Climate changes reconstructed from Lake Malawi, the southernmost of the East African Great Lakes and located within the Zambezi catchment, point to arid conditions and strong northerly wind anomalies during Northern Hemisphere cold events such as the Younger Dryas (YD) 2,3 . It has been inferred that these periods represent southward shifts of the ITCZ 2,3,6 . Dry conditions during the YD and Heinrich Stadial 1 (HS1) in Lake Tanganyika, located closer to the equator in East Africa, were interpreted to have been caused by lowered Indian Ocean SST 4 . Recently, widespread drought conditions during HS1 in East Africa have similarly been suggested to be driven by cold conditions in the Indian Ocean 5 . Such interpretations are based on meteorological observations that modern rainfall in eastern and southern Africa is strongly related to high SST in the western and south-western Indian Ocean, respectively 7 . In contrast, Lake Chilwa located south-east of Lake Malawi, recorded high-stands, which appear to be solely associated with northern Hemisphere cold events 8 . Further westward in the interior of subtropical southern African, paleoenvironmental information is sparse. Age dating of dunes in western Zambia and western Zimbabwe points to dry conditions at 18-17,000, 15-14,000, 11-8,000, and 6-4,000 years 9 before present (BP) implying that non-dune building periods around 16,000 and from 13-12,000 years BP roughly correspond to the wet periods found at Lake Chilwa 8 . Paleo-shorelines and other geomorphologic evidence from the Central Kalahari point to the existence of an extended lake system around the time of During austral winter a high pressure system over southern Africa leads to dry conditions, except in a small winter rainfall zone at its south-western tip 6 . The Zambezi River is the fourth-largest river in Africa originating in Zambia and flowing south-eastward to the Indian Ocean. The upper Zambezi is separated from its lower part by the Victoria Falls. After flowing through a series of gorges, the river enters a broad valley and spreads out over a large floodplain in its lower part. About 150 km from the coast, the catchment narrows where the river flows through the eastern Rift mountains. Maximum rainfall in the catchment during the peak of the southward ITCZ migration occurs in this area 12 (Fig. 1b), periodically causing extensive flooding 13 .The floodplain is dominated by papyrus swamps (dominated by Cyperus papyrus, a C 4 plant) with lower importance of reed swamps (Phragmites and Typha, C 3 plants) 14 . 4 The C 4 plant dominance in the lower Zambezi floodplain is seen in the relative abundance of C 4 plants (Fig. 1c, d) 15 . Downstream from the Rift mountains, the Zambezi splits up into a flat and wide delta 13 . Woodlands, savannah and extensive mangrove forests (C 3 plants) vegetate the delta and coastal areas 14 .The 6.51 m long marine sediment core GeoB9307-3 (18°33.9'S, 37°22.8'E, 542 m water depth) was retrieved about 100 km off the Zambezi delta. The core location is in the zone of high deg...

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[1] Past changes in North Pacific sea surface temperatures and sea-ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the North Atlantic. Here, we present new alkenone-based sea surface temperature records from the subarctic northwest Pacific and its marginal seas (Bering Sea and Sea of Okhotsk) for the time interval of the last 15 kyr, indicating millennial-scale sea surface temperature fluctuations similar to short-term deglacial climate oscillations known from Greenland ice core records. Past changes in sea-ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the IP 25 biomarker related to sea-ice diatoms. The deglacial variability in sea-ice extent matches the sea surface temperature fluctuations. These fluctuations suggest a linkage to deglacial variations in Atlantic meridional overturning circulation and a close atmospheric coupling between the North Pacific and North Atlantic. During the Holocene the subarctic North Pacific is marked by complex sea surface temperature trends, which do not support the hypothesis of a Holocene seesaw in temperature development between the North Atlantic and the North Pacific.

The Sahara Desert is the largest source of mineral dust in the world. Emissions of African dust increased sharply in the early 1970s (ref. 2), a change that has been attributed mainly to drought in the Sahara/Sahel region caused by changes in the global distribution of sea surface temperature. The human contribution to land degradation and dust mobilization in this region remains poorly understood, owing to the paucity of data that would allow the identification of long-term trends in desertification. Direct measurements of airborne African dust concentrations only became available in the mid-1960s from a station on Barbados and subsequently from satellite imagery since the late 1970s: they do not cover the onset of commercial agriculture in the Sahel region approximately 170 years ago. Here we construct a 3,200-year record of dust deposition off northwest Africa by investigating the chemistry and grain-size distribution of terrigenous sediments deposited at a marine site located directly under the West African dust plume. With the help of our dust record and a proxy record for West African precipitation we find that, on the century scale, dust deposition is related to precipitation in tropical West Africa until the seventeenth century. At the beginning of the nineteenth century, a sharp increase in dust deposition parallels the advent of commercial agriculture in the Sahel region. Our findings suggest that human-induced dust emissions from the Sahel region have contributed to the atmospheric dust load for about 200 years.

