Late Holocene linkages between decade–century scale climate variability and productivity at Lake Tanganyika, Africa

Abstract

Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between~2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals.Time series analyses of laminae thickness patterns demonstrate significant periodicities at interannual-centennial time scales. Longer time scale periodicities (multidecadal to centennial scale) of light and dark half couplet thicknesses are coherent and in some cases are similar to solar cycle periods on these time scales. Although laminae thickness cycles do not strongly covary with the actual D 14 C record for this same time period, two large D 14 C anomalies are associated with substantial decreases in both light and dark laminae thickness. In contrast to the multidecadal- centennial time scale, significant annual to decadal periodicities, which are broadly consistent with ENSO/PDO forcing and their impact on East African climate, are not coherent between light and dark half couplets. The coherency of light-dark couplets at decadal-centennial time scales, but not at shorter time scales, is consistent with a model of a long-term relationship between precipitation (recorded in wet season dark laminae thickness) and productivity (light laminae thickness), which is not manifest at shorter time scales. We hypothesize that this coupling results from long-term recharging of internal nutrient loading during wet periods (higher erosion of soil P) and reduced loading during drought intervals. The relationship is not expressed on short time scales during which the dominant control on productivity is wind-driven, dry season upwelling, which is uncorrelated with wet-season precipitation. Our record greatly extends the temporal record of this quasi-periodic behavior throughout the late Holocene and provides the first evidence linking decade-to century-scale episodes of enhanced productivity to enhanced precipitation levels and nutrient recharge in a productive tropical lake.

Western Indian Ocean marine and terrestrial records of climate variability: a review and new concepts on land–ocean interactions since AD 1660

“…The historical lake level trends in equatorial East Africa show strong similarities (Lake Victoria, Lake Naivasha, Lake Turkana, Lake Bogoria and Lake Baringo; Verschuren et al 2004). Most lakes show a major highstand between 1880 and 1920, a long decline to a lowstand in the 1950s and recovery thereafter (Verschuren 2004;Cohen et al 2006). We selected Lake Naivasha, Tanganyika and Lake Victoria representative for historical lake levels in many equatorial East African lakes (Fig.…”

“…O (Burns et al 2002), GB G. bulloides abundance Arabian Sea sediment core (Anderson et al 2002), KIL Kilimanjaro Ice Core (Thompson et al 2002), CAC Cold Air Cave (Holmgren et al 1999), ZIM Zimbabwe Tree rings (Therell et al 2006); Lake records: 1 Lake Victoria (Stager et al 2005), 2 Lake Naivasha (Verschuren et al 2000), 3 Lake Tanganyika (Cohen et al 2006), 4 Lake Malawi (Johnson et al 2001) Examining the relationship between tropical SST and land surface temperatures and precipitation on decadal scales is hindered by the relatively short observational database, particularly in the oceans. Proxy records can potentially extend the oceanic and land climate records far beyond instrumental data.…”

Primary production in a tropical large lake: The role of phytoplankton composition

“…Contrary to common assumptions on the constancy of ecological conditions in tropical lakes, pelagic primary production may vary considerably in African great lakes, at different time scales, from seasons to centuries (Melack, 1979;Cohen et al, 2006). At long time scales, Indian Ocean surface temperatures, determining rainfall, are the primary influence on East African climate (Tierney et al, 2013), which largely determines water column processes in the great Rift lakes (e.g.…”

The Hominin Sites and Paleolakes Drilling Project: inferring the environmental context of human evolution from eastern African rift lake deposits

“…Its goal was the collection and analysis of high-resolution paleoenvironmental records from paleo-lake drill cores near the depocenters of lacustrine basins of significant paleoanthropological importance in eastern Africa, each of which meets these conditions. As discontinuously exposed outcrops have shown these lakebeds to be commonly laminated (e.g., Wilson et al, 2014) with bedding characteristics often similar to demonstrably annual varves documented in modern African rift lakes (Pilskaln and Johnson, 1991;Cohen et al, 2006) and deposited at high sedimentation rates, their records fulfill the first criterion. The second criterion is fulfilled as each of the drill sites lies in close proximity to rich and diverse fossil vertebrate and archaeological sites, with sediments of the same age, and which collectively span some of the most critical intervals of hominin evolutionary history (e.g., earliest Homo, earliest stone tools, origin of Acheulian and Middle Stone Age technologies, earliest modern H. sapiens), and where new, important fossils and artifacts are still being recovered.…”