Paleoenvironmental signatures of aeolian and fluvial sedimentary end-members off NW Africa

This thesis presents a new approach to characterize properties of terrigenous sediments deposited off subtropical Africa. Grain-size distributions, geochemical compositions, and magnetic parameters of core material off the Gambia and Senegal rivers were analyzed. By end-member (EM) unmixing and least-square fitting, mixing coefficients and multi-parameters properties of fluvial and aeolian fractions were obtained. The properties are influenced by different factors and the joint characterization enables a three-level interpretation: (1) Grain-sizes reflect transport energy. (2) Geochemical composition differs in fluvial and aeolian sediments. (3) Magnetic mineralogy mirrors weathering and environmental conditions in the source areas. Volumetric EM representations enable to budget fluxes of aeolian and fluvial material. The highest dust accumulation occurred during Heinrich Stadial 1 and corresponds to a 100 times higher flux with respect to today. Such high values have not been reported yet off NW Africa and emphasize that disturbances of the meridional overturning circulation cause dramatic environmental changes also in low-latitudes

Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial–interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before  ∼  320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial–interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial–interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes

IODP Expedition 361 – Southern African Climates and Agulhas LGM Density Profile

IODP Expedition 361 drilled six sites (U1474 – U1479) on the southeast African margin and the Indian-Atlantic ocean gateway from 30 January to 31 March 2016. The sites, situated in the Mozambique Channel, Natal Valley, Agulhas Plateau, and Cape Basin, were targeted to reconstruct the history of the Greater Agulhas Current System over the past ~5 Ma. More specifically, the main objectives of Expedition 361 were: (i) to establish the sensitivity of the Agulhas Current to climate change during the Plio-Pleistocene in association with transient to long-term changes of high-latitude climates, tropical heat budgets, and the monsoon system; (ii) to determine the dynamics of the Indian-Atlantic gateway circulation in association with changing wind fields and migrating ocean fronts; (iii) to examine the connection of the Agulhas leakage and the Atlantic Meridional Overturning Circulation; (iv) to address the influence of the Agulhas Current on African terrestrial climates, notably rainfall patterns and river runoff, and potential links to hominid evolution. Additionally, the expedition set out to fulfill the needs of the Ancillary Project Letter, consisting of high-resolution interstitial water samples aiming at constraining the temperature and salinity profiles of the ocean during the Last Glacial Maximum. In total, 5175 m of core was recovered (average recovery 102 %) from a region poorly represented in the database of drill sites for scientific purposes. Physical property records derived from core-logging of the recovered sequences allowed complete spliced stratigraphic sections to be generated that span the interval of 0 to between ~0.13 and 7 Ma. A high-resolution program of interstitial water samples was carried out at Sites U1474, U1475, U1476, and U1478. The expedition made major strides toward fulfilling the scientific objectives despite of ~11 days of lost operational time due to weather conditions, a medical evacuation, and delays in attaining the necessary permissions to operate in Mozambique exclusive economic zone waters. Site U1474 (3034 meters below sea level [mbsl]), located in the northernmost Natal Valley, consists of eight holes ranging in penetration depth from 3.1 to 254.1 m drilling depth below seafloor (dsf). A total of 910.8 m of sediment was recovered, predominantly consisting of foraminifer-bearing clay with nannofossils. Based on the shipboard bio- and magnetistratigraphic datums, the sedimentary sequence extends back to the late Miocene (~6.2 Ma). This record represents the only site situated beneath the main flow of the fully constituted Agulhas Current and therefore provides the opportunity for high-resolution climate reconstructions of Agulhas Current warm-water transports and upstream variability that may allow the identification of connections between Agulhas leakage and its headwater variability. It also holds significant potential to investigate the connections between southern African terrestrial climates and southeast Indian Ocean heat budgets and the links to the cultural evolution of early modern humans. Site U1475 (2669 mbsl), located on the southwestern flank of the Agulhas Plateau, consists of six holes ranging in penetration depth from 1.5 to 277.0 m dsf. A total of 1015.9 m of sediment was recovered, predominantly consisting of nannofossil ooze. Shipboard bio- and magnetistratigraphic data suggest that the sedimentary sequence extends back to the late Miocene (~7 Ma). This record provides the opportunity for high-resolution climate reconstructions of the Agulhas Return Current and connections with the Sub-Tropical Front, productivity, and deep-water circulation. Site U1476 (2165 mbsl), located at the northern entrance of the Mozambique Channel, consists of five holes ranging in penetration depth from 5.7 to 234.8 m dsf. A total of 873.8 m of sediment was recovered, predominantly consisting of foraminifer-rich nannofossil ooze. The sedimentary sequence extends back to the late Miocene (~6.9 Ma), as inferred from the shiboard bio- and magnetostratigraphic data. The site boasts excellent biostratigraphy and notably cyclic physical properties. It therefore provides the opportunity for high-resolution reconstructions of tropical faunal assemblages, which will allow identification of connections be¬tween Agulhas leakage and its headwater variability. It also holds significant potential to investigate the connections between southern African terrestrial climates and southeast Indian Ocean heat budgets and thermocline and deep-water variability with likely links to the development of the Indonesian Throughflow as well as aridification of east Africa. Because of the excellent preservation of foraminifers, this an ideal site for a long record of surface-ocean pH from boron isotopes. Site U1477 (429 mbsl), located in the western Mozambique Channel east of the Zambezi River delta, consists of three holes ranging in penetration depth from 119.4 to 181.2 m dsf. A total of 490.0 m of sediment was recovered, predominantly consisting of sandy clay with foraminifers and nannofossils. Based on correlations to a nearby 14C dated cores and two biostratigrahic markers, the sedimentary sequence extends back to the Late Pleistocene (~0.13 Ma). The extreme accumulation rate (~1 m/ky) at this site provides the opportunity for exceptionally high resolution reconstructions of terrestrial climate and thermocline characteristics during the last glacial cycle. Site U1478 (488 mbsl), located in the western Mozambique Channel east of the Limpopo River delta, consists of four holes ranging in penetration depth from 216.0 to 248.4 m dsf. A total of 922.1 m of sediment was recovered, predominantly consisting of sand or clayey/sandy silt with foraminifers and nannofossils. The shipboard age-model suggests that the sedimentary sequence extends back to the Pliocene (~4 Ma). This record provides the opportunity for high-resolution climate reconstructions of faunal, biogeochemical, and terrigenous tracers that are characteristic of the upper reaches of the Agulhas Current warm-water transports that will allow connections between Agul¬has leakage and its headwater variability. The site also holds significant potential to investigate the connections between southern African terrestrial climates and southeast Indian Ocean heat budgets, and examine the relationship between such climate variability and early human evolution. Site U1479 (2615 mbsl), located in Cape Basin, consists of nine holes ranging in penetration depth from 1.0 to 300.7 m dsf. A total of 963.1 m of sediment was recovered, predominantly consisting of nannofossil ooze with or without foraminifers. According to the shipboard bio- and magnetostratigraphy-based age model, the sedimentary sequence extends back to the late Miocene (~7 Ma). This record represents the only site situated in the immediate Agulhas leakage pathway. It will therefore provide the opportunity for high-resolution climate reconstructions of the leakage and temporal comparisons with deep-water circulation

Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present

Lake Ohrid (Macedonia, Albania) is thought to be more than 1.2 million years old and host more than 300 endemic species. As a target of the International Continental scientific Drilling Program (ICDP), a successful deep drilling campaign was carried out within the scope of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project in 2013. Here, we present lithological, sedimentological, and (bio-)geochemical data from the upper 247.8 m composite depth of the overall 569 m long DEEP site sediment succession from the central part of the lake. According to an age model, which is based on 11 tephra layers (first-order tie points) and on tuning of bio-geochemical proxy data to orbital parameters (second-order tie points), the analyzed sediment sequence covers the last 637 kyr. The DEEP site sediment succession consists of hemipelagic sediments, which are interspersed by several tephra layers and infrequent, thin (< 5 cm) mass wasting deposits. The hemipelagic sediments can be classified into three different lithotypes. Lithotype 1 and 2 deposits comprise calcareous and slightly calcareous silty clay and are predominantly attributed to interglacial periods with high primary productivity in the lake during summer and reduced mixing during winter. The data suggest that high ion and nutrient concentrations in the lake water promoted calcite precipitation and diatom growth in the epilimnion during MIS15, 13, and 5. Following a strong primary productivity, highest interglacial temperatures can be reported for marine isotope stages (MIS) 11 and 5, whereas MIS15, 13, 9, and 7 were comparably cooler. Lithotype 3 deposits consist of clastic, silty clayey material and predominantly represent glacial periods with low primary productivity during summer and longer and intensified mixing during winter. The data imply that the most severe glacial conditions at Lake Ohrid persisted during MIS16, 12, 10, and 6, whereas somewhat warmer temperatures can be inferred for MIS14, 8, 4, and 2. Interglacial-like conditions occurred during parts of MIS14 and 8

Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present

Lake Ohrid (Macedonia, Albania) is thought to be more than 1.2 million years old and host more than 300 endemic species. As a target of the International Continental scientific Drilling Program (ICDP), a successful deep drilling campaign was carried out within the scope of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project in 2013. Here, we present lithological, sedimentological, and (bio-)geochemical data from the upper 247.8 m composite depth of the overall 569 m long DEEP site sediment succession from the central part of the lake. According to an age model, which is based on 11 tephra layers (first-order tie points) and on tuning of bio-geochemical proxy data to orbital parameters (second-order tie points), the analyzed sediment sequence covers the last 637 kyr. The DEEP site sediment succession consists of hemipelagic sediments, which are interspersed by several tephra layers and infrequent, thin (< 5 cm) mass wasting deposits. The hemipelagic sediments can be classified into three different lithotypes. Lithotype 1 and 2 deposits comprise calcareous and slightly calcareous silty clay and are predominantly attributed to interglacial periods with high primary productivity in the lake during summer and reduced mixing during winter. The data suggest that high ion and nutrient concentrations in the lake water promoted calcite precipitation and diatom growth in the epilimnion during MIS15, 13, and 5. Following a strong primary productivity, highest interglacial temperatures can be reported for marine isotope stages (MIS) 11 and 5, whereas MIS15, 13, 9, and 7 were comparably cooler. Lithotype 3 deposits consist of clastic, silty clayey material and predominantly represent glacial periods with low primary productivity during summer and longer and intensified mixing during winter. The data imply that the most severe glacial conditions at Lake Ohrid persisted during MIS16, 12, 10, and 6, whereas somewhat warmer temperatures can be inferred for MIS14, 8, 4, and 2. Interglacial-like conditions occurred during parts of MIS14 and 8. © Author(s) 2016

Environmental change during MIS4 and MIS 3 opened corridors in the Horn of Africa for <i>Homo sapiens</i> expansion

Archaeological findings, numerical human dispersal models and genome analyses suggest several time windows in the past 200 kyr (thousands of years ago) when anatomically modern humans (AMH) dispersed out of Africa into the Levant and/or Arabia. From close to the key hominin site of Omo-Kibish, we provide near continuous proxy evidence for environmental changes in lake sediment cores from the Chew Bahir basin, south Ethiopia. The data show highly variable hydroclimate conditions from 116 to 66 kyr BP with rapid shifts from very wet to extreme aridity. The wet phases coincide with the timing of the North African Humid Periods during MIS5, as defined by Nile discharge records from the eastern Mediterranean. The subsequent record at Chew Bahir suggests stable regional hydrological setting between 58 and 32 kyr (MIS4 and 3), which facilitated the development of more habitable ecosystems, albeit in generally dry climatic conditions. This shift, from more to less variable hydroclimate, may help account for the timing of later dispersal events of AMH out of Africa

The last 1 million years of the extinct genus Discoaster: Plio–Pleistocene environment and productivity at Site U1476 (Mozambique Channel)

A detailed paleoenvironment reconstruction from the Mozambique Channel, western Indian Ocean, based on the calcareous nannoplankton assemblages was conducted for the interval between 2.85 and 1.85 Myr. This study covers the period during which the successive extinction of the last five species of discoasters occurred. New productivity data obtained from the abundances of the Discoaster species (Discoaster brouweri, D. triradiatus, D. pentaradiatus, D. surculus, and D. tamalis) and other indicative calcareous nannoplankton taxa showed abundance variations, which were at paced with the 100, 41, and 23 kyr astronomical periodicities. A shift in the productivity and water-column stratification proxies occurred at ~2.4 Ma, after the onset of the Northern Hemisphere glaciation. Here we propose that the variability recorded at International Ocean Discovery Program Site U1476 reflects the interplay between forcing associated with warm tropical Pacific and cold southern ocean influences. The former is shown by consistent occurrence of warm water taxa (Calcidiscus leptoporus, Oolithotus spp., Rhabdosphaera clavigera, Syracosphaera spp., Umbellosphaera spp.), typical of Indonesian Throughflow surface waters. On the other hand, the occurrence of Coccolithus pelagicus indicates the influence of cold, nutrient-rich sub-Antarctic surface waters. A more mixed water column initiated at ~2.4 Ma, and a consequent productivity increase led to the gradual reduction of the Discoaster species, until their extinction at 1.91 Ma. This period was characterized by the low values of the Florisphaera profunda index and high abundances of upper photic zone flora, indicative of nutrient-rich surface water conditions. High productivity at the location during this period could have also been amplified by localized upwelling events driven by the Mozambique Channel eddies

