Description: Detailed knowledge about tropical South American precipitation patterns during Heinrich (H) and Dansgaard-Oeschger (DO) stadials provides relevant insights into the possible evolution of Amazonian hydroclimate under future climate change. Sediment core GeoB16224-1 (ca. 7°N), raised from a site in the continental slope off French Guiana in western equatorial Atlantic under the influence of the Amazon River discharge, documents the impacts of H and DO stadials on both inorganic (i.e., Fe/Ca record) and organic (i.e., alkenone C37 concentration and C37/C38 ratio) geochemistry between 41 and 13 ka BP. Our results show millennial-scale covariations of increased Fe/Ca values with decreased C37 concentration and C37/C38 ratios during H and DO stadials. Comparing our high temporal resolution data with previously published records from ca. 17°N to 4°S, we are able to differentiate the influence of H and DO stadials upon tropical South American precipitation. We find that records under the influence of the South American summer monsoon (e.g., western Amazon) and the northern edge of the Intertropical Convergence Zone (ITCZ) (e.g., northernmost South America) exhibit strong climate shifts during both H and DO stadials, but regions under the influence of the southern edge of the ITCZ (e.g., northeastern Brazil) experience a weaker reaction during DO stadials than during H stadials.

Description: Vegetation and climate change in nortwestern South America were studied using pollen analysis in combination with XRF scanning on marine sediments of ODP Site 1239 from the East Equatorial Pacific comprising the interval between 4.7 and 4.2 Ma. The study site is sensitive to latitudinal shifts of the Intertropical Convergence Zone (ITCZ) shifts insofar as a southward (northward) shift would result in increased (decreased) precipitation over Ecuador. The presented pollen record (46 samples) comprises representatives from five ecological groups: lowland rainforest, lower montane forest, upper montane forest, páramo, and broad range taxa. A broad tropical rainforest coverage persisted in the study area throughout the early Pliocene, without significant open vegetation below the forest line. Between 4.7 and 4.42 Ma, humidity increases, reaching its peak around 4.42 Ma, and slightly decreasing again afterwards. The stable, permanently humid conditions are rather in agreement with paleoceanographic data indicating a southward shift of the ITCZ, possibly in response to closure of the Central American Seaway. The presence of páramo vegetation indicates that the Western Cordillera of the northern Andes had already reached considerable elevation by the early Pliocene. The trend in iron/potassium-ratios (Fe/K) is similar to the pattern of humidity inferred from the pollen spectrum, showing the highest values around 4.46 Ma, thus supporting the hydrological interpretation of the pollen record.

Description: Atmospheric and oceanographic interactions between the Atlantic and Indian Oceans influence upwelling in the southern Benguela upwelling system. In order to obtain a better knowledge of paleoceanographic and paleoenvironmental changes in the southern Benguela region during the Holocene, 12 marine surface sediment samples and one gravity core GeoB8331-4 from the Namaqualand mudbelt off the west coast of South Africa have been studied for organic-walled dinoflagellate cysts in high temporal resolution. The results are compared with pollen and geochemical records from the same samples. Our study emphasizes significantly distinct histories in upwelling intensity as well as the influence of fluvial input during the Holocene. Three main phases were identified for the Holocene. High percentages of cysts produced by autotrophic taxa like Operculodinium centrocarpum and Spiniferites spp. indicate warmer and stratified conditions during the early Holocene (9900-8400 cal. yr BP), suggesting reduced upwelling likely due to a northward shift of the southern westerlies. In contrast, the middle Holocene (8400-3100 cal. yr BP) is characterized by a strong increase in heterotrophic taxa in particular Lejeunecysta paratenella and Echinidinium spp. at the expense of autotrophic taxa. This indicates cool and nutrient-rich waters with active upwelling probably caused by a southward shift of the southern westerlies. During the late Holocene (3100 cal. yr BP to modern), Brigantedinium spp. and other abundant taxa interpreted to indicate fluvial nutrient input such as cyst of Protoperidinium americanum and Lejeunecysta oliva imply strong river discharge with high nutrient supply between 3100 and 640 cal. yr BP.

Description: New Mg/Ca, Sr/Ca, and published stable oxygen isotope and 87Sr/86Sr data obtained on ostracods from gravity cores located on the northwestern Black Sea slope were used to infer changes in the Black Sea hydrology and water chemistry for the period between 30 to 8 ka B.P. (calibrated radiocarbon years). The period prior to 16.5 ka B.P. was characterized by stable conditions in all records until a distinct drop in d18O values combined with a sharp increase in 87Sr/86Sr occurred between 16.5 and 14.8 ka B.P. This event is attributed to an increased runoff from the northern drainage area of the Black Sea between Heinrich Event 1 and the onset of the Bølling warm period. While the Mg/Ca and Sr/Ca records remained rather unaffected by this inflow; they show an abrupt rise with the onset of the Bølling/Allerød warm period. This rise was caused by calcite precipitation in the surface water, which led to a sudden increase of the Sr/Ca and Mg/Ca ratios of the Black Sea water. The stable oxygen isotopes also start to increase around 15 ka B.P., although in a more gradual manner, due to isotopically enriched meteoric precipitation. While Sr/Ca remains constant during the following interval of the Younger Dryas cold period, a decrease in the Mg/Ca ratio implies that the intermediate water masses of the Black Sea temporarily cooled by 1-2°C during the Younger Dryas. The 87Sr/86Sr values drop after the cessation of the water inflow at 15 ka B.P. to a lower level until the Younger Dryas, where they reach values similar to those observed during the Last Glacial Maximum. This might point to a potential outflow to the Mediterranean Sea via the Sea of Marmara during this period. The inflow of Mediterranean water started around 9.3 ka B.P., which is clearly detectable in the abruptly increasing Mg/Ca, Sr/Ca, and 87Sr/86Sr values. The accompanying increase in the d18O record is less pronounced and would fit to an inflow lasting ~100 a.

