Research ArticleENVIRONMENTAL STUDIES

Solar irradiance and ENSO affect food security in Lake Tanganyika, a major African inland fishery

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Science Advances  09 Oct 2020:
Vol. 6, no. 41, eabb2191
DOI: 10.1126/sciadv.abb2191
  • Fig. 1 Lake Tanganyika.

    Inset map (A, upper right) shows the position of the lake in the east African rift valley. (A) Digital elevation and bathymetric data (courtesy tcarta.com) illustrate the topography and hydrography of the lake and its watershed. Other large lakes appear in black, and several support important regional fisheries. Mal, Lake Malawi; Ruk, Lake Rukwa; Mwe, Lake Mweru. Core LT17-2A (yellow dot) was collected from an outer ramp depositional setting (~420-m water depth) in Lake Tanganyika’s southern basin. (B) High-resolution core photo and Bacon-derived radiocarbon age-depth model. The core consists of laminated diatom ooze, structureless clayey silts, tephra, and sapropel and spans the interval ~670–1610 CE. The blue markers, dotted red line, and gray shading represent calibrated radiocarbon control points, the best age model solution based on the mean age for each depth, and 95% confidence interval, respectively.

  • Fig. 2 Multiple geochemical and paleoecological indicators used to reconstruct upwelling, primary production, and algal composition in southern Lake Tanganyika, ~670–1610 CE.

    Gray shading indicates periods of inferred upwelling. Stippled bar indicates location of tephra bed. Black triangles indicate radiocarbon control points. The scale on the δ15N is inverted; all other values increase upward. (A) Si/Ti chemostratigraphy. High values indicate elevated diatom production induced by upwelling. (B) Fe/Mn chemostratigraphy. Low values indicate lake ventilation associated with water column mixing and upwelling. (C) Centric/Nitzschia diatoms. Nitzschia requires dissolved silica in the photic zone, derived from upwelling, to be productive enough to dominate the fossil assemblage. (D) δ15N chemostratigraphy. Units are in ‰. Prevalence of diazotrophic cyanobacteria associated with upwelling results in lower values. (E) Total phosphorous (P) chemostratigraphy. Units are in μmol/g. High total P accompanies upwelling and elevated primary productivity, resulting in less nutrient recycling (see text for details).

  • Fig. 3 Proxy data comparison.

    Comparison of paleoclimate proxy data [change in total solar irradiance (TSI) (31), Lake Tanganyika surface warming (11), and Southern Oscillation Index (SOI) precipitation reconstruction (37)] with Si/Ti chemostratigraphy from core LT17-2A. Red and blue dots represent high and low estimates surrounding the mean (solid line) of the lake temperature record, respectively. Strong evidence of upwelling and diatom production in southern Lake Tanganyika is associated with solar irradiance maxima, La Niña–like conditions, and cool lake surface water, whereas solar irradiance minima, El Niño, and warm surface waters limit upwelling and algal production. LST, Lake surface temperature.

  • Fig. 4 Wavelet analysis of Si/Ti from core LT17-2A.

    The Fourier period is presented in years, and the thick black contour delineates >95% confidence interval. The cone of influence is indicated by the hatched area. The ~256- and 512-year bands are interpreted to reflect the influence of solar irradiance cycles, whereas the interannual frequencies most likely reflect ENSO.

Supplementary Materials

  • Supplementary Materials

    Solar irradiance and ENSO affect food security in Lake Tanganyika, a major African inland fishery

    M. M. McGlue, S. J. Ivory, J. R. Stone, A. S. Cohen, T. M. Kamulali, J. C. Latimer, M. A. Brannon, I. A. Kimirei, M. J. Soreghan

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    • Figs. S1 to S5
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