Abstract
Based on 17 AMS(14)C age data, we reconstructed high-resolution records of sea surface primary productivity (PP) in the southern Okinawa Trough (MD05-2908) over the last 6.8 ka BP using the calcareous nannofossil carbon isotope and the relative percentage contents of Florisphaera profunda indexes. The underlying mechanism controlling the sea surface PP was then discussed. The sea surface PP, indicated by the coccolith delta C-13 and %Fp conversional equations, decreased with some fluctuations since 6.8 ka BP. This decrease may be connected to the decreased terrigenous input resulting from the reduced East Asian Summer Monsoon (EASM) precipitation. Both the periods of 4-2 ka BP (PME) and 6.8-4.8 ka BP were characterized by relatively higher PP. The former was mainly controlled by the weakening of the Kuroshio Current, whereas the latter mainly resulted from the greater terrigenous input associated with the stronger EASM.
Highlights
Based on 17 AMS14C age data, we reconstructed high-resolution records of sea surface primary productivity (PP) in the southern Okinawa Trough (MD05-2908) over the last 6.8 ka BP using the calcareous nannofossil carbon isotope and the relative percentage contents of Florisphaera profunda indexes
Recent results of Quaternary sediments from the southern South China Sea, the western Pacific warm pool and the western Philippine Sea showed that coccolith δ13C could qualitatively reflect the sea surface PP, and lower δ13C values indicate lower PP values [27,30–32]
Previous studies have demonstrated that the Kuroshio Current was stronger in the Mid-Holocene than in the Late Holocene [10,36,59]. This result shows that, compared with 4 2 ka BP, the relatively higher PP during 6.8 4.8 ka BP was mainly controlled by stronger terrigenous inputs caused by the strengthened East Asian Summer Monsoon (EASM), and the effects of the Kuroshio Current are not obvious
Summary
Based on 17 AMS14C age data, we reconstructed high-resolution records of sea surface primary productivity (PP) in the southern Okinawa Trough (MD05-2908) over the last 6.8 ka BP using the calcareous nannofossil carbon isotope and the relative percentage contents of Florisphaera profunda indexes. The sea surface PP, indicated by the coccolith δ13C and %Fp conversional equations, decreased with some fluctuations since 6.8 ka BP This decrease may be connected to the decreased terrigenous input resulting from the reduced East Asian Summer Monsoon (EASM) precipitation. Both the periods of 4–2 ka BP (PME) and 6.8–4.8 ka BP were characterized by relatively higher PP. We discussed the sea surface PP changes in the southern Okinawa Trough over the last 6.8 ka BP based on the calcareous nannofossil proxies in core MD05-2908. When a stronger summer monsoon occurs, the enormous amount of runoff from the Yangtze River and Taiwan rivers induces a large amount of freshwater and nutrient input to the southern Okinawa Trough, with a resultant SSS decrease and PP increase [21]
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