Description: The influence of the large-scale ocean circulation on Sahel rainfall is elusive because of the shortness of the observational record. We reconstructed the history of eolian and fluvial sedimentation on the continental slope off Senegal during the past 57,000 years. Our data show that abrupt onsets of arid conditions in the West African Sahel were linked to cold North Atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with Heinrich Stadials. Climate modeling suggests that this drying is induced by a southward shift of the West African monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric African Easterly Jet.

Description: A late Pliocene high-resolution pollen record from the southeast Atlantic (Ocean Drilling Program Site 1082) registers vegetation development in southwest Africa. The marine record is continuous, ranges from 3.5 to 1.7 Ma, and has a millennial resolution between 2.9 and 1.9 Ma. Changes in climate and vegetation correspond to the Matuyama diatom maximum of the Namibian upwelling system and seem to be highly susceptible to latitudinal shifts in the Polar Front Zone of the Southern Ocean. A northward advance of the polar fronts is connected with an increase in winter rainfall in southwest Africa. Rapid desiccation in Namibia at 2.2 Ma is associated with increasing upwelling and decreasing sea- surface temperatures along the coast.

Description: Here we present evidence that the Holocene African monsoon system (AMS) varied in response to the eastern equatorial Atlantic sea-surface temperature (SST). Several short-term episodes of decreased moisture availability as a result of low eastern equatorial Atlantic SST are suggested by planktonic foraminiferal Mg/Ca ratios. These episodes promoted a weakening of the AMS and thus determined the timing and intensity of arid periods. Local sea-surface salinities also reveal regional patterns of precipitation in equatorial western Africa. The high eastern equatorial Atlantic SSTs occur in concert with seasonally increased insolation at low latitudes, suggesting a strong response of African monsoonal precipitation to oceanic conditions at low latitudes.

Description: The North Atlantic Ocean underwent an abrupt temperature increase of 9 °C at high latitudes within a couple of decades during the transition from Heinrich event 1 (H1) to the Bølling warm event, but the mechanism responsible for this warming remains uncertain. Here we address this issue, presenting high-resolution last deglaciation planktic and benthic foraminiferal records of temperature and oxygen isotopic composition of seawater (d18OSW) for the subtropical South Atlantic. We identify a warming of ~6.5 °C and an increase in d18Osw of 1.2 per mil at the permanent thermocline during the transition, and a simultaneous warming of ~3.5 °C with no significant change in d18Osw at intermediate depths. Most of the warming can be explained by tilting the South Atlantic east-west isopycnals from a flattened toward a steepened position associated with a collapsed (H1) and strong (Bølling) Atlantic meridional overturning circulation (AMOC). However, this zonal seesaw explains an increase of just 0.3 per mil in permanent thermocline d18Osw. Considering that d18Osw at the South Atlantic permanent thermocline is strongly influenced by the inflow of salty Indian Ocean upper waters, we suggest that a strengthening in the Agulhas leakage took place at the transition from H1 to the Bølling, and was responsible for the change in d18Osw recorded in our site. Our records high-light the important role played by Indian-Atlantic interocean exchange as the trigger for the resumption of the AMOC and the Bølling warm event. of the AMOC and the Bølling warm event.

Description: We compared particle data from a moored video camera system with sediment trap derived fluxes at ~1100 m depth in the highly dynamic coastal upwelling system off Cape Blanc, Mauritania. Between spring 2008 and winter 2010 the trap collected settling particles in 9-day intervals, while the camera recorded in-situ particle abundance and size-distribution every third day. Particle fluxes were highly variable (40-1200 mg m**-2 d**-1) and followed distinct seasonal patterns with peaks during spring, summer and fall. The particle flux patterns from the sediment traps correlated to the total particle volume captured by the video camera, which ranged from1 to 22 mm**3 l**-1. The measured increase in total particle volume during periods of high mass flux appeared to be better related to increases in the particle concentrations, rather than to increased average particle size. We observed events that had similar particle fluxes, but showed clear differences in particle abundance and size-distribution, and vice versa. Such observations can only be explained by shifts in the composition of the settling material, with changes both in particle density and chemical composition. For example, the input of wind-blown dust from the Sahara during September 2009 led to the formation of high numbers of comparably small particles in the water column. This suggests that, besides seasonal changes, the composition of marine particles in one region underlies episodical changes. The time between the appearance of high dust concentrations in the atmosphere and the increase lithogenic flux in the 1100 m deep trap suggested an average settling rate of 200 m d**-1, indicating a close and fast coupling between dust input and sedimentation of the material.