Abstract. The present paper is the result of a workshop sponsored by the DFG Research Center/Cluster of Excellence MARUM "The Ocean in the Earth System", the International Graduate College EUROPROX, and the Alfred Wegener Institute for Polar and Marine Research. The workshop brought together specialists on organic matter degradation and on proxy-based environmental reconstruction. The paper deals with the main theme of the workshop, understanding the impact of selective degradation/preservation of organic matter (OM) in marine sediments on the interpretation of the fossil record. Special attention is paid to (A) the influence of the molecular composition of OM in relation to the biological and physical depositional environment, including new methods for determining complex organic biomolecules, (B) the impact of selective OM preservation on the interpretation of proxies for marine palaeoceanographic and palaeoclimatic reconstruction, and (C) past marine productivity and selective preservation in sediments.It appears that most of the factors influencing OM preservation have been identified, but many of the mechanisms by which they operate are partly, or even fragmentarily, underCorrespondence to: G. J. M. Versteegh (versteegh@uni-bremen.de) stood. Some factors have not even been taken carefully into consideration. This incomplete understanding of OM breakdown hampers proper assessment of the present and past carbon cycle as well as the interpretation of OM based proxies and proxies affected by OM breakdown.To arrive at better proxy-based reconstructions "deformation functions" are needed, taking into account the transport and diagenesis-related molecular and atomic modifications following proxy formation.Some emerging proxies for OM degradation may shed light on such deformation functions. The use of palynomorph concentrations and selective changes in assemblage composition as models for production and preservation of OM may correct for bias due to selective degradation. Such quantitative assessment of OM degradation may lead to more accurate reconstruction of past productivity and bottom water oxygenation.Given the cost and effort associated with programs to recover sediment cores for paleoclimatological studies, as well as with generating proxy records, it would seem wise to develop a detailed sedimentological and diagenetic context for interpretation of these records. With respect to the latter, parallel acquisition of data that inform on the fidelity of the proxy signatures and reveal potential diagenetic biases would be of clear value.

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A substantial strengthening of the South American monsoon system (SAMS) during Heinrich Stadials (HS) points toward decreased cross‐equatorial heat transport as the main driver of monsoonal hydroclimate variability at millennial time scales. In order to better constrain the exact timing and internal structure of HS1 over tropical South America, we assessed two precisely dated speleothem records from central‐eastern and northeastern Brazil in combination with two marine records of terrestrial organic and inorganic matter input into the western equatorial Atlantic. During HS1, we recognize at least two events of widespread intensification of the SAMS across the entire region influenced by the South Atlantic Convergence Zone (SACZ) at 16.11–14.69 kyr B.P. and 18.1–16.66 kyr B.P. (labeled as HS1a and HS1c, respectively), separated by a dry excursion from 16.66 to 16.11 kyr B.P. (HS1b). In view of the spatial structure of precipitation anomalies, the widespread increase of monsoon precipitation over the SACZ domain was termed “Mega‐SACZ.”

Surface ocean conditions in the equatorial Pacific Ocean could hold the clue to whether millennial-scale global climate change during glacial times was initiated through tropical ocean-atmosphere feedbacks or by changes in the Atlantic thermohaline circulation. North Atlantic cold periods during Heinrich events and millennial-scale cold events (stadials) have been linked with climatic changes in the tropical Atlantic Ocean and South America, as well as the Indian and East Asian monsoon systems, but not with tropical Pacific sea surface temperatures. Here we present a high-resolution record of sea surface temperatures in the eastern tropical Pacific derived from alkenone unsaturation measurements. Our data show a temperature drop of approximately 1 degrees C, synchronous (within dating uncertainties) with the shutdown of the Atlantic meridional overturning circulation during Heinrich event 1, and a smaller temperature drop of approximately 0.5 degrees C synchronous with the smaller reduction in the overturning circulation during the Younger Dryas event. Both cold events coincide with maxima in surface ocean productivity as inferred from 230Th-normalized carbon burial fluxes, suggesting increased upwelling at the time. From the concurrence of equatorial Pacific cooling with the two North Atlantic cold periods during deglaciation, we conclude that these millennial-scale climate changes were probably driven by a reorganization of the oceans' thermohaline circulation, although possibly amplified by tropical ocean-atmosphere interaction as suggested before.