Abstract
Calcareous nannofossils were observed to reconstruct the surface water conditions during late Pliocene climate transition (2.55 to 2.88 Ma) from the southern Gardar Drift, in the subpolar North Atlantic IODP Site U1314 (56°21.9’1N, 27°53.3’W). A total of 24 species from 14 genera were identified by polarizing microscope observation. The coccolith assemblages are dominated by species belonging to genus Reticulofenestra with different (size-defined) morphotype. Hence, changes in paleoceanographic condition are shown by the size variation of Reticulofenstraspecimens. Before ~2.76 Ma, the studied interval is characterized by the presence of an abundant larger Reticulofenstra group. It indicates warm oligotrophic and stable surface waters. At ~2.76 Ma the abundance of large Reticulofenstra decreased abruptly and alternated with small Reticulofenstra, suggesting collapse of sea surface stability with strong mixing condition. This event coeval with the final closure of the Central American Seaway (CAS) and the onset of intensified North Hemisphere Glaciation (NHG). Subsequently, the size variation of Reticulofenestra specimens exhibits a sequential pattern that is somewhere consistent with the interglacial-glacial cycle. The pattern begins with a gradual increase in size upward during interglacial suggesting warm oligotrophic and stable condition, and ends with an abrupt decrease in coccolith size during glacial suggesting eutrophic or strong mixing condition and destabilized sea surface waters.
Highlights
Millennial-scale climate variability during Pliocene has received considerable attention in the past years because during this period a warm and stable global climate was gradually alternating to a cooler climate characterized by glacial-interglacial cycles
Our result confirms that the coccolith size variations of Reticulofenestra specimens are affected by the variability of sea surface condition
It is delineated by an abrupt decrease of maximum coccolith of Reticulofenestra, reflects the intensification of Northern Hemisphere Glaciation (NHG) and correlates with the final closure of Central American Seaway (CAS)
Summary
Millennial-scale climate variability during Pliocene has received considerable attention in the past years because during this period a warm and stable global climate was gradually alternating to a cooler climate characterized by glacial-interglacial cycles. Glacial amplitudes started to increase at ~2.75 Ma, reflected by the first obliquity cycles with high δ18O or the beginning of the 41-kyr world, marking the substantial waxing and waning of the Northern Hemisphere ice sheets subsequently become characteristic of the Quaternary climate This event appeared approximately coeval with the final closure of the Central American Seaway (CAS) and the associated change in thermohaline circulation [1] [2] [3] [4]. We focus on calcareous nannofossil assemblages to reconstruct the sea surface dynamic changes during late Pliocene climate transition between 2.87 and 2.55 Ma and deliberation of the timing of tectonic events, notably the closure of Central CAS
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