Lithostratigraphy, physical properties and organic matter variability in Lake Malawi Drillcore sediments over the past 145,000 years
Introduction
The tropical latitudes contribute significantly to the global climate system by receiving most of the solar energy that strikes the earth, and then redistributing energy to the high latitudes via atmospheric and oceanic circulation. The long-term natural variability of tropical climate on the continents is best known from lake deposits and speleothems, and new lake records are now extending our understanding of key regions around the continental tropics (e.g. Hodell et al., 2008, Peck et al., 2007, Scholz et al., 2006). Lake Malawi is situated between 9° and 14° S within the western branch of the east African rift (Fig. 1), and the sediments within this basin provide an opportunity for a continuous long-term record of natural climate variability in the continental tropics of southern hemisphere East Africa.
The climate of tropical East Africa is dominated by seasonal variability in rainfall and winds, with relatively minor seasonal temperature variability. Tropical convection associated with Intertropical Convergence Zone (ITCZ) gives rise to a single rainy season lasting from ~ December to March (Fig. 2). Moisture is derived from both the Atlantic and Indian Oceans in monsoonal circulation associated with summer heating of the continental interior.
Section snippets
Background
Lake Malawi is one of world's largest and deepest lakes extending more than 560 km from end to end, with a maximum water depth of about 700 m (Fig. 1). The lake is permanently stratified and anoxic at depth, with a chemocline depth that averages about 250 m (Patterson and Kachinjika, 1995). The strong seasonal pattern of a short, intense rainy season and then a strong windy season during the austral winter (Fig. 2) results in a bimodal sedimentation pattern of terrigenous inputs and then
Drilling and field program efforts
Lake Malawi is landlocked and located ~ 400 km from the Indian Ocean, with only overland connections to ports on the Indian Ocean coast. The project used the lake barge Viphya, as the drilling platform (Scholz et al., 2006, Scholz et al., 2011-this issue). Prior to this effort site survey studies carried out on small local vessels were used to help develop a stratigraphic framework for the basin, and to help identify preferred drill sites (Lyons et al., 2011-this issue; Fig. 1, Fig. 3).
At drill
Geochronology summary
Age dating of sediment drill cores recovered from Site 1C in Lake Malawi was completed using several different dating methods. For the interval from 0 to 52 kyr BP, 14C dating of bulk organic matter generated internally consistent results and a high-resolution chronology (Fig. 4, Fig. 5). The deeper, older parts of the core below 22 m were dated using Optically Stimulated Luminescence (OSL), and paleomagnetic inclination and paleointensity methods. Paleointensity was determined using the ratio of
Section 1: 10 ka–61 ka
The upper part of core 1C, from the top of the core at 6.51 mblf to 28 mblf is characterized by moderate to high organic carbon values, H2O-saturated, low-density diatomaceous mud in which Pediastrum may be prominent, and comprises a lithology (LI) comparable to that which has been accumulating in the lake over the last few thousand years (e.g. Barry, 2001, Johnson et al., 2002). Accordingly, this lithology is interpreted to be reflective of limnological conditions not unlike the modern lake,
Discussion and conclusions
- 1.
Lithology, organic matter, and physical properties vary markedly at Site 1 in Lake Malawi, a drill site set in 593 m of water in a hemipelagic setting in the central basin of the lake. The last ~ 150 kyr of record is observed in the upper 90 m of section in core 1C. Down-core variability in sediment lithology, physical properties, and organic matter character is pronounced on millennial and orbital timescales, especially for the period prior to 60 kyr BP.
- 2.
Over the past 60,000 years the water depths at
References (50)
- et al.
Vegetation response to glacial–interglacial climate variability near Lake Malawi in the southern African tropics
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2011) - et al.
Late Quaternary vegetation history of southeast Africa: the molecular isotopic record from Lake Malawi
Palaeogeography, Palaeoclimatology, Palaeoecology
(2009) - et al.
The palaeolimnology of northern Lake Malawi over the last 25 ka based upon the elemental and stable isotopic composition of sedimentary organic matter
Quaternary Science Reviews
(2005) - et al.
Black carbon and total carbon measurements at urban and rural sites in Kenya, East Africa
Atmosphere Environment
(2003) - et al.
The community composition, distribution, and nutrient status of epilithic periphyton from five rocky littoral zone sites in Lake Malawi, Africa
Journal of Great Lakes Research
(2003) - et al.
An 85-ka record of climate change in lowland Central America
Quaternary Science Reviews
(2008) - et al.
Glacial–interglacial environmental changes inferred from molecular and compound-specific del13C analyses of sediments from Sacred Lake, Mt. Kenya
Geochimica et Cosmochimica Acta
(1999) - et al.
Late Quaternary stratigraphic analysis of the Lake Malawi Rift, East Africa: An integration of drill-core and seismic reflection data
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2011) - et al.
Paleoecological response of ostracods to early-Late Pleistocene lake level changes in Lake Malawi, East Africa
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2011) - et al.
Microscopic charcoal as a fossil indicator of fire
Quaternary Science Reviews
(1987)