The Late Pleistocene-Holocene History of the Lake Kivu Ecosystem By R.E. Hecky1 and Peter Reinthal2 1Large Lakes Observatory and Department of Biology, University of Minnesota-Duluth, Duluth, Minnesota USA 55812 email: [email protected] 2Ecology and Evolu=onary Biology, University of Arizona, Tucson, Arizona USA 85721 email: [email protected] 1972 on Lake Kivu-Woods Hole Oceanographic Ins=tu=on survey Nyiragongo on the leA Mikeno on the right- Rwanda coastline to the right Edward Virunga Mts. Kivu Lake Kivu 1462 m ASL Tanganyika 485 m Depth hWp://rst.gsfc.nasa.gov/Sect17/Sect17_5.html Envisat SAR image 2060 km2 Landsat image The northwestern coast of the lake gives abundant evidence of episodic and con=nuing volcanic ac=vity. Note circular (crater) shapes on the land and on Tshegera Island in the lake. Verbeke also interpreted subaqueous volcanic cones penetra=ng the lake floor. Sublacustrine Volcanic cones? Schmid et al. 2008. Limnol. Oceanogr. Modern thermohaline stratification unique for a large lake 1) When was this stratification first initiated? 2) Has it been stable or variable over time 3) Have there been deep mixing events and were there catastrophic consequences 4) If so, what causes variability and deep Schmid et al. 2003. G3. mixing In 1971 (illustrated at right with seismic reflec=on transects ) and 1972 Kullenberg piston cores were taken. Loca=on of cores that have been described are below. 1972 cores marked with a prime All cores from < 300 m ended with evidence of low stands e.g. beach deposits, soils, dense carbonate deposits. The seismic reflection profiles similarly indicate thin sediment cover above that depth but thick deposits below 400 m depth. Sediment infill may occur in some valleys and shoals to the south into the Eastern Basin. Core 10 and other deep water cores >400 m taken in 1971 ended in volcanic ash Colour photo of some of the 1971 cores. Note bedding and colors. 6200 y BP 10670 y Locaon of core 4’ 1972 Cores 10 and 13 (1971) ended in massive Degens et al. 1973. Geol. Rundschau ash (not shown). Chaetoceros indicates higher Stephanodiscus salinity Only occurred prior to 5000 y BP when it was dominant Long, thin Characteris=c Nitzschia spp. microfossils in Dominate aAer brown layer- 5000 y BP aqua=c photosynthe=c organisms are rare HIGHLIGHTS OF DIATOM STRATIGRAPHY Initiation of thermohaline structure Initiation of Rusizi River Outlet Late Pleistocene Low Stand -300 m Highlights of chemical stratigaphy Initiation of thermohaline structure Initiation of Rusizi outflow Late Pleistocene low stand -300 m ? ? Weaker Salinity Deep mixing stratification declining? Kivu siliceous microfossil assemblages <5600 y BP Recurring Aquatic microfossils sparse Brown “gel” Paraphysomonas vestita scales layers-deep Colorless chrysophyte mixing >6000 y BP All bars are 8 microns Conclusions: When was thermohaline stratification first initiated? Approximately 5500 y BP Has it been stable or variable over time? Stability has likely strengthened and weakened multiple times over the past 5000 years Have there been deep mixing events and were there catastrophic consequences? Yes, there have been five deep mixing events (two major ones) and extinction has likely occurred? If so, what causes variability and deep mixing? A question we should answer! Two domains of Biodiversity Bioinformatics biological informatics • Sequence databases informatics • Species names (GenBank, Swiss-Prot, (Tropicos, ITIS) FlyBase) 1) Temporal and • Phylogenies • Structure (MMDB) spatial = Ecology (TreeBASE,ToLweb) • Functional genomics • Collections (PlantsP) 2) Genetic • Floras, faunas, • Gene expression Information = biogeography (Jepson (GXD, GEO) Interchange) Evolution • Proteomics • Ecosystems (SWISS-2DPAGE) (SALVIAS) • Traits (Digimorph; MorphBank) Phylogenetics of African Cichlids (Salzburger et al. 2005) Lake Victoria (600+ cichlid species) Lake Kivu (19+ cichlid species) & riverine Lake Malawi (1000+ cichlid species) Lake Kivu cichlids 1) Have genetic capabilities to speciate 2) Lake Victoria cichlid flock is derived from Lake Kivu cichlids (Verheyen et al. 2003; Salzburger et al. 2005) 3) Tanganyika origin for lineages 4) Kivu cichlids key for understanding evolution of Rift lake species flocks Microsatellites = DNA Fingerprints Population assignment test assumes 2 or 3 genetic clusters (K) for all haplocmines from the POPULATION TREE genetic analyses indicate Lake Victoria Region Superflock (LVR) – Shows monophyly of Lake Victoria region superflock Kivu is separate and LVR remains a cluster. (LVRS) and Lake Kivu is sister group Demonstrates haplochromines in Lake Victoria and the region are derived from Lake Kivu. KIVU CICHLIDS Elmer K R et al. PNAS 2009;106:13404-13409 ©2009 by National Academy of Sciences Genner, M. J. et al. Mol Biol Evol 2007 24:1269-1282 Fossil Teeth from Lake Malawi Core Deep, Shallow, Wet dry Luxury accomoda=on in the grain barge. Rats played at night; hammocks preferred. Needed research: 1) More cores 2) More stratigraphic detail and better dating control 3) More use of biomarkers of sources of organic C 4) High resolution metal stratigraphy 5) Side scan sonar surveys particularly along steep slopes (debris flows? Landslides? Vents) 6) More heat flow measurements from within the lake to identify hot spots and their temporal variability 7) Other suggestions Chaetoceros indicates higher Stephanodiscus salinity Only occurred prior to 5000 y BP when it was dominant Long, thin Characteris=c Nitzschia spp. microfossils in Dominate aAer brown layer- 5000 y BP aqua=c photosynthe=c organisms are rare Kivu haplotype 56 shared by six of the endemic species in Kivu is the essential link to the entire flock Kivu spp. are Verheyen et al Science 2003 ecologically diverse Lake Tanganyika detailed diatom, carbonate and major nutrient stratigraphy available for last 18000 y for southern end of lake (core depth 440 m) Sedimentation rates higher in late Pleistocene in both lakes Lake Kivu events likely effect Lake Tanganyika; Rusizi River provides 20% of riverine input (>Lukuga Outflow) and even greater proportion of the salt inputs to Tanganyika under modern conditions and affect likely stronger 5500 y BP Kivu Tanganyika (South Basin 440 m) 6200 y 9500 y Both lakes closed basins prior to 9500 y; hydrothermal activity begins catastrophically in Kivu about 5500 y and may have affected Lake Tanganyika increasing stability of stratification through more saline inflows. Salinity of Kivu has declined since initial event (decline of Chaetoceros). (Note different depth scales; C-14 dates in red). Kivu to Victoria link severed 30-40,000 y BP By molecular Major flock expansion 98,000 to 130,000 y BP .