Open AccessChanges in biological productivity along the northwest African margin over the past 20,000 years
Author(s) -
Bradtmiller Louisa I.,
McGee David,
Awalt Mitchell,
Evers Joseph,
Yerxa Haley,
Kinsley Christopher W.,
deMenocal Peter B.
Publication year - 2016
Publication title -
paleoceanography
Language(s) - English
Resource type - Journals
eISSN - 1944-9186
pISSN - 0883-8305
DOI - 10.1002/2015pa002862
Subject(s) - upwelling , geology , stadial , oceanography , monsoon , climatology , zonal and meridional , intertropical convergence zone , younger dryas , aeolian processes , orbital forcing , holocene , climate change , precipitation , geomorphology , geography , meteorology
The intertropical convergence zone and the African monsoon system are highly sensitive to climate forcing at orbital and millennial timescales. Both systems influence the strength and direction of the trade winds along northwest Africa and thus directly impact coastal upwelling. Sediment cores from the northwest African margin record upwelling‐related changes in biological productivity connected to changes in regional and hemispheric climate. We present records of 230 Th‐normalized biogenic opal and C org fluxes using a meridional transect of four cores from 19°N–31°N along the northwest African margin to examine changes in paleoproductivity since the last glacial maximum. We find large changes in biogenic fluxes synchronous with changes in eolian fluxes calculated using end‐member modeling, suggesting that paleoproductivity and dust fluxes were strongly coupled, likely linked by changes in wind strength. Opal and C org fluxes increase at all sites during Heinrich Stadial 1 and the Younger Dryas, consistent with an overall intensification of the trade winds, and changes in the meridional flux gradient indicate a southward wind shift at these times. Biogenic fluxes were lowest, and the meridional flux gradients were weakest during the African Humid Period when the monsoon was invigorated due to precessional changes, with greater rainfall and weaker trade winds over northwest Africa. These results expand the spatial coverage of previous paleoproxy studies showing similar changes, and they provide support for modeling studies showing changes in wind strength and direction consistent with increased upwelling during abrupt coolings and decreased upwelling during the African Humid Period.