The geodynamic and limnological evolution of Balkan Lake Ohrid, possibly the oldest extant lake in Europe

Studies of the upper 447 m of the DEEP site sediment succession from central Lake Ohrid, Balkan Peninsula, North Macedonia and Albania provided important insights into the regional climate history and evolutionary dynamics since permanent lacustrine conditions established at 1.36 million years ago (Ma). This paper focuses on the entire 584-m-long DEEP sediment succession and a comparison to a 197-m-long sediment succession from the Pestani site ~5 km to the east in the lake, where drilling ended close to the bedrock, to unravel the earliest history of Lake Ohrid and its basin development. 26Al/10Be dating of clasts from the base of the DEEP sediment succession implies that the sedimentation in the modern basin started at c. 2 Ma. Geophysical, sedimentological and micropalaeontological data allow for chronological information to be transposed from the DEEP to the Pestani succession. Fluvial conditions, slack water conditions, peat formation and/or complete desiccation prevailed at the DEEP and Pestani sites until 1.36 and 1.21 Ma, respectively, before a larger lake extended over both sites. Activation of karst aquifers to the east probably by tectonic activity and a potential existence of neighbouring Lake Prespa supported filling of Lake Ohrid. The lake deepened gradually, with a relatively constant vertical displacement rate of ~0.2 mm a−1 between the central and the eastern lateral basin and with greater water depth presumably during interglacial periods. Although the dynamic environment characterized by local processes and the fragmentary chronology of the basal sediment successions from both sites hamper palaeoclimatic significance prior to the existence of a larger lake, the new data provide an unprecedented and detailed picture of the geodynamic evolution of the basin and lake that is Europe’s presumed oldest extant freshwater lake

Data report: evaluation of shipboard magnetostratigraphy by alternating field demagnetization of discrete samples, Expedition 361, Site U1475

The paleomagnetic shipboard data of International Ocean Discovery Program Site U1475, with a record reaching back to approximately 7 Ma, allowed for the identification of major magnetic polarity chrons and subchrons back to ~3.5 Ma. However, the natural remanent magnetization (NRM) was very weak, and transitional intervals with unclear polarity were as thick as several meters. The midpoints of these transitional intervals were reported in the shipboard results without decimal places because of the poor data quality. To evaluate and possibly refine the shipboard magnetostratigraphy, subsampling was performed across the polarity transitions. Detailed alternating field (AF) demagnetization experiments were conducted on these discrete samples and were complemented by anhysteretic remanent magnetization acquisition measurements and subsequent demagnetization. AF demagnetization data of NRM were analyzed using anchored principal component analysis (PCA) to obtain the characteristic remanent magnetization. These PCA results generally confirm the smoothed signal across polarity transitions at Site U1475. However, the midpoint depths of the top of the Keana Subchron, the Gauss-Matuyama and Matuyama-Brunhes boundaries, and the base of the Olduvai Subchron were adjusted

The geodynamic and limnological evolution of Balkan Lake Ohrid, possibly the oldest extant lake in Europe

Studies of the upper 447 m of the DEEP site sediment succession from central Lake Ohrid, Balkan Peninsula, North Macedonia and Albania provided important insights into the regional climate history and evolutionary dynamics since permanent lacustrine conditions established at 1.36 million years ago (Ma). This paper focuses on the entire 584-m-long DEEP sediment succession and a comparison to a 197-m-long sediment succession from the Pestani site ~5 km to the east in the lake, where drilling ended close to the bedrock, to unravel the earliest history of Lake Ohrid and its basin development. 26Al/10Be dating of clasts from the base of the DEEP sediment succession implies that the sedimentation in the modern basin started at c. 2 Ma. Geophysical, sedimentological and micropalaeontological data allow for chronological information to be transposed from the DEEP to the Pestani succession. Fluvial conditions, slack water conditions, peat formation and/or complete desiccation prevailed at the DEEP and Pestani sites until 1.36 and 1.21 Ma, respectively, before a larger lake extended over both sites. Activation of karst aquifers to the east probably by tectonic activity and a potential existence of neighbouring Lake Prespa supported filling of Lake Ohrid. The lake deepened gradually, with a relatively constant vertical displacement rate of ~0.2 mm a−1 between the central and the eastern lateral basin and with greater water depth presumably during interglacial periods. Although the dynamic environment characterized by local processes and the fragmentary chronology of the basal sediment successions from both sites hamper palaeoclimatic significance prior to the existence of a larger lake, the new data provide an unprecedented and detailed picture of the geodynamic evolution of the basin and lake that is Europe’s presumed oldest extant freshwater lake