. The eastern Atlantic provides well-documented records of climate changes. We have selected a core from off Portugal and use it to examine Dansgaard/Oeschger events (D/O) at centennial-scale resolution (139 years on average between two data points). We have obtained a faunal data set for core MD01-2444, 37°N, 10°W, 2600 m water depth and use a group of species (Globigerina bulloides + Globigerinita glutinata) as a proxy of upwelling intensity driven by trade winds intensity changes. We tentatively relate the variation of this group to a North Atlantic Oscillation-like phenomenon (NAO) off Portugal. We observe that it resembles the rainfall index in the Caribbean as recorded at ODP Site 1002 (Cariaco Basin) which traces the Intertropical Convergence Zone (ITCZ) location through changes of terrigenous inputs. The driest intervals (ITZC to the south) at Site 1002 correspond to intervals of increased upwelling in MD01-2444 as well as the driest periods identified during stadials on similar cores in the area. Because the ITZC to the south is consistent with an El Niño-Southern Oscillation (ENSO+) situation, our study suggests a positive correlation between ENSO-like conditions and NAO-like conditions at a millennial timescale. During interstadial intervals when increased wetness over Cariaco is recorded (ITCZ to the north) and the upwelling in MD01-2444 is decreased, we see from both SSTs and faunal tropical indicators that MD01-2444 site is warm. In addition, interstadials are equally warm through each so-called Bond cycle. This contrasts with the Greenland Ice Core Project (GRIP) record where interstadial peaks are successively cooler through each Bond cycle. This record confirms a link between tropical climate linked to ITCZ position and the climate of southern Europe at millennial timescales, in spite of showing a very good correlation with polar latitudes (GRIP) through d18O on Globigerina bulloides. In addition, because the warmest SSTs and the d18O on G. bulloides are so remarkably different, our work points to changes in seasonality as a strong control over the climatic pattern of the North Atlantic area and the marked influence of winter conditions.

Sedimentology of core M74/4_1143-1

Periplatform ooze is an admixture of pelagic carbonate and sediment derived from neritic carbonate platforms. Compositional variations of periplatform ooze allow the rectonstruction of past sea-level changes. Periplatform ooze formed during sea-level highstands is finer grained and richer in aragonit through the elevated input of material from the flooded platform compared to periplatform ooze formed during the episodes of lowered sea level. In many cases, however, the sea floor around carbonate platforms is subjected to bottom currents which are expected to affect sediment composition, i.e. through winnowing of the fine fraction. The interaction of sea-level driven highstand shedding and current impact on the formation of periplatform ooze is influenced or even distorted by changing current activity, an integrated study using seismic, hydroacoustic and sedimentological data has been performed on periplatform ooze deposited in the Inner Sea of the Maldives. The Miocene to Pleistocene succession of drift deposits is subdivided into nine units; limits of seismostratigraphic units correspond to changes or turnarounds in grain size trends in cores recovered at ODP Site 716 and NEOMA Site 1143. For the Pleistocene it can be shown how changes in grain size occur in concert with sea-level changes and changes of the monsoonal system, which is thought to be a major driver bottom currents in the Maldives. A clear hightstand shedding pattern only appears in the data at a time of of relaxation of monsoonal strength during the last 315 ky. Results imply (1) that drift sediments provide a potential target for analyzing past changes in oceanic currents and (2) that the ooze composition bears a mixed signal of input and physical winnowing at the sea floor.

Sea-surface temperature and salinity reconstruction for sediment core GeoB5844-2

We present high-resolution paleoceanographic records of surface and deep water conditions within the northern Red Sea covering the last glacial maximum and termination I using alkenone paleothermometry, stable oxygen isotopes, and sediment compositional data. Paleoceanographic records in the restricted desert-surrounded northern Red Sea are strongly affected by the stepwise sea level rise and appear to record and amplify well-known millennial-scale climate events from the North Atlantic realm. During the last glacial maximum (LGM), sea surface temperatures were about 4°C cooler than the late Holocene. Pronounced coolings associated with Heinrich event 1 (~2°C below the LGM level) and the Younger Dryas imply strong atmospheric teleconnections to the North Atlantic. Owing to the restricted exchange with the Indian Ocean, Red Sea salinity is particularly sensitive to changes in global sea level. Paleosalinities exceeded 50 psu during the LGM. A pronounced freshening of the surface waters is associated with the meltwater peaks MWP1a and MWP1b owing to an increased surface-near inflow of "normal" saline water from the Indian Ocean. Vertical delta18O gradients are also increased during these phases, indicating stronger surface water stratification. The combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers, which were deposited under almost anoxic condition in a stagnant water body.

