Abstract
Reconstructions of ocean primary productivity (PP) help to explain past
and present biogeochemical cycles and climate changes in the oceans. We
document PP variations over the last 50 kyr in a currently oligotrophic
subtropical region, the Gulf of Cadiz (GoC). Data combine refined
results from previous investigations on dinoflagellate cyst (dinocyst)
assemblages, alkenones, and stable isotopes (18O,
13C) in planktonic (Globigerina bulloides) and
endobenthic (Uvigerina mediterranea) foraminifera from cores
MD04-2805 CQ and MD99-2339 with new isotopic measurements on epibenthic
(Cibicidoides species) foraminifera and dinocyst-based estimates
of PP using the new n = 1,968 modern database. We thus constrain
paleoproductivity variations and export production by integrating
qualitative information from micropaleontological bio-indicators with
quantitative reconstructions of parameters such as dinocyst-based PP and
seasonal sea-surface temperature (SST), as well as information about
remineralization from the benthic Dd13C. We show that
PP, carbon export, and remineralization were generally high in the NE
subtropical Atlantic Ocean during the last glacial period and that the
Last Glacial Maximum (LGM) had lower Dd13C than the
Heinrich Stadials with sustained high PP, likely allowing enhanced
carbon sequestration. This study also provides vital information on the
dynamics PP regime changes, as the dataset includes alkenone-based SST
and total organic carbon (TOC). We link these stimulated PP periods to
seasonal intensification of upwelling, active almost year-round during
stadials, but restricted to spring–summer during interstadials and LGM,
like today. During interstadials, nutrient advection through freshwater
inputs during autumn–winter rains need to be considered to fully
understand PP regimes.