Abstract
AbstractWe present a high‐resolution multiproxy middle Miocene sea surface temperature (SST) and productivity (SSP) reconstruction of Integrated Ocean Drilling Program Site U1318, from the upper slope edge (∼400 m water depth) of the Porcupine Basin continental margin, eastern North Atlantic Ocean. Biomarker and dinoflagellate cyst proxies reveal warm and mostly stratified waters during the Miocene Climatic Optimum (MCO) that cooled ∼3°C across the Miocene Climate Transition (MCT). The organic biomarker (TEX86 and ) paleothermometers document a series of 11 transient cooling events (CEs), superimposed on the long‐term climate evolution. These CEs are associated with increases in cold‐water dinocysts and correlate to global benthic δ18O shifts, including the Mi‐2, Mi‐3, and Mi‐4 events. Most CEs are also associated with increases in primary productivity. A prolonged interval of high SSP between ∼13.8 and 13.6 Ma supports the idea that carbon production (and burial) in shallow areas represents a feedback mechanism contributing to long‐term atmospheric CO2 decline and cooling during the MCT. SST comparison in three North Atlantic sites (Azores Site 608, Porcupine Basin Site U1318, and Rockall Plateau Site 982) reveals that MCO SSTs are much warmer at Site 608 than at the other two sites. The low‐resolution SST record of Site 982 shows no decrease in temperature around the MCT. This may be linked to contemporaneous tectonic changes in the Tethys, Central American, and Arctic Seaways impacting local ocean circulation, superimposed on global drivers of climate change.
Highlights
The climate dynamics of the Miocene epoch (23.03–5.33 million years, Ma) have gained increasing attention for their potential to improve our understanding of climate sensitivity to CO2 forcing and projected near future climate (e.g., Goldner et al, 2014; IPCC, 2014)
Middle Miocene sediments belong to the lithostratigraphic Unit 3 (Subunits A–C) which mainly consists of greenish-gray clay with Total Organic Carbon content (TOC%) for selected samples ranging from 0.27% to 0.70% and are divided into subunits based on their calcium carbonate content (Expedition 307 Scientists, 2006; Quaijtaal et al, 2017)
We presented the first high-resolution multiproxy middle Miocene sea surface temperature (SST) and sea surface productivity (SSP) record from a shelf site (Site U1318) in the Porcupine Basin, in the eastern North Atlantic
Summary
The climate dynamics of the Miocene epoch (23.03–5.33 million years, Ma) have gained increasing attention for their potential to improve our understanding of climate sensitivity to CO2 forcing and projected near future climate (e.g., Goldner et al, 2014; IPCC, 2014). Benthic oxygen isotope compilations indicate a global climate warmer than today (De Vleeschouwer et al, 2017; Zachos et al, 2008) at CO2 concentrations varying from preindustrial to higher than at present. Values of ∼500–600 ppm would be similar to those expected for the end of the 21st century given unabated carbon emissions (IPCC, 2014).
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