Age model and palaeoclimate records over the past 22,000 years of sediment core GeoB10053-7

The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region. However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years, based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern Java. We show that glacial-interglacial variations in the Australian-Indonesian winter monsoon were in phase with the Indian summer monsoon system, consistent with their modern linkage through cross-equatorial surface winds. Likewise, millennial-scale variability of upwelling shares similar sign and timing with upwelling variability in the Arabian Sea. On the basis of element composition and grain-size distribution as precipitation-sensitive proxies in the same archive, we infer that (austral) summer monsoon rainfall was highest during the Bølling-Allerød period and the past 2,500 years. Our results indicate drier conditions during Heinrich Stadial 1 due to a southward shift of summer rainfall and a relatively weak Hadley cell south of the Equator. We suggest that the Australian-Indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere.

Intact and core tetraether lipids in water column profiles of suspended particulate matter and of surface sediment samples off Cape Blanc, NW Africa

In the reconstruction of sea surface temperature (SST) from sedimentary archives, secondary sources, lateral transport and selective preservation are considered to be mainly negligible in terms of influencing the primary signal. This is also true for the archaeal glycerol dialkyl glycerol tetraethers (GDGTs) that form the basis for the TEX86 SST proxy. Our samples represent four years variability on a transect off Cape Blanc (NW Africa). We studied the subsurface production, vertical and lateral transport of intact polar lipids and core GDGTs in the water column at high vertical resolution on the basis of suspended particulate matter (SPM) samples from the photic zone, the subsurface oxygen minimum zone (OMZ), nepheloid layers (NL) and the water column between these. Furthermore we compared the water column SPM GDGT composition with that in underlying surface sediments. This is the first study that reports TEX86 values from the precursor intact polar lipids (IPLs) associated with specific head groups (IPL -specific TEX86). We show a clear deviation from the sea surface GDGT composition in the OMZ between 300 and 600 m. Since neither lateral transport nor selective degradation provides a satisfactory explanation for the observed TEX-derived temperature profiles with a bias towards higher temperatures for both core- and IPL -specific TEX86 values, we suggest that subsurface in situ production of archaea with a distinct relationship between lipid biosynthesis and temperature is the responsible mechanism. However, in the NW-African upwelling system the GDGT contribution of the OMZ to the surface sediments does not seem to affect the sedimentary TEX86 as it shows no bias and still reflects the signal of the surface waters between 0 and 60 m.

(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.

Abundance of organic-walled dinoflagellate cysts of sediment core GeoB3603-2

Here, we reconstruct the varying influence of the Agulhas Current (AgC), the South Atlantic Current and the Antarctic Circumpolar Current on the Agulhas Retroflection (AgR) in the eastern South Atlantic Ocean for the last 160,000 years on the basis of the dinoflagellate cysts, pollen and spores present in a sediment core (GeoB 3603-2) from the southeastern Cape Basin offshore South Africa, where the Agulhas Current enters the Atlantic Ocean. Our analyses reveal strong orbital forcing on the heat exchange between the Indian Ocean and the South Atlantic Ocean during the Late Quaternary. Maxima in local productivity appear to be primarily related to a strengthening of the ocean circulation as a result of the high seasonal contrast during precession maxima. During precession minima, seasonal contrast was low and stratified, oligo- to mesotrophic conditions prevailed, notably when these minima coincided with the glacial terminations. The clear presence of periodicities on a sub-Milankovitch scale as well as modulations of the primary frequencies demonstrate that the Agulhas Retroflection furthermore is modulated substantially by complex interactions between the subtropical, 'precession-driven', climate and ocean circulation systems, and the southern, 'obliquity-driven', high latitudes.